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- Institut für Chemie (347) (remove)
Health effects, attributed to the environmental pollution resulted from using solvents such as benzene, are relatively unexplored among petroleum workers, personal use, and laboratory researchers. Solvents can cause various health problems, such as neurotoxicity, immunotoxicity, and carcinogenicity. As such it can be absorbed via epidermal or respiratory into the human body resulting in interacting with molecules that are responsible for biochemical and physiological processes of the brain.
Owing to the ever-growing demand for finding a solution, an Ionic liquid can use as an alternative solvent. Ionic liquids are salts in a liquid state at low temperature (below 100 C), or even at room temperature. Ionic liquids impart a unique architectural platform, which has been interesting because of their unusual properties that can be tuned by simple ways such as mixing two ionic liquids.
Ionic liquids not only used as reaction solvents but they became a key developing for novel applications based on their thermal stability, electric conductivity with very low vapor pressure in contrast to the conventional solvents.
In this study, ionic liquids were used as a solvent and reactant at the same time for the novel nanomaterials synthesis for different applications including solar cells, gas sensors, and water splitting.
The field of ionic liquids continues to grow, and become one of the most important branches of science. It appears to be at a point where research and industry can work together in a new way of thinking for green chemistry and sustainable production.
The aim of this work was the generation of carbon materials with high surface area, exhibiting a hierarchical pore system in the macro- and mesorange. Such a pore system facilitates the transport through the material and enhances the interaction with the carbon matrix (macropores are pores with diameters > 50 nm, mesopores between 2 – 50 nm). Thereto, new strategies for the synthesis of novel carbon materials with designed porosity were developed that are in particular useful for the storage of energy. Besides the porosity, it is the graphene structure itself that determines the properties of a carbon material. Non-graphitic carbon materials usually exhibit a quite large degree of disorder with many defects in the graphene structure, and thus exhibit inherent microporosity (d < 2nm). These pores are traps and oppose reversible interaction with the carbon matrix. Furthermore they reduce the stability and conductivity of the carbon material, which was undesired for the proposed applications. As one part of this work, the graphene structures of different non-graphitic carbon materials were studied in detail using a novel wide-angle x-ray scattering model that allowed precise information about the nature of the carbon building units (graphene stacks). Different carbon precursors were evaluated regarding their potential use for the synthesis shown in this work, whereas mesophase pitch proved to be advantageous when a less disordered carbon microstructure is desired. By using mesophase pitch as carbon precursor, two templating strategies were developed using the nanocasting approach. The synthesized (monolithic) materials combined for the first time the advantages of a hierarchical interconnected pore system in the macro- and mesorange with the advantages of mesophase pitch as carbon precursor. In the first case, hierarchical macro- / mesoporous carbon monoliths were synthesized by replication of hard (silica) templates. Thus, a suitable synthesis procedure was developed that allowed the infiltration of the template with the hardly soluble carbon precursor. In the second case, hierarchical macro- / mesoporous carbon materials were synthesized by a novel soft-templating technique, taking advantage of the phase separation (spinodal decomposition) between mesophase pitch and polystyrene. The synthesis also allowed the generation of monolithic samples and incorporation of functional nanoparticles into the material. The synthesized materials showed excellent properties as an anode material in lithium batteries and support material for supercapacitors.
Self-assembly and crosslinking approaches of double hydrophilic linear-brush block copolymers
(2019)
The controlled dosage of substances from a device to its environment, such as a tissue or an organ in medical applications or a reactor, room, machinery or ecosystem in technical, should ideally match the requirements of the applications, e.g. in terms of the time point at which the cargo is released. On-demand dosage systems may enable such a desired release pattern, if the device contain suitable features that can translate external signals into a release function. This study is motivated by the opportunities arising from microsystems capable of an on-demand release and the contributions that geometrical design may have in realizing such features. The goals of this work included the design, fabrication, characterization and experimental proof-of-concept of geometry-assisted triggerable dosing effect (a) with a sequential dosing release and (b) in a self-sufficient dosage system. Structure-function relationships were addressed on the molecular, morphological and, with a particular attention, the device design level, which is on the micrometer scale. Models and/or computational tools were used to screen the parameter space and provide guidance for experiments.
Adsorption layers of soluble surfactants enable and govern a variety of phenomena in surface and colloidal sciences, such as foams. The ability of a surfactant solution to form wet foam lamellae is governed by the surface dilatational rheology. Only systems having a non-vanishing imaginary part in their surface dilatational modulus, E, are able to form wet foams. The aim of this thesis is to illuminate the dissipative processes that give rise to the imaginary part of the modulus. There are two controversial models discussed in the literature. The reorientation model assumes that the surfactants adsorb in two distinct states, differing in their orientation. This model is able to describe the frequency dependence of the modulus E. However, it assumes reorientation dynamics in the millisecond time regime. In order to assess this model, we designed a SHG pump-probe experiment that addresses the orientation dynamics. Results obtained reveal that the orientation dynamics occur in the picosecond time regime, being in strong contradiction with the two states model. The second model regards the interface as an interphase. The adsorption layer consists of a topmost monolayer and an adjacent sublayer. The dissipative process is due to the molecular exchange between both layers. The assessment of this model required the design of an experiment that discriminates between the surface compositional term and the sublayer contribution. Such an experiment has been successfully designed and results on elastic and viscoelastic surfactant provided evidence for the correctness of the model. Because of its inherent surface specificity, surface SHG is a powerful analytical tool that can be used to gain information on molecular dynamics and reorganization of soluble surfactants. They are central elements of both experiments. However, they impose several structural elements of the model system. During the course of this thesis, a proper model system has been identified and characterized. The combination of several linear and nonlinear optical techniques, allowed for a detailed picture of the interfacial architecture of these surfactants.
Polyelectrolyte multilayer capsules as controlled permeability vehicles and catalyst carriers
(2003)
Polymer optical fibers (POFs) are a rather new tool for high-speed data transfer by modulated light. They allow the transport of high amounts of data over distances up to about 100 m without be influenced by external electromagnetic fields. Due to organic chemical nature of POFs, they are sensitive to the climate of their environment and therefore the optical fiber properties are as well. Hence, the optical stability is a key issue for long-term applications of POFs. The causes for a loss of optical transmission due to climatic exposures (aging/degradation) are researched by means of chemical analytical tools such as chemiluminescence (CL) and Fourier transform infrared (FTIR) spectroscopy for five different (with respect to manufacturers) step-index multimode PMMA based POFs and for seven different climatic conditions. Three of the five POF samples are studied more in detail to realize the effects of individual parameters and for forecasting longterm optical stability by short-term exposure tests. At first, the unexposed POF components (core, cladding, and bare POF as combination of core and cladding) are characterized with respect to important physical and chemical properties. The glass transition temperature Tg, and the melting temperature Tm are in the region of 120 °C to 140 °C, the molecular weight (Mw) of cores is in the order of 105 g mol-1. POFs are found to have different chemical compositions of their claddings as could be detected by FTIR, but identical compositions of their cores. Two of the POFs are exposed as cables (core, cladding and jacket) for about 3300 hours to the climate 92 °C / 95 % relative humidity (RH) resulting in a different transmission decrease. Investigating the related unexposed and exposed bare POFs for degradation using CL, FTIR, thermogravimetry (TG), UV/visible transmittance and gel permeation chromatography (GPC) suggest that claddings of POFs are more affected than cores. Probably the observed loss of transmission is mainly due to increased light absorption and imperfections at the core-cladding boundary caused by a large degradation of claddings. Hence, it is highly possible that the optical transmission stability of POFs is governed mainly by the thermo-oxidative stability of the cladding and minor of the core. Three bare POFs (core and cladding only) are exposed for different duration of exposure time (30 hours to 4500 hours) to 92 °C / 95 %RH, 92 °C / 50 %RH, 50 °C / 95 %RH, 90 °C / low humidity, 100 °C / low humidity, 110 °C / low humidity and 120 °C / low humidity. In these climates their transmission variations are found to be different from each other, too. The outcomes strongly inform that under high temperature and high humid climates physical changes such as volume expansion, are the main sources for the loss of optical transmission. Also, the optical transmission stability of POFs is found to be dependent on chemical compositions of claddings. Under high temperature and low humid conditions, a loss of transmission at the early stages of the exposure is mainly caused by physical changes, presumable by corecladding interface imperfections. For the later stages of exposures it is proposed to an additional increase of light absorption by core and cladding owes to degradation. Optical simulation results obtained parallel by Mr. L. Jankowski (a PhD student of BAM) are found to confirm these results. For bare POFs, too, the optical stability of POFs seems to depend on their thermo-oxidative stability. Some short-term exposure tests are conducted to realize influences of individual climatic parameters on the transmission property of POFs. It is found that at stationary high temperature and variable humidity conditions POFs display to a certain amount a reversible transmission loss due to physically absorbed water. But in the case of varying temperature and constant high humidity such reversibility is hardly noticeable. However, at room temperature and varying humidity, POFs display fully reversible transmission loss. The whole research described above has to be regarded as a starting point for further investigations. The restricted distribution of fundamental POF data by the manufacturers and the time consuming aging by climatic exposures restrict the results more or less to the samples, investigated here. Significant general statements require for example additional information concerning the variation of POF properties due to production. Nevertheless the tests, described here, have the capability for approximating and forecasting the long-term optical transmission stability of POFs. -------------- Auch im Druck erschienen: Appajaiah, Anilkumar: Climatic stability of polymer optical fibers (POF) / Anilkumar Appajaiah. - Bremerhaven : Wirtschaftsverl. NW, Verl. für neue Wiss., 2005. - Getr. Zählung [ca. 175 S.]. : Ill., graph. Darst. - (BAM-Dissertationsreihe ; 9) ISBN 3-86509-302-7
Mixed 1,2-Dümine-1,2-Dithiolate Ligand Complexes : Structure, Proberties and EPR Spectroscopy
(2009)
Nonaqueous synthesis of metal oxide nanoparticles and their assembly into mesoporous materials
(2006)
This thesis mainly consist of two parts, the synthesis of several kinds of technologically interesting crystalline metal oxide nanoparticles via nonaqueous sol-gel process and the formation of mesoporous metal oxides using some of these nanoparticles as building blocks via evaporation induced self-assembly (EISA) technique. In the first part, the experimental procedures and characterization results of successful syntheses of crystalline tin oxide and tin doped indium oxide (ITO) nanoparticles are reported. SnO2 nanoparticles exhibit monodisperse particle size (3.5 nm in average), high crystallinity and particularly high dispersibility in THF, which enable them to become the ideal particulate precursor for the formation of mesoporous SnO2. ITO nanoparticles possess uniform particle morphology, narrow particle size distribution (5-10 nm), high crystallinity as well as high electrical conductivity. The synthesis approaches and characterization of various mesoporous metal oxides, including TiO2, SnO2, mixture of CeO2 and TiO2, mixture of BaTiO3 and SnO2, are reported in the second part of this thesis. Mesoporous TiO2 and SnO2 are presented as highlights of this part. Mesoporous TiO2 was produced in the forms of both films and bulk material. In the case of mesoporous SnO2, the study was focused on the high order of the porous structure. All these mesoporous metal oxides show high crystallinity, high surface area and rather monodisperse pore sizes, which demonstrate the validity of EISA process and the usage of preformed crystalline nanoparticles as nanobuilding blocks (NBBs) to produce mesoporous metal oxides.
