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We present the fabrication of TiO2 nanotube electrodes with high biocompatibility and extraordinary spectroscopic properties. Intense surface-enhanced resonance Raman signals of the heme unit of the redox enzyme Cytochromeb(5) were observed upon covalent immobilization of the protein matrix on the TiO2 surface, revealing overall preserved structural integrity and redox behavior. The enhancement factor could be rationally controlled by varying the electrode annealing temperature, reaching a record maximum value of over 70 at 475 degrees C. For the first time, such high values are reported for non-directly surface-interacting probes, for which the involvement of charge-transfer processes in signal amplification can be excluded. The origin of the surface enhancement is exclusively attributed to enhanced localized electric fields resulting from the specific optical properties of the nanotubular geometry of the electrode.
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.
The capability of electrospray ionization (ESI)-ion mobility (IM) spectrometry for reaction monitoring is assessed both as a stand-alone real-time technique and in combination with HPLC. A three-step chemical reaction, consisting of a Williamson ether synthesis followed by a hydrogenation and an N-alkylation step, is chosen for demonstration. Intermediates and products are determined with a drift time to mass-per-charge correlation. Addition of an HPLC column to the setup increases the separation power and allows the determination of further species. Monitoring of the intensities of the various species over the reaction time allows the detection of the end of reaction, determination of the rate-limiting step, observation of the system response in discontinuous processes, and optimization of the mass ratios of the starting materials. However, charge competition in ESI influences the quantitative detection of substances in the reaction mixture. Therefore, two different methods are investigated, which allow the quantification and investigation of reaction kinetics. The first method is based on the pre-separation of the compounds on an HPLC column and their subsequent individual detection in the ESI-IM spectrometer. The second method involves an extended calibration procedure, which considers charge competition effects and facilitates nearly real-time quantification.
The application of electrospray ionization (ESI) ion mobility (IM) spectrometry on the detection end of a high-performance liquid chromatograph has been a subject of study for some time. So far, this method has been limited to low flow rates or has required splitting of the liquid flow. This work presents a novel concept of an ESI source facilitating the stable operation of the spectrometer at flow rates between 10 mu L min(-1) and 1500 mu L min(-1) without flow splitting, advancing the T-cylinder design developed by Kurnin and co-workers. Flow rates eight times faster than previously reported were achieved because of a more efficient dispersion of the liquid at increased electrospray voltages combined with nebulization by a sheath gas. Imaging revealed the spray operation to be in a rotationally symmetric multijet-mode. The novel ESI-IM spectrometer tolerates high water contents (<= 90%) and electrolyte concentrations up to 10 mM, meeting another condition required of high-performance liquid chromatography (HPLC) detectors. Limits of detection of 50 nM for promazine in the positive mode and 1 mu M for 1,3-dinitrobenzene in the negative mode were established. Three mixtures of reduced complexity (five surfactants, four neuroleptics, and two isomers) were separated in the millisecond regime in stand-alone operation of the spectrometer. Separations of two more complex mixtures (five neuroleptics and 13 pesticides) demonstrate the application of the spectrometer as an HPLC detector. The examples illustrate the advantages of the spectrometer over the established diode array detector, in terms of additional IM separation of substances not fully separated in the retention time domain as well as identification of substances based on their characteristic IMs.
The combination of high-performance liquid chromatography and electrospray ionization ion mobility spectrometry facilitates the two-dimensional separation of complex mixtures in the retention and drift time plane. The ion mobility spectrometer presented here was optimized for flow rates customarily used in high-performance liquid chromatography between 100 and 1500 mu L/min. The characterization of the system with respect to such parameters as the peak capacity of each time dimension and of the 2D spectrum was carried out based on a separation of a pesticide mixture containing 24 substances. While the total ion current chromatogram is coarsely resolved, exhibiting coelutions for a number of compounds, all substances can be separately detected in the 2D plane due to the orthogonality of the separations in retention and drift dimensions. Another major advantage of the ion mobility detector is the identification of substances based on their characteristic mobilities. Electrospray ionization allows the detection of substances lacking a chromophore. As an example, the separation of a mixture of 18 amino acids is presented. A software built upon the free mass spectrometry package OpenMS was developed for processing the extensive 2D data. The different processing steps are implemented as separate modules which can be arranged in a graphic workflow facilitating automated processing of data.
The increasing development of antibiotic resistance in bacteria has been a major problem for years, both in human and veterinary medicine. Prophylactic measures, such as the use of vaccines, are of great importance in reducing the use of antibiotics in livestock. These vaccines are mainly produced based on formaldehyde inactivation. However, the latter damages the recognition elements of the bacterial proteins and thus could reduce the immune response in the animal. An alternative inactivation method developed in this work is based on gentle photodynamic inactivation using carbon nanodots (CNDs) at excitation wavelengths λex > 290 nm. The photodynamic inactivation was characterized on the nonvirulent laboratory strain Escherichia coli K12 using synthesized CNDs. For a gentle inactivation, the CNDs must be absorbed into the cytoplasm of the E. coli cell. Thus, the inactivation through photoinduced formation of reactive oxygen species only takes place inside the bacterium, which means that the outer membrane is neither damaged nor altered. The loading of the CNDs into E. coli was examined using fluorescence microscopy. Complete loading of the bacterial cells could be achieved in less than 10 min. These studies revealed a reversible uptake process allowing the recovery and reuse of the CNDs after irradiation and before the administration of the vaccine. The success of photodynamic inactivation was verified by viability assays on agar. In a homemade flow photoreactor, the fastest successful irradiation of the bacteria could be carried out in 34 s. Therefore, the photodynamic inactivation based on CNDs is very effective. The membrane integrity of the bacteria after irradiation was verified by slide agglutination and atomic force microscopy. The method developed for the laboratory strain E. coli K12 could then be successfully applied to the important avian pathogens Bordetella avium and Ornithobacterium rhinotracheale to aid the development of novel vaccines.
Decoupling of optical properties appears challenging, but vital to get better insight of the relationship between light and fruit attributes. In this study, nine solid phantoms capturing the ranges of absorption (μa) and reduced scattering (μs’) coefficients in fruit were analysed non-destructively using laser-induced backscattering imaging (LLBI) at 1060 nm. Data analysis of LLBI was carried out on the diffuse reflectance, attenuation profile obtained by means of Farrell’s diffusion theory either calculating μa [cm−1] and μs’ [cm−1] in one fitting step or fitting only one optical variable and providing the other one from a destructive analysis. The nondestructive approach was approved when calculating one unknown coefficient non-destructively, while no ability of the method was found to analysis both, μa and μs’, non-destructively. Setting μs’ according to destructive photon density wave (PDW) spectroscopy and fitting μa resulted in root mean square error (rmse) of 18.7% in comparison to fitting μs’ resulting in rmse of 2.6%, pointing to decreased measuring uncertainty, when the highly variable μa was known.
The approach was tested on European pear, utilizing destructive PDW spectroscopy for setting one variable, while LLBI was applied for calculating the remaining coefficient. Results indicated that the optical properties of pear obtained from PDW spectroscopy as well as LLBI changed concurrently in correspondence to water content mainly. A destructive batch-wise analysis of μs’ and online analysis of μa may be considered in future developments for improved fruit sorting results, when considering fruit with high variability of μs’.
Photovoltaic cells based on halide perovskites, possessing remarkably high power conversion efficiencies have been reported. To push the development of such devices further, a comprehensive and reliable understanding of their electronic properties is essential but presently not available. To provide a solid foundation for understanding the electronic properties of polycrystalline thin films, we employ single-crystal band structure data from angle-resolved photoemission measurements. For two prototypical perovskites (CH3NH3PbBr3 and CH3NH3PbI3), we reveal the band dispersion in two high-symmetry directions and identify the global valence band maxima. With these benchmark data, we construct "standard" photoemission spectra from polycrystalline thin film samples and resolve challenges discussed in the literature for determining the valence band onset with high reliability. Within the framework laid out here, the consistency of relating the energy level alignment in perovskite-based photovoltaic and optoelectronic devices with their functional parameters is substantially enhanced.
This article presents a simple and facile method to fabricate thermoresponsive polymer-grafted silica particles by direct surface-initiated photopolymerization of N-isopropylacrylamide (NIPAM). This method is based on silica particles bearing thiol functionalities, which are transformed into thiyl radicals by irradiation with UV light to initiate the polymerization of NIPAM in aqueous media at room temperature. The photopolymerization of NIPAM could be applied to smaller thiol-functionalized particles (approximate to 48 nm) as well as to larger particles (approximate to 692 nm). Hollow poly(NIPAM) capsules could be formed after etching away the silica cores from the composite particles. It is possible to produce tailor-made composite particles or capsules for particular applications by extending this approach to other vinyl monomers. (c) 2015 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 2015, 53, 1260-1267
The combination of gold nanoparticles with liposomes is important for nano- and biotechnology. Here, we present direct, label-free characterization of liposome structure and composition at the site of its interaction with citrate-stabilized gold nanoparticles by surface-enhanced Raman scattering (SERS) and cryogenic electron microscopy (cryo-EM). Evidenced by the vibrational spectra and cryo-EM, the gold nanoparticles destroy the bilayer structure of interacting liposomes in the presence of a high amount of citrate, while at lower citrate concentration the nanoparticles interact with the surface of the intact liposomes. The spectra of phosphatidylcholine and phosphatidylcholine/sphingomyelin liposomes show that at the site of interaction the lipid chains are in the gel phase. The SERS spectra indicate that cholesterol has strong effects on the contacts of the vesicles with the nanoparticles. By combining cryo-EM and SERS, the structure and properties of lipid nanoparticle composites could be tailored for the development of drug delivery systems.
Magnetic ionogels (MagIGs) were prepared from organosilane-coated iron oxide nanoparticles, N-isopropylacrylamide, and the ionic liquid trihexyl(tetradecyl)phosphonium dicyanamide. The ionogels prepared with the silane-modified nanoparticles are more homogeneous than ionogels prepared with unmodified magnetite particles. The silane-modified particles are immobilized in the ionogel and are resistant tonanoparticle leaching. The modified particles also render the ionogels mechanically more stable than the ionogels synthesized with unmodified nanoparticles. The ionogels respond to external permanent magnets and are therefore prototypes of a new soft magnetic actuator.
Polypropylene as one of the world's top commodity polymers is also widely used in the textile industry. However, its non-polar nature and partially crystalline structure significantly complicate the process of industrial coloring of polypropylene. Currently, textiles made of polypropylene or with a significant proportion of polypropylene are dyed under quite harsh conditions, including the use of high pressures and temperatures, which makes this process energy intensive. This research presents a three-step synthesis of coloring agents, capable of adhering onto synthetic polypropylene yarns without harsh energy-consuming conditions. This is possible by encapsulation of organic pigments using trimethoxyphenylsilane, introduction of surface double bonds via modification of the silica shell with trimethoxysilylpropylmethacrylate and final attachment of highly adhesive anchor peptides using thiol-ene chemistry. We demonstrate the applicability of this approach by dyeing polypropylene yarns in a simple process under ambient conditions after giving a step-by-step guide for the synthesis of these new dyeing agents. Finally, the successful dyeing of the yarns is visualized, and its practicability is discussed.
Polypropylene as one of the world's top commodity polymers is also widely used in the textile industry. However, its non-polar nature and partially crystalline structure significantly complicate the process of industrial coloring of polypropylene. Currently, textiles made of polypropylene or with a significant proportion of polypropylene are dyed under quite harsh conditions, including the use of high pressures and temperatures, which makes this process energy intensive. This research presents a three-step synthesis of coloring agents, capable of adhering onto synthetic polypropylene yarns without harsh energy-consuming conditions. This is possible by encapsulation of organic pigments using trimethoxyphenylsilane, introduction of surface double bonds via modification of the silica shell with trimethoxysilylpropylmethacrylate and final attachment of highly adhesive anchor peptides using thiol-ene chemistry. We demonstrate the applicability of this approach by dyeing polypropylene yarns in a simple process under ambient conditions after giving a step-by-step guide for the synthesis of these new dyeing agents. Finally, the successful dyeing of the yarns is visualized, and its practicability is discussed.
