@article{TebaldiCharanMavliutovaetal.2017, author = {Tebaldi, Marli Luiza and Charan, Himanshu and Mavliutova, Liliia and B{\"o}ker, Alexander and Glebe, Ulrich}, title = {Dual-Stimuli Sensitive Hybrid Materials: Ferritin-PDMAEMA by Grafting-From Polymerization}, series = {Macromolecular chemistry and physics}, volume = {218}, journal = {Macromolecular chemistry and physics}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1352}, doi = {10.1002/macp.201600529}, pages = {6}, year = {2017}, abstract = {The combination of stimuli-responsive polymers and proteins that can transport drugs is a promising approach for drug delivery. The formation of ferritin-poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) conjugates by atom-transfer radical polymerization from the protein macroinitiator is described. PDMAEMA is a dual-stimuli-responsive polymer and the thermo- and pH-responsive properties of the resulting conjugates are studied in detail with dynamic light scattering (DLS). Additionally, it is demonstrated that the lower critical solution temperature (LCST) of the protein-polymer conjugates can be further adjusted by the ionic strength of the solution. The conjugates are also characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), matrix-assisted laser desorption ionization-time of flight (MALDI-ToF) mass spectrometry, and NMR spectroscopy. The obtained MALDI-ToF mass spectra are exceptional for protein-polymer conjugates and have not been so often reported.}, language = {en} } @article{ZuehlkeZenichowskiRiebeetal.2017, author = {Z{\"u}hlke, Martin and Zenichowski, Karl and Riebe, Daniel and Beitz, Toralf and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Subambient pressure electrospray ionization ion mobility spectrometry}, series = {International journal for ion mobility spectrometry : official publication of the International Society for Ion Mobility Spectrometry}, volume = {20}, journal = {International journal for ion mobility spectrometry : official publication of the International Society for Ion Mobility Spectrometry}, publisher = {Springer}, address = {Heidelberg}, issn = {1435-6163}, doi = {10.1007/s12127-017-0215-x}, pages = {47 -- 56}, year = {2017}, abstract = {The pressure dependence of sheath gas assisted electrospray ionization (ESI) was investigated based on two complementary experimental setups, namely an ESI-ion mobility (IM) spectrometer and an ESI capillary - Faraday plate setup housed in an optically accessible vacuum chamber. The ESI-IM spectrometer is capable of working in the pressure range between 300 and 1000 mbar. Another aim was the assessment of the analytical capabilities of a subambient pressure ESI-IM spectrometer. The pressure dependence of ESI was characterized by imaging the electrospray and recording current-voltage (I-U) curves. Qualitatively different behavior was observed in both setups. While the current rises continuously with the voltage in the capillary-plate setup, a sharp increase of the current was measured in the IM spectrometer above a pressure-dependent threshold voltage. The different character can be attributed to the detection of different species in both experiments. In the capillary-plate experiment, a multitude of charged species are detected while only desolvated ions attribute to the IM spectrometer signal. This finding demonstrates the utility of IM spectrometry for the characterization of ESI, since in contrast to the capillary-plate setup, the release of ions from the electrospray droplets can be observed. The I-U curves change significantly with pressure. An important result is the reduction of the maximum current with decreasing pressure. The connected loss of ionization efficiency can be compensated by a more efficient transfer of ions in the IM spectrometer at increased E/N. Thus, similar limits of detection could be obtained at 500 mbar and 1 bar.}, language = {en} } @article{LiebigSarhanSanderetal.2017, author = {Liebig, Ferenc and Sarhan, Radwan Mohamed and Sander, Mathias and Koopman, Wouter-Willem Adriaan and Schuetz, Roman and Bargheer, Matias and Koetz, Joachim}, title = {Deposition of Gold Nanotriangles in Large Scale Close-Packed Monolayers for X-ray-Based Temperature Calibration and SERS Monitoring of Plasmon-Driven Catalytic Reactions}, series = {ACS applied materials \& interfaces}, volume = {9}, journal = {ACS applied materials \& interfaces}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.7b07231}, pages = {20247 -- 20253}, year = {2017}, language = {en} } @article{SchuermannTanzerDabkowskaetal.2017, author = {Schuermann, Robin and Tanzer, Katrin and Dabkowska, Iwona and Denifl, Stephan and Bald, Ilko}, title = {Stability of the Parent Anion of the Potential Radiosensitizer 8-Bromoadenine Formed by Low-Energy (< 3 eV) Electron Attachment}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {121}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.7b02130}, pages = {5730 -- 5734}, year = {2017}, abstract = {8-Bromoadenine ((8Br)A) is a potential DNA radiosensitizer for cancer radiation therapy due to its efficient interaction with low-energy electrons (LEEs). LEEs are a short-living species generated during the radiation damage of DNA by high-energy radiation as it is applied in cancer radiation therapy. Electron attachment to (8Br)A in the gas phase results in a stable parent anion below 3 eV electron energy in addition to fragmentation products formed by resonant exocyclic bond cleavages. Density functional theory (DFT) calculations of the (8Br)A(-) anion reveal an exotic bond between the bromine and the C8 atom with a bond length of 2.6 angstrom, where the majority of the charge is located on bromine and the spin is mainly located on the C8 atom. The detailed understanding of such long-lived anionic states of nucleobase analogues supports the rational development of new therapeutic agents, in which the enhancement of dissociative electron transfer to the DNA backbone is critical to induce DNA strand breaks in cancerous tissue.}, language = {en} } @article{FudickarPavasheLinker2017, author = {Fudickar, Werner and Pavashe, Prashant and Linker, Torsten}, title = {Thiocarbohydrates on Gold Nanoparticles: Strong Influence of Stereocenters on Binding Affinity and Interparticle Forces}, series = {Chemistry - a European journal}, volume = {23}, journal = {Chemistry - a European journal}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201700846}, pages = {8685 -- 8693}, year = {2017}, abstract = {Carbohydrates carrying thiol groups at the C-2 position have been attached to gold nanoparticles (AuNPs) with stereocenters in close proximity to the surface for the first time. Their configurations can be clearly distinguished by the tendency of particle aggregation. AuNP surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), and IR spectroscopy indicate that the thiocarbohydrates replace citrate molecules at different rates, causing aggregation and eventually precipitation. A quantitative formulation of this aggregation process shows that reactivities can vary by several magnitudes. Adsorption isotherms and kinetics also demonstrate that the number of thiocarbohydrates varies by a factor of two. Molecular mechanics force field (MMFF) calculations reveal their relative orientations. Based on these models, the different binding behavior can be ascribed to attractive van der Waals forces and hydrogen bonds. Such interactions occur either between the carbohydrate and AuNPs, by lateral intermolecular forces at the surface, or by interparticle attraction, in analogy to cell-surface carbohydrates of biological recognition systems. Aggregation of NPs therefore act as an indicator to differentiate between various carbohydrates with defined configurations.}, language = {en} } @article{ArminDurrantShoaee2017, author = {Armin, Ardalan and Durrant, James R. and Shoaee, Safa}, title = {Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {121}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.7b04825}, pages = {13969 -- 13976}, year = {2017}, abstract = {Despite the myriad of organic donor:acceptor materials, only few systems have emerged in the life of organic solar cells to, exhibit considerable reduced bimolecular recombination, with respect to the random encounter rate given by the Langevin equation. Monte Carlo simulations have revealed that the rate constant of the formation of electron-hole bound states depends on the random encounter of opposite charges and is nearly given by the Langevin equation for the domain sizes relevant to efficient bulk heterojunction systems. Recently, three studies :suggested that charge transfer states dissociating much faster than their decay rate to the ground state, can result in reduced bimolecular recombination by lowering the recombination rate to the ground state as a loss pathway. A separate study identified another loss pathway and suggested that forbidden back electron transfer from triplet charge transfer states to triplet excitons is a key to achieving reduced recombination. Herein we further explain the reduced bimolecular recombination by investigating the limitations of these two proposals. By solving kinetic rate equations for a BHJ system with realistic rates, we show that both of these previously presented conditions must only be held at the same time fora system to exhibit non-Langevin behavior. We demonstrate that suppression of both of the parallel loss channels of singlet and triplet states can be achieved through increasing the dissociation rate of the charge transfer states; a crucial requirement to achieve a high charge carrier extraction efficiency.}, language = {en} } @article{PehLiedelTaubertetal.2017, author = {Peh, Eddie and Liedel, Clemens and Taubert, Andreas and Tauer, Klaus}, title = {Composition inversion to form calcium carbonate mixtures}, series = {CrystEngComm}, volume = {19}, journal = {CrystEngComm}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1466-8033}, doi = {10.1039/c7ce00433h}, pages = {3573 -- 3583}, year = {2017}, abstract = {Composition inversion takes place in equimolar solid mixtures of sodium or ammonium carbonate and calcium chloride with respect to the combination of anions and cations leading to the corresponding chloride and calcite in complete conversion. The transformation takes place spontaneously under a variety of different situations, even in a powdery mixture resting under ambient conditions. Powder X-ray diffraction data and scanning electron microscopy micrographs are presented to describe the course of the reaction and to characterize the reaction products. The incomplete reaction in the interspace between two compressed tablets of pure starting materials leads to an electric potential due to the presence of uncompensated charges.}, language = {en} } @article{KnechtReiterSchlaadetal.2017, author = {Knecht, Volker and Reiter, Guenter and Schlaad, Helmut and Reiter, Renate}, title = {Structure Formation in Langmuir Peptide Films As Revealed from Coarse-Grained Molecular Dynamics Simulations}, series = {Langmuir}, volume = {33}, journal = {Langmuir}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.7b01455}, pages = {6492 -- 6502}, year = {2017}, abstract = {Molecular dynamics simulations in conjunction with the Martini coarse-grained model have been used to investigate the (nonequilibrium) behavior of helical 22-residue poly(gamma-benzyl-L-glutamate) (PBLG) peptides at the water/vapor interface. Preformed PBLG mono- or bilayers homogeneously covering the water surface laterally collapse in tens of nanoseconds, exposing significant proportions of empty water surface. This behavior was also observed in recent AFM experiments at similar areas per monomer, where a complete coverage had been assumed in earlier work. In the simulations, depending on the area per monomer, either elongated clusters or fibrils form, whose heights (together with the portion of empty water surface) increase over time. Peptides tend to align with respect to the fiber axis or with the major principal axis of the cluster, respectively. The aspect ratio of the cluster observed is 1.7 and, hence, comparable to though somewhat smaller than the aspect ratio of the peptides in alpha-helical conformation, which is 2.2. The heights of the fibrils is 3 nm after 20 ns and increases to 4.5 nm if the relaxation time is increased by 2 orders of magnitude, in agreement with the experiment. Aggregates with heights of about 3 or 4.5 nm are found to correspond to local bi- or trilayer structures, respectively.}, language = {en} } @article{SungKochovskiZhangetal.2017, author = {Sung, Jian-Ke and Kochovski, Zdravko and Zhang, Wei-Yi and Kirmse, Holm and Lu, Yan and Antonietti, Markus and Yuan, Jiayin}, title = {General Synthetic Route toward Highly Dispersed Metal Clusters Enabled by Poly(ionic liquid)s}, series = {Journal of the American Chemical Society}, volume = {139}, journal = {Journal of the American Chemical Society}, publisher = {American Chemical Society}, address = {Washington}, issn = {0002-7863}, doi = {10.1021/jacs.7b03357}, pages = {8971 -- 8976}, year = {2017}, abstract = {The ability to synthesize a broad spectrum of metal clusters (MCs) with their size controllable on a subnanometer scale presents an enticing prospect for exploring nanosize-dependent properties. Here we report an innovative design of a capping agent from a polytriazolium poly(ionic liquid) (PIL) in a vesicular form in solution that allows for crafting a variety of MCs including transition metals, noble metals, and their bimetallic alloy with precisely controlled sizes (similar to 1 nm) and record-high catalytic performance. The ultrastrong stabilization power is a result of an unusual synergy between the conventional binding sites in the heterocyclic cations in PIL and an in situ generated polycarbene structure induced simultaneously to the reduction reaction.}, language = {en} } @article{KleinpeterWernerLinker2017, author = {Kleinpeter, Erich and Werner, Peter and Linker, Torsten}, title = {Synthesis and NMR spectroscopic conformational analysis of benzoic acid esters of mono- and 1,4-dihydroxycyclohexane, 4-hydroxycyclohexanone and the -ene analogue - The more polar the molecule the more stable the axial conformer}, series = {Tetrahedron}, volume = {73}, journal = {Tetrahedron}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2017.04.029}, pages = {3801 -- 3809}, year = {2017}, abstract = {para-Substituted benzoic acid esters of cyclohexanol, 1,4-dihydroxycyclohexane, 4-hydroxy-cyclohexanone and of the corresponding exo-methylene derivative were synthesized and the conformational equilibria of the cyclohexane skeleton studied by low temperature H-1 and C-13 NMR spectroscopy. The geometry optimized structures of the axial/equatorial chair conformers were computed at the DFT level of theory. Only one preferred conformation of the ester group was obtained for both the axial and the equatorial conformer, respectively. The content of the axial conformer increases with growing polarity of the 6-membered ring moiety; hereby, in addition, the effect of sp(2) hybridization/polarity of C(4)= O/C(4)= CH2 on the present conformational equilibria is critically evaluated. Another dynamic process could be studied, for the first time in this kind of compounds. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{MeiJaftaLauermannetal.2017, author = {Mei, Shilin and Jafta, Charl J. and Lauermann, Iver and Ran, Qidi and Kaergell, Martin and Ballauff, Matthias and Lu, Yan}, title = {Porous Ti4O7 Particles with Interconnected-Pore Structure as a High-Efficiency Polysulfide Mediator for Lithium-Sulfur Batteries}, series = {Advanced functional materials}, volume = {27}, journal = {Advanced functional materials}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.201701176}, pages = {10}, year = {2017}, abstract = {Multifunctional Ti4O7 particles with interconnected-pore structure are designed and synthesized using porous poly(styrene-b-2-vinylpyridine) particles as a template. The particles can work efficiently as a sulfur-host material for lithium-sulfur batteries. Specifically, the well-defined porous Ti4O7 particles exhibit interconnected pores in the interior and have a high-surface area of 592 m(2) g(-1); this shows the advantage of mesopores for encapsulating of sulfur and provides a polar surface for chemical binding with polysulfides to suppress their dissolution. Moreover, in order to improve the conductivity of the electrode, a thin layer of carbon is coated on the Ti4O7 surface without destroying its porous structure. The porous Ti4O7 and carbon-coated Ti4O7 particles show significantly improved electrochemical performances as cathode materials for Li-S batteries as compared with those of TiO2 particles.}, language = {en} } @article{KhademHilleLoehmannsroebenetal.2017, author = {Khadem, S. M. J. and Hille, Carsten and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Sokolov, Igor M.}, title = {Spot variation fluorescence correlation spectroscopy by data post-processing}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-05672-8}, pages = {1 -- 9}, year = {2017}, abstract = {Spot variation fluorescence correlation spectroscopy (SV-FCS) is a variant of the FCS techniques which may give useful information about the structural organisation of the medium in which the diffusion takes place. We show that the same results can be obtained by post-processing the photon count data from ordinary FCS measurements. By using this method, one obtains the fluorescence autocorrelation functions for sizes of confocal volume, which are effectively smaller than that of the initial FCS measurement. The photon counts of the initial experiment are first transformed into smooth intensity trace using kernel smoothing method or to a piecewise-continuous intensity trace using binning and then a non-linear transformation is applied to this trace. The result of this transformation mimics the photon count rate in an experiment performed with a smaller confocal volume. The applicability of the method is established in extensive numerical simulations and directly supported in in-vitro experiments. The procedure is then applied to the diffusion of AlexaFluor647-labeled streptavidin in living cells.