TY - GEN A1 - Roder, Phillip A1 - Hille, Carsten T1 - A Multifunctional Frontloading Approach for Repeated Recycling of a Pressure-Controlled AFM Micropipette N2 - Fluid force microscopy combines the positional accuracy and force sensitivity of an atomic force microscope (AFM) with nanofluidics via a microchanneled cantilever. However, adequate loading and cleaning procedures for such AFM micropipettes are required for various application situations. Here, a new frontloading procedure is described for an AFM micropipette functioning as a force- and pressure-controlled microscale liquid dispenser. This frontloading procedure seems especially attractive when using target substances featuring high costs or low available amounts. Here, the AFM micropipette could be filled from the tip side with liquid from a previously applied droplet with a volume of only a few μL using a short low-pressure pulse. The liquid-loaded AFM micropipettes could be then applied for experiments in air or liquid environments. AFM micropipette frontloading was evaluated with the well-known organic fluorescent dye rhodamine 6G and the AlexaFluor647-labeled antibody goat anti-rat IgG as an example of a larger biological compound. After micropipette usage, specific cleaning procedures were tested. Furthermore, a storage method is described, at which the AFM micropipettes could be stored for a few hours up to several days without drying out or clogging of the microchannel. In summary, the rapid, versatile and cost-efficient frontloading and cleaning procedure for the repeated usage of a single AFM micropipette is beneficial for various application situations from specific surface modifications through to local manipulation of living cells, and provides a simplified and faster handling for already known experiments with fluid force microscopy. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 209 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-86592 ER - TY - JOUR A1 - Roder, Phillip A1 - Hille, Carsten T1 - A Multifunctional Frontloading Approach for Repeated Recycling of a Pressure-Controlled AFM Micropipette JF - PLoS ONE N2 - Fluid force microscopy combines the positional accuracy and force sensitivity of an atomic force microscope (AFM) with nanofluidics via a microchanneled cantilever. However, adequate loading and cleaning procedures for such AFM micropipettes are required for various application situations. Here, a new frontloading procedure is described for an AFM micropipette functioning as a force- and pressure-controlled microscale liquid dispenser. This frontloading procedure seems especially attractive when using target substances featuring high costs or low available amounts. Here, the AFM micropipette could be filled from the tip side with liquid from a previously applied droplet with a volume of only a few μL using a short low-pressure pulse. The liquid-loaded AFM micropipettes could be then applied for experiments in air or liquid environments. AFM micropipette frontloading was evaluated with the well-known organic fluorescent dye rhodamine 6G and the AlexaFluor647-labeled antibody goat anti-rat IgG as an example of a larger biological compound. After micropipette usage, specific cleaning procedures were tested. Furthermore, a storage method is described, at which the AFM micropipettes could be stored for a few hours up to several days without drying out or clogging of the microchannel. In summary, the rapid, versatile and cost-efficient frontloading and cleaning procedure for the repeated usage of a single AFM micropipette is beneficial for various application situations from specific surface modifications through to local manipulation of living cells, and provides a simplified and faster handling for already known experiments with fluid force microscopy. Y1 - 2015 U6 - https://doi.org/10.1371/journal.pone.0144157 SN - 1932-6203 VL - 10 IS - 12 PB - Public Library of Science CY - Lawrence, Kan. ER - TY - THES A1 - Schwarz, Dana T1 - Nanoporous melamine resin materials BT - synthetic strategies, shape control and adsorption proberties Y1 - 2015 ER - TY - THES A1 - Chen, Zupeng T1 - Novel strategies to improve (photo)catalytic performance of carbon nitride-based composites Y1 - 2015 ER - TY - JOUR A1 - Bodrova, Anna A1 - Chechkin, Aleksei V. A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf T1 - Quantifying non-ergodic dynamics of force-free granular gases JF - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies N2 - Brownianmotion is ergodic in the Boltzmann–Khinchin sense that long time averages of physical observables such as the mean squared displacement provide the same information as the corresponding ensemble average, even at out-of-equilibrium conditions. This property is the fundamental prerequisite for single particle tracking and its analysis in simple liquids. We study analytically and by event-driven molecular dynamics simulations the dynamics of force-free cooling granular gases and reveal a violation of ergodicity in this Boltzmann– Khinchin sense as well as distinct ageing of the system. Such granular gases comprise materials such as dilute gases of stones, sand, various types of powders, or large molecules, and their mixtures are ubiquitous in Nature and technology, in particular in Space. We treat—depending on the physical-chemical properties of the inter-particle interaction upon their pair collisions—both a constant and a velocity-dependent (viscoelastic) restitution coefficient e. Moreover we compare the granular gas dynamics with an effective single particle stochastic model based on an underdamped Langevin equation with time dependent diffusivity. We find that both models share the same behaviour of the ensemble mean squared displacement (MSD) and the velocity correlations in the limit of weak dissipation. Qualitatively, the reported non-ergodic behaviour is generic for granular gases with any realistic dependence of e on the impact velocity of particles. Y1 - 2015 U6 - https://doi.org/10.1039/C5CP02824H SN - 1463-9084 IS - 17 SP - 21791 EP - 21798 ER - TY - GEN A1 - Bodrova, Anna A1 - Chechkin, Aleksei V. A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf T1 - Quantifying non-ergodic dynamics of force-free granular gases N2 - Brownianmotion is ergodic in the Boltzmann–Khinchin sense that long time averages of physical observables such as the mean squared displacement provide the same information as the corresponding ensemble average, even at out-of-equilibrium conditions. This property is the fundamental prerequisite for single particle tracking and its analysis in simple liquids. We study analytically and by event-driven molecular dynamics simulations the dynamics of force-free cooling granular gases and reveal a violation of ergodicity in this Boltzmann-Khinchin sense as well as distinct ageing of the system. Such granular gases comprise materials such as dilute gases of stones, sand, various types of powders, or large molecules, and their mixtures are ubiquitous in Nature and technology, in particular in Space. We treat—depending on the physical-chemical properties of the inter-particle interaction upon their pair collisions—both a constant and a velocity-dependent (viscoelastic) restitution coefficient e. Moreover we compare the granular gas dynamics with an effective single particle stochastic model based on an underdamped Langevin equation with time dependent diffusivity. We find that both models share the same behaviour of the ensemble mean squared displacement (MSD) and the velocity correlations in the limit of weak dissipation. Qualitatively, the reported non-ergodic behaviour is generic for granular gases with any realistic dependence of e on the impact velocity of particles. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 206 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-85200 ER - TY - JOUR A1 - Mai, Tobias A1 - Boye, Susanne A1 - Yuan, Jiayin A1 - Völkel, Antje A1 - Gräwert, Marlies A1 - Günter, Christina A1 - Lederer, Albena A1 - Taubert, Andreas T1 - Poly(ethylene oxide)-based block copolymers with very high molecular weights for biomimetic calcium phosphate mineralization JF - RSC Advances : an international journal to further the chemical sciences N2 - The present article is among the first reports on the effects of poly(ampholyte)s and poly(betaine)s on the biomimetic formation of calcium phosphate. We have synthesized a series of di- and triblock copolymers based on a non-ionic poly(ethylene oxide) block and several charged methacrylate monomers, 2-(trimethylammonium)ethyl methacrylate chloride, 2-((3-cyanopropyl)-dimethylammonium)ethyl methacrylate chloride, 3-sulfopropyl methacrylate potassium salt, and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide. The resulting copolymers are either positively charged, ampholytic, or betaine block copolymers. All the polymers have very high molecular weights of over 106 g mol−1. All polymers are water-soluble and show a strong effect on the precipitation and dissolution of calcium phosphate. The strongest effects are observed with triblock copolymers based on a large poly(ethylene oxide) middle block (nominal Mn = 100 000 g mol−1). Surprisingly, the data show that there is a need for positive charges in the polymers to exert tight control over mineralization and dissolution, but that the exact position of the charge in the polymer is of minor importance for both calcium phosphate precipitation and dissolution. Y1 - 2015 U6 - https://doi.org/10.1039/c5ra20035k SN - 2046-2069 IS - 5 SP - 103494 EP - 103505 PB - RSC Publishing CY - London ER - TY - GEN A1 - Mai, Tobias A1 - Boye, Susanne A1 - Yuan, Jiayin A1 - Völkel, Antje A1 - Gräwert, Marlies A1 - Günter, Christina A1 - Lederer, Albena A1 - Taubert, Andreas T1 - Poly(ethylene oxide)-based block copolymers with very high molecular weights for biomimetic calcium phosphate mineralization N2 - The present article is among the first reports on the effects of poly(ampholyte)s and poly(betaine)s on the biomimetic formation of calcium phosphate. We have synthesized a series of di- and triblock copolymers based on a non-ionic poly(ethylene oxide) block and several charged methacrylate monomers, 2-(trimethylammonium)ethyl methacrylate chloride, 2-((3-cyanopropyl)-dimethylammonium)ethyl methacrylate chloride, 3-sulfopropyl methacrylate potassium salt, and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide. The resulting copolymers are either positively charged, ampholytic, or betaine block copolymers. All the polymers have very high molecular weights of over 106 g mol−1. All polymers are water-soluble and show a strong effect on the precipitation and dissolution of calcium phosphate. The strongest effects are observed with triblock copolymers based on a large poly(ethylene oxide) middle block (nominal Mn = 100 000 g mol−1). Surprisingly, the data show that there is a need for positive charges in the polymers to exert tight control over mineralization and dissolution, but that the exact position of the charge in the polymer is of minor importance for both calcium phosphate precipitation and dissolution. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 208 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-85299 ER - TY - JOUR A1 - Mardoukhi, Yousof A1 - Jeon, Jae-Hyung A1 - Metzler, Ralf T1 - Geometry controlled anomalous diffusion in random fractal geometries BT - looking beyond the infinite cluster JF - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies N2 - We investigate the ergodic properties of a random walker performing (anomalous) diffusion on a random fractal geometry. Extensive Monte Carlo simulations of the motion of tracer particles on an ensemble of realisations of percolation clusters are performed for a wide range of percolation densities. Single trajectories of the tracer motion are analysed to quantify the time averaged mean squared displacement (MSD) and to compare this with the ensemble averaged MSD of the particle motion. Other complementary physical observables associated with ergodicity are studied, as well. It turns out that the time averaged MSD of individual realisations exhibits non-vanishing fluctuations even in the limit of very long observation times as the percolation density approaches the critical value. This apparent non-ergodic behaviour concurs with the ergodic behaviour on the ensemble averaged level. We demonstrate how the non-vanishing fluctuations in single particle trajectories are analytically expressed in terms of the fractal dimension and the cluster size distribution of the random geometry, thus being of purely geometrical origin. Moreover, we reveal that the convergence scaling law to ergodicity, which is known to be inversely proportional to the observation time T for ergodic diffusion processes, follows a power-law BT� h with h o 1 due to the fractal structure of the accessible space. These results provide useful measures for differentiating the subdiffusion on random fractals from an otherwise closely related process, namely, fractional Brownian motion. Implications of our results on the analysis of single particle tracking experiments are provided. Y1 - 2015 U6 - https://doi.org/10.1039/c5cp03548a SN - 1439-7641 IS - 17 SP - 30134 EP - 30147 PB - Wiley-VCH Verl. CY - Weinheim ER - TY - GEN A1 - Mardoukhi, Yousof A1 - Jeon, Jae-Hyung A1 - Metzler, Ralf T1 - Geometry controlled anomalous diffusion in random fractal geometries BT - looking beyond the infinite cluster N2 - We investigate the ergodic properties of a random walker performing (anomalous) diffusion on a random fractal geometry. Extensive Monte Carlo simulations of the motion of tracer particles on an ensemble of realisations of percolation clusters are performed for a wide range of percolation densities. Single trajectories of the tracer motion are analysed to quantify the time averaged mean squared displacement (MSD) and to compare this with the ensemble averaged MSD of the particle motion. Other complementary physical observables associated with ergodicity are studied, as well. It turns out that the time averaged MSD of individual realisations exhibits non-vanishing fluctuations even in the limit of very long observation times as the percolation density approaches the critical value. This apparent non-ergodic behaviour concurs with the ergodic behaviour on the ensemble averaged level. We demonstrate how the non-vanishing fluctuations in single particle trajectories are analytically expressed in terms of the fractal dimension and the cluster size distribution of the random geometry, thus being of purely geometrical origin. Moreover, we reveal that the convergence scaling law to ergodicity, which is known to be inversely proportional to the observation time T for ergodic diffusion processes, follows a power-law BT� h with h o 1 due to the fractal structure of the accessible space. These results provide useful measures for differentiating the subdiffusion on random fractals from an otherwise closely related process, namely, fractional Brownian motion. Implications of our results on the analysis of single particle tracking experiments are provided. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 207 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-85247 ER - TY - GEN A1 - Jahn, Karolina A1 - Buschmann, Volker A1 - Hille, Carsten T1 - Simultaneous Fluorescence and Phosphorescence Lifetime Imaging Microscopy in Living Cells N2 - In living cells, there are always a plethora of processes taking place at the same time. Their precise regulation is the basis of cellular functions, since small failures can lead to severe dysfunctions. For a comprehensive understanding of intracellular homeostasis, simultaneous multiparameter detection is a versatile tool for revealing the spatial and temporal interactions of intracellular parameters. Here, a recently developed time-correlated single-photon counting (TCSPC) board was evaluated for simultaneous fluorescence and phosphorescence lifetime imaging microscopy (FLIM/PLIM). Therefore, the metabolic activity in insect salivary glands was investigated by recording ns-decaying intrinsic cellular fluorescence, mainly related to oxidized flavin adenine dinucleotide (FAD) and the μs-decaying phosphorescence of the oxygen-sensitive ruthenium-complex Kr341. Due to dopamine stimulation, the metabolic activity of salivary glands increased, causing a higher pericellular oxygen consumption and a resulting increase in Kr341 phosphorescence decay time. Furthermore, FAD fluorescence decay time decreased, presumably due to protein binding, thus inducing a quenching of FAD fluorescence decay time. Through application of the metabolic drugs antimycin and FCCP, the recorded signals could be assigned to a mitochondrial origin. The dopamine-induced changes could be observed in sequential FLIM and PLIM recordings, as well as in simultaneous FLIM/PLIM recordings using an intermediate TCSPC timing resolution. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 202 KW - Confocal microscopy KW - Fluorescence imaging KW - Fluorescence spectroscopy KW - Fluorescent probes Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-82156 ER - TY - JOUR A1 - Jahn, Karolina A1 - Buschmann, Volker A1 - Hille, Carsten T1 - Simultaneous Fluorescence and Phosphorescence Lifetime Imaging Microscopy in Living Cells JF - Scientific Reports N2 - In living cells, there are always a plethora of processes taking place at the same time. Their precise regulation is the basis of cellular functions, since small failures can lead to severe dysfunctions. For a comprehensive understanding of intracellular homeostasis, simultaneous multiparameter detection is a versatile tool for revealing the spatial and temporal interactions of intracellular parameters. Here, a recently developed time-correlated single-photon counting (TCSPC) board was evaluated for simultaneous fluorescence and phosphorescence lifetime imaging microscopy (FLIM/PLIM). Therefore, the metabolic activity in insect salivary glands was investigated by recording ns-decaying intrinsic cellular fluorescence, mainly related to oxidized flavin adenine dinucleotide (FAD) and the μs-decaying phosphorescence of the oxygen-sensitive ruthenium-complex Kr341. Due to dopamine stimulation, the metabolic activity of salivary glands increased, causing a higher pericellular oxygen consumption and a resulting increase in Kr341 phosphorescence decay time. Furthermore, FAD fluorescence decay time decreased, presumably due to protein binding, thus inducing a quenching of FAD fluorescence decay time. Through application of the metabolic drugs antimycin and FCCP, the recorded signals could be assigned to a mitochondrial origin. The dopamine-induced changes could be observed in sequential FLIM and PLIM recordings, as well as in simultaneous FLIM/PLIM recordings using an intermediate TCSPC timing resolution. KW - Confocal microscopy KW - Fluorescence imaging KW - Fluorescence spectroscopy KW - Fluorescent probes Y1 - 2015 U6 - https://doi.org/10.1038/srep14334 SN - 2045-2322 IS - 5 PB - Nature Publishing Group CY - London ER - TY - THES A1 - Taßler, Stephanie T1 - Physical-Chemical Investigation of newly-synthesised Lysine-Based Amino-Functionalised Lipids for gene transfection in 2D and 3D model systems Y1 - 2015 ER - TY - GEN A1 - Kröner, Dominik T1 - Laser-driven electron dynamics for circular dichroism in mass spectrometry BT - from one-photon excitations to multiphoton ionization N2 - The distinction of enantiomers is a key aspect of chemical analysis. In mass spectrometry the distinction of enantiomers has been achieved by ionizing the sample with circularly polarized laser pulses and comparing the ion yields for light of opposite handedness. While resonant excitation conditions are expected to be most efficient, they are not required for the detection of a circular dichroism (CD) in the ion yield. However, the prediction of the size and sign of the circular dichroism becomes challenging if non-resonant multiphoton excitations are used to ionize the sample. Employing femtosecond laser pulses to drive electron wavepacket dynamics based on ab initio calculations, we attempt to reveal underlying mechanisms that determine the CD under non-resonant excitation conditions. Simulations were done for (R)-1,2-propylene oxide, using time-dependent configuration interaction singles with perturbative doubles (TD-CIS(D)) and the aug-cc-pVTZ basis set. Interactions between the electric field and the electric dipole and quadrupole as well as between the magnetic field and the magnetic dipole were explicitly accounted for. The ion yield was determined by treating states above the ionization potential as either stationary or non-stationary with energy-dependent lifetimes based on an approved heuristic approach. The observed population dynamics do not allow for a simple interpretation, because of highly non-linear interactions. Still, the various transition pathways are governed by resonant enantiospecific n-photon excitation, with preferably high transition dipole moments, which eventually dominate the CD in the ionized population. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 201 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-82109 ER - TY - JOUR A1 - Kröner, Dominik T1 - Laser-driven electron dynamics for circular dichroism in mass spectrometry BT - from one-photon excitations to multiphoton ionization JF - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies N2 - The distinction of enantiomers is a key aspect of chemical analysis. In mass spectrometry the distinction of enantiomers has been achieved by ionizing the sample with circularly polarized laser pulses and comparing the ion yields for light of opposite handedness. While resonant excitation conditions are expected to be most efficient, they are not required for the detection of a circular dichroism (CD) in the ion yield. However, the prediction of the size and sign of the circular dichroism becomes challenging if non-resonant multiphoton excitations are used to ionize the sample. Employing femtosecond laser pulses to drive electron wavepacket dynamics based on ab initio calculations, we attempt to reveal underlying mechanisms that determine the CD under non-resonant excitation conditions. Simulations were done for (R)-1,2-propylene oxide, using time-dependent configuration interaction singles with perturbative doubles (TD-CIS(D)) and the aug-cc-pVTZ basis set. Interactions between the electric field and the electric dipole and quadrupole as well as between the magnetic field and the magnetic dipole were explicitly accounted for. The ion yield was determined by treating states above the ionization potential as either stationary or non-stationary with energy-dependent lifetimes based on an approved heuristic approach. The observed population dynamics do not allow for a simple interpretation, because of highly non-linear interactions. Still, the various transition pathways are governed by resonant enantiospecific n-photon excitation, with preferably high transition dipole moments, which eventually dominate the CD in the ionized population. Y1 - 2015 U6 - https://doi.org/10.1039/C5CP02193F SN - 1463-9076 SN - 1463-9084 VL - 29 IS - 17 SP - 19643 EP - 19655 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Lohren, Hanna A1 - Bornhorst, Julia A1 - Galla, Hans-Joachim A1 - Schwerdtle, Tanja T1 - The blood–cerebrospinal fluid barrier BT - First evidence for an active transport of organic mercury compounds out of the brain N2 - Exposure to organic mercury compounds promotes primarily neurological effects. Although methylmercury is recognized as a potent neurotoxicant, its transfer into the central nervous system (CNS) is not fully evaluated. While methylmercury and thiomersal pass the blood–brain barrier, limited data are available regarding the second brain regulating interface, the blood–cerebrospinal fluid (CSF) barrier. This novel study was designed to investigate the effects of organic as well as inorganic mercury compounds on, and their transfer across, a porcine in vitro model of the blood–CSF barrier for the first time. The barrier system is significantly more sensitive towards organic Hg compounds as compared to inorganic compounds regarding the endpoints cytotoxicity and barrier integrity. Whereas there are low transfer rates from the blood side to the CSF side, our results strongly indicate an active transfer of the organic mercury compounds out of the CSF. These results are the first to demonstrate an efflux of organic mercury compounds regarding the CNS and provide a completely new approach in the understanding of mercury compounds specific transport. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 200 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-82089 ER - TY - JOUR A1 - Lohren, Hanna A1 - Bornhorst, Julia A1 - Galla, Hans-Joachim A1 - Schwerdtle, Tanja T1 - The blood–cerebrospinal fluid barrier BT - First evidence for an active transport of organic mercury compounds out of the brain JF - Metallomics : integrated biometal science N2 - Exposure to organic mercury compounds promotes primarily neurological effects. Although methylmercury is recognized as a potent neurotoxicant, its transfer into the central nervous system (CNS) is not fully evaluated. While methylmercury and thiomersal pass the blood–brain barrier, limited data are available regarding the second brain regulating interface, the blood–cerebrospinal fluid (CSF) barrier. This novel study was designed to investigate the effects of organic as well as inorganic mercury compounds on, and their transfer across, a porcine in vitro model of the blood–CSF barrier for the first time. The barrier system is significantly more sensitive towards organic Hg compounds as compared to inorganic compounds regarding the endpoints cytotoxicity and barrier integrity. Whereas there are low transfer rates from the blood side to the CSF side, our results strongly indicate an active transfer of the organic mercury compounds out of the CSF. These results are the first to demonstrate an efflux of organic mercury compounds regarding the CNS and provide a completely new approach in the understanding of mercury compounds specific transport. Y1 - 2015 U6 - https://doi.org/10.1039/C5MT00171D SN - 1756-5901 SN - 1756-591X VL - 10 IS - 7 SP - 1420 EP - 1430 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Meyer, S. A1 - Raber, G. A1 - Ebert, Franziska A1 - Leffers, L. A1 - Müller, Sandra Marie A1 - Taleshi, M. S. A1 - Francesconi, Kevin A. A1 - Schwerdtle, Tanja T1 - In vitro toxicological characterisation of arsenic-containing fatty acids and three of their metabolites N2 - Arsenic-containing fatty acids are a group of fat-soluble arsenic species (arsenolipids) which are present in marine fish and other seafood. Recently, it has been shown that arsenic-containing hydrocarbons, another group of arsenolipids, exert toxicity in similar concentrations comparable to arsenite although the toxic modes of action differ. Hence, a risk assessment of arsenolipids is urgently needed. In this study the cellular toxicity of a saturated (AsFA 362) and an unsaturated (AsFA 388) arsenic-containing fatty acid and three of their proposed metabolites (DMAV, DMAPr and thio-DMAPr) were investigated in human liver cells (HepG2). Even though both arsenic-containing fatty acids were less toxic as compared to arsenic-containing hydrocarbons and arsenite, significant effects were observable at μM concentrations. DMAV causes effects in a similar concentration range and it could be seen that it is metabolised to its highly toxic thio analogue thio-DMAV in HepG2 cells. Nevertheless, DMAPr and thio-DMAPr did not exert any cytotoxicity. In summary, our data indicate that risks to human health related to the presence of arsenic-containing fatty acids in marine food cannot be excluded. This stresses the need for a full in vitro and in vivo toxicological characterisation of these arsenolipids. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 199 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-82008 ER - TY - JOUR A1 - Meyer, S. A1 - Raber, G. A1 - Ebert, Franziska A1 - Leffers, L. A1 - Müller, Sandra Marie A1 - Taleshi, M. S. A1 - Francesconi, Kevin A. A1 - Schwerdtle, Tanja T1 - In vitro toxicological characterisation of arsenic-containing fatty acids and three of their metabolites JF - Toxicology research N2 - Arsenic-containing fatty acids are a group of fat-soluble arsenic species (arsenolipids) which are present in marine fish and other seafood. Recently, it has been shown that arsenic-containing hydrocarbons, another group of arsenolipids, exert toxicity in similar concentrations comparable to arsenite although the toxic modes of action differ. Hence, a risk assessment of arsenolipids is urgently needed. In this study the cellular toxicity of a saturated (AsFA 362) and an unsaturated (AsFA 388) arsenic-containing fatty acid and three of their proposed metabolites (DMAV, DMAPr and thio-DMAPr) were investigated in human liver cells (HepG2). Even though both arsenic-containing fatty acids were less toxic as compared to arsenic-containing hydrocarbons and arsenite, significant effects were observable at μM concentrations. DMAV causes effects in a similar concentration range and it could be seen that it is metabolised to its highly toxic thio analogue thio-DMAV in HepG2 cells. Nevertheless, DMAPr and thio-DMAPr did not exert any cytotoxicity. In summary, our data indicate that risks to human health related to the presence of arsenic-containing fatty acids in marine food cannot be excluded. This stresses the need for a full in vitro and in vivo toxicological characterisation of these arsenolipids. Y1 - 2015 U6 - https://doi.org/10.1039/c5tx00122f SN - 2045-4538 VL - 5 IS - 4 SP - 1289 EP - 1296 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Kirchhecker, Sarah A1 - Tröger-Müller, Steffen A1 - Bake, Sebastian A1 - Antonietti, Markus A1 - Taubert, Andreas A1 - Esposito, Davido T1 - Renewable pyridinium ionic liquids from the continuous hydrothermal decarboxylation of furfural-amino acid derived pyridinium zwitterions JF - Green chemistry N2 - Fully renewable pyridinium ionic liquids were synthesised via the hydrothermal decarboxylation of pyridinium zwitterions derived from furfural and amino acids in flow. The functionality of the resulting ionic liquid (IL) can be tuned by choice of different amino acids as well as different natural carboxylic acids as the counterions. A representative member of this new class of ionic liquids was successfully used for the synthesis of ionogels and as a solvent for the Heck coupling. Y1 - 2015 U6 - https://doi.org/10.1039/c5gc00913h SN - 1463-9262 SN - 1463-9270 VL - 8 IS - 17 SP - 4151 EP - 4156 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Kirchhecker, Sarah A1 - Tröger-Müller, Steffen A1 - Bake, Sebastian A1 - Antonietti, Markus A1 - Taubert, Andreas A1 - Esposito, Davido T1 - Renewable pyridinium ionic liquids from the continuous hydrothermal decarboxylation of furfural-amino acid derived pyridinium zwitterions N2 - Fully renewable pyridinium ionic liquids were synthesised via the hydrothermal decarboxylation of pyridinium zwitterions derived from furfural and amino acids in flow. The functionality of the resulting ionic liquid (IL) can be tuned by choice of different amino acids as well as different natural carboxylic acids as the counterions. A representative member of this new class of ionic liquids was successfully used for the synthesis of ionogels and as a solvent for the Heck coupling. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 198 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-81390 ER - TY - GEN A1 - Bartoloni, Marco A1 - Jin, Xian A1 - Marcaida, Maria José A1 - Banha, Joao A1 - Dibonaventura, Ivan A1 - Bongoni, Swathi A1 - Bartho, Kathrin A1 - Gräbner, Olivia A1 - Sefkow, Michael A1 - Darbre, Tamis A1 - Reymond, Jean-Louis T1 - Bridged bicyclic peptides as potential drug scaffolds BT - synthesis, structure, protein binding and stability N2 - Double cyclization of short linear peptides obtained by solid phase peptide synthesis was used to prepare bridged bicyclic peptides (BBPs) corresponding to the topology of bridged bicyclic alkanes such as norbornane. Diastereomeric norbornapeptides were investigated by 1H-NMR, X-ray crystallography and CD spectroscopy and found to represent rigid globular scaffolds stabilized by intramolecular backbone hydrogen bonds with scaffold geometries determined by the chirality of amino acid residues and sharing structural features of β-turns and α-helices. Proteome profiling by capture compound mass spectrometry (CCMS) led to the discovery of the norbornapeptide 27c binding selectively to calmodulin as an example of a BBP protein binder. This and other BBPs showed high stability towards proteolytic degradation in serum. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 197 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-81239 ER - TY - JOUR A1 - Bartoloni, Marco A1 - Jin, Xian A1 - Marcaida, Maria José A1 - Banha, Joao A1 - Dibonaventura, Ivan A1 - Bongoni, Swathi A1 - Bartho, Kathrin A1 - Gräbner, Olivia A1 - Sefkow, Michael A1 - Darbre, Tamis A1 - Reymond, Jean-Louis T1 - Bridged bicyclic peptides as potential drug scaffolds BT - synthesis, structure, protein binding and stability JF - Chemical Science N2 - Double cyclization of short linear peptides obtained by solid phase peptide synthesis was used to prepare bridged bicyclic peptides (BBPs) corresponding to the topology of bridged bicyclic alkanes such as norbornane. Diastereomeric norbornapeptides were investigated by 1H-NMR, X-ray crystallography and CD spectroscopy and found to represent rigid globular scaffolds stabilized by intramolecular backbone hydrogen bonds with scaffold geometries determined by the chirality of amino acid residues and sharing structural features of β-turns and α-helices. Proteome profiling by capture compound mass spectrometry (CCMS) led to the discovery of the norbornapeptide 27c binding selectively to calmodulin as an example of a BBP protein binder. This and other BBPs showed high stability towards proteolytic degradation in serum. Y1 - 2015 U6 - https://doi.org/10.1039/C5SC01699A SN - 2041-6520 SN - 2041-6539 VL - 10 IS - 6 SP - 5473 EP - 5490 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Schulze, Michael A1 - Utecht, Manuel Martin A1 - Moldt, Thomas A1 - Przyrembel, Daniel A1 - Gahl, Cornelius A1 - Weinelt, Martin A1 - Saalfrank, Peter A1 - Tegeder, Petra T1 - Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers N2 - The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10−18 cm2 for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 196 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-81198 ER - TY - JOUR A1 - Schulze, Michael A1 - Utecht, Manuel Martin A1 - Moldt, Thomas A1 - Przyrembel, Daniel A1 - Gahl, Cornelius A1 - Weinelt, Martin A1 - Saalfrank, Peter A1 - Tegeder, Petra T1 - Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers JF - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies N2 - The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10−18 cm2 for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions. Y1 - 2015 U6 - https://doi.org/10.1039/c5cp03093e SN - 1463-9076 SN - 1463-9084 VL - 27 IS - 17 SP - 18079 EP - 18086 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Guha, S. A1 - Warsinke, A. A1 - Tientcheu, Ch. M. A1 - Schmalz, K. A1 - Meliani, C. A1 - Wenger, Ch. T1 - Label free sensing of creatinine using a 6 GHz CMOS near-field dielectric immunosensor N2 - In this work we present a CMOS high frequency direct immunosensor operating at 6 GHz (C-band) for label free determination of creatinine. The sensor is fabricated in standard 0.13 μm SiGe:C BiCMOS process. The report also demonstrates the ability to immobilize creatinine molecules on a Si3N4 passivation layer of the standard BiCMOS/CMOS process, therefore, evading any further need of cumbersome post processing of the fabricated sensor chip. The sensor is based on capacitive detection of the amount of non-creatinine bound antibodies binding to an immobilized creatinine layer on the passivated sensor. The chip bound antibody amount in turn corresponds indirectly to the creatinine concentration used in the incubation phase. The determination of creatinine in the concentration range of 0.88–880 μM is successfully demonstrated in this work. A sensitivity of 35 MHz/10 fold increase in creatinine concentration (during incubation) at the centre frequency of 6 GHz is gained by the immunosensor. The results are compared with a standard optical measurement technique and the dynamic range and sensitivity is of the order of the established optical indication technique. The C-band immunosensor chip comprising an area of 0.3 mm2 reduces the sensing area considerably, therefore, requiring a sample volume as low as 2 μl. The small analyte sample volume and label free approach also reduce the experimental costs in addition to the low fabrication costs offered by the batch fabrication technique of CMOS/BiCMOS process. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 195 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-81177 ER - TY - JOUR A1 - Guha, S. A1 - Warsinke, A. A1 - Tientcheu, Ch. M. A1 - Schmalz, K. A1 - Meliani, C. A1 - Wenger, Ch. T1 - Label free sensing of creatinine using a 6 GHz CMOS near-field dielectric immunosensor JF - The analyst : the analytical journal of the Royal Society of Chemistry N2 - In this work we present a CMOS high frequency direct immunosensor operating at 6 GHz (C-band) for label free determination of creatinine. The sensor is fabricated in standard 0.13 μm SiGe:C BiCMOS process. The report also demonstrates the ability to immobilize creatinine molecules on a Si3N4 passivation layer of the standard BiCMOS/CMOS process, therefore, evading any further need of cumbersome post processing of the fabricated sensor chip. The sensor is based on capacitive detection of the amount of non-creatinine bound antibodies binding to an immobilized creatinine layer on the passivated sensor. The chip bound antibody amount in turn corresponds indirectly to the creatinine concentration used in the incubation phase. The determination of creatinine in the concentration range of 0.88–880 μM is successfully demonstrated in this work. A sensitivity of 35 MHz/10 fold increase in creatinine concentration (during incubation) at the centre frequency of 6 GHz is gained by the immunosensor. The results are compared with a standard optical measurement technique and the dynamic range and sensitivity is of the order of the established optical indication technique. The C-band immunosensor chip comprising an area of 0.3 mm2 reduces the sensing area considerably, therefore, requiring a sample volume as low as 2 μl. The small analyte sample volume and label free approach also reduce the experimental costs in addition to the low fabrication costs offered by the batch fabrication technique of CMOS/BiCMOS process. Y1 - 2015 U6 - https://doi.org/10.1039/c4an02194k SN - 0003-2654 SN - 1364-5528 VL - 9 IS - 140 SP - 3019 EP - 3027 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Niedl, Robert Raimund A1 - Beta, Carsten T1 - Hydrogel-driven paper-based microfluidics JF - LAB on a chip : miniaturisation for chemistry and biology N2 - Paper-based microfluidics provide an inexpensive, easy to use technology for point-of-care diagnostics in developing countries. Here, we combine paper-based microfluidic devices with responsive hydrogels to add an entire new class of functions to these versatile low-cost fluidic systems. The hydrogels serve as fluid reservoirs. In response to an external stimulus, e.g. an increase in temperature, the hydrogels collapse and release fluid into the structured paper substrate. In this way, chemicals that are either stored on the paper substrate or inside the hydrogel pads can be dissolved, premixed, and brought to reaction to fulfill specific analytic tasks. We demonstrate that multi-step sequences of chemical reactions can be implemented in a paper-based system and operated without the need for external precision pumps. We exemplify this technology by integrating an antibody-based E. coli test on a small and easy to use paper device. Y1 - 2015 U6 - https://doi.org/10.1039/c5lc00276a SN - 1473-0197 SN - 1473-0189 VL - 11 IS - 15 SP - 2452 EP - 2459 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Niedl, Robert Raimund A1 - Beta, Carsten T1 - Hydrogel-driven paper-based microfluidics N2 - Paper-based microfluidics provide an inexpensive, easy to use technology for point-of-care diagnostics in developing countries. Here, we combine paper-based microfluidic devices with responsive hydrogels to add an entire new class of functions to these versatile low-cost fluidic systems. The hydrogels serve as fluid reservoirs. In response to an external stimulus, e.g. an increase in temperature, the hydrogels collapse and release fluid into the structured paper substrate. In this way, chemicals that are either stored on the paper substrate or inside the hydrogel pads can be dissolved, premixed, and brought to reaction to fulfill specific analytic tasks. We demonstrate that multi-step sequences of chemical reactions can be implemented in a paper-based system and operated without the need for external precision pumps. We exemplify this technology by integrating an antibody-based E. coli test on a small and easy to use paper device. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 193 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-81083 SP - 2452 EP - 2459 ER - TY - JOUR A1 - Nöchel, Ulrich A1 - Reddy, Chaganti Srinivasa A1 - Wang, Ke A1 - Cui, Jing A1 - Zizak, Ivo A1 - Behl, Marc A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Nanostructural changes in crystallizable controlling units determine the temperature-memory of polymers JF - Journal of Materials Chemistry A, Materials for energy and sustainability N2 - Temperature-memory polymers remember the temperature, where they were deformed recently, enabled by broad thermal transitions. In this study, we explored a series of crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) comprising crystallizable polyethylene (PE) controlling units exhibiting a pronounced temperature-memory effect (TME) between 16 and 99 °C related to a broad melting transition (∼100 °C). The nanostructural changes in such cPEVAs during programming and activation of the TME were analyzed via in situ X-ray scattering and specific annealing experiments. Different contributions to the mechanism of memorizing high or low deformation temperatures (Tdeform) were observed in cPEVA, which can be associated to the average PE crystal sizes. At high deformation temperatures (>50 °C), newly formed PE crystals, which are established during cooling when fixing the temporary shape, dominated the TME mechanism. In contrast, at low Tdeform (<50 °C), corresponding to a cold drawing scenario, the deformation led preferably to a disruption of existing large crystals into smaller ones, which then fix the temporary shape upon cooling. The observed mechanism of memorizing a deformation temperature might enable the prediction of the TME behavior and the knowledge based design of other TMPs with crystallizable controlling units. Y1 - 2015 U6 - https://doi.org/10.1039/c4ta06586g SN - 2050-7488 SN - 2050-7496 VL - 16 IS - 3 SP - 8284 EP - 8293 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Nöchel, Ulrich A1 - Reddy, Chaganti Srinivasa A1 - Wang, Ke A1 - Cui, Jing A1 - Zizak, Ivo A1 - Behl, Marc A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Nanostructural changes in crystallizable controlling units determine the temperature-memory of polymers N2 - Temperature-memory polymers remember the temperature, where they were deformed recently, enabled by broad thermal transitions. In this study, we explored a series of crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) comprising crystallizable polyethylene (PE) controlling units exhibiting a pronounced temperature-memory effect (TME) between 16 and 99 °C related to a broad melting transition (∼100 °C). The nanostructural changes in such cPEVAs during programming and activation of the TME were analyzed via in situ X-ray scattering and specific annealing experiments. Different contributions to the mechanism of memorizing high or low deformation temperatures (Tdeform) were observed in cPEVA, which can be associated to the average PE crystal sizes. At high deformation temperatures (>50 °C), newly formed PE crystals, which are established during cooling when fixing the temporary shape, dominated the TME mechanism. In contrast, at low Tdeform (<50 °C), corresponding to a cold drawing scenario, the deformation led preferably to a disruption of existing large crystals into smaller ones, which then fix the temporary shape upon cooling. The observed mechanism of memorizing a deformation temperature might enable the prediction of the TME behavior and the knowledge based design of other TMPs with crystallizable controlling units. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 194 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-81124 SP - 8284 EP - 8293 ER - TY - THES A1 - Primus, Philipp-Alexander T1 - High resolution spectroscopy as a tool to unravel structure-reactivity relationships in Eu3+ doped ceria/ceria-zirconia based catalyst nanomaterials Y1 - 2015 ER - TY - THES A1 - Yuan, Jiayin T1 - Poly(Ionic Liquid)s BT - innovative polyelectrolytes for materials applications Y1 - 2015 ER - TY - THES A1 - Grygiel, Konrad T1 - Poly(ionic liquid) stabilizers and new synthetic approaches T1 - Polyionische Flüssigkeiten als Stabilisatoren und neue Synthesewege N2 - The main focus of the present thesis was to investigate the stabilization ability of poly(ionic liquid)s (PILs) in several examples as well as develop novel chemical structures and synthetic routes of PILs. The performed research can be specifically divided into three parts that include synthesis and application of hybrid material composed of PIL and cellulose nanofibers (CNFs), thiazolium-containing PILs, and main-chain imidazolium-type PILs. In the first chapter, a vinylimidazolium-type IL was polymerized in water in the presence of CNFs resulting in the in situ electrostatic grafting of polymeric chains onto the surface of CNFs. The synthesized hybrid material merged advantages of its two components, that is, superior mechanical strength of CNFs and anion dependent solution properties of PILs. In contrast to unmodified CNFs, the hybrid could be stabilized and processed in organic solvents enabling its application as reinforcing agent for porous polyelectrolyte membranes. In the second part, PILs and ionic polymers containing two types of thiazolium repeating units were synthesized. Such polymers displayed counterion dependent thermal stability and solubility in organic solvents of various dielectric constants. This new class of PILs was tested as stabilizers and phase transfer agents for carbon nanotubes in aqueous and organic media, and as binder materials to disperse electroactive powders and carbon additives in solid electrode in lithium-ion batteries. The incorporation of S and N atoms into the polymeric structures make such PILs also potential precursors for S, N - co-doped carbons. In the last chapter, reactants originating from biomass were successfully harnessed to synthesize main-chain imidazolium-type PILs. An imidazolium-type diester IL obtained via a modified Debus-Radziszewski reaction underwent transesterification with diol in a polycondensation reaction. This yielded a polyester-type PIL which CO2 sorption properties were investigated. In the next step, the modified Debus-Radziszewski reaction was further applied to synthesize main-chain PILs according to a convenient, one-step protocol, using water as a green solvent and simple organic molecules as reagents. Depending on the structure of the employed diamine, the synthesized PILs after anion exchange showed superior thermal stability with unusually high carbonization yields. Overall, the outcome of these studies will actively contribute to the current research on PILs by introducing novel PIL chemical structures, improved synthetic routes, and new examples of stabilized materials. The synthesis of main-chain imidazolium-type PILs by a modified Debus-Radziszewski reaction is of a special interest for the future work on porous ionic liquid networks as well as colloidal PIL nanoparticles. N2 - Im Mittelpunkt der vorliegenden Arbeit stand die Entwicklung neuer polymerer ionischen Flüssigkeiten (PILs) mittels neuer Synthesewege als auch auf diesen PILs basierenden Kompositmaterialien. Die hergestellten Materialien wurden folgend hinsichtlich ihrer Tauglichkeit als Stabilisatoren, Phasentransferreagenzien, „binder“ oder CO2-Absorber untersucht. Die Untersuchungen lassen sich in drei Teile untergliedern und beinhalten Herstellung und Anwendungsuntersuchungen von Hybridmaterialien basierend auf PILs und Cellulosefasern im Nanometerbereich (CNF), von PILs mit Thiazoliumgruppen und schließlich PILs welche teilweise oder vollständig aus Biomaterialien hergestellt wurden mit Imidazoliumgruppen in der Hauptkette. In Gegenwart von CNF wurde eine vinylimidazoliumbasierte ionische Flüssigkeit (IL) in Wasser polymerisiert. Dies führte in situ zu einem elektrostatischen angraften der Ketten auf der Oberfläche der CNFs. Diese Kompositmaterialien vereinigen die Vorteile beider Komponenten, die außerordentliche mechanische Stabilität der CNFs und die vielseitigen mittels Gegenionen einstellbaren Lösungseigenschaften der PIL. Beispielsweise können diese Hybridmaterialien im Gegensatz zu den unmodifizierten CNFs in organischen Lösungsmitteln und somit zur Verstärkung für poröse Polyelektrolytmembranen eingesetzt werden. Im zweiten Teil wurden PILs und ioniosche Polymere synthetisiert mit Thiazoliumkationen in den Monomerbausteinen. Diese Polymere zeigten eine vom Gegenion abhängige thermische Stabilität und Löslichkeit in Lösungsmitteln verschiedenster Dielektrizitätskonstanten. Diese neue Klasse der PILs bzw. ionischen Polymere wurde hinsichtlich der Nutzbarkeit als Vorläufer für Stickstoff- und Schwefel-codotierte Kohlenstoffsysteme, Stabilisator sowie Phasentransferreagenz für „carbon nanotubes“ in wässrigem und organischen Lösungsmitteln und „binder“ für Elektrodenmaterialien in Lithiumionenbatterien. Im letzten Teil wurden aus Biomaterialien die Ausgangsstoffe für PILs mit imidazoliumbasierter Hauptkette gewonnen. Hierzu wurde der imidazoliumbasierende Diester mittels abgewandelter Debus-Radziszewski-Reaktion gewonnen und eine Umesterung mittels eines ebenfalls aus Biomaterialien stammenden Diols vorgenommen. Die erhaltene polyesterbasierte PIL wurde folgend hinsichtlich ihres CO2 – Absorbtionspotentials untersucht. Die geänderte Debus-Radziszewski-Reaktion wurde folgend für eine PIL-Einstufensynthese mit Wasser als grünem Lösungsmittel und einfachen hauptsächlich aus Biomasse gewonnen Reagenzien herangezogen. Abhängig von den eingesetzten Diaminen und Gegenionen konnten für die hergestellten PILs hervorragende thermische Stabilitäten oder beträchtliche Karbonisierungsausbeuten erreicht werden, welche für PILs zu den höchsten publizierten Werten in der Literatur zählen. Die vorgelegten Studien stellen einen wichtigen Beitrag auf dem Gebiet der PIL-Forschung dar mit neuen PIL-Strukturen, verbesserten Synthesewegen und neuen Stabilisierungsmöglichkeiten. Die Synthese der Hauptkettenimidazolium-PIL mittels angepasster Debus-Radziszewski-Reaktion ist eine vielversprechende Methode sowohl für die Herstellung poröser IL-Netzwerke als auch kolloidaler PIL-Nanopartikel. KW - ionic polymers KW - polymerised ionic liquids KW - ionic liquids KW - Debus-Radziszewski polymerization KW - thiazolium KW - ionische Flüssigkeit KW - Thiazol-Salze KW - ionischen Polymere KW - elektroaktive Polymere Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-80367 ER - TY - GEN A1 - Mondal, Suvendu Sekhar A1 - Behrens, Karsten A1 - Matthes, Philipp R. A1 - Schönfeld, Fabian A1 - Nitsch, Jörn A1 - Steffen, Andreas A1 - Primus, Philipp-Alexander A1 - Kumke, Michael Uwe A1 - Müller-Buschbaum, Klaus A1 - Holdt, Hans-Jürgen T1 - White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+ N2 - Co-doping of the MOF 3∞[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a–d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 190 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-79953 SP - 4623 EP - 4631 ER - TY - JOUR A1 - Mondal, Suvendu Sekhar A1 - Behrens, Karsten A1 - Matthes, Philipp R. A1 - Schönfeld, Fabian A1 - Nitsch, Jörn A1 - Steffen, Andreas A1 - Primus, Philipp-Alexander A1 - Kumke, Michael Uwe A1 - Müller-Buschbaum, Klaus A1 - Holdt, Hans-Jürgen T1 - White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+ JF - Journal of materials chemistry : C, Materials for optical and electronic devices N2 - Co-doping of the MOF 3∞[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a–d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+. Y1 - 2015 U6 - https://doi.org/10.1039/C4TC02919D SN - 2050-7534 SN - 2050-7526 VL - 18 IS - 3 SP - 4623 EP - 4631 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Megow, Jörg A1 - Röhr, Merle I. S. A1 - Schmidt am Busch, Marcel A1 - Renger, Thomas A1 - Mitrić, Roland A1 - Kirstein, Stefan A1 - Rabe, Jürgen P. A1 - May, Volkhard T1 - Site-dependence of van der Waals interaction explains exciton spectra of double-walled tubular J-aggregates N2 - The simulation of the optical properties of supramolecular aggregates requires the development of methods, which are able to treat a large number of coupled chromophores interacting with the environment. Since it is currently not possible to treat large systems by quantum chemistry, the Frenkel exciton model is a valuable alternative. In this work we show how the Frenkel exciton model can be extended in order to explain the excitonic spectra of a specific double-walled tubular dye aggregate explicitly taking into account dispersive energy shifts of ground and excited states due to van der Waals interaction with all surrounding molecules. The experimentally observed splitting is well explained by the site-dependent energy shift of molecules placed at the inner or outer side of the double-walled tube, respectively. Therefore we can conclude that inclusion of the site-dependent dispersive effect in the theoretical description of optical properties of nanoscaled dye aggregates is mandatory. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 191 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-79978 SP - 6741 EP - 6747 ER - TY - JOUR A1 - Megow, Jörg A1 - Röhr, Merle I. S. A1 - Schmidt am Busch, Marcel A1 - Renger, Thomas A1 - Mitrić, Roland A1 - Kirstein, Stefan A1 - Rabe, Jürgen P. A1 - May, Volkhard T1 - Site-dependence of van der Waals interaction explains exciton spectra of double-walled tubular J-aggregates JF - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies N2 - The simulation of the optical properties of supramolecular aggregates requires the development of methods, which are able to treat a large number of coupled chromophores interacting with the environment. Since it is currently not possible to treat large systems by quantum chemistry, the Frenkel exciton model is a valuable alternative. In this work we show how the Frenkel exciton model can be extended in order to explain the excitonic spectra of a specific double-walled tubular dye aggregate explicitly taking into account dispersive energy shifts of ground and excited states due to van der Waals interaction with all surrounding molecules. The experimentally observed splitting is well explained by the site-dependent energy shift of molecules placed at the inner or outer side of the double-walled tube, respectively. Therefore we can conclude that inclusion of the site-dependent dispersive effect in the theoretical description of optical properties of nanoscaled dye aggregates is mandatory. Y1 - 2015 U6 - https://doi.org/10.1039/c4cp05945j SN - 1463-9084 SN - 1463-9076 VL - 17 IS - 10 SP - 6741 EP - 6747 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Crone, Barbara A1 - Aschner, Michael A. A1 - Schwerdtle, Tanja A1 - Karst, Uwe A1 - Bornhorst, Julia T1 - Elemental bioimaging of Cisplatin in Caenorhabditis elegans by LA-ICP-MS N2 - cis-Diamminedichloroplatinum(II) (Cisplatin) is one of the most important and frequently used cytostatic drugs for the treatment of various solid tumors. Herein, a laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) method incorporating a fast and simple sample preparation protocol was developed for the elemental mapping of Cisplatin in the model organism Caenorhabditis elegans (C. elegans). The method allows imaging of the spatially-resolved elemental distribution of platinum in the whole organism with respect to the anatomic structure in L4 stage worms at a lateral resolution of 5 μm. In addition, a dose- and time-dependent Cisplatin uptake was corroborated quantitatively by a total reflection X-ray fluorescence spectroscopy (TXRF) method, and the elemental mapping indicated that Cisplatin is located in the intestine and in the head of the worms. Better understanding of the distribution of Cisplatin in this well-established model organism will be instrumental in deciphering Cisplatin toxicity and pharmacokinetics. Since the cytostatic effect of Cisplatin is based on binding the DNA by forming intra- and interstrand crosslinks, the response of poly(ADP-ribose)metabolism enzyme 1 (pme-1) deletion mutants to Cisplatin was also examined. Loss of pme-1, which is the C. elegans ortholog of human poly(ADP-ribose) polymerase 1 (PARP-1) led to disturbed DNA damage response. With respect to survival and brood size, pme-1 deletion mutants were more sensitive to Cisplatin as compared to wildtype worms, while Cisplatin uptake was indistinguishable. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 192 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-80031 SP - 1189 EP - 1195 ER - TY - JOUR A1 - Crone, Barbara A1 - Aschner, Michael A. A1 - Schwerdtle, Tanja A1 - Karst, Uwe A1 - Bornhorst, Julia T1 - Elemental bioimaging of Cisplatin in Caenorhabditis elegans by LA-ICP-MS JF - Metallomics N2 - cis-Diamminedichloroplatinum(II) (Cisplatin) is one of the most important and frequently used cytostatic drugs for the treatment of various solid tumors. Herein, a laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) method incorporating a fast and simple sample preparation protocol was developed for the elemental mapping of Cisplatin in the model organism Caenorhabditis elegans (C. elegans). The method allows imaging of the spatially-resolved elemental distribution of platinum in the whole organism with respect to the anatomic structure in L4 stage worms at a lateral resolution of 5 μm. In addition, a dose- and time-dependent Cisplatin uptake was corroborated quantitatively by a total reflection X-ray fluorescence spectroscopy (TXRF) method, and the elemental mapping indicated that Cisplatin is located in the intestine and in the head of the worms. Better understanding of the distribution of Cisplatin in this well-established model organism will be instrumental in deciphering Cisplatin toxicity and pharmacokinetics. Since the cytostatic effect of Cisplatin is based on binding the DNA by forming intra- and interstrand crosslinks, the response of poly(ADP-ribose)metabolism enzyme 1 (pme-1) deletion mutants to Cisplatin was also examined. Loss of pme-1, which is the C. elegans ortholog of human poly(ADP-ribose) polymerase 1 (PARP-1) led to disturbed DNA damage response. With respect to survival and brood size, pme-1 deletion mutants were more sensitive to Cisplatin as compared to wildtype worms, while Cisplatin uptake was indistinguishable. Y1 - 2015 U6 - https://doi.org/10.1039/c5mt00096c SN - 1756-591X SN - 1756-5901 VL - 2015 IS - 7 SP - 1189 EP - 1195 PB - Royal Society of Chemistry CY - Cambridge ER - TY - THES A1 - Kirchhecker, Sarah T1 - Renewable imidazolium zwitterions as platform molecules for the synthesis of ionic liquids and materials T1 - Neue funktionalisierte Imidazoliumverbindungen als Bausteinmoleküle aus Biomasse und ihre Verwendung zur Synthese von ionischen Flüssigkeiten und Materialien N2 - Following the principles of green chemistry, a simple and efficient synthesis of functionalised imidazolium zwitterionic compounds from renewable resources was developed based on a modified one-pot Debus-Radziszewski reaction. The combination of different carbohydrate-derived 1,2-dicarbonyl compounds and amino acids is a simple way to modulate the properties and introduce different functionalities. A representative compound was assessed as an acid catalyst, and converted into acidic ionic liquids by reaction with several strong acids. The reactivity of the double carboxylic functionality was explored by esterification with long and short chain alcohols, as well as functionalised amines, which led to the straightforward formation of surfactant-like molecules or bifunctional esters and amides. One of these di-esters is currently being investigated for the synthesis of poly(ionic liquids). The functionalisation of cellulose with one of the bifunctional esters was investigated and preliminary tests employing it for the functionalisation of filter papers were carried out successfully. The imidazolium zwitterions were converted into ionic liquids via hydrothermal decarboxylation in flow, a benign and scalable technique. This method provides access to imidazolium ionic liquids via a simple and sustainable methodology, whilst completely avoiding contamination with halide salts. Different ionic liquids can be generated depending on the functionality contained in the ImZw precursor. Two alanine-derived ionic liquids were assessed for their physicochemical properties and applications as solvents for the dissolution of cellulose and the Heck coupling. N2 - In dieser Arbeit wurden, den Prinzipien der nachhaltigen Chemie folgend, neue funktionalisierte Imidazolium-Verbindungen aus Biomasse hergestellt. Diese wurden als Plattformmoleküle verwendet, die durch einfache Derivation in verschiedene andere Verbindungen überführt, und als Bausteine für die Herstellung von Materialien genutzt werden können. Imidazolium Zwitterionen (ImZw) wurden in Eintopfreaktionen in Wasser dargestellt, wobei alle Ausgangsstoffe auf nachwachsenden Rohstoffen basierten Durch die Verwendung von Aminosaeuren wurden die ImZw durch die Wahl der verschiedenen Seitenketten direkt funktionalisiert. Die Säureeigenschaften der Moleküle wurden bestimmt und ihre Eignung als Katalysatoren überprüft. An einer Modellverbindung ewurden verschiedene Modifikationen der Carboxylgruppen unternommen, u.a. wurde es mit verschiedenen Alkoholen esterifiziert, und anfolgend auch mit verschiedenen Aminen amidiert. Eines von den esterifizierten ImZw wurde als Monomer für die Synthese einer komplett aus nachwachsenden Rohstoffen hergestellten polyionischen Flüssigkeit verwendet, sowie für die Funktionalisierung von Cellulosefasern und Filterpapieren. Des weiteren wurden die ImZw unter hydrothermalen Bedingungen in der Gegenwart von Essigsäure decarboxyliert und so in ionische Flüssigkeiten überführt. Diese Reaktionen wurden in einem Durchflußreaktor durchgeführt, der gegenüber anderen Synthesemethoden weniger Energie verwendet. Die so hergestellten ionischen Flüssigkeiten wurden in zwei Anwendungen getestet, wo sie sehr vielversprechende Ergebnisse zeigten. Eine wurde als Lösungsmittel in einer Heck Reaktion verwendet, wo der Pd-Katalysator 5 mal ohne Aktivitätsverlust recycelt werden konnte eine andere konnte einen hohe Menge an Cellulose (16.9 wt%) lösen. KW - ionic liquids KW - platform chemicals KW - renewables KW - imidazolium KW - green chemistry KW - hydrothermal KW - ionische Flüssigkeiten KW - nachhaltige Chemie KW - Imidazolium KW - Zwitterionen KW - nachwachsende Rohstoffe Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-77412 ER - TY - THES A1 - Ippen, Christian Justus T1 - Indium phosphide and zinc selenide quantum dots for light-emitting devices BT - relationships between surface structure and device performance Y1 - 2014 ER - TY - GEN A1 - Ghosh, Surya K. A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf T1 - Non-universal tracer diffusion in crowded media of non-inert obstacles N2 - We study the diffusion of a tracer particle, which moves in continuum space between a lattice of excluded volume, immobile non-inert obstacles. In particular, we analyse how the strength of the tracer–obstacle interactions and the volume occupancy of the crowders alter the diffusive motion of the tracer. From the details of partitioning of the tracer diffusion modes between trapping states when bound to obstacles and bulk diffusion, we examine the degree of localisation of the tracer in the lattice of crowders. We study the properties of the tracer diffusion in terms of the ensemble and time averaged mean squared displacements, the trapping time distributions, the amplitude variation of the time averaged mean squared displacements, and the non-Gaussianity parameter of the diffusing tracer. We conclude that tracer–obstacle adsorption and binding triggers a transient anomalous diffusion. From a very narrow spread of recorded individual time averaged trajectories we exclude continuous type random walk processes as the underlying physical model of the tracer diffusion in our system. For moderate tracer–crowder attraction the motion is found to be fully ergodic, while at stronger attraction strength a transient disparity between ensemble and time averaged mean squared displacements occurs. We also put our results into perspective with findings from experimental single-particle tracking and simulations of the diffusion of tagged tracers in dense crowded suspensions. Our results have implications for the diffusion, transport, and spreading of chemical components in highly crowded environments inside living cells and other structured liquids. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 186 KW - escence correlation spectroscopy KW - single-particle tracking KW - anomalous diffusion KW - living cells KW - physiological consequences KW - langevin equation KW - infection pathway KW - excluded volume KW - brownian-motion KW - random-walks Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-77128 SP - 1847 EP - 1858 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Ghosh, Surya K. A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf ED - Metzler, Ralf T1 - Non-universal tracer diffusion in crowded media of non-inert obstacles JF - Physical Chemistry Chemical Physics N2 - We study the diffusion of a tracer particle, which moves in continuum space between a lattice of excluded volume, immobile non-inert obstacles. In particular, we analyse how the strength of the tracer–obstacle interactions and the volume occupancy of the crowders alter the diffusive motion of the tracer. From the details of partitioning of the tracer diffusion modes between trapping states when bound to obstacles and bulk diffusion, we examine the degree of localisation of the tracer in the lattice of crowders. We study the properties of the tracer diffusion in terms of the ensemble and time averaged mean squared displacements, the trapping time distributions, the amplitude variation of the time averaged mean squared displacements, and the non-Gaussianity parameter of the diffusing tracer. We conclude that tracer–obstacle adsorption and binding triggers a transient anomalous diffusion. From a very narrow spread of recorded individual time averaged trajectories we exclude continuous type random walk processes as the underlying physical model of the tracer diffusion in our system. For moderate tracer–crowder attraction the motion is found to be fully ergodic, while at stronger attraction strength a transient disparity between ensemble and time averaged mean squared displacements occurs. We also put our results into perspective with findings from experimental single-particle tracking and simulations of the diffusion of tagged tracers in dense crowded suspensions. Our results have implications for the diffusion, transport, and spreading of chemical components in highly crowded environments inside living cells and other structured liquids. KW - fluorescence correlation spectroscopy KW - single-particle tracking KW - anomalous diffusion KW - living cells KW - physiological consequences KW - langevin equation KW - infection pathway KW - excluded volume KW - brownian-motion KW - random-walks Y1 - 2014 SN - 1463-9076 VL - 3 IS - 17 SP - 1847 EP - 1858 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Shin, Jaeoh A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf T1 - Kinetics of polymer looping with macromolecular crowding: effects of volume fraction and crowder size N2 - The looping of polymers such as DNA is a fundamental process in the molecular biology of living cells, whose interior is characterised by a high degree of molecular crowding. We here investigate in detail the looping dynamics of flexible polymer chains in the presence of different degrees of crowding. From the analysis of the looping–unlooping rates and the looping probabilities of the chain ends we show that the presence of small crowders typically slows down the chain dynamics but larger crowders may in fact facilitate the looping. We rationalise these non-trivial and often counterintuitive effects of the crowder size on the looping kinetics in terms of an effective solution viscosity and standard excluded volume. It is shown that for small crowders the effect of an increased viscosity dominates, while for big crowders we argue that confinement effects (caging) prevail. The tradeoff between both trends can thus result in the impediment or facilitation of polymer looping, depending on the crowder size. We also examine how the crowding volume fraction, chain length, and the attraction strength of the contact groups of the polymer chain affect the looping kinetics and hairpin formation dynamics. Our results are relevant for DNA looping in the absence and presence of protein mediation, DNA hairpin formation, RNA folding, and the folding of polypeptide chains under biologically relevant high-crowding conditions. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 185 KW - gene-regulation kinetics KW - physiological consequences KW - spatial-organization KW - anomalous diffusion KW - folding kinetics KW - living cells KW - dna coiling KW - in-vitro KW - dynamics KW - mixtures Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-76961 SP - 472 EP - 488 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Shin, Jaeoh A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf ED - Metzler, Ralf T1 - Kinetics of polymer looping with macromolecular crowding: effects of volume fraction and crowder size JF - Soft Matter N2 - The looping of polymers such as DNA is a fundamental process in the molecular biology of living cells, whose interior is characterised by a high degree of molecular crowding. We here investigate in detail the looping dynamics of flexible polymer chains in the presence of different degrees of crowding. From the analysis of the looping–unlooping rates and the looping probabilities of the chain ends we show that the presence of small crowders typically slows down the chain dynamics but larger crowders may in fact facilitate the looping. We rationalise these non-trivial and often counterintuitive effects of the crowder size on the looping kinetics in terms of an effective solution viscosity and standard excluded volume. It is shown that for small crowders the effect of an increased viscosity dominates, while for big crowders we argue that confinement effects (caging) prevail. The tradeoff between both trends can thus result in the impediment or facilitation of polymer looping, depending on the crowder size. We also examine how the crowding volume fraction, chain length, and the attraction strength of the contact groups of the polymer chain affect the looping kinetics and hairpin formation dynamics. Our results are relevant for DNA looping in the absence and presence of protein mediation, DNA hairpin formation, RNA folding, and the folding of polypeptide chains under biologically relevant high-crowding conditions. KW - gene-regulation kinetics KW - physiological consequences KW - spatial-organization KW - anomalous diffusion KW - folding kinetics KW - living cells KW - dna coiling KW - in-vitro KW - dynamics KW - mixtures Y1 - 2014 SN - 1744-683X SP - 472 EP - 488 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Roder, Phillip A1 - Hille, Carsten T1 - ANG-2 for quantitative Na+ determination in living cells by time-resolved fluorescence microscopy N2 - Sodium ions (Na+) play an important role in a plethora of cellular processes, which are complex and partly still unexplored. For the investigation of these processes and quantification of intracellular Na+ concentrations ([Na+]i), two-photon coupled fluorescence lifetime imaging microscopy (2P-FLIM) was performed in the salivary glands of the cockroach Periplaneta americana. For this, the novel Na+-sensitive fluorescent dye Asante NaTRIUM Green-2 (ANG-2) was evaluated, both in vitro and in situ. In this context, absorption coefficients, fluorescence quantum yields and 2P action cross-sections were determined for the first time. ANG-2 was 2P-excitable over a broad spectral range and displayed fluorescence in the visible spectral range. Although the fluorescence decay behaviour of ANG-2 was triexponential in vitro, its analysis indicates a Na+-sensitivity appropriate for recordings in living cells. The Na+-sensitivity was reduced in situ, but the biexponential fluorescence decay behaviour could be successfully analysed in terms of quantitative [Na+]i recordings. Thus, physiological 2P-FLIM measurements revealed a dopamine-induced [Na+]i rise in cockroach salivary gland cells, which was dependent on a Na+-K+-2Cl− cotransporter (NKCC) activity. It was concluded that ANG-2 is a promising new sodium indicator applicable for diverse biological systems. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 184 KW - cockroach salivary-glands KW - intracellular na+ KW - sodium green KW - periplaneta-americana KW - ventricular myocytes KW - lifetime microscopy KW - acinar-cells KW - hela-cells KW - rat Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-76851 SP - 1699 EP - 1710 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Roder, Phillip A1 - Hille, Carsten ED - Hille, Carsten T1 - ANG-2 for quantitative Na+ determination in living cells by time-resolved fluorescence microscopy JF - Photochemical & Photobiological Sciences N2 - Sodium ions (Na+) play an important role in a plethora of cellular processes, which are complex and partly still unexplored. For the investigation of these processes and quantification of intracellular Na+ concentrations ([Na+]i), two-photon coupled fluorescence lifetime imaging microscopy (2P-FLIM) was performed in the salivary glands of the cockroach Periplaneta americana. For this, the novel Na+-sensitive fluorescent dye Asante NaTRIUM Green-2 (ANG-2) was evaluated, both in vitro and in situ. In this context, absorption coefficients, fluorescence quantum yields and 2P action cross-sections were determined for the first time. ANG-2 was 2P-excitable over a broad spectral range and displayed fluorescence in the visible spectral range. Although the fluorescence decay behaviour of ANG-2 was triexponential in vitro, its analysis indicates a Na+-sensitivity appropriate for recordings in living cells. The Na+-sensitivity was reduced in situ, but the biexponential fluorescence decay behaviour could be successfully analysed in terms of quantitative [Na+]i recordings. Thus, physiological 2P-FLIM measurements revealed a dopamine-induced [Na+]i rise in cockroach salivary gland cells, which was dependent on a Na+-K+-2Cl− cotransporter (NKCC) activity. It was concluded that ANG-2 is a promising new sodium indicator applicable for diverse biological systems. KW - cockroach salivary-glands KW - intracellular na+ KW - sodium green KW - periplaneta-americana KW - ventricular myocytes KW - lifetime microscopy KW - cytosolic sodium KW - acinar-cells KW - hela-cells KW - rat Y1 - 2014 SN - 1474-905X VL - 12 IS - 13 SP - 1699 EP - 1710 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Meyer, Sören A1 - Schulz, Jacqueline A1 - Jeibmann, Astrid A1 - Taleshi, Mojtaba S. A1 - Ebert, Franziska A1 - Francesconi, Kevin A1 - Schwerdtle, Tanja T1 - Arsenic-containing hydrocarbons are toxic in the in vivo model Drosophila melanogaster N2 - Arsenic-containing hydrocarbons (AsHC) constitute one group of arsenolipids that have been identified in seafood. In this first in vivo toxicity study for AsHCs, we show that AsHCs exert toxic effects in Drosophila melanogaster in a concentration range similar to that of arsenite. In contrast to arsenite, however, AsHCs cause developmental toxicity in the late developmental stages of Drosophila melanogaster. This work illustrates the need for a full characterisation of the toxicity of AsHCs in experimental animals to finally assess the risk to human health related to the presence of arsenolipids in seafood. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 183 KW - cod-liver KW - arsenolipids present KW - fatty-acids KW - rp-hplc KW - identification KW - fish KW - oil Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-76819 VL - 11 IS - 6 SP - 2010 EP - 2014 ER - TY - JOUR A1 - Meyer, Sören A1 - Schulz, Jacqueline A1 - Jeibmann, Astrid A1 - Taleshi, Mojtaba S. A1 - Ebert, Franziska A1 - Francesconi, Kevin A1 - Schwerdtle, Tanja ED - Schwerdtle, Tanja T1 - Arsenic-containing hydrocarbons are toxic in the in vivo model Drosophila melanogaster JF - Metallomics N2 - Arsenic-containing hydrocarbons (AsHC) constitute one group of arsenolipids that have been identified in seafood. In this first in vivo toxicity study for AsHCs, we show that AsHCs exert toxic effects in Drosophila melanogaster in a concentration range similar to that of arsenite. In contrast to arsenite, however, AsHCs cause developmental toxicity in the late developmental stages of Drosophila melanogaster. This work illustrates the need for a full characterisation of the toxicity of AsHCs in experimental animals to finally assess the risk to human health related to the presence of arsenolipids in seafood. KW - arsenolipids present KW - cod-liver KW - fatty-acids KW - identification KW - rp-hplc KW - fish KW - oil Y1 - 2014 SN - 1756-5901 SP - 2010 EP - 2014 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Schwarze, Thomas A1 - Müller, Holger A1 - Ast, Sandra A1 - Steinbrück, Dörte A1 - Eidner, Sascha A1 - Geißler, Felix A1 - Kumke, Michael Uwe A1 - Holdt, Hans-Jürgen T1 - Fluorescence lifetime-based sensing of sodium by an optode N2 - We report a 1,2,3-triazol fluoroionophore for detecting Na+ that shows in vitro enhancement in the Na+-induced fluorescence intensity and decay time. The Na+-selective molecule 1 was incorporated into a hydrogel as a part of a fiber optical sensor. This sensor allows the direct determination of Na+ in the range of 1–10 mM by measuring reversible fluorescence decay time changes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 182 KW - ion optodes KW - sensors KW - indicators KW - chromoionophore KW - ionophore KW - membrane KW - switches KW - systems KW - samples KW - green Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-76785 SP - 14167 EP - 14170 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schwarze, Thomas A1 - Müller, Holger A1 - Ast, Sandra A1 - Steinbrück, Dörte A1 - Eidner, Sascha A1 - Geißler, Felix A1 - Kumke, Michael Uwe A1 - Holdt, Hans-Jürgen ED - Kumke, Michael Uwe T1 - Fluorescence lifetime-based sensing of sodium by an optode JF - Chemical Communications N2 - We report a 1,2,3-triazol fluoroionophore for detecting Na+ that shows in vitro enhancement in the Na+-induced fluorescence intensity and decay time. The Na+-selective molecule 1 was incorporated into a hydrogel as a part of a fiber optical sensor. This sensor allows the direct determination of Na+ in the range of 1–10 mM by measuring reversible fluorescence decay time changes. KW - ion optodes KW - sensors KW - indicators KW - chromoionophore KW - ionophore KW - membrane KW - switches KW - systems KW - samples KW - green Y1 - 2014 SN - 0022-4936 SN - 0009-241X SP - 14167 EP - 14170 PB - The Royal Society Chemistry CY - Cambridge ER - TY - GEN A1 - Unterberg, Marlies A1 - Leffers, Larissa A1 - Hübner, Florian A1 - Humpf, Hans-Ulrich A1 - Lepikhov, Konstantin A1 - Walter, Jörn A1 - Ebert, Franziska A1 - Schwerdtle, Tanja T1 - Toxicity of arsenite and thio-DMAV after long-term (21 days) incubation of human urothelial cells: cytotoxicity, genotoxicity and epigenetics N2 - This study aims to further mechanistically understand toxic modes of action after chronic inorganic arsenic exposure. Therefore long-term incubation studies in cultured cells were carried out, to display chronically attained changes, which cannot be observed in the generally applied in vitro short-term incubation studies. Particularly, the cytotoxic, genotoxic and epigenetic effects of an up to 21 days incubation of human urothelial (UROtsa) cells with pico- to nanomolar concentrations of iAsIII and its metabolite thio-DMAV were compared. After 21 days of incubation, cytotoxic effects were strongly enhanced in the case of iAsIII and might partly be due to glutathione depletion and genotoxic effects on the chromosomal level. These results are in strong contrast to cells exposed to thio-DMAV. Thus, cells seemed to be able to adapt to this arsenical, as indicated among others by an increase in the cellular glutathione level. Most interestingly, picomolar concentrations of both iAsIII and thio-DMAV caused global DNA hypomethylation in UROtsa cells, which was quantified in parallel by 5-medC immunostaining and a newly established, reliable, high resolution mass spectrometry (HRMS)-based test system. This is the first time that epigenetic effects are reported for thio-DMAV; iAsIII induced epigenetic effects occur in at least 8000 fold lower concentrations as reported in vitro before. The fact that both arsenicals cause DNA hypomethylation at really low, exposure-relevant concentrations in human urothelial cells suggests that this epigenetic effect might contribute to inorganic arsenic induced carcinogenicity, which for sure has to be further investigated in future studies. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 178 KW - induced malignant-transformation KW - genomic dna methylation KW - vitro toxicological characterization KW - thio-dimethylarsinic acid KW - bladder-cancer KW - methyltransferases dnmt3a KW - cytosine methylation KW - carcinogen exposure KW - mass-spectrometry KW - gene-expression Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-76239 SP - 456 EP - 464 ER - TY - JOUR A1 - Unterberg, Marlies A1 - Leffers, Larissa A1 - Hübner, Florian A1 - Humpf, Hans-Ulrich A1 - Lepikhov, Konstantin A1 - Walter, Jörn A1 - Ebert, Franziska A1 - Schwerdtle, Tanja T1 - Toxicity of arsenite and thio-DMAV after long-term (21 days) incubation of human urothelial cells: cytotoxicity, genotoxicity and epigenetics JF - Toxicology Research N2 - This study aims to further mechanistically understand toxic modes of action after chronic inorganic arsenic exposure. Therefore long-term incubation studies in cultured cells were carried out, to display chronically attained changes, which cannot be observed in the generally applied in vitro short-term incubation studies. Particularly, the cytotoxic, genotoxic and epigenetic effects of an up to 21 days incubation of human urothelial (UROtsa) cells with pico- to nanomolar concentrations of iAsIII and its metabolite thio-DMAV were compared. After 21 days of incubation, cytotoxic effects were strongly enhanced in the case of iAsIII and might partly be due to glutathione depletion and genotoxic effects on the chromosomal level. These results are in strong contrast to cells exposed to thio-DMAV. Thus, cells seemed to be able to adapt to this arsenical, as indicated among others by an increase in the cellular glutathione level. Most interestingly, picomolar concentrations of both iAsIII and thio-DMAV caused global DNA hypomethylation in UROtsa cells, which was quantified in parallel by 5-medC immunostaining and a newly established, reliable, high resolution mass spectrometry (HRMS)-based test system. This is the first time that epigenetic effects are reported for thio-DMAV; iAsIII induced epigenetic effects occur in at least 8000 fold lower concentrations as reported in vitro before. The fact that both arsenicals cause DNA hypomethylation at really low, exposure-relevant concentrations in human urothelial cells suggests that this epigenetic effect might contribute to inorganic arsenic induced carcinogenicity, which for sure has to be further investigated in future studies. KW - induced malignant-transformation KW - genomic dna methylation KW - vitro toxicological characterization KW - thio-dimethylarsinic acid KW - bladder-cancer KW - methyltransferases dnmt3a KW - cytosine methylation KW - carcinogen exposure KW - mass-spectrometry KW - gene-expression Y1 - 2014 SN - 2045-4538 SN - 2045-452X VL - 3 IS - 6 SP - 456 EP - 464 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Wirth, Jonas A1 - Neumann, Rainer A1 - Antonietti, Markus A1 - Saalfrank, Peter T1 - Adsorption and photocatalytic splitting of water on graphitic carbon nitride BT - a combined first principles and semiempirical study JF - physical chemistry, chemical physics : PCCP N2 - Graphitic carbon nitride, g-C₃N₄, is a promising organic photo-catalyst for a variety of redox reactions. In order to improve its efficiency in a systematic manner, however, a fundamental understanding of the microscopic interaction between catalyst, reactants and products is crucial. Here we present a systematic study of water adsorption on g-C₃N₄ by means of density functional theory and the density functional based tight-binding method as a prerequisite for understanding photocatalytic water splitting. We then analyze this prototypical redox reaction on the basis of a thermodynamic model providing an estimate of the overpotential for both water oxidation and H⁺ reduction. While the latter is found to occur readily upon irradiation with visible light, we derive a prohibitive overpotential of 1.56 eV for the water oxidation half reaction, comparing well with the experimental finding that in contrast to H₂ production O₂ evolution is only possible in the presence of oxidation cocatalysts. KW - initio molecular-dynamics KW - augmented-wave method KW - visible-light KW - tight-binding KW - transition KW - oxidation KW - photooxidation KW - simulations KW - reduction KW - hydrogen Y1 - 2014 U6 - https://doi.org/10.1039/c4cp02021a SN - 1463-9076 SN - 1463-9084 VL - 2014 IS - 16 SP - 15917 EP - 15926 ER - TY - THES A1 - Giordano, Cristina T1 - A neglected world: transition metal nitride and metal carbide based nanostructures T1 - Eine vernachlässigte Welt: Übergangsmetallnitrid- und Metallcarbid-basierte Nanostrukturen BT - novel synthesis and future perspectives BT - neuartige Synthese und Zukunftsperspektiven N2 - Potentiality of nanosized materials has been largely proved but a closer look shows that a significant percentage of this research is related to oxides and metals, while the number drastically drops for metallic ceramics, namely transition metal nitrides and metal carbides. The lack of related publications do not reflect their potential but rather the difficulties related to their synthesis as dense and defect-free structures, fundamental prerequisites for advanced mechanical applications. The present habilitation work aims to close the gap between preparation and processing, indicating novel synthetic pathways for a simpler and sustainable synthesis of transition metal nitride (MN) and carbide (MC) based nanostructures and easier processing thereafter. In spite of simplicity and reliability, the designed synthetic processes allow the production of functional materials, with the demanded size and morphology. The goal was achieved exploiting classical and less-classical precursors, ranging from common metal salts and molecules (e.g. urea, gelatin, agar, etc), to more exotic materials, such as leafs, filter paper and even wood. It was found that the choice of precursors and reaction conditions makes it possible to control chemical composition (going for instance from metal oxides to metal oxy-nitrides to metal nitrides, or from metal nitrides to metal carbides, up to quaternary systems), size (from 5 to 50 nm) and morphology (going from mere spherical nanoparticles to rod-like shapes, fibers, layers, meso-porous and hierarchical structures, etc). The nature of the mixed precursors also allows the preparation of metal nitrides/carbides based nanocomposites, thus leading to multifunctional materials (e.g. MN/MC@C, MN/MC@PILs, etc) but also allowing dispersion in liquid media. Control over composition, size and morphology is obtained with simple adjustment of the main route, but also coupling it with processes such as electrospin, aerosol spray, bio-templating, etc. Last but not least, the nature of the precursor materials also allows easy processing, including printing, coating, casting, film and thin layers preparation, etc). The designed routes are, concept-wise, similar and they all start by building up a secondary metal ion-N/C precursor network, which converts, upon heat treatment, into an intermediate “glass”. This glass stabilizes the nascent nanoparticles during their nucleation and impairs their uncontrolled growth during the heat treatment (scheme 1). This way, one of the main problems related to the synthesis of MN/MC, i.e. the need of very high temperature, could also be overcome (from up to 2000°C, for classical synthesis, down to 700°C in the present cases). The designed synthetic pathways are also conceived to allow usage of non-toxic compounds and to minimize (or even avoid) post-synthesis purification, still bringing to phase pure and well-defined (crystalline) nanoparticles. This research aids to simplify the preparation of MN/MC, making these systems now readily available in suitable amounts both for fundamental and applied science. The prepared systems have been tested (in some cases for the first time) in many different fields, e.g. battery (MnN0.43@C shown a capacity stabilized at a value of 230 mAh/g, with coulombic efficiencies close to 100%), as alternative magnetic materials (Fe3C nanoparticles were prepared with different size and therefore different magnetic behavior, superparamagnetic or ferromagnetic, showing a saturation magnetization value up to 130 emu/g, i.e. similar to the value expected for the bulk material), as filters and for the degradation of organic dyes (outmatching the performance of carbon), as catalysts (both as active phase but also as active support, leading to high turnover rate and, more interesting, to tunable selectivity). Furthermore, with this route, it was possible to prepare for the first time, to the best of our knowledge, well-defined and crystalline MnN0.43, Fe3C and Zn1.7GeN1.8O nanoparticles via bottom-up approaches. Once the synthesis of these materials can be made straightforward, any further modification, combination, manipulation, is in principle possible and new systems can be purposely conceived (e.g. hybrids, nanocomposites, ferrofluids, etc). N2 - Materialien sind wichtige Hilfsmittel, die wir täglich benutzen, um unser Leben einfacher zu machen. Materialien werden durch ihre Eigenschaften charakterisiert. Manche sind stark, manche sind elektrisch, manche magnetisch, usw. Wenn ein Stoff auf die Dimension eines Virus verkleinert wird, zeigen sich besondere Veränderungen. War das Material groß z.B. elektrisch, hat es klein diese Eigenschaft nicht mehr. Groß war es glanzlos, aber klein ist es transparent... Das heißt, dass jedes bekannte Material prinzipiell ein neues Material werden kann, nur durch die Veränderung seiner Größe. Wegen dieser besonderen Entdeckung, ist seit vielen Jahren ein Großteil der Forschung Nanopartikeln gewidmet. Dennoch werden in diesem Gebiet meistens besondere Materialien untersucht, weil ihre Anwendungsfelder weithin bekannt und wichtig sind. Meine Forschung basiert auf der Untersuchung neuer oder weniger bekannter Materialien, nämlich Übergangsmetallnitride und Übergangsmetallcarbide als Nanostrukturen. Sie sind nicht so bekannt, weil sie nicht so einfach herzustellen waren (die klassische Synthese braucht eine hohe Temperatur bis 2000°C, und oft toxische Reaktionsmittel). Trotzdem sind sie sehr interessante Materialien, weil sie auf der Grenze zwischen reinen Metallen und reinen keramischen Materialien hinsichtlich der Eigenschaften liegen. Das heißt, sie sind z.B. sehr fest, aber auch leitend, sie haben einen hohen Schmelzpunkt und sind magnetisch, etc. Durch die hier vorgestellte Forschung wird die Synthese dieser Materialien einfacher gemacht, bei niedrigen Temperaturen, mit natürlichen Produkten (z.B. Harnstoff, Gelatine, Agar, Zellulose, etc). Die Eigenschaften und Anwendungsmöglichkeiten dieser Systeme wurden auch studiert, ebenso wie die Kontrolle der Größe und Form. So konnten wir sphärische, rohrförmige, und fiber-basierte Nanostrukturen synthetisieren, aber sogar Blätter und Holz konnten als Reaktionsmittel benutzt werden und in Nitrid und Carbid umgewandelt werden, ohne die Form zu ändern. Weil die Synthese dieser Materialien direkt gemacht werden konnte, ist prinzipiell jede weitere Modifikation, Kombination und Manipulation möglich. So können jetzt neue Systeme entworfen werden. KW - metal carbides KW - metal nitrides KW - nanostructures KW - sol-gel KW - Metallnitride KW - Metallcarbide KW - Nanostrukturen KW - Sol-Gel Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-75375 ER - TY - JOUR A1 - Zamponi, Flavio A1 - Penfold, Thomas J. A1 - Nachtegaal, Maarten A1 - Lübcke, Andrea A1 - Rittmann, Jochen A1 - Milne, Chris J. A1 - Chergui, Majed A1 - van Bokhoven, Jeroen A. T1 - Probing the dynamics of plasmon-excited hexanethiol-capped gold nanoparticles by picosecond X-ray absorption spectroscopy JF - physical chemistry, chemical physics : PCCP N2 - Picosecond X-ray absorption spectroscopy (XAS) is used to investigate the electronic and structural dynamics initiated by plasmon excitation of 1.8 nm diameter Au nanoparticles (NPs) functionalised with 1-hexanethiol. We show that 100 ps after photoexcitation the transient XAS spectrum is consistent with an 8% expansion of the Au–Au bond length and a large increase in disorder associated with melting of the NPs. Recovery of the ground state occurs with a time constant of ∼1.8 ns, arising from thermalisation with the environment. Simulations reveal that the transient spectrum exhibits no signature of charge separation at 100 ps and allows us to estimate an upper limit for the quantum yield (QY) of this process to be <0.1. KW - TiO2 nanoparticles KW - diimine-complexes KW - electron-transfer KW - supported gold KW - visible-light KW - water KW - surface KW - reactivity KW - nanoclusters KW - excitation Y1 - 2014 U6 - https://doi.org/10.1039/c4cp03301a SN - 1463-9076 SN - 1463-9084 VL - 2014 IS - 16 SP - 23157 EP - 23163 ER - TY - GEN A1 - Zamponi, Flavio A1 - Penfold, Thomas J. A1 - Nachtegaal, Maarten A1 - Lübcke, Andrea A1 - Rittmann, Jochen A1 - Milne, Chris J. A1 - Chergui, Majed A1 - van Bokhoven, Jeroen A. T1 - Probing the dynamics of plasmon-excited hexanethiol-capped gold nanoparticles by picosecond X-ray absorption spectroscopy N2 - Picosecond X-ray absorption spectroscopy (XAS) is used to investigate the electronic and structural dynamics initiated by plasmon excitation of 1.8 nm diameter Au nanoparticles (NPs) functionalised with 1-hexanethiol. We show that 100 ps after photoexcitation the transient XAS spectrum is consistent with an 8% expansion of the Au–Au bond length and a large increase in disorder associated with melting of the NPs. Recovery of the ground state occurs with a time constant of ∼1.8 ns, arising from thermalisation with the environment. Simulations reveal that the transient spectrum exhibits no signature of charge separation at 100 ps and allows us to estimate an upper limit for the quantum yield (QY) of this process to be <0.1. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 176 KW - TiO2 nanoparticles KW - diimine-complexes KW - electron-transfer KW - excitation KW - nanoclusters KW - reactivity KW - supported gold KW - surface KW - visible-light KW - water Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74492 SP - 23157 EP - 23163 ER - TY - GEN A1 - Wessig, Pablo A1 - Gerngroß, Maik A1 - Pape, Simon A1 - Bruhns, Philipp A1 - Weber, Jens T1 - Novel porous materials based on oligospiroketals (OSK) N2 - New porous materials based on covalently connected monomers are presented. The key step of the synthesis is an acetalisation reaction. In previous years we used acetalisation reactions extensively to build up various molecular rods. Based on this approach, investigations towards porous polymeric materials were conducted by us. Here we wish to present the results of these studies in the synthesis of 1D polyacetals and porous 3D polyacetals. By scrambling experiments with 1D acetals we could prove that exchange reactions occur between different building blocks (evidenced by MALDI-TOF mass spectrometry). Based on these results we synthesized porous 3D polyacetals under the same mild conditions. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 175 KW - construction KW - frameworks KW - membranes KW - microporous organic polymers KW - models KW - molecular rods KW - sorption Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74466 SP - 31123 EP - 31129 ER - TY - JOUR A1 - Wessig, Pablo A1 - Gerngroß, Maik A1 - Pape, Simon A1 - Bruhns, Philipp A1 - Weber, Jens T1 - Novel porous materials based on oligospiroketals (OSK) JF - RSC Advances : an international journal to further the chemical sciences N2 - New porous materials based on covalently connected monomers are presented. The key step of the synthesis is an acetalisation reaction. In previous years we used acetalisation reactions extensively to build up various molecular rods. Based on this approach, investigations towards porous polymeric materials were conducted by us. Here we wish to present the results of these studies in the synthesis of 1D polyacetals and porous 3D polyacetals. By scrambling experiments with 1D acetals we could prove that exchange reactions occur between different building blocks (evidenced by MALDI-TOF mass spectrometry). Based on these results we synthesized porous 3D polyacetals under the same mild conditions. KW - microporous organic polymers KW - molecular rods KW - construction KW - frameworks KW - membranes KW - sorption KW - models Y1 - 2014 U6 - https://doi.org/10.1039/c4ra04437a SN - 2046-2069 VL - 2014 IS - 4 SP - 31123 EP - 31129 ER - TY - GEN A1 - Metzler, Ralf A1 - Jeon, Jae-Hyung A1 - Cherstvy, Andrey G. A1 - Barkai, Eli T1 - Anomalous diffusion models and their properties BT - non-stationarity, non-ergodicity, and ageing at the centenary of single particle tracking N2 - Modern microscopic techniques following the stochastic motion of labelled tracer particles have uncovered significant deviations from the laws of Brownian motion in a variety of animate and inanimate systems. Such anomalous diffusion can have different physical origins, which can be identified from careful data analysis. In particular, single particle tracking provides the entire trajectory of the traced particle, which allows one to evaluate different observables to quantify the dynamics of the system under observation. We here provide an extensive overview over different popular anomalous diffusion models and their properties. We pay special attention to their ergodic properties, highlighting the fact that in several of these models the long time averaged mean squared displacement shows a distinct disparity to the regular, ensemble averaged mean squared displacement. In these cases, data obtained from time averages cannot be interpreted by the standard theoretical results for the ensemble averages. Here we therefore provide a comparison of the main properties of the time averaged mean squared displacement and its statistical behaviour in terms of the scatter of the amplitudes between the time averages obtained from different trajectories. We especially demonstrate how anomalous dynamics may be identified for systems, which, on first sight, appear to be Brownian. Moreover, we discuss the ergodicity breaking parameters for the different anomalous stochastic processes and showcase the physical origins for the various behaviours. This Perspective is intended as a guidebook for both experimentalists and theorists working on systems, which exhibit anomalous diffusion. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 174 KW - Fokker-Planck equations KW - flight search patterns KW - fluctuation-dissipation theorem KW - fluorescence photobleaching recovery KW - fractional dynamics approach KW - intermittent chaotic systems KW - levy flights KW - photon-counting statistics KW - time random-walks KW - weak ergodicity breaking Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74448 SP - 24128 EP - 24164 ER - TY - JOUR A1 - Metzler, Ralf A1 - Jeon, Jae-Hyung A1 - Cherstvy, Andrey G. A1 - Barkai, Eli T1 - Anomalous diffusion models and their properties BT - non-stationarity, non-ergodicity, and ageing at the centenary of single particle tracking JF - physical chemistry, chemical physics : PCCP N2 - Modern microscopic techniques following the stochastic motion of labelled tracer particles have uncovered significant deviations from the laws of Brownian motion in a variety of animate and inanimate systems. Such anomalous diffusion can have different physical origins, which can be identified from careful data analysis. In particular, single particle tracking provides the entire trajectory of the traced particle, which allows one to evaluate different observables to quantify the dynamics of the system under observation. We here provide an extensive overview over different popular anomalous diffusion models and their properties. We pay special attention to their ergodic properties, highlighting the fact that in several of these models the long time averaged mean squared displacement shows a distinct disparity to the regular, ensemble averaged mean squared displacement. In these cases, data obtained from time averages cannot be interpreted by the standard theoretical results for the ensemble averages. Here we therefore provide a comparison of the main properties of the time averaged mean squared displacement and its statistical behaviour in terms of the scatter of the amplitudes between the time averages obtained from different trajectories. We especially demonstrate how anomalous dynamics may be identified for systems, which, on first sight, appear to be Brownian. Moreover, we discuss the ergodicity breaking parameters for the different anomalous stochastic processes and showcase the physical origins for the various behaviours. This Perspective is intended as a guidebook for both experimentalists and theorists working on systems, which exhibit anomalous diffusion. KW - intermittent chaotic systems KW - Fokker-Planck equations KW - time random-walks KW - fluorescence photobleaching recovery KW - fluctuation-dissipation theorem KW - fractional dynamics approach KW - photon-counting statistics KW - weak ergodicity breaking KW - flight search patterns KW - levy flights Y1 - 2014 U6 - https://doi.org/10.1039/c4cp03465a SN - 1463-9076 SN - 1463-9084 VL - 2014 IS - 16 SP - 24128 EP - 24164 ER - TY - GEN A1 - Ehlert, Christopher A1 - Unger, Wolfgang E. S. A1 - Saalfrank, Peter T1 - C K-edge NEXAFS spectra of graphene with physical and chemical defects BT - a study based on density functional theory N2 - Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 173 KW - absorbtion fine-structure KW - graphite Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74429 SP - 14083 EP - 14095 ER - TY - JOUR A1 - Ehlert, Christopher A1 - Unger, Wolfgang E. S. A1 - Saalfrank, Peter T1 - C K-edge NEXAFS spectra of graphene with physical and chemical defects BT - a study based on density functional theory JF - physical chemistry, chemical physics : PCCP N2 - Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes. KW - absorbtion fine-structure KW - graphite Y1 - 2014 U6 - https://doi.org/10.1039/c4cp01106f SN - 1463-9076 SN - 1463-9084 VL - 2014 IS - 16 SP - 14083 EP - 14095 ER - TY - GEN A1 - Wirth, Jonas A1 - Neumann, Rainer A1 - Antonietti, Markus A1 - Saalfrank, Peter T1 - Adsorption and photocatalytic splitting of water on graphitic carbon nitride BT - a combined first principles and semiempirical study N2 - Graphitic carbon nitride, g-C₃N₄, is a promising organic photo-catalyst for a variety of redox reactions. In order to improve its efficiency in a systematic manner, however, a fundamental understanding of the microscopic interaction between catalyst, reactants and products is crucial. Here we present a systematic study of water adsorption on g-C₃N₄ by means of density functional theory and the density functional based tight-binding method as a prerequisite for understanding photocatalytic water splitting. We then analyze this prototypical redox reaction on the basis of a thermodynamic model providing an estimate of the overpotential for both water oxidation and H⁺ reduction. While the latter is found to occur readily upon irradiation with visible light, we derive a prohibitive overpotential of 1.56 eV for the water oxidation half reaction, comparing well with the experimental finding that in contrast to H₂ production O₂ evolution is only possible in the presence of oxidation cocatalysts. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 172 KW - augmented-wave method KW - hydrogen KW - initio molecular-dynamics KW - oxidation KW - photooxidation KW - reduction KW - simulations KW - tight-binding KW - transition KW - visible-light Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74391 SP - 15917 EP - 15926 ER - TY - GEN A1 - Pieper, Imke A1 - Wehe, Christoph A. A1 - Bornhorst, Julia A1 - Ebert, Franziska A1 - Leffers, Larissa A1 - Holtkamp, Michael A1 - Höseler, Pia A1 - Weber, Till A1 - Mangerich, Aswin A1 - Bürkle, Alexander A1 - Karst, Uwe A1 - Schwerdtle, Tanja T1 - Mechanisms of Hg species induced toxicity in cultured human astrocytes BT - genotoxicity and DNA-damage response N2 - The toxicologically most relevant mercury (Hg) species for human exposure is methylmercury (MeHg). Thiomersal is a common preservative used in some vaccine formulations. The aim of this study is to get further mechanistic insight into the yet not fully understood neurotoxic modes of action of organic Hg species. Mercury species investigated include MeHgCl and thiomersal. Additionally HgCl2 was studied, since in the brain mercuric Hg can be formed by dealkylation of the organic species. As a cellular system astrocytes were used. In vivo astrocytes provide the environment necessary for neuronal function. In the present study, cytotoxic effects of the respective mercuricals increased with rising alkylation level and correlated with their cellular bioavailability. Further experiments revealed for all species at subcytotoxic concentrations no induction of DNA strand breaks, whereas all species massively increased H2O2-induced DNA strand breaks. This co- genotoxic effect is likely due to a disturbance of the cellular DNA damage response. Thus, at nanomolar, sub-cytotoxic concentrations, all three mercury species strongly disturbed poly(ADP-ribosyl)ation, a signalling reaction induced by DNA strand breaks. Interestingly, the molecular mechanism behind this inhibition seems to be different for the species. Since chronic PARP-1 inhibition is also discussed to sacrifice neurogenesis and learning abilities, further experiments on neurons and in vivo studies could be helpful to clarify whether the inhibition of poly(ADP-ribosyl) ation contributes to organic Hg induced neurotoxicity. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 171 KW - adduct formation KW - cell-death KW - exposure KW - manganese KW - methylmercury KW - neurodegenerative diseases KW - neurotoxicity KW - poly(ADP-ribose) polymerase-1 KW - repair KW - thimerosal Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74379 SP - 662 EP - 671 ER - TY - GEN A1 - Meyer, Sören A1 - Matissek, M. A1 - Müller, Sandra Marie A1 - Taleshi, M. S. A1 - Ebert, Franziska A1 - Francesconi, Kevin A. A1 - Schwerdtle, Tanja T1 - In vitro toxicological characterisation of three arsenic-containing hydrocarbons N2 - Arsenic-containing hydrocarbons are one group of fat-soluble organic arsenic compounds (arsenolipids) found in marine fish and other seafood. A risk assessment of arsenolipids is urgently needed, but has not been possible because of the total lack of toxicological data. In this study the cellular toxicity of three arsenic-containing hydrocarbons was investigated in cultured human bladder (UROtsa) and liver (HepG2) cells. Cytotoxicity of the arsenic-containing hydrocarbons was comparable to that of arsenite, which was applied as the toxic reference arsenical. A large cellular accumulation of arsenic, as measured by ICP-MS/MS, was observed after incubation of both cell lines with the arsenolipids. Moreover, the toxic mode of action shown by the three arsenic-containing hydrocarbons seemed to differ from that observed for arsenite. Evidence suggests that the high cytotoxic potential of the lipophilic arsenicals results from a decrease in the cellular energy level. This first in vitro based risk assessment cannot exclude a risk to human health related to the presence of arsenolipids in seafood, and indicates the urgent need for further toxicity studies in experimental animals to fully assess this possible risk. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 170 KW - cod-liver KW - human-cells KW - arsenolipids present KW - excision-repair KW - fatty-acids KW - marine oils KW - RP-HPLC KW - metabolites KW - identification KW - trivalent Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74201 SP - 1023 EP - 1033 ER - TY - JOUR A1 - Meyer, Sören A1 - Matissek, M. A1 - Müller, Sandra Marie A1 - Taleshi, M. S. A1 - Ebert, Franziska A1 - Francesconi, Kevin A. A1 - Schwerdtle, Tanja T1 - In vitro toxicological characterisation of three arsenic-containing hydrocarbons JF - Metallomics N2 - Arsenic-containing hydrocarbons are one group of fat-soluble organic arsenic compounds (arsenolipids) found in marine fish and other seafood. A risk assessment of arsenolipids is urgently needed, but has not been possible because of the total lack of toxicological data. In this study the cellular toxicity of three arsenic-containing hydrocarbons was investigated in cultured human bladder (UROtsa) and liver (HepG2) cells. Cytotoxicity of the arsenic-containing hydrocarbons was comparable to that of arsenite, which was applied as the toxic reference arsenical. A large cellular accumulation of arsenic, as measured by ICP-MS/MS, was observed after incubation of both cell lines with the arsenolipids. Moreover, the toxic mode of action shown by the three arsenic-containing hydrocarbons seemed to differ from that observed for arsenite. Evidence suggests that the high cytotoxic potential of the lipophilic arsenicals results from a decrease in the cellular energy level. This first in vitro based risk assessment cannot exclude a risk to human health related to the presence of arsenolipids in seafood, and indicates the urgent need for further toxicity studies in experimental animals to fully assess this possible risk. KW - cod-liver KW - human-cells KW - arsenolipids present KW - excision-repair KW - fatty-acids KW - marine oils KW - RP-HPLC KW - metabolites KW - identification KW - trivalent Y1 - 2014 U6 - https://doi.org/10.1039/c4mt00061g SN - 1756-591X SN - 1756-5901 VL - 2014 IS - 6 SP - 1023 EP - 1033 ER - TY - GEN A1 - Mondal, Suvendu Sekhar A1 - Bhunia, Asamanjoy A1 - Kelling, Alexandra A1 - Schilde, Uwe A1 - Janiak, Christoph A1 - Holdt, Hans-Jürgen T1 - A supramolecular Co(II)₁₄-metal–organic cube in a hydrogen-bonded network and a Co(II)–organic framework with a flexible methoxy substituent N2 - The reaction of 4,5-dicyano-2-methoxyimidazole (L1) with Co(NO3)2·6H2O under solvothermal conditions in DMF, a MOF, IFP-8 and a hydrogen-bonded network consisting of tetradecanuclear Co(II)14-metal organic cube (1) are achieved. 1 shows the bcu net with 14 cobalt atoms. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 169 KW - zinc Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74098 IS - 169 SP - 5441 EP - 5443 ER - TY - GEN A1 - Cherstvy, Andrey G. A1 - Chechkin, Aleksei V. A1 - Metzler, Ralf T1 - Particle invasion, survival, and non-ergodicity in 2D diffusion processes with space-dependent diffusivity N2 - We study the thermal Markovian diffusion of tracer particles in a 2D medium with spatially varying diffusivity D(r), mimicking recently measured, heterogeneous maps of the apparent diffusion coefficient in biological cells. For this heterogeneous diffusion process (HDP) we analyse the mean squared displacement (MSD) of the tracer particles, the time averaged MSD, the spatial probability density function, and the first passage time dynamics from the cell boundary to the nucleus. Moreover we examine the non-ergodic properties of this process which are important for the correct physical interpretation of time averages of observables obtained from single particle tracking experiments. From extensive computer simulations of the 2D stochastic Langevin equation we present an in-depth study of this HDP. In particular, we find that the MSDs along the radial and azimuthal directions in a circular domain obey anomalous and Brownian scaling, respectively. We demonstrate that the time averaged MSD stays linear as a function of the lag time and the system thus reveals a weak ergodicity breaking. Our results will enable one to rationalise the diffusive motion of larger tracer particles such as viruses or submicron beads in biological cells. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 168 KW - adenoassociated virus KW - anomalous diffusion KW - cytoplasm KW - endosomal escape KW - escherichia-coli KW - infection pathway KW - intracellular-transport KW - living cells KW - models KW - trafficking Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74021 IS - 168 SP - 1591 EP - 1601 ER - TY - GEN A1 - Bald, Ilko A1 - Kopyra, Janina A1 - Keller, Adrian T1 - On the role of fluoro-substituted nucleosides in DNA radiosensitization for tumor radiation therapy N2 - Gemcitabine (2′,2′-difluorocytidine) is a well-known radiosensitizer routinely applied in concomitant chemoradiotherapy. During irradiation of biological media with high-energy radiation secondary low-energy (<10 eV) electrons are produced that can directly induce chemical bond breakage in DNA by dissociative electron attachment (DEA). Here, we investigate and compare DEA to the three molecules 2′-deoxycytidine, 2′-deoxy-5-fluorocytidine, and gemcitabine. Fluorination at specific molecular sites, i.e., nucleobase or sugar moiety, is found to control electron attachment and subsequent dissociation pathways. The presence of two fluorine atoms at the sugar ring results in more efficient electron attachment to the sugar moiety and subsequent bond cleavage. For the formation of the dehydrogenated nucleobase anion, we obtain an enhancement factor of 2.8 upon fluorination of the sugar, whereas the enhancement factor is 5.5 when the nucleobase is fluorinated. The observed fragmentation reactions suggest enhanced DNA strand breakage induced by secondary electrons when gemcitabine is incorporated into DNA. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 167 KW - low-energy electrons KW - single-strand breaks KW - gas-phase KW - chemoradiation therapy KW - molecular-mechanisms KW - resonant formation KW - damage KW - attachment KW - drugs Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-73412 SP - 6825 EP - 6829 ER - TY - JOUR A1 - Bald, Ilko A1 - Keller, Adrian A1 - Kopyra, Janina T1 - On the role of fluoro-substituted nucleosides in DNA radiosensitization for tumor radiation therapy JF - RSC Advances : an international journal to further the chemical sciences N2 - Gemcitabine (2′,2′-difluorocytidine) is a well-known radiosensitizer routinely applied in concomitant chemoradiotherapy. During irradiation of biological media with high-energy radiation secondary low-energy (<10 eV) electrons are produced that can directly induce chemical bond breakage in DNA by dissociative electron attachment (DEA). Here, we investigate and compare DEA to the three molecules 2′-deoxycytidine, 2′-deoxy-5-fluorocytidine, and gemcitabine. Fluorination at specific molecular sites, i.e., nucleobase or sugar moiety, is found to control electron attachment and subsequent dissociation pathways. The presence of two fluorine atoms at the sugar ring results in more efficient electron attachment to the sugar moiety and subsequent bond cleavage. For the formation of the dehydrogenated nucleobase anion, we obtain an enhancement factor of 2.8 upon fluorination of the sugar, whereas the enhancement factor is 5.5 when the nucleobase is fluorinated. The observed fragmentation reactions suggest enhanced DNA strand breakage induced by secondary electrons when gemcitabine is incorporated into DNA. KW - low-energy electrons KW - single-strand breaks KW - gas-phase KW - chemoradiation therapy KW - molecular-mechanisms KW - resonant formation KW - damage KW - attachment KW - drugs Y1 - 2014 U6 - https://doi.org/10.1039/C3RA46735J SN - 2046-2069 VL - 4 IS - 13 SP - 6825 EP - 6829 PB - Royal Society of Chemistry ER - TY - THES A1 - Secker, Christian T1 - Polypeptoid block coloymers BT - synthesis, modification, and structure formation Y1 - 2014 ER - TY - THES A1 - Faivre, Damien T1 - Biological and biomimetic formation and organization of magnetic nanoparticles T1 - Biologische und biomimetische Bildung und Anordnung von magnetischen Nanopartikel N2 - Biological materials have ever been used by humans because of their remarkable properties. This is surprising since the materials are formed under physiological conditions and with commonplace constituents. Nature thus not only provides us with inspiration for designing new materials but also teaches us how to use soft molecules to tune interparticle and external forces to structure and assemble simple building blocks into functional entities. Magnetotactic bacteria and their chain of magnetosomes represent a striking example of such an accomplishment where a very simple living organism controls the properties of inorganics via organics at the nanometer-scale to form a single magnetic dipole that orients the cell in the Earth magnetic field lines. My group has developed a biological and a bio-inspired research based on these bacteria. My research, at the interface between chemistry, materials science, physics, and biology focuses on how biological systems synthesize, organize and use minerals. We apply the design principles to sustainably form hierarchical materials with controlled properties that can be used e.g. as magnetically directed nanodevices towards applications in sensing, actuating, and transport. In this thesis, I thus first present how magnetotactic bacteria intracellularly form magnetosomes and assemble them in chains. I developed an assay, where cells can be switched from magnetic to non-magnetic states. This enabled to study the dynamics of magnetosome and magnetosome chain formation. We found that the magnetosomes nucleate within minutes whereas chains assembles within hours. Magnetosome formation necessitates iron uptake as ferrous or ferric ions. The transport of the ions within the cell leads to the formation of a ferritin-like intermediate, which subsequently is transported and transformed within the magnetosome organelle in a ferrihydrite-like precursor. Finally, magnetite crystals nucleate and grow toward their mature dimension. In addition, I show that the magnetosome assembly displays hierarchically ordered nano- and microstructures over several levels, enabling the coordinated alignment and motility of entire populations of cells. The magnetosomes are indeed composed of structurally pure magnetite. The organelles are partly composed of proteins, which role is crucial for the properties of the magnetosomes. As an example, we showed how the protein MmsF is involved in the control of magnetosome size and morphology. We have further shown by 2D X-ray diffraction that the magnetosome particles are aligned along the same direction in the magnetosome chain. We then show how magnetic properties of the nascent magnetosome influence the alignment of the particles, and how the proteins MamJ and MamK coordinate this assembly. We propose a theoretical approach, which suggests that biological forces are more important than physical ones for the chain formation. All these studies thus show how magnetosome formation and organization are under strict biological control, which is associated with unprecedented material properties. Finally, we show that the magnetosome chain enables the cells to find their preferred oxygen conditions if the magnetic field is present. The synthetic part of this work shows how the understanding of the design principles of magnetosome formation enabled me to perform biomimetic synthesis of magnetite particles within the highly desired size range of 25 to 100 nm. Nucleation and growth of such particles are based on aggregation of iron colloids termed primary particles as imaged by cryo-high resolution TEM. I show how additives influence magnetite formation and properties. In particular, MamP, a so-called magnetochrome proteins involved in the magnetosome formation in vivo, enables the in vitro formation of magnetite nanoparticles exclusively from ferrous iron by controlling the redox state of the process. Negatively charged additives, such as MamJ, retard magnetite nucleation in vitro, probably by interacting with the iron ions. Other additives such as e.g. polyarginine can be used to control the colloidal stability of stable-single domain sized nanoparticles. Finally, I show how we can “glue” magnetic nanoparticles to form propellers that can be actuated and swim with the help of external magnetic fields. We propose a simple theory to explain the observed movement. We can use the theoretical framework to design experimental conditions to sort out the propellers depending on their size and effectively confirm this prediction experimentally. Thereby, we could image propellers with size down to 290 nm in their longer dimension, much smaller than what perform so far. N2 - Biologische Materialien wie Knochen, Muscheln und Holz wurden von den Menschen seit den ältesten Zeiten verwendet. Diese biologisch gebildeten Materialien haben bemerkenswerte Eigenschaften. Dies ist besonders überraschend, da sie unter physiologischen Bedingungen und mit alltäglichen Bestandteilen gebildet sind. Die Natur liefert uns also nicht nur mit Inspiration für die Entwicklung neuer Materialien, sondern lehrt uns auch, wie biologische Additiven benutzen werden können, um einfache synthetische Bausteine in funktionale Einheiten zu strukturieren. Magnetotaktischen Bakterien und ihre Kette von Magnetosomen sind ein Beispiel, wo einfache Lebewesen die Eigenschaften von anorganischen Materialien steuern, um sich entlang den magnetischen Feldlinien der Erde zu orientieren. Die von den Bakterien gebildeten Magnetosomen sind von besonderem Interesse, da mit magnetischen Eisenoxid-Nanopartikeln in den letzten zehn Jahren einer Vielzahl von Bio-und nanotechnologischen Anwendungen entwickelt worden sind. In dieser Arbeit stelle ich eine biologische und eine bio-inspirierte Forschung auf der Grundlage der magnetotaktischen Bakterien vor. Diese Forschung verbindet die neuesten Entwicklungen von Nanotechnik in der chemischen Wissenschaft, die neuesten Fortschritte der Molekularbiologie zusammen mit modernen Messverfahren. Mein Forschungsschwerpunkt liegt somit an der Schnittstelle zwischen Chemie, Materialwissenschaften, Physik und Biologie. Ich will verstehen, wie biologische Systeme Materialien synthetisieren und organisieren, um Design-Prinzipien zu extrahieren, damit hierarchischen Materialien mit kontrollierten Eigenschaften nachhaltig gebildet werden. KW - magnetotaktische Bakterien KW - Magnetit Nanopartikel KW - Biomineralisation KW - magnetite KW - nanoparticle KW - biomineralization KW - magnetosome KW - magnetotactic bacteria Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-72022 ER - TY - THES A1 - Ermeydan, Mahmut Ali T1 - Wood cell wall modification with hydrophobic molecules T1 - Modifikation von Holzzellwänden durch hydrophobe Moleküle N2 - Wood is used for many applications because of its excellent mechanical properties, relative abundance and as it is a renewable resource. However, its wider utilization as an engineering material is limited because it swells and shrinks upon moisture changes and is susceptible to degradation by microorganisms and/or insects. Chemical modifications of wood have been shown to improve dimensional stability, water repellence and/or durability, thus increasing potential service-life of wood materials. However current treatments are limited because it is difficult to introduce and fix such modifications deep inside the tissue and cell wall. Within the scope of this thesis, novel chemical modification methods of wood cell walls were developed to improve both dimensional stability and water repellence of wood material. These methods were partly inspired by the heartwood formation in living trees, a process, that for some species results in an insertion of hydrophobic chemical substances into the cell walls of already dead wood cells, In the first part of this thesis a chemistry to modify wood cell walls was used, which was inspired by the natural process of heartwood formation. Commercially available hydrophobic flavonoid molecules were effectively inserted in the cell walls of spruce, a softwood species with low natural durability, after a tosylation treatment to obtain “artificial heartwood”. Flavonoid inserted cell walls show a reduced moisture absorption, resulting in better dimensional stability, water repellency and increased hardness. This approach was quite different compared to established modifications which mainly address hydroxyl groups of cell wall polymers with hydrophilic substances. In the second part of the work in-situ styrene polymerization inside the tosylated cell walls was studied. It is known that there is a weak adhesion between hydrophobic polymers and hydrophilic cell wall components. The hydrophobic styrene monomers were inserted into the tosylated wood cell walls for further polymerization to form polystyrene in the cell walls, which increased the dimensional stability of the bulk wood material and reduced water uptake of the cell walls considerably when compared to controls. In the third part of the work, grafting of another hydrophobic and also biodegradable polymer, poly(ɛ-caprolactone) in the wood cell walls by ring opening polymerization of ɛ-caprolactone was studied at mild temperatures. Results indicated that polycaprolactone attached into the cell walls, caused permanent swelling of the cell walls up to 5%. Dimensional stability of the bulk wood material increased 40% and water absorption reduced more than 35%. A fully biodegradable and hydrophobized wood material was obtained with this method which reduces disposal problem of the modified wood materials and has improved properties to extend the material’s service-life. Starting from a bio-inspired approach which showed great promise as an alternative to standard cell wall modifications we showed the possibility of inserting hydrophobic molecules in the cell walls and supported this fact with in-situ styrene and ɛ-caprolactone polymerization into the cell walls. It was shown in this thesis that despite the extensive knowledge and long history of using wood as a material there is still room for novel chemical modifications which could have a high impact on improving wood properties. N2 - Der nachwachsende Rohstoff Holz wird aufgrund seiner guten mechanischen Eigenschaften und der leichten Verfügbarkeit für viele Anwendungszwecke genutzt. Quellen und Schrumpfen bei Feuchtigkeitsänderungen des hygroskopischen Werkstoffs Holz limitieren jedoch die Einsatzmöglichkeiten. Ein weiteres Problem stellt der mitunter leichte Abbau – u.a. bei feuchtem Holz - durch Mikroorganismen und/oder Insekten dar. Durch chemische Modifizierungen können die Dimensionsstabilität, die Hydrophobizität und die Dauerhaftigkeit verbessert und damit die potentielle Lebensdauer des Werkstoffes erhöht werden. Dabei ist die dauerhafte Modifikation der Zellwand nur äußerst schwer realisierbar. Inspiriert von der Kernholzbildung in lebenden Bäumen, ein zellwandverändernder Prozess, der Jahre nach der Holzbildung erfolgt, wurden im Rahmen dieser Arbeit neue Ansätze zur chemischen Modifizierung der Zellwände entwickelt, um die Dimensionsstabilität und Hydrophobizität zu erhöhen. Der erste Teil der Arbeit ist stark vom Prozess der Kernholzbildung inspiriert, eine abgeleitete Chemie wurde verwendet, um die Zellwände von Fichte, einem Nadelholz von geringer natürlicher Dauerhaftigkeit, zu modifizieren. Kommerziell verfügbare hydrophobe Flavonoide wurden nach einem Tosylierungsschritt erfolgreich in die Zellwand eingebracht, um so „artifizielles Kernholz“ zu erzeugen. Die modifizierten Holzproben zeigten eine verringerte Wasseraufnahme, die zu erhöhter Dimensionsstabilität und Härte führte. Dieser Ansatz unterscheidet sich grundlegend von bereits etablierten Modifikationen, die hauptsächlich hypdrophile Substanzen an die Hydroxylgruppen der Zellwand anlagern. Der zweite Teil der Arbeit beschäftigt sich mit der Polymerisation von Styren in tosylierten Zellwänden. Es ist bekannt, dass es nur eine schwache Adhäsion zwischen den hydrophoben Polymeren und den hydrophilen Zellwandkomponenten gibt. Die hydrophoben Styren-Monomere wurden in die tosylierte Zellwand eingebracht und zu Polystyren polymerisiert. Wie bei der Modifikation mit Flavonoiden konnte eine erhöhte Dimensionsstabilität und reduzierte Wasseraufnahme der Zellwände beobachtet werden. Im dritten Teil der Arbeit wurde das biologisch abbaubare, hydrophobe poly(ɛ-caprolacton) in der Zellwand aufpolymerisiert. Die Ergebnisse deuten darauf hin, dass Polycaprolacton in der Zellwand gebunden ist und zu einer permanenten Quellung führt (bis zu 5 %). Die Dimensionsstabilität nahm um 40 % zu und die Wasseraufnahmerate konnte um mehr als 35 % reduziert werden. Mit dieser Methode kann nicht nur dimensionsstabileres Holz realisiert werden, auch biologische Abbaubarkeit und damit eine einfache Entsorgung sind gewährleistest. KW - Holzmodifikation KW - hydrophobe Moleküle KW - Dimensionsstabilität KW - Wassergehalt KW - wood modification KW - hydrophobic molecules KW - dimensional stability KW - moisture content Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-71325 ER - TY - THES A1 - Chung, Kang Ko T1 - Heteroatom-containing carbons for high energy density supercapacitor T1 - Heteroatomhaltige Kohlenstoffe für Superkondensatoren mit hohen Energiedichten N2 - The supercapacitor is one of the most important energy storage devices as its construction allows for addressing many of the drawbacks related to batteries, but the low energy density of current systems is a major issue. In this doctoral dissertation, with a view to attaining high energy density supercapacitor systems that can be comparable to those for batteries, new heteroatom-containing carbons in the form of particles and three-dimensional films were investigated. A nitrogen-containing material, acrodam, was chosen as the carbon precursor due to the inexpensiveness, high carbonization yield, oligomerizability, etc. The carbon particles were prepared from acrodam together with caesium acetate as a meltable flux agent, and disclosed excellent properties in hydroquinone-loaded sulphuric acid electrolyte with high energy densities (up to 133.0 Wh kg–1) and sufficient cycle stabilities. These properties are already now comparable to those of batteries. Besides, conductive carbon three-dimensional films were fabricated using acrodam oligomer as the precursor by the inexpensive spin coating method. The films were found to be homogeneous, flat, void- and crack-free, and high conductivities (up to 334 S cm–1) could be obtained at the carbonization temperature of 1000 ºC. Furthermore, a porous carbon three-dimensional film could be formed using an organic template at the first attempt. This finding demonstrates the film’s potentiality for various applications such as supercapacitor electrode; the essential absence of contact resistance within the network should contribute to effective transportation of electron within the electrode. The progress made in this dissertation will open a new way to further enhancement of energy density for supercapacitor as well as other applications that exceeds the current properties. N2 - Der Superkondensator ist einer der wichtigsten Energiespeicher da seine Konstruktion die Lösung vieler Nachteile von Batterien erlaubt. Allerdings weisen derzeitige Systeme noch zu geringe Energiedichten auf. Um Superkondensatoren mit Energiedichten vergleichbar zu Batterien zu ermöglichen, wurden in der vorliegenden Dissertation neue, heteroatomhaltige Kohlenstoffe in Form von Partikeln und Filmen untersucht. Aufgrund geringer Kosten, hohen Ausbeuten, Polymerisierbarkeit usw. wurde die stickstoffhaltige Substanz Acrodam als Kohlenstoffvorstufe verwendet. Die Kohlenstoffpartikel wurden ausgehend von Acrodam zusammen mit Cäsiumacetat als schmelzbares Flussmittel hergestellt und wiesen ausgezeichnete Eigenschaften in Hydrochinon geladenen Schwefelsäure-Elektrolyten mit hohen Energiedichten (bis zu 133,0 Wh kg–1) und guten Zyklusstabilitäten auf. Diese Eigenschaften sind bereits jetzt vergleichbar mit denen von Batterien. Weiterhin wurden unter Verwendung von Acrodamoligomeren als Vorstufe und mit Hilfe der kostengünstigen Rotationsbeschichtung leitfähige, dreidimensionale Kohlenstofffilme hergestellt. Bei einer Karbonisierungstemperatur von 1000 °C konnten die Materialien als homogene, flache, Hohlraum-und Riss-freie Filme erhalten werden, die eine hohe Leitfähigkeit (bis zu 334 S cm–1) aufwiesen. Darüber hinaus konnte mit einem organischen Templat ein dreidimensionaler, poröser Kohlenstoff geformt werden. Dies zeigt das Potential der Filme für verschiedene Anwendungen wie Superkondensatorelektroden; die Abwesenheit von Übergangswiderständen im Netzwerk sollte zu einem effizienten Transport von Elektronen in der Elektrode beitragen. Die Ergebnisse dieser Dissertation werden neue Wege zur Verbesserung der Energiedichte von Superkondensatoren sowie weiteren Anwendungen eröffnen. KW - supercapacitor KW - carbon KW - heteroatom KW - energy density Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-69826 ER - TY - THES A1 - Santan, Harshal Diliprao T1 - Synthesis and characterization of thermosensitive hydrogels derived from polysaccharides N2 - In this work, thermosensitive hydrogels having tunable thermo-mechanical properties were synthesized. Generally the thermal transition of thermosensitive hydrogels is based on either a lower critical solution temperature (LCST) or critical micelle concentration/ temperature (CMC/ CMT). The temperature dependent transition from sol to gel with large volume change may be seen in the former type of thermosensitive hydrogels and is negligible in CMC/ CMT dependent systems. The change in volume leads to exclusion of water molecules, resulting in shrinking and stiffening of system above the transition temperature. The volume change can be undesired when cells are to be incorporated in the system. The gelation in the latter case is mainly driven by micelle formation above the transition temperature and further colloidal packing of micelles around the gelation temperature. As the gelation mainly depends on concentration of polymer, such a system could undergo fast dissolution upon addition of solvent. Here, it was envisioned to realize a thermosensitive gel based on two components, one responsible for a change in mechanical properties by formation of reversible netpoints upon heating without volume change, and second component conferring degradability on demand. As first component, an ABA triblockcopolymer (here: Poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) (PEPE) with thermosensitive properties, whose sol-gel transition on the molecular level is based on micellization and colloidal jamming of the formed micelles was chosen, while for the additional macromolecular component crosslinking the formed micelles biopolymers were employed. The synthesis of the hydrogels was performed in two ways, either by physical mixing of compounds showing electrostatic interactions, or by covalent coupling of the components. Biopolymers (here: the polysaccharides hyaluronic acid, chondroitin sulphate, or pectin, as well as the protein gelatin) were employed as additional macromolecular crosslinker to simultaneously incorporate an enzyme responsiveness into the systems. In order to have strong ionic/electrostatic interactions between PEPE and polysaccharides, PEPE was aminated to yield predominantly mono- or di-substituted PEPEs. The systems based on aminated PEPE physically mixed with HA showed an enhancement in the mechanical properties such as, elastic modulus (G′) and viscous modulus (G′′) and a decrease of the gelation temperature (Tgel) compared to the PEPE at same concentration. Furthermore, by varying the amount of aminated PEPE in the composition, the Tgel of the system could be tailored to 27-36 °C. The physical mixtures of HA with di-amino PEPE (HA·di-PEPE) showed higher elastic moduli G′ and stability towards dissolution compared to the physical mixtures of HA with mono-amino PEPE (HA·mono-PEPE). This indicates a strong influence of electrostatic interaction between –COOH groups of HA and –NH2 groups of PEPE. The physical properties of HA with di-amino PEPE (HA·di-PEPE) compare beneficially with the physical properties of the human vitreous body, the systems are highly transparent, and have a comparable refractive index and viscosity. Therefore,this material was tested for a potential biological application and was shown to be non-cytotoxic in eluate and direct contact tests. The materials will in the future be investigated in further studies as vitreous body substitutes. In addition, enzymatic degradation of these hydrogels was performed using hyaluronidase to specifically degrade the HA. During the degradation of these hydrogels, increase in the Tgel was observed along with decrease in the mechanical properties. The aminated PEPE were further utilised in the covalent coupling to Pectin and chondroitin sulphate by using EDC as a coupling agent. Here, it was possible to adjust the Tgel (28-33 °C) by varying the grafting density of PEPE to the biopolymer. The grafting of PEPE to Pectin enhanced the thermal stability of the hydrogel. The Pec-g-PEPE hydrogels were degradable by enzymes with slight increase in Tgel and decrease in G′ during the degradation time. The covalent coupling of aminated PEPE to HA was performed by DMTMM as a coupling agent. This method of coupling was observed to be more efficient compared to EDC mediated coupling. Moreover, the purification of the final product was performed by ultrafiltration technique, which efficiently removed the unreacted PEPE from the final product, which was not sufficiently achieved by dialysis. Interestingly, the final products of these reaction were in a gel state and showed enhancement in the mechanical properties at very low concentrations (2.5 wt%) near body temperature. In these hydrogels the resulting increase in mechanical properties was due to the combined effect of micelle packing (physical interactions) by PEPE and covalent netpoints between PEPE and HA. PEPE alone or the physical mixtures of the same components were not able to show thermosensitive behavior at concentrations below 16 wt%. These thermosensitive hydrogels also showed on demand solubilisation by enzymatic degradation. The concept of thermosensitivity was introduced to 3D architectured porous hydrogels, by covalently grafting the PEPE to gelatin and crosslinking with LDI as a crosslinker. Here, the grafted PEPE resulted in a decrease in the helix formation in gelatin chains and after fixing the gelatin chains by crosslinking, the system showed an enhancement in the mechanical properties upon heating (34-42 °C) which was reversible upon cooling. A possible explanation of the reversible changes in mechanical properties is the strong physical interactions between micelles formed by PEPE being covalently linked to gelatin. Above the transition temperature, the local properties were evaluated by AFM indentation of pore walls in which an increase in elastic modulus (E) at higher temperature (37 °C) was observed. The water uptake of these thermosensitive architectured porous hydrogels was also influenced by PEPE and temperature (25 °C and 37 °C), showing lower water up take at higher temperature and vice versa. In addition, due to the lower water uptake at high temperature, the rate of hydrolytic degradation of these systems was found to be decreased when compared to pure gelatin architectured porous hydrogels. Such temperature sensitive architectured porous hydrogels could be important for e.g. stem cell culturing, cell differentiation and guided cell migration, etc. Altogether, it was possible to demonstrate that the crosslinking of micelles by a macromolecular crosslinker increased the shear moduli, viscosity, and stability towards dissolution of CMC-based gels. This effect could be likewise be realized by covalent or non-covalent mechanisms such as, micelle interactions, physical interactions of gelatin chains and physical interactions between gelatin chains and micelles. Moreover, the covalent grafting of PEPE will create additional net-points which also influence the mechanical properties of thermosensitive architectured porous hydrogels. Overall, the physical and chemical interactions and reversible physical interactions in such thermosensitive architectured porous hydrogels gave a control over the mechanical properties of such complex system. The hydrogels showing change of mechanical properties without a sol-gel transition or volume change are especially interesting for further study with cell proliferation and differentiation. N2 - In der vorliegenden Arbeit wurden thermosensitive Hydrogele mit einstellbaren thermo-mechanischen Eigenschaften synthetisiert. Im Allgemeinen basiert der thermische Übergang thermosensitiver Gele auf einer niedrigsten kritischen Löslichkeitstemperatur (LCST) oder kritischer Mizellkonzentration bzw. –temperatur(CMC/ CMT). Der temperaturabhängige Übergang von Sol zu Gel mit großer Volumenänderung wurde im ersten Fall bei thermosensitiven Hydrogelen beobachtet und ist vernachlässigbar für CMC/ CMT abhängige Systeme. Die Änderung des Volumens führt zum Ausschluss von Wassermolekülen, was zum Schrumpfen und Versteifen des Systems oberhalb der Übergangstemperatur führt. Die Volumenänderung kann unerwünscht sein, wenn Zellen in das Gel eingeschlossen werden sollen. Die Gelierung im zweiten Fall beruht hauptsächlich auf der Mizellbildung oberhalb der Übergangstemperatur und weiterem kolloidalem Packen von Mizellen im Bereich der Gelierungstemperatur. Weil die Gelierung hauptsächlich von der Polymerkonzentration abhängt, kann sich das Gel bei Zugabe von Lösungsmittel leicht wieder lösen. Hier sollten thermosensitive Gele entwickelt werden, die auf zwei Komponenten beruhen. Eine Komponente sollte aus einem ABA-Triblockcopolymer mit thermosensitiven Eigenschaften bestehen, dem Poly(ethylen glycol)-b-Poly(propylenglycol)-b-Poly(ethylen glycol) (PEPE), dessen Sol-Gel-Übergang auf Mizellierung und kolloidalem Jamming der gebildeten Mizellen basiert, und einer weiteren makromolekularen Komponente, einem Biopolymer, dass die Mizellen vernetzt. Auf diese Weise sollten thermosensitive Gele realisiert werden, die keine oder nur eine kleine Volumenänderung während der Änderung der mechanischen Eigenschaften zeigen, die stabiler gegenüber Verdünnung sein sollten als klassische Hydrogele mit einem CMC-basierten Übergang und die jedoch gezielt abgebaut werden können. Die Hydrogele wurden auf zwei Arten vernetzt, entweder durch physikalisches Vermischen, bei dem die Vernetzung durch elektrostatische Wechselwirkungen erfolgte, oder durch kovalente Kopplung der beiden Komponenten. Als makromolekulare Komponente zur Vernetzung der Mizellen wurden Biopolymere (hier: die Polysaccharide Hyaluronsäure (HA), Chondroitinsulfat oder Pektin oder das Protein Gelatin) verwendet, um die Hydrogele enzymatisch abbaubar zu gestalten. Um eine starke ionische/elektrostatische Wechselwirkung zwischen dem PEPE und den Polysachariden zu erzielen, wurde PEPE aminiert, um hauptsächlich monoaminiertes bzw. diaminiertes PEPE einsetzen zu können. Die Gele, die auf der physikalischen Mischung von aminierten PEPE mit HA bestehen, zeigten im Vergleich zu PEPE bei gleicher Konzentration eine Zunahme der mechanischen Eigenschaften, wie beispielsweise dem elastischem Modulus (G′) und dem Viskositätsmodulus (G′′) bei gleichzeitiger Abnahme der Gelierungstemperatur (Tgel). Durch Variation des Gehalts an aminierten PEPE-, konnte die Tgel in einem Bereich von 27-36 °C eingestellt werden. Interessanterweise zeigten die physikalischen Mischungen mit diaminierten PEPE (HA·di-PEPE) höhere mechanische Eigenschaften (elastischer Modulus G′) und eine höhere Stabilität gegenüber Verdünnungseffekten als Mischungen mit monoaminiertem PEPE (HA·mono-PEPE). Dies zeigt den starken Einfluss der elektrostatischen Wechselwirkungen zwischen der Carboxylgruppe der HA und der Amingruppe von PEPE. Die physikalischen Eigenschaften HA·di-PEPE sind vergleichbar mit den physikalischen Eigenschaften des Glaskörpers im Auge hinsichtlich Transparenz, Brechungsindex und Viskosität. Deswegen wurde das Material hinsichtlich seiner biologischen Anwendung getestet und zeigte sich sowohl im Überstand als auch im direkten Kontakt als nichtzytotoxisch. Zukünftig wird dieses Material in weiteren Untersuchungen bezüglich seiner Eignung als Glaskörperersatz geprüft werden. Zusätzlich konnte der enzymatische Abbau der Hydrogele mit Hyaluronidase gezeigt werden, die spezifisch HA abbaut. Beim Abbau der Hydrogele stieg Tgel bei gleichzeitiger Abnahme der mechanischen Eigenschaften. Aminiertes PEPE wurde zusätzlich zur kovalenten Bindung unter Verwendung von EDC als Aktivator an Pektin und Chondroitinsulfat eingesetzt. Tgel konnte auf 28 – 33 °C eingestellt werden durch Variation der Pfropfungsdichte am Biopolymer bei gleichzeitiger Zunahme der thermischen Stabilität. Die Pec-g-PEPE Hydrogele waren enzymatisch abbaubar, was zu einer leichten Erhöhung von Tgel und zu einer Abnahme von G′ führte. Die kovalente Bindung der aminierten PEPE an HA erfolgte unter Verwendung von DMTMM als Aktivator, der sich in diesem Fall als effektiver als EDC herausstellte. Die Reinigung mittels Ultrafiltration führte zu einer deutlich besseren Aufreinigung des Produkts als mittels Dialyse. Die gegrafteten Systeme waren in Nähe der Körpertemperatur bereits im Gelstadium und zeigten eine Erhöhung der mechanischen Eigenschaften bereits bei sehr geringen Konzentrationen von 2.5Gew.%. Die höheren mechanischen Eigenschaften dieser Hydrogele erklären sich durch die Kombination der Mizellbildung (physikalische Wechselwirkung) des PEPE und der Bildung kovalenter Netzpunkte zwischen PEPE und HA. PEPE bzw. entsprechende physikalische Mischungen derselben Komponenten zeigten kein thermosensitives Verhalten bei einer Konzentration unterhalb von 16 Gew%. Diese thermosensitiven Hydrogele zeigten auch eine Löslichkeit auf Abruf durch enzymatischen Abbau. Das Konzept der Thermosensitivität wurde in 3D strukturierte, poröse Hydrogele (TArcGel)eingeführt, bei dem PEPE kovalent an Gelatin gebunden wurde und mit LDI vernetzt wurde. Das gepfropfte PEPE führte zu einer Erniedrigung der Helixbildung der Gelatinketten. Nach Fixierung der Gelatinketten durch Vernetzung zeigte das System eine Erhöhung der mechanischen Eigenschaften bei Erwärmung (34-42 °C). Dieses Phänomen war reversibel beim Abkühlen. Eine mögliche Erklärung der reversiblen Änderungen bezüglich der mechanischen Eigenschaften sind die starken physikalischen Wechselwirkungen zwischen den Mizellen des PEPE, die kovalent an Gelatin gebunden wurden. Ferner wurde durch AFM Untersuchungen festgestellt, dass bei Temperaturerhöhung (37 °C) die örtlichen elastischen Moduli (E) der Zellwände zugenommen haben. Zusätzlich wurde die Wasseraufnahme der TArcGele durch PEPE und die Temperatur (25 °C und 37 °C) beeinflusst und zeigte eine niedrigere Wasseraufnahme bei höherer Temperatur und umgekehrt. Durch die niedrigere Wasseraufnahme bei hohen Temperaturen erniedrigte sich die Geschwindigkeit des hydrolytischen Abbaus im Vergleich zu dem strukturierten Hydrogel aus reiner Gelatin. Diese temperatursensitiven ArcGele könnten bedeutsam sein für Anwendungen im Bereich Stammzellkultivierung, Zelldifferenzierung und gerichteter Zellmigration. Zusammenfassend konnte bei den thermosensitiven Hydrogelen gezeigt werden, dass die Vernetzung von Mizellen mit einem makromolekularen Vernetzer die Schermoduli, Viskosität und Löslichkeitsstabilität im Vergleich zu reinen ABATriblockcopolymeren mit CMC-Übergang erhöht. Dieser Effekt konnte durch kovalente und nichtkovalente Mechanismen, wie beispielsweise Mizell- Wechselwirkungen, physikalische Interaktionen von Gelatinketten und physikalische Interaktionen von Gelatinketten und Mizellen, realisiert werden. Das Pfropfen von PEPE führte zu zusätzlichen Netzpunkten, die die mechanischen Eigenschaften der thermosensitiven architekturisierten, porösen Hydrogele beeinflussten. Insgesamt ermöglichten die physikalischen und chemischen Bindungen und die reversiblen physikalischen Wechselwirkungen in den strukturierten, porösen Hydrogelen eine Kontrolle der mechanischen Eigenschaften in diesem sehr komplexen System. Die Hydrogele, die eine Veränderung ihrer mechanischen Eigenschaften ohne Volumenänderung oder Sol-Gel-Übergang zeigen sind besonders interessant für Untersuchungen bezüglich Zellproliferation und –differenzierung. KW - thermosensitive KW - hydrogels KW - biomaterials KW - biopolymers KW - sol-gel Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-69793 ER - TY - THES A1 - Titirici, Maria-Magdalena T1 - Hydrothermal carbonisation T1 - Hydrothermale Karbonisierung BT - A sustainable alternative to versatile carbon materials BT - Eine nachhaltige Alternative zu Kohle N2 - The world’s appetite for energy is producing growing quantities of CO2, a pollutant that contributes to the warming of the planet and which currently cannot be removed or stored in any significant way. Other natural reserves are also being devoured at alarming rates and current assessments suggest that we will need to identify alternative sources in the near future. With the aid of materials chemistry it should be possible to create a world in which energy use needs not be limited and where usable energy can be produced and stored wherever it is needed, where we can minimize and remediate emissions as new consumer products are created, whilst healing the planet and preventing further disruptive and harmful depletion of valuable mineral assets. In achieving these aims, the creation of new and very importantly greener industries and new sustainable pathways are crucial. In all of the aforementioned applications, new materials based on carbon, ideally produced via inexpensive, low energy consumption methods, using renewable resources as precursors, with flexible morphologies, pore structures and functionalities, are increasingly viewed as ideal candidates to fulfill these goals. The resulting materials should be a feasible solution for the efficient storage of energy and gases. At the end of life, such materials ideally must act to improve soil quality and to act as potential CO2 storage sinks. This is exactly the subject of this habilitation thesis: an alternative technology to produce carbon materials from biomass in water using low carbonisation temperatures and self-generated pressures. This technology is called hydrothermal carbonisation. It has been developed during the past five years by a group of young and talented researchers working under the supervision of Dr. Titirici at the Max-Planck Institute of Colloids and Interfaces and it is now a well-recognised methodology to produce carbon materials with important application in our daily lives. These applications include electrodes for portable electronic devices, filters for water purification, catalysts for the production of important chemicals as well as drug delivery systems and sensors. N2 - Der stets wachsende globale Energiebedarf führt zu immer weiter zunehmenden Emissionen von Kohlenstoffdioxid, einem umweltschädlichen Gas, das als eines der Hauptprobleme im weltweiten Klimawandel darstellt. Bislang ist es jedoch nicht möglich, dieses Kohlenstoffdioxid in sinnvoller Weise zu verwerten oder einzulagern. Zudem existieren weitere Probleme in der globalen Energieversorgung, da viele natürlich vorkommende Rohstoffe sehr schnell ausgebeutet werden, so dass in naher Zukunft dringend alternative Energiequellen gefunden werden müssen, um den aktuellen Problemen zu begegnen. Der Wissenschaftszweig der Materialchemie zielt in diesem Zusammenhang darauf ab, dazu beizutragen, die bestehende Energieinfrastruktur nachhaltig zu verändern. Dabei stehen verschiedene Aspekte im Vordergrund: Energie sollte in allen gewünschten Mengen jederzeit verfügbar und auch speicherbar sein. Zudem sollte ihre Erzeugung ohne umweltschädliche Abfallprodukte ablaufen. Tiefgreifende Eingriffe in die Umwelt, v.a. durch den übermäßigen Abbau von Rohstoffen, sollte nicht mehr erforderlich sein. Auf diese Weise können die Folgen des bisherigen Klimawandels eingedämmt werden und neue Schäden an der Umwelt vermieden werden. Neue, grüne Industrie- und Energieprozesse schützen hier also nachhaltig den Planeten. Bei der Forschung an nachhaltigen Formen der Energieversorgung beschäftigen sich Materialchemiker in mannigfaltiger Weise mit Kohlenstoffmaterialien. Diese sollten idealerweise kostengünstig und ohne hohen Energiebedarf produziert werden können. Am vielversprechendsten sind Materialien, die eine flexibel gestaltbare Morphologie besitzen, d.h. die besondere strukturelle Eigenschaften besitzen, wie z.B. Porosität oder chemisch veränderte und damit funktionale Oberflächen. Idealerweise sollten solche neu entwickelten Materialien nicht nur als Speicher von Energie oder Energieträgern dienen, sondern auch nach ihrer Lebensdauer als funktionales Material zur Verbesserung der Bodenqualität eingesetzt werden können und dort noch weiter als potentielle Senke für Kohlenstoffdioxid dienen können. Die zuvor beschriebenen Themen und Probleme stellen den Gegenstand der vorliegenden Habilitationsschrift dar: die Entwicklung einer alternativen Methode zur Herstellung von Kohlenstoffmaterialien aus Biomasse in Wasser bei geringen Temperaturen. Dabei handelt es sich um die sogenannte hydrothermale Karbonisierung, die in den letzten fünf Jahren von einer Gruppe junger, talentierter Wissenschaftler unter der Anleitung von Frau Dr. Titirici am Max-Planck-Institut für Kolloid- und Grenzflächenforschung erarbeitet und weiterentwickelt wurde zu einer heutzutage anerkannten und verbreiteten Methode. Zudem wurden die über diesen Weg gewonnenen Materialien erfolgreich in zahlreichen, für den Alltag wichtigen Anwendungen eingesetzt, so z.B. als Elektroden in tragbaren elektronischen Geräten, als Filtermaterialien für die Aufreinigung kontaminierten Wassers, als Katalysatoren für wichtige chemische Reaktionen, als Trägermaterial für Arzneimittel und als Sensoren. KW - Hydrothermale Karbonisierung KW - Kohlenstoffe auf Biomasse-Basis KW - hydrothermal carbonization KW - biomass-derived carbons Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-66885 ER - TY - THES A1 - Fechler, Nina T1 - Salts as highly diverse porogens : functional ionic liquid-derived carbons and carbon-based