A straightforward approach for the precise multifunctional surface modification of particles with three-dimensional patches using microcontact printing is presented. By comparison to previous works it was possible to not only control the diameter, but also to finely tune the thickness of the deposited layer, opening up the way for three-dimensional structures and orthogonal multifunctionality. The use of PEI as polymeric ink, PDMS stamps for microcontact printing on silica particles and the influence of different solvents during particle release on the creation of functional particles with three-dimensional patches are described. Finally, by introducing fluorescent properties by incorporation of quantum dots into patches and by particle self-assembly via avidin-biotin coupling, the versatility of this novel modification method is demonstrated.
This publication demonstrates the abilities of a precise and straightforward microcontact printing approach for the preparation of patchy silica particles. In a broad particle size range, it is possible to finely tune the number and parameters of three-dimensional patches like diameter and thickness using only polyethyleneimine ink, poly(dimethoxysilane) as stamp material and a suitable release solvent.
This research addressed the question, if it is possible to simplify current microcontact printing systems for the production of anisotropic building blocks or patchy particles, by using common chemicals while still maintaining reproducibility, high precision and tunability of the Janus-balance
Chapter 2 introduced the microcontact printing materials as well as their defined electrostatic interactions. In particular polydimethylsiloxane stamps, silica particles and high molecular weight polyethylenimine ink were mainly used in this research. All of these components are commercially available in large quantities and affordable, which gives this approach a huge potential for further up-scaling developments. The benefits of polymeric over molecular inks was described including its flexible influence on the printing pressure. With this alteration of the µCP concept, a new method of solvent assisted particle release mechanism enabled the switch from two-dimensional surface modification to three-dimensional structure printing on colloidal silica particles, without changing printing parameters or starting materials. This effect opened the way to use the internal volume of the achieved patches for incorporation of nano additives, introducing additional physical properties into the patches without alteration of the surface chemistry.
The success of this system and its achievable range was further investigated in chapter 3 by giving detailed information about patch geometry parameters including diameter, thickness and yield. For this purpose, silica particles in a size range between 1µm and 5µm were printed with different ink concentrations to change the Janus-balance of these single patched particles. A necessary intermediate step, consisting of air-plasma treatment, for the production of trivalent particles using "sandwich" printing was discovered and comparative studies concerning the patch geometry of single and double patched particles were conducted. Additionally, the usage of structured PDMS stamps during printing was described. These results demonstrate the excellent precision of this approach and opens the pathway for even greater accuracy as further parameters can be finely tuned and investigated, e.g. humidity and temperature during stamp loading.
The performance of these synthesized anisotropic colloids was further investigated in chapter 4, starting with behaviour studies in alcoholic and aqueous dispersions. Here, the stability of the applied patches was studied in a broad pH range, discovering a release mechanism by disabling the electrostatic bonding between particle surface and polyelectrolyte ink. Furthermore, the absence of strong attractive forces between divalent particles in water was investigated using XPS measurements. These results lead to the conclusion that the transfer of small PDMS oligomers onto the patch surface is shielding charges, preventing colloidal agglomeration. However, based on this knowledge, further patch modifications for particle self-assembly were introduced including physical approaches using magnetic nano additives, chemical patch functionalization with avidin-biotin or the light responsive cyclodextrin-arylazopyrazoles coupling as well as particle surface modification for the synthesis of highly amphiphilic colloids. The successful coupling, its efficiency, stability and behaviour in different solvents were evaluated to find a suitable coupling system for future assembly experiments. Based on these results the possibility of more sophisticated structures by colloidal self-assembly is given.
Certain findings needed further analysis to understand their underlying mechanics, including the relatively broad patch diameter distribution and the decreasing patch thickness for smaller silica particles. Mathematical assumptions for both effects are introduced in chapter 5. First, they demonstrate the connection between the naturally occurring particle size distribution and the broadening of the patch diameter, indicating an even higher precision for this µCP approach. Second, explaining the increase of contact area between particle and ink surface due to higher particle packaging, leading to a decrease in printing pressure for smaller particles.
These calculations ultimately lead to the development of a new mechanical microcontact printing approach, using centrifugal forces for high pressure control and excellent parallel alignment of printing substrates. First results with this device and the comparison with previously conducted by-hand experiments conclude this research. It furthermore displays the advantages of such a device for future applications using a mechanical printing approach, especially for accessing even smaller nano particles with great precision and excellent yield.
In conclusion, this work demonstrates the successful adjustment of the µCP approach using commercially available and affordable silica particles and polyelectrolytes for high flexibility, reduced costs and higher scale-up value. Furthermore, its was possible to increase the modification potential by introducing three-dimensional patches for additional functionalization volume. While keeping a high colloidal stability, different coupling systems showed the self-assembly capabilities of this toolbox for anisotropic particles.
Sulfated biomolecules are known to influence numerous biological processes in all living organisms. Particularly, they contribute to prevent and inhibit the hypercoagulation condition. The failure of polymeric implants and blood contacting devices is often related to hypercoagulation and microbial contamination. Here, bioactive sulfated biomacromolecules are mimicked by sulfation of poly(glycerol glycidyl ether) (polyGGE) films. Autoclaving, gamma-ray irradiation and ethylene oxide (EtO) gas sterilization techniques were applied to functionalized materials. The sulfate group density and hydrophilicity of sulfated polymers were decreased while chain mobility and thermal degradation were enhanced post autoclaving when compared to those after EtO sterilization. These results suggest that a quality control after sterilization is mandatory to ensure the amount and functionality of functionalized groups are retained.
Cardiovascular diseases are the main cause of death worldwide, and their prevalence is expected to rise in the coming years. Polymer-based artificial replacements have been widely used for the treatment of cardiovascular diseases. Coagulation and thrombus formation on the interfaces between the materials and the human physiological environment are key issues leading to the failure of the medical device in clinical implantation. The surface properties of the materials have a strong influence on the protein adsorption and can direct the blood cell adhesion behavior on the interfaces. Furthermore, implant-associated infections will be induced by bacterial adhesion and subsequent biofilm formation at the implantation site. Thus, it is important to improve the hemocompatibility of an implant by altering the surface properties. One of the effective strategies is surface passivation to achieve protein/cell repelling ability to reduce the risk of thrombosis.
This thesis consists of synthesis, functionalization, sterilization, and biological evaluation of bulk poly(glycerol glycidyl ether) (polyGGE), which is a highly crosslinked polyether-based polymer synthesized by cationic ring-opening polymerization. PolyGGE is hypothesized to be able to resist plasma protein adsorption and bacterial adhesion due to analogous chemical structure as polyethylene glycol and hyperbranched polyglycerol. Hydroxyl end groups of polyGGE provide possibilities to be functionalized with sulfates to mimic the anti-thrombogenic function of the endothelial glycocalyx.
PolyGGE was synthesized by polymerization of the commercially available monomer glycerol glycidyl ether, which was characterized as a mixture of mono-, di- and tri-glycidyl ether. Cationic ring opening-polymerization of this monomer was carried out by ultraviolet (UV) initiation of the photo-initiator diphenyliodonium hexafluorophosphate. With the increased UV curing time, more epoxides in the side chains of the monomers participated in chemical crosslinking, resulting in an increase of Young’s modulus, while the value of elongation at break of polyGGE first increased due to the propagation of the polymer chains then decreased with the increase of crosslinking density. Eventually, the chain propagation can be effectively terminated by potassium hydroxide aqueous solution. PolyGGE exhibited different tensile properties in hydrated conditions at body temperature compared to the values in the dry state at room temperature. Both Young’s modulus and values of elongation at break were remarkably reduced when tested in water at 37 °C, which was above the glass transition temperature of polyGGE. At physiological conditions, entanglements of the ployGGE networks unfolded and the free volume of networks were replaced by water molecules as softener, which increased the mobility of the polymer chains, resulting in a lower Young’s modulus.
Protein adsorption analysis was performed on polyGGE films with 30 min UV curing using an enzyme-linked immunosorbent assay. PolyGGE could effectively prevent the adsorption of human plasma fibrinogen, albumin, and fibronectin at the interface of human plasma and polyGGE films. The protein resistance of polyGGE was comparable to the negative controls: the hemocompatible polydimethylsiloxane (PDMS), showing its potential as a coating material for cardiovascular implants. Moreover, antimicrobial tests of bacterial activity using isothermal microcalorimetry and the microscopic image of direct bacteria culturing demonstrated that polyGGE could directly interfere biofilm formation and growth of both Gram-negative and antibiotic-resistant Gram-positive bacteria, indicating the potential application of polyGGE for combating the risk of hospital-acquired infections and preventing drug-resistant superbug spreading.
To investigate its cell compatibility, polyGGE films were extracted by different solvents (ethanol, chloroform, acetone) and cell culture medium. Indirect cytotoxicity tests showed extracted polyGGE films still had toxic effects on L929 fibroblast cells. High-performance liquid chromatography/electrospray ionization mass spectrometry revealed the occurrence of organochlorine-containing compounds released during the polymer-cell culture medium interaction. A constant level of those organochlorine-containing compounds was confirmed from GGE monomer by a specific peak of C-Cl stretching in infrared spectra of GGE. This is assumed to be the main reason causing the increased cell membrane permeability and decreased metabolic activity, leading to cell death. Attempts as changing solvents were made to remove toxic substances, however, the release of these small molecules seems to be sluggish. The densely crosslinked polyGGE networks can possibly contribute to the trapping of organochlorine-containing compounds. These results provide valuable information for exploring the potentially toxic substances, leaching from polyGGE networks, and propose a feasible strategy for minimizing the cytotoxicity via reducing their crosslinking density.
Sulfamic acid/ N-Methyl-2-pyrrolidone (NMP) were selected as the reagents for the sulfation of polyGGE surfaces. Fourier transform attenuated total reflection infrared spectroscopy (ATR-FT-IR) was used to monitor the functionalization kinetics and the results confirmed the successful sulfate grafting on the surface of polyGGE with the covalent bond -C-O-S-. X-ray photoelectron spectroscopy was used to determine the element composition on the surface and the cross-section of the functionalized polyGGE and sulfation within 15 min guarantees the sulfation only takes place on the surface while not occurring in the bulk of the polymer. The concentration of grafted sulfates increased with the increasing reaction time. The hydrophilicity of the surface of polyGGE was highly increased due to the increase of negatively charged end groups. Three sterilization techniques including autoclaving, gamma irradiation, and ethylene oxide (EtO) sterilization were used for polyGGE sulfates. Results from ATR-FT-IR and Toluidine Blue O quantitative assay demonstrated the total loss of the sulfates after autoclave sterilization, which was also confirmed by the increased water contact angle. Little influence on the concentration of sulfates was found for gamma-irradiated and autoclaving sterilized polyGGE sulfates. To investigate the thermal influence on polyGGE sulfates, one strategy was to use poly(hydroxyethyl acrylate) sulfates (PHEAS) for modeling. The thermogravimetric analysis profile of PHEAS demonstrated that sulfates are not thermally stable independent of the substrate materials and decomposition of sulfates occurs at around 100 °C. Although gamma irradiation also showed little negative effect on the sulfate content, the color change in the polyGGE sulfates indicates chemical or physical change might occur in the polymer. EtO sterilization was validated as the most suitable sterilization technique to maintain the chemical structure of polyGGE sulfates.
In conclusion, the conducted work proved that bulk polyGGE can be used as an antifouling coating material and shows its antimicrobial potential. Sulfates functionalization can be effectively realized using sulfamic acid/NMP. EtO sterilization is the most suitable sterilization technique for grafted sulfates. Besides, this thesis also offers a good strategy for the analysis of toxic leachable substances using suitable physicochemical characterization techniques. Future work will focus on minimizing/eliminating the release of toxic substances via reducing the crosslinking density. Another interesting aspect is to study whether grafted sulfates can meet the need for anti-thrombogenicity.
Tailoring cell–surface interactions is important for the of design medical implants as well as regenerative medicine and tissue engineering materials. Here the single parameter system is transcended via translating hard nanotopology into soft polymeric hydrogel structures via hydrogel imprinting lithography. The response of these cells to the nanotopology of the same dimensions but with different mechanical properties displays unexpected behavior between “hard” tissue cells and “soft” tissue cells.