}, language = {en} } @article{KleinpeterKoch2017, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Identification of mesomeric substructures by through-space NMR shieldings (TSNMRS). Trimethine cyanine/merocyanine-like or aromatic pi-electron delocalization?}, series = {Tetrahedron}, volume = {73}, journal = {Tetrahedron}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2017.05.062}, pages = {4265 -- 4274}, year = {2017}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of amino-substituted heteraromatic six-membered ring systems such as pyrylium/thiopyrylium analogues have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to quantify and visualize the existing aromaticity of the studied compounds. Due to strong conjugation of six-membered ring pi-electrons and lone pairs of the exo-cyclic amino substituents (restricted rotation about partial C,N double bonds) the interplay of still aromatic and already dominating trimethine cyanine/merocyanine-like substructures can be estimated. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{BogomolovaSeckerKoetzetal.2017, author = {Bogomolova, Anna and Secker, Christian and Koetz, Joachim and Schlaad, Helmut}, title = {Thermo-induced multistep assembly of double-hydrophilic block copolypeptoids in water}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {295}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-017-4044-6}, pages = {1305 -- 1312}, year = {2017}, abstract = {The aqueous solution behavior of thermoresponsive-hydrophilic block copolypeptoids, i.e., poly(N-(n-propyl)glycine) (x) -block-poly(N-methylglycine) (y) (x = 70; y = 23, 42, 76), in the temperature range of 20-45 A degrees C is studied. Turbidimetric analyses of the 0.1 wt\% aqueous solutions reveal two cloud points at T (cp)similar to 30 and 45 A degrees C and a clearing point in between at T (cl)similar to 42 A degrees C. Temperature-dependent dynamic light scattering (DLS) suggest that right above the first collapse temperature, single polymer molecules assemble into large structures which upon further heating, i.e., at the clearing point temperature, disassemble into micelle-like structures. Upon further heating, the aggregates start to grow again in size, as recognized by the second cloud point, through a crystallization process.}, language = {en} } @article{DaniTauberZhangetal.2017, author = {Dani, Alessandro and Tauber, Karoline and Zhang, Weiyi and Schlaad, Helmut and Yuan, Jiayin}, title = {Stable Covalently Photo-Crosslinked Poly(Ionic Liquid) Membrane with Gradient Pore Size}, series = {Macromolecular rapid communications}, volume = {38}, journal = {Macromolecular rapid communications}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201700167}, pages = {4}, year = {2017}, abstract = {Porous polyelectrolyte membranes stable in a highly ionic environment are obtained by covalent crosslinking of an imidazolium-based poly(ionic liquid). The crosslinking reaction involves the UV light-induced thiol-ene (click) chemistry, and the phase separation, occurring during the crosslinking step, generates a fully interconnected porous structure in the membrane. The porosity is on the order of the micrometer scale and the membrane shows a gradient of pore size across the membrane cross-section. The membrane can separate polystyrene latex particles of different size and undergoes actuation in contact with acetone due to the asymmetric porous structure.}, language = {en} } @article{WuGlebeBoeker2017, author = {Wu, Lei and Glebe, Ulrich and B{\"o}ker, Alexander}, title = {Fabrication of Thermoresponsive Plasmonic Core-Satellite Nanoassemblies with a Tunable Stoichiometry via Surface-Initiated Reversible Addition-Fragmentation Chain Transfer Polymerization from Silica Nanoparticles}, series = {Advanced materials interfaces}, volume = {4}, journal = {Advanced materials interfaces}, publisher = {Wiley}, address = {Hoboken}, issn = {2196-7350}, doi = {10.1002/admi.201700092}, pages = {10}, year = {2017}, abstract = {This work presents a fabrication of thermoresponsive plasmonic core-satellite nanoassemblies. The structure has a silica nanoparticle core surrounded by gold nanoparticle satellites using thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) chains as scaffolds. The thiol-terminated PNIPAM shell is densely grafted on the silica core via surface-initiated reversible addition-fragmentation chain transfer polymerization and used to anchor numerous gold nanoparticle satellites with a tunable stoichiometry. Below and above lower critical solution temperature, the chain conformation of PNIPAM reversibly changes between swollen and shrunken state. The reversible change of the polymer size varies the refractive index of the local medium surrounding the satellites and the distance between them. The two effects together lead to the thermoresponsive plasmonic properties of the nanoassemblies. Under different satellite densities, two distinctive plasmonic features appear.}, language = {en} } @article{GhaisariWinklhoferStrauchetal.2017, author = {Ghaisari, Sara and Winklhofer, Michael and Strauch, Peter and Klumpp, Stefan and Faivre, Damien}, title = {Magnetosome Organization in Magnetotactic Bacteria Unraveled by Ferromagnetic Resonance Spectroscopy}, series = {Biophysical journal}, volume = {113}, journal = {Biophysical journal}, publisher = {Cell Press}, address = {Cambridge}, issn = {0006-3495}, doi = {10.1016/j.bpj.2017.06.031}, pages = {637 -- 644}, year = {2017}, abstract = {Magnetotactic bacteria form assemblies of magnetic nanoparticles called magnetosomes. These magnetosomes are typically arranged in chains, but other forms of assemblies such as clusters can be observed in some species and genetic mutants. As such, the bacteria have developed as a model for the understanding of how organization of particles can influence the magnetic properties. Here, we use ferromagnetic resonance spectroscopy to measure the magnetic anisotropies in different strains of Magnetosprillum gtyphiswaldense MSR-1, a bacterial species that is amendable to genetic mutations. We combine our experimental results with a model describing the spectra. The model includes chain imperfections and misalignments following a Fisher distribution function, in addition to the intrinsic magnetic properties of the magnetosomes. Therefore, by applying the model to analyze the ferromagnetic resonance data, the distribution of orientations in the bulk sample can be retrieved in addition to the average magnetosome arrangement. In this way, we quantitatively characterize the magnetosome arrangement in both wild-type cells and Delta mamJ mutants, which exhibit differing magnetosome organization.}, language = {en} } @article{RietzeTitovLindneretal.2017, author = {Rietze, Clemens and Titov, Evgenii and Lindner, Steven and Saalfrank, Peter}, title = {Thermal isomerization of azobenzenes: on the performance of Eyring transition state theory}, series = {Journal of physics : Condensed matter}, volume = {29}, journal = {Journal of physics : Condensed matter}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0953-8984}, doi = {10.1088/1361-648X/aa75bd}, pages = {12}, year = {2017}, abstract = {The thermal Z -> E (back-) isomerization of azobenzenes is a prototypical reaction occurring in molecular switches. It has been studied for decades, yet its kinetics is not fully understood. In this paper, quantum chemical calculations are performed to model the kinetics of an experimental benchmark system, where a modified azobenzene (AzoBiPyB) is embedded in a metal-organic framework (MOF). The molecule can be switched thermally from cis to trans, under solvent-free conditions. We critically test the validity of Eyring transition state theory for this reaction. As previously found for other azobenzenes (albeit in solution), good agreement between theory and experiment emerges for activation energies and activation free energies, already at a comparatively simple level of theory, B3LYP/6-31G* including dispersion corrections. However, theoretical Arrhenius prefactors and activation entropies are in qualitiative disagreement with experiment. Several factors are discussed that may have an influence on activation entropies, among them dynamical and geometric constraints (imposed by the MOF). For a simpler model-Z -> E isomerization in azobenzene-a systematic test of quantum chemical methods from both density functional theory and wavefunction theory is carried out in the context of Eyring theory. Also, the effect of anharmonicities on activation entropies is discussed for this model system. Our work highlights capabilities and shortcomings of Eyring transition state theory and quantum chemical methods, when applied for the Z -> E (back-) isomerization of azobenzenes under solvent-free conditions.}, language = {en} } @article{AndrewsFergusonRangaswamyetal.2017, author = {Andrews, N. L. P. and Ferguson, T. and Rangaswamy, A. M. M. and Bernicky, A. R. and Henning, N. and Dudelzak, A. and Reich, Oliver and Barnes, Jack A. and Loock, Hans-Peter}, title = {Hadamard-Transform Fluorescence Excitation-Emission-Matrix Spectroscopy}, series = {Analytical chemistry}, volume = {89}, journal = {Analytical chemistry}, publisher = {American Chemical Society}, address = {Washington}, issn = {0003-2700}, doi = {10.1021/acs.analchem.7b02400}, pages = {8554 -- 8564}, year = {2017}, abstract = {We present a fluorescence excitation-emission-matrix spectrometer with superior data acquisition rates over previous instruments. Light from a white light emitting diode (LED) source is dispersed onto a digital micromirror array (DMA) and encoded using binary n-size Walsh functions ("barcodes"). The encoded excitation light is used to irradiate the liquid sample and its fluorescence is dispersed and detected using a conventional array spectrometer. After exposure to excitation light encoded in n different ways, the 2-dimensional excitation-emission-matrix (EEM) spectrum is obtained by inverse Hadamard transformation. Using this technique we examined the kinetics of the fluorescence of rhodamine B as a function of temperature and the acid-driven demetalation of chlorophyll into pheophytin-a. For these experiments, EEM spectra with 31 excitation channels and 2048 emission channels were recorded every 15 s. In total, data from over 3000 EEM spectra were included in this report. It is shown that the increase in data acquisition rate can be as high as [{n(n + 1)}/2]-fold over conventional EEM spectrometers. Spectral acquisition rates of more than two spectra per second were demonstrated.}, language = {en} } @article{ZhongMetwalliRawolleetal.2017, author = {Zhong, Qi and Metwalli, Ezzeldin and Rawolle, Monika and Kaune, Gunar and Bivigou Koumba, Achille Mayelle and Laschewsky, Andre and Papadakis, Christine M. and Cubitt, Robert and Wang, Jiping and M{\"u}ller-Buschbaum, Peter}, title = {Vacuum induced dehydration of swollen poly(methoxy diethylene glycol acrylate) and polystyrene-block-poly(methoxy diethylene glycol acrylate)-block-polystyrene films probed by in-situ neutron reflectivity}, series = {Polymer : the international journal for the science and technology of polymers}, volume = {124}, journal = {Polymer : the international journal for the science and technology of polymers}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-3861}, doi = {10.1016/j.polymer.2017.07.066}, pages = {263 -- 273}, year = {2017}, abstract = {The isothermal vacuum-induced dehydration of thin films made of poly(methoxy diethylene glycol acrylate) (PMDEGA), which were swollen under ambient conditions, is studied. The dehydration behavior of the homopolymer film as well as of a nanostructured film of the amphiphilic triblock copolymer polystyrene-block-poly(methoxy diethylene glycol acrylate)-block-polystyrene, abbreviated as PS-b-PMDEGA-b-PS, are probed, and compared to the thermally induced dehydration behavior of such thin thermo-responsive films when they pass through their LCST-type coil-to globule collapse transition. The dehydration kinetics is followed by in-situ neutron reflectivity measurements. Contrast results from the use of deuterated water. Water content and film thickness are significantly reduced during the process, which can be explained by Schott second order kinetics theory for both films. The water content of the dehydrated equilibrium state from this model is very close to the residual water content obtained from the final static measurements, indicating that residual water still remains in the film even after prolonged exposure to the vacuum. In the PS-b-PMDEGA-b-PS film that shows micro-phase separation, the hydrophobic PS domains modify the dehydration process by hindering the water removal, and thus retarding dehydration by about 30\%. Whereas residual water remains tightly bound in the PMDEGA domains, water is completely removed from the PS domains of the block copolymer film. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{ZhangWillaSunetal.2017, author = {Zhang, Weiyi and Willa, Christoph and Sun, Jian-Ke and Guterman, Ryan and Taubert, Andreas and Yuan, Jiayin}, title = {Polytriazolium poly(ionic liquid) bearing triiodide anions: Synthesis, basic properties and electrochemical behaviors}, series = {Polymer : the international journal for the science and technology of polymers}, volume = {124}, journal = {Polymer : the international journal for the science and technology of polymers}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-3861}, doi = {10.1016/j.polymer.2017.07.059}, pages = {246 -- 251}, year = {2017}, abstract = {4-Methyl-1-vinyl-1,2,4-triazolium triiodide ionic liquid and its polymer poly(4-methyl-1-vinyl-1,2,4-triazolium) triiodide were prepared for the first time from their iodide precursors via the reaction of iodide (I-) with elemental iodine (I-2). The change from iodide to triiodide (I-3(-)) was found to introduce particular variations in the physical properties of these two compounds, including lower melting point/glass transition temperature and altered solubility. The compounds were characterized by single-crystal X-ray diffraction, elemental analysis, and their electrochemical properties examined in solution and in the solid-state. Compared with their iodide analogues, the triiodide salts exhibited lower electrical impedance and higher current in the cyclic voltammetry. We found that poly(4-methyl-1,2,4-triazolium triiodide) was proven to be a promising solid polymer electrolyte candidate. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{VacogneSchlaad2017, author = {Vacogne, Charlotte D. and Schlaad, Helmut}, title = {Controlled ring-opening polymerization of alpha-amino acid N-carboxyanhydrides in the presence of tertiary amines}, series = {Polymer : the international journal for the science and technology of polymers}, volume = {124}, journal = {Polymer : the international journal for the science and technology of polymers}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-3861}, doi = {10.1016/j.polymer.2017.07.062}, pages = {203 -- 209}, year = {2017}, abstract = {The mechanism of the primary ammonium/tertiary amine-mediated ring-opening polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) was investigated. Kinetic analyses revealed that the normal amine mechanism (NAM) together with a dormant-active chain end equilibrium were responsible for the controlled nature of this polymerization pathway, but that the polymerization also proceeded via the activated monomer mechanism (AMM). Mixtures of primary amines (1 equiv) and tertiary amines (0-1.5 equiv) were therefore tested to confirm the co-existence of the NAM and AMM and determine the limits for a controlled polymerization. For tertiary amine molar fractions smaller than 0.8 equiv, the reaction times were greatly reduced (compared to primary amine-initiated polymerization) without compromising the control of the reaction. Hence, the polymerization of NCA can proceed in a controlled manner even when the AMM contributes to the overall chain growth mechanism. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{SchuermannTseringTanzeretal.2017, author = {Sch{\"u}rmann, Robin Mathis and Tsering, Thupten and Tanzer, Katrin and Denifl, Stephan and Kumar, S. V. K. and Bald, Ilko}, title = {Resonant Formation of Strand Breaks in Sensitized Oligonucleotides Induced by Low-Energy Electrons (0.5-9 eV)}, series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, volume = {56}, journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1433-7851}, doi = {10.1002/anie.201705504}, pages = {10952 -- 10955}, year = {2017}, abstract = {Halogenated nucleobases are used as radiosensitizers in cancer radiation therapy, enhancing the reactivity of DNA to secondary low-energy electrons (LEEs). LEEs induce DNA strand breaks at specific energies (resonances) by dissociative electron attachment (DEA). Although halogenated nucleobases show intense DEA resonances at various electron energies in the gas phase, it is inherently difficult to investigate the influence of halogenated nucleobases on the actual DNA strand breakage over the broad range of electron energies at which DEA can take place (<12 eV). By using DNA origami nanostructures, we determined the energy dependence of the strand break cross-section for oligonucleotides modified with 8-bromoadenine ((8Br)A). These results were evaluated against DEA measurements with isolated (8Br)A in the gas phase. Contrary to expectations, the major contribution to strand breaks is from resonances at around 7 eV while resonances at very low energy (<2 eV) have little influence on strand breaks.