composites for energy-related applications T1 - Salze als vielfältige Porogene : funktionelle, ionische Flüssigkeiten basierte Kohlenstoffe und Kohlenstoff basierte Komposite für Energieanwendungen N2 - The present thesis is to be brought into line with the current need for alternative and sustainable approaches toward energy management and materials design. In this context, carbon in particular has become the material of choice in many fields such as energy conversion and storage. Herein, three main topics are covered: 1)An alternative synthesis strategy toward highly porous functional carbons with tunable porosity using ordinary salts as porogen (denoted as “salt templating”) 2)The one-pot synthesis of porous metal nitride containing functional carbon composites 3)The combination of both approaches, enabling the generation of highly porous composites with finely tunable properties All approaches have in common that they are based on the utilization of ionic liquids, salts which are liquid below 100 °C, as precursors. Just recently, ionic liquids were shown to be versatile precursors for the generation of heteroatom-doped carbons since the liquid state and a negligible vapor pressure are highly advantageous properties. However, in most cases the products do not possess any porosity which is essential for many applications. In the first part, “salt templating”, the utilization of salts as diverse and sustainable porogens, is introduced. Exemplarily shown for ionic liquid derived nitrogen- and nitrogen-boron-co-doped carbons, the control of the porosity and morphology on the nanometer scale by salt templating is presented. The studies within this thesis were conducted with the ionic liquids 1-Butyl-3-methyl-pyridinium dicyanamide (Bmp-dca), 1-Ethyl-3-methyl-imidazolium dicyanamide (Emim-dca) and 1 Ethyl 3-methyl-imidazolium tetracyanoborate (Emim-tcb). The materials are generated through thermal treatment of precursor mixtures containing one of the ionic liquids and a porogen salt. By simple removal of the non-carbonizable template salt with water, functional graphitic carbons with pore sizes ranging from micro- to mesoporous and surface areas up to 2000 m2g-1 are obtained. The carbon morphologies, which presumably originate from different onsets of demixing, mainly depend on the nature of the porogen salt whereas the nature of the ionic liquid plays a minor role. Thus, a structural effect of the porogen salt rather than activation can be assumed. This offers an alternative to conventional activation and templating methods, enabling to avoid multiple-step and energy-consuming synthesis pathways as well as employment of hazardous chemicals for the template removal. The composition of the carbons can be altered via the heat-treatment procedure, thus at lower synthesis temperatures rather polymeric carbonaceous materials with a high degree of functional groups and high surface areas are accessible. First results suggest the suitability of the materials for CO2 utilization. In order to further illustrate the potential of ionic liquids as carbon precursors and to expand the class of carbons which can be obtained, the ionic liquid 1-Ethyl-3-methyl-imidazolium thiocyanate (Emim-scn) is introduced for the generation of nitrogen-sulfur-co-doped carbons in combination with the already studied ionic liquids Bmp-dca and Emim-dca. Here, the salt templating approach should also be applicable eventually further illustrating the potential of salt templating, too. In the second part, a one-pot and template-free synthesis approach toward inherently porous metal nitride nanoparticle containing nitrogen-doped carbon composites is presented. Since ionic liquids also offer outstanding solubility properties, the materials can be generated through the carbonization of homogeneous solutions of an ionic liquid acting as nitrogen as well as carbon source and the respective metal precursor. The metal content and surface area are easily tunable via the initial metal precursor amount. Furthermore, it is also possible to synthesize composites with ternary nitride nanoparticles whose composition is adjustable by the metal ratio in the precursor solution. Finally, both approaches are combined into salt templating of the one-pot composites. This opens the way to the one-step synthesis of composites with tunable composition, particle size as well as precisely controllable porosity and morphology. Thereby, common synthesis strategies where the product composition is often negatively affected by the template removal procedure can be avoided. The composites are further shown to be suitable as electrodes for supercapacitors. Here, different properties such as porosity, metal content and particle size are investigated and discussed with respect to their influence on the energy storage performance. Because a variety of ionic liquids, metal precursors and salts can be combined and a simple closed-loop process including salt recycling is imaginable, the approaches present a promising platform toward sustainable materials design. N2 - Die vorliegende Arbeit basiert auf der Notwendigkeit für eine alternative und nachhaltige Energiewirtschaft sowie alternativer Herstellungsmethoden der damit verbundenen Materialien. Hierbei kommt besonders Kohlenstoffen und kohlenstoffbasierten Systemen eine hohe Bedeutung zu. Im Rahmen der Dissertation wurden drei Ansätze verfolgt, die zu der Entwicklung alternativer Strategien zur Herstellung poröser Heteroatom-enthaltender Kohlenstoffe und deren Komposite beitragen. Die Materialien wurden des Weiteren für die CO2 Nutzung sowie Energiespeicherung in Form von Superkondensatoren getestet. Allen Materialien ist gemeinsam, dass sie ausgehend von ionischen Flüssigkeiten, Salze mit einem Schmelzpunkt unterhalb von 100 °C, als Kohlenstoffvorstufe durch Hochtemperaturverfahren hergestellt wurden. Im ersten Teil wird ein alternatives und nachhaltiges Verfahren zur Herstellung hochporöser Stickstoff und Stickstoff-Bor-haltiger Kohlenstoffe vorgestellt. Bei dieser als „Salztemplatierung“ bezeichneten Methode werden herkömmliche Salze als Porogen verwendet. Damit sind sehr hohe Oberflächen erreichbar, die neben der Porengröße und dem Porenvolumen durch die Variation der Salzspezies und Salzmenge einstellbar sind. Dies bietet gegenüber herkömmlichen Templatierungsverfahren den Vorteil, dass das Salz nach erfolgter Karbonisierung der ionischen Flüssigkeit in Anwesenheit der nicht karbonisierbaren Salzspezies einfach mit Wasser auswaschbar ist. Hierbei ist ein Recyclingprozess denkbar. Bei hohen Synthesetemperaturen werden graphitische, bei niedrigen hochfunktionalisierte, polymerartige Produkte erhalten. Letztere erwiesen sich als vielversprechende Materialien für die CO2 Nutzung. Unter Verwendung einer bisher nicht eingesetzten ionische Flüssigkeit konnte weiterhin die Einführung von Schwefel als Heteroatom ermöglicht werden. Im zweiten Teil wird eine Templat-freie Einschrittsynthese von porösen Kompositen aus Metallnitrid Nanopartikeln und Stickstoff-dotiertem Kohlenstoff vorgestellt. Die Materialien werden ausgehend von einer Lösung aus einer ionischen Flüssigkeit und einem Metallvorläufer hergestellt, wobei die ionische Flüssigkeit sowohl als Kohlenstoffvorläufer als auch als Stickstoffquelle für die Metallnitride dient. Der Metallgehalt, das Metallverhältnis in ternären Nitriden und die Oberfläche sind über den Anteil des Metallvorläufers einstellbar. Schließlich werden beide Ansätze zur Salztemplatierung von den Kompositen kombiniert. Dadurch wird die Einschrittsynthese von Kompositen mit einstellbarer Oberfläche, Zusammensetzung, Partikelgröße und Morphologie ermöglicht. Diese Materialien wurden schließlich als Elektroden für Superkondensatoren getestet und der Einfluss verschiedener Parameter auf die Leistungsfähigkeit untersucht. Aufgrund verschiedener Kombinationsmöglichkeiten von ionischen Flüssigkeiten, Metallvorläufern und Salzen, stellen die hier präsentierten Ansätze eine vielversprechende Plattform für die nachhaltige Materialsynthese dar. KW - Salze KW - Poröse Materialien KW - Heteroatom-dotierte Kohlenstoffe KW - Metallnitrid-Kohlenstoff Komposite KW - Superkondensator KW - Salts KW - porous materials KW - heteroatom-doped carbons KW - metal nitride carbon composites KW - supercapacitors Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-64775 ER - TY - THES A1 - Robinson, Joshua Wayne T1 - Novel Poly(N-substituted glycine)s : synthesis, post-modification, and physical properties T1 - Neuartige Poly(N-substituierte glycine) : Synthese, polymeranaloge Modifikation und physikalische Eigenschaften N2 - Various synthetic approaches were explored towards the preparation of poly(N-substituted glycine) homo/co-polymers (a.k.a. polypeptoids). In particular, monomers that would facilitate in the preparation of bio-relevant polymers via either chain- or step-growth polymerization were targeted. A 3-step synthetic approach towards N-substituted glycine N-carboxyanhydrides (NNCA) was implemented, or developed, and optimized allowing for an efficient gram scale preparation of the aforementioned monomer (chain-growth). After exploring several solvents and various conditions, a reproducible and efficient ring-opening polymerization (ROP) of NNCAs was developed in benzonitrile (PhCN). However, achieving molecular weights greater than 7 kDa required longer reaction times (>4 weeks) and sub-sequentially allowed for undesirable competing side reactions to occur (eg. zwitterion monomer mechanisms). A bulk-polymerization strategy provided molecular weights up to 11 kDa within 24 hours but suffered from low monomer conversions (ca. 25%). Likewise, a preliminary study towards alcohol promoted ROP of NNCAs suffered from impurities and a suspected alternative activated monomer mechanism (AAMM) providing poor inclusion of the initiator and leading to multi-modal dispersed polymeric systems. The post-modification of poly(N-allyl glycine) via thiol-ene photo-addition was observed to be quantitative, with the utilization of photo-initiators, and facilitated in the first glyco-peptoid prepared under environmentally benign conditions. Furthermore, poly(N-allyl glycine) demonstrated thermo-responsive behavior and could be prepared as a semi-crystalline bio-relevant polymer from solution (ie. annealing). Initial efforts in preparing these polymers via standard poly-condensation protocols were insufficient (step-growth). However, a thermally induced side-product, diallyl diketopiperazine (DKP), afforded the opportunity to explore photo-induced thiol-ene and acyclic diene metathesis (ADMET) polymerizations. Thiol-ene polymerization readily led to low molecular weight polymers (<2.5 kDa), that were insoluble in most solvents except heated amide solvents (ie. DMF), whereas ADMET polymerization, with diallyl DKP, was unsuccessful due to a suspected 6 member complexation/deactivation state of the catalyst. This understanding prompted the preparation of elongated DKPs most notably dibutenyl DKP. SEC data supports the aforementioned understanding but requires further optimization studies in both the preparation of the DKP monomers and following ADMET polymerization. This work was supported by NMR, GC-MS, FT-IR, SEC-IR, and MALDI-Tof MS characterization. Polymer properties were measured by UV-Vis, TGA, and DSC. N2 - Die Annehmlichkeiten des Alltags und das hohe Alter das Menschen in der heutigen Zeit erreichen sind ein Ergebnis des wissenschaftlichen und technologischen Fortschritts. Insbesondere in der Medizin haben die Entwicklung neuartiger Medikamente und Therapien, künstlicher Knochen und Gewebeteile sowie der Einsatz von neuen Geräten für die Diagnostik und Assistenz bei Operationen enorm zu diesen Errungenschaften beigetragen. Jede Entwicklung fundierte letztlichen auf den Ergebnissen der Grundlagenforschung sei es von Mikro-/biologen (Identifikation anormalen Verhaltens), Biochemikern (Identifikation von Auslösern und Wirkzentren) Bio-/ organischen Chemikern (Synthese von Makro-/molekülen), Material-/chemikern (Materialsynthese) und/oder Ingenieuren/Mathematikern/Physikern (theoretischen Modelle und Berechnungen). Biomedizinische Anwendungen wie z.B. Biosensoren, künstliche Gewebeteile und Trägersubstanzen zur gezielten Wirkstofffreisetzung sind von besonderem Interesse. Materialien, die nach Kontakt mit einer Zelloberfläche in der Lage sind definiert ihre Struktur oder mechanischen Eigenschaften zu verändern und anschließend bioabbaubar sind ohne toxische Nebenwirkungen zu entfalten befriedigen die zuvor genannten Bedürfnisse. Organismen entwickeln Biomaterialien bereits seit Millionen von Jahren und sind daher ein typischer Startpunkt für die Inspiration zu vielversprechenden Substanzen. Peptoide, als Mimetika von Peptiden, werden bereits längerem von Bio-/chemikern synthetisiert und auf ihren therapeutischen Nutzen hin, neuerdings auch auf ihre Materialeigenschaften untersucht. Grundlegende Eigenschaften dieser Materialien sind ihre Biokompatibilität, kontrollierte Bioabbaubarkeit, thermische Prozessierbarkeit sowie ihre Fähigkeit zur Selbstorganisation in höher geordnete Strukturen. Die sequenzdefinierte Synthese ist jedoch aufwendig und teuer. In dieser Arbeit habe ich ein alternatives Herstellungsverfahren (Ringöffnungspolymerisation) entwickelt mit dem es möglich ist hochmolekulare Substanzen - genannt poly(N-substituierte Glycine) – herzustellen. Ich erwarte, dass diese Materialien ähnliche stimulus responsive und thermische Eigenschaften wie Polypeptide, die bereits intensiv auf ihre biomedizinische Anwendbarkeit untersucht werden, haben. Im Vergleich zu den strukturgleichen Peptiden erwarte ich eine höhere Biokompatibilität sodass diese Materialen eine vielversprechende neue Klasse biorelevanter Materialien darstellen könnte. Die fundamentalen Ergebnisse dieser Arbeit stellen eine Alternative zu den bekannten Methoden zur Herstellung poly(N-substituierter Glycine) dar. Selbige weisen stimulus responsives Verhalten und thermische Prozessierbarkeit auf, das vergleichbar ist mit bereits bekannten Materialien. Darüber hinaus erlauben sie die einfache und vielseitige Funktionalisierung für vielschichtige Anwendungen. KW - Glycopeptoid KW - Polyglycin KW - NCA KW - biorelevant KW - thermoresponsiv KW - glycopeptoid KW - polyglycine KW - NCA KW - biorelevant KW - thermoresponsive Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-64789 ER - TY - THES A1 - Borisova, Dimitriya T1 - Feedback active coatings based on mesoporous silica containers T1 - Rückkopplungsaktive Beschichtungen basierend auf mesoporösen Silika-Behältern N2 - Metalle werden oft während ihrer Anwendung korrosiven Bedingungen ausgesetzt, was ihre Alterungsbeständigkeit reduziert. Deswegen werden korrosionsanfällige Metalle, wie Aluminiumlegierungen mit Schutzbeschichtungen versehen, um den Korrosionsprozess aktiv oder passiv zu verhindern. Die klassischen Schutzbeschichtungen funktionieren als physikalische Barriere zwischen Metall und korrosiver Umgebung und bieten einen passiven Korrosionsschutz nur, wenn sie unbeschädigt sind. Im Gegensatz dazu kann die Korrosion auch im Fall einer Beschädigung mittels aktiver Schutzbeschichtungen gehemmt werden. Chromathaltige Beschichtungen bieten heutzutage den besten aktiven Korrosionsschutz für Aluminiumlegierungen. Aufgrund ihrer Giftigkeit wurden diese weltweit verboten und müssen durch neue umweltfreundliche Schutzbeschichtungen ersetzt werden. Ein potentieller Ersatz sind Schutzbeschichtungen mit integrierten Nano- und Mikrobehältern, die mit ungiftigem Inhibitor gefüllt sind. In dieser Arbeit werden die Entwicklung und Optimierung solcher aktiver Schutzbeschichtungen für die industriell wichtige Aluminiumlegierung AA2024-T3 dargestellt Mesoporöse Silika-Behälter wurden mit dem ungiftigen Inhibitor (2-Mercaptobenzothiazol) beladen und dann in die Matrix anorganischer (SiOx/ZrOx) oder organischer (wasserbasiert) Schichten dispergiert. Zwei Sorten von Silika-Behältern mit unterschiedlichen Größen (d ≈ 80 and 700 nm) wurden verwendet. Diese haben eine große spezifische Oberfläche (≈ 1000 m² g-1), eine enge Porengrößenverteilung mit mittlerer Porenweite ≈ 3 nm und ein großes Porenvolumen (≈ 1 mL g-1). Dank dieser Eigenschaften können große Inhibitormengen im Behälterinneren adsorbiert und gehalten werden. Die Inhibitormoleküle werden bei korrosionsbedingter Erhöhung des pH-Wertes gelöst und freigegeben. Die Konzentration, Position und Größe der integrierten Behälter wurden variiert um die besten Bedingungen für einen optimalen Korrosionsschutz zu bestimmen. Es wurde festgestellt, dass eine gute Korrosionsschutzleistung durch einen Kompromiss zwischen ausreichender Inhibitormenge und guten Barriereeigenschaften hervorgerufen wird. Diese Studie erweitert das Wissen über die wichtigsten Faktoren, die den Korrosionsschutz beeinflussen. Somit wurde die Entwicklung effizienter, aktiver Schutzbeschichtungen ermöglicht, die auf mit Inhibitor beladenen Behältern basieren. N2 - Metals are often used in environments that are conducive to corrosion, which leads to a reduction in their mechanical properties and durability. Coatings are applied to corrosion-prone metals such as aluminum alloys to inhibit the destructive surface process of corrosion in a passive or active way. Standard anticorrosive coatings function as a physical barrier between the material and the corrosive environment and provide passive protection only when intact. In contrast, active protection prevents or slows down corrosion even when the main barrier is damaged. The most effective industrially used active corrosion inhibition for aluminum alloys is provided by chromate conversion coatings. However, their toxicity and worldwide restriction provoke an urgent need for finding environmentally friendly corrosion preventing systems. A promising approach to replace the toxic chromate coatings is to embed particles containing nontoxic inhibitor in a passive coating matrix. This work presents the development and optimization of effective anticorrosive coatings for the industrially important aluminum alloy, AA2024-T3 using this approach. The protective coatings were prepared by dispersing mesoporous silica containers, loaded with the nontoxic corrosion inhibitor 2-mercaptobenzothiazole, in a passive sol-gel (SiOx/ZrOx) or organic water-based layer. Two types of porous silica containers with different sizes (d ≈ 80 and 700 nm, respectively) were investigated. The studied robust containers exhibit high surface area (≈ 1000 m² g-1), narrow pore size distribution (dpore ≈ 3 nm) and large pore volume (≈ 1 mL g-1) as determined by N2 sorption measurements. These properties favored the subsequent adsorption and storage of a relatively large amount of inhibitor as well as its release in response to pH changes induced by the corrosion process. The concentration, position and size of the embedded containers were varied to ascertain the optimum conditions for overall anticorrosion performance. Attaining high anticorrosion efficiency was found to require a compromise between delivering an optimal amount of corrosion inhibitor and preserving the coating barrier properties. This study broadens the knowledge about the main factors influencing the coating anticorrosion efficiency and assists the development of optimum active anticorrosive coatings doped with inhibitor loaded containers. KW - Korrosion KW - Beschichtungen KW - Aluminiumlegierung KW - Silika KW - Nanopartikel KW - mesoporös KW - corrosion KW - coating KW - aluminum alloy KW - silica nanoparticles KW - mesoporous Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-63505 ER - TY - THES A1 - Zenichowski, Karl T1 - Quantum dynamical study of Si(100) surface-mounted, STM-driven switches at the atomic and molecular scale T1 - Quantendynamische Untersuchung von Si(100) Oberflächen-gebundenen, STM-gesteuerten atomaren und molekularen Schaltern N2 - The aim of this thesis is the quantum dynamical study of two examples of scanning tunneling microscope (STM)-controllable, Si(100)(2x1) surface-mounted switches of atomic and molecular scale. The first example considers the switching of single H-atoms between two dangling-bond chemisorption sites on a Si-dimer of the Si(100) surface (Grey et al., 1996). The second system examines the conformational switching of single 1,5-cyclooctadiene molecules chemisorbed on the Si(100) surface (Nacci et al., 2008). The temporal dynamics are provided by the propagation of the density matrix in time via an according set of equations of motion (EQM). The latter are based on the open-system density matrix theory in Lindblad form. First order perturbation theory is used to evaluate those transition rates between vibrational levels of the system part. In order to account for interactions with the surface phonons, two different dissipative models are used, namely the bilinear, harmonic and the Ohmic bath model. IET-induced vibrational transitions in the system are due to the dipole- and the resonance-mechanism. A single surface approach is used to study the influence of dipole scattering and resonance scattering in the below-threshold regime. Further, a second electronic surface was included to study the resonance-induced switching in the above-threshold regime. Static properties of the adsorbate, e.g., potentials and dipole function and potentials, are obtained from quantum chemistry and used within the established quantum dynamical models. N2 - Die vorliegende Doktorarbeit befasst sich mit kleinsten schaltbaren Einheiten in Form des Moleküls Cyclooctadien (COD) und dem Wasserstoff-Atom, die chemisch fest mit einer Oberfläche aus kristallinem Silizium verbunden sind. Jeder dieser Schalter kann mittels einer winzigen Spitze, eines so genannten Rastertunnelmikroskops (RTM), von atomarem Durchmesser in zwei unterscheidbare und stabile Schaltpositionen gebracht werden. Dabei besteht das Schalten entweder in einer Änderung der Geometrie des molekularen Schalters oder im Brechen und Neu-knüpfen chemischer Bindungen. Dabei ist es entscheidend, dass durch die geringe Grösse dieser Schalter eine hohe Anzahl dieser Schalter auf einer Oberfläche deponiert werden können. Mit der in den Schaltern speicherbaren Informationen an oder aus, 0 oder 1 ließen sich sehr hohe Speicherkapazitäten erreichen. Vor einer Anwendung dieser Art ist es wichtig zunächst ein grundlegendes Verständnis der Schaltprozesse auf der Oberfläche zu gewinnen. Wenn alle wesentlichen Faktoren berücksichtigt wurden und der Mechanismus des Schaltens verstanden ist, kann das Ergebnis des Experiments mit Hilfe eines theoretischen Modells vorhergesagt werden. Für die Handhabbarkeit muss sich das theoretisches Modell auf wesentliche Einflüsse beschränken und diese so einfach wie möglich beschreiben. So wurde die simultane Bewegung der 12 Atome des COD in die Bewegung eines gemittelten Massenpunktes entlang von einer oder von zwei räumlichen Freiheitsgraden übersetzt. Dabei kann der Massenpunkt im klassischen Bild anschaulich als eine rollende Kugel beschrieben werden, die in einer Seite einer Doppelmulde gefangen ist. Die Kugel kann durch äußere Anregung zum Schwingen gebracht werden und schließlich über eine Barriere in die benachbarte Mulde schalten. Nun muss die Schwingung der Kugel gebremst werden, um ein Zurück-Schwingen der Kugel zu verhindern. Die Anregung erfolgt durch elektrische Ladungen die von der Spitze des RTM zur Oberfläche wandern oder durch eine schwingende, d.h. warme Oberfläche. Das Bremsen wird über die elastische Bindung zu einer kalten Oberfläche vermittelt. Um Quanteneffekte wie das Tunneln der Kugel durch die Barriere zu beschreiben wurde die Kugel durch ein Wellenpaket beschrieben und dessen Aufenthaltswahrscheinlichkeit in der Doppelmulde untersucht. Im Fall des Wasserstoffatoms war die experimentelle Prüfung des entworfenen Modells für ein Schalten bei starkem Strom leider nicht möglich. Für das COD Molekül konnte jedoch nicht nur die Übereinstimmung mit den experimentellen Befunden, sondern im Fall des Schaltens in Abhängigkeit der Oberflächentemperatur auch die Vorhersagefähigkeit des Modells unter Beweis gestellt werden. KW - Kerndynamik KW - molekulare Schalter KW - Nanotechnologie KW - STM KW - Oberflächen KW - Quantum dynamics KW - molecular switches KW - nanotechnology KW - STM KW - surfaces Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-62156 ER - TY - THES A1 - Kristen, Juliane Ute T1 - Amphiphilic BAB-triblock copolymers bearing fluorocarbon groups : synthesis and self-organization in aqueous media T1 - Amphiphile BAB-Triblockcopolymere mit Fluorcarbon-Gruppen : Synthese und Selbstorganisation in wässrigen Medien N2 - In this work new fluorinated and non-fluorinated mono- and bifunctional trithiocarbonates of the structure Z-C(=S)-S-R and Z-C(=S)-S-R-S-C(=S)-Z were synthesized for the use as chain transfer agents (CTAs) in the RAFT-process. All newly synthesized CTAs were tested for their efficiency to moderate the free radical polymerization process by polymerizing styrene (M3). Besides characterization of the homopolymers by GPC measurements, end- group analysis of the synthesized block copolymers via 1H-, 19F-NMR, and in some cases also UV-vis spectroscopy, were performed attaching suitable fluorinated moieties to the Z- and/or R-groups of the CTAs. Symmetric triblock copolymers of type BAB and non-symmetric fluorine end- capped polymers were accessible using the RAFT process in just two or one polymerization step. In particular, the RAFT-process enabled the controlled polymerization of hydrophilic monomers such as N-isopropylacrylamide (NIPAM) (M1) as well as N-acryloylpyrrolidine (NAP) (M2) for the A-blocks and of the hydrophobic monomers styrene (M3), 2-fluorostyrene (M4), 3-fluorostyrene (M5), 4-fluorostyrene (M6) and 2,3,4,5,6-pentafluorostyrene (M7) for the B-blocks. The properties of the BAB-triblock copolymers were investigated in dilute, concentrated and highly concentrated aqueous solutions using DLS, turbidimetry, 1H- and 19F-NMR, rheology, determination of the CMC, foam height- and surface tension measurements and microscopy. Furthermore, their ability to stabilize emulsions and microemulsions and the wetting behaviour of their aqueous solutions on different substrates was investigated. The behaviour of the fluorine end-functionalized polymers to form micelles was studied applying DLS measurements in diluted organic solution. All investigated BAB-triblock copolymers were able to form micelles and show surface activity at room temperature in dilute aqueous solution. The aqueous solutions displayed moderate foam formation. With different types and concentrations of oils, the formation of emulsions could be detected using a light microscope. A boosting effect in microemulsions could not be found adding BAB-triblock copolymers. At elevated polymer concentrations, the formation of hydrogels was proved applying rheology measurements. N2 - Im Rahmen dieser Arbeit wurden neue fluorierte und unfluorierte mono- und bifunktionelle Trithiocarbonate der Typen Z-C(=S)-S-R und Z-C(=S)-S-R-S-C(=S)-Z zur Anwendung als CTAs (chain- transfer agents) im RAFT-Polymerisationsverfahren hergestellt. Alle CTAs wurden erfolgreich auf ihre Effizienz zur Steuerung des radikalischen Polymerisationsverfahrens hin durch Polymerisation von Styrol (M3) getestet. Neben GPC-Messungen wurden Endgruppenanalysen der synthetisierten Blockcopolymere mittels 1H-, 19F-NMR und in manchen Fällen auch UV-Vis Spektroskopie durchgeführt. Dazu wurden die Z- und/oder R-Gruppen der CTAs mit geeigneten fluorierten Gruppen versehen. Durch Anwendung des RAFT Verfahrens konnten symmetrische Triblockcopolymere vom Typ BAB bzw. mit einer Fluoralkylgruppe endgecappte unsymmetrische Polymere in nur zwei bzw. einem Polymerisationsschritt hergestellt werden. Das RAFT- Polymerisationsverfahren ermöglicht sowohl die Polymerisation hydrophiler Monomere wie N-Isopropylacrylamid (NIPAM) (M1) oder N-Acryloylpyrrolidin (NAP) (M2) für die A-Blöcke als auch der hydropoben Monomere Styrol (M3), 2-Fluorostyrol (M4), 3-Fluorostyrol (M5), 4- Fluorostyrol (M6) und 2,3,4,5,6- Pentafluorostyrol (M7) für die B-Blöcke. Die Eigenschaften der Blockcopolymere in verdünnten, konzentrierten und hochkonzentrierten wässrigen Lösungen wurden mittels DLS, Trübungsphotometrie, 1H- und 19F-NMR, Rheologie, CMC- sowie Schaumhöhen- und Oberflächenspannungsmessungen und Lichtmikroskopie untersucht. Weiterhin wurden ihre Eigenschaften als Emulgatoren und in Mikroemulsion untersucht. Das Micellbildungsverhalten der hydrophob endfunktionalisierten Polymere wurde mittels DLS Messungen in verdünnter organischer Lösung untersucht. Alle untersuchten BAB-Triblöcke bildeten Micellen und zeigten Oberflächenaktivität bei Raumtemperatur in verdünnter, wässriger Lösung. Weiterhin zeigen die wässrigen Lösungen der Polymere mäßige Schaumbildung. Mit verschiedenen Öltypen und Ölkonzentrationen wurden Emulsionen bzw. Mikroemulsionen gebildet. In Mikroemulsion wurde durch Zugabe von BAB-Triblockopolymeren kein Boosting-Effekt erzielt werden. Bei Untersuchung höherer Polymerkonzentrationen wurde die Bildung von Hydrogelen mittels rheologischer Messungen nachgewiesen. Verschiedene Substrate konnten benetzt werden. Die hydrophob endgecappten Polymere bilden in verdünnter organischer Lösung Micellen, die mittels DLS untersucht wurden, und zeigen somit Tensidverhalten in nichtwässriger Lösung. KW - Fluorierte Blockcopolymere KW - RAFT KW - Rheologie KW - Tenside KW - Gele KW - wässrige Systeme KW - thermisch schaltbare Polymere KW - fluorinated Blockcopolymers KW - RAFT-Polymerisation KW - rheology KW - surfactants KW - gels KW - aqueous systems KW - thermosensitive polymers Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-61782 ER - TY - THES A1 - Jeromenok, Jekaterina T1 - Polymers from the natural product betulin : a microstructural investigation T1 - Polymere aus dem Naturstoff Betulin und Untersuchungen ihrer Mikrostruktur N2 - Porous materials (e.g. zeolites, activated carbon, etc.) have found various applications in industry, such as the use as sorbents, catalyst supports and membranes for separation processes. Recently, much attention has been focused on synthesizing porous polymer materials. A vast amount of tailor-made polymeric systems with tunable properties has been investigated. Very often, however, the starting substances for these polymers are of petrochemical origin, and the processes are all in all not sustainable. Moreover, the new polymers have challenged existing characterizing methodologies. These have to be further developed to address the upcoming demands of the novel materials. Some standard techniques for the analysis of porous substances like nitrogen sorption at 77 K do not seem to be sufficient to answer all arising questions about the microstructure of such materials. In this thesis, microporous polymers from an abundant natural resource, betulin, will be presented. Betulin is a large-scale byproduct of the wood industry, and its content in birch bark can reach 30 wt.%. Based on its rigid structure, polymer networks with intrinsic microporosity could be synthesized and characterized. Apart from standard nitrogen and carbon dioxide sorption at 77 K and 273 K, respectively, gas sorption has been examined not only with various gases (hydrogen and argon) but also at various temperatures. Additional techniques such as X-ray scattering and xenon NMR have been utilized to enable insight into the microporous structure of the material. Starting from insoluble polymer networks with promising gas selectivities, soluble polyesters have been synthesized and processed to a cast film. Such materials are feasible for membrane applications in gas separation. Betulin as a starting compound for polyester synthesis has aided to prepare, and for the first time to thoroughly analyse a microporous polyester with respect to its pores and microstructure. It was established that nitrogen adsorption at 87 K can be a better method to solve the microstructure of the material. In addition to that, other betulin-based polymers such as polyurethanes and polyethylene glycol bioconjugates are presented. Altogether, it has been shown that as an abundant natural resource betulin is a suitable and cheap starting compound for some polymers with various potential applications. N2 - Das Bestreben, ölbasierte Produkte durch nachwachsende Rohstoffe zu ersetzen, hat dazu geführt, dass in immer größerer Zahl günstige, reichlich vorhandene Naturstoffe als Ausgangsstoffe für chemische Synthesen untersucht werden. In dieser Arbeit werden Polymere auf Basis von Betulin, einem aus Birkenrinde extrahierten Naturstoff, vorgestellt. Betulin ist zu 30 Gewichtsprozent in Birkenrinde enthalten. Da Betulin ein Nebenprodukt der Holzindustrie ist, ist es kostengünstig und sein Einsatz als Ausgangsstoff äußerst lukrativ. Die ersten Berichte über Betulin-basierte Polymere sind in den 1980er Jahren in Russland und Finnland erschienen, in den Ländern mit großen natürlichen Vorkommen an Birken. Betulin wurde in dieser Arbeit verwendet, um sogenannte mikroporöse Polymere herzustellen. Dies sind Stoffe mit Poren von molekularer Dimension. Mikroporöse Materialien sind wegen ihrer potentiellen Anwendung als Katalysatorträger und Gasseparationsmembranen hochinteressant. Die Klasse mikroporöser Polymere wurde durch die Synthese von unlöslichen Betulin-basierten Polyesternetzwerken erweitert. Außerdem gelang es, lösliche Polyester in Form dünner Filme herzustellen. Diese zeigten vielversprechende Ergebnisse in der Trennung von Stickstoff und Kohlendioxid und weisen somit Potential für die Nutzung als Membran auf. Dies könnte z. B. für Kohlendioxid-Reduzierung in Postcombustion-Verfahren interessant sein. Überdies wurde gezeigt, dass Stickstoffadsorption bei 77 K nicht ohne weiteres als Standardmethode für die Analyse von mikroporösen Materialien geeignet ist und dass die mikroporösen Materialien ferner durch Stickstoffadsorption bei 87 K und andere Gassorptionsmethoden bei verschiedenen Temperaturen zu charakterisieren sind. Diese Arbeit trägt zum besseren Verständnis mikroporöser Polymere bei. KW - Betulin KW - mikroporöse Polymere KW - Polyeste r KW - Gaspermeation KW - Naturstoff KW - Betulin KW - gas permeation KW - microporous polymers KW - polyesters KW - renewable resources Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-61380 ER - TY - THES A1 - Latnikova, Alexandra T1 - Polymeric capsules for self-healing anticorrosion coatings T1 - Polymerische Kapseln für selbstheilende Korrosionsschutzbeschichtungen N2 - The present work is devoted to establishing of a new generation of self-healing anti-corrosion coatings for protection of metals. The concept of self-healing anticorrosion coatings is based on the combination of the passive part, represented by the matrix of conventional coating, and the active part, represented by micron-sized capsules loaded with corrosion inhibitor. Polymers were chosen as the class of compounds most suitable for the capsule preparation. The morphology of capsules made of crosslinked polymers, however, was found to be dependent on the nature of the encapsulated liquid. Therefore, a systematic analysis of the morphology of capsules consisting of a crosslinked polymer and a solvent was performed. Three classes of polymers such as polyurethane, polyurea and polyamide were chosen. Capsules made of these polymers and eight solvents of different polarity were synthesized via interfacial polymerization. It was shown that the morphology of the resulting capsules is specific for every polymer-solvent pair. Formation of capsules with three general types of morphology, such as core-shell, compact and multicompartment, was demonstrated by means of Scanning Electron Microscopy. Compact morphology was assumed to be a result of the specific polymer-solvent interactions and be analogues to the process of swelling. In order to verify the hypothesis, pure polyurethane, polyurea and polyamide were synthesized; their swelling behavior in the solvents used as the encapsulated material was investigated. It was shown that the swelling behavior of the polymers in most cases correlates with the capsules morphology. Different morphologies (compact, core-shell and multicompartment) were therefore attributed to the specific polymer-solvent interactions and discussed in terms of “good” and “poor” solvent. Capsules with core-shell morphology are formed when the encapsulated liquid is a “poor” solvent for the chosen polymer while compact morphologies are formed when the solvent is “good”. Multicompartment morphology is explained by the formation of infinite networks or gelation of crosslinked polymers. If gelation occurs after the phase separation in the system is achieved, core-shell morphology is present. If gelation of the polymer occurs far before crosslinking is accomplished, further condensation of the polymer due to the crosslinking may lead to the formation of porous or multicompartment morphologies. It was concluded that in general, the morphology of capsules consisting of certain polymer-solvent pairs can be predicted on the basis of polymer-solvent behavior. In some cases, the swelling behavior and morphology may not match. The reasons for that are discussed in detail in the thesis. The discussed approach is only capable of predicting capsule morphology for certain polymer-solvent pairs. In practice, the design of the capsules assumes the trial of a great number of polymer-solvent combinations; more complex systems consisting of three, four or even more components are often used. Evaluation of the swelling behavior of each component pair of such systems becomes unreasonable. Therefore, exploitation of the solubility parameter approach was found to be more useful. The latter allows consideration of the properties of each single component instead of the pair of components. In such a manner, the Hansen Solubility Parameter (HSP) approach was used for further analysis. Solubility spheres were constructed for polyurethane, polyurea and polyamide. For this a three-dimensional graph is plotted with dispersion, polar and hydrogen bonding components of solubility parameter, obtained from literature, as the orthogonal axes. The HSP of the solvents are used as the coordinates for the points on the HSP graph. Then a sphere with a certain radius is located on a graph, and the “good” solvents would be located inside the sphere, while the “poor” ones are located outside. Both the location of the sphere center and the sphere radius should be fitted according to the information on polymer swelling behavior in a number of solvents. According to the existing correlation between the capsule morphology and swelling behavior of polymers, the solvents located inside the solubility sphere of a polymer give capsules with compact morphologies. The solvents located outside the solubility sphere of the solvent give either core-shell or multicompartment capsules in combination with the chosen polymer. Once the solubility sphere of a polymer is found, the solubility/swelling behavior is approximated to all possible substances. HSP theory allows therefore prediction of polymer solubility/swelling behavior and consequently the capsule