Chitooligosaccharides are composed of glycosamin and N-acetylglycisamin residues. Gel permeations chromatography is employed for the separation of oligomers, cation exchange chromatography is used for the separation of homologes and isomers. Trideuterioacetylation of the chitooligosaccharides followed by MALDI-TOF mass spectrometry allowes for the quantitation of mixtures of homologes. vMALDI LTQ multiple-stage MS is employed for quantitative sequencing of complex mixtures of heterochitooligosaccharides. Pure homologes and isomers are applied to biological assays. Chitooligosaccahrides form high-affinity non-covalent complexes with HC gp-39 (human cartilage glycoprotein of 39 kDa). The affinity of the chitooligosaccharides depends on DP, FA and the sequence of glycosamin and N-acetylglycosamin moieties. (+)nanoESI Q TOF MS/MS is used for identification of a high-affinity binding chitooligosaccharide of a non-covalent chitinase B - chitooligosaccharide complex. DADAA is identified as the heterochitoisomer binding with highest affinity and biostability to HC gp-39. Fluorescence based enzyme assays confirm the results.
Core-shell upconversion nanoparticles - investigation of dopant intermixing and surface modification
(2022)
Frequency upconversion nanoparticles (UCNPs) are inorganic nanocrystals capable to up-convert incident photons of the near-infrared electromagnetic spectrum (NIR) into higher energy photons. These photons are re-emitted in the range of the visible (Vis) and even ultraviolet (UV) light. The frequency upconversion process (UC) is realized with nanocrystals doped with trivalent lanthanoid ions (Ln(III)). The Ln(III) ions provide the electronic (excited) states forming a ladder-like electronic structure for the Ln(III) electrons in the nanocrystals. The absorption of at least two low energy photons by the nanoparticle and the subsequent energy transfer to one Ln(III) ion leads to the promotion of one Ln(III) electron into higher excited electronic states. One high energy photon will be emitted during the radiative relaxation of the electron in the excited state back into the electronic ground state of the Ln(III) ion. The excited state electron is the result of the previous absorption of at least two low energy photons.
The UC process is very interesting in the biological/medical context. Biological samples (like organic tissue, blood, urine, and stool) absorb high-energy photons (UV and blue light) more strongly than low-energy photons (red and NIR light). Thanks to a naturally occurring optical window, NIR light can penetrate deeper than UV light into biological samples. Hence, UCNPs in bio-samples can be excited by NIR light. This possibility opens a pathway for in vitro as well as in vivo applications, like optical imaging by cell labeling or staining of specific organic tissue. Furthermore, early detection and diagnosis of diseases by predictive and diagnostic biomarkers can be realized with bio-recognition elements being labeled to the UCNPs. Additionally, "theranostic" becomes possible, in which the identification and the treatment of a disease are tackled simultaneously.
For this to succeed, certain parameters for the UCNPs must be met: high upconversion efficiency, high photoluminescence quantum yield, dispersibility, and dispersion stability in aqueous media, as well as availability of functional groups to introduce fast and easy bio-recognition elements. The UCNPs used in this work were prepared with a solvothermal decomposition synthesis yielding in particles with NaYF4 or NaGdF4 as host lattice. They have been doped with the Ln(III) ions Yb3+ and Er3+, which is only one possible upconversion pair. Their upconversion efficiency and photoluminescence quantum yield were improved by adding a passivating shell to reduce surface quenching.
However, the brightness of core-shell UCNPs stays behind the expectations compared to their bulk material (being at least μm-sized particles). The core-shell structures are not clearly separated from each other, which is a topic in literature. Instead, there is a transition layer between the core and the shell structure, which relates to the migration of the dopants within the host lattice during the synthesis. The ion migration has been examined by time-resolved laser spectroscopy and the interlanthanoid resonance energy transfer (LRET) in the two different host lattices from above. The results are
presented in two publications, which dealt with core-shell-shell structured nanoparticles. The core is doped with the LRET-acceptor (either Nd3+ or Pr3+). The intermediate shell serves as an insulation shell of pure host lattice material, whose shell thickness has been varied within one set of samples having the same composition, so that the spatial separation of LRET-acceptor and -donor changes. The outer shell with the same host lattice is doped with the LRET-donor (Eu3+). The effect of the increasing insulation shell thickness is significant, although the LRET cannot be suppressed completely.
Next to the Ln(III) migration within a host lattice, various phase transfer reactions were investigated in order to subsequently perform surface modifications for bioapplications. One result out of this research has been published using a promising ligand, that equips the UCNP with bio-modifiable groups and has good potential for bio-medical applications. This particular ligand mimics natural occurring mechanisms of mussel protein adhesion and of blood coagulation, which is why the UCNPs are encapsulated very effectively. At the same time, bio-functional groups are introduced. In a proof-of-concept, the encapsulated UCNP has been coupled successfully with a dye (which is representative for a biomarker) and the system’s photoluminescence properties have been investigated.
New bio-based polymers
(2018)
Redox-responsive polymers, such as poly(disulfide)s, are a versatile class of polymers with potential applications including gene- and drug-carrier systems. Their degradability under reductive conditions allows for a controlled response to the different redox states that are present throughout the body. Poly(disulfide)s are typically synthesized by step growth polymerizations. Step growth polymerizations, however, may suffer from low conversions and therefore low molar masses, limiting potential applications. The purpose of this thesis was therefore to find and investigate new synthetic routes towards the synthesis of amino acid-based poly(disulfide)s.
The different routes in this thesis include entropy-driven ring opening polymerizations of novel macrocyclic monomers, derived from cystine derivatives. These monomers were obtained with overall yields of up to 77% and were analyzed by mass spectrometry as well as by 1D and 2D NMR spectroscopy. The kinetics of the entropy-driven ring-opening metathesis polymerization (ED-ROMP) were thoroughly investigated in dependence of temperature, monomer concentration, and catalyst concentration. The polymerization was optimized to yield poly(disulfide)s with weight average molar masses of up to 80 kDa and conversions of ~80%, at the thermodynamic equilibrium. Additionally, an alternative metal free polymerization, namely the entropy-driven ring-opening disulfide metathesis polymerization (ED-RODiMP) was established for the polymerization of the macrocyclic monomers. The effect of different solvents, concentrations and catalyst loadings on the polymerization process and its kinetics were studied. Polymers with very high weight average molar masses of up to 177 kDa were obtained. Moreover, various post-polymerization reactions were successfully performed.
This work provides the first example of the homopolymerization of endo-cyclic disulfides by ED-ROMP and the first substantial study into the kinetics of the ED-RODiMP process.
The selective infrared (IR) excitation of molecular vibrations is a powerful tool to control the photoreactivity prior to electronic excitation in the ultraviolet / visible (UV/Vis) light regime ("vibrationally mediated chemistry"). For adsorbates on surfaces it has been theoretically predicted that IR preexcitation will lead to higher UV/Vis photodesorption yields and larger cross sections for other photoreactions. In a recent experiment, IR-mediated desorption of molecular hydrogen from a Si(111) surface on which atomic hydrogen and deuterium were co-adsorbed was achieved, following a vibrational mechanism as indicated by the isotope-selectivity. In the present work, selective vibrational IR excitation of adsorbate molecules, treated as multi-dimensional oscillators on dissipative surfaces, has been simulated within the framework of open-system density matrix theory. Not only potential-mediated, inter-mode coupling poses an obstacle to selective excitation but also the coupling of the adsorbate ("system") modes to the electronic and phononic degrees of freedom of the surface ("bath") does. Vibrational relaxation thereby takes place, depending on the availabilty of energetically fitting electron-hole (e/h) pairs and/or phonons (lattice vibrations) in the surface, on time-scales ranging from milliseconds to several hundreds of femtoseconds. On metal surfaces, where the relaxation process of the adsorbate via the e/h pair mechanism dominates, vibrational lifetimes are usually shorter than on insulator or semiconductor surfaces, in the range of picoseconds, being also the timescale of the IR pulses used here. Further inhibiting factors for selectivity can be the harmonicity of a mode and weak dipole activities ("dark modes") rendering vibrational excitation with moderate field intensities difficult. In addition to simple analytical pulses, optimal control theory (OCT) has been employed here to generate a suitable electric field to populate the target state/mode maximally. The complex OCT fields were analyzed by Husimi transformation, resolving the control field in time and energy. The adsorbate/surface systems investigated were CO/Cu(100), H/Si(100) and 2H/Ru(0001). These systems proved to be suitable models to study the above mentioned effects. Further, effects of temperature, pure dephasing (elastic scattering processes), pulse duration and dimensionality (up to four degrees of freedom) were studied. It was possible to selectively excite single vibrational modes, often even state-selective. Special processes like hot-band excitation, vibrationally mediated desorption and the excitation of "dark modes" were simulated. Finally, a novel OCT algorithm in density matrix representation has been developed which allows for time-dependent target operators and thus enables to control the excitation mechanism instead of only the final state. The algorithm is based on a combination of global (iterative) and local (non-iterative) OCT schemes, such that short, globally controlled time-intervals are coupled locally in time. Its numerical performance and accuracy were tested and verified and it was successfully applied to stabilize a two-state linear-combination and to enforce a successive "ladder climbing" in a rather harmonic system, where monochromatic, analytical pulses simultaneously excited several states, leading to a population loss in the target state.
The goal of regenerative medicine is to guide biological systems towards natural healing outcomes using a combination of niche-specific cells, bioactive molecules and biomaterials. In this regard, mimicking the extracellular matrix (ECM) surrounding cells and tissues in vivo is an effective strategy to modulate cell behaviors. Cellular function and phenotype is directed by the biochemical and biophysical signals present in the complex 3D network of ECMs composed mainly of glycoproteins and hydrophilic proteoglycans. While cellular modulation in response to biophysical cues emulating ECM features has been investigated widely, the influence of biochemical display of ECM glycoproteins mimicking their presentation in vivo is not well characterized. It remains a significant challenge to build artificial biointerfaces using ECM glycoproteins that precisely match their presentation in nature in terms of morphology, orientation and conformation. This challenge becomes clear, when one understands how ECM glycoproteins self-assemble in the body. Glycoproteins produced inside the cell are secreted in the extra-cellular space, where they are bound to the cell membrane or other glycoproteins by specific interactions. This leads to elevated local concentration and 2Dspatial confinement, resulting in self-assembly by the reciprocal interactions arising from the molecular complementarity encoded in the glycoprotein domains. In this thesis, air-water (A-W) interface is presented as a suitable platform, where self-assembly parameters of ECM glycoproteins such as pH, temperature and ionic strength can be controlled to simulate in vivo conditions (Langmuir technique), resulting in the formation of glycoprotein layers with defined characteristics. The layer can be further compressed with surface barriers to enhance glycoprotein-glycoprotein contacts and defined layers of glycoproteins can be immobilized on substrates by horizontal lift and touch method, called Langmuir-Schäfer (LS) method. Here, the benefit of Langmuir and LS methods in achieving ECM glycoprotein biointerfaces with controlled network morphology and ligand density on substrates is highlighted and contrasted with the commonly used (glyco)protein solution deposition (SO) method on substrates. In general, the (glyco)protein layer formation by SO is rather uncontrolled, influenced strongly by (glyco)protein-substrate interactions and it results in multilayers and aggregations on substrates, while the LS method results in (glyco)proteins layers with a more homogenous presentation. To achieve the goal of realizing defined ECM layers on substrates, ECM glycoproteins having the ability to self-assemble were selected: Collagen-IV (Col-IV) and fibronectin (FN). Highly packed FN layer with uniform presentation of ligands was deposited on polydimethysiloxane VIII (PDMS) by LS method, while a heterogeneous layer was formed on PDMS by SO with prominent aggregations visible. Mesenchymal stem cells (MSC) on PDMS equipped with FN by LS exhibited more homogeneous and elevated vinculin expression and weaker stress fiber formation than on PDMS equipped with FN by SO and these divergent responses could be attributed to the differences in glycoprotein presentation at the interface. Col-IV are scaffolding components of specialized ECM called basement membranes (BM), and have the propensity to form 2D networks by self-polymerization associated with cells. Col- IV behaves as a thin-disordered network at the A-W interface. As the Col-IV layer was compressed at the A-W interface using trough barriers, there was negligible change in thickness (layer thickness ~ 50 nm) or orientation of molecules. The pre-formed organization of Col-IV was transferred by LS method in a controlled fashion onto substrates meeting the wettability criterion (CA ≤ 80°). MSC adhesion (24h) on PET substrates deposited with Col-IV LS films at 10, 15 and 20 mN·m-1 surface pressures was (12269.0 ± 5856.4) cells for LS10, (16744.2 ± 1280.1) cells for LS15 and (19688.3 ± 1934.0) cells for LS20 respectively. Remarkably, by selecting the surface areal density of Col-IV on the Langmuir trough on PET, there is a linear increase between the number of adherent MSCs and the Col-IV ligand density. Further, FN has the ability to self-stabilize and form 2D networks (even without compression) while preserving native β-sheet structure at the A-W interface on a defined subphase (pH = 2). This provides the possibility to form such layers on any vessel (even on standard six-well culture plates) and the cohesive FN layers can be deposited by LS transfer, without the need for expensive LB instrumentation. Multilayers of FN can be immobilized on substrates by this approach, as easily as Layer-by-Layer method, even without the need for secondary adlayer or activated bare substrate. Thus, this facile glycoprotein coating strategy approach is accessible to many researchers to realize defined FN films on substrates for cell culture. In conclusion, Langmuir and LS methods can create biomimetic glycoprotein biointerfaces on substrates controlling aspects of presentation such as network morphology and ligand density. These methods will be utilized to produce artificial BM mimics and interstitial ECM mimics composed of more than one ECM glycoprotein layer on substrates, serving as artificial niches instructing stem cells for cell-replacement therapies in the future.