The effect of chain architecture on the swelling and thermal response of thin films obtained from an amphiphilic three-arm star-shaped thermo-responsive block copolymer poly(methoxy diethylene glycol acrylate)-block-polystyrene ((PMDEGA-b-PS)(3)) is investigated by in situ neutron reflectivity (NR) measurements. The PMDEGA and PS blocks are micro-phase separated with randomly distributed PS nanodomains. The (PMDEGA-b-PS)(3) films show a transition temperature (TT) at 33 degrees C in white light interferometry. The swelling capability of the (PMDEGA-b-PS)(3) films in a D2O vapor atmosphere is better than that of films from linear PS-b-PMDEGA-b-PS triblock copolymers, which can be attributed to the hydrophilic end groups and limited size of the PS blocks in (PMDEGA-b-PS)(3). However, the swelling kinetics of the as-prepared (PMDEGA-b-PS)(3) films and the response of the swollen film to a temperature change above the TT are significantly slower than that in the PS-b-PMDEGA-b-PS films, which may be related to the conformation restriction by the star-shape. Unlike in the PS-b-PMDEGA-b-PS films, the amount of residual D2O in the collapsed (PMDEGA-b-PS)(3) films depends on the final temperature. It decreases from (9.7 +/- 0.3)% to (7.0 +/- 0.3)% or (6.0 +/- 0.3)% when the final temperatures are set to 35 degrees C, 45 degrees C and 50 degrees C, respectively. This temperature-dependent reduction of embedded D2O originates from the hindrance of chain conformation from the star-shaped chain architecture.
The rehydration of thermoresponsive poly(monomethoxydiethylene glycol acrylate) (PMDEGA) films exhibiting a lower critical solution temperature (LCST) type demixing phase transition in aqueous environments, induced by a decrease in temperature, is investigated in situ with real-time neutron reflectivity. Two different starting conditions (collapsed versus partially swollen chain conformation) are compared. In one experiment, the temperature is reduced from above the demixing temperature to well below the demixing temperature. In a second experiment, the starting temperature is below the demixing temperature, but within the transition regime, and reduced to the same final temperature. In both cases, the observed rehydration process can be divided into three stages: first condensation of water from the surrounding atmosphere, then absorption of water by the PMDEGA film and evaporation of excess water, and finally, rearrangement of the PMDEGA chains. The final rehydrated film is thicker and contains more absorbed water as compared with the initially swollen film at the same temperature well below the demixing temperature.
Thin thermoresponsive films of the triblock copolymer polystyrene-block-poly(methoxydiethylene glycol acrylate)-block-polystyrene (P(S-b-MDEGA-b-S)) are investigated on silicon substrates. By spin coating, homogeneous and smooth films are prepared for a range of film thicknesses from 6 to 82 nm. Films are stable with respect to dewetting as investigated with optical microscopy and atomic force microscopy. P(S-b-MDEGA-b-S) films with a thickness of 39 nm exhibit a phase transition of the lower critical solution temperature (LCST) type at 36.5 degrees C. The swelling and the thermoresponsive behavior of the films with respect to a sudden thermal stimulus are probed with in-situ neutron reflectivity. In undersaturated water vapor swelling proceeds without thickness increase. The thermoresponse proceeds in three steps: First, the film rejects water as the temperature is above LCST. Next, it stays constant for 600 s, before the collapsed film takes up water again. With ATR-FTIR measurements, changes of bound water in the film caused by different thermal stimuli are studied. Hydrogen bonds only form between C=O and water in the swollen film. Above the LCST most hydrogen bonds with water are broken, but some amount of bound water remains inside the film in agreement with the neutron reflectivity data. Grazing-incidence small-angle X-ray scattering (GISAXS) shows that the inner lateral structure is not significantly influenced by the different thermal stimuli.
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.
The rehydration of thermoresponsive polystyrene-block-poly(methoxy diethylene glycol acrylate)-block-polystyrene (PS-b-PMDEGA-b-PS) films forming a lamellar microphase-separated structure is investigated by in situ neutron reflectivity in a D2O vapor atmosphere. The rehydration of collapsed PS-b-PMDEGA-b-PS films is realized by a temperature change from 45 to 23 degrees C and comprises (1) condensation and absorption of D2O, (2) evaporation of D2O, and (3) reswelling of the film due to internal rearrangement. The hydrophobic PS layers hinder the absorption of condensed D2O, and a redistribution of embedded D2O between the hydrophobic PS layers and the hydrophilic PMDEGA layers is observed. In contrast, the rehydration of semiswollen PS-b-PMDEGA-b-PS films (temperature change from 35 to 23 degrees C) shows two prominent differences: A thicker D2O layer condenses on the surface, causing a more enhanced evaporation of D2O. The rehydrated films differ in film thickness and volume fraction of D2O, which is due to the different thermal protocols, although the final temperature is identical.
The switching kinetics of thin thermo-responsive hydrogel films of poly(monomethoxy-diethyleneglycol-acrylate) (PMDEGA) are investigated. Homogeneous and smooth PMDEGA films with a thickness of 35.9 nm are prepared on silicon substrates by spin coating. As probed with white light interferometry, PMDEGA films with a thickness of 35.9 nm exhibit a phase transition temperature of the lower critical solution temperature (LCST) type of 40 degrees C. In situ neutron reflectivity is performed to investigate the thermo-responsive behavior of these PMDEGA hydrogel films in response to a sudden thermal stimulus in deuterated water vapor atmosphere. The collapse transition proceeds in a complex way which can be seen as three steps. The first step is the shrinkage of the initially swollen film by a release of water. In the second step the thickness remains constant with water molecules embedded in the film. In the third step, perhaps due to a conformational rearrangement of the collapsed PMDEGA chains, water is reabsorbed from the vapor atmosphere, thereby giving rise to a relaxation process. Both the shrinkage and relaxation processes can be described by a simple model of hydrogel deswelling.
Thick poly(styrene-b-monomethoxydiethylenglycol-acrylate-b-styrene) [P(S-b-MDEGA-b-S)] films (thickness 5 mu m) are prepared from different solvents on flexible substrates by solution casting and investigated with small-angle X-ray scattering. As the solvents are either PS- or PMDEGA-selective, micelles with different core-shell micellar structures are formed. In PMDEGA-selective solvents, the PS block is the core and PMDEGA is the shell, whereas in PS-selective solvents, the order is reversed. After exposing the films to liquid D2O, the micellar structure inside the films prepared from PMDEGA-selective solvents remains unchanged and only the PMDEGA (shell part) swells. On the contrary, in the films prepared from PS-selective solvents, the micelles revert the core and the shell. This reversal causes more entanglements of the PMDEGA chains between the micelles. Moreover, the thermal collapse transition of the PMDEGA block in liquid D2O is significantly broadened. Irrespective of the solvent used for film preparation, the swollen PMDEGA shell does not show a prominent shrinkage when passing the phase transition, and the transition process occurs via compaction. The collapsed micelles have a tendency to densely pack above the transition temperature.
Polypeptoids are noticeable biological materials due to their versatile properties and various applications in drug delivery, surface modification, self-assembly, etc. N-Substituted glycine N-thiocarboxyanhydrides (NNTAs) are more stable monomers than the corresponding N-carboxyanhydrides (NNCAs) and enable one to prepare polypeptoids via ring-opening polymerization even in the presence of water. However, larger amounts of water (>10,000 ppm) cause inhibition of the polymerization. Herein, we discover that during polymerization hydrogen sulfide evolves from the hydrolysis of carbonyl sulfide, which is the byproduct of ring-opening reaction, and reacts with NNTA to produce cyclic oligopeptoids. The capture of N-ethylethanethioic acid as an intermediate product confirms the reaction mechanism together with density functional theory quantum computational results. By bubbling the polymerization solution with argon, the side reaction can be suppressed to allow the synthesis of polysarcosine with high molar mass (M-n = 11,200 g/mol, D = 1.25) even in the presence of similar to 10,000 ppm of water.
Bimetallic nanostructures comprising plasmonic and catalytic components have recently emerged as a promising approach to generate a new type of photo-enhanced nanoreactors. Most designs however concentrate on plasmon-induced charge separation, leaving photo-generated heat as a side product.
This work presents a photoreactor based on Au-Pd nanorods with an optimized photothermal conversion, which aims to effectively utilize the photo-generated heat to increase the rate of Pd-catalyzed reactions. Dumbbell-shaped Au nanorods were fabricated via a seed-mediated growth method using binary surfactants. Pd clusters were selectively grown at the tips of the Au nanorods, using the zeta potential as a new synthetic parameter to indicate the surfactant remaining on the nanorod surface.
The photothermal conversion of the Au-Pd nanorods was improved with a thin layer of polydopamine (PDA) or TiO2.
As a result, a 60% higher temperature increment of the dispersion compared to that for bare Au rods at the same light intensity and particle density could be achieved.
The catalytic performance of the coated particles was then tested using the reduction of 4-nitrophenol as the model reaction. Under light, the PDA-coated Au-Pd nanorods exhibited an improved catalytic activity, increasing the reaction rate by a factor 3.
An analysis of the activation energy confirmed the photoheating effect to be the dominant mechanism accelerating the reaction. Thus, the increased photothermal heating is responsible for the reaction acceleration.
Interestingly, the same analysis shows a roughly 10% higher reaction rate for particles under illumination compared to under dark heating, possibly implying a crucial role of localized heat gradients at the particle surface.
Finally, the coating thickness was identified as an essential parameter determining the photothermal conversion efficiency and the reaction acceleration.
In this study, the kinetics of the adsorption of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ) on the surface of Ag nanoparticles (Ag NPs) in chloroform has been intensively investigated, as molecular doping is known to play a crucial role in organic electronic devices. Based on the results obtained from UV-visible (vis)-near-infrared (NIR) absorption spectroscopy, cryogenic transmission electron microscopy, scanning nanobeam electron diffraction, and electron energy loss spectroscopy, a two-step interaction kinetics has been proposed for the Ag NPs and F(4)TCNQ molecules, which includes the first step of electron transfer from Ag NPs to F(4)TCNQ indicated by the ionization of F(4)TCNQ and the second step of the formation of a Ag-F(4)TCNQ complex. The whole process has been followed via UV-vis-NIR absorption spectroscopy, which reveals distinct kinetics at two stages: the instantaneous ionization and the long-term complex formation. The kinetics and the influence of the molar ratio of Ag NPs/F(4)TCNQ molecules on the interaction between Ag NPs and F(4)TCNQ molecules in an organic solution are reported herein for the first time. Furthermore, the control experiment with silica-coated Ag NPs manifests that the charge transfer at the surface between Ag NPs and F(4)TCNQ molecules is prohibited by a silica layer of 18 nm.
This thesis focuses on the synthesis of novel functional materials based on plasmonic nanoparticles. Three systems with targeted surface modification and functionalization have been designed and synthesized, involving modified perylenediimide doped silica-coated silver nanowires, polydopamine or TiO2 coated gold-palladium nanorods and thiolated poly(ethylene glycol) (PEG-SH)/dodecanethiol (DDT) modified silver nanospheres. Their possible applications as plasmonic resonators, chiral sensors as well as photo-catalysts have been studied. In addition, the interaction between silver nanospheres and 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) molecules has also been investigated in detail.
In the first part of the thesis, surface modification on Ag nanowires (NWs) with optimized silica coating through a modified Stöber method has been firstly conducted, employing sodium hydroxide (NaOH) to replace ammonia solution (NH4OH). The coated silver nanowires with a smooth silica shell have been investigated by single-particle dark-field scattering spectroscopy, transmission electron microscopy and electron-energy loss spectroscopy to characterize the morphologies and structural components. The silica-coated silver nanowires can be further functionalized with fluorescent molecules in the silica shell via a facile one-step coating method. The as-synthesized nanowire is further coupled with a gold nanosphere by spin-coating for the application of the sub-diffractional chiral sensor for the first time. The exciton-plasmon-photon interconversion in the system eases the signal detection in the perfectly matched 1D nanostructure and contributes to the high contrast of the subwavelength chiral sensing for the polarized light.
In the second part of the thesis, dumbbell-shaped Au-Pd nanorods coated with a layer of polydopamine (PDA) or titanium dioxide (TiO2) have been constructed. The PDA- and TiO2- coated Au-Pd nanorods show a strong photothermal conversion performance under NIR illumination. Moreover, the catalytic performance of the particles has been investigated using the reduction of 4-nitrophenol (4-NP) as the model reaction. Under light irradiation, the PDA-coated Au-Pd nanorods exhibit a superior catalytic activity by increasing the reaction rate constant of 3 times. The Arrhenius-like behavior of the reaction with similar activation energies in the presence and absence of light irradiation indicates the photoheating effect to be the dominant mechanism of the reaction acceleration. Thus, we attribute the enhanced performance of the catalysis to the strong photothermal effect that is driven by the optical excitation of the gold surface plasmon as well as the synergy with the PDA layer.