}, language = {en} } @article{YangDingKochovskietal.2017, author = {Yang, Guang and Ding, Hong-ming and Kochovski, Zdravko and Hu, Rongting and Lu, Yan and Ma, Yu-qiang and Chen, Guosong and Jiang, Ming}, title = {Highly Ordered Self-Assembly of Native Proteins into 1D, 2D, and 3D Structures Modulated by the Tether Length of Assembly-Inducing Ligands}, series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, volume = {56}, journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1433-7851}, doi = {10.1002/anie.201703052}, pages = {10691 -- 10695}, year = {2017}, abstract = {In nature, proteins self-assemble into various structures with different dimensions. To construct these nanostructures in laboratories, normally proteins with different symmetries are selected. However, most of these approaches are engineering-intensive and highly dependent on the accuracy of the protein design. Herein, we report that a simple native protein LecA assembles into one-dimensional nanoribbons and nanowires, two-dimensional nanosheets, and three-dimensional layered structures controlled mainly by small-molecule assembly-inducing ligands RnG (n = 1, 2, 3, 4, 5) with varying numbers of ethylene oxide repeating units. To understand the formation mechanism of the different morphologies controlled by the small-molecule structure, molecular simulations were performed from microscopic and mesoscopic view, which presented a clear relationship between the molecular structure of the ligands and the assembled patterns. These results introduce an easy strategy to control the assembly structure and dimension, which could shed light on controlled protein assembly.}, language = {en} } @article{RyabchunSakhnoStumpeetal.2017, author = {Ryabchun, Alexander and Sakhno, Oksana and Stumpe, Joachim and Bobrovsky, Alexey}, title = {Full-Polymer Cholesteric Composites for Transmission and Reflection Holographic Gratings}, series = {Advanced optical materials}, volume = {5}, journal = {Advanced optical materials}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {2195-1071}, doi = {10.1002/adom.201700314}, pages = {376 -- 379}, year = {2017}, abstract = {A new type of self-organized materials based on cholesteric networks filled with photoactive side-chain copolymer is being developed. Supramolecular helical structure of cholesteric polymer network resulting in the selective reflection is used as a photonic scaffold. Photochromic azobenzene-containing nematic copolymer is embedded in cholesteric scaffold and utilized as a photoactive media for optical pattering. 1D and 2D transmission diffraction gratings are successfully recorded in composite films by holographic technique. For the first time the possibility to create selective reflection gratings in cholesteric material mimicking the natural optical properties of cholesteric mesophase is demonstrated. That enables the coexistence of two selective gratings, where one has an intrinsic cholesteric periodic helical structure and the other is a holographic grating generated in photochromic polymer. The full-polymer composites provide high light-induced optical anisotropy due to effective photo-orientation of side-chain fragments of the azobenzene-containing liquid crystalline polymer, and prevent the degradation of the helical superstructure maintaining all optical properties of cholesteric mesophase. The proposed class of optical materials could be easily applied to a broad range of polymeric materials with specific functionality. The versatility of the adjustment and material preprogramming combined with high optical performance makes these materials a highly promising candidate for modern optical and photonic applications.}, language = {en} } @misc{IhmelsLinkerTrofimov2017, author = {Ihmels, Heiko and Linker, Torsten and Trofimov, Aleksei}, title = {Editorial}, series = {Journal of physical organic chemistry}, volume = {30}, journal = {Journal of physical organic chemistry}, publisher = {Wiley}, address = {Hoboken}, issn = {0894-3230}, doi = {10.1002/poc.3745}, pages = {1}, year = {2017}, language = {en} } @article{BauchKrtitschkaLinker2017, author = {Bauch, Marcel and Krtitschka, Angela and Linker, Torsten}, title = {Photooxygenation of oxygen-substituted naphthalenes}, series = {Journal of physical organic chemistry}, volume = {30}, journal = {Journal of physical organic chemistry}, publisher = {Wiley}, address = {Hoboken}, issn = {0894-3230}, doi = {10.1002/poc.3734}, pages = {6803 -- 6813}, year = {2017}, abstract = {The reaction of oxygen-substituted naphthalenes with singlet oxygen (O-1(2)) has been investigated, and labile endoperoxides have been isolated and characterized at -78 degrees C for the first time. Low-temperature kinetics by UV spectroscopy revealed that alkoxy and silyloxy substituents remarkably increase the rate of photooxygenations compared to 1,4-dimethylnaphthalene, whereas acyloxy-substituted acenes are inert towards O-1(2). The reactivities nicely correlate with HOMO energies and free activation energies, which we determined by density functional theory calculations. The lability of the isolated endoperoxides is due to their very fast back reaction to the corresponding naphthalenes even at -20 degrees C under release of O-1(2), making them to superior sources of this reactive species under very mild conditions. Finally, a carbohydrate-substituted naphthalene has been synthesized, which reacts reversibly with O-1(2) and might be applied for enantioselective oxidations in future work.}, language = {en} } @article{FudickarLinker2017, author = {Fudickar, Werner and Linker, Torsten}, title = {Synthesis of Pyridylanthracenes and Their Reversible Reaction with Singlet Oxygen to Endoperoxides}, series = {The journal of organic chemistry}, volume = {82}, journal = {The journal of organic chemistry}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/acs.joc.7b01765}, pages = {9258 -- 9262}, year = {2017}, abstract = {The ortho, meta, and para isomers of 9,10-dipyridylanthracene 1 have been synthesized and converted into their endoperoxides 1-O-2 upon oxidation with singlet oxygen. The kinetics of this reaction can be controlled by the substitution pattern and the solvent: in highly polar solvents, the meta isomer is the most reactive, whereas the ortho isomer is oxidized fastest in nonpolar solvents. Heating of the endoperoxides affords the parent anthracenes by release of singlet oxygen.}, language = {en} } @article{GrunwaldKellingHoldtetal.2017, author = {Grunwald, Nicolas and Kelling, Alexandra and Holdt, Hans-J{\"u}rgen and Schilde, Uwe}, title = {The crystal structure of 1,1\&\#8242;-bisisoquinoline, C18H12N2}, series = {Zeitschrift f{\"u}r Kristallographie : international journal for structural, physical and chemical aspects of crystalline materials ; New crystal structures}, volume = {232}, journal = {Zeitschrift f{\"u}r Kristallographie : international journal for structural, physical and chemical aspects of crystalline materials ; New crystal structures}, publisher = {De Gruyter}, address = {Berlin}, issn = {1433-7266}, doi = {10.1515/ncrs-2017-0088}, pages = {839 -- 841}, year = {2017}, abstract = {C18H12N2, tetragonal, I4(1)/a (no. 88), a = 13.8885(6) angstrom, c = 13.6718(6) angstrom, V = 2637.2(3) angstrom(3), Z = 8, R-gt(F) = 0.0295, wR(ref)(F-2) = 0.0854, T = 210 K.}, language = {en} } @article{MarcoDeyouGruhonjicetal.2017, author = {Marco, Makungu and Deyou, Tsegaye and Gruhonjic, Amra and Holleran, John and Duffy, Sandra and Heydenreich, Matthias and Firtzpatrick, Paul A. and Landberg, Goran and Koch, Andreas and Derese, Solomon and Pelletier, Jerry and Avery, Vicky M. and Erdelyi, Mate and Yenesew, Abiy}, title = {Pterocarpans and isoflavones from the root bark of Millettia micans and of Millettia dura}, series = {Phytochemistry letters}, volume = {21}, journal = {Phytochemistry letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1874-3900}, doi = {10.1016/j.phytol.2017.07.012}, pages = {216 -- 220}, year = {2017}, language = {en} } @article{WadeWoodColladoFregosoetal.2017, author = {Wade, Jessica and Wood, Sebastian and Collado-Fregoso, Elisa and Heeney, Martin and Durrant, James and Kim, Ji-Seon}, title = {Impact of Fullerene Intercalation on Structural and Thermal Properties of Organic Photovoltaic Blends}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {121}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.7b05893}, pages = {20976 -- 20985}, year = {2017}, abstract = {The performance of organic photovoltaic blend devices is critically dependent on the polymer:fullerene interface. These interfaces are expected to impact the structural and thermal properties of the polymer with regards to the conjugated backbone planarity and transition temperatures during annealing/cooling processes. Here, we report the impact of fullerene intercalation on structural and thermal properties of poly(2,5-bis(3-tetradecylthiophen-2-yOthieno[3,2-b]thiophene (PBTTT), a highly stable material known to exhibit liquid crystalline behavior. We undertake a detailed systematic study of the extent of intercalation in the PBTTT:fullerene blend, considering the use of four different fullerene derivatives and also varying the loading ratios. Resonant Raman spectroscopy allows morphology in situ during controlled heating and cooling. We find that small fullerene molecules readily intercalate into PBTTT crystallites, resulting in a planarization of the polymer backbone, but high fullerene loading ratios or larger fullerenes result in nonintercalated domains. During cooling from melt, nonintercalated blend films are found to return to their original morphology and reproduce all thermal transitions on cooling with minimal hysteresis. Intercalated blend films show significant hysteresis on cooling due to the crystallized fullerene attempting to reintercalate. The strongest hysteresis is for intercalated blend films with excess fullerene loading ratio, which form a distinct nanoribbon morphology and exhibit a reduced geminate recombination rate. These results reveal that careful consideration should be taken during device fabrication, as postdeposition thermal treatments significantly impact the charge generation and recombination dynamics.}, language = {en} } @article{YanFangWeigeletal.2017, author = {Yan, Wan and Fang, Liang and Weigel, Thomas and Behl, Marc and Kratz, Karl and Lendlein, Andreas}, title = {The influence of thermal treatment on the morphology in differently prepared films of a oligodepsipeptide based multiblock copolymer}, series = {Polymers for advanced technologies}, volume = {28}, journal = {Polymers for advanced technologies}, publisher = {Wiley}, address = {Hoboken}, issn = {1042-7147}, doi = {10.1002/pat.3953}, pages = {1339 -- 1345}, year = {2017}, abstract = {Degradable multiblock copolymers prepared from equal weight amounts of poly(epsilon-caprolactone)-diol (PCL-diol) and poly[oligo(3S-iso-butylmorpholine-2,5-dione)]-diol (PIBMD-diol), named PCL-PIBMD, provide a phase-segregated morphology. It exhibits a low melting temperature from PCL domains (T-m,T-PCL) of 382 degrees C and a high T-m,T-PIBMD of 170 +/- 2 degrees C with a glass transition temperature (T-g,T-PIBMD) at 42 +/- 2 degrees C from PIBMD domains. In this study, we explored the influence of applying different thermal treatments on the resulting morphologies of solution-cast and spin-coated PCL-PIBMD thin films, which showed different initial surface morphologies. Differential scanning calorimetry results and atomic force microscopy images after different thermal treatments indicated that PCL and PIBMD domains showed similar crystallization behaviors in 270 +/- 30 mu m thick solution-cast films as well as in 30 +/- 2 and 8 +/- 1nm thick spin-coated PCL-PIBMD films. Existing PIBMD crystalline domains highly restricted the generation of PCL crystalline domains during cooling when the sample was annealed at 180 degrees C. By annealing the sample above 120 degrees C, the PIBMD domains crystallized sufficiently and covered the free surface, which restricted the crystallization of PCL domains during cooling. The PCL domains can crystallize by hindering the crystallization of PIBMD domains via the fast vitrification of PIBMD domains when the sample was cooled/quenched in liquid nitrogen after annealing at 180 degrees C. These findings contribute to a better fundamental understanding of the crystallization mechanism of multi-block copolymers containing two crystallizable domains whereby the T-g of the higher melting domain type is in the same temperature range as the T-m of the lower melting domain type. Copyright (c) 2016 John Wiley \& Sons, Ltd.}, language = {en} } @article{PilusoLendleinNeffe2017, author = {Piluso, Susanna and Lendlein, Andreas and Neffe, Axel T.}, title = {Enzymatic action as switch of bulk to surface degradation of clicked gelatin-based networks}, series = {Polymers for advanced technologies}, volume = {28}, journal = {Polymers for advanced technologies}, publisher = {Wiley}, address = {Hoboken}, issn = {1042-7147}, doi = {10.1002/pat.3962}, pages = {1318 -- 1324}, year = {2017}, abstract = {Polymer degradation occurs under physiological conditions in vitro and in vivo, especially when bonds susceptible to hydrolysis are present in the polymer. Understanding of the degradation mechanism, changes of material properties over time, and overall rate of degradation is a necessary prerequisite for the knowledge-based design of polymers with applications in biomedicine. Here, hydrolytic degradation studies of gelatin-based networks synthesized by copper-catalyzed azide-alkyne cycloaddition reaction are reported, which were performed with or without addition of an enzyme. In all cases, networks with a stilbene as crosslinker proofed to be more resistant to degradation than when an octyl diazide was used. Without addition of an enzyme, the rate of degradation was ruled by the crosslinking density of the network and proceeded via a bulk degradation mechanism. Addition of Clostridium histolyticum collagenase resulted in a much enhanced rate of degradation, which furthermore occurred via surface erosion. The mesh size of the hydrogels (>7nm) was in all cases larger than the hydrodynamic radius of the enzyme (4.5nm) so that even in very hydrophilic networks with large mesh size enzymes may be used to induce a fast surface degradation mechanism. This observation is of general interest when designing hydrogels to be applied in the presence of enzymes, as the degradation mechanism and material performance are closely interlinked. Copyright (c) 2016 John Wiley \& Sons, Ltd.}, language = {en} } @article{HommesSchattmannNeffeAhmadetal.2017, author = {Hommes-Schattmann, Paul J. and Neffe, Axel T. and Ahmad, Bilal and Williams, Gareth R. and Vanneaux, Valerie and Menasche, Philippe and Kalfa, David and Lendlein, Andreas}, title = {RGD constructs with physical anchor groups as polymer co-electrospinnable cell adhesives}, series = {Polymers for advanced technologies}, volume = {28}, journal = {Polymers for advanced technologies}, publisher = {Wiley}, address = {Hoboken}, issn = {1042-7147}, doi = {10.1002/pat.3963}, pages = {1312 -- 1317}, year = {2017}, abstract = {The tissue integration of synthetic polymers can be promoted by displaying RGD peptides at the biointerface with the objective of enhancing colonization of the material by endogenous cells. A firm but flexible attachment of the peptide to the polymer matrix, still allowing interaction with receptors, is therefore of interest. Here, the covalent coupling of flexible physical anchor groups, allowing for temporary immobilization on polymeric surfaces via hydrophobic or dipole-dipole interactions, to a RGD peptide was investigated. For this purpose, a stearate or an oligo(ethylene glycol) (OEG) was attached to GRGDS in 51-69\% yield. The obtained RGD linker constructs were characterized by NMR, IR and MALDI-ToF mass spectrometry, revealing that the commercially available OEG and stearate linkers are in fact mixtures of similar compounds. The RGD linker constructs were co-electrospun with poly(p-dioxanone) (PPDO). After electrospinning, nitrogen could be detected on the surface of the PPDO fibers by X-ray photoelectron spectroscopy. The nitrogen content exceeded the calculated value for the homogeneous material mixture suggesting a pronounced presentation of the peptide on the fiber surface. Increasing amounts of RGD linker constructs in the electrospinning solution did not lead to a detection of an increased amount of peptide on the scaffold surface, suggesting inhomogeneous distribution of the peptide on the PPDO fiber surface. Human adipose-derived stem cells cultured on the patches showed similar viability as when cultured on PPDO containing pristine RGD. The fully characterized RGD linker constructs could serve as valuable tools for the further development of tissue-integrating polymeric scaffolds. Copyright (c) 2016 John Wiley \& Sons, Ltd.