In this work approaches for new detection system development for an Analytical Ultracentrifuge (AUC) were explored. Unlike its counterpart in chromatography fractionation techniques, the use of a Multidetection system for AUC has not yet been implemented to full extent despite its potential benefit. In this study we tried to couple existing fundamental spectroscopic and scattering techniques that are used in day to day science as tool for extracting analyte information. Trials were performed for adapting Raman, Light scattering and UV/Vis (with possibility to work with the whole range of wavelengths) to AUC. Conclusions were drawn for Raman and Light scattering to be a possible detection system for AUC, while the development for a fast fiber optics based multiwavelength detector was completed. The multiwavelength detector demonstrated the capability of data generation matching the literature and reference measurement data and faster data collection than that of the commercial instrument. It became obvious that with the generation of data in 3-D space in the UV/Vis detection system, the user can select the wavelength for the evaluation of experimental results as the data set contains the whole range of information from UV/Vis wavelength. The detector showed the data generation with much faster speed unlike the commercial instruments. The advantage of fast data generation was exemplified with the evaluation of data for a mixture of three colloids. These data were in conformity with measurement results from normal radial experiments and without significant diffusion broadening. Thus conclusions were drawn that with our designed Multiwavelength detector, meaningful data in 3-D space can be collected with much faster speed of data generation.
This work presents the synthesis and the self-assembly of symmetrical amphiphilic ABA and BAB triblock copolymers in dilute, semi-concentrated and highly concentrated aqueous solution. A series of new bifunctional bistrithiocarbonates as RAFT agents was used to synthesise these triblock copolymers, which are characterised by a long hydrophilic middle block and relatively small, but strongly hydrophobic end blocks. As hydrophilic A blocks, poly(N-isopropylacrylamide) (PNIPAM) and poly(methoxy diethylene glycol acrylate) (PMDEGA) were employed, while as hydrophobic B blocks, poly(4-tert-butyl styrene), polystyrene, poly(3,5-dibromo benzyl acrylate), poly(2-ethylhexyl acrylate), and poly(octadecyl acrylate) were explored as building blocks with different hydrophobicities and glass transition temperatures. The five bifunctional trithiocarbonates synthesised belong to two classes: the first are RAFT agents, which position the active group of the growing polymer chain at the outer ends of the polymer (Z-C(=S)-S-R-S-C(=S)-Z, type I). The second class places the active groups in the middle of the growing polymer chain (R-S-C(=S)-Z-C(=S)-S-R, type II). These RAFT agents enable the straightforward synthesis of amphiphilic triblock copolymers in only two steps, allowing to vary the nature of the hydrophobic blocks as well as the length of the hydrophobic and hydrophilic blocks broadly with good molar mass control and narrow polydispersities. Specific side reactions were observed among some RAFT agents including the elimination of ethylenetrithiocarbonate in the early stage of the polymerisation of styrene mediated by certain agents of the type II, while the use of the RAFT agents of type I resulted in retardation of the chain extension of PNIPAM with styrene. These results underline the need of a careful choice of RAFT agents for a given task. The various copolymers self-assemble in dilute and semi-concentrated aqueous solution into small flower-like micelles. No indication for the formation of micellar clusters was found, while only at high concentration, physical hydrogels are formed. The reversible thermoresponsive behaviour of the ABA and BAB type copolymer solutions in water with A made of PNIPAM was examined by turbidimetry and dynamic light scattering (DLS). The cloud point of the copolymers was nearly identical to the cloud point of the homopolymer and varied between 28-32 °C with concentrations from 0.01 to 50 wt%. This is attributed to the formation of micelles where the hydrophobic blocks are shielded from a direct contact with water, so that the hydrophobic interactions of the copolymers are nearly the same as for pure PNIPAM. Dynamic light scattering measurements showed the presence of small micelles at ambient temperature. The aggregate size dramatically increased above the cloud point, indicating a change of aggregate morphology into clusters due to the thermosensitivity of the PNIPAM block. The rheological behaviour of the amphiphilic BAB triblock copolymers demonstrated the formation of hydrogels at high concentrations, typically above 30-35 wt%. The minimum concentration to induce hydrogels decreased with the increasing glass transition temperatures and increasing length of the end blocks. The weak tendency to form hydrogels was attributed to a small share of bridged micelles only, due to the strong segregation regime occurring. In order to learn about the role of the nature of the thermoresponsive block for the aggregation, a new BAB triblock copolymer consisting of short polystyrene end blocks and PMDEGA as stimuli-responsive middle block was prepared and investigated. Contrary to PNIPAM, dilute aqueous solutions of PMDEGA and of its block copolymers showed reversible phase transition temperatures characterised by a strong dependence on the polymer composition. Moreover, the PMDEGA block copolymer allowed the formation of physical hydrogels at lower concentration, i.e. from 20 wt%. This result suggests that PMDEGA has a higher degree of water-swellability than PNIPAM.
In the first section of the thesis graphitic carbon nitride was for the first time synthesised using the high-temperature condensation of dicyandiamide (DCDA) – a simple molecular precursor – in a eutectic salt melt of lithium chloride and potassium chloride. The extent of condensation, namely next to complete conversion of all reactive end groups, was verified by elemental microanalysis and vibrational spectroscopy. TEM- and SEM-measurements gave detailed insight into the well-defined morphology of these organic crystals, which are not based on 0D or 1D constituents like known molecular or short-chain polymeric crystals but on the packing motif of extended 2D frameworks. The proposed crystal structure of this g-C3N4 species was derived in analogy to graphite by means of extensive powder XRD studies, indexing and refinement. It is based on sheets of hexagonally arranged s-heptazine (C6N7) units that are held together by covalent bonds between C and N atoms. These sheets stack in a graphitic, staggered fashion adopting an AB-motif, as corroborated by powder X-ray diffractometry and high-resolution transmission electron microscopy. This study was contrasted with one of many popular – yet unsuccessful – approaches in the last 30 years of scientific literature to perform the condensation of an extended carbon nitride species through synthesis in the bulk. The second section expands the repertoire of available salt melts introducing the lithium bromide and potassium bromide eutectic as an excellent medium to obtain a new phase of graphitic carbon nitride. The combination of SEM, TEM, PXRD and electron diffraction reveals that the new graphitic carbon nitride phase stacks in an ABA’ motif forming unprecedentedly large crystals. This section seizes the notion of the preceding chapter, that condensation in a eutectic salt melt is the key to obtain a high degree of conversion mainly through a solvatory effect. At the close of this chapter ionothermal synthesis is seen established as a powerful tool to overcome the inherent kinetic problems of solid state reactions such as incomplete polymerisation and condensation in the bulk especially when the temperature requirement of the reaction in question falls into the proverbial “no man’s land” of classical solvents, i.e. above 250 to 300 °C. The following section puts the claim to the test, that the crystalline carbon nitrides obtained from a salt melt are indeed graphitic. A typical property of graphite – namely the accessibility of its interplanar space for guest molecules – is transferred to the graphitic carbon nitride system. Metallic potassium and graphitic carbon nitride are converted to give the potassium intercalation compound, K(C6N8)3 designated according to its stoichiometry and proposed crystal structure. Reaction of the intercalate with aqueous solvents triggers the exfoliation of the graphitic carbon nitride material and – for the first time – enables the access of singular (or multiple) carbon nitride sheets analogous to graphene as seen in the formation of sheets, bundles and scrolls of carbon nitride in TEM imaging. The thus exfoliated sheets form a stable, strongly fluorescent solution in aqueous media, which shows no sign in UV/Vis spectroscopy that the aromaticity of individual sheets was subject to degradation. The final section expands on the mechanism underlying the formation of graphitic carbon nitride by literally expanding the distance between the covalently linked heptazine units which constitute these materials. A close examination of all proposed reaction mechanisms to-date in the light of exhaustive DSC/MS experiments highlights the possibility that the heptazine unit can be formed from smaller molecules, even if some of the designated leaving groups (such as ammonia) are substituted by an element, R, which later on remains linked to the nascent heptazine. Furthermore, it is suggested that the key functional groups in the process are the triazine- (Tz) and the carbonitrile- (CN) group. On the basis of these assumptions, molecular precursors are tailored which encompass all necessary functional groups to form a central heptazine unit of threefold, planar symmetry and then still retain outward functionalities for self-propagated condensation in all three directions. Two model systems based on a para-aryl (ArCNTz) and para-biphenyl (BiPhCNTz) precursors are devised via a facile synthetic procedure and then condensed in an ionothermal process to yield the heptazine based frameworks, HBF-1 and HBF-2. Due to the structural motifs of their molecular precursors, individual sheets of HBF-1 and HBF-2 span cavities of 14.2 Å and 23.0 Å respectively which makes both materials attractive as potential organic zeolites. Crystallographic analysis confirms the formation of ABA’ layered, graphitic systems, and the extent of condensation is confirmed as next-to-perfect by elemental analysis and vibrational spectroscopy.
Metals are often used in environments that are conducive to corrosion, which leads to a reduction in their mechanical properties and durability. Coatings are applied to corrosion-prone metals such as aluminum alloys to inhibit the destructive surface process of corrosion in a passive or active way. Standard anticorrosive coatings function as a physical barrier between the material and the corrosive environment and provide passive protection only when intact. In contrast, active protection prevents or slows down corrosion even when the main barrier is damaged. The most effective industrially used active corrosion inhibition for aluminum alloys is provided by chromate conversion coatings. However, their toxicity and worldwide restriction provoke an urgent need for finding environmentally friendly corrosion preventing systems. A promising approach to replace the toxic chromate coatings is to embed particles containing nontoxic inhibitor in a passive coating matrix. This work presents the development and optimization of effective anticorrosive coatings for the industrially important aluminum alloy, AA2024-T3 using this approach. The protective coatings were prepared by dispersing mesoporous silica containers, loaded with the nontoxic corrosion inhibitor 2-mercaptobenzothiazole, in a passive sol-gel (SiOx/ZrOx) or organic water-based layer. Two types of porous silica containers with different sizes (d ≈ 80 and 700 nm, respectively) were investigated. The studied robust containers exhibit high surface area (≈ 1000 m² g-1), narrow pore size distribution (dpore ≈ 3 nm) and large pore volume (≈ 1 mL g-1) as determined by N2 sorption measurements. These properties favored the subsequent adsorption and storage of a relatively large amount of inhibitor as well as its release in response to pH changes induced by the corrosion process. The concentration, position and size of the embedded containers were varied to ascertain the optimum conditions for overall anticorrosion performance. Attaining high anticorrosion efficiency was found to require a compromise between delivering an optimal amount of corrosion inhibitor and preserving the coating barrier properties. This study broadens the knowledge about the main factors influencing the coating anticorrosion efficiency and assists the development of optimum active anticorrosive coatings doped with inhibitor loaded containers.