In the third part, the kinetic study on the adsorption of 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquino-dimethane (F4TCNQ) on the surface of Ag nanoparticles (Ag NPs) in chloroform has been reported in detail. Based on the results obtained from the UV-vis-NIR absorption spectroscopy, cryogenic transmission electron microscopy (cryo-TEM), scanning nano-beam electron diffraction (NBED) and electron energy loss spectroscopy (EELS), a two-step interaction kinetics has been proposed for the Ag NPs and F4TCNQ molecules. It includes the first step of electron transfer from Ag NPs to F4TCNQ indicated by the ionization of F4TCNQ, and the second step of the formation of Ag-F4TCNQ complex. The whole process has been followed via UV-vis-NIR absorption spectroscopy, which reveals distinct kinetics at two stages: the instantaneous ionization and the long-term complex formation. The kinetics and the influence of the molar ratio of Ag NPs/F4TCNQ molecules on the interaction between Ag NPs and F4TCNQ molecules in the organic solution are reported herein for the first time. Furthermore, the control experiment with silica-coated Ag NPs indicates that the charge transfer at the surface between Ag NPs and F4TCNQ molecules has been prohibited by a silica layer of 18 nm.
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.
Facile organization of the inorganic sandwiched heteropolytungstomolybdate K-13[Eu(SiW9Mo2O39)(2)] (E) into highly ordered supramolecular nanostructured materials by complexation with a series of cationic surfactants is achieved by the ionic self-assembly (ISA) route. The structure and phase behavior of the complexes were examined by IR spectroscopy, differential scanning calorimetry, optical microscopy, and small- and wide-angle X-ray scattering. This class of materials shows a number of interesting physicochemical properties, namely liquid-crystalline phases (both thermotropic and lyotropic) and strong photoluminescence. The photophysical behavior (fluorescence spectra, fluorescence lifetimes, fluorescence quantum yield) of the complexes differs widely in solid powders, films, and solutions. The amphiphilic cationic surfactants not only play a structural role but also have a strong influence on the photophysical properties of E. The photophysical behavior of E can in this way be easily modified by its organizational motifs
Exploration of metal clusters (MCs) adaptive to both aqueous and oil phases without disturbing their size is promising for a broad scope of applications. The state-of-the-art approach via ligand-binding may perturb MCs' size due to varied metal–ligand binding strength when shuttling between solvents of different polarity. Herein, we applied physical confinement of a series of small noble MCs (<1 nm) inside ionic organic cages (I-Cages), which by means of anion exchange enables reversible transfer of MCs between aqueous and hydrophobic solutions without varying their ultrasmall size. Moreover, the MCs@I-Cage hybrid serves as a recyclable, reaction-switchable catalyst featuring high activity in liquid-phase NH3BH3 (AB) hydrolysis reaction with a turnover frequency (TOF) of 115 min−1.
Observation of Spin Relaxation in a Vanadate Chloride with Quasi-One-Dimensional Linear Chain
(2019)
A new cobalt(II) vanadate chloride, Pb2Co(OH)(V2O7)Cl, has been synthesized under mild hydrothermal conditions. It contains quasi-one-dimensional (1D) linear chains built by edge-sharing of (CoO6)-O-II octahedra. The cobalt(II) oxide chains are further interconnected by (V2O7)(4-) dimers into a three-dimensional (3D) anionic framework with Pb2+ and Cl- ions residing in Co4V8 12-member ring tunnels. The intrachain Co center dot center dot center dot Co distance is 3.041 angstrom, while the interchain distances are 8.742 and 9.256 angstrom. Magnetic measurements suggest the ferromagnetic intrachain and the antiferromagnetic interchain interactions with a specific value of J(intra)/J(inter) = 1.7 x 10(3). Zero-field heat capacity demonstrates the magnetic long-range ordering at 5.5 K. Alternating current (AC) magnetic susceptibility under zero external direct current (DC) fields displays two slow magnetic relaxations at low temperatures, giving characteristic relaxations (tau(0)) of 1.2(3) x 10(-12) and 1.9(4) x 10(-10) s with effective energy barriers (Delta(r)) of 76.1(2) and 48.4(5) K. The energy barrier between the spin up and spin-down states can be ascribed to the ferromagnetic spin chain and the Ising-like magnetic anisotropy in Pb2Co(OH)(V2O7)Cl.
2-Deoxy-D-ribose-5-phosphate aldolase (DERA) is a biocatalyst that is capable of converting acetaldehyde and a second aldehyde as acceptor into enantiomerically pure mono- and diyhydroxyaldehydes, which are important structural motifs in a number of pharmaceutically active compounds. However, substrate as well as product inhibition requires a more-sophisticated process design for the synthesis of these motifs. One way to do so is to the couple aldehyde conversion with transport processes, which, in turn, would require an immobilization of the enzyme within a thin film that can be deposited on a membrane support. Consequently, we developed a fabrication process for such films that is based on the formation of DERA-poly(N-isopropylacrylamide) conjugates that are subsequently allowed to self-assemble at an air-water interface to yield the respective film. In this contribution, we discuss the conjugation conditions, investigate the interfacial properties of the conjugates, and, finally, demonstrate a successful film formation under the preservation of enzymatic activity.
This thesis covers the synthesis of conjugates of 2-Deoxy-D-ribose-5-phosphate aldolase (DERA) with suitable polymers and the subsequent immobilization of these conjugates in thin films via two different approaches.
2-Deoxy-D-ribose-5-phosphate aldolase (DERA) is a biocatalyst that is capable of converting acetaldehyde and a second aldehyde as acceptor into enantiomerically pure mono- and diyhydroxyaldehydes, which are important structural motifs in a number of pharmaceutically active compounds. Conjugation and immobilization renders the enzyme applicable for utilization in a continuously run biocatalytic process which avoids the common problem of product inhibition. Within this thesis, conjugates of DERA and poly(N-isopropylacrylamide) (PNIPAm) for immobilization via a self-assembly approach were synthesized and isolated, as well as conjugates with poly(N,N-dimethylacrylamide) (PDMAA) for a simplified and scalable spray-coating approach. For the DERA/PNIPAm-conjugates different synthesis routes were tested, including grafting-from and grafting-to, both being common methods for the conjugation. Furthermore, both lysines and cysteines were addressed for the conjugation in order to find optimum conjugation conditions. It turned out that conjugation via lysine causes severe activity loss as one lysine plays a key role in the catalyzing mechanism. The conjugation via the cysteines by a grafting-to approach using pyridyl disulfide (PDS) end-group functionalized polymers led to high conjugation efficiencies in the presence of polymer solubilizing NaSCN. The resulting conjugates maintained enzymatic activity and also gained high acetaldehyde tolerance which is necessary for their use later on in an industrial relevant process after their immobilization.
The resulting DERA/PNIPAm conjugates exhibited enhanced interfacial activity at the air/water interface compared to the single components, which is an important pre-requisite for the immobilization via the self-assembly approach. Conjugates with longer polymer chains formed homogeneous films on silicon wafers and glass slides while the ones with short chains could only form isolated aggregates. On top of that, long chain conjugates showed better activity maintenance upon the immobilization.
The crosslinking of conjugates, as well as their fixation on the support materials, are important for the mechanical stability of the films obtained from the self-assembly process. Therefore, in a second step, we introduced the UV-crosslinkable monomer DMMIBA to the PNIPAm polymers to be used for conjugation. The introduction of DMMIBA reduced the lower critical solution temperature (LCST) of the polymer and thus the water solubility at ambient conditions, resulting in lower conjugation efficiencies and in turn slightly poorer acetaldehyde tolerance of the resulting conjugates. Unlike the DERA/PNIPAm, the conjugates from the copolymer P(NIPAM-co-DMMIBA) formed continuous, homogenous films only after the crosslinking step via UV-treatment. For a firm binding of the crosslinked films, a functionalization protocol for the model support material cyclic olefin copolymer (COC) and the final target support, PAN based membranes, was developed that introduces analogue UV-reactive groups to the support surface. The conjugates immobilized on the modified COC films maintained enzymatic activity and showed good mechanical stability after several cycles of activity assessment. Conjugates with longer polymer chains, however, showed a higher degree of crosslinking after the UV-treatment leading to a pronounced loss of activity. A porous PAN membrane onto which the conjugates were immobilized as well, was finally transferred to a dead end filtration membrane module to catalyze the aldol reaction of the industrially relevant mixture of acetaldehyde and hexanal in a continuous mode. Mono aldol product was detectable, but yields were comparably low and the operational stability needs to be further improved
Another approach towards immobilization of DERA conjugates that was followed, was to generate the conjugates in situ by simply mixing enzyme and polymer and spray coat the mixture onto the membrane support. Compared to the previous approach, the focus was more put on simplicity and a possible scalability of the immobilization. Conjugates were thus only generated in-situ and not further isolated and characterized. For the conjugation, PDMAA equipped with N-2-thiolactone acrylamide (TlaAm) side chains was used, an amine-reactive comonomer that can react with the lysine residues of DERA, as well as with amino groups introduced to a desired support surface. Furthermore disulfide formation after hydrolysis of the Tla groups causes a crosslinking effect. The synthesized copolymer poly(N,N-Dimethylacrylamide-co-N-2-thiolactone acrylamide) (P(DMAA-co-TlaAm)) thus serves a multiple purpose including protein binding, crosslinking and binding to support materials. The mixture of DERA and polymer could be immobilized on the PAN support by spray-coating under partial maintenance of enzymatic activity. To improve the acetaldehyde tolerance, the polymer in used was further equipped with cysteine reactive PDS end-groups that had been used for the conjugation as described in the first part of the thesis. The generated conjugates indeed showed good acetaldehyde tolerance and were thus used to be coated onto PAN membrane supports. Post treatment with a basic aqueous solution of H2O2 was supposed to further crosslink the spray-coated film hydrolysis and oxidation of the thiolactone groups. However, a washing off of the material was observed. Optimization is thus still necessary.
Collagen-based biomaterials with oriented fibrils have shown great application potential in medicine. However, it is still challenging to control the type I collagen fibrillogenesis in ultrathin films. Here, we report an approach to produce cohesive and well-organized type I collagen ultrathin films of about 10 nm thickness using the Langmuir-Blodgett technique. Ellipsometry, rheology, and Brewster angle microscopy are applied to investigate in situ how the molecules behave at the air-water interface, both at room temperature and 37 degrees C. The interfacial storage modulus observed at room temperature vanishes upon heating, indicating the existence and disappearance of the network structure in the protein nanosheet. The films were spanning over holes as large as 1 mm diameter when transferred at room temperature, proving the strong cohesive interactions. A highly aligned and fibrillar structure was observed by atomic force microscopy (AFM) and optical microscopy.
Shape-Memory Capability of Copolyetheresterurethane Microparticles Prepared via Electrospraying
(2015)
Multifunctional thermo-responsive and degradable microparticles exhibiting a shapememory effect (SME) have attracted widespread interest in biomedicine as switchable delivery vehicles or microactuators. In this work almost spherical solid microparticles with an average diameter of 3.9 +/- 0.9 mm are prepared via electrospraying of a copolyetheresterurethane named PDC, which is composed of crystallizable oligo(p-dioxanone) (OPDO) hard and oligo(e-caprolactone) (OCL) switching segments. The PDC microparticles are programmed via compression at different pressures and their shapememory capability is explored by off-line and online heating experiments. When a low programming pressure of 0.2 MPa is applied a pronounced thermally-induced shape-memory effect is achieved with a shape recovery ratio about 80%, while a high programming pressure of 100 MPa resulted in a weak shape-memory performance. Finally, it is demonstrated that an array of PDC microparticles deposited on a polypropylene (PP) substrate can be successfully programmed into a smart temporary film, which disintegrates upon heating to 60 degrees C.