}, language = {en} } @article{ThierbachNeissGallandietal.2017, author = {Thierbach, Adrian and Neiss, Christian and Gallandi, Lukas and Marom, Noa and Koerzdoerfer, Thomas and Goerling, Andreas}, title = {Accurate Valence Ionization Energies from Kohn-Sham Eigenvalues with the Help of Potential Adjustors}, series = {Journal of chemical theory and computation}, volume = {13}, journal = {Journal of chemical theory and computation}, publisher = {American Chemical Society}, address = {Washington}, issn = {1549-9618}, doi = {10.1021/acs.jctc.7b00490}, pages = {4726 -- 4740}, year = {2017}, abstract = {An accurate yet computationally very efficient and formally well justified approach to calculate molecular ionization potentials is presented and tested. The first as well as higher ionization potentials are obtained as the negatives of the Kohn-Sham eigenvalues of the neutral molecule after adjusting the eigenvalues by a recently [Gorling Phys. Rev. B 2015, 91, 245120] introduced potential adjustor for exchange-correlation potentials. Technically the method is very simple. Besides a Kohn-Sham calculation of the neutral molecule, only a second Kohn-Sham calculation of the cation is required. The eigenvalue spectrum of the neutral molecule is shifted such that the negative of the eigenvalue of the highest occupied molecular orbital equals the energy difference of the total electronic energies of the cation minus the neutral molecule. For the first ionization potential this simply amounts to a Delta SCF calculation. Then, the higher ionization potentials are obtained as the negatives of the correspondingly shifted Kohn-Sham eigenvalues. Importantly, this shift of the Kohn-Sham eigenvalue spectrum is not just ad hoc. In fact, it is formally necessary for the physically correct energetic adjustment of the eigenvalue spectrum as it results from ensemble density-functional theory. An analogous approach for electron affinities is equally well obtained and justified. To illustrate the practical benefits of the approach, we calculate the valence ionization energies of test sets of small- and medium-sized molecules and photoelectron spectra of medium-sized electron acceptor molecules using a typical semilocal (PBE) and two typical global hybrid functionals (B3LYP and PBE0). The potential adjusted B3LYP and PBE0 eigenvalues yield valence ionization potentials that are in very good agreement with experimental values, reaching an accuracy that is as good as the best G(0)W(0) methods, however, at much lower computational costs. The potential adjusted PBE eigenvalues result in somewhat less accurate ionization energies, which, however, are almost as accurate as those obtained from the most commonly used G(0)W(0) variants.}, language = {en} } @article{FarhanRudolphNoecheletal.2017, author = {Farhan, Muhammad and Rudolph, Tobias and N{\"o}chel, Ulrich and Yan, Wan and Kratz, Karl and Lendlein, Andreas}, title = {Noncontinuously Responding Polymeric Actuators}, series = {ACS applied materials \& interfaces}, volume = {9}, journal = {ACS applied materials \& interfaces}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.7b11316}, pages = {33559 -- 33564}, year = {2017}, abstract = {Reversible movements of current polymeric actuators stem from the continuous response to signals from a controlling unit, and subsequently cannot be interrupted without stopping or eliminating the input trigger. Here, we present actuators based on cross-linked blends of two crystallizable polymers capable of pausing their movements in a defined manner upon continuous cyclic heating and cooling. This noncontinuous actuation can be adjusted by varying the applied heating and cooling rates. The feasibility of these devices for technological applications was shown in a 140 cycle experiment of free-standing noncontinuous shape shifts, as well as by various demonstrators.}, language = {en} } @article{LoncaricFuchselJuaristietal.2017, author = {Loncaric, Ivor and Fuchsel, Gernot and Juaristi, J. I. and Saalfrank, Peter}, title = {Strong Anisotropic Interaction Controls Unusual Sticking and Scattering of CO at Ru(0001)}, series = {Physical review letters}, volume = {119}, journal = {Physical review letters}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.146101}, pages = {5}, year = {2017}, abstract = {Complete sticking at low incidence energies and broad angular scattering distributions at higher energies are often observed in molecular beam experiments on gas-surface systems which feature a deep chemisorption well and lack early reaction barriers. Although CO binds strongly on Ru(0001), scattering is characterized by rather narrow angular distributions and sticking is incomplete even at low incidence energies. We perform molecular dynamics simulations, accounting for phononic (and electronic) energy loss channels, on a potential energy surface based on first-principles electronic structure calculations that reproduce the molecular beam experiments. We demonstrate that the mentioned unusual behavior is a consequence of a very strong rotational anisotropy in the molecule-surface interaction potential. Beyond the interpretation of scattering phenomena, we also discuss implications of our results for the recently proposed role of a precursor state for the desorption and scattering of CO from ruthenium.}, language = {en} } @article{MondalHovestadtDeyetal.2017, author = {Mondal, Suvendu Sekhar and Hovestadt, Maximilian and Dey, Subarna and Paula, Carolin and Glomb, Sebastian and Kelling, Alexandra and Schilde, Uwe and Janiak, Christoph and Hartmann, Martin and Holdt, Hans-J{\"u}rgen}, title = {Synthesis of a partially fluorinated ZIF-8 analog for ethane/ethene separation}, series = {CrystEngComm}, volume = {19}, journal = {CrystEngComm}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1466-8033}, doi = {10.1039/c7ce01438d}, pages = {5882 -- 5891}, year = {2017}, abstract = {The separation of ethane/ethene mixtures (as well as other paraffin/olefin mixtures) is one of the most important but challenging processes in the petrochemical industry. In this work, we report the synthesis of ZIF-318, isostructural to ZIF-8 but built from the mixed linkers of 2-methylimidazole (L1) and 2-trifluoromethylimidazole (L2) (ZIF-318 = [(Zn(L1)(L2)](n)). The synthesis has been optimized to proceed without ZnO-formation. Using only the L2 linker under solvothermal conditions afforded ZnO-embedded in the H-bonded and non-porous coordination polymer ZnO@[Zn-2(L2)(2)(HCOO)(OH)](n). The slight differences in the size of the substituents (-CH3 vs. -CF3) possibly in combination with different electronic inductive effects led to small but significant changes to the pore size and properties respectively, though the effective pore opening (aperture) size of ZIF-318 remained the same in comparison with ZIF-8. ZIF-318 is chemically (boiling water, methanol, benzene, and wide pH range at room temperature for 1 day), thermally (up to 310 degrees C) stable, and more hydrophobic than ZIF-8 which is proven by contact angle measurement. ZIF-318 can be activated for N-2, CO2, CH4, H-2, ethane, ethane, propane, and propene gases sorptions. Consequently, in breakthrough experiments, the ethane/ethene mixtures can be separated.}, language = {en} } @article{HovestadtBendtMondaletal.2017, author = {Hovestadt, Maximilian and Bendt, Stephan and Mondal, Suvendu Sekhar and Behrens, Karsten and Reif, Florian and Dopken, Merle and Holdt, Hans-J{\"u}rgen and Keil, Frerich J. and Hartmann, Martin}, title = {Experimental and Theoretical Analysis of the Influence of Different Linker Molecules in Imidazolate Frameworks Potsdam (IFP-n) on the Separation of Olefin-Paraffin Mixtures}, series = {Langmuir}, volume = {33}, journal = {Langmuir}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.7b02016}, pages = {11170 -- 11179}, year = {2017}, abstract = {Four metal organic frameworks with similar topology but different chemical environment inside the pore structure, namely, IFP-1, IFP-3, IFP-5, and IFP-7, have been investigated with respect to the separation potential for olefin paraffin mixtures as well as the influence of the different linkers on adsorption properties using experiments and Monte Carlo simulations. All IFP structures show a higher adsorption of ethane compared to ethene with the exception of IFP-7 which shows no selectivity in breakthrough experiments. For propane/propane separation, all adsorbents show a higher adsorption for the olefin. The experimental results agree quite well with the simulated values except for the IFP-7, which is presumably due to the flexibility of the structure. Moreover, the experimental and simulated isotherms were confirmed with breakthrough experiments that render IFP-1, IFP-3, and IFP-5 as suitable for the purification of ethene from ethane.}, language = {en} } @article{HentrichBrezesinskiKuebeletal.2017, author = {Hentrich, Doreen and Brezesinski, Gerald and Kuebel, Christian and Bruns, Michael and Taubert, Andreas}, title = {Cholesteryl Hemisuccinate Monolayers Efficiently Control Calcium Phosphate Nucleation and Growth}, series = {Crystal growth \& design : integrating the fields of crystal engineering and crystal growth for the synthesis and applications of new materials}, volume = {17}, journal = {Crystal growth \& design : integrating the fields of crystal engineering and crystal growth for the synthesis and applications of new materials}, publisher = {American Chemical Society}, address = {Washington}, issn = {1528-7483}, doi = {10.1021/acs.cgd.7b00753}, pages = {5764 -- 5774}, year = {2017}, abstract = {The article describes the phase behavior of cholesteryl hemisuccinate at the air-liquid interface and its effect on calcium phosphate (CP) mineralization. The amphiphile forms stable monolayers with phase transitions at the air-liquid interface from a gas to a tilted liquid-condensed (TLC) and finally to an untilted liquid-condensed (ULC) phase. CP mineralization beneath these monolayers leads to crumpled CP layers made from individual plates. The main crystal phase is octacalcium phosphate (OCP) along with a minor fraction of hydroxyapatite (HAP), as confirmed by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, bright field transmission electron microscopy, and electron diffraction.}, language = {en} } @article{WangNaolouMaetal.2017, author = {Wang, Weiwei and Naolou, Toufik and Ma, Nan and Deng, Zijun and Xu, Xun and Mansfeld, Ulrich and Wischke, Christian and Gossen, Manfred and Neffe, Axel T. and Lendlein, Andreas}, title = {Polydepsipeptide Block-Stabilized Polyplexes for Efficient Transfection of Primary Human Cells}, series = {Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences}, volume = {18}, journal = {Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences}, publisher = {American Chemical Society}, address = {Washington}, issn = {1525-7797}, doi = {10.1021/acs.biomac.7b01034}, pages = {3819 -- 3833}, year = {2017}, abstract = {The rational design of a polyplex gene carrier aims to balance maximal effectiveness of nucleic acid transfection into cells with minimal adverse effects. Depsipeptide blocks with an M (n) similar to 5 kDa exhibiting strong physical interactions were conjugated with PEI moieties (2.5 or 10 kDa) to di- and triblock copolymers. Upon nanoparticle formation and complexation with DNA, the resulting polyplexes (sizes typically 60-150 nm) showed remarkable stability compared to PEI-only or lipoplex and facilitated efficient gene delivery. Intracellular trafficking was visualized by observing fluorescence-labeled pDNA and highlighted the effective cytoplasmic uptake of polyplexes and release of DNA to the perinuclear space. Specifically, a triblock copolymer with a middle depsipeptide block and two 10 kDa PEI swallowtail structures mediated the highest levels of transgenic VEGF secretion in mesenchymal stem cells with low cytotoxicity. These nanocarriers form the basis for a delivery platform technology, especially for gene transfer to primary human cells.}, language = {en} } @article{KlaussConradHille2017, author = {Klauß, Andr{\´e} and Conrad, Florian and Hille, Carsten}, title = {Binary phase masks for easy system alignment and basic aberration sensing with spatial light modulators in STED microscopy}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-15967-5}, pages = {11}, year = {2017}, language = {en} } @article{WessigSchulzePfennigetal.2017, author = {Wessig, Pablo and Schulze, Tanja and Pfennig, Alexandra and Weidner, Steffen M. and Prentzel, Sascha and Schlaad, Helmut}, title = {Thiol-ene polymerization of oligospiroketal rods}, series = {Polymer Chemistry}, volume = {8}, journal = {Polymer Chemistry}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1759-9954}, doi = {10.1039/c7py01569k}, pages = {6879 -- 6885}, year = {2017}, abstract = {The nucleophilic thiol-ene (thia-Michael) reaction between molecular rods bearing terminal thiols and bis-maleimides was investigated. The molecular rods have oligospiroketal (OSK) and oligospirothioketal (OSTK) backbones. Contrary to the expectations, cyclic oligomers were always obtained instead of linear rigid-rod polymers. Replacing the OS(T)K rods with a flexible chain yielded polymeric products, suggesting that the OS(T) K structure is responsible for the formation of cyclic products. The reason for the preferred formation of cyclic products is due to the presence of folded conformations, which have already been described for articulated rods.}, language = {en} } @article{KleinpeterHeydenreichKochetal.2017, author = {Kleinpeter, Erich and Heydenreich, Matthias and Koch, Andreas and Krtitschka, Angela and Kr{\"u}ger, Tobias and Linker, Torsten}, title = {NMR spectroscopic conformational analysis of 4-methylene-cyclohexyl pivalateThe effect of sp(2) hybridization}, series = {Magnetic resonance in chemistry}, volume = {55}, journal = {Magnetic resonance in chemistry}, publisher = {Wiley}, address = {Hoboken}, issn = {0749-1581}, doi = {10.1002/mrc.4630}, pages = {1073 -- 1078}, year = {2017}, abstract = {The conformational equilibrium of the axial/equatorial conformers of 4-methylene-cyclohexyl pivalate is studied by dynamic NMR spectroscopy in a methylene chloride/freon mixture. At 153K, the ring interconversion gets slow on the nuclear magnetic resonance timescale, the conformational equilibrium (-G degrees) can be examined, and the barrier to ring interconversion (G(\#)) can be determined. The structural influence of sp(2) hybridization on both G degrees and G(\#) of the cyclohexyl moiety can be quantified.}, language = {en} } @article{SchwarzeMertensMuelleretal.2017, author = {Schwarze, Thomas and Mertens, Monique and Mueller, Peter and Riemer, Janine and Wessig, Pablo and Holdt, Hans-J{\"u}rgen}, title = {Highly K+-Selective Fluorescent Probes for Lifetime Sensing of K+ in Living Cells}, series = {Chemistry - a European journal}, volume = {23}, journal = {Chemistry - a European journal}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201704368}, pages = {17186 -- 17190}, year = {2017}, abstract = {The new K+-selective fluorescent probes 1 and 2 were obtained by Cu-I-catalyzed 1,3-dipolar azide alkyne cycloaddition (CuAAC) reactions of an alkyne-substituted [1,3]dioxolo[4,5-f][1,3]benzodioxole (DBD) ester fluorophore with azido-functionalized N-phenylaza-18-crown-6 ether and N-(o-isopropoxy) phenylaza-18-crown-6 ether, respectively. Probes 1 and 2 allow the detection of K+ in the presence of Na+ in water by fluorescence enhancement (2.2 for 1 at 2000mm K+ and 2.5 for 2 at 160mm K+). Fluorescence lifetime measurements in the absence and presence of K+ revealed bi-exponential decay kinetics with similar lifetimes, however with different proportions changing the averaged fluorescence decay times ((f(av))). For 1 a decrease of (f(av)) from 12.4 to 9.3ns and for 2 an increase from 17.8 to 21.8ns was observed. Variation of the substituent in ortho position of the aniline unit of the N-phenylaza-18-crown-6 host permits the modulation of the K-d value for a certain K+ concentration. For example, substitution of H in 1 by the isopropoxy group (2) decreased the K-d value from >300mm to 10mm. 2 was chosen for studying the efflux of K+ from human red blood cells (RBC). Upon addition of the Ca2+ ionophor ionomycin to a RBC suspension in a buffer containing Ca2+, the fluorescence of 2 slightly rose within 10min, however, after 120min a significant increase was observed.}, language = {en} } @article{DiPietroErdmannCarpenteretal.2017, author = {Di Pietro, Riccardo and Erdmann, Tim and Carpenter, Joshua H. and Wang, Naixiang and Shivhare, Rishi Ramdas and Formanek, Petr and Heintze, Cornelia and Voit, Brigitte and Neher, Dieter and Ade, Harald W. and Kiriy, Anton}, title = {Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility}, series = {Chemistry of materials : a publication of the American Chemical Society}, volume = {29}, journal = {Chemistry of materials : a publication of the American Chemical Society}, publisher = {American Chemical Society}, address = {Washington}, issn = {0897-4756}, doi = {10.1021/acs.chemmater.7b04423}, pages = {10220 -- 10232}, year = {2017}, language = {en} } @article{ShainyanKirpichenkoKleinpeter2017, author = {Shainyan, Bagrat A. and Kirpichenko, Svetlana V. and Kleinpeter, Erich}, title = {Conformational Preferences of the Phenyl Group in 1-Phenyl-1-X-1-silacyclo-hexanes (X = MeO, HO) and 3-Phenyl-3-X-3-silatetrahydropyrans (X = HO, H) by Low Temperature C-13 NMR Spectroscopy and Theoretical Calculations}, series = {The journal of organic chemistry}, volume = {82}, journal = {The journal of organic chemistry}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/acs.joc.7b02505}, pages = {13414 -- 13422}, year = {2017}, abstract = {New Si-phenyl-substituted silacyclohexanes and 3-silatetrahydropyrans have been synthesized and studied with respect to the conformational equilibria of the heterosix-membered ring by low temperature C-13 NMR spectroscopy and quantum chemical calculations. For 1-methoxy-1-phenylsilacyclohexane 1 and 3-phenyl-3-silatetrahydropyran 4 the conformational equilibria could be frozen and assigned. The Ph-ax reversible arrow Ph-eq equilibrium constants at 103 K are 2.21 for 1 and 4.59 for 4. In complete agreement with former studies of similar silicon compounds, molecules 1 and 4 prefer to adopt the Pheq conformation. The conformational equilibria of 1-hydroxy-1-phenylsilacydohexane 2 and 3-hydroxy-3-phenyl-3-silatetrahydropyran 3 could not be frozen at 100 K and proved to be heavily one-sided (if not anancomeric). Obviously, there is a general trend of predominance of Phax conformer in the gas phase and of Pheq in solution. For the isolated molecules of silanols 2 and 3, calculations allowed to explain the axial predominance of the phenyl group by a larger polarization of the Si-Ph than of the Si-O bond in the Phax conformer and additional destabilization of 3-Ph-eq conformer by repulsion of unidirectional dipoles of the endocyclic oxygen lone pair and of the highly polar axial Si-O bond.