The negative impact of crude oil on the environment has led to a necessary transition toward alternative, renewable, and sustainable resources. In this regard, lignocellulosic biomass (LCB) is a promising renewable and sustainable alternative to crude oil for the production of fine chemicals and fuels in a so-called biorefinery process. LCB is composed of polysaccharides (cellulose and hemicellulose), as well as aromatics (lignin). The development of a sustainable and economically advantageous biorefinery depends on the complete and efficient valorization of all components. Therefore, in the new generation of biorefinery, the so-called biorefinery of type III, the LCB feedstocks are selectively deconstructed and catalytically transformed into platform chemicals. For this purpose, the development of highly stable and efficient catalysts is crucial for progress toward viability in biorefinery. Furthermore, a modern and integrated biorefinery relies on process and reactor design, toward more efficient and cost-effective methodologies that minimize waste. In this context, the usage of continuous flow systems has the potential to provide safe, sustainable, and innovative transformations with simple process integration and scalability for biorefinery schemes.
This thesis addresses three main challenges for future biorefinery: catalyst synthesis, waste feedstock valorization, and usage of continuous flow technology. Firstly, a cheap, scalable, and sustainable approach is presented for the synthesis of an efficient and stable 35 wt.-% Ni catalyst on highly porous nitrogen-doped carbon support (35Ni/NDC) in pellet shape. Initially, the performance of this catalyst was evaluated for the aqueous phase hydrogenation of LCB-derived compounds such as glucose, xylose, and vanillin in continuous flow systems. The 35Ni/NDC catalyst exhibited high catalytic performances in three tested hydrogenation reactions, i.e., sorbitol, xylitol, and 2-methoxy-4-methylphenol with yields of 82 mol%, 62 mol%, and 100 mol% respectively. In addition, the 35Ni/NDC catalyst exhibited remarkable stability over a long time on stream in continuous flow (40 h). Furthermore, the 35Ni/NDC catalyst was combined with commercially available Beta zeolite in a dual–column integrated process for isosorbide production from glucose (yield 83 mol%).
Finally, 35Ni/NDC was applied for the valorization of industrial waste products, namely sodium lignosulfonate (LS) and beech wood sawdust (BWS) in continuous flow systems. The LS depolymerization was conducted combining solvothermal fragmentation of water/alcohol mixtures (i.e.,methanol/water and ethanol/water) with catalytic hydrogenolysis/hydrogenation (SHF). The depolymerization was found to occur thermally in absence of catalyst with a tunable molecular weight according to temperature. Furthermore, the SHF generated an optimized cumulative yield of lignin-derived phenolic monomers of 42 mg gLS-1. Similarly, a solvothermal and reductive catalytic fragmentation (SF-RCF) of BWS was conducted using MeOH and MeTHF as a solvent. In this case, the optimized total lignin-derived phenolic monomers yield was found of 247 mg gKL-1.
The valorization of carbohydrates is one of the most promising fields in green chemistry, as it enables to produce bulk chemicals and fuels out of renewable and abundant resources, instead of further exploiting fossil feedstocks. The focus in this thesis is the conversion of fructose, using dehydration and hydrodeoxygenation reactions. The main goal is to find an easy continuous process, including the solubility of the sugar in a green solvent, the conversion over a solid acid as well as over a metal@tungsten carbide catalyst.
At the beginning of this thesis, solid acid catalysts are synthesized by using carbohydrate material like glucose and starch at high temperatures (up to 600 °C). Additionally a third carbon is synthesized, using an activation method based on Ca(OH)2. After carbonization and further sulfonation, using fuming sulfuric acid, the three resulting catalysts are characterized together with sulfonated carbon black and Amberlyst 15 as references. In order to test all solid acid catalysts in reaction, a 250 mm x 4.6 mm stainless steel column is used as a fixed-bed continuous reactor. The temperature (110 °C to 250 °C) and residence time (2 to 30 minutes) is varied, and a direct relationship between contact time and selectivity is determined. The reaction mechanism, as well as the product distribution is showing a dehydration step of fructose towards 5-hydroxymethylfurfural (HMF). These furan-ring molecules are considered as “sleeping giants”, due to the possibility of using them as fuel, but also for upgrading them to chemicals like terephthalic acid or p-xylene. Consecutive reactions are producing levulinic acid, as well as condensation products with ethanol and formic acid. The activated carbon is additionally showing a 2 % yield of 2,5-Dimethylfuran (DMF) production, pointing towards the extraordinary properties of this catalyst. Without a metal catalyst present, what is normally necessary for hydrogenation reactions, a transferhydrogenation (with formic acid) is observed. The active catalyst was therefore carbon itself, what activated the hydrogen on its surface. This phenomenon was just very rarely observed so far. Expensive noble metals are the material of choice, when it comes to hydrogenation reactions nowadays and cheaper alternatives are necessary.
By postulating a similar electronic structure of tungsten carbide (WC) to platinum by Lewy and Boudart, research is focusing on the replacement of Pt. The production of nano-sized tungsten carbide particles (7.5 ± 2.5 nm, 70 m2 g-1) is enabled by the so called “urea glass route” and its catalytic performances are compared to commercial material. It is shown, that the activity is strongly dependent on the size of the particles as well as the surface area. Nano-sized tungsten carbide is showing activity for hydrogenation reactions under mild conditions (maximum 150 °C, 30 bar). This material therefore opens up new possibilities for replacing the rare and expensive platinum with tungsten carbide based catalysts.
Additionally different metal nanoparticles of palladium, copper and nickel are deposited on top of WC to further promote its reactivity. The nickel nanoparticles are strongly connected to WC and showed the best activity as well as selectivity for upgrading HMF with hydrodeoxygenation. The Ni@WC is not leaching and is showing very good hydrodeoxygenation properties with DMF yields up to 90 percent. Copper@WC is not showing good activity and palladium@WC enables undesired consecutive reactions, hydrogenating the furan ring system.
In order to enable the upgrade of fructose to DMF directly in a continuous system, the current H CUBE Pro TM hydrogenation system is customized with a second reaction column. A 250 mm x 4.6 mm stainless steel reactor column is connected ahead of the hydrogen insertion, enabling the dehydration of fructose to HMF derivatives, before pumping these products into the second column for hydrogenation. The overall residence time in the two column reactor system is 14 minutes. The overall results are an almost full conversion with a yield of 38.5 % DMF and 47 % yield of EL. The main disadvantage is the formation of higher mass products, so called humins, which start depositing on top of the catalysts, blocking their active sites.
In general it can be stated, that a two column system goes along with a higher investment as well as more maintenance costs, compared to a one column catalytic approach. To develop a catalyst, which is on the one hand able to dehydrate as well as hydrodeoxygenate the reactants, is aimed for at the last part of the thesis. The activated carbon however shows already activity for hydrodeoxygenation without any metal present and offers itself therefore as an alternative to overcome the temperature instability of Amberlyst 15 (max. 120 °C) for a combined DMF production directly from fructose. The activity for the upgrade to DMF is increased from 2 % to 12 % DMF yield in one mixed continuous column.
In order to scale up the entire one column approach, an 800 mm x 28.5 mm inner diameter column was planned and manufactured. The system is scaled up and assembled, whereas this flow reactor system is able to be run with 50 mL min-1 maximum flow rate, to stand a pressure of maximum 100 bar and be heated to around 500 °C. The tubing and connections, as well as the used devices are planned according to be safe and easy in use. The scaled-up approach offers a reaction column 120 times bigger (510 ml) then the first extension of the commercial system. This further extension offers the possibility of ranging between 1 and 1000 mL min-1, making it possible to use the approach in pilot plant applications.
Nanostructured materials are materials consisting of nanoparticulate building blocks on the scale of nanometers (i.e. 10-9 m). Composition, crystallinity and morphology can enhance or even induce new properties of the materials, which are desirable for todays and future technological applications. In this work, we have shown new strategies to synthesise metal oxide and metal nitride nanomaterials. The first part of the work deals with the study of nonaqueous synthesis of metal oxide nanoparticles. We succeeded in the synthesis of In2O3 nanopartcles where we could clearly influence the morphology by varying the type of the precursors and the solvents; of ZnO mesocrystals by using acetonitrile as a solvent; of transition metal oxides (Nb2O5, Ta2O5 and HfO2) that are particularly hard to obtain on the nanoscale and other technologically important materials. Solvothermal synthesis however is not restricted to formation of oxide materials only. In the second part we show examples of nonaqueous, solvothermal reactions of metal nitrides, but the main focus lies on the investigation of the influence of different morphologies of metal oxide precursors on the formation of the metal nitride nanoparticles. In spite of various reports, the number and variety of nanocrystalline metal nitrides is marginally small by comparison to metal oxides; hence preformed metal oxides as precursors for the preparation of metal nitrides are a logical choice. By reacting oxide nanoparticles with cyanamide, urea or melamine, at temperatures of 800 to 900 °C under nitrogen flow metal nitrides could be obtained. We studied in detail the influence of the starting material and realized that size, crystallinity, type of nitrogen source and temperature play the most important role. We have managed to propose and verify a dissolution-recrystallisation model as the formation mechanism. Furthermore we could show that the initial morphology of the oxides could be retained when ammonia flow was used instead.
Biomimicry is the art of mimicking nature to overcome a particular technical or scientific challenge. The approach studies how evolution has found solutions to the most complex problems in nature. This makes it a powerful method for science. In combination with the rapid development of manufacturing and information technologies into the digital age, structures and material that were before thought to be unrealizable can now be created with simple sketch and the touch of a button. This doctoral thesis had as its primary goal to investigate how digital tools, such as programming, modelling, 3D-Design tools and 3D-Printing, with the help from biomimicry, could lead to new analysis methods in science and new medical devices in medicine.
The Electrical Discharge Machining (EDM) process is applied commonly to deform or mold hard metals that are difficult to work using normal machinery. A workpiece submerged in an electrolyte is deformed while being in close vicinity to an electrode. When high voltage is put between the workpiece and the electrode it will cause sparks that create cavitations on the substrate which in turn removes material and is flushed away by the electrolyte. Usually, such surfaces are analysed based on roughness, in this work another method using a novel curvature analysis method is presented as an alternative. In addition, to better understand how the surface changes during process time of the EDM process, a digital impact model was created which created craters on ridges on an originally flat substrate. These substrates were then analysed using the curvature analysis method at different processing times of the modelling. It was found that a substrate reaches an equilibrium at around 10000 impacts. The proposed curvature analysis method has potential to be used in the design of new cell culture substrates for stem cell.
The Venus flytrap can shut its jaws at an amazing speed. The shutting mechanism may be interesting to use in science and is an example of a so-called mechanical bi-stable system – there are two stable states. In this work two truncated pyramid structures were modelled using a non-linear mechanical model called the Chained Beam Constraint Model (CBCM). The structure with a slope angle of 30 degrees is not bi-stable and the structure with a slope angle of 45 degrees is bi-stable. Developing this idea further by using PEVA, which has a shape-memory effect, the structure which is not bi-stable could be programmed to be bi-stable and then turned off again. This could be used as an energy storage system. Another species which has interesting mechanism is the tapeworm. Some species of this animal has a crown of hooks and suckers located on its side. The parasite commonly is found in mammals in the lower intestine and attaches to the walls by using its suckers. When the tapeworm has found a suitable spot, it ejects its hooks and permanently attaches to the wall. This function could be used in minimally invasive medicine to have better control of implants during the implantation process. By using the CBCM model and a 3D-printer capable of tuning how hard or soft a printed part is, a design strategy was developed to investigate how one could create a device that mimics the tapeworm. In the end a prototype was created which was able attach to a pork loin at an under pressure of 20 kPa and to ejects its hooks at an under pressure of 50 kPa or above.