Fibrous membranes capable of dynamically responding to external stimuli are highly desirable in textiles and biomedical materials, where adaptive behavior is required to accommodate complex environmental changes. For example, the creation of fabrics with temperature-dependent moisture permeability or self-regulating membranes for air filtration is dependent on the development of materials that exhibit a reversible stimuli-responsive pore size change. Here, by imbuing covalently crosslinked poly(ε-caprolactone) (cPCL) fibrous meshes with a reversible bidirectional shape-memory polymer actuation (rbSMPA) we create a material capable of temperature-controlled changes in porosity. Cyclic thermomechanical testing was used to characterize the mechanical properties of the meshes, which were composed of randomly arranged microfibers with diameters of 2.3 ± 0.6 μm giving an average pore size of approx. 10 μm. When subjected to programming strains of εm = 300% and 100% reversible strain changes of εʹrev = 22% ± 1% and 6% ± 1% were measured, with switching temperature ranges of 10 °C–30 °C and 45 °C–60 °C for heating and cooling, respectively. The rbSMPA of cPCL fibrous meshes generated a microscale reversible pore size change of 11% ± 3% (an average of 1.5 ± 0.6 μm), as measured by scanning electron microscopy. The incorporation of a two-way shape-memory actuation capability into fibrous meshes is anticipated to advance the development and application of smart membrane materials, creating commercially viable textiles and devices with enhanced performance and novel functionality.
The ongoing trend of miniaturizing multifunctional devices, especially for minimally-invasive medical or sensor applications demands new strategies for designing the required functional polymeric micro-components or micro-devices. Here, polymers, which are capable of active movement, when an external stimulus is applied (e.g. shape-memory polymers), are intensively discussed as promising material candidates for realization of multifunctional micro-components. In this context further research activities are needed to gain a better knowledge about the underlying working principles for functionalization of polymeric micro-scale objects with a shape-memory effect. First reports about electrospun solid microfiber scaffolds, demonstrated a much more pronounced shape-memory effect than their bulk counterparts, indicating the high potential of electrospun micro-objects.
Based on these initial findings this thesis was aimed at exploring whether the alteration of the geometry of micro-scale electrospun polymeric objects can serve as suitable parameter to tailor their shape-memory properties. The central hypothesis was that different geometries should result in different degrees of macromolecular chain orientation in the polymeric micro-scale objects, which will influence their mechanical properties as well as thermally-induced shape-memory function. As electrospun micro-scale objects, microfiber scaffolds composed of hollow microfibers with different wall thickness and electrosprayed microparticles as well as their magneto-sensitive nanocomposites all prepared from the same polymer exhibiting pronounced bulk shape-memory properties were investigated. For this work a thermoplastic multiblock copolymer, named PDC, with excellent bulk shape-memory properties, associated with crystallizable oligo(ε-caprolactone) (OCL) switching domains, was chosen for the preparation of electrospun micro-scale objects, while crystallizable oligo(p-dioxanone) (OPDO) segments serve as hard domains in PDC.
In the first part of the thesis microfiber scaffolds with different microfiber geometries (solid or hollow with different wall thickness) were discussed. Hollow microfiber based PDC scaffolds were prepared by coaxial electrospinning from a 1, 1, 1, 3, 3, 3 hexafluoro-2-propanol (HFP) solution with a polymer concentration of 13% w·v-1. Here as a first step core-shell fiber scaffolds consisting of microfibers with a PDC shell and sacrificial poly(ethylene glycol) (PEG) core are generated. The hollow PDC microfibers were achieved after dissolving the PEG core with water. The utilization of a fixed electrospinning setup and the same polymer concentration of the PDC spinning solution could ensure the fabrication of microfibers with almost identical outer diameters of 1.4 ± 0.3 µm as determined by scanning electron microscopy (SEM). Different hollow microfiber wall thicknesses of 0.5 ± 0.2 and 0.3 ± 0.2 µm (analyzed by SEM) have been realized by variation of the mass flow rate, while solid microfibers were obtained by coaxial electrospinning without supplying any core solution. Differential scanning calorimetry experiments and tensile tests at ambient temperature revealed an increase in degree of OCL crystallinity form χc,OCL = 34 ± 1% to 43 ± 1% and a decrease in elongation of break from 800 ± 40% to 200 ± 50% associated with an increase in Young´s modulus and failture stress for PDC hollow microfiber scaffolds when compared with soild fibers. The observed effects were enhanced with decreasing wall thickness of the single hollow fibers. The shape-memory properties of the electrospun PDC scaffolds were quantified by cyclic, thermomechanical tensile tests. Here, scaffolds comprising hollow microfibers exhibited lower shape fixity ratios around Rf = 82 ± 1% and higher shape recovery ratios of Rr = 67 ± 1% associated to more pronounced relaxation at constant strain during the first test cycle and a lower switching temperature of Tsw = 33 ± 1 °C than the fibrous meshes consisting of solid microfibers. These findings strongly support the central hypothesis that different fiber geometries (solid or hollow with different wall thickness) in electrospun scaffolds result in different degrees of macromolecular chain orientation in the polymeric micro-scale objects, which can be applied as design parameter for tailoring their mechanical and shape-memory properties.
The second part of the thesis deals with electrosprayed particulate PDC micro-scale objects. Almost spherical PDC microparticles with diameters of 3.9 ± 0.9 μm (as determined by SEM) were achieved by electrospraying of HFP solution with a polymer concentration of 2% w·v-1. In contrast, smaller particles with sizes of 400 ± 100 nm or 1.2 ± 0.3 μm were obtained for the magneto-sensitive composite PDC microparticles containing 23 ± 0.5 wt% superparamagnetic magnetite nanoparticles (mNPs). All prepared PDC microparticles exhibited a similar overall crystallinity like the PDC bulk material as analyzed by DSC. AFM nanoindentation results revealed no influence of the nanofiller incorporation on the local mechanical properties represented by the reduced modulus determined for pure PDC microparticles and magneto-sensitive composite PDC microparticles with similar diameters around 1.3 µm. It was found that the reduced modulus of the nanocomposite microparticles increased substantially with decreasing particles size from 2.4 ± 0.9 GPa (1.2 µm) to 11.9 ± 3.1 GPa (0.4 µm), which can be related to a higher orientation of the macromolecules at the surface of smaller sized microparticles. The magneto-sensitivity of such nanocomposite microparticles could be demonstrated in two aspects. One was by attracting/collecting the composite micro-objects with an external permanent magnet. The other one was by a inductive heating to 44 ± 1 °C, which is well above the melting transition of the OCL switching domains, when compacted to a 10 x 10 mm2 film with a thickness of 10 µm and exposed to an alternating magnet field with an magnetic field strength of 30 kA·m-1. Both functions are of great relevance for designing next generation drug delivery systems combining targeting and on demand release.
By a compression approach shape-memory functionalization of individual microparticles could be realized. Here different programming pressures and compression temperatures were applied. The shape-recovery capability of the programmed PDC microparticles was quantified by online and off-line heating experiments analyzed via microscopy measurement. The obtained shape-memory properties were found to be strongly depending on the applied programming pressure and temperature. The best shape-memory performance with a high shape recovery rate of about Rr = 80±1% was obtained when a low pressure of 0.2 MPa was applied at 55 °C. Finally, it was demonstrated that PDC microparticles can be utilized as micro building parts for preparation of a macroscopic film with temporary stability by compression of a densely packed array of PDC microparticles at 60 °C followed by subsequent cooling to ambient temperature. This film disintegrates into individual microparticles upon heating to 60 °C. Based on this technology the design of stable macroscopic release systems can be envisioned, which can be easily fixed at the site of treatment (i.e. by suturing) and disintegrate on demand to microparticles facilitating the drug release.
In summary, the results of this thesis could confirm the central hypothesis that the variation of the geometry of polymeric micro-objects is a suitable parameter to adjust their shape-memory performance by changing the degree of macromolecular chain orientation in the specimens or by enabling new functions like on demand disintegration. These fundamental findings might be relevant for designing novel miniaturized multifunctional polymer-based devices.
The need for multifunctional materials is driven by emerging technologies and innovations, such as in the field of soft robotics and tactile or haptic systems, where minimizing the number of operational components is not only desirable, but can also be essential for realizing such devices. This study report on designing a multifunctional soft polymer material that can address a number of operating requirements such as solvent resistance, reshaping ability, self-healing capability, fluorescence stimuli-responsivity, and anisotropic structural functions. The numerous functional abilities are associated to rhodium(I)-phosphine coordination bonds, which in a polymer network act with their dynamic and non-covalently bonded nature as multifunctional crosslinks. Reversible aggregation of coordination bonds leads to changes in fluorescence emission intensity that responds to chemical or mechanical stimuli. The fast dynamics and diffusion of rhodium-phosphine ions across and through contacting areas of the material provide for reshaping and self-healing abilities that can be further exploited for assembly of multiple pieces into complex forms, all without any loss to material-sensing capabilities.
Inspired by the application of ultrasonic cavitation based mechanical force (CMF) to open small channels in natural soft materials (skin or tissue), it is explored whether an artificial polymer network can be created, in which shape-changes can be induced by CMF. This concept comprises an interconnected macroporous rhodium-phosphine (Rh-P) coordination polymer network, in which a CMF can reversibly dissociate the Rh-P microphases. In this way, the ligand exchange of Rh-P coordination bonds in the polymer network is accelerated, resulting in a topological rearrangement of molecular switches. This rearrangement of molecular switches enables the polymer network to release internal tension under ultrasound exposure, resulting in a CMF-induced shape-memory capability. The interconnected macroporous structure with thin pore walls is essential for allowing the CMF to effectively permeate throughout the polymer network. Potential applications of this CMF-induced shape-memory polymer can be mechanosensors or ultrasound controlled switches.
Chemoresponsive polymers are of technological significance for smart sensors or systems capable of molecular recognition. An important key requirement for these applications is the material’s structural integrity after stimulation. We explored whether covalently cross-linked metal ion–phosphine coordination polymers (MPN) can be shaped into any temporary shape and are capable of recovering from this upon chemoresponsive exposure to triphenylphosphine (Ph3P) ligands, whereas the MPN provide structural integrity. Depending on the metal-ion concentration used during synthesis of the MPN, the degree of swelling of the coordination polymer networks could be adjusted. Once the MPN was immersed into Ph3P solution, the reversible ligand-exchange reaction between the metal ions and the free Ph3P in solution causes a decrease of the coordination cross-link density in MPN again. The Ph3P-treated MPN was able to maintain its original shape, indicating a certain stability of shape even after stimulation. In this way, chemoresponsive control of the elastic properties (increase in volume and decrease of mechanical strength) of the MPN was demonstrated. This remarkable behavior motivated us to explore whether the MPN are capable of a chemoresponsive shape-memory effect. In initial experiments, shape fixity of around 60% and shape recovery of almost 90% were achieved when the MPN was exposed to Ph3P in case of rhodium. Potential applications for chemoresponsive shape-memory systems could be shapable semiconductors, e.g., for lighting or catalysts, which provide catalytic activity on demand.
On-demand motion of highly swollen polymer systems can be triggered by changes in pH, ion concentrations, or by heat. Here, shape-programmable, architectured hydrogels are introduced, which respond to ultrasonic-cavitation-based mechanical forces (CMF) by directed macroscopic movements. The concept is the implementation and sequential coupling of multiple functions (swellability in water, sensitivity to ultrasound, shape programmability, and shape-memory) in a semi-interpenetrating polymer network (s-IPN). The semi-IPN-based hydrogels are designed to function through rhodium coordination (Rh-s-IPNH). These coordination bonds act as temporary crosslinks. The porous hydrogels with coordination bonds (degree of swelling from 300 +/- 10 to 680 +/- 60) exhibit tensile strength sigma(max) up to 250 +/- 60 kPa. Shape fixity ratios up to 90% and shape recovery ratios up to 94% are reached. Potential applications are switches or mechanosensors.
Swelling of Polyelectrolyte Multilayers: The Relation Between, Surface and Bulk Characteristics
(2015)
The odd even effect, i.e., the influence of the outermost layer of polyelectrolyte multilayers (PEMs) on their swelling behavior, is investigated. For that purpose poly(styrene sodium sulfonate) (PSS)/poly(diallyl-dimethylammonium chloride) (PDADMAC) polyelectrolyte multilayers are studied in air with 1% relative humidity (RH), 30% RH, 95% RH, and in liquid water by ellipsometry, atomic force microscopy (AFM), and X-ray reflectometry (XRR). Since the total amount of water uptake in swollen PEMs is divided into two fractions, the void water and the swelling water, a correct evaluation of the odd even effect is only possible if both fractions are examined separately. In order to allow measuring samples over a larger thickness regime the investigation of a larger amount of samples is required. Therefore, the concept of separating void water from swelling water using neutron reflectometry is for the first time transferred to ellipsometry. The subsequent analysis of swelling water, void water, and roughness revealed the existence of two types of odd even effects: an odd even effect which addresses only the surface of the PEM (surface-odd even effect) and an odd even effect which addresses also the bulk of the PEM (bulk-odd even effect). The appearance of both effects is dependent on the environment; the surface-odd even effect is only detectable in humid air while the bulk-odd even effect is only detectable in liquid water. The bulk-odd even effect is related to the osmotic pressure between the PEM and the surrounding water. A correlation between the amount of void water and both odd even effects is not found. The amount of void water is independent of the terminated layer and the thickness of PEMs.