}, language = {en} } @article{AbouserieZehbeMetzneretal.2017, author = {Abouserie, Ahed and Zehbe, Kerstin and Metzner, Philipp and Kelling, Alexandra and G{\"u}nter, Christina and Schilde, Uwe and Strauch, Peter and K{\"o}rzd{\"o}rfer, Thomas and Taubert, Andreas}, title = {Alkylpyridinium Tetrahalidometallate Ionic Liquids and Ionic Liquid Crystals: Insights into the Origin of Their Phase Behavior}, series = {European journal of inorganic chemistry : a journal of ChemPubSoc Europe}, journal = {European journal of inorganic chemistry : a journal of ChemPubSoc Europe}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-1948}, doi = {10.1002/ejic.201700826}, pages = {5640 -- 5649}, year = {2017}, abstract = {Six N-alkylpyridinium salts [CnPy](2)[MCl4] (n = 4 or 12 and M = Co, Cu, Zn) were synthesized, and their structure and thermal properties were studied. The [C4Py](2)[MCl4] compounds are monoclinic and crystallize in the space group P2(1)/n. The crystals of the longer chain analogues [C12Py](2)[MCl4] are triclinic and crystallize in the space group P (1) over bar. Above the melting temperature, all compounds are ionic liquids (ILs). The derivatives with the longer C12 chain exhibit liquid crystallinity and the shorter chain compounds only show a melting transition. Consistent with single-crystal analysis, electron paramagnetic resonance spectroscopy suggests that the [CuCl4](2-) ions in the Cu-based ILs have a distorted tetrahedral geometry.}, language = {en} } @article{AbouserieZehbeMetzneretal.2017, author = {Abouserie, Ahed and Zehbe, Kerstin and Metzner, Philipp and Kelling, Alexandra and G{\"u}nter, Christina and Schilde, Uwe and Strauch, Peter and K{\"o}rzd{\"o}rfer, Thomas and Taubert, Andreas}, title = {Alkylpyridinium Tetrahalidometallate Ionic Liquids and Ionic Liquid Crystals: Insights into the Origin of Their Phase Behavior}, series = {European journal of inorganic chemistry : a journal of ChemPubSoc Europe}, journal = {European journal of inorganic chemistry : a journal of ChemPubSoc Europe}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-1948}, doi = {10.1002/ejic.201700826}, pages = {5640 -- 5649}, year = {2017}, abstract = {Six N-alkylpyridinium salts [CnPy](2)[MCl4] (n = 4 or 12 and M = Co, Cu, Zn) were synthesized, and their structure and thermal properties were studied. The [C4Py](2)[MCl4] compounds are monoclinic and crystallize in the space group P2(1)/n. The crystals of the longer chain analogues [C12Py](2)[MCl4] are triclinic and crystallize in the space group P (1) over bar. Above the melting temperature, all compounds are ionic liquids (ILs). The derivatives with the longer C12 chain exhibit liquid crystallinity and the shorter chain compounds only show a melting transition. Consistent with single-crystal analysis, electron paramagnetic resonance spectroscopy suggests that the [CuCl4](2-) ions in the Cu-based ILs have a distorted tetrahedral geometry.}, language = {en} } @phdthesis{Doriti2017, author = {Doriti, Afroditi}, title = {Sustainable bio-based poly-N-glycines and polyesters}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-411286}, school = {Universit{\"a}t Potsdam}, pages = {vi, 117}, year = {2017}, abstract = {Nowadays, the need to protect the environment becomes more urgent than ever. In the field of chemistry, this translates to practices such as waste prevention, use of renewable feedstocks, and catalysis; concepts based on the principles of green chemistry. Polymers are an important product in the chemical industry and are also in the focus of these changes. In this thesis, more sustainable approaches to make two classes of polymers, polypeptoids and polyesters, are described. Polypeptoids or poly(alkyl-N-glycines) are isomers of polypeptides and are biocompatible, as well as degradable under biologically relevant conditions. In addition to that, they can have interesting properties such as lower critical solution temperature (LCST) behavior. They are usually synthesized by the ring opening polymerization (ROP) of N-carboxy anhydrides (NCAs), which are produced with the use of toxic compounds (e.g. phosgene) and which are highly sensitive to humidity. In order to avoid the direct synthesis and isolation of the NCAs, N-phenoxycarbonyl-protected N-substituted glycines are prepared, which can yield the NCAs in situ. The conditions for the NCA synthesis and its direct polymerization are investigated and optimized for the simplest N-substituted glycine, sarcosine. The use of a tertiary amine in less than stoichiometric amounts compared to the N-phenoxycarbonyl--sarcosine seems to accelerate drastically the NCA formation and does not affect the efficiency of the polymerization. In fact, well defined polysarcosines that comply to the monomer to initiator ratio can be produced by this method. This approach was also applied to other N-substituted glycines. Dihydroxyacetone is a sustainable diol produced from glycerol, and has already been used for the synthesis of polycarbonates. Here, it was used as a comonomer for the synthesis of polyesters. However, the polymerization of dihydroxyacetone presented difficulties, probably due to the insolubility of the macromolecular chains. To circumvent the problem, the dimethyl acetal protected dihydroxyacetone was polymerized with terephthaloyl chloride to yield a soluble polymer. When the carbonyl was recovered after deprotection, the product was insoluble in all solvents, showing that the carbonyl in the main chain hinders the dissolution of the polymers. The solubility issue can be avoided, when a 1:1 mixture of dihydroxyacetone/ ethylene glycol is used to yield a soluble copolyester.}, language = {en} } @phdthesis{Braun2017, author = {Braun, Max}, title = {Heterogeneous Catalysis for the Conversion of Fructose to Chemicals and Fuel in a Continuous Flow Process}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-410370}, school = {Universit{\"a}t Potsdam}, pages = {151}, year = {2017}, abstract = {Die Umsetzung von Zucker (Kohlenhydrate) in einem kontinuierlichen Prozess er{\"o}ffnet M{\"o}glichkeiten der Synthese diverser Chemikalien und Treibstoff aus erneuerbaren Ressourcen, welche heute {\"u}berwiegend aus fossilen Quellen stammen. Passend zum Konzept der Bioraffinerie und der „gr{\"u}nen Chemie", liegt der Fokus dieser Arbeit auf der Umsetzung von in Ethanol gel{\"o}ster Fruktose in einem kontinuierlichen Verfahren, mit Hilfe eigens entwickelter heterogener Katalysatoren. Die Dehydratisierung von Fruktose wird mit einem heterogenen S{\"a}urekatalysator realisiert, w{\"a}hrend die Folgeprodukte mittels einer Hydrodesoxygenierung umgesetzt werden. F{\"u}r den zweiten Schritt kommen Metallkatalysatoren auf Basis von Nickel und Wolframcarbid (WC) zum Einsatz, wodurch der Einsatz teurer Edelmetalle vermieden werden kann. Hauptprodukte des zweistufigen Verfahrens sind 2,5-Dimethylfuran (DMF) und Ethyllevulinat (EL). Beide Molek{\"u}le sind vielversprechende alternative Treibstoffe, bzw. k{\"o}nnen gebr{\"a}uchlichen Treibstoffen beigemischt werden, um deren Einsatz zu reduzieren und schrittweise zu substituieren. Alternativ k{\"o}nnen die Zwischenprodukte der Dehydratisierung, sowie DMF und EL weiter zu Chemikalien umgesetzt werden, welche in der Polymersynthese, als L{\"o}sungsmittel oder als Grundchemikalien eingesetzt werden k{\"o}nnen. Die Entwicklung der jeweiligen Katalysatoren f{\"u}r Dehydratisierungs- und Hydrodesoxygenierungsreaktionen erfolgt auf Basis von karbonisierter Biomasse, sowie Wolframcarbid. Die jeweiligen Reaktivit{\"a}ten werden durch Standardreaktionen getestet, wobei sich Wolframcarbid in Nanopartikelform, in Kombination mit Wasserstoff als sehr aktiv erwiesen hat. Der selbst entwickelte aktivierte Kohlenstoff, das kommerzielle Amberlyst 15, sowie Wolframcarbid mit zus{\"a}tzlichen Nickel-Nanopartikeln werden f{\"u}r weiterf{\"u}hrende Reaktionen in einem kontinuierlichen Prozess herangezogen und kombiniert. Um den Umsatz von Fruktose zu DMF in einer „zwei Reaktoren Anlage" zu erm{\"o}glichen, wird eine Erweiterung eines kommerziellen Reaktorsystems um einen weiteren Reaktor vorgenommen. Die Verweilzeit in der Reaktoranlage betr{\"a}gt somit ca. 14 Minuten, wobei 11 Minuten auf die erste S{\"a}ule (Dehydratisierung) und 3 Minuten auf die zweite S{\"a}ule (Hydrodesoxygenierung) entfallen. In diesem kontinuierlichen und zweistufigen System lassen sich Ausbeuten von 38.5 \% DMF und 47 \% EL erzielen. Ein kontinuierlicher Lauf von sieben Stunden zeigt die Stabilit{\"a}t der eingesetzten Katalysatoren, auch wenn eine geringe Deaktivierung des Dehydratisierungskatalysators beobachtet werden kann. Der Ni@WC Katalysator zeigte hingegen keine Abnahme der Nickel Konzentration und somit kommt es zu keiner Auswaschung des Metalls. Das gebildete EL wurde hingegen nicht umgesetzt und verbleibt unver{\"a}ndert in L{\"o}sung. Das zweistufige System wurde schließlich in einem Mischkatalysatorsystem kombiniert, wobei auf aktivierten und sulfonierten Kohlenstoff zur{\"u}ckgegriffen wurde. Dieser zeigte bereits eine Transferhydrodesoxygenierungsaktivit{\"a}t. Diese Beobachtung ist deshalb bemerkenswert, da erst seit kurzem bekannt ist, dass Graphenstrukturen an sich katalytisch aktiv sein k{\"o}nnen. Um diese Aktivit{\"a}t weiter zu steigern, wurde der aktivierte Kohlenstoff mit 10 wt\% Ni@WC gemischt, sodass beide Katalysatoren in einer S{\"a}ule vorliegen. Die urspr{\"u}nglichen 2 \% DMF Ausbeute mit reinem aktivierten Kohlenstoff k{\"o}nnen somit auf 12 \% gesteigert werden, da das Folgeprodukt EL hierbei vermieden wird und das Zwischenprodukt „HMF Derivat" direkt zu DMF weiter reagieren kann. Dieses Ergebnis zeigt das Potential der „ein Reaktor Umsetzung", weshalb eine kontinuierliche Durchflussreaktoranlage im Litermaßstab als Scale-Up des vorhergehenden Labormaßstabs realisiert wurde. Der 800 mm x 28.5 mm Reaktor bedient eine maximale Flussrate von 50 mL min-1, Dr{\"u}cke von 100 bar und Temperaturen bis zu 500 °C.}, language = {en} } @phdthesis{Meiling2017, author = {Meiling, Till Thomas}, title = {Development of a reliable and environmentally friendly synthesis for fluorescence carbon nanodots}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-410160}, school = {Universit{\"a}t Potsdam}, pages = {198}, year = {2017}, abstract = {Carbon nanodots (CNDs) have generated considerable attention due to their promising properties, e.g. high water solubility, chemical inertness, resistance to photobleaching, high biocompatibility and ease of functionalization. These properties render them ideal for a wide range of functions, e.g. electrochemical applications, waste water treatment, (photo)catalysis, bio-imaging and bio-technology, as well as chemical sensing, and optoelectronic devices like LEDs. In particular, the ability to prepare CNDs from a wide range of accessible organic materials makes them a potential alternative for conventional organic dyes and semiconductor quantum dots (QDs) in various applications. However, current synthesis methods are typically expensive and depend on complex and time-consuming processes or severe synthesis conditions and toxic chemicals. One way to reduce overall preparation costs is the use of biological waste as starting material. Hence, natural carbon sources such as pomelo peal, egg white and egg yolk, orange juice, and even eggshells, to name a few; have been used for the preparation of CNDs. While the use of waste is desirable, especially to avoid competition with essential food production, most starting-materials lack the essential purity and structural homogeneity to obtain homogeneous carbon dots. Furthermore, most synthesis approaches reported to date require extensive purification steps and have resulted in carbon dots with heterogeneous photoluminescent properties and indefinite composition. For this reason, among others, the relationship between CND structure (e.g. size, edge shape, functional groups and overall composition) and photophysical properties is yet not fully understood. This is particularly true for carbon dots displaying selective luminescence (one of their most intriguing properties), i.e. their PL emission wavelength can be tuned by varying the excitation wavelength. In this work, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain CNDs with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch, carboxylic acids and Tris-EDTA (TE) buffer as carbon- and nitrogen source, respectively. The presented microwave-assisted hydrothermal precursor carbonization (MW-hPC) is characterized by its cost-efficiency, simplicity, short reaction times, low environmental footprint, and high yields of approx. 80\% (w/w). Furthermore, only a single synthesis step is necessary to obtain homogeneous water-soluble CNDs with no need for further purification. Depending on starting materials and reaction conditions different types of CNDs have been prepared. The as-prepared CNDs exhibit reproducible, highly homogeneous and favourable PL properties with narrow emission bands (approx. 70nm FWHM), are non-blinking, and are ready to use without need for further purification, modification or surface passivation agents. Furthermore, the CNDs are comparatively small (approx. 2.0nm to 2.4nm) with narrow size distributions; are stable over a long period of time (at least one year), either in solution or as a dried solid; and maintain their PL properties when re-dispersed in solution. Depending on CND type, the PL quantum yield (PLQY) can be adjusted from as low as 1\% to as high as 90\%; one of the highest reported PLQY values (for CNDs) so far. An essential part of this work was the utilization of a microwave synthesis reactor, allowing various batch sizes and precise control over reaction temperature and -time, pressure, and heating- and cooling rate, while also being safe to operate at elevated reaction conditions (e.g. 230 ±C and 30 bar). The hereby-achieved high sample throughput allowed, for the first time, the thorough investigation of a wide range of synthesis parameters, providing valuable insight into the CND formation. The influence of carbon- and nitrogen source, precursor concentration and -combination, reaction time and -temperature, batch size, and post-synthesis purification steps were carefully investigated regarding their influence on the optical properties of as-synthesized CNDs. In addition, the change in photophysical properties resulting from the conversion of CND solution into solid and back into the solution was investigated. Remarkably, upon freeze-drying the initial brown CND-solution turns into a non-fluorescent white/slightly yellow to brown solid which recovers PL in aqueous solution. Selected CND samples were also subject to EDX, FTIR, NMR, PL lifetime (TCSPC), particle size (TEM), TGA and XRD analysis. Besides structural characterization, the pH- and excitation dependent PL characteristics (i.e. selective luminescence) were examined; giving inside into the origin of photophysical properties and excitation dependent behaviour of CNDs. The obtained results support the notion that for CNDs the nature of the surface states determines the PL properties and that excitation dependent behaviour is caused by the "Giant Red-Edge Excitation Shift" (GREES).}, language = {en} } @phdthesis{Heck2017, author = {Heck, Christian}, title = {Gold and silver nanolenses self-assembled by DNA origami}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-409002}, school = {Universit{\"a}t Potsdam}, pages = {ix, 125}, year = {2017}, abstract = {Nanolenses are linear chains of differently-sized metal nanoparticles, which can theoretically provide extremely high field enhancements. The complex structure renders their synthesis challenging and has hampered closer analyses so far. Here, the technique of DNA origami was used to self-assemble DNA-coated 10 nm, 20 nm, and 60 nm gold or silver nanoparticles into gold or silver nanolenses. Three different geometrical arrangements of gold nanolenses were assembled, and for each of the three, sets of single gold nanolenses were investigated in detail by atomic force microscopy, scanning electron microscopy, dark-field scattering and Raman spectroscopy. The surface-enhanced Raman scattering (SERS) capabilities of the single nanolenses were assessed by labelling the 10 nm gold nanoparticle selectively with dye molecules. The experimental data was complemented by finite-difference time-domain simulations. For those gold nanolenses which showed the strongest field enhancement, SERS signals from the two different internal gaps were compared by selectively placing probe dyes on the 20 nm or 60 nm gold particles. The highest enhancement was found for the gap between the 20 nm and 10 nm nanoparticle, which is indicative of a cascaded field enhancement. The protein streptavidin was labelled with alkyne groups and served as a biological model analyte, bound between the 20 nm and 10 nm particle of silver nanolenses. Thereby, a SERS signal from a single streptavidin could be detected. Background peaks observed in SERS measurements on single silver nanolenses could be attributed to amorphous carbon. It was shown that the amorphous carbon is generated in situ.