These three projects is an exhibit of how digital tools and biomimicry can be used together to come up with applicable solutions in science and in medicine.
Advanced hybrid materials are recognized as one of the most significant enablers for new technologies, which holds true especially on the quest for sustainable energy sources and energy production schemes (e.g., semiconductor based photocatalytic materials). Usually, a single component is far from meeting all the demands needed for these advanced applications. Hybrid materials are composed of at least two components commonly an inorganic and an organic material on the molecular level, which feature novel properties exceeding the sum of the individual parts and might be the milestones of next-generation applications. This dissertation aims to provide novel combinations of the metal-free semiconductor graphitic carbon nitride (g-C3N4) with polymers to obtain materials with advanced properties and applications. Visible light constitutes the core of the present work as it is the only energy source utilized either in synthesis or in the application process. In the area of applications by combination of g-C3N4 and polymers, two different hybrids were thoroughly elucidated, i.e.. their design and construction as well as potential application in photocatalysis. Novel soft 3D liquid objects were formed via charge-interaction driven interfacial jamming between polyelectrolytes in aqueous environment and colloidal dispersions of g-C3N4 in edible sunflower oil. As such, stable liquid objects could be molded into specific shapes and utilized for photodegradation of organic dyes in water. Furthermore, the grafting of polymers onto g-C3N4 was investigated. Allyl-end functionalized polymers were grafted onto g-C3N4 by a photoinitiated process to yield g-C3N4 with versatile and improved properties, e.g. advanced dispersibility enabling processing via spin coating. As g-C3N4 produces radicals under visible light irradiation, which is of significant interest for polymer science, g-C3N4 containing polymer latex and macrogel beads (MGB) were synthesized by emulsion photopolymerization and inverse suspension photopolymerization, respectively. A well-controlled emulsion photopolymerization process via g-C3N4 initiation was designed, which features synthesis of well-defined and cross-linked polymer particles. Furthermore, the polymerization process was investigated thoroughly, indicating an ad-layer polymerization in early stages of the process. The utilization of functionalized g-C3N4 allowed the polymerization of various monomer types. Moreover, g-C3N4 was utilized as photoinitiator in hydrogel MGB formation. The formed MGB properties could be tailored via process design, e.g. stirring rate, cross-linker content and g-C3N4 content. Finally, MGBs were introduced as photocatalyst for waste water remediation, i.e. the degradation of Rhodamine B in aqueous solution was studied. The present thesis therefore builds a bridge between g-C3N4 and polymers and provides strategies for hybrid material formation. Furthermore, several potential applications are revealed with significant implications for photocatalysis, polymerization processes and polymer materials.
Magnetotactic bacteria comprise a heterogeneous group of Gram negative bacteria which share the ability to synthesise intracellular magnetic nanoparticles surrounded by a lipid bilayer, known as magnetosomes, which are arranged in linear chains. The bacteria exert a unique level of control onto the biomineralization of these nanoparticles, which is seen in the controlled size and shape they have. These characteristics have attracted great attention on understanding the process by which the bacteria synthesise the magnetosomes. Moreover, the magnetosome chain impart the bacteria with a net magnetic dipole which makes them susceptible to interact with magnetic fields and thus orient with the Earth’s magnetic field. This feature has attracted as well much interest to understand how the swimming motility of these microorganisms is affected by the presence of magnetic fields. Most of the studies performed in these bacteria so far have been conducted in the traditional manner using large populations of cells. Such studies have the disadvantage of averaging many different individuals with heterogeneous behaviours and fail to consider individual variations. In addition, in large populations each bacterium will be subjected to a different microenvironment that will influence the bacterial behaviour, but which cannot be defined using these traditional methods. In this thesis, different microfluidic platforms are proposed to overcome these limitations and to offer the possibility to study magnetotactic bacteria in defined environments and down to a single-cell resolution. First, a sediment-like microfluidic platform is presented with the purpose of mimicking the porous environment they bacteria naturally dwell in. The platform allows to observe via transmitted light microscopy that bacterial navigation in crowded environments is enhanced by the Earth’s magnetic field strengths (B = 50 μT) rather than by null (B = 0 μT) or higher magnetic fields (B = 500 μT). Second, a microfluidic system to confine single-bacterial cells in physically defined environments is presented. The system allows to study via transmitted light microscopy the interplay between wall curvature, magnetic fields and bacterial speed affect the motion of a confined bacterium, and shows how bacterial trajectories depend on those three parameters. Third, a microfluidic platform to conduct semi in vivo magnetosome nucleation with a single-cell resolution via X-ray fluorescence is fabricated. It is shown that signal arising from magnetosome full chains can be observed individually in each bacterium. Finally, the iron uptake kinetics of a single bacterium are studied via a fluorescent reporter through confocal microscopy. Two different approaches are used for this: one of the previously mentioned platforms, as well as giant lipid vesicles. It is observed how iron uptake rates vary between cells, as well as how these rates are consistent with magnetosome formation taking place within some hours. The present thesis shows therefore how microfluidic technologies can be implemented for the study of magnetotactic bacteria at different degrees, and the level of resolution that can be attained by going into the single- cell scale.
The utilization of lignin as renewable electrode material for electrochemical energy storage is a sustainable approach for future batteries and supercapacitors. The composite electrode was fabricated from Kraft lignin and conductive carbon and the charge storage contribution was determined in terms of electrical double layer (EDL) and redox reactions. The important factors at play for achieving high faradaic charge storage capacity contribute to high surface area, accessibility of redox sites in lignin and their interaction with conductive additives. A thinner layer of lignin covering the high surface area of carbon facilitates the electron transfer process with a shorter pathway from the active sites of nonconductive lignin to the current collector leading to the improvement of faradaic charge storage capacity.
Composite electrodes from lignin and carbon would be even more sustainable if the fluorinated binder can be omitted. A new route to fabricate a binder-free composite electrode from Kraft lignin and high surface area carbon has been proposed by crosslinking lignin with glyoxal. A high molecular weight of lignin is obtained to enhance both electroactivity and binder capability in composite electrodes. The order of the processing step of crosslinking lignin on the composite electrode plays a crucial role in achieving a stable electrode and high charge storage capacity. The crosslinked lignin based electrodes are promising since they allow for more stable, sustainable, halogen-free and environmentally benign devices for energy storage applications. Furthermore, improvement of the amount of redox active groups (quinone groups) in lignin is useful to enhance the capacity in lithium battery applications. Direct oxidative demethylation by cerium ammonium nitrate has been carried out under mild conditions. This proves that an increase of quinone groups is able to enhance the performance of lithium battery. Thus, lignin is a promising material and could be a good candidate for application in sustainable energy storage devices.
Synthesis of stimuli-responsive and switchable inorganic nanoparticles for biomedical applications
(2010)
Eukaryotic cells can be regarded as complex microreactors capable of performing various biochemical reactions in parallel which are necessary to sustain life. An essential prerequisite for these complex metabolic reactions to occur is the evolution of lipid membrane-bound organelles enabling compartmental- ization of reactions and biomolecules. This allows for a spatiotemporal control over the metabolic reactions within the cellular system. Intracellular organi- zation arising due to compartmentalization is a key feature of all living cells and has inspired synthetic biologists to engineer such systems with bottom-up approaches.
Artificial cells provide an ideal platform to isolate and study specific re- actions without the interference from the complex network of biomolecules present in biological cells. To mimic the hierarchical architecture of eukaryotic cells, multi-compartment assemblies with nested liposomal structures also re- ferred to as multi-vesicular vesicles (MVVs) have been widely adopted. Most of the previously reported multi-compartment systems adopt bulk method- ologies which suffer from low yield and poor control over size. Microfluidic strategies help circumvent these issues and facilitate a high-throughput and robust technique to assemble MVVs of uniform size distribution.
In this thesis, firstly, the bulk methodologies are explored to build MVVs and implement a synthetic signalling cascade. Next, a polydimethylsiloxane (PDMS)-based microfluidic platform is introduced to build MVVs and the significance of PEGylated lipids for the successful encapsulation of inner com- partments to generate stable multi-compartment systems is highlighted.
Next, a novel two-inlet channel PDMS-based microfluidic device to create MVVs encompassing a three-step enzymatic reaction cascade is presented. A directed reaction pathway comprising of the enzymes α-glucosidase (α-Glc), glucose oxidase (GOx), and horseradish peroxidase (HRP) spanning across three compartments via reconstitution of size-selective membrane proteins is described. Furthermore, owing to the monodispersity of our MVVs due to microfluidic strategies, this platform is employed to study the effect of com- partmentalization on reaction kinetics.
Further integration of cell-free expression module into the MVVs would allow for gene-mediated signal transduction within artificial eukaryotic cells. Therefore, the chemically inducible cell-free expression of a membrane protein alpha-hemolysin and its further reconstitution into liposomes is carried out.
In conclusion, the present thesis aims to build artificial eukaryotic cells to achieve size-selective chemical communication that also show potential for applications as micro reactors and as vehicles for drug delivery.
This project was focused on generating ultra thin stimuli responsive membranes with an embedded transmembrane protein to act as the pore. The membranes were formed by crosslinking of transmembrane protein polymer conjugates. The conjugates were self assembled on air water interface and the polymer chains crosslinked using a UV crosslinkable comonomer to engender the membrane. The protein used for the studies reported herein was one of the largest transmembrane channel proteins, ferric hydroxamate uptake protein component A (FhuA), found in the outer membrane of Escherichia coli (E. coli). The wild type protein and three genetic variants of FhuA were provided by the group of Prof. Schwaneberg in Aachen. The well known thermo responsive poly(N isopropylacrylamide) (PNIPAAm) and the pH and thermo responsive polymer poly((2-dimethylamino)ethyl methacrylate) (PDMAEMA) were conjugated to FhuA and the genetic variants via controlled radical polymerization (CRP) using grafting from technique. These polymers were chosen because they would provide stimuli handles in the resulting membranes. The reported polymerization was the first ever attempt to attach polymer chains onto a membrane protein using site specific modification.
The conjugate synthesis was carried out in two steps – a) FhuA was first converted into a macroinitiator by covalently linking a water soluble functional CRP initiator to the lysine residues. b) Copper mediated CRP was then carried out in pure buffer conditions with and without sacrificial initiator to generate the conjugates.
The challenge was carrying out the modifications on FhuA without denaturing it. FhuA, being a transmembrane protein, requires amphiphilic species to stabilize its highly hydrophobic transmembrane region. For the experiments reported in this thesis, the stabilizing agent was 2 methyl 2,4-pentanediol (MPD). Since the buffer containing MPD cannot be considered a purely aqueous system, and also because MPD might interfere with the polymerization procedure, the reaction conditions were first optimized using a model globular protein, bovine serum albumin (BSA). The optimum conditions were then used for the generation of conjugates with FhuA.
The generated conjugates were shown to be highly interfacially active and this property was exploited to let them self assemble onto polar apolar interfaces. The emulsions stabilized by particles or conjugates are referred to as Pickering emulsions. Crosslinking conjugates with a UV crosslinkable co monomer afforded nano thin micro compartments. Interfacial self assembly at the air water interface and subsequent UV crosslinking also yielded nano thin, stimuli responsive membranes which were shown to be mechanically robust. Initial characterization of the flux and permeation of water through these membranes is also reported herein. The generated nano thin membranes with PNIPAAm showed reduced permeation at elevated temperatures owing to the resistance by the hydrophobic and thus water-impermeable polymer matrix, hence confirming the stimulus responsivity.