The scanning tunnelling microscope (STM)-induced switching of a single cyclooctadiene molecule between two stable conformations chemisorbed on a Si(100) surface is investigated using an above threshold model including a neutral ground state and an ionic excited state potential. Switching was recently achieved experimentally with an STM operated at cryogenic temperatures (Nacci et al 2008 Phys. Rev. B 77 121405(R)) and rationalized by a below threshold model using just a single potential energy surface (Nacci et al 2009 Nano Lett. 9 2997).
In the present paper, we show that experimental key findings on the inelastic electron tunnelling (IET) switching can also be rationalized using an above threshold density matrix model, which includes, in addition to the neutral ground state potential, an anionic or cationic excited potential. We use one and two-dimensional potential energy surfaces. Furthermore, the influence of two key parameters of the density matrix description, namely the electronic lifetime of the ionic resonance and the vibrational lifetimes, on the ground state potential are discussed.
The switching of single cyclooctadiene molecules chemisorbed on a Si(100) surface between two stable conformations, can be achieved with a scanning tunneling microscope [Nacci , Phys. Rev. B 77, 121405(R) (2008)]. Recently, it was shown by quantum chemical and quantum dynamical simulations that major experimental facts can be explained by a single-mode model with switching enforced by inelastic electron tunneling (IET) excitations and perturbed by vibrational relaxation [Nacci , Nano Lett. 9, 2997 (2009)]. In the present paper, we extend the previous theoretical work in several respects: (1) The model is generalized to a two-mode description in which two C2H4 units of COD can move independently; (2) contributions of dipole and, in addition, (cation and anion) resonance-IET rates are considered; (3) the harmonic-linear vibrational relaxation model used previously is generalized to anharmonic vibrations. While the present models highlight generic aspects of IET-switching between two potential minima, they also rationalize specific experimental findings for COD/Si(100): (1) A single-electron excitation mechanism with a linear dependence of the switching rate on tunneling current I, (2) the capability to switch both at negative and positive sample biases, and (3) a crossover temperature around similar to 60 K from an IET-driven, T-independent atom tunneling regime, to classical over-the-barrier isomerization with exponential T-dependence at higher temperatures for a bias voltage of +1.5 V and an average tunneling current of 0.73 nA.
The aim of this thesis is the quantum dynamical study of two examples of scanning tunneling microscope (STM)-controllable, Si(100)(2x1) surface-mounted switches of atomic and molecular scale. The first example considers the switching of single H-atoms between two dangling-bond chemisorption sites on a Si-dimer of the Si(100) surface (Grey et al., 1996). The second system examines the conformational switching of single 1,5-cyclooctadiene molecules chemisorbed on the Si(100) surface (Nacci et al., 2008). The temporal dynamics are provided by the propagation of the density matrix in time via an according set of equations of motion (EQM). The latter are based on the open-system density matrix theory in Lindblad form. First order perturbation theory is used to evaluate those transition rates between vibrational levels of the system part. In order to account for interactions with the surface phonons, two different dissipative models are used, namely the bilinear, harmonic and the Ohmic bath model. IET-induced vibrational transitions in the system are due to the dipole- and the resonance-mechanism. A single surface approach is used to study the influence of dipole scattering and resonance scattering in the below-threshold regime. Further, a second electronic surface was included to study the resonance-induced switching in the above-threshold regime. Static properties of the adsorbate, e.g., potentials and dipole function and potentials, are obtained from quantum chemistry and used within the established quantum dynamical models.
Recently, two different groups have reported independently that the mobility of field-effect transistors made from regioregular poly(3-hexylthiophene) (P3HT) increases strongly with molecular weight. Two different models were presented: one proposing carrier trapping at grain boundaries and the second putting emphasis on the conformation and packing of the polymer chains in the thin layers for different molecular weights. Here, we present the results of detailed investigations of powders and thin films of deuterated P3HT fractions with different molecular weight. For powder samples, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were used to investigate the structure and crystallization behavior of the polymers. The GPC investigations show that all weight fractions possess a rather broad molecular weight distribution. DSC measurements reveal a strong decrease of the crystallization temperature and, most important, a significant decrease of the degree of crystallinity with decreasing molecular weight. To study the structure of thin layers in lateral and vertical directions, both transmission electron microscopy (TEM) and X-ray grazing incidence diffraction (GID) were utilized. These methods show that thin layers of the low molecular weight fraction consist of well-defined crystalline domains embedded in a disordered matrix. We propose that the transport properties of layers prepared from fractions of poly(3-hexylthiophene) with different molecular weight are largely determined by the crystallinity of the samples and not by the perfection of the packing of the chains in the individual crystallites
Molecular brush diblock copolymers were synthesized by the orthogonal overlay of the RAFT (reversible addition-fragmentation chain transfer), the ATRP (atom transfer radical polymerization), and the NMP (nitroxide-mediated polymerization) techniques. This unique combination enabled the synthesis of the complex amphiphilic polymers without the need of postpolymerization modifications, using a diblock copolymer intermediate made from two selectively addressable inimers and applying a sequence of four controlled free radical polymerization steps in total. The resulting polymers are composed of a thermosensitive poly(N-isopropylacrylamide) brush as hydrophilic block and a polystyrene brush as hydrophobic block, thus translating the structure of the established amphiphilic diblock copolymers known as macro surfactants to the higher size level of "giant surfactants". The dual molecular brushes and the aggregates formed on ultra flat solid substrates were visualized by scanning force microscopy (SFM).
The combination of two techniques of controlled free radical polymerization, namely the reversible addition fragmentation chain transfer (RAFT) and the atom transfer radical polymerization (ATRP) techniques, together with the use of a macromonomer allowed the synthesis of symmetrical triblock copolymers, designed as amphiphilic dual brushes. One type of brush was made of poly(n-butyl acrylate) as soft hydrophobic block, i.e. characterized by a low glass transition temperature, while the other one was made of hydrophilic poly(ethylene glycol) (PEG). The new triblock polymers represent "giant surfactants" according to their molecular architecture. The hydrophobic and hydrophilic blocks microphase separate in the bulk. In aqueous solution, they aggregate into globular micellar aggregates, their size being determined by the length of the stretched polymer molecules. As determined by the combination of various scattering techniques for the dual brush copolymer, a rather compact structure is formed, which is dominated by the large hydrophobic poly(n-butyl acrylate) block. The aggregation number for the dual brush is about 10 times larger than for the "semi-brush" precursor copolymer, due to the packing requirements for the much bulkier hydrophobic core. On mica surfaces the triblock copolymers adsorb with worm-like backbones and stretched out side chains.
Amphiphilic dual brush block copolymers as "giant surfactants" and their aqueous self-assembly
(2010)
Amphiphilic dual brush diblock as well as symmetrical triblock polymers were synthesized by the overlay of the reversible addition-fragmentation chain transfer and the nitroxide mediated polymerization (NMP) techniques. While poly(ethylene glycol) brushes served as hydrophilic block, the hydrophobic block was made of polystyrene brushes. The resulting "giant surfactants" correspond structurally to the established amphiphilic diblock and triblock copolymer known as macrosurfactants. The aggregation behavior of the novel "giant surfactants" in aqueous solution was studied by dynamic light scattering, small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS) over a large range in reciprocal space. Further, the self-assembled aggregates Were investigated by scanning force microscopy (SFM) after deposition on differently functionalized ultraflat solid substrates. Despite the high fraction of hydrophobic segments, the polymers form stable mesoscopic, spherical aggregates with hydrodynamic diameters in the range of 150-350 nm. Though prepared from well-defined individual polymers, the aggregates show several similarities to hard core latexes. They are stable enough to he deposited without much changes onto surfaces, where they cluster and show Spontaneous sorting according to their size within the clusters, with the larger aggregates being in the center.
A series of 9,10-diarylanthracenes with various substituents at the ortho positions have been synthesised by palladium-catalysed cross-coupling reactions. Such compounds exhibit interesting physical properties and can be applied as molecular switches. Despite the high steric demand of the substituents, products were formed in moderate-to-good yields. In some cases, microwave conditions further improved yields. Bis-coupling afforded two isomers (syn and anti) that do not interconvert at room temperature. These products were easily separated and their relative stereochemistries were unequivocally assigned by NMR spectroscopy and X-ray analysis. The syn and anti isomers exhibit different physical properties (e.g., melting points and solubilities) and interconversion by rotation around the aryl-aryl axis commences at <100 °C for fluoro-substituted diarylanthracenes and at >300 °C for alkyl- or alkoxy-substituted diarylanthracenes. The reactions with singlet oxygen were studied separately and revealed different reactivities and reaction pathways. The yields and reactivities depend on the size and electronic nature of the substituents. The anti isomers form the same 9,10-endoperoxides as the syn species, occasionally accompanied by unexpected 1,4-endoperoxides as byproducts. Thermolysis of the endoperoxides exclusively yielded the syn isomers. The interesting rotation around the aryl-aryl axis allows the application of 9,10-diarylanthracenes as molecular switches, which are triggered by light and air under mild conditions. Finally, the oxygenation and thermolysis sequence provides a simple, synthetic access to a single stereoisomer (syn) from an unselective coupling step.
In the reconstruction and regeneration of bone tissue, a primary goal is to initiate bone growth and to stabilize the surrounding bone. In this regard, a potentially useful component in biomaterials for bone tissue engineering is strontium, which acts as cationic active agent, triggering certain intracellular pathways and acting as so called dual action bone agent which inhibits bone resorption while stimulating bone regeneration. In this study we established a novel processing for the foaming of a polymer (poly-epsilon-caprolactone) and simultaneous chemical reaction of a mixture of calcium and strontium hydroxides to the respective carbonates using supercritical carbon dioxide. The resultant porous composite scaffold was optimized in composition and strontium content and was characterized via different spectroscopic (infrared and Raman spectroscopy, energy dispersive X-ray spectroscopy), imaging (SEM, mu CT), mechanical testing and in vitro methods (fluorescence vital staining, MTT-assay). As a result, the composite scaffold showed good in vitro biocompatibility with partly open pore structure and the expected chemistry. First mechanical testing results indicate sufficient mechanical stability to support future in vivo applications. (C) 2016 Elsevier B.V. All rights reserved.
New ionogels (IGs) were prepared by combination of a series of sulfonate-based ionic liquids (ILs), 1-methyl-3-(4-sulfobutyl)imidazolium para-toluenesulfonate [BmimSO(3)][pTS], 1-methyl-1-butylpiperidiniumsulfonate para-toluenesul-fonate [BmpipSO(3)] [pTS], and 1-methyl-3-(4-sulfobutyl) imidazolium methylsulfonate [BmimSO(3)H][MeSO3] with a commercial stereolithography photoreactive resin. The article describes both the fundamental properties of the ILs and the resulting IGs. The IGs obtained from the ILs and the resin show high ionic conductivity of up to ca. 0.7.10(-4) S/cm at room temperature and 3.4-10(-3) S/cm at 90 degrees C. Moreover, the IGs are thermally stable to about 200 degrees C and mechanically robust. Finally, and most importantly, the article demonstrates that the IGs can be molded three-dimensionally using stereolithography. This provides, for the first time, access to IGs with complex 3D shapes with potential application in battery or fuel cell technology.
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.
As a part of searching for fully aromatic chelate compounds, copper complexes of malondialdehyde as well as its sulfur and selenium derivatives were investigated using the DFT quantum chemical methods. Chelate complexes of both Cu(I) and Cu(II) ions wereconsidered. Aromaticity of the metal complexes studied were analyzed using NICS(0), NICS(1), PDI, I-ring, MCI, ICMCI and I-B aromaticity indices, and by TSNMRS visualizations of the spatial magnetic properties. It seems that partial aromaticityof studied chelates increases when oxygen atoms in malondialdehyde are replaced by sulfur and selenium.