morphology for any given substance with known HSP parameters on the basis of limited data. The latter makes the theory so attractive for application in chemistry and technology, since the choice of the system components is usually performed on the basis of a large number of different parameters that should mutually match. Even slight change of the technology sometimes leads to the necessity to find the analogue of this or that solvent in a sense of solvency but carrying different chemistry. Usage of the HSP approach in this case is indispensable. In the second part of the work examples of the HSP application for the fabrication of capsules with on-demand-morphology are presented. Capsules with compact or core-shell morphology containing corrosion inhibitors were synthesized. Thus, alkoxysilanes possessing long hydrophobic tail, combining passivating and water-repelling properties, were encapsulated in polyurethane shell. The mechanism of action of the active material required core-shell morphology of the capsules. The new hybrid corrosion inhibitor, cerium diethylhexyl phosphate, was encapsulated in polyamide shells in order to facilitate the dispersion of the substance and improve its adhesion to the coating matrix. The encapsulation of commercially available antifouling agents in polyurethane shells was carried out in order to control its release behavior and colloidal stability. Capsules with compact morphology made of polyurea containing the liquid corrosion inhibitor 2-methyl benzothiazole were synthesized in order to improve the colloidal stability of the substance. Capsules with compact morphology allow slower release of the liquid encapsulated material compared to the core-shell ones. If the “in-situ” encapsulation is not possible due to the reaction of the oil-soluble monomer with the encapsulated material, a solution was proposed: loading of the capsules should be performed after monomer deactivation due to the accomplishment of the polymerization reaction. Capsules of desired morphologies should be preformed followed by the loading step. In this way, compact polyurea capsules containing the highly effective but chemically active corrosion inhibitors 8-hydroxyquinoline and benzotriazole were fabricated. All the resulting capsules were successfully introduced into model coatings. The efficiency of the resulting “smart” self-healing anticorrosion coatings on steel and aluminium alloy of the AA-2024 series was evaluated using characterization techniques such as Scanning Vibrating Electron Spectroscopy, Electrochemical Impedance Spectroscopy and salt-spray chamber tests. N2 - In Anlehnung an den Selbstheilungsmechanismus der menschlichen Haut entwickeln wir ein innovatives Verfahren zur Funktionalisierung von Korrosionsschutzbeschichtungen, um auch diese in die Lage zu versetzen Beschädigungen selbstständig „auszuheilen“. Dazu werden winzige Mikro- und Nanobehälter mit aktiven Substanzen (z. B. Korrosionshemmstoffen, Versiegelungsmitteln, Bioziden etc.) befüllt und anschließend in eine Korrosionsschutzbeschichtung eingebettet. Kommt es nun im Zeitablauf zu korrosionsauslösenden Beschädigungen der Schutzbeschichtung (z. B. durch Kratzer oder Risse) werden an der Defektstelle die eingebetteten Behälter zerstört und aktiv wirkende Gegensubstanzen freigesetzt. Dadurch wird die verletzte Stelle sofort wieder verschlossen und die Korrosionsgefahr eliminiert. Der entscheidende Vorteil derart funktionalisierter Schutzbeschichtungen ist ihre aktive Rückkopplung mit dem Korrosionsauslöser: Die aktive Schutzsubstanz wird nur an der Defektstelle und nur in der zur Korrosionsvermeidung erforderlichen Menge freigegeben. Somit werden eine länger anhaltende Wirkdauer sowie eine deutlich höhere Nachhaltigkeit der Beschichtungen ermöglicht. Dieses „intelligente Verhalten“ der neuen aktiven Korrosionsschutzbeschichtungen ist nur dank ihrer innovativen Mikrostruktur möglich. Die winzigen Mikro- und Nanobehälter beinhalten nicht nur aktive Substanzen in ihrem Inneren sondern besitzen auch eine intelligent konstruierte Hüllenstruktur, deren Durchlässigkeit sich je nach Art des Korrosionsauslösers ändert. Wird die eingekapselte aktive Substanz freigesetzt, fängt diese sofort an gegen die korrosionsverursachenden Einflüsse zu wirken. Ist die Gefahr beseitigt verringert sich die Durchlässigkeit der Behälterhülle wieder. Diese bedingte Reversibilität zwischen geschlossenem und geöffnetem Zustand des Behälters sorgt für einen sehr sparsamen Verbrauch der aktiven Substanz und für die stark verbesserte Schutzwirkung darauf basierender Antikorrosionsbeschichtungen. Diese Arbeit befasst sich mit dem Aufbau polymerer Kern-Schale-Mikrokapseln, die entsprechende Korrosionsinhibitoren und Biocide enthalten. Der Morphologie wird für zahlreiche Lösungsmittel und Polymere mit Hilfe der Hansen-Löslichkeitsparameter in guter Übereinstimmung mit elektronenmikroskopischen Experimenten beschrieben. Die Wirkungsweise in technischen Beschichtungen wird quantifiziert anhand von elektrochemischer Impedanzspektroskopie, Rastervibrationssondenmessungen und industrienahen Testverfahren. KW - Korrosion KW - Selbstheilende Beschichtungen KW - Einkapselung KW - Morphologie von Kapseln KW - corrosion KW - self-healing coatings KW - encapsulation KW - capsule morphology Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-60432 ER - TY - THES A1 - Zarafshani, Zoya T1 - Chain-end functionalization and modification of polymers using modular chemical reactions T1 - Ketten-Ende Funktionalisierung und Modifikation von Polymeren mittels modulare chemischen Reaktionen N2 - Taking advantage of ATRP and using functionalized initiators, different functionalities were introduced in both α and ω chain-ends of synthetic polymers. These functionalized polymers could then go through modular synthetic pathways such as click cycloaddition (copper-catalyzed or copper-free) or amidation to couple synthetic polymers to other synthetic polymers, biomolecules or silica monoliths. Using this general strategy and designing these co/polymers so that they are thermoresponsive, yet bioinert and biocompatible with adjustable cloud point values (as it is the case in the present thesis), the whole generated system becomes "smart" and potentially applicable in different branches. The applications which were considered in the present thesis were in polymer post-functionalization (in situ functionalization of micellar aggregates with low and high molecular weight molecules), hydrophilic/hydrophobic tuning, chromatography and bioconjugation (enzyme thermoprecipitation and recovery, improvement of enzyme activity). Different α-functionalized co/polymers containing cholesterol moiety, aldehyde, t-Boc protected amine, TMS-protected alkyne and NHS-activated ester were designed and synthesized in this work. N2 - In dieser Arbeit wurden mittels der ATRP Methode sowie durch Benutzung funktioneller Initiatoren verschiedene Funktionalitäten an der α- und ω-Position der synthetischen Polymere (Kettenenden) eingeführt. Diese funktionalisierten Polymere können durch modulare synthetische Methoden wie z.B. die “Klick-Zykloaddition” (kupferkatalysiert oder auch kupferfreie Methoden möglich), Amidierung mit anderen synthetischen Polymeren oder Biomolekülen, oder auch mit Silikatmonolithen gekuppelt werden. Den beschriebenen Strategien folgend und unter Benutzung von thermoresponsiven, bioinerten und biokompartiblen (Co-) Polymeren mit einstellbaren Trübungspunkten können mittels Temperaturänderungen leicht steuerbare, „smarte“ Polymersysteme für verschiedene Anwendungen hergestellt werden. Im Rahmen dieser Arbeit wurden speziell Anwendungen wie die Postfunktionalisierung (in situ Funktionalisierung mizellarer Aggregate mit Molekülen, die sowohl niedrige als auch höhere Molekulargewichte aufweisen), hydrophiles/hydrophobes Tuning von Polymeren, Chromatographie an Polymeren sowie Biokonjugation von Polymeren (Enzymthermoprezipitation und -Gewinnung, Enzymaktivitätsmodifizierung) genauer untersucht. Es wurden verschiedene α-funktionalisierte (Co-)Polymere, die Cholesterol, Aldehyde, t-Boc geschützte Amine, TMS-geschützte Alkine und NHS-aktivierte Ester entwickelt und hergestellt und mittels passender ATRP Initiatoren eingeführt. KW - Atom Transfer Radical Polymerization KW - Klick-Chemie KW - Biokonjugation KW - Funktionalisierung KW - Modifizierung von Polymeren KW - ATRP KW - Click chemistry KW - Bioconjugation KW - Functionalization KW - Polymer Modification Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-59723 ER - TY - THES A1 - Wohlgemuth, Stephanie-Angelika T1 - Functional nanostructured hydrothermal carbons for sustainable technologies : heteroatom doping and superheated vapor T1 - Funktionelle, Nanostrukturierte Hydrothermal-Kohlenstoffe für Nachhaltige Technnologien: Heteroatom-Dotierung und Überkritischer Dampf N2 - The underlying motivation for the work carried out for this thesis was the growing need for more sustainable technologies. The aim was to synthesize a “palette” of functional nanomaterials using the established technique of hydrothermal carbonization (HTC). The incredible diversity of HTC was demonstrated together with small but steady advances in how HTC can be manipulated to tailor material properties for specific applications. Two main strategies were used to modify the materials obtained by HTC of glucose, a model precursor representing biomass. The first approach was the introduction of heteroatoms, or “doping” of the carbon framework. Sulfur was for the first time introduced as a dopant in hydrothermal carbon. The synthesis of sulfur and sulfur/nitrogen doped microspheres was presented whereby it was shown that the binding state of sulfur could be influenced by varying the type of sulfur source. Pyrolysis may additionally be used to tune the heteroatom binding states which move to more stable motifs with increasing pyrolysis temperature. Importantly, the presence of aromatic binding states in the as synthesized hydrothermal carbon allows for higher heteroatom retention levels after pyrolysis and hence more efficient use of dopant sources. In this regard, HTC may be considered as an “intermediate” step in the formation of conductive heteroatom doped carbon. To assess the novel hydrothermal carbons in terms of their potential for electrochemical applications, materials with defined nano-architectures and high surface areas were synthesized via templated, as well as template-free routes. Sulfur and/or nitrogen doped carbon hollow spheres (CHS) were synthesized using a polystyrene hard templating approach and doped carbon aerogels (CA) were synthesized using either the albumin directed or borax-mediated hydrothermal carbonization of glucose. Electrochemical testing showed that S/N dual doped CHS and aerogels derived via the albumin approach exhibited superior catalytic performance compared to solely nitrogen or sulfur doped counterparts in the oxygen reduction reaction (ORR) relevant to fuel cells. Using the borax mediated aerogel formation, nitrogen content and surface area could be tuned and a carbon aerogel was engineered to maximize electrochemical performance. The obtained sample exhibited drastically improved current densities compared to a platinum catalyst (but lower onset potential), as well as excellent long term stability. In the second approach HTC was carried out at elevated temperatures (550 °C) and pressure (50 bar), corresponding to the superheated vapor regime (htHTC). It was demonstrated that the carbon materials obtained via htHTC are distinct from those obtained via ltHTC and subsequent pyrolysis at 550 °C. No difference in htHTC-derived material properties could be observed between pentoses and hexoses. The material obtained from a polysaccharide exhibited a slightly lower degree of carbonization but was otherwise similar to the monosaccharide derived samples. It was shown that in addition to thermally induced carbonization at 550 °C, the SHV environment exhibits a catalytic effect on the carbonization process. The resulting materials are chemically inert (i.e. they contain a negligible amount of reactive functional groups) and possess low surface area and electronic conductivity which distinguishes them from carbon obtained from pyrolysis. Compared to the materials presented in the previous chapters on chemical modifications of hydrothermal carbon, this makes them ill-suited candidates for electronic applications like lithium ion batteries or electrocatalysts. However, htHTC derived materials could be interesting for applications that require chemical inertness but do not require specific electronic properties. The final section of this thesis therefore revisited the latex hard templating approach to synthesize carbon hollow spheres using htHTC. However, by using htHTC it was possible to carry out template removal in situ because the second heating step at 550 °C was above the polystyrene latex decomposition temperature. Preliminary tests showed that the CHS could be dispersed in an aqueous polystyrene latex without monomer penetrating into the hollow sphere voids. This leaves the stagnant air inside the CHS intact which in turn is promising for their application in heat and sound insulating coatings. Overall the work carried out in this thesis represents a noteworthy development in demonstrating the great potential of sustainable carbon materials. N2 - Das Ziel der vorgelegten Arbeit war es, mit Hilfe der Hydrothermalen Carbonisierung (HTC) eine Palette an verschiedenen Materialien herzustellen, deren physikalische und chemische Eigenschaften auf spezifische Anwendungen zugeschnitten werden können. Die Motivation hierfür stellt die Notwendigkeit, Alternativen zu Materialien zu finden, die auf fossilen Brennstoffen basieren. Dabei stellen vor allem nachhaltige Energien eine der größten Herausforderungen der Zukunft dar. HTC ist ein mildes, nachhaltiges Syntheseverfahren welches prinzipiell die Nutzung von biologischen Rohstoffen (z. B. landwirtschaftlichen Abfallprodukten) für die Herstellung von wertvollen, Kohlenstoff-basierten Materialien erlaubt. Es wurden zwei verschiedene Ansätze verwendet, um hydrothermalen Kohlenstoff zu modifizieren. Zum einen wurde HTC unter „normalen“ Bedingungen ausgeführt, d. h. bei 180 °C und einem Druck von etwa 10 bar. Der Zucker Glukose diente in allen Fällen als Kohlenstoff Vorläufer. Durch Zugabe von stickstoff und /oder schwefelhaltigen Additiven konnte dotierte Hydrothermalkohle hergestellt werden. Dotierte Kohlenstoffe sind bereits für ihre positiven Eigenschaften, wie verbesserte Leitfähigkeit oder erhöhte Stabilität, bekannt. Zusätzlich zu Stickstoff dotierter Hydrothermalkohle, die bereits von anderen Gruppen hergestellt werden konnte, wurde in dieser Arbeit zum ersten Mal Schwefel in Hydrothermalkohle eingebaut. Außerdem wurden verschiedene Ansätze verwendet, um Oberfläche und definierte Morphologie der dotierten Materialien zu erzeugen, welche wichtig für elektrochemische Anwendungen sind. Schwefel- und/oder stickstoffdotierte Kohlenstoff Nanohohlkugeln sowie Kohlenstoff Aerogele konnten hergestellt werden. Mit Hilfe von einem zusätzlichen Pyrolyseschritt (d. h. Erhitzen unter Schutzgas) konnte die Leitfähigkeit der Materialien hergestellt werden, die daraufhin als Nichtmetall-Katalysatoren für Wasserstoff-Brennstoffzellen getestet wurden. Im zweiten Ansatz wurde HTC unter extremen Bedingungen ausgeführt, d. h. bei 550 °C und einem Druck von ca. 50 bar, welches im Wasser Phasendiagram dem Bereich des Heißdampfes entspricht. Es konnte gezeigt werden, dass die so erhaltene Hydrothermalkohle ungewöhnliche Eigenschaften besitzt. So hat die Hochtemperatur-Hydrothermalkohle zwar einen hohen Kohlenstoffgehalt (mehr als 90 Massenprozent), enthält aber auch viele Wasserstoffatome und ist dadurch schlecht leitfähig. Da damit elektrochemische Anwendungen so gut wie ausgeschlossen sind, wurde die Hochtemperatur-Hydrothermalkohle für Anwendungen vorgesehen, welche chemische Stabilität aber keine Leitfähigkeit voraussetzen. So wurden beispielsweise Hochtemperatur-Kohlenstoff-Nanohohlkugeln synthetisiert, die großes Potential als schall- und wärmeisolierende Additive für Beschichtungen darstellen. Insgesamt konnten erfolgreich verschiedenste Materialien mit Hilfe von HTC hergestellt werden. Es ist zu erwarten, dass sie in Zukunft zu nachhaltigen Technologien und damit zu einem weiteren Schritt weg von fossilen Brennstoffen beitragen werden. KW - Hydrothermale Karbonisierung KW - Heteroatom-Dotierung KW - Aerogele KW - Hohlkugeln KW - Elektrokatalyse KW - Hydrothermal Carbonization KW - Heteroatom Doping KW - Aerogels KW - Hollow Spheres KW - Electrocatalysis Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-60120 ER - TY - THES A1 - Piluso, Susanna T1 - Design of biopolymer-based networks with defined molecular architecture T1 - Design biopolymer-basierter Netzwerke mit definierter molekularer Architektur N2 - In this work, the synthesis of biopolymer-based hydrogel networks with defined architecture is presented. In order to obtain materials with defined properties, the chemoselective copper-catalyzed azide-alkyne cycloaddition (or Click Chemistry) was used for the synthesis of gelatin-based hydrogels. Alkyne-functionalized gelatin was reacted with four different diazide crosslinkers above its sol-gel transition to suppress the formation of triple helices. By variation of the crosslinking density and the crosslinker flexibility, the swelling (Q: 150-470 vol.-%;) and the Young’s and shear moduli (E: 50 kPa - 635 kPa, G’: 0.1 kPa - 16 kPa) could be tuned in the kPa range. In order to understand the network structure, a method based on the labelling of free functional groups within the hydrogel was developed. Gelatin-based hydrogels were incubated with alkyne-functionalized fluorescein to detect the free azide groups, resulting from the formation of dangling chains. Gelatin hydrogels were also incubated with azido-functionalized fluorescein to check the presence of alkyne groups available for the attachment of bioactive molecules. By using confocal laser scanning microscopy and fluorescence spectroscopy, the amount of crosslinking, grafting and free alkyne groups could be determined. Dangling chains were observed in samples prepared by using an excess of crosslinker and also when using equimolar amounts of alkyne:azide. In the latter case the amount of dangling chains was affected by the crosslinker structure. Specifically, 0.1% of dangling chains were found using 4,4’-diazido-2,2’-stilbene-disulfonic acid as cosslinker, 0.06% with 1,8-diazidooctane, 0.05% with 1,12-diazidododecane and 0.022 % with PEG-diazide. This observation could be explained considering the structure of the crosslinkers. During network formation, the movements of the gelatin chains are restricted due to the formation of covalent netpoints. A further crosslinking will be possible only in the case of crosslinker that are flexible and long enough to reach another chain. The method used to obtain defined gelatin-based hydrogels enabled also the synthesis of hyaluronic acid-based hydrogels with tailorable properties. Alkyne-functionalized hyaluronic acid was crosslinked with three different linkers having two terminal azide functionalities. By variation of the crosslinking density and crosslinker type, hydrogels with elastic moduli in the range of 0.5-3 kPa have been prepared. The variation of the crosslinking density and crosslinker type had furthermore an influence also on the hydrolytic and enzymatic degradation of gelatin-based hydrogels. Hydrogels with a low crosslinker amount experienced a faster decrease in mass loss and elastic modulus compared to hydrogels with higher crosslinker content. Moreover, the structure of the crosslinker had a strong influence on the enzymatic degradation. Hydrogels containing a crosslinker with a rigid structure were much more resistant to enzymatic degradation than hydrogels containing a flexible crosslinker. During hydrolytic degradation, the hydrogel became softer while maintaining the same outer dimensions. These observations are in agreement with a bulk degradation mechanism, while the decrease in size of the hydrogels during enzymatic degradation suggested a surface erosion mechanism. Because of the use of small amount of crosslinker (0.002 mol.% 0.02 mol.%) the networks synthesized can still be defined as biopolymer-based hydrogels. However, they contain a small percentage of synthetic residues. Alternatively, a possible method to obtain biopolymer-based telechelics, which could be used as crosslinkers, was investigated. Gelatin-based fragments with defined molecular weight were obtained by controlled degradation of gelatin with hydroxylamine, due to its specific action on asparaginyl-glycine bonds. The reaction of gelatin with hydroxylamine resulted in fragments with molecular weights of 15, 25, 37, and 50 kDa (determined by SDS-PAGE) independently of the reaction time and conditions. Each of these fragments could be potentially used for the synthesis of hydrogels in which all components are biopolymer-based materials. N2 - In dieser Arbeit wird die Synthese Biopolymer-basierter Hydrogelnetzwerke mit definierter Architektur beschrieben. Um Materialien mit definierten und einstellbaren Eigenschaften zu erhalten, wurde die chemoselektive Kupferkatalysierte Azid-Alkin-Cycloadditionsreaktion (auch als Click-Chemie bezeichnet) für die Synthese Gelatine-basierter Netzwerke eingesetzt. Alkin-funktionalisierte Gelatine wurde mit vier verschiedenen Diazid-Quervernetzern oberhalb der Gel-Sol-Übergangstemperatur umgesetzt, um die Formierung tripelhelikaler Bereiche durch Gelatineketten zu unterdrücken. Durch Variation der Menge an Quervernetzer (und damit der Netzdichte) sowie der Länge und Flexibilität der Quervernetzer konnten u.a. die Quellung (Q: 150-470 vol.-%) sowie der Young’s - und Schermodul im kPa Bereich eingestellt werden (E: 50 kPa - 635 kPa, G’: 0.1 kPa - 16 kPa). Um die Netzwerkarchitektur zu verstehen, wurde eine Methode basierend auf dem Labeln unreagierter Azid- und Alkingruppen im Hydrogel entwickelt. Die Gelatine-basierten Hydrogele wurden mit Alkin-funktionalisiertem Fluorescein umgesetzt, um freie Azidgruppen zu detektieren, die bei einem Grafting entstehen. Darüber hinaus wurden die Hydrogele mit Azid-funktionalisiertem Fluorescein reagiert, um die Menge an freien Alkingruppen zu bestimmen, die zudem potentiell für die Anbindung bioaktiver Moleküle geeignet sind. Quervernetzung, Grafting, und die Anzahl freier Alkingruppen konnten dann mit Hilfe der konfokalen Laser Scanning Mikroskopie und der Fluoreszenzmikroskopie qualitativ und quantitativ nachgewiesen werden. Gegraftete Ketten wurden in Systemen nachgewiesen, die mit einem Überschuss an Quervernetzer hergestellt wurden, entstanden aber auch beim Einsatz äquimolarer Mengen Alkin- und Azidgruppen. Im letzteren Fall wurde in Abhängigkeit von der Struktur des Diazids unterschiedliche Anteile gegrafteter Ketten festgestellt. 0.1 mol-% von gegrafteten Ketten wurden für 4,4’-Diazido-2,2’-stilbendisulfonsäure gefunden, 0.06 mol-% für 1,8-Diazidooktan, 0.05 mol% für 1,12-diazidododecan und 0.022 mol-% für PEG-Diazid. Diese Beobachtung kann durch die unterschiedliche Flexibilität der Vernetzer erklärt werden. Während der Netzwerkbildung werden die Bewegungen der Gelatineketten eingeschränkt, so dass kovalente Netzpunkte nur erhalten werden können, wenn der Vernetzer lang und flexibel genug ist, um eine andere Alkingruppe zu erreichen. Die Strategie zur Synthese von Biopolymer-basierten Hydrogelen mit einstellbaren Eigenschaften wurde von Gelatine- auf Hyaluronsäure-basierte Gele übertragen. Alkin-funktionalisierte Hyaluronäure wurde mit drei verschiedenen Diaziden quervernetzt, wobei Menge, Länge, und Flexibilität des Quervernetzers variiert wurden. In dieser Weise wurden sehr weiche Hydrogele mit E-Moduli im Bereich von 0.5-3 kPa hergestellt. Die Variation der Vernetzungsdichte und des Vernetzertyps beeinflusste weiterhin den hydrolytischen und enzymatischen Abbau der Hydrogele. Hydrogele mit einem geringerem Anteil an Quervernetzer wurden schneller abgebaut als solche mit einem höheren Quervernetzeranteil. Darüber hinaus konnte gezeigt werden, dass Hydrogele mit Quervernetzern mit einer rigiden Struktur deutlich langsamer degradierten als Hydrogele mit flexibleren Quervernetzern. Während des hydrolytischen Abbau wurden die Materialien weicher, behielten aber ihre Form bei, was mit einem Bulk-Abbau-Modell übereinstimmt. Während des enzymatischen Abbaus hingegen änderten sich die Materialeigenschaften kaum, jedoch wurden die Proben kleiner. Diese Beobachtung stimmt mit einem Oberflächenabbaumechanismus überein. Da in allen vorgestellten Systemen nur eine kleine Menge synthetischer Vernetzer eingesetzt wurde (0.002 – 0.02 mol%), können die Materialien noch als Biopolymer-basierte Materialien klassifiziert werden. Jedoch enthalten die Materialien synthetische Abschnitte. In Zukunft könnte es interessant sein, einen Zugang zu Materialien zu haben, die ausschließlich aus Biopolymeren aufgebaut sind. Daher wurde der Zugang zu Biopolymer basierten Telechelen untersucht, die potentiell als Vernetzer dienen können. Dazu wurden durch die kontrollierte Spaltung von Gelatine mit Hydroxylamin Gelatinefragmente mit definiertem Molekulargewicht hergestellt. Hydroxalamin reagiert unter Spaltung mit der Amidbindung zwischen Asparagin und Glycin, wobei Aspartylhydroxamate und Aminoendgruppen entstehen. Die Reaktion von Gelatine mit Hydroxylamin ergab Fragmente mit Molekulargewichten von 15, 25, 37, und 50 kDa (bestimmt mit SDS-PAGE), und die Formierung dieser Fragmente war unabhängig von den weiteren Reaktionsbedingungen und der Reaktionszeit. Jedes dieser Fragmente kann potentiell für die Synthese von Hydrogelen eingesetzt werden, die ausschließlich aus Biopolymeren bestehen. KW - Klickchemie KW - Gelatine KW - Hyaluronsäure KW - Abbau KW - Kollagenase KW - Click Chemistry KW - Gelatin KW - Hyaluronic acid KW - Degradation KW - Collagenase Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-59865 ER - TY - THES A1 - Miasnikova, Anna T1 - New hydrogel forming thermo-responsive block copolymers of increasing structural complexity T1 - Neue Hydrogel-bildende thermisch schaltbare Blockcopolymere von zunehmender struktureller Komplexität N2 - This work describes the synthesis and characterization of stimuli-responsive polymers made by reversible addition-fragmentation chain transfer (RAFT) polymerization and the investigation of their self-assembly into “smart” hydrogels. In particular the hydrogels were designed to swell at low temperature and could be reversibly switched to a collapsed hydrophobic state by rising the temperature. Starting from two constituents, a short permanently hydrophobic polystyrene (PS) block and a thermo-responsive poly(methoxy diethylene glycol acrylate) (PMDEGA) block, various gelation behaviors and switching temperatures were achieved. New RAFT agents bearing tert-butyl benzoate or benzoic acid groups, were developed for the synthesis of diblock, symmetrical triblock and 3-arm star block copolymers. Thus, specific end groups were attached to the polymers that facilitate efficient macromolecular characterization, e.g by routine 1H-NMR spectroscopy. Further, the carboxyl end-groups allowed functionalizing the various polymers by a fluorophore. Because reports on PMDEGA have been extremely rare, at first, the thermo-responsive behavior of the polymer was investigated and the influence of factors such as molar mass, nature of the end-groups, and architecture, was studied. The use of special RAFT agents enabled the design of polymer with specific hydrophobic and hydrophilic end-groups. Cloud points (CP) of the polymers proved to be sensitive to all molecular variables studied, namely molar mass, nature and number of the end-groups, up to relatively high molar masses. Thus, by changing molecular parameters, CPs of the PMDEGA could be easily adjusted within the physiological interesting range of 20 to 40°C. A second responsivity, namely to light, was added to the PMDEGA system via random copolymerization of MDEGA with a specifically designed photo-switchable azobenzene acrylate. The composition of the copolymers was varied in order to determine the optimal conditions for an isothermal cloud point variation triggered by light. Though reversible light-induced solubility changes were achieved, the differences between the cloud points before and after the irradiation were small. Remarkably, the response to light differed from common observations for azobenzene-based systems, as CPs decreased after UV-irradiation, i.e with increasing content of cis-azobenzene units. The viscosifying and gelling abilities of the various block copolymers made from PS and PMDEGA blocks were studied by rheology. Important differences were observed between diblock copolymers, containing one hydrophobic PS block only, the telechelic symmetrical triblock copolymers made of two associating PS termini, and the star block copolymers having three associating end blocks. Regardless of their hydrophilic block length, diblock copolymers PS11 PMDEGAn were freely flowing even at concentrations as high as 40 wt. %. In contrast, all studied symmetrical triblock copolymers PS8-PMDEGAn-PS8 formed gels at low temperatures and at concentrations as low as 3.5 wt. % at best. When heated, these gels underwent a gel-sol transition at intermediate temperatures, well below the cloud point where phase separation occurs. The gel-sol transition shifted to markedly higher transition temperatures with increasing length of the hydrophilic inner block. This effect increased also with the number of arms, and with the length of the hydrophobic end blocks. The mechanical properties of the gels were significantly altered at the cloud point and liquid-like dispersions were formed. These could be reversibly transformed into hydrogels by cooling. This thesis demonstrates that high molar mass PMDEGA is an easily accessible, presumably also biocompatible and at ambient temperature well water-soluble, non-ionic thermo-responsive polymer. PMDEGA can be easily molecularly engineered via the RAFT method, implementing defined end-groups, and producing different, also complex, architectures, such as amphiphilic triblock and star block copolymers, having an analogous structure to associative telechelics. With appropriate design, such amphiphilic copolymers give way to efficient, “smart” viscosifiers and gelators displaying tunable gelling and mechanical properties. N2 - Diese Arbeit befasst sich mit der RAFT-vermittelten Synthese und Charakterisierung von stimuli-empfindlichen Polymeren und ihrer Selbstorganisation zu „intelligenten” Hydrogelen. Die Hydrogele wurden so entwickelt, dass sie bei niedrigen Temperaturen stark quellen, bei Temperaturerhöhung jedoch reversibel in einem hydrophoben, kollabierten Zustand umgewandelt werden. Mit dem permanent hydrophoben Polystyrol (PS) und dem hydrophilen, thermisch schaltbaren Poly(methoxy-diethylen¬glycol-acrylat) (PMDEGA) als Bausteine, wurden unterschiedliche Gelierungsverhalten und thermische Übergangstemperaturen erreicht. Zur Synthese von Diblock-, symmetrischen Triblock- und dreiarmigen Sternblock-Copolymeren wurden neue funktionelle Kettenüberträger entwickelt. Diese gestatteten es, tert-butyl Benzoeester und Benzoesäure Endgruppen in die Polymere einzubauen, die einerseits eine effiziente Analyse mittels Routine 1H-NMR und darüber hinaus eine spätere Funktionalisierung der Endgruppen mit einer Fluoreszenzsonde ermöglichten. Da über PMDEGA kaum Daten vorlagen, wurde der Einfluss von Molekulargewicht, Endgruppen und Architektur auf das thermo-responsive Verhalten untersucht. Die speziellen Kettenüberträger ermöglichten es, gezielt hydrophobe wie hydrophile Endgruppen in die Polymere einzuführen. Die Trübungspunkte der wässerigen Lösungen von PMDEGA zeigten sich bis zu relativ hohen molaren Massen abhängig gegenüber allen untersuchten Variablen, nämlich dem Molekulargewicht, der Art und Zahl von Endgruppen. Durch Variation der diversen Parameter ließ sich die Schalttemperatur von PMDEGA in physiologisch relevanten Temperaturbereich von 20 bis 40 °C einstellen. Um die Polymere für einen zweiten Stimulus, nämlich Licht, empfindlich zu machen, wurden Azobenzol-funktionalisierte Acrylate synthetisiert und statistisch mit MDEGA copolymerisiert. Die Zusammensetzung der Polymeren wurde variiert und das isotherme Schalten der Löslichkeit durch Licht untersucht. Obwohl ein reversibles Schalten erreicht wurde, waren die Unterschiede zwischen den Trübungstemperaturen von UV-Licht bestrahlten und unbestrahlten Proben nur gering. Interessanterweise senkte die UV-Bestrahlung, d.h. ein erhöhter Gehalt von cis-Azobenzol-Gruppen, die Trübungstemperaturen herab. Dies ist genau umgekehrt als für azobenzolbasierten Systeme klassisch beschrieben. Die Gelbildung der verschiedenen Blockcopolymere von PS und PMDEGA wurde mittels Rheologie untersucht. Dabei traten deutliche Unterschiede auf, zwischen dem Gelierungsverhalten der Diblockcopolymere, die nur einen PS Block enthalten, dem der symmetrischen Triblockcopolymere, die zwei assoziative PS Endblöcken besitzen, und dem der Sternpolymere, die drei assoziative PS Blöcke aufweisen. Unabhängig von der Länge des hydrophilen Blockes, bilden Diblockcopolymere des Typs PS11-PMDEGAn keine Gele, sondern selbst bei hohen Konzentrationen von 40 Gew. % Lösungen. Im Gegensatz dazu bildeten die Triblockcopolymere des Typs PS8-PMDEGAn-PS8 Gele bei niedrigen Temperaturen, vereinzelt schon ab 3.5 wt. %. Mit steigender Temperatur, tritt bereits unterhalb des Trübungspunktes für diese Systeme ein Gel-Sol Übergang auf. Der Gel-Sol Übergang bewegt sich zu höheren Temperaturen mit steigende Länge des hydrophilen inneren Blocks. Dieser Trend verstärkt sich mit zunehmender Anzahl von Endblöcken und deren Länge. An der Trübungstemperatur veränderten sich die mechanischen Eigenschaften aller Gele signifikant und die gebildeten flüssigen Dispersionen ließen sich reversibel beim Abkühlen wieder zu Gel schalten. Diese Arbeit, zeigt dass PMDEGA ein bei niedrigen Temperaturen gut wasserlösliches, nicht-ionisches, thermisch-schaltbares und wahrscheinlich biokompatibles Polymer ist. PMDEGA liest sich einfach mittels den RAFT-Verfahren molekular maßschneiden, mit spezifischen Endgruppen und komplexen Polymerarchitekturen. Solche amphiphilen Triblock- und Sternblock-Copolymeren hoher Molmasse, wirken als assoziative Telechele. Daher eigenen sich bei entsprechendem Design diese amphiphilen Blockcopolymere als effiziente Verdicker und Gelbildner mit einstellbaren mechanischen und thermischen Eigenschaften. KW - Blockcopolymere KW - Selbstorganisation KW - thermisch schaltbar KW - LCST KW - RAFT KW - block copolymers KW - self-assembly KW - thermoresponsive KW - LCST KW - RAFT Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-59953 ER - TY - THES A1 - Falco, Camillo T1 - Sustainable biomass-derived hydrothermal carbons for energy applications T1 - Nachhaltiger, Biomasse-basierter Hydrothermalkohlenstoff für Energieanwendungen N2 - The need to reduce humankind reliance on fossil fuels by exploiting sustainably the planet renewable resources is a major driving force determining the focus of modern material research. For this reason great interest is nowadays focused on finding alternatives to fossil fuels derived products/materials. For the short term the most promising substitute is undoubtedly biomass, since it is the only renewable and sustainable alternative to fossil fuels as carbon source. As a consequence efforts, aimed at finding new synthetic approaches to convert biomass and its derivatives into carbon-based materials, are constantly increasing. In this regard, hydrothermal carbonisation (HTC) has shown to be an effective means of conversion of biomass-derived precursors into functional carbon materials. However the attempts to convert raw biomass, in particular lignocellulosic one, directly into such products have certainly been rarer. Unlocking the direct use of these raw materials as carbon precursors would definitely be beneficial in terms of HTC sustainability. For this reason, in this thesis the HTC of carbohydrate and protein-rich biomass was systematically investigated, in order to obtain more insights on the potentials of this thermochemical processing technique in relation to the production of functional carbon materials from crude biomass. First a detailed investigation on the HTC conversion mechanism of lignocellulosic biomass and its single components (i.e. cellulose, lignin) was developed based on a comparison with glucose HTC, which was adopted as a reference model. In the glucose case it was demonstrated that varying the HTC temperature allowed tuning the chemical structure of the synthesised carbon materials from a highly cross-linked furan-based structure (T = 180oC) to a carbon framework composed of polyaromatic arene-like domains. When cellulose or lignocellulosic biomass was used as carbon precursor, the furan rich structure could not be isolated at any of the investigated processing conditions. These evidences were indicative of a different HTC conversion mechanism for cellulose, involving reactions that are commonly observed during pyrolytic processes. The evolution of glucose-derived HTC carbon chemical structure upon pyrolysis was also investigated. These studies revealed that upon heat treatment (Investigated temperatures 350 – 900 oC) the furan-based structure was progressively converted into highly curved aromatic pre-graphenic domains. This thermal degradation process was observed to produce an increasingly more hydrophobic surface and considerable microporosity within the HTC carbon structure. In order to introduce porosity in the HTC carbons derived from lignocellulosic biomass, KOH chemical activation was investigated as an HTC post-synthesis functionalisation step. These studies demonstrated that HTC carbons are excellent precursors for the production of highly microporous activated carbons (ACs) and that the porosity development upon KOH chemical activation is dependent on the chemical structure of the HTC carbon, tuned by employing different HTC temperatures. Preliminary testing of the ACs for CO2 capture or high pressure CH4 storage yielded very promising results, since the measured uptakes of both adsorbates (i.e. CO2 and CH4) were comparable to top-performing and commercially available adsorbents, usually employed for these end-applications. The combined use of HTC and KOH chemical activation was also employed to produce highly microporous N-doped ACs from microalgae. The hydrothermal treatment of the microalgae substrate was observed to cause the depletion of the protein and carbohydrate fractions and the near complete loss (i.e. 90%) of the microalgae N-content, as liquid hydrolysis/degradation products. The obtained carbonaceous product showed a predominantly aliphatic character indicating the presence of alkyl chains presumably derived from the lipid fractions. Addition of glucose to the initial reaction mixture was found out to be extremely beneficial, because it allowed the fixation of a higher