Additionally, as a part of collaborative work with Dr. Changzhu Wu, TU Dresden, conjugates of three enzymes with current/potential industrial relevance (candida antarctica lipase B, benzaldehyde lyase and glucose oxidase) with stimuli responsive polymers were synthesized. This work aims at carrying out cascade reactions in the Pickering emulsions generated by self assembled enzyme polymer conjugate.
The importance of carbohydrate structures is enormous due to their ubiquitousness in our lives. The development of so-called glycomaterials is the result of this tremendous significance. These are not exclusively used for research into fundamental biological processes, but also, among other things, as inhibitors of pathogens or as drug delivery systems. This work describes the development of glycomaterials involving the synthesis of glycoderivatives, -monomers and -polymers. Glycosylamines were synthesized as precursors in a single synthesis step under microwave irradiation to significantly shorten the usual reaction time. Derivatization at the anomeric position was carried out according to the methods developed by Kochetkov and Likhorshetov, which do not require the introduction of protecting groups. Aminated saccharide structures formed the basis for the synthesis of glycomonomers in β-configuration by methacrylation. In order to obtain α-Man-based monomers for interactions with certain α-Man-binding lectins, a monomer synthesis by Staudinger ligation was developed in this work, which also does not require protective groups. Modification of the primary hydroxyl group of a saccharide was accomplished by enzyme-catalyzed synthesis. Ribose-containing cytidine was transesterified using the lipase Novozym 435 and microwave irradiation. The resulting monomer synthesis was optimized by varying the reaction partners. To create an amide bond instead of an ester bond, protected cytidine was modified by oxidation followed by amide coupling to form the monomer. This synthetic route was also used to isolate the monomer from its counterpart guanosine. After obtaining the nucleoside-based monomers, they were block copolymerized using the RAFT method. Pre-synthesized pHPMA served as macroCTA to yield cytidine- or guanosine-containing block copolymer. These isolated block copolymers were then investigated for their self-assembly behavior using UV-Vis, DLS and SEM to serve as a potential thermoresponsive drug delivery system.
Lanthanide based ceria nanomaterials are important practical materials due to their redox properties that are useful in technology and life sciences. This PhD thesis examined various properties and potential for catalytic and bio-applications of Ln3+-doped ceria nanomaterials. Ce1-xGdxO2-y: Eu3+, gadolinium doped ceria (GDC) (0 ≤ x ≤ 0.4) nanoparticles were synthesized by flame spray pyrolysis (FSP) and studied, followed by 15 % CexZr1-xO2-y: Eu3+|YSZ (0 ≤ x ≤ 1) nanocomposites. Furthermore, Ce1-xYb xO2-y (0.004 ≤ x ≤ 0.22) nanoparticles were synthesized by thermal decomposition and characterized. Finally, CeO2-y: Eu3+ nanoparticles were synthesized by a microemulsion method, biofunctionalized and characterized. The studies undertaken presents a novel approach to structurally elucidate ceria-based nanomaterials by way of Eu3+ and Yb3+ spectroscopy and processing the spectroscopic data with the multi-way decomposition method PARAFAC. Data sets of the three variables: excitation wavelength, emission wavelength and time were used to perform the deconvolution of spectra.
GDC nanoparticles from FSP are nano-sized and of roughly cubic shape and crystal structure (Fm3̅m). Raman data revealed four vibrational modes exhibited by Gd3+ containing samples whereas CeO2-y: Eu3+ displays only two. The room temperature, time-resolved emission spectra recorded at λexcitation = 464 nm show that Gd3+ doping results in significantly altered emission spectra compared to pure ceria. The PARAFAC analysis for the pure ceria samples reveals two species; a high-symmetry species and a low-symmetry species. The GDC samples yield two low-symmetry spectra in the same experiment. High-resolution emission spectra recorded at 4 K after probing the 5D0-7F0 transition revealed additional variation in the low symmetry Eu3+ sites in pure ceria and GDC. The data of the Gd3+-containing samples indicates that the average charge density around the Eu3+ ions in the lattice is inversely related to Gd3+ and oxygen vacancy concentration.
The particle crystallites of the 773 K and 1273 K annealed Yb3+ -ceria nanostructure materials are nano-sized and have a cubic fluorite structure with four Raman vibrational modes. Elemental maps clearly show that cluster formation occurs for 773 K annealed with high Yb3+ ion concentration from 15 mol % in the ceria lattice. These clusters are destroyed with annealing to 1273 K. The emission spectra observed from room temperature and 4 K measurements for the Ce1-xYb xO2-y samples have a manifold that corresponds to the 2F5/2-2F7/2 transition of Yb3+ ions. Some small shifts are observed in the Stark splitting pattern and are induced by the variations of the crystal field influenced by where the Yb3+ ions are located in the crystal lattices in the samples. Upon mixing ceria with high Yb3+ concentrations, the 2F5/2-2F7/2 transition is also observed in the Stark splitting pattern, but the spectra consist of two broad high background dominated peaks. Annealing the nanomaterials at 1273 K for 2 h changes the spectral signature as new peaks emerge. The deconvolution yielded luminescence decay kinetics as well as the accompanying luminescence spectra of three species for each of the low Yb3+ doped ceria samples annealed at 773 K and one species for the 1273 K annealed samples. However, the ceria samples with high Yb3+ concentration annealed at the two temperatures yielded one species with lower decay times as compared to the Yb3+ doped ceria samples after PARAFAC analysis.
Through the calcination of the nanocomposites at two high temperatures, the evolution of the emission patterns from specific Eu3+ lattice sites to indicate structural changes for the nanocomposites was followed. The spectroscopy results effectively complemented the data obtained from the conventional techniques. Annealing the samples at 773 K, resulted in amorphous, unordered domains whereas the TLS of the 1273 K nanocomposites reveal two distinct sites, with most red shifted Eu3+ species coming from pure Eu3+ doped ZrO2 on the YSZ support.
Finally, for Eu3+ doped ceria, successful transfer from hydrophobic to water phase and subsequent biocompatibility was achieved using ssDNA. PARAFAC analysis for the Eu3+ in nanoparticles dispersed in toluene and water revealed one Eu3+ species, with slightly differing surface properties for the nanoparticles as far as the luminescence kinetics and solvent environments were concerned. Several functionalized nanoparticles conjugated onto origami triangles after hybridization were visualized by atomic force microscopy (AFM). Putting all into consideration, Eu3+ and Yb3+ spectroscopy was used to monitor the structural changes and determining the feasibility of the nanoparticle transfer into water. PARAFAC proves to be a powerful tool to analyze lanthanide spectra in crystalline solid materials and in solutions, which are characterized by numerous Stark transitions and where measurements usually yield a superposition of different emission contributions to any given spectrum.
Nanoparticles (NPs) are particles between 1 and 100 nanometers in size. They have attracted enormous research interests owing to their remarkable physicochemical properties and potential applications in the optics, catalysis, sensing, electronics, or optical devices. The thesis investigates systems of NPs attached to planar substrates.
In the first part of the results section of the thesis a new method is presented to immobilize NPs. In many NP applications a strong, persistent adhesion to substrates is a key requirement. Up to now this has been achieved with various methods, which are not always the optimum regarding adhesion strength or applicability. We propose a new method which uses capillarity to enhance the binding agents in the contact area between NP and substrate. The adhesion strength resulting from the new approach is investigated in detail and it is shown that the new approach is superior to older methods in several ways.
The following section presents the optical visualization of nano-sized objects through a combination of thin film surface distortion and interference enhanced optical reflection microscopy. It is a new, fast and non-destructive technique. It not only reveals the location of NPs as small as 20nm attached to planar surfaces and embedded in a molecularly thin liquid film. It also allows the measurement of the geometry of the surface distortion of the liquid film. Even for small NPs the meniscus reaches out for micrometers, which is the reason why the NPs produce such a pronounced optical footprint.
The nucleation and growth of individual bubbles is presented in chapter 5. Nucleation is a ubiquitous natural phenomenon and of great importance in numerous industrial processes. Typically it occurs on very small scales (nanometers) and it is of a random nature (thermodynamics of small systems). Up to now most experimental nucleation studies deal with a large number of individual nucleation processes to cope with its inherently statistical, spatio-temporal character. In contrast, in this thesis the individual O2-bubble formation from single localized platinum NP active site is studied experimentally. The bubble formation is initiated by the catalytic reaction of H2O2 on the Pt surface. It is studied how the bubble nucleation and growth depends on the NP size, the H2O2 concentration and the substrate surface properties. It is observed that in some cases the bubbles move laterally over the substrate surface, driven by the O2-production and the film ablation.
This project was focused on exploring the phase behavior of poly(styrene)187000-block-poly(2-vinylpyridine)203000 (SV390) with high molecular weight (390 kg/mol) in thin films, in which the self-assembly of block copolymers (BCPs) was realized via thermo-solvent annealing. The advanced processing technique of solvent vapor treatment provides controlled and stable conditions.
In Chapter 3, the factors to influence the annealing process and the swelling behavior of homopolymers are presented and discussed. The swelling behavior of BCP in films is controlled by the temperature of the vapor and of the substrate, on one hand, and variation of the saturation of the solvent vapor atmosphere (different solvents), on the other hand. Additional factors like the geometry and material of the chamber, the type of flow inside the chamber etc. also influence the reproducibility and stability of the processing. The slightly selective solvent vapor of chloroform gives 10% more swelling of P2VP than PS in films with thickness of ~40 nm.
The tunable morphology in ultrathin films of high molecular weight BCP (SV390) was investigated in Chapter 4. First, the swelling behavior can be precisely tuned by temperature and/or vapor flow separately, which provided information for exploring the multiple-parameter-influenced segmental chain mobility of polymer films. The equilibrium state of SV390 in thin films influenced by temperature was realized at various temperatures with the same degree of swelling. Various methods including characterization with SFM, metallization and RIE were used to identify the morphology of films as porous half-layer with PS dots and P2VP matrix. The kinetic investigations demonstrate that on substrates with either weak or strong interaction the original morphology of the BCP with high molecular weight is changed very fast within 5 min, and the further annealing serves for annihilation of defects.
The morphological development of symmetric BCP in films with thickness increasing from half-layer to one-layer influenced by confinement factors of gradient film thicknesses and various surface properties of substrates was studied in Chapter 5. SV390 and SV99 films show bulk lamella-forming morphology after slightly selective solvent vapor (chloroform) treatment. SV99 films show cylinder-forming morphology under strongly selective solvent vapor (toluene) treatment since the asymmetric structure (caused by toluene uptake in PS blocks only) of SV99 block copolymer during annealing. Both kinds of morphology (lamella and cylinder) are influenced by the film thickness. The annealed morphology of SV390 and SV99 influenced by the combination of confined film and substrate property is similar to the morphology on flat silicon wafers. In this chapter the gradients in the film thickness and surface properties of the substrates with regard to their influence on the morphological development in thin BCP films are presented. Directed self-assembly (graphoepitaxy) of this SV390 was also investigated to compare with systematically reported SV99.
In Chapter 6 an approach to induced oriented microphase separation in thick block copolymer films via treatment with the oriented vapor flow using mini-extruder is envisaged to be an alternative to existing methodologies, e.g. via non-solvent-induced phase separation. The preliminary tests performed in this study confirm potential perspective of this method, which alters the structure through the bulk of the film (as revealed by SAXS measurements), but more detailed studies have to be conducted in order to optimize the preparation.