}, language = {en} } @phdthesis{Firkala2017, author = {Firkala, Tam{\´a}s}, title = {Investigation of nanoparticle-molecule interactions and pharmaceutical model formulations by means of surface enhanced raman spectroscopy}, school = {Universit{\"a}t Potsdam}, pages = {118}, year = {2017}, language = {en} } @phdthesis{Willersinn2017, author = {Willersinn, Jochen}, title = {Self-Assembly of double hydrophilic block copolymers}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-408578}, school = {Universit{\"a}t Potsdam}, pages = {119, clxxiv}, year = {2017}, abstract = {The motivation of this work was to investigate the self-assembly of a block copolymer species that attended little attraction before, double hydrophilic block copolymers (DHBCs). DHBCs consist of two linear hydrophilic polymer blocks. The self-assembly of DHBCs towards suprastructures such as particles and vesicles is determined via a strong difference in hydrophilicity between the corresponding blocks leading to a microphase separation due to immiscibility. The benefits of DHBCs and the corresponding particles and vesicles, such as biocompatibility, high permeability towards water and hydrophilic compounds as well as the large amount of possible functionalizations that can be addressed to the block copolymers make the application of DHBC based structures a viable choice in biomedicine. In order to assess a route towards self-assembled structures from DHBCs that display the potential to act as cargos for future applications, several block copolymers containing two hydrophilic polymer blocks were synthesized. Poly(ethylene oxide)-b-poly(N-vinylpyrrolidone) (PEO-b-PVP) and Poly(ethylene oxide)-b-poly(N-vinylpyrrolidone-co-N-vinylimidazole) (PEO-b-P(VP-co-VIm) block copolymers were synthesized via reversible deactivation radical polymerization (RDRP) techniques starting from a PEO-macro chain transfer agent. The block copolymers displayed a concentration dependent self-assembly behavior in water which was determined via dynamic light scattering (DLS). It was possible to observe spherical particles via laser scanning confocal microscopy (LSCM) and cryogenic scanning electron microscopy (cryo SEM) at highly concentrated solutions of PEO-b-PVP. Furthermore, a crosslinking strategy with (PEO-b-P(VP-co-VIm) was developed applying a diiodo derived crosslinker diethylene glycol bis(2-iodoethyl) ether to form quaternary amines at the VIm units. The formed crosslinked structures proved stability upon dilution and transfer into organic solvents. Moreover, self-assembly and crosslinking in DMF proved to be more advantageous and the crosslinked structures could be successfully transferred to aqueous solution. The afforded spherical submicron particles could be visualized via LSCM, cryo SEM and Cryo TEM. Double hydrophilic pullulan-b-poly(acrylamide) block copolymers were synthesized via copper catalyzed alkyne azide cycloaddition (CuAAC) starting from suitable pullulan alkyne and azide functionalized poly(N,N-dimethylacrylamide) (PDMA) and poly(N-ethylacrylamide) (PEA) homopolymers. The conjugation reaction was confirmed via SEC and 1H-NMR measurements. The self-assembly of the block copolymers was monitored with DLS and static light scattering (SLS) measurements indicating the presence of hollow spherical structures. Cryo SEM measurements could confirm the presence of vesicular structures for Pull-b-PEA block copolymers. Solutions of Pull-b-PDMA displayed particles in cryo SEM. Moreover, an end group functionalization of Pull-b-PDMA with Rhodamine B allowed assessing the structure via LSCM and hollow spherical structures were observed indicating the presence of vesicles, too. An exemplified pathway towards a DHBC based drug delivery vehicle was demonstrated with the block copolymer Pull-b-PVP. The block copolymer was synthesized via RAFT/MADIX techniques starting from a pullulan chain transfer agent. Pull-b-PVP displayed a concentration dependent self-assembly in water with an efficiency superior to the PEO-b-PVP system, which could be observed via DLS. Cryo SEM and LSCM microscopy displayed the presence of spherical structures. In order to apply a reversible crosslinking strategy on the synthesized block copolymer, the pullulan block was selectively oxidized to dialdehydes with NaIO4. The oxidation of the block copolymer was confirmed via SEC and 1H-NMR measurements. The self-assembled and oxidized structures were subsequently crosslinked with cystamine dihiydrochloride, a pH and redox responsive crosslinker resulting in crosslinked vesicles which were observed via cryo SEM. The vesicular structures of crosslinked Pull-b-PVP could be disassembled by acid treatment or the application of the redox agent tris(2-carboxyethyl)-phosphin-hydrochloride. The successful disassembly was monitored with DLS measurements. To conclude, self-assembled structures from DHBCs such as particles and vesicles display a strong potential to generate an impact on biomedicine and nanotechnologies. The variety of DHBC compositions and functionalities are very promising features for future applications.}, language = {en} } @phdthesis{You2017, author = {You, Zewang}, title = {Conformational transition of peptide-functionalized cryogels enabling shape-memory capability}, school = {Universit{\"a}t Potsdam}, pages = {144}, year = {2017}, language = {en} } @phdthesis{MbayaMani2017, author = {Mbaya Mani, Christian}, title = {Functional nanoporous carbon-based materials derived from oxocarbon-metal coordination complexes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407866}, school = {Universit{\"a}t Potsdam}, pages = {IV, 135}, year = {2017}, abstract = {Nanoporous carbon based materials are of particular interest for both science and industry due to their exceptional properties such as a large surface area, high pore volume, high electroconductivity as well as high chemical and thermal stability. Benefiting from these advantageous properties, nanoporous carbons proved to be useful in various energy and environment related applications including energy storage and conversion, catalysis, gas sorption and separation technologies. The synthesis of nanoporous carbons classically involves thermal carbonization of the carbon precursors (e.g. phenolic resins, polyacrylonitrile, poly(vinyl alcohol) etc.) followed by an activation step and/or it makes use of classical hard or soft templates to obtain well-defined porous structures. However, these synthesis strategies are complicated and costly; and make use of hazardous chemicals, hindering their application for large-scale production. Furthermore, control over the carbon materials properties is challenging owing to the relatively unpredictable processes at the high carbonization temperatures. In the present thesis, nanoporous carbon based materials are prepared by the direct heat treatment of crystalline precursor materials with pre-defined properties. This synthesis strategy does not require any additional carbon sources or classical hard- or soft templates. The highly stable and porous crystalline precursors are based on coordination compounds of the squarate and croconate ions with various divalent metal ions including Zn2+, Cu2+, Ni2+, and Co2+, respectively. Here, the structural properties of the crystals can be controlled by the choice of appropriate synthesis conditions such as the crystal aging temperature, the ligand/metal molar ratio, the metal ion, and the organic ligand system. In this context, the coordination of the squarate ions to Zn2+ yields porous 3D cube crystalline particles. The morphology of the cubes can be tuned from densely packed cubes with a smooth surface to cubes with intriguing micrometer-sized openings and voids which evolve on the centers of the low index faces as the crystal aging temperature is raised. By varying the molar ratio, the particle shape can be changed from truncated cubes to perfect cubes with right-angled edges. These crystalline precursors can be easily transformed into the respective carbon based materials by heat treatment at elevated temperatures in a nitrogen atmosphere followed by a facile washing step. The resulting carbons are obtained in good yields and possess a hierarchical pore structure with well-organized and interconnected micro-, meso- and macropores. Moreover, high surface areas and large pore volumes of up to 1957 m2 g-1 and 2.31 cm3 g-1 are achieved, respectively, whereby the macroscopic structure of the precursors is preserved throughout the whole synthesis procedure. Owing to these advantageous properties, the resulting carbon based materials represent promising supercapacitor electrode materials for energy storage applications. This is exemplarily demonstrated by employing the 3D hierarchical porous carbon cubes derived from squarate-zinc coordination compounds as electrode material showing a specific capacitance of 133 F g-1 in H2SO4 at a scan rate of 5 mV s-1 and retaining 67\% of this specific capacitance when the scan rate is increased to 200 mV s-1. In a further application, the porous carbon cubes derived from squarate-zinc coordination compounds are used as high surface area support material and decorated with nickel nanoparticles via an incipient wetness impregnation. The resulting composite material combines a high surface area, a hierarchical pore structure with high functionality and well-accessible pores. Moreover, owing to their regular micro-cube shape, they allow for a good packing of a fixed-bed flow reactor along with high column efficiency and a minimized pressure drop throughout the packed reactor. Therefore, the composite is employed as heterogeneous catalyst in the selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran showing good catalytic performance and overcoming the conventional problem of column blocking. Thinking about the rational design of 3D carbon geometries, the functions and properties of the resulting carbon-based materials can be further expanded by the rational introduction of heteroatoms (e.g. N, B, S, P, etc.) into the carbon structures in order to alter properties such as wettability, surface polarity as well as the electrochemical landscape. In this context, the use of crystalline materials based on oxocarbon-metal ion complexes can open a platform of highly functional materials for all processes that involve surface processes.}, language = {en} } @phdthesis{Muzdalo2017, author = {Muzdalo, Anja}, title = {Thermal cis-trans isomerization of azobenzene studied by path sampling and QM/MM stochastic dynamics}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-405814}, school = {Universit{\"a}t Potsdam}, pages = {144}, year = {2017}, abstract = {Azobenzene-based molecular photoswitches have extensively been applied to biological systems, involving photo-control of peptides, lipids and nucleic acids. The isomerization between the stable trans and the metastable cis state of the azo moieties leads to pronounced changes in shape and other physico-chemical properties of the molecules into which they are incorporated. Fast switching can be induced via transitions to excited electronic states and fine-tuned by a large number of different substituents at the phenyl rings. But a rational design of tailor-made azo groups also requires control of their stability in the dark, the half-lifetime of the cis isomer. In computational chemistry, thermally activated barrier crossing on the ground state Born-Oppenheimer surface can efficiently be estimated with Eyring's transition state theory (TST) approach; the growing complexity of the azo moiety and a rather heterogeneous environment, however, may render some of the underlying simplifying assumptions problematic. In this dissertation, a computational approach is established to remove two restrictions at once: the environment is modeled explicitly by employing a quantum mechanical/molecular mechanics (QM/MM) description; and the isomerization process is tracked by analyzing complete dynamical pathways between stable states. The suitability of this description is validated by using two test systems, pure azo benzene and a derivative with electron donating and electron withdrawing substituents ("push-pull" azobenzene). Each system is studied in the gas phase, in toluene and in polar DMSO solvent. The azo molecules are treated at the QM level using a very recent, semi-empirical approximation to density functional theory (density functional tight binding approximation). Reactive pathways are sampled by implementing a version of the so-called transition path sampling method (TPS), without introducing any bias into the system dynamics. By analyzing ensembles of reactive trajectories, the change in isomerization pathway from linear inversion to rotation in going from apolar to polar solvent, predicted by the TST approach, could be verified for the push-pull derivative. At the same time, the mere presence of explicit solvation is seen to broaden the distribution of isomerization pathways, an effect TST cannot account for. Using likelihood maximization based on the TPS shooting history, an improved reaction coordinate was identified as a sine-cosine combination of the central bend angles and the rotation dihedral, r (ω,α,α′). The computational van't Hoff analysis for the activation entropies was performed to gain further insight into the differential role of solvent for the case of the unsubstituted and the push-pull azobenzene. In agreement with the experiment, it yielded positive activation entropies for azobenzene in the DMSO solvent while negative for the push-pull derivative, reflecting the induced ordering of solvent around the more dipolar transition state associated to the latter compound. Also, the dynamically corrected rate constants were evaluated using the reactive flux approach where an increase comparable to the experimental one was observed for a high polarity medium for both azobenzene derivatives.}, language = {en} } @phdthesis{Charan2017, author = {Charan, Himanshu}, title = {Self assembled transmembrane protein polymer conjugates for the generation of nano thin membranes and micro compartments}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402060}, school = {Universit{\"a}t Potsdam}, pages = {xii, 138}, year = {2017}, abstract = {This project was focused on generating ultra thin stimuli responsive membranes with an embedded transmembrane protein to act as the pore. The membranes were formed by crosslinking of transmembrane protein polymer conjugates. The conjugates were self assembled on air water interface and the polymer chains crosslinked using a UV crosslinkable comonomer to engender the membrane. The protein used for the studies reported herein was one of the largest transmembrane channel proteins, ferric hydroxamate uptake protein component A (FhuA), found in the outer membrane of Escherichia coli (E. coli). The wild type protein and three genetic variants of FhuA were provided by the group of Prof. Schwaneberg in Aachen. The well known thermo responsive poly(N isopropylacrylamide) (PNIPAAm) and the pH and thermo responsive polymer poly((2-dimethylamino)ethyl methacrylate) (PDMAEMA) were conjugated to FhuA and the genetic variants via controlled radical polymerization (CRP) using grafting from technique. These polymers were chosen because they would provide stimuli handles in the resulting membranes. The reported polymerization was the first ever attempt to attach polymer chains onto a membrane protein using site specific modification. The conjugate synthesis was carried out in two steps - a) FhuA was first converted into a macroinitiator by covalently linking a water soluble functional CRP initiator to the lysine residues. b) Copper mediated CRP was then carried out in pure buffer conditions with and without sacrificial initiator to generate the conjugates. The challenge was carrying out the modifications on FhuA without denaturing it. FhuA, being a transmembrane protein, requires amphiphilic species to stabilize its highly hydrophobic transmembrane region. For the experiments reported in this thesis, the stabilizing agent was 2 methyl 2,4-pentanediol (MPD). Since the buffer containing MPD cannot be considered a purely aqueous system, and also because MPD might interfere with the polymerization procedure, the reaction conditions were first optimized using a model globular protein, bovine serum albumin (BSA). The optimum conditions were then used for the generation of conjugates with FhuA. The generated conjugates were shown to be highly interfacially active and this property was exploited to let them self assemble onto polar apolar interfaces. The emulsions stabilized by particles or conjugates are referred to as Pickering emulsions. Crosslinking conjugates with a UV crosslinkable co monomer afforded nano thin micro compartments. Interfacial self assembly at the air water interface and subsequent UV crosslinking also yielded nano thin, stimuli responsive membranes which were shown to be mechanically robust. Initial characterization of the flux and permeation of water through these membranes is also reported herein. The generated nano thin membranes with PNIPAAm showed reduced permeation at elevated temperatures owing to the resistance by the hydrophobic and thus water-impermeable polymer matrix, hence confirming the stimulus responsivity. Additionally, as a part of collaborative work with Dr. Changzhu Wu, TU Dresden, conjugates of three enzymes with current/potential industrial relevance (candida antarctica lipase B, benzaldehyde lyase and glucose oxidase) with stimuli responsive polymers were synthesized. This work aims at carrying out cascade reactions in the Pickering emulsions generated by self assembled enzyme polymer conjugate.