N amount, in the algae derived HTC carbons (i.e.  60%), and the attainment of higher product yields (50%). Both positive effects were attributed to Maillard type cascade reactions taking place between the monosaccharides and the microalgae derived liquid hydrolysis/degradation products, which were in this way recovered from the liquid phase. KOH chemical activation of the microalgae/glucose mixture derived HTC carbons produced highly microporous N-doped carbons. Although the activation process led to a major reduction of the N-content, the retained N-amount in the ACs was still considerable. These features render these materials ideal candidates for supercapacitors electrodes, since they provide extremely high surface areas, for the formation of electric double-layer, coupled to abundant heteroatom doping (i.e. N and O) necessary to obtain a pseudocapacitance contribution. N2 - Die Notwendigkeit, die Abhängigkeit der Menschheit von fossilen Brennstoffen zu reduzieren ist die treibende Kraft hinter aktuellen Forschungsanstrengungen in den Materialwissenschaften. Folglich besteht heutzutage ein erhebliches Interesse daran Alternativen zu Materialien, die aus fossilen Resourcen gewonnen werden, zu finden. Kurzfristig ist zweifellos Biomasse die vielversprechendste Alternative, da sie aus heutiger Sicht die einzige nicht-fossile, nachhaltige und nachwachsende Kohlenstoffquelle ist. Konsequenterweise werden die Antrengungen neue Syntheseansätze zur Konvertierung von Biomasse und ihren Derivaten in kohlenstoffbasierten Materialien forwährend erhöht. In diesem Zusammenhang hat sich die Hydrothermalkarbonisierung (HTC) als sehr vielseitiges Werkzeug zur Konvertierung von Biomasse-basierten Ausgangsstoffen in funktionale Kohlenstoffmaterialien herausgestellt. Dennoch gibt es bisher wenige Ansätze um rohe Biomasse, genauer gesagt Lignicellulose, direkt in funktionale Materialien umzusetzen. Könnte der direkte Einsatz von roher Biomasse Verfahren wie der HTC zugänglich gemacht werden, würde dies die Nachhaltigkeit des Verfahrens immens steigern. Daher wurde in dieser Dissertation die Hydrothermalkarbonisierung von kohlenhydratreicher (d. h. Lignicelluse) und proteinreicher (d. h. Microalgae) Biomasse systematisch analysiert. Diese Untersuchung galt dem Ziel einen besseren Einblick in das Potential dieser thermochemischen Verarbeitungsmethode funktionale Kohlenstoffmaterialien aus unverarbeiteter Biomasse hervorzubringen zu gewinnen. Die hergestellten Materialien wurden mittels chemischer Aktivierung nachträglich weiter behandelt. Dieser zusätzliche Verarbeitungsschritt ermöglichte die Herstellung hochporöser aktiverter Kohlenstoffe (AC). Die aus Lignicellulose gewonnenen ACs zeigten exzellente Eigenschaften bei der Aufnahme von CO2 und der Hochdruckspeicherung von CH4 währen die aus Microalgae gewonnen Eigenschaften an den Tag legten (z. B. hohe Oberfläche und N-Dotierung), welche sie zu vielversprechenden Materialien für Superkondensatoren machen. Die in dieser Dissertation präsentierte Arbeit zeigte außergewöhnliche Fortschritte in Richtung der Anwendung von unbehandelter Biomasse als Ausgangsmaterial für die Produktion von funktionalen Kohlenstoffen. KW - Biomasse KW - Kohlenmaterialien KW - Grüne Chemie KW - Nachhaltigkeit KW - Enegieanwendungen KW - Biomass KW - Carbon materials KW - Green Chemistry KW - Sustainability KW - Energy Applications Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-59785 ER - TY - THES A1 - Federico, Stefania T1 - Synthetic peptides derived from decorin as building blocks for biomaterials based on supramolecular interactions T1 - Synthetische Peptide Basierend auf Decorin als Bausteine für Supramolekulare Biomaterialien N2 - In this work, the development of a new molecular building block, based on synthetic peptides derived from decorin, is presented. These peptides represent a promising basis for the design of polymer-based biomaterials that mimic the ECM on a molecular level and exploit specific biological recognition for technical applications. Multiple sequence alignments of the internal repeats of decorin that formed the inner and outer surface of the arch-shaped protein were used to develop consensus sequences. These sequences contained conserved sequence motifs that are likely to be related to structural and functional features of the protein. Peptides representative for the consensus sequences were synthesized by microwave-assisted solid phase peptide synthesis and purified by RP-HPLC, with purities higher than 95 mol%. After confirming the desired masses by MALDI-TOF-MS, the primary structure of each peptide was investigated by 1H and 2D NMR, from which a full assignment of the chemical shifts was obtained. The characterization of the peptides conformation in solution was performed by CD spectroscopy, which demonstrated that using TFE, the peptides from the outer surface of decorin show a high propensity to fold into helical structures as observed in the original protein. To the contrary, the peptides from the inner surface did not show propensity to form stable secondary structure. The investigation of the binding capability of the peptides to Collagen I was performed by surface plasmon resonance analyses, from which all but one of the peptides representing the inner surface of decorin showed binding affinity to collagen with values of dissociation constant between 2•10-7 M and 2.3•10-4 M. On the other hand, the peptides representative for the outer surface of decorin did not show any significant interaction to collagen. This information was then used to develop experimental demonstration for the binding capabilities of the peptides from the inner surface of decorin to collagen even when used in more complicated situations close to possible appications. With this purpose, the peptide (LRELHLNNN) which showed the highest binding affinity to collagen (2•10-7 M) was functionalized with an N-terminal triple bond in order to obtain a peptide dimer via copper(I)-catalyzed cycloaddition reaction with 4,4'-diazidostilbene-2,2'-disulfonic acid. Rheological measurements showed that the presence of the peptide dimer was able to enhance the elastic modulus (G') of a collagen gel from ~ 600 Pa (collagen alone) to ~ 2700 Pa (collagen and peptide dimer). Moreover, it was shown that the mechanical properties of a collagen gel can be tailored by using different molar ratios of peptide dimer respect to collagen. The same peptide, functionalized with the triple bond, was used to obtain a peptide-dye conjugate by coupling it with N-(5'-azidopentanoyl)-5-aminofluorescein. An aqueous solution (5 vol% methanol) of the peptide dye conjugate was injected into a collagen and a hyaluronic acid (HA) gel and images of fluorescence detection showed that the diffusion of the peptide was slower in the collagen gel compared to the HA gel. The third experimental demonstration was gained using the peptide (LSELRLHNN) which showed the lower binding affinity (2.3•10-4 M) to collagen. This peptide was grafted to hyaluronic acid via EDC-chemistry, with a degree of functionalization of 7 ± 2 mol% as calculated by 1H-NMR. The grafting was further confirmed by FTIR and TGA measurements, which showed that the onset of decomposition for the HA-g-peptide decreased by 10 °C compared to the native HA. Rheological measurements showed that the elastic modulus of a system based on collagen and HA-g-peptide increased by almost two order of magnitude (G' = 200 Pa) compared to a system based on collagen and HA (G' = 0.9 Pa). Overall, this study showed that the synthetic peptides, which were identified from decorin, can be applied as potential building blocks for biomimetic materials that function via biological recognition. N2 - In dieser Arbeit wird das Design, die Synthese und Analyse neuer molekularer Bausteine für Biomaterialien basierend auf synthetischen, von Decorin abgeleiteten Peptiden beschrieben. Diese Peptide sind deshalb als Baustein für polymer-basierte Biomaterialien von besonderem Interesse, da sie die extrazelluläre Matrix (ECM) auf molekularer Ebene nachempfinden und spezifische, biologische wichtige Interaktionen für technische Anwendungen nutzbar machen. Das Alignment multipler Sequenzen der internen Repeats von Decorin, die jeweils die innere bzw. äußere Seite des sichelförmigen Decorins bilden, wurde genutzt, um Konsensus-Sequenzen zu definieren. Diese Sequenzen beinhalten stark konservierte Sequenzmotive, die wahrscheinlich wichtig für Struktur und Funktion des Proteins sind. Ausgewählte Peptide, die repräsentativ für die Konsensus-Sequenzen sind, wurden dann mittels Mikrowellen unterstützter Festphasensynthese synthetisiert und mit RP-HPLC aufgereinigt, so dass Peptide mit Reinheiten ≥ 95 mol% erhalten wurden. Die Peptide wurden per MALDI-TOF-MS sowie 1D und 2D NMR Spektroskopie charakterisiert, wobei die Zuordnung der chemischen Verschiebungen zu einzelnen Protonen und Kohlenstoffen aus den 2D NMR Experimenten erfolgte. In Lösung wurden die Peptide zudem mit CD Spektroskopie untersucht, wobei gezeigt werden konnte, dass nur Peptide, die von der äußeren Seite des Decorins abgeleitet wurden, sich durch Zugabe von 2,2,2-Trifluorethanol zu α-Helices falten. Diese Faltung ist auch in der Röntgenstruktur bei den korrespondierenden Abschnitten zu finden. Im Gegensatz dazu zeigten Peptide, die von der inneren Seite des Decorins abgeleitet wurden, keine stabilen Sekundärstrukturen in Lösung (β-Faltblattstruktur in der Röntgenstruktur). Bindungsstudien der Peptide zu Kollagen I wurden mit Oberflächenplasmonenresonanz durchgeführt, wobei gezeigt werden konnte, dass alle bis auf ein Peptid, die von der innneren Seite abgeleitet wurden, an Kollagen mit Dissoziationskonstanten von 2•10-7 M bis 2.3•10-4 M binden, während Peptide, die für die äußere Seite von Decorin repräsentativ sind, keine Bindung an Kollagen I zeigten. Diese Information wurde genutzt, um experimentelle Demonstrationsobjekte dieser Interaktion in komplexeren, einer späteren Anwendung näheren Situation, zu entwickeln. Dazu wurde das Peptide LRELHLNNN, welches die stärkste Bindung zu Kollagen I zeigte (KD = 2•10-7 M), N-terminal mit einer Alkinbindung funktionalisiert, so dass durch Kupfer (I) katalysierte Reaktion mit 4,4'-Diazidostilben-2,2'-disulfonsäure ein Peptid-Dimer erhalten werden konnte. Rheologische Untersuchungen zeigten, dass durch Zugabe des Peptid-Dimers der Elastizitätsmodul G' von Kollagen-Gelen von ~ 600 Pa (nur Kollagen) auf ~ 2700 Pa (Kollagen und Peptide-Dimer) gesteigert werden konnte. Darüber hinaus konnte gezeigt werden, dass die Veränderung der mechanischen Eigenschaften der Gele durch Veränderung des Kollagen:Peptid-Dimer Verhältnisses angepasst werden konnten. Das gleiche, mit einer Alkin-Bindung funktionaliserte Peptid wurde dann zur Darstellung eines Peptid-Fluorescein Konjugats genutzt, indem es mit N-(5'-azidopentanoyl)-5-aminofluorescein umgesetzt wurde. Eine wässrige Lösung des Peptid-Farbstoff-Konjugats wurde dann in Kollagen- bzw. Hyaluronsäuregele injiziert. Die Diffusion des Peptid-Farbstoff-Konjugats war in Kollagengelen im Vergleich zu Hyaluronsäuregelen deutlich verlangsamt. Das dritte Demonstrationsobjekt wurde erhalten, indem das Peptid LSELRLHNN, welches die geringste Bindung an Kollagen zeigte (KD = 2.3•10-4 M), auf Hyaluronsäure (HA) gegrafted wurde. Die Reaktion wurde durch Carbodiimid-mediierte Kupplung erreicht, und ein Funktionalisierungsgrad von 7 ± 2 mol% wurde durch Integration der 1H-NMR Spektren bestimmt. Das erfolgreiche Grafting wurde durch FTIR- und TGA-Untersuchungen bestätigt. In letzteren wurde gezeigt, dass der thermische Abbau durch das Grafting bei etwas niedrigeren Temperaturen beginnt als der Abbau reiner Hyaluronsäure (ΔT = 10 °C). Rheologische Untersuchungen zeigten, dass ein System aus Kollagen und HA-g-Peptid ein um zwei Größenordnungen höheren Elastizitätsmodul G' hat (G' = 200 Pa) als Systeme, die aus einer physikalischen Mischung von Kollagen und HA bestehen (G' = 0.9 Pa). Zusammenfassend konnte gezeigt werden, dass die Peptide, die von Decorin abgeleitet wurden, als Kollagen-bindende Bausteine für biomimetische Materialien genutzt werden können. KW - Decorin KW - Peptide KW - Supramolekularen Wechselwirkungen KW - Kollagen KW - Physikalische Vernetzung KW - Decorin KW - Peptides KW - Supramolecular Interactions KW - Collagen KW - Physical Crosslinking Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-59661 ER - TY - THES A1 - Fellinger, Tim-Patrick T1 - Hydrothermal and ionothermal carbon structures T1 - Hydrothermale und ionothermale Kohlenstoffstrukturen BT - from carbon negative materials to energy applications N2 - The needs for sustainable energy generation, but also a sustainable chemistry display the basic motivation of the current thesis. By different single investigated cases, which are all related to the element carbon, the work can be devided into two major topics. At first, the sustainable synthesis of “useful” carbon materials employing the process of hydrothermal carbonisation (HC) is described. In the second part, the synthesis of heteroatom - containing carbon materials for electrochemical and fuel cell applications employing ionic liquid precursors is presented. On base of a thorough review of the literature on hydrothermolysis and hydrothermal carbonisation of sugars in addition to the chemistry of hydroxymethylfurfural, mechanistic considerations of the formation of hydrothermal carbon are proposed. On the base of these reaction schemes, the mineral borax, is introduced as an additive for the hydrothermal carbonisation of glucose. It was found to be a highly active catalyst, resulting in decreased reaction times and increased carbon yields. The chemical impact of borax, in the following is exploited for the modification of the micro- and nanostructure of hydrothermal carbon. From the borax - mediated aggregation of those primary species, widely applicable, low density, pure hydrothermal carbon aerogels with high porosities and specific surface areas are produced. To conclude the first section of the thesis, a short series of experiments is carried out, for the purpose of demonstrating the applicability of the HC model to “real” biowaste i.e. watermelon waste as feedstock for the production of useful materials. In part two cyano - containing ionic liquids are employed as precursors for the synthesis of high - performance, heteroatom - containing carbon materials. By varying the ionic liquid precursor and the carbonisation conditions, it was possible to design highly active non - metal electrocatalyst for the reduction of oxygen. In the direct reduction of oxygen to water (like used in polymer electrolyte fuel cells), compared to commercial platinum catalysts, astonishing activities are observed. In another example the selective and very cost efficient electrochemical synthesis of hydrogen peroxide is presented. In a last example the synthesis of graphitic boron carbon nitrides from the ionic liquid 1 - Ethyl - 3 - methylimidazolium - tetracyanoborate is investigated in detail. Due to the employment of unreactive salts as a new tool to generate high surface area these materials were first time shown to be another class of non - precious metal oxygen reduction electrocatalyst. N2 - Die Notwendigkeit einer nachhaltigen Energiewirtschaft, sowie der nachhaltigen Chemie stellen die Motivation der vorgelegten Arbeit. Auf Grundlage separater Untersuchungen, die jeweils in engem Bezug zum Element Kohlenstoff stehen, kann die Arbeit in zwei Themenfelder geordnet werden. Der erste Teil behandelt die nachhaltige Herstellung nützlicher Kohlenmaterialien mit Hilfe des Verfahrens der hydrothermalen Carbonisierung. Im zweiten Teil wird die Synthese von Bor und Stickstoff angereicherten Kohlen aus ionischen Flüssigkeiten für elektrochemische Anwendungen abgehandelt. Insbesondere geht es um die Anwendung in Wasserstoff-Brennstoffzellen. Als Ergebnis einer sorgfältigen Literatur¬zusammenfassung der Bereiche Hydrothermolyse, hydrothermale Carbonisierung und Chemie des Hydroxymethylfurfurals wird ein chemisch-mechanistisches Modell zur Entstehung der Hydrothemalkohle vorgestellt. Auf der Basis dieses Modells wird ein neues Additiv zur hydrothermalen Carbonisierung von Zuckern vorgestellt. Die Verwendung des einfachen Additivs, genauer Borax, erlaubt eine wesentlich verkürzte und zu niedrigeren Temperaturen hin verschobene Prozessführung mit höheren Ausbeuten. Anhand des mechanistischen Modells wird ein Einfluss auf die Reaktion von Zuckern mit der reaktiven Kohlenvorstufe (Hydroxymethylfurfural) identifiziert. Die chemische Wirkung des Minerals Borax in der hydrothermalen Carbonisierung wird im Folgenden zur Herstellung vielfältig anwendbarer, hochporöser Kohlen mit einstellbarer Partikelgröße genutzt. Zum Abschluss des ersten Teils ist in einer Serie einfacher Experimente die Anwendbarkeit des mechanischen Modells auf die Verwendung „echter“ Biomasse in Form von Wassermelonenabfall gezeigt. Im zweiten Teil werden verschiedene cyano-haltige ionische Flüssigkeiten zur ionothermalen Synthese von Hochleistungskohlen verwendet. Durch Variation der ionischen Flüssigkeiten und Verwendung unterschiedlicher Synthesebedingungen wird die Herstellung hochaktiver, metallfreier Katalysatoren für die elektrochemische Reduktion von Sauerstoff erreicht. In der direkten Reduktion von Sauerstoff zu Wasser (wie sie in Brennstoffzellen Anwendung findet) werden, verglichen zu konventionellen Platin-basierten elektrochemischen Katalysatoren, erstaunliche Aktivitäten erreicht. In einem anderen Beispiel wird die selektive Herstellung von Wasserstoffperoxid zu sehr geringen Kosten vorgestellt. Abschließend wird anhand der Verwendung der ionischen Flüssigkeit 1-Ethyl-3-methylimidazolium-tetracyanoborat eine detaillierte Betrachtung zur Herstellung von graphitischem Borcarbonitrid vorgestellt. Unter Verwendung unreaktiver Salze, als einfaches Werkzeug zur Einführung großer inneren Oberflächen wird erstmals die elektrokatalytische Aktivität eines solchen Materials in der elektrochemischen Sauerstoffreduktion gezeigt. KW - Hydrothermalkohle KW - ionische Flüssigkeiten KW - poröse Materialien KW - Elektrokatalyse KW - hydrothermal carbon KW - ionic liquids KW - porous materials KW - electrocatalysis Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-57825 ER - TY - THES A1 - Haase, Martin F. T1 - Modification of nanoparticle surfaces for emulsion stabilization and encapsulation of active molecules for anti-corrosive coatings T1 - Nanopartikel Oberflächenmodifikationen zur Emulsionsstabilisierung und Verkapselung von Wirkstoffen für Antikorrosionsbeschichtungen N2 - Within this work, three physicochemical methods for the hydrophobization of initially hydrophilic solid particles are investigated. The modified particles are then used for the stabilization of oil-in-water (o/w) emulsions. For all introduced methods electrostatic interactions between strongly or weakly charged groups in the system are es-sential. (i) Short chain alkylammonium bromides (C4 – C12) adsorb on oppositely charged solid particles. Macroscopic contact angle measurements of water droplets under air and hexane on flat silica surfaces in dependency of the surface charge density and alkylchain-length allow the calculation of the surface energy and give insights into the emulsification properties of solid particles modified with alkyltrimethylammonium bromides. The measure-ments show an increase of the contact angle with increasing surface charge density, due to the enhanced adsorp-tion of the oppositely charged alkylammonium bromides. Contact angles are higher for longer alkylchain lengths. The surface energy calculations show that in particular the surface-hexane or surface-air interfacial en-ergy is being lowered upon alkylammonium adsorption, while a significant increase of the surface-water interfa-cial energy occurs only at long alkyl chain lengths and high surface charge densities. (ii) The thickness and the charge density of an adsorbed weak polyelectrolyte layer (e.g. PMAA, PAH) influence the wettability of nanoparticles (e.g. alumina, silica, see Scheme 1(b)). Furthermore, the isoelectric point and the pH range of colloidal stability of particle-polyelectrolyte composites depend on the thickness of the weak polye-lectrolyte layer. Silica nanoparticles with adsorbed PAH and alumina nanoparticles with adsorbed PMAA be-come interfacially active and thus able to stabilize o/w emulsions when the degree of dissociation of the polye-lectrolyte layer is below 80 %. The average droplet size after emulsification of dodecane in water depends on the thickness and the degree of dissociation of the adsorbed PE-layer. The visualization of the particle-stabilized o/w emulsions by cryogenic SEM shows that for colloidally stable alumina-PMAA composites the oil-water interface is covered with a closely packed monolayer of particles, while for the colloidally unstable case closely packed aggregated particles deposit on the interface. (iii) By emulsifying a mixture of the corrosion inhibitor 8-hydroxyquinoline (8-HQ) and styrene with silica nanoparticles a highly stable o/w emulsion can be obtained in a narrow pH window. The amphoteric character of 8-HQ enables a pH dependent electrostatic interaction with silica nanoparticles, which can render them interfa-cially active. Depending on the concentration and the degree of dissociation of 8-HQ the adsorption onto silica results from electrostatic or aromatic interactions between 8-HQ and the particle-surface. At intermediate amounts of adsorbed 8-HQ the oil wettability of the particles becomes sufficient for stabilizing o/w emulsions. Cryogenic SEM visualization shows that the particles arrange then in a closely packed shell consisting of partly of aggregated domains on the droplet interface. For further increasing amounts of adsorbed 8-HQ the oil wet-tability is reduced again and the particles ability to stabilize emulsions decreases. By the addition of hexadecane to the oil phase the size of the droplets can be reduced down to 200 nm by in-creasing the silica mass fraction. Subsequent polymerization produces corrosion inhibitor filled (20 wt-%) poly-styrene-silica composite particles. The measurement of the release of 8-hydroxyquinoline shows a rapid increase of 8-hydroxyquinoline in a stirred aqueous solution indicating the release of the total content in less than 5 min-utes. The method is extended for the encapsulation of other organic corrosion inhibitors. The silica-polymer-inhibitor composite particles are then dispersed in a water based alkyd emulsion, and the dispersion is used to coat flat aluminium substrates. After drying and cross-linking the polmer-film Confocal Laser Scanning Micros-copy is employed revealing a homogeneous distribution of the particles in the film. Electrochemical Impedance Spectroscopy in aqueous electrolyte solutions shows that films with aggregated particle domains degrade with time and don’t provide long-term corrosion protection of the substrate. However, films with highly dispersed particles have high barrier properties for corrosive species. The comparison of films containing silica-polystyrene composite particles with and without 8-hydroxyquinoline shows higher electrochemical impedances when the inhibitor is present in the film. By applying the Scanning Vibrating Electrode Technique the localized corrosion rate in the fractured area of scratched polymer films containing the silica-polymer-inhibitor composite particles is studied. Electrochemical corrosion cannot be suppressed but the rate is lowered when inhibitor filled composite particles are present in the film. By depositing six polyelectrolyte layers on particle stabilized emulsion droplets their surface morphology changes significantly as shown by SEM visualization. When the oil wettability of the outer polyelectrolyte layer increases, the polyelectrolyte coated droplets can act as emulsion stabilizers themselves by attaching onto bigger oil droplets in a closely packed arrangement. In the presence of 3 mM LaCl3 8-HQ hydrophobized silica particles aggregate strongly on the oil-water inter-face. The application of an ultrasonic field can remove two dimensional shell-compartments from the droplet surface, which are then found in the aqueous bulk phase. Their size ranges up to 1/4th of the spherical particle shell. N2 - Im Rahmen dieser Arbeit wurden drei Oberflächenmodifikationen zur Hydrophobierung von ursprünglich hydrophilen Feststoffpartikeln entwickelt. Die so modifizierten Partikel werden dann zur Stabilisierung von Öl-in-Wasser Emulsionen verwendet. Für sämtliche entwickelte Methoden sind elektrostatische Wechselwirkungen zwischen stark oder schwach dissoziierten chemischen Gruppen essentiell. (i) Kurzkettige Alkyltrimethylammonium Bromide (C4-C12) adsorbieren auf entgegengesetzt geladenen Partikeln. Makroskopische Kontaktwinkelmessungen von Wasser Tropfen in Luft und Hexan auf flachen Siliziumoxid Oberflächen mit variabler Oberflächenladungsdichte und Alkylkettenlänge ermöglichen die Berechnung der Oberflächenenergie und geben Einblicke in die Emulgationseigenschaften von so modifizierten Feststoffpartikeln. Die Messungen zeigen einen Anstieg des Kontakwinkels mit steigender Oberflächenladungsdichte, bedingt durch die verstärkte Adsorption von entgegengesetzt geladenen Alkyltrimethylammonium Bromiden. Die Kontaktwinkel sind zudem größer für längerkettige Alkyltrimethylammonium Bromide. Die Berechnungen der Oberflächenenergie zeigen, dass besonders die Feststoff-Hexan oder Feststoff-Luft Grenzflächenenergie durch die Adsorption verringert wird, wohingegen die Feststoff-Wasser Oberflächenenergie nur bei längeren Alkylkettenlängen und hohen Oberflächenladungsdichten signifikant ansteigt. (ii) Die Schichtdicke und Ladungsdichte von adsorbierten schwachen Polyelektrolyten (z.B. PMAA, PAH) beeinflusst die Benetzbarkeit von Nanopartikeln (z.B. Aluminiumoxid, Siliziumoxid). Der isoelektrische Punkt und der pH Bereich für kolloidale Stabilität solcher Polyelektrolyt modifizierter Partikel hängt von der Dicke der Polyelektrolytschicht ab. Siliziumoxid und Aluminiumoxid Nanopartikel mit adsorbierten PAH bzw. PMAA werden Grenzflächenaktiv und dadurch befähigt Öl-in-Wasser Emulsionen zu stabilisieren, wenn der Dissoziationsgrad der Polyelektrolytschicht geringer als 80 % ist. Die durchschnittliche Tropfengröße von Dodecan-in-Wasser Emulsionen ist abhängig von der Polyelektrolytschichtdicke und dem Dissoziationsgrad. Die Visualisierung von Partikel stabilisierten Öl-in-Wasser Emulsionen durch kryogene REM zeigt, dass im Falle von kolloidal stabilen Aluminiumoxid-PMAA Partikeln die Öl-Tröpfchen mit einer dichtgepackten Partikelhülle belegt sind, während für kolloidal destabilisierte Partikel eine Hülle aus aggregierten Partikeln gefunden wird. (iii) Durch das Emulgieren einer Lösung des Korrosionsinhibitors 8-Hydroxychinolins (8HQ) in Styrol mit Siliziumoxid Nanopartikeln können stabile Öl-in-Wasser Emulsionen in einem pH Fenster von 4 - 6 hergestellt werden. Der amphoterische Charakter von 8HQ ermöglicht eine pH abhängige elektrostatische Wechselwirkung mit den Siliziumdioxid Nanopartikeln, welche diese Grenzflächenaktiv werden lässt. In Abhängigkeit der Konzentration und des Dissoziationsgrads von 8HQ folgt die Adsorption auf Siliziumdioxid aus elektrostatischen oder aromatischen Wechselwirkungen zwischen 8HQ und der Partikeloberfläche. Bei mittleren adsorbierten Mengen wird die Öl Benetzbarkeit der Partikel ausreichend erhöht um Öl-in-Wasser Emulsionen zu stabilisieren. Kryogene REM zeigt, dass die Partikel dann in dicht gepackte Hüllen, mit teilweise aggregierten Domänen auf der Öltröpfchenoberfläche vorliegen. Durch weiter ansteigende adsorbierte 8HQ Mengen wird die Öl-Benetzbarkeit wieder zurückgesetzt und die Emulgationsfähigkeit der Partikel aufgehoben. Durch die Zugabe von Hexadecan zur Öl Phase kann die Tropfengröße durch Erhöhung des Siliziumdioxid Anteils auf 200 nm herabgesetzt werden. Anschließende Polymerisation des Styrols generiert Korrosionsinhibitor gefüllte (20 Gew-%) Polystyrol-Silizumoxid Komposite. Die Messung der Freisetzungsrate von 8HQ zeigt einen schnellen Anstieg der 8HQ Konzentration in einer gerührten wässrigen Lösung innerhalb von 5 Minuten. Die Verkapselungsmethode wird auch für andere organische Korrosionsinhibitoren erweitert. Die Komposite werden dann in einer wasserbasierten Alkydpräpolymeremulsion dispergiert und diese Mischung wird zur Beschichtung von flachen Aluminiumplatten genutzt. Nach Trocknung und Quervernetzung des Films wird Konfokale Laser Mikroskopie dazu verwendet um die räumliche Verteilung der Composite im Film zu visualisieren. Elektrochemische Impedanzspektroskopie zeigt, dass die Barriereeigenschaften des Films durch die Anwesenheit der Komposite verbessert sind. Raster Vibrationselektroden Messungen zeigen, dass die Korrosionsrate in einem Kratzer des Films durch die Anwesenheit der Inhibitor efüllten Komposite reduziert ist. Durch die Ablagerung von 6 Polyelektroytschichten auf Feststoffstabilisierten Emulsionströpfchen verändert sich deren Oberflächenmorphologie deutlich (gezeigt durch REM). Wenn die Ölbenetzbarkeit der äußeren Polyelektrolytschicht ansteigt, dann können solche Polyelektolytbeschichteten Feststoffstabilisierte Emulsionströpfchen selber als Emulsionsstabilisatoren verwendet werden. Diese lagern sich dann in einer dicht gepackten Schicht auf der Oberfläche von größeren Emulsionstropfen ab. In der Gegenwart von 3 mM LaCl3 aggregieren 8HQ modifizierte Siliziumoxid Partikel stark auf der Öl-Wasser Grenzfläche. Der Einsatz von Ultraschall kann aggregierte Schalenbestandteile von der Tropfenoberfläche wegreißen. Diese Wracks können bis zu einem Viertel der Kugelhülle ausmachen und liegen dann als kolloidale Schalen im Wasser vor. KW - Nanopartikel KW - Emulsionen KW - Polyelektrolyte KW - Korrosion KW - Adsorption KW - nanoparticles KW - emulsions KW - polyelectrolytes KW - corrosion KW - adsorption Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-55413 ER - TY - THES A1 - Valverde Serrano, Clara T1 - Self-assembly behavior in hydrophilic block copolymers T1 - Selbstorganisation von hydrophilen Blockcopolymeren N2 - Block copolymers are receiving increasing attention in the literature. Reports on amphiphilic block copolymers have now established the basis of their self-assembly behavior: aggregate sizes, morphologies and stability can be explained from the absolute and relative block lengths, the nature of the blocks, the architecture and also solvent selectiveness. In water, self-assembly of amphiphilic block copolymers is assumed to be driven by the hydrophobic. The motivation of this thesis is to study the influence on the self-assembly in water of A b B type block copolymers (with A hydrophilic) of the variation of the hydrophilicity of B from non-soluble (hydrophobic) to totally soluble (hydrophilic). Glucose-modified polybutadiene-block-poly(N-isopropylacrylamide) copolymers were prepared and their self-assembly behavior in water studied. The copolymers formed vesicles with an asymmetric membrane with a glycosylated exterior and poly(N-isopropylacrylamide) on the inside. Above the low critical solution temperature (LCST) of poly(N-isopropylacrylamide), the structure collapsed into micelles with a hydrophobic PNIPAM core and glycosylated exterior. This collapse was found to be reversible. As a result, the structures showed a temperature-dependent interaction with L-lectin proteins and were shown to be able to encapsulate organic molecules. Several families of double hydrophilic block copolymers (DHBC) were prepared. The blocks of these copolymers were biopolymers or polymer chimeras used in aqueous two-phase partition systems. Copolymers based on dextran and poly(ethylene glycol) blocks were able to form aggregates in water. Dex6500-b-PEG5500 copolymer spontaneously formed vesicles with PEG as the “less hydrophilic” barrier and dextran as the solubilizing block. The aggregates were found to be insensitive to the polymer's architecture and concentration (in the dilute range) and only mildly sensitive to temperature. Variation of the block length, yielded different morphologies. A longer PEG chain seemed to promote more curved aggregates following the inverse trend usually observed in amphiphilic block copolymers. A shorter dextran promoted vesicular structures as usually observed for the amphiphilic counterparts. The linking function was shown to have an influence of the morphology but not on the self-assembly capability in itself. The vesicles formed by dex6500-b-PEG5500 showed slow kinetics of clustering in the presence of Con A lectin. In addition both dex6500-b-PEG5500 and its crosslinked derivative were able to encapsulate fluorescent dyes. Two additional dextran-based copolymers were synthesized, dextran-b-poly(vinyl alcohol) and dextran-b-poly(vinyl pyrrolidone). The study of their self-assembly allowed to conclude that aqueous two-phase systems (ATPS) is a valid source of inspiration to conceive DHBCs capable of self-assembling. In the second part the principle was extended to polypeptide systems with the synthesis of a poly(N-hydroxyethylglutamine)-block-poly(ethylene glycol) copolymer. The copolymer that had been previously reported to have emulsifying properties was able to form vesicles by direct dissolution of the solid in water. Last, a series of thermoresponsive copolymers were prepared, dextran-b-PNIPAMm. These polymers formed aggregates below the LCST. Their structure could not be unambiguously elucidated but seemed to correspond to vesicles. Above the LCST, the collapse of the PNIPAM chains induced the formation of stable objects of several hundreds of nanometers in radius that evolved with increasing temperature. The cooling of these solution below LCST restored the initial aggregates. This self-assembly of DHBC outside any stimuli of pH, ionic strength, or temperature has only rarely been described in the literature. This work constituted the first formal attempt to frame the phenomenon. Two reasons were accounted for the self-assembly of such systems: incompatibility of the polymer pairs forming the two blocks (enthalpic) and a considerable solubility difference (enthalpic and entropic). The entropic contribution to the positive Gibbs free energy of mixing is believed to arise from the same loss of conformational entropy that is responsible for “the hydrophobic effect” but driven by a competition for water of the two blocks. In that sense this phenomenon should be described as the “hydrophilic effect”. N2 - Blockcopolymere erfahren ein stetig wachsendes Interesse, was an der steigenden Anzahl an Publikationen zu diesem Thema erkennbar ist. Zahlreiche Studien zu amphiphilen Blockcopolymeren haben dabei einige grundlegende Erkenntnisse über deren chemisches und physikalisches Verhalten, vor allem über die Selbstorganisation, hervorgebracht. So können die Größe, die verschiedenen Morphologien und auch die Stabilität der gebildeten Aggregate anhand der relativen und absoluten Blocklängen, die chemischen Struktur der Blöcke, der molekularen Architektur und der Eigenschaften des verwendeten Lösungsmittel erklärt werden. Im speziellen Fall des Wassers als Lösungsmittel bist die Selbstorganisation amphiphiler Blockcopolymere durch den hydrophoben Effekt bedingt. Dieser Arbeit liegt das Interesse an der Selbstorganisation in wässrigem Medium von Blockcopolymeren des Typs A-b-B mit A als hydrophilem Block und B als Block mit variierender Hydrophilie bzw. Hydrophpobie von unlöslich bis vollständig löslich zugrunde. Durch Variation dieser Eigenschaften von Block B soll dessen Einfluss auf das Selbstorganisationsverhalten untersucht werden. Dazu wurden mit Glucose modifizierte Polybutadien-block-Poly(N-Isopropylacrylamid)-Copolymere hergestellt und deren Selbstorganisation in Wasser untersucht. Die Copolymere bilden Vesikel mit einer asymmetrischen Membran, wobei im äußeren Bereich glycolysierte Gruppen und im inneren Bereich Poly(N-Isopropylacrylamid) (PNIPAM) vorliegen. Beim Überschreiten der low critical solution temperature (LCST) kollabiert die vesikuläre Struktur unter Bildung von Mizellen mit einem hydrophoben PNIPAM-Mizellinneren und nach außen gerichteten glycolysierten Blöcken. Diese strukturelle Umwandlung ist reversibel. Die Strukturen zeigten außerdem eine temperaturabhängige Wechselwirkung mit L-Lectin-Proteinen und die Möglichkeit zur Einkapselung organischer Moleküle konnte belegt werden. Des weiteren wurden verschiedene Gruppen von Blockcopolymeren mit zwei hydrophilen Blöcken synthetisiert (double hydrophilic block copolymers – DHBC). Die Blöcke dieser Systeme waren entweder Biopolymere oder Polymerchimäre, die in wässrigen Zwei-Phasen-Trennverfahren eingesetzt werden. Polymere, die auf Dextran- und Poly(ethylenglycol)-Blöcken basieren, zeigen Aggregatbildung in wässriger Phase. Dex6500-b-PEG5500 bildet spontan Vesikel mit PEG als „weniger hydrophilem“ Bestandteil und Dextran als löslichem Block. Die Bildung dieser Vesikel zeigte keine Emfpindlichkeit gegenüber einer Veränderung der Polymerarchitektur und der Konzentration, und nur eine geringe Sensitivität gegenüber Temperaturänderungen. Veränderungen der Blocklängen dagegen beeinflussten die Selbstorganisation und führten zu unterschiedlichen Morphologien. Längere PEG-Blöcke bevorzugten dabei die Bildung eher gekrümmter Aggregate, entgegen dem Trend, der gewöhnlicherweise für amphiphile Blockcopolymere beobachtet wird. Die Verkürzung des Dextran-Blocks fördert die Ausbildung vesikulärer Strukturen, was dem Verhalten der amphiphilen Gegenspieler der DHBC-Systeme entspricht. Die funktionelle Gruppe zur Verbindung der beiden Blöcke hat zwar einen Einfluss auf die Morphologie der gebildeten Aggregate, nicht jedoch auf die eigentliche Fähigkeit der Systeme zur Selbstorganisation. Die Dex6500-b-PEG5500-Vesikel wiesen zudem eine langsame Bildungskinetik in Gegenwart von Con-A-Lectin auf. Des Weiteren waren sowohl Dex6500-b-PEG5500 als auch das quervernetzte Derivate dieses Copolymers in der Lage, Fluoreszenzfarbstoffe einzulagern. Um zu zeigen, dass wässrige Zwei-Phasen-Systeme (aqueous two phase systems – ATPS) eine belastbare Grundlage für die Untersuchung und Entwicklung selbstorganisierender DHBC-Systeme sind, wurden weitere Dextran-basierte Copolymere synthetsisiert: Dextran-b-Poly(vinylalokohol) und Detran-b-Poly(vinylpyrrolidon). In einem zweiten Teil dieser Arbeit wurde das zuvor erarbeitete Prinzip auf auf Polypeptidsysteme ausgeweitet. Dazu wurde ein Poly(N-Hydroxyethylglutamin)-block-Poly(ethylenglycol)-Copolymer hergestellt. Dieses Copolymer, dessen emulgierenden Eigenschaften bereits bekannt waren, wies unmittelbar nach Lösung des Feststoffes in Wasser Vesikelbildung auf. In einem dritten Teil der Studie wurden thermoresponsive Copolymere hergestellt und untersucht: Dextran-b-PNIPAMm. Unterhalb der LCST konnte die Bildung von Aggregaten nachgewiesen werden, deren Struktur nicht zweifelsfrei entschlüsselt werden konnte, wobei jedoch zahlreiche Hinweise auf eine vesikuläre Struktur hindeuten. Oberhalb der LCST wurde durch die Kollabierung der PNIPAM-Ketten die Bildung stabiler Strukturen mit Radien von mehreren hundert