Nanophotonics is the field of science and engineering aimed at studying the light-matter interactions on the nanoscale. One of the key aspects in studying such optics at the nanoscale is the ability to assemble the material components in a spatially controlled manner. In this work, DNA origami nanostructures were used to self-assemble dye molecules and DNA coated plasmonic nanoparticles. Optical properties of dye nanoarrays, where the dyes were arranged at distances where they can interact by Förster resonance energy transfer (FRET), were systematically studied according to the size and arrangement of the dyes using fluorescein (FAM) as the donor and cyanine 3 (Cy 3) as the acceptor. The optimized design, based on steady-state and time-resolved fluorometry, was utilized in developing a ratiometric pH sensor with pH-inert coumarin 343 (C343) as the donor and pH-sensitive FAM as the acceptor. This design was further applied in developing a ratiometric toxin sensor, where the donor C343 is unresponsive and FAM is responsive to thioacetamide (TAA) which is a well-known hepatotoxin. The results indicate that the sensitivity of the ratiometric sensor can be improved by simply arranging the dyes into a well-defined array. The ability to assemble multiple fluorophores without dye-dye aggregation also provides a strategy to amplify the signal measured from a fluorescent reporter, and was utilized here to develop a reporter for sensing oligonucleotides. By incorporating target capturing sequences and multiple fluorophores (ATTO 647N dye molecules), a reporter for microbead-based assay for non-amplified target oligonucleotide sensing was developed. Analysis of the assay using VideoScan, a fluorescence microscope-based technology capable of conducting multiplex analysis, showed the DNA origami nanostructure based reporter to have a lower limit of detection than a single stranded DNA reporter. Lastly, plasmonic nanostructures were assembled on DNA origami nanostructures as substrates to study interesting optical behaviors of molecules in the near-field. Specifically, DNA coated gold nanoparticles, silver nanoparticles, and gold nanorods, were placed on the DNA origami nanostructure aiming to study surface-enhanced fluorescence (SEF) and surface-enhanced Raman scattering (SERS) of molecules placed in the hotspot of coupled plasmonic structures.
The supercapacitor is one of the most important energy storage devices as its construction allows for addressing many of the drawbacks related to batteries, but the low energy density of current systems is a major issue. In this doctoral dissertation, with a view to attaining high energy density supercapacitor systems that can be comparable to those for batteries, new heteroatom-containing carbons in the form of particles and three-dimensional films were investigated. A nitrogen-containing material, acrodam, was chosen as the carbon precursor due to the inexpensiveness, high carbonization yield, oligomerizability, etc. The carbon particles were prepared from acrodam together with caesium acetate as a meltable flux agent, and disclosed excellent properties in hydroquinone-loaded sulphuric acid electrolyte with high energy densities (up to 133.0 Wh kg–1) and sufficient cycle stabilities. These properties are already now comparable to those of batteries. Besides, conductive carbon three-dimensional films were fabricated using acrodam oligomer as the precursor by the inexpensive spin coating method. The films were found to be homogeneous, flat, void- and crack-free, and high conductivities (up to 334 S cm–1) could be obtained at the carbonization temperature of 1000 ºC. Furthermore, a porous carbon three-dimensional film could be formed using an organic template at the first attempt. This finding demonstrates the film’s potentiality for various applications such as supercapacitor electrode; the essential absence of contact resistance within the network should contribute to effective transportation of electron within the electrode. The progress made in this dissertation will open a new way to further enhancement of energy density for supercapacitor as well as other applications that exceeds the current properties.
In this thesis, a route to temperature-, pH-, solvent-, 1,2-diol-, and protein-responsive sensors made of biocompatible and low-fouling materials is established. These sensor devices are based on the sensitivemodulation of the visual band gap of a photonic crystal (PhC), which is induced by the selective binding of analytes, triggering a volume phase transition.
The PhCs introduced by this work show a high sensitivity not only for small biomolecules, but also for large analytes, such as glycopolymers or proteins. This enables the PhC to act as a sensor that detects analytes without the need of complex equipment.
Due to their periodical dielectric structure, PhCs prevent the propagation of specific wavelengths. A change of the periodicity parameters is thus indicated by a change in the reflected wavelengths. In the case explored, the PhC sensors are implemented as periodically structured responsive hydrogels in formof an inverse opal.
The stimuli-sensitive inverse opal hydrogels (IOHs) were prepared using a sacrificial opal template of monodispersed silica particles. First, monodisperse silica particles were assembled with a hexagonally packed structure via vertical deposition onto glass slides. The obtained silica crystals, also named colloidal crystals (CCs), exhibit structural color. Subsequently, the CCs templates were embedded in polymer matrix with low-fouling properties. The polymer matrices were composed of oligo(ethylene glycol) methacrylate derivatives (OEGMAs) that render the hydrogels thermoresponsive. Finally, the silica particles were etched, to produce highly porous hydrogel replicas of the CC. Importantly, the inner structure and thus the ability for light diffraction of the IOHs formed was maintained.
The IOH membrane was shown to have interconnected pores with a diameter as well as interconnections between the pores of several hundred nanometers. This enables not only the detection of small analytes, but also, the detection of even large analytes that can diffuse into the nanostructured IOH membrane. Various recognition unit – analyte model systems, such as benzoboroxole – 1,2-diols, biotin – avidin and mannose – concanavalin A, were studied by incorporating functional
comonomers of benzoboroxole, biotin and mannose into the copolymers. The incorporated recognition units specifically bind to certain low and highmolar mass biomolecules, namely to certain saccharides, catechols, glycopolymers or proteins.
Their specific binding strongly changes the overall hydrophilicity, thus modulating the swelling of the IOH matrices, and in consequence, drastically changes their internal periodicity. This swelling is amplified by the thermoresponsive properties of the polymer matrix. The shift of the interference band gap due to the specific molecular recognition is easily visible by the naked eye (up to 150 nm shifts). Moreover, preliminary trial were attempted to detect even larger entities. Therefore anti-bodies were immobilized on hydrogel platforms via polymer-analogous esterification. These platforms incorporate comonomers made of tri(ethylene glycol) methacrylate end-functionalized with a carboxylic acid. In these model systems, the bacteria analytes are too big to penetrate into the IOH membranes, but can only interact with their surfaces. The selected model bacteria, as Escherichia coli, show a specific affinity to anti-body-functionalized hydrogels. Surprisingly in the case functionalized IOHs, this study produced weak color shifts, possibly opening a path to detect directly living organism, which will need further investigations.
Carbon nitride and poly(ionic liquid)s (PILs) have been successfully applied in various fields of materials science owing to their outstanding properties. This thesis aims at the successful application of these polymers as innovative materials in the interfaces of hybrid organic–inorganic perovskite solar cells. A critical problem in harnessing the full thermodynamic potential of halide perovskites in solar cells is the design and modification of interfaces to reduce carrier recombination. Therefore, the interface must be properly studied and improved. This work investigated the effect of applying carbon nitride and PILs on a perovskite surface on the device performance. The facile synthetic method for modifying carbon nitride with vinyl thiazole and barbituric acid (CMB-vTA) yields 2.3 nm layers when solution processing is performed using isopropanol. The nanosheets were applied as a metal-free electron transport layer in inverted perovskite solar cells. The application of carbon nitride layers (CMB-vTA) resulted in negligible current-voltage hysteresis with a high open circuit voltage (Voc) of 1.1 V and a short-circuit current (Jsc) of 20.28 mA cm-2, which afforded efficiencies of up to 17%. Thus, the successful implementation of a carbon nitride-based structure enabled good charge extraction with minimized interface recombination between the perovskite and PCBM. Similarly, PILs represent a new strategy of interfacial modification using an ionic polymer in an n-i-p perovskite architecture.. The application of PILs as an interfacial modifier resulted in solar cell devices with an extraordinarily high efficiency of 21.8% and a Voc of 1.17 V. The implementation reduced non-radiative recombination at the perovskite surface through defect passivation. Finally, our work proposes a novel method to efficiently suppress non-radiative charge recombination using the unexplored properties of carbon nitride and PILs in the solar cell field. Additionally, the method for interfacial modification has general applicability because of the simplicity of the post-treatment approach, and therefore has potential applicability in other solar cells. Thus, this work opens the door to a new class of materials to be implemented.
Synthesis of artificial building blocks for sortase-mediated ligation and their enzymatic linkage
(2018)
The enzyme Sortase A catalyzes the formation of a peptide bond between the recognition sequence LPXTG and an oligoglycine. While manifold ligations between proteins and various biomolecules, proteins and small synthetic molecules as well as proteins and surfaces have been reported, the aim of this thesis was to investigate the sortase-catalyzed linkage between artificial building blocks. Hence, this could pave the way for the use of sortase A for tasks from a chemical point of view and maybe even materials science.
For the proof of concept, the studied systems were kept as simple as possible at first by choosing easily accessible silica NPs and commercially available polymers. These building blocks were functionalized with peptide motifs for sortase-mediated ligation. Silica nanoparticles were synthesized with diameters of 60 and 200 nm and surface modified with C=C functionalities. Then, peptides bearing a terminal cysteine were covalently linked by means of a thiol-ene reaction. 60 nm SiO2 NPs were functionalized with pentaglycines, while peptides with LPETG motif were linked to 200 nm silica particles. Polyethyleneglycol (PEG) and poly(N isopropylacrylamide) (PNIPAM) were likewise functionalized with peptides by thiol-ene reaction between cysteine residues and C=C units in the polymer end groups. Hence, G5-PEG and PNIPAM-LPETG conjugates were obtained. With this set of building blocks, NP–polymer hybrids, NP–NP, and polymer–polymer structures were generated by sortase-mediated ligation and the product formation shown by transmission electron microscopy, MALDI-ToF mass spectrometry and dynamic light scatting, among others. Thus, the linkage of these artificial building blocks by the enzyme sortase A could be demonstrated.
However, when using commercially available polymers, the purification of the polymer–peptide conjugates was impossible and resulted in a mixture containing unmodified polymer. Therefore, strategies were developed for the own synthesis of pure peptide-polymer and polymer-peptide conjugates as building blocks for sortase-mediated ligation. The designed routes are based on preparing polymer blocks via RAFT polymerization from CTAs that are attached to N- or C-terminus, respectively, of a peptide. GG-PNIPAM was synthesized through attachment of a suitable RAFT CTA to Fmoc-GG in an esterification reaction, followed by polymerization of NIPAM and cleavage of the Fmoc protection group. Furthermore, several peptides were synthesized by solid-phase peptide synthesis. The linkage of a RAFT CTA (or
polymerization initiator) to the N-terminus of a peptide can be conducted in an automated fashion as last step in a peptide synthesizer. The synthesis of such a conjugate couldn’t be realized in the time frame of this thesis, but many promising strategies exist to continue this strategy using different coupling reagents. Such polymer building blocks can be used to synthesize protein-polymer conjugates catalyzed by sortase A and the approach can be carried on to the synthesis of block copolymers by using polymer blocks with peptide motifs on both ends.
Although the proof of concept demonstrated in this thesis only shows examples that can be also synthesized by exclusively chemical techniques, a toolbox of such building blocks will enable the future formation of new materials and pave the way for the application of enzymes in materials science. In addition to nanoparticle systems and block copolymers, this also includes combination with protein-based building blocks to form hybrid materials. Hence, sortase could become an enzymatic tool that complements established chemical linking technologies and provides specific peptide motifs that are orthogonal to all existing chemical functional groups.
Cellulose derived polymers
(2019)
Plastics, such as polyethylene, polypropylene, and polyethylene terephthalate are part of our everyday lives in the form of packaging, household goods, electrical insulation, etc. These polymers are non-degradable and create many environmental problems and public health concerns. Additionally, these polymers are produced from finite fossils resources. With the continuous utilization of these limited resources, it is important to look towards renewable sources along with biodegradation of the produced polymers, ideally. Although many bio-based polymers are known, such as polylactic acid, polybutylene succinate adipate or polybutylene succinate, none have yet shown the promise of replacing conventional polymers like polyethylene, polypropylene and polyethylene terephthalate. Cellulose is one of the most abundant renewable resources produced in nature. It can be transformed into various small molecules, such as sugars, furans, and levoglucosenone. The aim of this research is to use the cellulose derived molecules for the synthesis of polymers.