}, language = {en} } @misc{GrunwaldKellingHoldtetal.2017, author = {Grunwald, Nicolas and Kelling, Alexandra and Holdt, Hans-J{\"u}rgen and Schilde, Uwe}, title = {The crystal structure of 1,1′-bisisoquinoline, C18H12N2}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-401952}, pages = {3}, year = {2017}, abstract = {C18H12N2, tetragonal, I41/a (no. 88), a=13.8885(6) {\AA}, c=13.6718(6) {\AA}, V =2637.2(3) {\AA}3, Z =8, Rgt(F)=0.0295, wRref(F2)=0.0854, T =210 K. CCDC no.: 631823}, language = {en} } @article{GrunwaldKellingHoldtetal.2017, author = {Grunwald, Nicolas and Kelling, Alexandra and Holdt, Hans-J{\"u}rgen and Schilde, Uwe}, title = {The crystal structure of 1,1′-bisisoquinoline, C18H12N2}, series = {Zeitschrift f{\"u}r Kristallographie : international journal for structural, physical and chemical aspects of crystalline materials. New crystal structures}, volume = {232}, journal = {Zeitschrift f{\"u}r Kristallographie : international journal for structural, physical and chemical aspects of crystalline materials. New crystal structures}, number = {5}, publisher = {de Gruyter}, address = {Berlin}, doi = {10.1515/ncrs-2017-0088}, pages = {839 -- 841}, year = {2017}, abstract = {C18H12N2, tetragonal, I41/a (no. 88), a=13.8885(6) {\AA}, c=13.6718(6) {\AA}, V =2637.2(3) {\AA}3, Z =8, Rgt(F)=0.0295, wRref(F2)=0.0854, T =210 K. CCDC no.: 631823}, language = {en} } @misc{SchildePazOrtiz2017, author = {Schilde, Uwe and Paz, Christian and Ortiz, Leandro}, title = {Crystal structure of erioflorin isolated from Podanthus mitiqui (L.)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-401832}, pages = {4}, year = {2017}, abstract = {The title compound, erioflorin, C19H24O6 [systematic name: (1aR,3S,4Z,5aR,8aR,9R,10aR)-1a, 2,3,5a, 7,8,8a, 9,10,10a-decahydro-3-hydroxy-4,10a-dimethyl-8-methylidene-7-oxooxireno[5,6] cyclodeca[1,2-b]furan-9-yl methacrylate], is a tricyclic germacrane sesquiterpene lactone, which was isolated from Podanthus mitiqui (L.). The compound crystallizes in the space group P2(1)2(1)2(1), and its molecular structure consists of a methacrylic ester of a ten-membered ring sesquiterpenoid annelated with an epoxide and a butyrolactone. The structure is stabilized by one intramolecular C-H center dot center dot center dot O hydrogen bond. An O-H center dot center dot center dot O hydrogen bond and further C-H center dot center dot center dot O interactions can be observed in the packing.}, language = {en} } @article{SchildePazOrtiz2017, author = {Schilde, Uwe and Paz, Christian and Ortiz, Leandro}, title = {Crystal structure of erioflorin isolated from Podanthus mitiqui (L.)}, series = {Acta Crystallographica Section E : Crystallographic Communications}, volume = {73}, journal = {Acta Crystallographica Section E : Crystallographic Communications}, number = {3}, publisher = {International Union of Crystallography}, address = {Chester}, doi = {10.1107/S2056989017001700}, pages = {334 -- 337}, year = {2017}, abstract = {The title compound, erioflorin, C19H24O6 [systematic name: (1aR,3S,4Z,5aR,8aR,9R,10aR)-1a, 2,3,5a, 7,8,8a, 9,10,10a-decahydro-3-hydroxy-4,10a-dimethyl-8-methylidene-7-oxooxireno[5,6] cyclodeca[1,2-b]furan-9-yl methacrylate], is a tricyclic germacrane sesquiterpene lactone, which was isolated from Podanthus mitiqui (L.). The compound crystallizes in the space group P2(1)2(1)2(1), and its molecular structure consists of a methacrylic ester of a ten-membered ring sesquiterpenoid annelated with an epoxide and a butyrolactone. The structure is stabilized by one intramolecular C-H center dot center dot center dot O hydrogen bond. An O-H center dot center dot center dot O hydrogen bond and further C-H center dot center dot center dot O interactions can be observed in the packing.}, language = {en} } @misc{MirskovaAdamovichMirskovetal.2017, author = {Mirskova, Anna N. and Adamovich, Sergey N. and Mirskov, Rudolf G. and Schilde, Uwe}, title = {Reaction of pharmacological active tris-(2-hydroxyethyl)ammonium 4-chlorophenylsulfanylacetate with ZnCl2 or NiCl2}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-401099}, pages = {5}, year = {2017}, abstract = {The reaction of pharmacological active protic ionic liquid tris-(2-hydroxyethyl)ammonium 4-chlorophenylsulfanylacetate H + N(CH 2 CH 2 OH) 3 ∙ ( - OOCCH 2 SC 6 H 4 Cl-4) (1) with zinc or nickel chloride in a ratio of 2:1 affords stable at room temperature powder-like adducts [H + N(CH 2 CH 2 OH) 3 ] 2 ∙ [M(OOCCH 2 SC 6 H 4 Cl-4) 2 Cl 2 ] 2- , M = Zn (2), Ni (3). By recrystallization from aqueous alcohol compound 2 unexpectedly gives Zn(OOCCH 2 SC 6 H 4 Cl-4) 2 ∙ 2H 2 O (4). Unlike 2, compound 3 gives crystals [N(CH 2 CH 2 OH) 3 ] 2 Ni 2+ · [ - OOCCH 2 SC 6 H 4 Cl-4] 2 (5), which have a structure of metallated ionic liquid. The structure of 5 has been proved by X-ray diffraction analysis. It is the first example of the conversion of a protic ionic liquid into potentially biological active metallated ionic liquid (1 → 3 → 5).}, language = {en} } @misc{AdamovichMirskovaMirskovetal.2017, author = {Adamovich, Sergey N. and Mirskova, Anna N. and Mirskov, Rudolf G. and Schilde, Uwe}, title = {Synthesis and crystal structure of 1,4,10,13-tetraoxa-7,16-diazoniumcyclo-octadecane bis(4-chloro-2-methyl-phenoxyacetate)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400905}, pages = {4}, year = {2017}, abstract = {The title compound was prepared by the reaction of 1,4,10,13-tetraoxa-7,16-diazacyclo-octadecane with 4-chloro-2-methyl-phenoxyacetic acid in a ratio of 1:2. The structure has been proved by the data of elemental analysis, IR spectroscopy, NMR ( 1 H, 13 C) technique and by X-ray diffraction analysis. Intermolecular hydrogen bonds between the azonium protons and oxygen atoms of the carboxylate groups were found. Immunoactive properties of the title compound have been screened. The compound has the ability to suppress spontaneous and Con A-stimulated cell proliferation in vitro and therefore can be considered as immunodepressant.}, language = {en} } @phdthesis{Peh2017, author = {Peh, Eddie K.W.}, title = {Calcium carbonate formation}, school = {Universit{\"a}t Potsdam}, pages = {133}, year = {2017}, language = {en} } @misc{EnzenbergLaschewskyBoeffeletal.2017, author = {Enzenberg, Anne and Laschewsky, Andr{\´e} and Boeffel, Christine and Wischerhoff, Erik}, title = {Influence of the near molecular vicinity on the temperature regulated fluorescence response of poly(N-vinylcaprolactam)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400634}, pages = {21}, year = {2017}, abstract = {A series of new fluorescent dye bearing monomers, including glycomonomers, based on maleamide and maleic esteramide was synthesized. The dye monomers were incorporated by radical copolymerization into thermo-responsive poly(N-vinyl-caprolactam) that displays a lower critical solution temperature (LCST) in aqueous solution. The effects of the local molecular environment on the polymers' luminescence, in particular on the fluorescence intensity and the extent of solvatochromism, were investigated below as well as above the phase transition. By attaching substituents of varying size and polarity in the close vicinity of the fluorophore, and by varying the spacer groups connecting the dyes to the polymer backbone, we explored the underlying structure-property relationships, in order to establish rules for successful sensor designs, e.g., for molecular thermometers. Most importantly, spacer groups of sufficient length separating the fluorophore from the polymer backbone proved to be crucial for obtaining pronounced temperature regulated fluorescence responses.}, language = {en} } @misc{ZehbeKolloscheLardongetal.2017, author = {Zehbe, Kerstin and Kollosche, Matthias and Lardong, Sebastian and Kelling, Alexandra and Schilde, Uwe and Taubert, Andreas}, title = {Ionogels based on poly(methyl methacrylate) and metal-containing ionic liquids}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400607}, pages = {16}, year = {2017}, abstract = {Ionogels (IGs) based on poly(methyl methacrylate) (PMMA) and the metal-containing ionic liquids (ILs) bis-1-butyl-3-methlimidazolium tetrachloridocuprate(II), tetrachloride cobaltate(II), and tetrachlorido manganate(II) have been synthesized and their mechanical and electrical properties have been correlated with their microstructure. Unlike many previous examples, the current IGs show a decreasing stability in stress-strain experiments on increasing IL fractions. The conductivities of the current IGs are lower than those observed in similar examples in the literature. Both effects are caused by a two-phase structure with micrometer-sized IL-rich domains homogeneously dispersed an IL-deficient continuous PMMA phase. This study demonstrates that the IL-polymer miscibility and the morphology of the IGs are key parameters to control the (macroscopic) properties of IGs.}, language = {en} } @misc{KoenigKellingSchildeetal.2017, author = {K{\"o}nig, Jana and Kelling, Alexandra and Schilde, Uwe and Strauch, Peter}, title = {[µ2-O,O′,Oʺ,Oʺ′-Bis(1,2-dithiooxalato-S,S′)nickel(II)]bis[-O,O′-bis(1,2-dithiooxalato-S,S′)-nickel(II)pentaquaholmium(III)]hydrate, [Ho2Ni3(dto)6(H2O)10]}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400598}, pages = {5}, year = {2017}, abstract = {Planar bis(1,2-dithiooxalato)nickelate(II), [Ni(dto)]2- reacts in aqueous solutions with lanthanide ions (Ln3+) to form pentanuclear, hetero-bimetallic complexes of the general composition [{Ln(H2O)n}2{Ni(dto)2}3]·xH2O. (n = 4 or 5; x = 9-12). The complex [{Ho(H2O)5}2{Ni(dto)2}3]·10H2O, Ho2Ni3, was synthesized and characterized by single crystal X-ray structure analysis and powder diffraction. The Ho2Ni3 complex crystallizes as monoclinic crystals in the space group P21/c. The channels and cavities, appearing in the crystal packing of the complex molecules, are occupied by a varying amount of non-coordinated water molecules.}, language = {en} } @misc{HardyTorresRendonLealEganaetal.2017, author = {Hardy, John G. and Torres-Rendon, Jose Guillermo and Leal-Ega{\~n}a, Aldo and Walther, Andreas and Schlaad, Helmut and C{\"o}lfen, Helmut and Scheibel, Thomas R.}, title = {Biomineralization of engineered spider silk protein-based composite materials for bone tissue engineering}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400519}, pages = {13}, year = {2017}, abstract = {Materials based on biodegradable polyesters, such as poly(butylene terephthalate) (PBT) or poly(butylene terephthalate-co-poly(alkylene glycol) terephthalate) (PBTAT), have potential application as pro-regenerative scaffolds for bone tissue engineering. Herein, the preparation of films composed of PBT or PBTAT and an engineered spider silk protein, (eADF4(C16)), that displays multiple carboxylic acid moieties capable of binding calcium ions and facilitating their biomineralization with calcium carbonate or calcium phosphate is reported. Human mesenchymal stem cells cultured on films mineralized with calcium phosphate show enhanced levels of alkaline phosphatase activity suggesting that such composites have potential use for bone tissue engineering.}, language = {en} } @misc{TaubertBalischewskiHentrichetal.2017, author = {Taubert, Andreas and Balischewski, Christian and Hentrich, Doreen and Elschner, Thomas and Eidner, Sascha and G{\"u}nter, Christina and Behrens, Karsten and Heinze, Thomas}, title = {Water-soluble cellulose derivatives are sustainable additives for biomimetic calcium phosphate mineralization}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400453}, pages = {17}, year = {2017}, abstract = {The effect of cellulose-based polyelectrolytes on biomimetic calcium phosphate mineralization is described. Three cellulose derivatives, a polyanion, a polycation, and a polyzwitterion were used as additives. Scanning electron microscopy, X-ray diffraction, IR and Raman spectroscopy show that, depending on the composition of the starting solution, hydroxyapatite or brushite precipitates form. Infrared and Raman spectroscopy also show that significant amounts of nitrate ions are incorporated in the precipitates. Energy dispersive X-ray spectroscopy shows that the Ca/P ratio varies throughout the samples and resembles that of other bioinspired calcium phosphate hybrid materials. Elemental analysis shows that the carbon (i.e., polymer) contents reach 10\% in some samples, clearly illustrating the formation of a true hybrid material. Overall, the data indicate that a higher polymer concentration in the reaction mixture favors the formation of polymer-enriched materials, while lower polymer concentrations or high precursor concentrations favor the formation of products that are closely related to the control samples precipitated in the absence of polymer. The results thus highlight the potential of (water-soluble) cellulose derivatives for the synthesis and design of bioinspired and bio-based hybrid materials.}, language = {en} } @phdthesis{Witt2017, author = {Witt, Barbara}, title = {Toxicological characterization of lipid-soluble arsenic species in human brain cells}, school = {Universit{\"a}t Potsdam}, pages = {118, V}, year = {2017}, language = {en} } @phdthesis{Jordan2017, author = {Jordan, Thomas}, title = {CxNy-materials from supramolecular precursors for "All-Carbon" composite materials}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-398855}, school = {Universit{\"a}t Potsdam}, pages = {157}, year = {2017}, abstract = {Among modern functional materials, the class of nitrogen-containing carbons combines non-toxicity and sustainability with outstanding properties. The versatility of this materials class is based on the opportunity to tune electronic and catalytic properties via the nitrogen content and -motifs: This ranges from the electronically conducting N-doped carbon, where few carbon atoms in the graphitic lattice are substituted by nitrogen, to the organic semiconductor graphitic carbon nitride (g-C₃N₄), with a structure based on tri-s-triazine units. In general, composites can reveal outstanding catalytic properties due to synergistic behavior, e.g. the formation of electronic heterojunctions. In this thesis, the formation of an "all-carbon" heterojunction was targeted, i.e. differences in the electronic properties of the single components were achieved by the introduction of different nitrogen motives into the carbon lattice. Such composites are promising as metal-free catalysts for the photocatalytic water splitting. Here, hydrogen can be generated from water by light irradiation with the use of a photocatalyst. As first part of the heterojunction, the organic semiconductor g-C₃N₄ was employed, because of its suitable band structure for photocatalytic water splitting, high stability and non-toxicity. The second part was chosen as C₂N, a recently discovered semiconductor. Compared to g-C₃N₄, the less nitrogen containing C₂N has a smaller band gap and a higher absorption coefficient in the visible light range, which is expected to increase the optical absorption in the composite eventually leading to an enhanced charge carrier separation due to the formation of an electronic heterojunction. The aim of preparing an "all-carbon" composite included the research on appropriate precursors for the respective components g-C₃N₄ and C₂N, as well as strategies for appropriate structuring. This was targeted by applying precursors which can form supramolecular pre-organized structures. This allows for more control over morphology and atom patterns during the carbonization process. In the first part of this thesis, it was demonstrated how the photocatalytic activity of g-C₃N₄ can be increased by the targeted introduction of defects or surface terminations. This was achieved by using caffeine as a "growth stopping" additive during the formation of the hydrogen-bonded supramolecular precursor complexes. The increased photocatalytic activity of the obtained materials was demonstrated with dye degradation experiments. The second part of this thesis was focused on the synthesis of the second component C₂N. Here, a deep eutectic mixture from hexaketocyclohexane and urea was structured using the biopolymer chitosan. This scaffolding resulted in mesoporous nitrogen-doped carbon monoliths and beads. CO₂- and dye-adsorption experiments with the obtained monolith material revealed a high isosteric heat of CO₂-adsorption and showed the accessibility of the monolithic pore system to larger dye molecules. Furthermore, a novel precursor system for C₂N was explored, based on organic crystals from squaric acid and urea. The respective C₂N carbon with an unusual sheet-like morphology could be synthesized by carbonization of the crystals at 550 °C. With this precursor system, also microporous C₂N carbon with a BET surface area of 865 m²/g was obtained by "salt-templating" with ZnCl₂. Finally, the preparation of a g-C₃N₄/C₂N "all carbon" composite heterojunction was attempted by the self-assembly of g-C₃N₄ and C₂N nanosheets and tested for photocatalytic water splitting. Indeed, the composites revealed high rates of hydrogen evolution when compared to bulk g-C₃N₄. However, the increased catalytic activity was mainly attributed to the high surface area of the nanocomposites rather than to the composition. With regard to alternative composite synthesis ways, first experiments indicated N-Methyl-2-pyrrolidon to be suitable for higher concentrated dispersion of C₂N nanosheets. Eventually, the results obtained in this thesis provide precious synthetic contributions towards the preparation and processing of carbon/nitrogen compounds for energy applications.