Biomaterials are used in regenerative medicine for induced autoregeneration and tissue engineering. This is often challenging, however, due to difficulties in tailoring and controlling the respective material properties. Since functionalization is expected to offer better control, in this study gelatin chains were modified with physically interacting groups based on tyrosine with the aim of causing the formation of physical crosslinks. This method permits application-specific properties like swelling and better tailoring of mechanical properties. The design of the crosslink strategy was supported by molecular dynamic (MD) simulations of amorphous bulk models for gelatin and functionalized gelatins at different water contents (0.8 and 25 wt.-%). The results permitted predictions to be formulated about the expected crosslink density and its influence on equilibrium swelling behavior and on elastic material properties. The models of pure gelatin were used to validate the strategy by comparison between simulated and experimental data such as density, backbone conformation angle distribution, and X-ray scattering spectra. A key result of the simulations was the prediction that increasing the number of aromatic functions attached to the gelatin chain leads to an increase in the number of physical netpoints observed in the simulated bulk packing models. By comparison with the Flory-Rehner model, this suggested reduced equilibrium swelling of the functionalized materials in water, a prediction that was subsequently confirmed by our experimental work. The reduction and control of the equilibrium degree of swelling in water is a key criterion for the applicability of functionalized gelatins when used, for example, as matrices for induced autoregeneration of tissues.
Taking advantage of ATRP and using functionalized initiators, different functionalities were introduced in both α and ω chain-ends of synthetic polymers. These functionalized polymers could then go through modular synthetic pathways such as click cycloaddition (copper-catalyzed or copper-free) or amidation to couple synthetic polymers to other synthetic polymers, biomolecules or silica monoliths. Using this general strategy and designing these co/polymers so that they are thermoresponsive, yet bioinert and biocompatible with adjustable cloud point values (as it is the case in the present thesis), the whole generated system becomes "smart" and potentially applicable in different branches. The applications which were considered in the present thesis were in polymer post-functionalization (in situ functionalization of micellar aggregates with low and high molecular weight molecules), hydrophilic/hydrophobic tuning, chromatography and bioconjugation (enzyme thermoprecipitation and recovery, improvement of enzyme activity). Different α-functionalized co/polymers containing cholesterol moiety, aldehyde, t-Boc protected amine, TMS-protected alkyne and NHS-activated ester were designed and synthesized in this work.
Picosecond X-ray absorption spectroscopy (XAS) is used to investigate the electronic and structural dynamics initiated by plasmon excitation of 1.8 nm diameter Au nanoparticles (NPs) functionalised with 1-hexanethiol. We show that 100 ps after photoexcitation the transient XAS spectrum is consistent with an 8% expansion of the Au–Au bond length and a large increase in disorder associated with melting of the NPs. Recovery of the ground state occurs with a time constant of ∼1.8 ns, arising from thermalisation with the environment. Simulations reveal that the transient spectrum exhibits no signature of charge separation at 100 ps and allows us to estimate an upper limit for the quantum yield (QY) of this process to be <0.1.
Picosecond X-ray absorption spectroscopy (XAS) is used to investigate the electronic and structural dynamics initiated by plasmon excitation of 1.8 nm diameter Au nanoparticles (NPs) functionalised with 1-hexanethiol. We show that 100 ps after photoexcitation the transient XAS spectrum is consistent with an 8% expansion of the Au–Au bond length and a large increase in disorder associated with melting of the NPs. Recovery of the ground state occurs with a time constant of ∼1.8 ns, arising from thermalisation with the environment. Simulations reveal that the transient spectrum exhibits no signature of charge separation at 100 ps and allows us to estimate an upper limit for the quantum yield (QY) of this process to be <0.1.
A unified model for quantitative description of harmonic spectra of gases obtained by wavelength modulation spectroscopy (WMS) technique is presented. In the model, both intensity modulation (IM) and frequency modulation (FM) of the laser emission are taken into account using minimum number of parameters. For the first time, the static behavior of a laser is described as a limiting case of its dynamic response. Laser and its driver are considered as a single device converting applied bias to laser emission. This allows application of the model to any type of laser and the introduced parameters can be assigned to the corresponding laser and/or driver properties. The approach was tested using a distributed feedback (DFB) laser spectrometer. Correctness of the proposed model is justified by very good agreement between the measured and modeled/fitted spectra, which allowed evaluation of the setup performance and assessment of modulation parameters of the DFB laser. An algorithm to minimize the time of numerical calculation of harmonic spectra using numerically approximated Voigt lineshape function was developed. Absolute values of the absorption line parameters (line strength and line width) were obtained from a single calibration- and reference-free spectrum scan with accuracy better than 0.1%.
We report a new synthetic route to a series of a-carboxynitrobenzyl photocaged L-aspartates for application in time-resolved structural biology. The resulting compounds were characterised in terms of UV/Vis absorption properties, aqueous solubility and stability, and photocleavage rates (tau = ms to ms) and quantum yields (phi = 0.05 to 0.14).
Metal-containing ionic liquids (ILs) are of interest for a variety of technical applications, e.g., particle synthesis and materials with magnetic or thermochromic properties. In this paper we report the synthesis of, and two structures for, some new tetrabromidocuprates(II) with several “onium” cations in comparison to the results of electron paramagnetic resonance (EPR) spectroscopic analyses. The sterically demanding cations were used to separate the paramagnetic Cu(II) ions for EPR measurements. The EPR hyperfine structure in the spectra of these new compounds is not resolved, due to the line broadening resulting from magnetic exchange between the still-incomplete separated paramagnetic Cu(II) centres. For the majority of compounds, the principal g values (g|| and gK) of the tensors could be determined and information on the structural changes in the [CuBr4]2- anions can be obtained. The complexes have high potential, e.g., as ionic liquids, as precursors for the synthesis of copper bromide particles, as catalytically active or paramagnetic ionic liquids.
Metal-containing ionic liquids (ILs) are of interest for a variety of technical applications, e.g., particle synthesis and materials with magnetic or thermochromic properties. In this paper we report the synthesis of, and two structures for, some new tetrabromidocuprates(II) with several “onium” cations in comparison to the results of electron paramagnetic resonance (EPR) spectroscopic analyses. The sterically demanding cations were used to separate the paramagnetic Cu(II) ions for EPR measurements. The EPR hyperfine structure in the spectra of these new compounds is not resolved, due to the line broadening resulting from magnetic exchange between the still-incomplete separated paramagnetic Cu(II) centres. For the majority of compounds, the principal g values (g|| and gK) of the tensors could be determined and information on the structural changes in the [CuBr4]2- anions can be obtained. The complexes have high potential, e.g., as ionic liquids, as precursors for the synthesis of copper bromide particles, as catalytically active or paramagnetic ionic liquids.
Metal-containing ionic liquids (ILs) are of interest for a variety of technical applications, e.g., particle synthesis and materials with magnetic or thermochromic properties. In this paper we report the synthesis of, and two structures for, some new tetrabromidocuprates(II) with several "onium" cations in comparison to the results of electron paramagnetic resonance (EPR) spectroscopic analyses. The sterically demanding cations were used to separate the paramagnetic Cu(II) ions for EPR measurements. The EPR hyperfine structure in the spectra of these new compounds is not resolved, due to the line broadening resulting from magnetic exchange between the still-incomplete separated paramagnetic Cu(II) centres. For the majority of compounds, the principal g values (g|| and g(perpendicular to)) of the tensors could be determined and information on the structural changes in the [CuBr4](2-) anions can be obtained. The complexes have high potential, e.g., as ionic liquids, as precursors for the synthesis of copper bromide particles, as catalytically active or paramagnetic ionic liquids.
Regulation of respiration and fermentation to control the plant internal oxygen concentration
(2009)
Plant internal oxygen concentrations can drop well below ambient even when the plant grows under optimal conditions. Using pea (Pisum sativum) roots, we show how amenable respiration adapts to hypoxia to save oxygen when the oxygen availability decreases. The data cannot simply be explained by oxygen being limiting as substrate but indicate the existence of a regulatory mechanism, because the oxygen concentration at which the adaptive response is initiated is independent of the actual respiratory rate. Two phases can be discerned during the adaptive reaction: an initial linear decline of respiration is followed by a nonlinear inhibition in which the respiratory rate decreased progressively faster upon decreasing oxygen availability. In contrast to the cytochrome c pathway, the inhibition of the alternative oxidase pathway shows only the linear component of the adaptive response. Feeding pyruvate to the roots led to an increase of the oxygen consumption rate, which ultimately led to anoxia. The importance of balancing the in vivo pyruvate availability in the tissue was further investigated. Using various alcohol dehydrogenase knockout lines of Arabidopsis (Arabidopsis thaliana), it was shown that even under aerobic conditions, alcohol fermentation plays an important role in the control of the level of pyruvate in the tissue. Interestingly, alcohol fermentation appeared to be primarily induced by a drop in the energy status of the tissue rather than by a low oxygen concentration, indicating that sensing the energy status is an important component of optimizing plant metabolism to changes in the oxygen availability.
The alpha-Al2O3(0001) surface has been extensively studied because of its significance in both fundamental research and application. Prior work suggests that in ultra-high-vacuum (UHV), in the absence of water, the so-called Al-I termination is thermodynamically favored, while in ambient, in contact with liquid water, a Gibbsite-like layer is created. While the view of the alpha- Al2O3(0001)/H2O(l) interface appears relatively clear in theory, experimental characterization of this system has resulted in estimates of surface acidity, i.e., isoelectric points, that differ by 4 pH units and surface structure that in some reports has non-hydrogen-bonded surface aluminol (Al-OH) groups and in others does not. In this study, we employed vibrational sum frequency spectroscopy (VSFS) and density functional theory (DFT) simulation to study the surface phonon modes of the differently terminated alpha-Al2O3(0001) surfaces in both UHV and ambient. We find that, on either water dosing of the Al-I in UHV or heat-induced dehydroxylation of the Gibbsite-like in ambient, the surfaces do not interconvert. This observation offers a new explanation for disagreements in prior work on the alpha-Al2O3(0001)/liquid water interface -different preparation methods may create surfaces that do not interconvert-and shows that the surface phonon spectral response offers a novel probe of interfacial hydrogen bonding structure.
Classic rotating engines are powerful and broadly used but are of complex design and difficult to miniaturize. It has long remained challenging to make large-stroke, high-speed, high-energy microengines that are simple and robust. We show that torsionally stiffened shape memory nanocomposite fibers can be transformed upon insertion of twist to store and provide fast and high-energy rotations. The twisted shape memory nanocomposite fibers combine high torque with large angles of rotation, delivering a gravimetric work capacity that is 60 times higher than that of natural skeletal muscles. The temperature that triggers fiber rotation can be tuned. This temperature memory effect provides an additional advantage over conventional engines by allowing for the tunability of the operation temperature and a stepwise release of stored energy.
Commercially available 1,2-PB was transformed into a well-defined reactive intermediate by quantitative bromination. The brominated polymer was used as a polyfunctional macroinitiator for the cationic ring-opening polymerization of 2-ethyl-2-oxazoline to yield a water-soluble brush polymer. Nucleophilic substitution of bromide by 1-methyl imidazole resulted in the formation of polyelectrolyte copolymers consisting of mixed units of imidazolium, bromo, and double bond. These copolymers, which were soluble in water without forming aggregates, were used as stabilizers in the heterophase polymerization of styrene and were also studied for their ionic conducting properties.
Poly(Ionic Liquid)s
(2015)
Ligands incorporating a tetraazamacrocycle receptor, a 'click'-derived triazole and a 1,8-naphthalimide fluorophore have proven utility as probes for metal ions. Three new cyclam-based molecular probes are reported, in which a piperidinyl group has been introduced at the 4-position of the naphthalimide fluorophore. These compounds have been synthesized using the copper(I)-catalyzed azide-alkyne Huisgen cycloaddition and their photophysical properties studied in detail. The alkylamino group induces the expected red-shift in absorption and emission spectra relative to the simple naphthalimide derivatives and gives rise to extended fluorescence lifetimes in aqueous buffer. The photophysical properties of these systems are shown to be highly solvent-dependent. Screening the fluorescence responses of the new conjugates to a wide variety of metal ions reveals significant and selective fluorescence quenching in the presence of copper(II), yet no fluorescence enhancement with zinc(II) as observed previously for the simple naphthalimide derivatives. Reasons for this different behaviour are proposed. Cytotoxicity testing shows that these new cyclam-triazole-dye conjugates display little or no toxicity against either DLD-1 colon carcinoma cells or MDA-MB-231 breast carcinoma cells, suggesting a potential role for these and related systems in biological sensing applications.