Nanometern induziert, deren weitere Entwicklung durch eine weitere Temperaturerhöhung gefördert werden konnte. Durch Rückkühlung in den Temperaturebereich unterhalb der LCST konnten die zuvor beobachteten Aggregate reversibel zurückgebildet werden. Das Selbstorganisationsverhalten von DHBC, unabhängig vom Einfluss des pH-Werts, der Ionenstärke oder der Temperatur are bisher nur in sehr geringem Umfang Gegenstand wissenschaftlicher Veröffentlichungen. Diese Arbeit stellt damit den ersten umfassenden Beitrag zur systematischen Erarbeitung dieses Phänomens dar. Es konnten dabei zwei Ursachen für die beobachteten Selbstorganisationseffekte bestimmt werden: die Inkompatibilität der beiden Polymerblöcke (enthalpischer Effekt) und der Unterschied in deren Löslichkeit (enthalpische und entropische Effekte). Der entropische Beitrag zur positiven Gibbs’schen Freien Mischungsenergie wird dem selben Verlust konformativer Entropie zugeordnet, der auch für den hydrophoben Effekt verantwortlich ist, allerdings angetrieben durch einen Wettbewerb der beiden Polymerblöcke um das Wasser. In diesem Sinne kann man das beobachtete Phänomen als „hydrophilen Effekt“ bezeichnen. KW - Selbstorganisation KW - Blockcopolymere KW - hydrophil KW - self-assembly KW - copolymers KW - hydrophilic Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-54163 ER - TY - THES A1 - Klinkusch, Stefan T1 - Simulations of laser-induced correlated many-electron dynamics in molecular systems T1 - Simulationen laserinduzierter korrelierter Vielelektronendynamik in molekularen Systemen N2 - In this thesis, simulations of laser-driven many-electron dynamics in molecules are presented, i.e., the interaction between molecules and an electromagnetic field is demonstrated. When a laser field is applied to a molecular system, a population of higher electronic states takes place as well as other processes, e.g. photoionization, which is described by an appropriate model. Also, a finite lifetime of an excited state can be described by such a model. In the second part, a method is postulated that is capable of describing electron correlation in a time-dependent scheme. This is done by introducing a single-electron entropy that is at least temporarily minimized in a further step. N2 - Im Rahmen dieser Doktorarbeit werden Simulationen lasergetriebener Vielelektronendynamik in Molekülen präsentiert, d.h., die Wechselwirkung zwischen Molekülen und einem elektromagnetischen Feld wird demonstriert. Bei Laseranregungen finden nicht nur elektronische Übergänge statt, sondern auch weitere Prozesse wie die Photoionisation, die mit einem geeigneten Modell beschrieben wird. Auch die endliche Lebensdauer angeregter Zustände kann mit einem solchen Modell beschrieben werden. Im zweiten Teil wird eine Methode postuliert, die fähig ist, die Elektronenkorrelation zeitabhängig zu beschreiben. Dies wird durch die Einführung einer Einelektronenentropie erreicht, die in einem weiteren Schritt zumindest kurzzeitig minimiert wird. KW - Elektronendynamik KW - Laserpulse KW - Photoionisation KW - Elektronenkorrelation KW - electron dynamics KW - laser pulses KW - photoionization KW - electron correlation Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-55445 ER - TY - THES A1 - Popovic, Jelena T1 - Novel lithium iron phosphate materials for lithium-ion batteries T1 - Neuartige Lithium-Eisen-Phosphat-Materialien für Lithium-Ionen-Batterien N2 - Conventional energy sources are diminishing and non-renewable, take million years to form and cause environmental degradation. In the 21st century, we have to aim at achieving sustainable, environmentally friendly and cheap energy supply by employing renewable energy technologies associated with portable energy storage devices. Lithium-ion batteries can repeatedly generate clean energy from stored materials and convert reversely electric into chemical energy. The performance of lithium-ion batteries depends intimately on the properties of their materials. Presently used battery electrodes are expensive to be produced; they offer limited energy storage possibility and are unsafe to be used in larger dimensions restraining the diversity of application, especially in hybrid electric vehicles (HEVs) and electric vehicles (EVs). This thesis presents a major progress in the development of LiFePO4 as a cathode material for lithium-ion batteries. Using simple procedure, a completely novel morphology has been synthesized (mesocrystals of LiFePO4) and excellent electrochemical behavior was recorded (nanostructured LiFePO4). The newly developed reactions for synthesis of LiFePO4 are single-step processes and are taking place in an autoclave at significantly lower temperature (200 deg. C) compared to the conventional solid-state method (multi-step and up to 800 deg. C). The use of inexpensive environmentally benign precursors offers a green manufacturing approach for a large scale production. These newly developed experimental procedures can also be extended to other phospho-olivine materials, such as LiCoPO4 and LiMnPO4. The material with the best electrochemical behavior (nanostructured LiFePO4 with carbon coating) was able to delive a stable 94% of the theoretically known capacity. N2 - Konventionelle Energiequellen sind weder nachwachsend und daher nachhaltig nutzbar, noch weiterhin langfristig verfügbar. Sie benötigen Millionen von Jahren um gebildet zu werden und verursachen in ihrer Nutzung negative Umwelteinflüsse wie starke Treibhausgasemissionen. Im 21sten Jahrhundert ist es unser Ziel nachhaltige und umweltfreundliche, sowie möglichst preisgünstige Energiequellen zu erschließen und nutzen. Neuartige Technologien assoziiert mit transportablen Energiespeichersystemen spielen dabei in unserer mobilen Welt eine große Rolle. Li-Ionen Batterien sind in der Lage wiederholt Energie aus entsprechenden Prozessen nutzbar zu machen, indem sie reversibel chemische in elektrische Energie umwandeln. Die Leistung von Li-Ionen Batterien hängen sehr stark von den verwendeten Funktionsmaterialien ab. Aktuell verwendete Elektrodenmaterialien haben hohe Produktionskosten, verfügen über limitierte Energiespeichekapazitäten und sind teilweise gefährlich in der Nutzung für größere Bauteile. Dies beschränkt die Anwendungsmöglichkeiten der Technologie insbesondere im Gebiet der hybriden Fahrzeugantriebe. Die vorliegende Dissertation beschreibt bedeutende Fortschritte in der Entwicklung von LiFePO4 als Kathodenmaterial für Li-Ionen Batterien. Mithilfe einfacher Syntheseprozeduren konnten eine vollkommen neue Morphologie (mesokristallines LiFePo4) sowie ein nanostrukturiertes Material mit exzellenten elektrochemischen Eigenschaften hergestellt werden. Die neu entwickelten Verfahren zur Synthese von LiFePo4 sind einschrittig und bei signifikant niedrigeren Temperaturen im Vergleich zu konventionellen Methoden. Die Verwendung von preisgünstigen und umweltfreundlichen Ausgangsstoffen stellt einen grünen Herstellungsweg für die large scale Synthese dar. Mittels des neuen Synthesekonzepts konnte meso- und nanostrukturiertes LiFe PO4 generiert werden. Die Methode ist allerdings auch auf andere phospho-olivin Materialien (LiCoPO4, LiMnPO4) anwendbar. Batterietests der besten Materialien (nanostrukturiertes LiFePO4 mit Kohlenstoffnanobeschichtung) ergeben eine mögliche Energiespeicherung von 94%. KW - Li-Ionen-Akkus KW - Kathode KW - LiFePO4 KW - Mesokristalle KW - Nanopartikel KW - Li-ion batteries KW - cathode KW - LiFePO4 KW - mesocrystals KW - nanoparticles Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-54591 ER - TY - THES A1 - Weiß, Jan T1 - Synthesis and self-assembly of multiple thermoresponsive amphiphilic block copolymers T1 - Synthese und Selbstorganisation von mehrfach thermisch schaltbaren amphiphilen Blockcopolymeren N2 - In the present thesis, the self-assembly of multi thermoresponsive block copolymers in dilute aqueous solution was investigated by a combination of turbidimetry, dynamic light scattering, TEM measurements, NMR as well as fluorescence spectroscopy. The successive conversion of such block copolymers from a hydrophilic into a hydrophobic state includes intermediate amphiphilic states with a variable hydrophilic-to-lipophilic balance. As a result, the self-organization is not following an all-or-none principle but a multistep aggregation in dilute solution was observed. The synthesis of double thermoresponsive diblock copolymers as well as triple thermoresponsive triblock copolymers was realized using twofold-TMS labeled RAFT agents which provide direct information about the average molar mass as well as residual end group functionality from a routine proton NMR spectrum. First a set of double thermosensitive diblock copolymers poly(N-n-propylacrylamide)-b-poly(N-ethylacrylamide) was synthesized which differed only in the relative size of the two blocks. Depending on the relative block lengths, different aggregation pathways were found. Furthermore, the complementary TMS-labeled end groups served as NMR-probes for the self-assembly of these diblock copolymers in dilute solution. Reversible, temperature sensitive peak splitting of the TMS-signals in NMR spectroscopy was indicative for the formation of mixed star-/flower-like micelles in some cases. Moreover, triple thermoresponsive triblock copolymers from poly(N-n-propylacrylamide) (A), poly(methoxydiethylene glycol acrylate) (B) and poly(N-ethylacrylamide) (C) were obtained from sequential RAFT polymerization in all possible block sequences (ABC, BAC, ACB). Their self-organization behavior in dilute aqueous solution was found to be rather complex and dependent on the positioning of the different blocks within the terpolymers. Especially the localization of the low-LCST block (A) had a large influence on the aggregation behavior. Above the first cloud point, aggregates were only observed when the A block was located at one terminus. Once placed in the middle, unimolecular micelles were observed which showed aggregation only above the second phase transition temperature of the B block. Carrier abilities of such triple thermosensitive triblock copolymers tested in fluorescence spectroscopy, using the solvatochromic dye Nile Red, suggested that the hydrophobic probe is less efficiently incorporated by the polymer with the BAC sequence as compared to ABC or ACB polymers above the first phase transition temperature. In addition, due to the problem of increasing loss of end group functionality during the subsequent polymerization steps, a novel concept for the one-step synthesis of multi thermoresponsive block copolymers was developed. This allowed to synthesize double thermoresponsive di- and triblock copolymers in a single polymerization step. The copolymerization of different N-substituted maleimides with a thermosensitive styrene derivative (4-vinylbenzyl methoxytetrakis(oxyethylene) ether) led to alternating copolymers with variable LCST. Consequently, an excess of this styrene-based monomer allowed the synthesis of double thermoresponsive tapered block copolymers in a single polymerization step. N2 - Die Selbstorganisation von mehrfach thermisch schaltbaren Blockcopolymeren in verdünnter wässriger Lösung wurde mittels Trübungsphotometer, dynamischer Lichtstreuung, TEM Messungen, NMR sowie Fluoreszenzspektroskopie untersucht. Die schrittweise Überführung eines hydrophilen in ein hydrophobes Blockcopolymer beinhaltet ein oder mehr amphiphile Zwischenstufen mit einstellbarem hydrophilen zu lipophilen Anteil (HLB). Dies führt dazu, dass die Selbstorganisation solcher Polymere in Lösung nicht nur einem Alles-oder-nichts-Prinzip folgt sondern ein mehrstufiges Aggregationsverhalten beobachtet wird. Die Synthese von doppelt thermisch schaltbaren Diblockcopolymeren und dreifach thermisch schaltbaren Triblockcopolymeren wurde durch sequenzielle RAFT Polymerisation realisiert. Dazu wurden zweifach TMS-markierte RAFT Agentien verwendet, welche die Bestimmung der molaren Masse sowie der verbliebenen Endgruppenfunktionalität direkt aus einem Protonen NMR Spektrum erlauben. Mit diesen RAFT Agentien wurde zunächst eine Serie von doppelt thermisch schaltbaren Diblockcopolymeren aus Poly(N-n-propylacrylamid)-b-Poly(N-ethylacrylamid), welche sich lediglich durch die relativen Blocklängen unterscheiden, hergestellt. In Abhängigkeit von der relativen Blocklänge wurde ein unterschiedliches Aggregationsverhalten der Diblockcopolymere in verdünnter wässriger Lösung beobachtet. Des Weiteren wirken die komplementär TMS-markierten Endgruppen als NMR-Sonden während der schrittweisen Aggregation dieser Polymere. Reversible, temperaturabhängige Peakaufspaltung der TMS-Signale in der NMR Spektroskopie spricht für eine Aggregation in gemischte stern-/blumenartige Mizellen, in denen ein Teil der hydrophoben Endgruppen in den hyrophoben Kern zurückfaltet. Obendrein wurden dreifach thermisch schaltbare Triblockcopolymere aus Poly(N-n-propylacrylamid) (A), Poly(methoxydiethylen glycol acrylat) (B) und Poly(N-ethylacrylamid) (C) in allen möglichen Blocksequenzen (ABC, BAC, ACB) durch schrittweisen Aufbau mittels RAFT Polymerisation erhalten. Das Aggregationsverhalten dieser Polymere in verdünnter wässriger Lösung war relativ komplex und hing stark von der Position der einzelnen Blöcke in den Triblockcopolymeren ab. Besonders die Position des Blocks mit der niedrigsten LCST (A) war ausschlaggebend für die resultierenden Aggregate. So wurde oberhalb der ersten Phasenübergangstemperatur nur Aggregation der Triblockcopolymere beobachtet, wenn der A Block an einem der beiden Enden der Polymere lokalisiert war. Wurde der A Block hingegen in der Mitte der Polymere positioniert, entstanden unimere Mizellen zwischen der ersten und zweiten Phasenübergangstemperatur, welche erst aggregierten, nachdem der zweite Block (B) seinen Phasenübergang durchlief. Die Transportereigenschaften dieser Triblockcopolymere wurden mittels Fluoreszenzspektroskopie getestet. Dazu wurde die Einlagerung eines hydrophoben, solvatochromen Fluoreszenzfarbstoffes, Nilrot, in Abhängigkeit der Temperatur untersucht. Im Gegensatz zu den Polymeren mit der Blocksequenz ABC oder ACB, zeigten die Polymere mit der Sequenz BAC eine verminderte Aufnahmefähigkeit des hydrophoben Farbstoffes oberhalb des ersten Phasenübergangs, was auf die fehlende Aggregation und die damit verbundenen relativ kleinen hydrophoben Domänen der unimolekularen Mizellen zwischen der ersten und zweiten Phasenübergangstemperatur zurückzuführen ist. Aufgrund des zunehmenden Verlustes von funktionellen Endgruppen während der RAFT Synthese von Triblockcopolymeren wurde ein neuartiges Konzept zur Einschrittsynthese von mehrfach schaltbaren Blockcopolymeren entwickelt. Dieses erlaubt die Synthese von mehrfach schaltbaren Diblock- und Triblockcopoylmeren in einem einzelnen Reaktionsschritt. Die Copolymeriation von verschiedenen N-substituierten Maleimiden mit einem thermisch schaltbaren Styrolderivat (4-Vinylbenzylmethoxytetrakis(oxyethylene) ether) ergab alternierende Copolymere mit variabler LCST. Die Verwendung eines Überschusses dieses styrolbasierten Monomers erlaubt ferner die Synthese von Gradientenblockcopolymeren in einem einzelnen Polymerisationsschritt. KW - Selbstorganisation KW - Blockcopolymer KW - RAFT KW - temperaturschaltbar KW - Mizelle KW - self-assembly KW - block copolymer KW - RAFT KW - thermoresponsive KW - micelle Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-53360 ER - TY - THES A1 - Kubo, Shiori T1 - Nanostructured carbohydrate-derived carbonaceous materials T1 - Nanostrukturierte kohlenstoffbasierte Materialien aus Kohlenhydraten N2 - Nanoporous carbon materials are widely used in industry as adsorbents or catalyst supports, whilst becoming increasingly critical to the developing fields of energy storage / generation or separation technologies. In this thesis, the combined use of carbohydrate hydrothermal carbonisation (HTC) and templating strategies is demonstrated as an efficient route to nanostructured carbonaceous materials. HTC is an aqueous-phase, low-temperature (e.g. 130 – 200 °C) carbonisation, which proceeds via dehydration / poly-condensation of carbon precursors (e.g. carbohydrates and their derivatives), allowing facile access to highly functional carbonaceous materials. Whilst possessing utile, modifiable surface functional groups (e.g. -OH and -C=O-containing moieties), materials synthesised via HTC typically present limited accessible surface area or pore volume. Therefore, this thesis focuses on the development of fabrication routes to HTC materials which present enhanced textural properties and well-defined porosity. In the first discussed synthesis, a combined hard templating / HTC route was investigated using a range of sacrificial inorganic templates (e.g. mesoporous silica beads and macroporous alumina membranes (AAO)). Via pore impregnation of mesoporous silica beads with a biomass-derived carbon source (e.g. 2-furaldehyde) and subsequent HTC at 180 oC, an inorganic / carbonaceous hybrid material was produced. Removal of the template component by acid etching revealed the replication of the silica into mesoporous carbonaceous spheres (particle size ~ 5 μm), representing the inverse morphological structure of the original inorganic body. Surface analysis (e.g. FTIR) indicated a material decorated with hydrophilic (oxygenated) functional groups. Further thermal treatment at increasingly elevated temperatures (e.g. at 350, 550, 750 oC) under inert atmosphere allowed manipulation of functionalities from polar hydrophilic to increasingly non-polar / hydrophobic structural motifs (e.g. extension of the aromatic / pseudo-graphitic nature), thus demonstrating a process capable of simultaneous control of nanostructure and surface / bulk chemistry. As an extension of this approach, carbonaceous tubular nanostructures with controlled surface functionality were synthesised by the nanocasting of uniform, linear macropores of an AAO template (~ 200 nm). In this example, material porosity could be controlled, showing increasingly microporous tube wall features as post carbonisation temperature increased. Additionally, by taking advantage of modifiable surface groups, the introduction of useful polymeric moieties (i.e. grafting of thermoresponsive poly(N-isopropylacrylamide)) was also demonstrated, potentially enabling application of these interesting tubular structures in the fields of biotechnology (e.g. enzyme immobilization) and medicine (e.g. as drug micro-containers). Complimentary to these hard templating routes, a combined HTC / soft templating route for the direct synthesis of ordered porous carbonaceous materials was also developed. After selection of structural directing agents and optimisation of synthesis composition, the F127 triblock copolymer (i.e. ethylene oxide (EO)106 propylene oxide (PO)70 ethylene oxide (EO)106) / D-Fructose system was extensively studied. D-Fructose was found to be a useful carbon precursor as the HTC process could be performed at 130 oC, thus allowing access to stable micellular phase. Thermolytic template removal from the synthesised ordered copolymer / carbon composite yielded functional cuboctahedron single crystalline-like particles (~ 5 μm) with well ordered pore structure of a near perfect cubic Im3m symmetry. N2 sorption analysis revealed a predominantly microporous carbonaceous material (i.e. Type I isotherm, SBET = 257 m2g-1, 79 % microporosity) possessing a pore size of ca. 0.9 nm. The addition of a simple pore swelling additive (e.g. trimethylbenzene (TMB)) to this system was found to direct pore size into the mesopore size domain (i.e. Type IV isotherm, SBET = 116 m2g-1, 60 % mesoporosity) generating pore size of ca. 4 nm. It is proposed that in both cases as HTC proceeds to generate a polyfuran-like network, the organised block copolymer micellular phase is essentially “templated”, either via hydrogen bonding between hydrophilic poly(EO) moiety and the carbohydrate or via hydrophobic interaction between hydrophobic poly(PO) moiety and forming polyfuran-like network, whilst the additive TMB presumably interact with poly(PO) moieties, thus swelling the hydrophobic region expanding the micelle template size further into the mesopore range. N2 - Nanoporöse kohlenstoffbasierte Materialien sind in der Industrie als Adsorbentien und Katalysatorträger weit verbreitet und gewinnen im aufstrebenden Bereich der Energiespeicherung/erzeugung und für Trennverfahren an wachsender Bedeutung. In der vorliegenden Arbeit wird gezeigt, dass die Kombination aus hydrothermaler Karbonisierung von Zuckern (HTC) mit Templatierungsstrategien einen effizienten Weg zu nanostrukturierten kohlenstoffbasierten Materialien darstellt. HTC ist ein in Wasser und bei niedrigen Temperaturen (130 - 200 °C) durchgeführter Karbonisierungsprozess, bei dem Zucker und deren Derivate einen einfachen Zugang zu hochfunktionalisierten Materialien erlauben. Obwohl diese sauerstoffhaltige Funktionalitäten auf der Oberfläche besitzen, an welche andere chemische Gruppen gebunden werden könnten, was die Verwendung für Trennverfahren und in der verzögerten Wirkstofffreisetzung ermöglichen sollte, ist die mittels HTC hergestellte Kohle für solche Anwendungen nicht porös genug. Das Ziel dieser Arbeit ist es daher, Methoden zu entwickeln, um wohldefinierte Poren in solchen Materialien zu erzeugen. Hierbei führte unter anderem der Einsatz von anorganischen formgebenden mesoporösen Silikapartikeln und makroporösen Aluminiumoxid-Membranen zum Erfolg. Durch Zugabe einer Kohlenstoffquelle (z. B. 2-Furfural), HTC und anschließender Entfernung des Templats konnten poröse kohlenstoffbasierte Partikel und röhrenförmige Nanostrukturen hergestellt werden. Gleichzeitig konnte durch eine zusätzliche Nachbehandlung bei hoher Temperatur (350-750 °C) auch noch die Oberflächenfunktionalität hin zu aromatischen Systemen verschoben werden. Analog zur Formgebung durch anorganische Template konnte mit sog. Soft-Templaten, z. B. PEO-PPO-PEO Blockcopolymeren, eine funktionelle poröse Struktur induziert werden. Hierbei machte man sich die Ausbildung geordneter Mizellen mit der Kohlenstoffquelle D-Fructose zu Nutze. Das erhaltene Material wies hochgeordnete Mikroporen mit einem Durchmesser von ca. 0,9 nm auf. Dieser konnte desweiteren durch Zugabe von Quell-Additiven (z. B. Trimethylbenzol) auf 4 nm in den mesoporösen Bereich vergrößert werden. Zusammenfassend lässt sich sagen, dass beide untersuchten Synthesewege nanostrukturierte kohlenstoffbasierte Materialien mit vielfältiger Oberflächenchemie liefern, und das mittels einer bei relativ niedriger Temperatur in Wasser ablaufenden Reaktion und einer billigen, nachhaltigen Kohlenstoffquelle. Die so hergestellten Produkte eröffnen vielseitige Anwendungsmöglichkeiten, z. B. zur Molekültrennung in der Flüssigchromatographie, in der Energiespeicherung als Anodenmaterial in Li-Ionen Akkus oder Superkondensatoren, oder als Trägermaterial für die gezielte Pharmakotherapie. KW - Nanostruktur KW - Kohlenstoff KW - Kohlenhydrate KW - Templating KW - hydrothermale Carbonisierung KW - Nanostructure KW - Carbon KW - Carbohydrate KW - Templating KW - Hydrothermal carbonisation Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-53157 ER - TY - THES A1 - Tan, Irene T1 - Towards greener stationary phases : thermoresponsive and carbonaceous chromatographic supports T1 - Zu grüner Separation : thermoresponsive und kohlenstoffhaltige chromatographische Trägermaterialien N2 - Polymers which are sensitive towards external physical, chemical and electrical stimuli are termed as ‘intelligent materials’ and are widely used in medical and engineering applications. Presently, polymers which can undergo a physical change when heat is applied at a certain temperature (cloud point) in water are well-studied for this property in areas of separation chemistry, gene and drug delivery and as surface modifiers. One example of such a polymer is the poly (N-isopropylacrylamide) PNIPAAM, where it is dissolved well in water below 32 oC, while by increasing the temperature further leads to its precipitation. In this work, an alternative polymer poly (2-(2-methoxy ethoxy)ethyl methacrylate-co- oligo(ethylene glycol) methacrylate) (P(MEO2MA-co-OEGMA)) is studied due to its biocompatibility and the ability to vary its cloud points in water. When a layer of temperature responsive polymer was attached to a single continuous porous piece of silica-based material known as a monolith, the thermoresponsive characteristic was transferred to the column surfaces. The hybrid material was demonstrated to act as a simple temperature ‘switch’ in the separation of a mixture of five steroids under water. Different analytes were observed to be separated under varying column temperatures. Furthermore, more complex biochemical compounds such as proteins were also tested for separation. The importance of this work is attributed to separation processes utilizing environmentally friendly conditions, since harsh chemical environments conventionally used to resolve biocompounds could cause their biological activities to be rendered inactive. N2 - Polymere, welche empfindlich gegenüber externen physikalischen, chemischen und elektrischen Einflüssen sind, werden „intelligente Materialien“ genannt. Diese werden weitverbreitet in medizinischen und technischen Anwendungen eingesetzt. Auf diesem Gebiet ausführlich erforschte Materialien sind Polymere, welche durch Hitze bei einer bestimmten Temperatur (Trübungspunkt) eine physikalische Veränderung eingehen können, genannt thermoresponsive Polymere. Eingesetzt werden diese z.B. in chromatographischen Trennverfahren, in Gen- und Wirkstofftransport Vorgängen und zur Oberflächenmodifikation. Ein Beispiel für so ein Polymer ist das poly(N-isopropylacrylamide) PNIPAAM, welches unter 32 °C in Wasser gelöst vorliegt und mit Erhöhung der Temperatur als Niederschlag ausfällt. In dieser Arbeit wurde ein alternatives Polymer, das poly(2-(2-methoxyethoxy)ethylmethacrylate-co-oligo(ethyleneglycol) methacrylate) (P(MEO2MA-co-OEGMA)), untersucht, in Bezug auf Biokompatibilität und der Änderung des Trübungspunktes in Wasser. Wenn eine Schicht eines temperaturempfindlichen Polymers auf einen Monolithen (einteiliger, poröser und auf Silika-basierendes Material) aufgebracht wird, werden die thermoresponsiven Eigenschaften auf die Oberfläche dieses Monolithen übertragen. Der Monolith dient hier als Säule in einer HPLC-Anlage. Es wurde gezeigt, dass das Hybrid-Material als einfacher „Temperaturschalter“ in der Trennung von fünf verschiedenen Steroiden in Wasser agieren kann. Untersucht wurde die Separation verschiedener Analyten mit dem Variieren der Säulentemperatur. Zusätzlich wurden mehr komplexe biochemische Stoffe, wie Proteine, getestet. Die Bedeutung dieser Arbeit ist zurückzuführen auf Separationsprozesse, welche umweltfreundlichen Bedingungen nutzen, da die rauen chemischen Bedingungen in konventionellen Separationsprozessen die biologische Inaktivität der Verbindungen zur Folge haben können. Der zweite Teil der Arbeit beschäftigte sich mit der Entwicklung eines alternativen Trägermaterials als Ersatz zu den Silika-basierende Trennungssäulen. Kohlenstoffmaterialien sind aufgrund ihrer ausgezeichneten mechanischen Härte und chemischen Stabilität eine vielversprechend Alternative. Die Synthese von Kohlenstoffkugeln als Trägermaterial kann als „grüner“ Prozess in meiner Arbeit angesehen werden, da milde Synthesebedingungen in purem Wasser verwendet wurden. Die Leistungsfähigkeit des Materials wurde mit einer Serie von Separationsreaktionen gezeigt. KW - thermoresponsive KW - poly(N-isopropylacrylamide) KW - oligo(ethyleneglycol) KW - Monolith KW - Chromatographie KW - thermoresponsive KW - poly(N-isopropyl acrylamide) KW - oligo(ethylene glycol) KW - monolith KW - chromatography Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-53130 ER - TY - THES A1 - Schumacher, Soeren T1 - Saccharide recognition : boronic acids as receptors in polymeric networks T1 - Zuckererkennung in polymeren Netzwerken mittels Boronsäuren als Rezeptoren N2 - In this thesis entitled “Saccharide Recognition - Boronic acids as Receptors in Polymeric Networks” different aspects of boronic acid synthesis, their analysis and incorporation or attachment to different polymeric networks and characterisation thereof were investigated. The following key aspects were considered: • Provision of a variety of different characterised arylboronic acids and benzoboroxoles • Attachment of certain derivatives to nanoparticles and the characterisation of saccharide binding by means of isothermal titration calorimetry and displacement assay (ARS) to enhance the association constant to saccharides at pH 7.4 • Enhancement of selectivity in polymeric systems by means of molecular imprinting using fructose as template and a polymerisable benzoboroxole as functional monomer for the recognition at pH 7.4 (Joined by a diploma thesis of F. Grüneberger) • Development of biomimetic saccharide structures and the development of saccharide (especially glucose and fructose) binding MIPs by using these structures as template molecules. In the first part of the thesis different arylboronic acid derivatives were synthesised and their binding to glucose or fructose was investigated by means of isothermal titration calorimetry (ITC). It could be derived, which is in parallel to the literature, that derivatives bearing a methylhydroxyl-group in ortho-position to the boron (benzoboroxole) exhibit in most cases a two-fold higher association constant compared to the corresponding phenylboronic acid derivative. To gain a deeper understanding NMR spectroscopy and mass spectrometry with the benzoboroxole and glucose or fructose was performed. It could be shown that the exchange rate in terms of NMR time scale is quite slow since in titration experiments new peaks appeared. Via mass spectrometry of a mixture between benzoboroxole and glucose or fructose, different binding stoichiometries could be detected showing that the binding of saccharides is comparable with their binding to phenylboronic acid. In addition, the use of Alizarin Red S as an electrochemical reporter was described for the first time to monitor the saccharide binding to arylboronic acids not only with spectroscopy. Here, the redox behaviour and the displacement were recorded by cyclic voltammograms. In the second part different applications of boronic acids in polymeric networks were investigated. The attachment of benzoboroxoles to nanoparticles was investigated and monitored by means of isothermal titration calorimetry and a colourimetric assay with Alizarin Red S as the report dye. The investigations by isothermal titration calorimetry compared the fructose binding of arylboronic acids and benzoboroxoles coupled to these nanoparticles and “free” in solution. It could be shown that the attached derivatives showed a higher binding constant due to an increasing entropy term. This states for possible multivalent binding combined with a higher water release. Since ITC could not characterise the binding of glucose to these nanoparticles due to experimental restrictions the glucose binding at pH 7.4 was shown with ARS. Here, the displacement of ARS by fructose and also glucose could be followed and consequently these nanoparticles can be used for saccharide determination. Within this investigation also the temperature stability of these nanoparticles was examined and after normal sterilisation procedures (121°C, 20 min.) the binding behaviour was still unchanged. To target the selectivity of the used polymeric networks, molecular imprinting was used as a technique for creating artificial binding pockets on a molecular scale. As functional monomer 3-methacrylamidobenzoboroxole was introduced for the recognition of fructose. In comparison to polymers prepared with vinylphenylboronic acid the benzoboroxole containing polymer had a stronger binding at pH 7.4 which was shown for the first time. In addition, another imprinted polymer was synthesised especially for the recognition of glucose and fructose employing biomimetic saccharide analogues as template molecule. The advantage to use the saccharide analogues is the defined template-functional monomer complex during the polymerisation which is not the case, for example, for glucose-boronic acid interaction. The biomimetic character was proven through structural superimposition of crystal structures of the analogues with already described crystal structures of boronic acid esters of glucose and fructose. A molecularly imprinted polymer was synthesised with vinylphenylboronic acid as the functional monomer to show that both glucose and fructose are able to bind to the polymer which was predicted by the structural similarity of the analogues. The major scientific contributions of this thesis are • the determination of binding constants for some, not yet reported saccharide – boronic acid / benzoboroxole pairs, • the use of ARS as electrochemical reporter for saccharide detection, • the thermodynamic characterisation of a saccharide binding nanoparticle system containing benzoboroxole and functioning at pH 7.4, • the use of a polymerisable benzoboroxole as functional monomer for saccharide recognition in neutral, aqueous environments • and the synthesis and utilisation of biomimetic saccharide analogues as template molecules especially for the development of a glucose binding MIP. N2 - Die vorliegende Arbeit beschäftigte sich mit der Synthese verschiedener Boronsäurederivate und deren Charakterisierung und Anbindung oder Einbau in polymeren Netzwerken. Die synthetisierten Polymere werden charakterisiert bezüglich ihrer Morphologie und besonders hinsichtlich ihrer Saccharidbindung. Im Wesentlichen wurden die folgenden Aspekte bearbeitet: • Bereitstellung einer Reihe von verschiedenen Arylboronsäuren und Benzoboroxolderivaten • Modifizierung von Nanopartikeln mit verschiedenen Derivaten aus der Bibliothek mit dem Ziel die Bindingkonstanten zu Monosacchariden bei pH 7.4. zu erhöhen. Dabei werden isothermale Titrationskalorimetrie und ein spektroskopischer Verdrängungsassay (Alizarin Rot S) zum Bindungsnachweis verwendet. • Erhöhung der Selektivität von Polymeren mittels molekularen Prägens von Fruktose als Matrizenmolekül. Durch den Einsatz eines polymerisierbaren Benzoboroxolderivatives konnte die Anbindung bei pH 7.4 stattfinden (Dieser Teil der Arbeit wurde durch eine Diplomarbeit von F. Grüneberger unterstützt). • Entwicklung von biomimetischen saccharidanalogen Strukturen, die als Matrizenmoleküle während des molekularen Prägens eingesetzt werden, um ein Polymer für die Anbindung von Monosacchariden wie etwa Fruktose oder Glukose zu generieren. Im ersten Teil der Arbeit wurde die Synthese und Charakterisierung von verschiedenen Boronsäurederivaten beschrieben. Die Charakterisierung der Bindungskonstanten wurde mittels isothermaler Titrationskalorimetrie durchgeführt. Dabei konnte im Einklang mit der Literatur gezeigt werden, dass Derivative, die zusätzlich mit einer Methylhydroxygruppe in ortho-Position zum Bor (Benzoboroxol) derivatisiert sind, eine meist zweifach höhere Bindungskonstante als gleich substituierte Arylboronsäurederivate aufweisen. Durch 1H-NMR-Spektroskopie und Massenspektrometrie mit Benzoboroxol und Glukose oder Fruktose konnten die Bindung weiter charakterisiert werden. Dabei zeigten die Ergebnisse der 1H-NMR-Spektroskopie, dass die Bindung bezogen auf NMR-Zeitskalen recht langsam stattfindet, da es zu einer Verbreiterung der Peaks kommt. Die Ergebnisse der Massenspektrometrie zeigen, dass hinsichtlich der Stöchiometrie der Binding verschiedene Komplexe möglich sind, was in ähnlicher Weise für Phenylboronsäure schon gezeigt wurde. Zusätzlich wurde in diesem Teil der Arbeit wurde die Elektrochemie von Alizarin Rot S untersucht, um den Farbstoff, der spektroskopisch schon für den Bindungsnachweis zwischen einem Boronsäurederivat und verschiedenen Zuckern beschrieben ist, auch elektrochemisch zu nutzen. Im zweiten Teil der Arbeit wurden verschiedene Anwendungen von den charakterisierten Boronsäuren in polymeren Netzwerken beschrieben. Dabei wurde zunächst ein Polystyrollatex mit Benzoboroxol modifiziert und die Bindung von Glukose oder Fruktose mittels isothermaler Titrationskalorimetrie und einem spektroskopischen Farbassay untersucht. Die Untersuchungen mittels isothermaler Titrationskalorimetrie (ITC) wurden vergleichend zu frei in Lösung befindlichem Benzoboroxol durchgeführt. Es wurde eine höhere Bindungskonstante für die modifizierten Nanopartikel ermittelt, was auf die Erhöhung der Entropie im System zurückzuführen ist. Dies kann durch eine mutivalente Bindung und einer einhergehenden erhöhten Wasserfreisetzung erklärt werden. Da es nicht möglich war, die Glukosebindung mittels ITC zu verfolgen, wurde zusätzlich ein spektroskopischer Assay bei pH 7.4. durchgeführt. Bei diesem wird die Bindung von Fruktose oder Glukose durch Freisetzung von Alizarin Rot S verfolgt. In diesem Zusammenhang konnte auch gezeigt werden, dass die Nanopartikel nach Sterilisation bei 121°C für 20 Minuten eine vergleichbare Bindung des Farbstoffes zeigen, was die Temperaturstabilität der Partikel unterstreicht. Da in diesem System die Bindung von Zuckern abhängig von der Affinität der Zucker zu den Boronsäuren bestimmt wird, wurden molekular geprägte Polymere synthetisiert, die eine Selektivität für bestimmte Zucker zeigen. Als Funktionsmonomer wurde 3-Methacrylamidobenzboroxol verwendet. Im Vergleich zu Polymeren, die mit 3-Vinylphenylboronsäure als literaturbekanntes Funktionsmonomer synthetisiert worden sind, zeigt sich bei pH 7.4 eine höhere Bindung von Fruktose an Benzoboroxolpolymere. In einem anderen geprägten Polymer wurden biomimetische (zuckeranaloge) Substanzen als Matrizenmolekül verwendet. Der Vorteil dieser Substanz ist die Bildung eines definierten Boronsäureesters, der als Templat-Funktionsmonomerkomplexes einpolymerisiert wird. Im Gegensatz dazu weist beispielsweise ein Boronsäureester der Glukose keine definierte Struktur auf. Der biomimetische Charakter wurde durch strukturelle Überlagerung mit schon publizierten Kristallstrukturen von Boronsäureestern von Glukose und Fruktose gezeigt. Das zugehörige molekular geprägte Polymer wurde mit Vinylphenylboronsäure synthetisiert und zeigt eine Bindung von Glukose und Fruktose, was durch die Strukturüberlagerungen vorhergesagt wurde. Zusammenfassend sind die wesentlichen wissenschaftlichen Ergebnisse: • Bindungskostanten von neuen Zucker-Benzoboroxolpaaren, • Eignung von ARS als elektrochemische Nachweissubstanz der Saccharidbindung • Die thermodynamische Charakterisierung der Bindung von Fruktose oder Glukose an Nanopartikel, die Benzoboroxol - modifziert sind und so bei pH 7.4 Zucker binden können • Einsatz von Benzoboroxol als Funktionsmonomer • die Synthese und Nutzung von biomimetischen zuckeranalogen Matrizenmolekülen für die Entwicklung von molekular geprägten Polymeren für die Glukosebindung. KW - Zuckererkennung KW - Glucose KW - physiolgischer pH KW - Boronsäure KW - Benzoboroxol KW - Saccharide Recognition KW - Glucose KW - physiological pH KW - boronic acid KW - benzoboroxole Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-52869 ER -