}, language = {en} } @phdthesis{LorenteSanchez2017, author = {Lorente S{\´a}nchez, Alejandro Jose}, title = {Synthesis of side-chain polystyrenes for all organic solution processed OLEDs}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-398006}, school = {Universit{\"a}t Potsdam}, pages = {xiv, 131}, year = {2017}, abstract = {In the present work side-chain polystyrenes were synthesized and characterized, in order to be applied in multilayer OLEDs fabricated by solution process techniques. Manufacture of optoelectronic devices by solution process techniques is meant to decrease significantly fabrication cost and allow large scale production of such devices. This dissertation focusses in three series, enveloped in two material classes. The two classes differ to each other in the type of charge transport exhibited, either ambipolar transport or electron transport. All materials were applied in all-organic solution processed green Ir-based devices. In the first part, a series of ambipolar host materials were developed to transport both charge types, holes and electrons, and be applied especially as matrix for green Ir-based emitters. It was possible to increase devices efficacy by modulating the predominant charge transport type. This was achieved by modification of molecules electron transport part with more electron-deficient heterocycles or by extending the delocalization of the LUMO. Efficiencies up to 28.9 cd/A were observed for all-organic solution-process three layer devices. In the second part, suitability of triarylboranes and tetraphenylsilanes as electron transport materials was studied. High triplet energies were obtained, up to 2.95 eV, by rational combination of both molecular structures. Although the combination of both elements had a low effect in materials electron transport properties, high efficiencies around 24 cd/A were obtained for the series in all-organic solution-processed two layer devices. In the last part, benzene and pyridine were chosen as the series electron-transport motif. By controlling the relative pyridine content (RPC) solubility into methanol was induced for polystyrenes with bulky side-chains. Materials with RPC ≥ 0.5 could be deposited orthogonally from solution without harming underlying layers. From the best of our knowledge, this is the first time such materials are applied in this architecture showing moderate efficiencies around 10 cd/A in all-organic solution processed OLEDs. Overall, the outcome of these studies will actively contribute to the current research on materials for all-solution processed OLEDs.}, language = {en} } @phdthesis{Dippel2017, author = {Dippel, Sandor}, title = {Development of functional hydrogels for sensor applications}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-398252}, school = {Universit{\"a}t Potsdam}, pages = {127}, year = {2017}, abstract = {In this work, a sensor system based on thermoresponsive materials is developed by utilizing a modular approach. By synthesizing three different key monomers containing either a carboxyl, alkene or alkyne end group connected with a spacer to the methacrylic polymerizable unit, a flexible copolymerization strategy has been set up with oligo ethylene glycol methacrylates. This allows to tune the lower critical solution temperature (LCST) of the polymers in aqueous media. The molar masses are variable thanks to the excurse taken in polymerization in ionic liquids thus stretching molar masses from 25 to over 1000 kDa. The systems that were shown shown to be effective in aqueous solution could be immobilized on surfaces by copolymerizing photo crosslinkable units. The immobilized systems were formulated to give different layer thicknesses, swelling ratios and mesh sizes depending on the demand of the coupling reaction. The coupling of detector units or model molecules is approached via reactions of the click chemistry pool, and the reactions are evaluated on their efficiency under those aspects, too. These coupling reactions are followed by surface plasmon resonance spectroscopy (SPR) to judge efficiency. With these tools at hand, Salmonella saccharides could be selectively detected by SPR. Influenza viruses were detected in solution by turbidimetry in solution as well as by a copolymerized solvatochromic dye to track binding via the changes of the polymers' fluorescence by said binding event. This effect could also be achieved by utilizing the thermoresponsive behavior. Another demonstrator consists of the detection system bound to a quartz surface, thus allowing the virus detection on a solid carrier. The experiments show the great potential of combining the concepts of thermoresponsive materials and click chemistry to develop technically simple sensors for large biomolecules and viruses.}, language = {en} } @phdthesis{Pavashe2017, author = {Pavashe, Prashant}, title = {Synthesis and transformations of 2-thiocarbohydrates}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-397739}, school = {Universit{\"a}t Potsdam}, pages = {xi, 132}, year = {2017}, abstract = {I. Ceric ammonium nitrate (CAN) mediated thiocyanate radical additions to glycals In this dissertation, a facile entry was developed for the synthesis of 2-thiocarbohydrates and their transformations. Initially, CAN mediated thiocyanation of carbohydrates was carried out to obtain the basic building blocks (2-thiocyanates) for the entire studies. Subsequently, 2-thiocyanates were reduced to the corresponding thiols using appropriate reagents and reaction conditions. The screening of substrates, stereochemical outcome and the reaction mechanism are discussed briefly (Scheme I). Scheme I. Synthesis of the 2-thiocyanates II and reductions to 2-thiols III \& IV. An interesting mechanism was proposed for the reduction of 2-thiocyanates II to 2-thiols III via formation of a disulfide intermediate. The water soluble free thiols IV were obtained by cleaving the thiocyanate and benzyl groups in a single step. In the subsequent part of studies, the synthetic potential of the 2-thiols was successfully expanded by simple synthetic transformations. II. Transformations of the 2-thiocarbohydrates The 2-thiols were utilized for convenient transformations including sulfa-Michael additions, nucleophilic substitutions, oxidation to disulfides and functionalization at the anomeric position. The diverse functionalizations of the carbohydrates at the C-2 position by means of the sulfur linkage are the highlighting feature of these studies. Thus, it creates an opportunity to expand the utility of 2-thiocarbohydrates for biological studies. Reagents and conditions: a) I2, pyridine, THF, rt, 15 min; b) K2CO3, MeCN, rt, 1 h; c) MeI, K2CO3, DMF, 0 °C, 5 min; d) Ac2O, H2SO4 (1 drop), rt, 10 min; e) CAN, MeCN/H2O, NH4SCN, rt, 1 h; f) NaN3, ZnBr2, iPrOH/H2O, reflux, 15 h; g) NaOH (1 M), TBAI, benzene, rt, 2 h; h) ZnCl2, CHCl3, reflux, 3 h. Scheme II. Functionalization of 2-thiocarbohydrates. These transformations have enhanced the synthetic value of 2-thiocarbohydrates for the preparative scale. Worth to mention is the Lewis acid catalyzed replacement of the methoxy group by other nucleophiles and the synthesis of the (2→1) thiodisaccharides, which were obtained with complete β-selectivity. Additionally, for the first time, the carbohydrate linked thiotetrazole was synthesized by a (3 + 2) cycloaddition approach at the C-2 position. III. Synthesis of thiodisaccharides by thiol-ene coupling. In the final part of studies, the synthesis of thiodisaccharides by a classical photoinduced thiol-ene coupling was successfully achieved. Reagents and conditions: 2,2-Dimethoxy-2-phenylacetophenone (DPAP), CH2Cl2/EtOH, hv, rt. Scheme III. Thiol-ene coupling between 2-thiols and exo-glycals. During the course of investigations, it was found that the steric hindrance plays an important role in the addition of bulky thiols to endo-glycals. Thus, we successfully screened the suitable substrates for addition of various thiols to sterically less hindered alkenes (Scheme III). The photochemical addition of 2-thiols to three different exo-glycals delivered excellent regio- and diastereoselectivities as well as yields, which underlines the synthetic potential of this convenient methodology.}, language = {en} } @phdthesis{Zhang2017, author = {Zhang, Weiyi}, title = {Functional Poly(ionic liquid) Materials based on Poly(1,2,4-triazolium)s}, school = {Universit{\"a}t Potsdam}, pages = {108}, year = {2017}, language = {en} } @phdthesis{Olejko2017, author = {Olejko, Lydia}, title = {F{\"o}rster resonance energy transfer (FRET)-based nanophotonics using DNA origami structures}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-396747}, school = {Universit{\"a}t Potsdam}, year = {2017}, abstract = {The field of nanophotonics focuses on the interaction between electromagnetic radiation and matter on the nanometer scale. The elements of nanoscale photonic devices can transfer excitation energy non-radiatively from an excited donor molecule to an acceptor molecule by F{\"o}rster resonance energy transfer (FRET). The efficiency of this energy transfer is highly dependent on the donor-acceptor distance. Hence, in these nanoscale photonic devices it is of high importance to have a good control over the spatial assembly of used fluorophores. Based on molecular self-assembly processes, various nanostructures can be produced. Here, DNA nanotechnology and especially the DNA origami technique are auspicious self-assembling methods. By using DNA origami nanostructures different fluorophores can be introduced with a high local control to create a variety of nanoscale photonic objects. The applications of such nanostructures range from photonic wires and logic gates for molecular computing to artificial light harvesting systems for artificial photosynthesis. In the present cumulative doctoral thesis, different FRET systems on DNA origami structures have been designed and thoroughly analyzed. Firstly, the formation of guanine (G) quadruplex structures from G rich DNA sequences has been studied based on a two-color FRET system (Fluorescein (FAM)/Cyanine3 (Cy3)). Here, the influences of different cations (Na+ and K+), of the DNA origami structure and of the DNA sequence on the G-quadruplex formation have been analyzed. In this study, an ion-selective K+ sensing scheme based on the G-quadruplex formation on DNA origami structures has been developed. Subsequently, the reversibility of the G-quadruplex formation on DNA origami structures has been evaluated. This has been done for the simple two-color FRET system which has then been advanced to a switchable photonic wire by introducing additional fluorophores (FAM/Cy3/Cyanine5 (Cy5)/IRDye®700). In the last part, the emission intensity of the acceptor molecule (Cy5) in a three-color FRET cascade has been tuned by arranging multiple donor (FAM) and transmitter (Cy3) molecules around the central acceptor molecule. In such artificial light harvesting systems, the excitation energy is absorbed by several donor and transmitter molecules followed by an energy transfer to the acceptor leading to a brighter Cy5 emission. Furthermore, the range of possible excitation wavelengths is extended by using several different fluorophores (FAM/Cy3/Cy5). In this part of the thesis, the light harvesting efficiency (antenna effect) and the FRET efficiency of different donor/transmitter/acceptor assemblies have been analyzed and the artificial light harvesting complex has been optimized in this respect.}, language = {en} } @phdthesis{Titov2017, author = {Titov, Evgenii}, title = {Quantum chemistry and surface hopping dynamics of azobenzenes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394610}, school = {Universit{\"a}t Potsdam}, pages = {205}, year = {2017}, abstract = {This cumulative doctoral dissertation, based on three publications, is devoted to the investigation of several aspects of azobenzene molecular switches, with the aid of computational chemistry. In the first paper, the isomerization rates of a thermal cis → trans isomerization of azobenzenes for species formed upon an integer electron transfer, i.e., with added or removed electron, are calculated from Eyring's transition state theory and activation energy barriers, computed by means of density functional theory. The obtained results are discussed in connection with an experimental study of the thermal cis → trans isomerization of azobenzene derivatives in the presence of gold nanoparticles, which is demonstrated to be greatly accelerated in comparison to the same isomerization reaction in the absence of nanoparticles. The second paper is concerned with electronically excited states of (i) dimers, composed of two photoswitchable units placed closely side-by-side, as well as (ii) monomers and dimers adsorbed on a silicon cluster. A variety of quantum chemistry methods, capable of calculating molecular electronic absorption spectra, based on density functional and wave function theories, is employed to quantify changes in optical absorption upon dimerization and covalent grafting to a surface. Specifically, the exciton (Davydov) splitting between states of interest is determined from first-principles calculations with the help of natural transition orbital analysis, allowing for insight into the nature of excited states. In the third paper, nonadiabatic molecular dynamics with trajectory surface hopping is applied to model the photoisomerization of azobenzene dimers, (i) for the isolated case (exhibiting the exciton coupling between two molecules) as well as (ii) for the constrained case (providing the van der Waals interaction with environment in addition to the exciton coupling between two monomers). For the latter, the additional azobenzene molecules, surrounding the dimer, are introduced, mimicking a densely packed self-assembled monolayer. From obtained results it is concluded that the isolated dimer is capable of isomerization likewise the monomer, whereas the steric hindrance considerably suppresses trans → cis photoisomerization. Furthermore, the present dissertation comprises the general introduction describing the main features of the azobenzene photoswitch and objectives of this work, theoretical basis of the employed methods, and discussion of gained findings in the light of existing literature. Also, additional results on (i) activation parameters of the thermal cis → trans isomerization of azobenzenes, (ii) an approximate scheme to account for anharmonicity of molecular vibrations in calculation of the activation entropy, as well as (iii) absorption spectra of photoswitch-silicon composites obtained from time-demanding wave function-based methods are presented.}, language = {en} } @phdthesis{Graglia2017, author = {Graglia, Micaela}, title = {Lignin valorization}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-104863}, school = {Universit{\"a}t Potsdam}, pages = {133}, year = {2017}, abstract = {The topic of this project is the use of lignin as alternative source of aromatic building blocks and oligomers to fossil feedstocks. Lignin is known as the most abundant aromatic polymer in nature and is isolated from the lignocellulosic component of plants by different possible extraction treatments. Both the biomass source and the extraction method affect the structure of the isolated lignin, therefore influencing its further application. Lignin was extracted from beech wood by two different hydrothermal alkaline treatments, which use NaOH and Ba(OH)2 as base and by an acid-catalyzed organosolv process. Moreover, lignin was isolated from bamboo, beech wood and coconut by soda treatment of the biomasses. A comparison of the structural features of such isolated lignins was performed through the use of a wide range of analytical methods. Alkaline lignins resulted in a better candidate as carbon precursor and macromonomers for the synthesis of polymer than organosolv lignin. In fact, alkaline lignins showed higher residual mass after carbonization and higher content of the reactive hydroxy functionalities. In contrast, the lignin source turned out to slightly affect the lignin hydroxyl content. One of the most common lignin modifications is its deconstruction to obtain aromatic molecules, which can be used as starting materials for the synthesis of fine chemicals. Lignin deconstruction leads to a complex mixture of aromatic molecules. A gas chromatographic analytical method was developed to characterize the mixture of products obtained by lignin deconstruction via heterogeneous catalytic hydrogenolysis. The analytical protocol allowed the quantification of three main groups of molecules by means of calibration curves, internal standard and a preliminary silylation step of the sample. The analytical method was used to study the influence of the hydrogenolysis catalyst, temperature and system (flow and batch reactor) on the yield and selectivity of the aromatic compounds. Lignin extracted from beech wood by a hydrothermal process using Ba(OH)2 as base, was functionalized by aromatic nitration in order to add nitrogen functionalities. The final goal was the synthesis of a nitrogen doped carbon. Nitrated lignin was reduced to the amino form in order to compare the influence of different nitrogen functionalities on the porosity of the final carbon. The carbons were obtained by ionothermal treatment of the precursors in the presence of the eutectic salt mixture KCl/ZnCl2 Such synthesized carbons showed micro-, macro- and mesoporosity and were tested for their electrocatalytic activity towards the oxygen reduction reaction. Mesoporous carbon derived from nitro lignin displayed the highest electrocatalytic activity. Lignins isolated from coconut, beech wood and bamboo were used as macromonomers for the synthesis of biobased polyesters. A condensation reaction was performed between lignin and a hyper branched poly(ester-amine), previously obtained by condensation of triethanolamine and adipic acid. The influence of the lignin source and content on the thermochemical and mechanical properties of the final material was investigated. The prepolymer showed adhesive properties towards aluminum and its shear strength was therefore measured. The gluing properties of such synthesized glues turned out to be independent from the lignin source but affected by the amount of lignin in the final material. This work shows that, although still at a laboratory scale, the valorization of lignin can overcome the critical issues of lignin´s structure variability and complexity.}, language = {en} }