HighlightsFacile electrodeposition for fabricating active Ni nanodots (NiNDs) on Ni foam (NF) is shown.Binder- and heteroatom-free recyclable NiO/NiNDs@NF electrodes are efficiently made.NiO/NiNDs@NF bifunctional catalytic electrodes are used for water splitting. AbstractIn past decades, Ni-based catalytic materials and electrodes have been intensively explored as low-cost hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts for water splitting. With increasing demands for Ni worldwide, simplifying the fabrication process, increasing Ni recycling, and reducing waste are tangible sustainability goals. Here, binder-free, heteroatom-free, and recyclable Ni-based bifunctional catalytic electrodes were fabricated via a one-step quick electrodeposition method. Typically, active Ni nanodot (NiND) clusters are electrodeposited on Ni foam (NF) in Ni(NO3)(2) acetonitrile solution. After drying in air, NiO/NiND composites are obtained, leading to a binder-free and heteroatom-free NiO/NiNDs@NF catalytic electrode. The electrode shows high efficiency and long-term stability for catalyzing hydrogen and oxygen evolution reactions at low overpotentials ((10)(HER)=119mV and (50)(OER)=360mV) and can promote water catalysis at 1.70V@10mAcm(-2). More importantly, the recovery of raw materials (NF and Ni(NO3)(2)) is quite easy because of the solubility of NiO/NiNDs composites in acid solution for recycling the electrodes. Additionally, a large-sized (S similar to 70cm(2)) NiO/NiNDs@NF catalytic electrode with high durability has also been constructed. This method provides a simple and fast technology to construct high-performance, low-cost, and environmentally friendly Ni-based bifunctional electrocatalytic electrodes for water splitting.
The synthesis of sp(2)-conjugated, heteroatom-rich, "carbonaceous" materials from economically feasible raw materials and salt templates is reported. Low cost citrazinic acid (2,6-dihydroxy-4-pyridinecarboxylic acid) and melamine are used as components to form a microporous, amorphous framework, where edges of the covalent frameworks are tightly terminated with nitrogen and oxygen moieties. ZnCl2 as the porogen stabilizes structural microporosity as well as nitrogen and oxygen heteroatoms up to comparably high condensation temperatures of 750 and 950 degrees C. The specific surface area up to 1265 m(2) g(-1) is mainly caused by micropores and typical of heteroatom-rich carbon materials with such structural porosity. The unusually high heteroatom content reveals that the edges and pores of the covalent structures are tightly lined with heteroatoms, while C-C or C-H bonds are expected to have a minor contribution as compared to typical carbon materials without or with minor content of heteroatoms. Adsorption of water vapor and carbon dioxide are exemplarily chosen to illustrate the impact of this heteroatom functionalization under salt-templating conditions on the adsorption properties of the materials. 27.10 mmol g(-1) of H2O uptake (at p/p(0) = 0.9) can be achieved, which also proves the very hydrophilic character of the pore walls, while the maximum CO2 uptake (at 273 K) is 5.3 mmol g(-1). At the same time the CO2/N-2 adsorption selectivity at 273 K can reach values of up to 60. All these values are beyond those of ordinary high surface area carbons, also differ from those of N-doped carbons, and are much closer to those of organized framework species, such as C2N.
The world energy consumption has constantly increased every year due to economic development and population growth. This inevitably caused vast amount of CO2 emission, and the CO2 concentration in the atmosphere keeps increasing with economic growth. To reduce CO2 emission, various methods have been developed but there are still many bottlenecks to be solved. Solvents easily absorbing CO2 such as monoethanol-amine (MEA) and diethanolamine, for example, have limitations of solvent loss, amine degradation, vulnerability to heat and toxicity, and the high cost of regeneration which is especially caused due to chemisorption process. Though some of these drawbacks can be compensated through physisorption with zeolites and metal-organic frameworks (MOFs) by displaying significant adsorption selectivity and capacity even in ambient conditions, limitations for these materials still exist. Zeolites demand relatively high regeneration energy and have limited adsorption kinetics due to the exceptionally narrow pore structure. MOFs have low stability against heat and moisture and high manufacturing cost.
Nanoporous carbons have recently received attention as an attractive functional porous material due to their unique properties. These materials are crucial in many applications of modern science and industry such as water and air purification, catalysis, gas separation, and energy storage/conversion due to their high chemical and thermal stability, and in particular electronic conductivity in combination with high specific surface areas. Nanoporous carbons can be used to adsorb environmental pollutants or small gas molecules such as CO2 and to power electrochemical energy storage devices such as batteries and fuel cells. In all fields, their pore structure or electrical properties can be modified depending on their purposes.
This thesis provides an in-depth look at novel nanoporous carbons from the synthetic and the application point of view. The interplay between pore structure, atomic construction, and the adsorption properties of nanoporous carbon materials are investigated. Novel nanoporous carbon materials are synthesized by using simple precursor molecules containing heteroatoms through a facile
templating method. The affinity, and in turn the adsorption capacity, of carbon materials toward polar gas molecules (CO2 and H2O) is enhanced by the modification of their chemical construction. It is also shown that these properties are important in electrochemical energy storage, here especially for supercapacitors with aqueous electrolytes which are basically based on the physisorption of ions on carbon surfaces. This shows that nanoporous carbons can be a “functional” material with specific physical or chemical interactions with guest species just like zeolites and MOFs.
The synthesis of sp2-conjugated materials with high heteroatom content from a mixture of citrazinic acid and melamine in which heteroatoms are already bonded in specific motives is illustrated. By controlling the removal procedure of the salt-template and the condensation temperature, the role of salts in the formation of porosity and as coordination sites for the stabilization of heteroatoms is proven. A high amount of nitrogen of up to 20 wt. %, oxygen contents of up to 19 wt.%, and a high CO2/N2 selectivity with maximum CO2 uptake at 273 K of 5.31 mmol g–1 are achieved. Besides, the further controlled thermal condensation of precursor molecules and advanced functional properties on applications of the synthesized porous carbons are described. The materials have different porosity and atomic construction exhibiting a high nitrogen content up to 25 wt. % as well as a high porosity with a specific surface area of more than 1800 m2 g−1, and a high performance in selective CO2 gas adsorption of 62.7. These pore structure as well as properties of surface affect to water adsorption with a remarkably high Qst of over 100 kJ mol−1 even higher than that of zeolites or CaCl2 well known as adsorbents. In addition to that, the pore structure of HAT-CN-derived carbon materials during condensation in vacuum is fundamentally understood which is essential to maximize the utilization of porous system in materials showing significant difference in their pore volume of 0.5 cm3 g−1 and 0.25 cm3 g−1 without and with vacuum, respectively.
The molecular designs of heteroatom containing porous carbon derived from abundant and simple molecules are introduced in the presented thesis. Abundant precursors that already containing high amount of nitrogen or oxygen are beneficial to achieve enhanced interaction with adsorptives. The physical and chemical properties of these heteroatom-doped porous carbons are affected by mainly two parameters, that is, the porosity from the pore structure and the polarity from the atomic composition on the surface. In other words, controlling the porosity as well as the polarity of the carbon materials is studied to understand interactions with different guest species which is a fundamental knowledge for the utilization on various applications.
N-terminal methacrylation of peptide MAXI, which is capable of conformational changes variation of the pH, results in a peptide, named VK20. Increasing the reactivity of this terminal group enables further coupling reactions or chemical modifications of the peptidc. However, this end group functionalization may influence the ability of confonnational changes of VK20; as well as its properties. In this paper; the influence of pH on the transition between random coil and beta-sheet conformation of VK20; including the transition kinetics, were investigated. At pH values of 9 and higher, the kinetics beta-sheet formation increased tor VK(2 0, compared to MAXI. The self-assembly into beta-sheets recognized by the formation of a physically crosslinked gel was furthermore indicated by a significant increase of G. An increase in pH (from 9 to 9.5) led to a faster gelation of the peptide VK20. Simultaneously, G was increased from 460 +/- 70 Pa (at pH 9) to 1520 +/- 180 Pa (at pH 9.5). At the nanoscale, the gel showed a highly interconnected fibrillar/network structure with uniform fibril widths of approximately 3.4 +/- 0.5 nm (N=30). The recovery of the peptide conformation back to random coil resulted in the dissolution of the gel; whereby the kinetics of the recovery depended on the pH. Conclusively, the ability of MAXI to undergo confommtional changes was not affected by N-terminal methacrylation whereas the kinetics of pH-sensitive beta-sheet formations has been increased.
Conformational transition of peptide-functionalized cryogels enabling shape-memory capability
(2017)
CAMPHOR: A GOOD MODEL FOR ILLUSTRATING NMR TECHNIQUES. The use of Nuclear Magnetic Resonance spectroscopy to establish the three-dimensional structures of molecules is an important component of modern Chemistry courses. The combination of techniques that can be used for this purpose is conveniently illustrated by their application to the camphor molecule. This paper presents applications of several techniques used in NMR spectral interpretation in an increasing order of complexity. The result of individual experiments is illustrated in order to familiarize the user with the way connectivity through bonds and through space is established from 1D/2D-NMR spectra and molecular stereochemistry is determined from different NMR experiments
Closed and re-opened for business: C-2 branched carbohydrates 1 cyclize under conditions of decarboxylation to the hitherto unknown carbohydrate 1,2-lactones 2 in high yields. The gluco isomer can be opened at the anomeric position with various nuceophiles in the presence of Sc(OTf)3, which allows the stereoselective synthesis of 1-functionalized glucose derivatives 3. Thus, 1,2-bis-C-branched saccharides become available in only a few steps starting from glycals.
Bicyclic carbohydrate 1,2-lactones have been synthesized in only two steps and high yields by saponification and subsequent cyclization from known malonate addition products to glycals. The gluco-configured lactone serves as an important precursor for diversity-oriented syntheses. Thus, stereoselective opening of the lactone ring was realized with various nucleophiles in the presence of Sc(OTf)(3). This enabled the introduction of different substituents at the anomeric position, to afford a broad variety of 1-functionalized carbohydrates. On the other hand, stereoselective alpha-substitution of the gluco-configured lactone with different electrophiles and subsequent ring opening gives a collection of 2-functionalized saccharides. More than 30 products have been isolated in analytically pure form, and their configurations were unequivocally established by various NMR methods. Thus, carbohydrate 1,2-lactones are attractive precursors for the stereoselective synthesis of diverse saccharides.
C-branched carbohydrates are of current interest for glycochemistry, are widely found in nature and serve as important subunits in many antibiotics, bacterial polysaccharides and macrolides. Among C-functionalized saccharides, 2-C-branched carbohydrates represent challenging structures for synthetic chemists, since in contrast to C-glycosides they are not easily accessible from glycosyl bromides or other simple precursors. In this perspective we want to summarize recent approaches to 2-C-branched carbohydrates over the past fifteen years. The two main strategies are based on ring-opening of 1,2-cyclopropanated carbohydrates by various reagents, as well as radical additions to glycals and further transformations, developed in our group. Both methods are characterized by high stereoselectivities and good yields and give access to a broad variety of functionalized carbohydrate 2-C-analogs.
Tuning of the excited-state properties and photovoltaic performance in PPV-based polymer blends
(2008)
This paper presents a study of the surface properties of two Ce/Zr mixed oxides with different reducibility, obtained by applying distinct thermal ageing treatments to an oxide with the composition Ce0.62Zr0.38O2. The surface composition was investigated by XPS. Chemical reactivity of the surface was studied by adsorption of the probe molecules CO2, D-2 and methanol. Nanostructural characterization was carried out by XRD, Raman and high-resolution Eu3+ spectroscopy (FLNS). The characterization showed only slight variations in surface composition and bulk Ce-Zr distribution, but hardy differences concerning the type and strength of acidic surface centres, as well as strong differences in the ability to dissociate hydrogen. Structural variations between both samples were identified by comparing the optical spectra of Eu3+ in surface doped samples.