Acid-treated cellulose was subjected to thermal pyrolysis to obtain levoglucosenone, which was reduced to levoglucosenol. Levoglucosenol was polymerized, for the first time, by ring-opening metathesis polymerization (ROMP) yielding high molar mass polymers of up to ~150 kg/mol. The poly(levoglucosenol) is thermally stable up to ~220 ℃, amorphous, and is exhibiting a relatively high glass transition temperature of ~100 ℃. The poly(levoglucosenol) can be converted to a transparent film, resembling common plastic, and was found to degrade in a moist acidic environment. This means that poly(levoglucosenol) may find its use as an alternative to conventional plastic, for instance, polystyrene.
Levoglucosenol was also converted into levoglucosenyl methyl ether, which was polymerized by cationic ring-opening metathesis polymerization (CROP). Polymers were obtained with molar masses up to ~36 kg/mol. These polymers are thermally stable up to ~220 ℃ and are semi-crystalline thermoplastics, having a glass transition temperature of ~35 ℃ and melting transition of 70-100 ℃. Additionally, the polymers underwent cross-linking, hydrogenation and thiol-ene click chemistry.
Nanostructured materials are the materials having structural features on the scale of nanometers i.e. 10-9 m. the structural features can enhance the natural properties of the materials or induce additional properties, which are useful for day to technology as well as the future technologies One way to synthesize nanostructured materials is using templating techniques. The templating process involves use of a certain “mould” or “scaffold” to generate the structure. The mould is called as the template, can be a single molecule or assembly of molecule or a larger object, which has its own structure. The product material can be obtained by filling the space around the template with a “precursor”, transformation of precursor into the desired material and then removal of template to get product. The precursor can be any chemical moiety that can be easily transformed in to the desired material. Alternatively the desired material is processed into very tiny bricks or “nano building blocks (NBB)” and the product is obtained by arrangement of the NBB by using a scaffold. We synthesized porous metal oxide spheres of namely TiO2-M2O3: titanium dioxide- M-oxide (M = aluminum, gallium and indium) TiO2-M2O3 and cerium oxide-zirconium oxide solid solution. We used porous polymeric beads as templates. These beads used for chromatographic purposes. For the synthesis of TiO2-M2O3 we used metal- alkoxides as precursor. The pore of beads were filled with precursor and then reacted with water to give transformation of the precursor to amorphous oxide network. The network is crystallized and template is removed by heat treatment at high temperatures. In a similar way we obtained porous spheres of CexZr1-xO2. For this we synthesized nanoparticle of CexZr1-xO2 and used then for the templating process to obtain porous CexZr1-xO2 spheres. Additionally, using the same nanoparticles we synthesized nano-porous powder using self-assembly process between a block-copolymers scaffold and nanoparticles. Morphological and physico-chemical properties of these materials were studies systematically by using various analytical techniques TiO2-M2O3 material were tested for photocatalytic degradation of 2-Chlorophenol a poisonous pollutant. While CexZr1-xO2 spheres were tested for methanol steam reforming reaction to generate hydrogen, which is a fuel for future generation power sources like fuel cells. All the materials showed good catalytic performance.
In this work, a sensor system based on thermoresponsive materials is developed by utilizing a modular approach. By synthesizing three different key monomers containing either a carboxyl, alkene or alkyne end group connected with a spacer to the methacrylic polymerizable unit, a flexible copolymerization strategy has been set up with oligo ethylene glycol methacrylates. This allows to tune the lower critical solution temperature (LCST) of the polymers in aqueous media. The molar masses are variable thanks to the excurse taken in polymerization in ionic liquids thus stretching molar masses from 25 to over 1000 kDa. The systems that were shown shown to be effective in aqueous solution could be immobilized on surfaces by copolymerizing photo crosslinkable units. The immobilized systems were formulated to give different layer thicknesses, swelling ratios and mesh sizes depending on the demand of the coupling reaction.
The coupling of detector units or model molecules is approached via reactions of the click chemistry pool, and the reactions are evaluated on their efficiency under those aspects, too. These coupling reactions are followed by surface plasmon resonance spectroscopy (SPR) to judge efficiency. With these tools at hand, Salmonella saccharides could be selectively detected by SPR. Influenza viruses were detected in solution by turbidimetry in solution as well as by a copolymerized solvatochromic dye to track binding via the changes of the polymers’ fluorescence by said binding event. This effect could also be achieved by utilizing the thermoresponsive behavior. Another demonstrator consists of the detection system bound to a quartz surface, thus allowing the virus detection on a solid carrier.
The experiments show the great potential of combining the concepts of thermoresponsive materials and click chemistry to develop technically simple sensors for large biomolecules and viruses.
Complex emulsions are dispersions of kinetically stabilized multiphasic emulsion droplets comprised of two or more immiscible liquids that provide a novel material platform for the generation of active and dynamic soft materials. In recent years, the intrinsic reconfigurable morphological behavior of complex emulsions, which can be attributed to the unique force equilibrium between the interfacial tensions acting at the various interfaces, has become of fundamental and applied interest. As such, particularly biphasic Janus droplets have been investigated as structural templates for the generation of anisotropic precision objects, dynamic optical elements or as transducers and signal amplifiers in chemo- and bio-sensing applications. In the present thesis, switchable internal morphological responses of complex droplets triggered by stimuli-induced alterations of the balance of interfacial tensions have been explored as a universal building block for the design of multiresponsive, active, and adaptive liquid colloidal systems. A series of underlying principles and mechanisms that influence the equilibrium of interfacial tensions have been uncovered, which allowed the targeted design of emulsion bodies that can alter their shape, bind and roll on surfaces, or change their geometrical shape in response to chemical stimuli. Consequently, combinations of the unique triggerable behavior of Janus droplets with designer surfactants, such as a stimuli-responsive photosurfactant (AzoTAB) resulted for instance in shape-changing soft colloids that exhibited a jellyfish inspired buoyant motion behavior, holding great promise for the design of biological inspired active material architectures and transformable soft robotics.
In situ observations of spherical Janus emulsion droplets using a customized side-view microscopic imaging setup with accompanying pendant dropt measurements disclosed the sensitivity regime of the unique chemical-morphological coupling inside complex emulsions and enabled the recording of calibration curves for the extraction of critical parameters of surfactant effectiveness. The deduced new "responsive drop" method permitted a convenient and cost-efficient quantification and comparison of the critical micelle concentrations (CMCs) and effectiveness of various cationic, anionic, and nonionic surfactants. Moreover, the method allowed insightful characterization of stimuli-responsive surfactants and monitoring of the impact of inorganic salts on the CMC and surfactant effectiveness of ionic and nonionic surfactants. Droplet functionalization with synthetic crown ether surfactants yielded a synthetically minimal material platform capable of autonomous and reversible adaptation to its chemical environment through different supramolecular host-guest recognition events. Addition of metal or ammonium salts resulted in the uptake of the resulting hydrophobic complexes to the hydrocarbon hemisphere, whereas addition of hydrophilic ammonium compounds such as amino acids or polypeptides resulted in supramolecular assemblies at the hydrocarbon-water interface of the droplets. The multiresponsive material platform enabled interfacial complexation and
thus triggered responses of the droplets to a variety of chemical triggers including metal ions, ammonium compounds, amino acids, antibodies, carbohydrates as well as amino-functionalized solid surfaces.
In the final chapter, the first documented optical logic gates and combinatorial logic circuits based on complex emulsions are presented. More specifically, the unique reconfigurable and multiresponsive properties of complex emulsions were exploited to realize droplet-based logic gates of varying complexity using different stimuli-responsive surfactants in combination with diverse readout methods. In summary, different designs for multiresponsive, active, and adaptive liquid colloidal systems were presented and investigated, enabling the design of novel transformative chemo-intelligent soft material platforms.
This thesis deals with the synthesis of protein and composite protein-mineral microcapsules by the application of high-intensity ultrasound at the oil-water interface. While one system is stabilized by BSA molecules, the other system is stabilized by different nanoparticles modified with BSA. A comprehensive study of all synthesis stages as well as of resulting capsules were carried out and a plausible explanation of the capsule formation mechanism was proposed. During the formation of BSA microcapsules, the protein molecules adsorb firstly at the O/W interface and unfold there forming an interfacial network stabilized by hydrophobic interactions and hydrogen bonds between neighboring molecules. Simultaneously, the ultrasonic treatment causes the cross-linking of the BSA molecules via the formation of intermolecular disulfide bonds. In this thesis, the experimental evidences of ultrasonically induced cross-linking of the BSA in the shells of protein-based microcapsules are demonstrated. Therefore, the concept proposed many years ago by Suslick and co-workers is confirmed by experimental evidences for the first time. Moreover, a consistent mechanism for the formation of intermolecular disulfide bonds in capsule shells is proposed that is based on the redistribution of thiol and disulfide groups in BSA under the action of high-energy ultrasound. The formation of composite protein-mineral microcapsules loaded with three different oils and shells composed of nanoparticles was also successful. The nature of the loaded oil and the type of nanoparticles in the shell, had influence on size and shape of the microcapsules. The examination of the composite capsule revealed that the BSA molecules adsorbed on the nanoparticles surface in the capsule shell are not cross-linked by intermolecular disulfide bonds. Instead, a Pickering emulsion formation takes place. The surface modification of composite microcapsules through both pre-modification of main components and also the post-modification of the surface of ready composite microcapsules was successfully demonstrated. Additionally, the mechanical properties of protein and composite protein-mineral microcapsules were compared. The results showed that the protein microcapsules are more resistant to elastic deformation.
Molecular photoswitches are attracting much attention lately mostly because of their possible applications in nano technology, and their role in biology. One of the widely studied representatives of photochromic molecules is azobenzene (AB). With light, by a static electric field, or with tunneling electrons this specie can be "switched" from the flat and energetically more stable trans form, into the compact cis form. The back reaction can be induced optically or thermally. Quantum chemical calculations, mostly based on density functional theory, on the AB molecule, AB derivatives and related systems are presented. All the calculations were done for isolated species, however, with implications for latest experimental results aiming at the switching of surface mounted ABs. In some of these experiments, it is assumed that the switching process is substrate mediated, by attaching an electron or a hole to the adsorbate forming short-lived anion or cation resonances. Therefore, we calculated also cationic and anionic ABs in this work. An influence of external electric fields on the potential energy surfaces, was also studied. Further, by the type, number and positioning of various substituent groups, systematic changes on activation energies and rates for the thermal cis-to-trans isomerization can be enforced. The nature of the transition state for ground state isomerization was investigated. Applying Eyring's transition state theory, trends in activation energies and rates were predicted and are, where a comparison was possible, in good agreement with experimental data. Further, thermal isomerization was studied in solution, for which a polarizable continuum model was employed. The influence of substitution and an environment leaves its traces on structural properties of molecules and quantitative appearance of calculated UV/Vis spectra, as well. Finally, an explicit treatment of a solid substrate was demonstrated for the conformational switching, by scanning tunneling microscope, of a 1,5-cyclooctadiene (COD) molecule at a Si(001) surface, treated by a cluster model. At first, we studied energetics and potential energy surfaces along relevant switching coordinates by quantum chemical calculations, followed by the switching dynamics using wave packet methods. We show that, in spite the simplicity of the model, our calculations support the switching of adsorbed COD, by inelastic electron tunneling at low temperatures.
Nowadays, the need to protect the environment becomes more urgent than ever. In the field of chemistry, this translates to practices such as waste prevention, use of renewable feedstocks, and catalysis; concepts based on the principles of green chemistry. Polymers are an important product in the chemical industry and are also in the focus of these changes. In this thesis, more sustainable approaches to make two classes of polymers, polypeptoids and polyesters, are described.
Polypeptoids or poly(alkyl-N-glycines) are isomers of polypeptides and are biocompatible, as well as degradable under biologically relevant conditions. In addition to that, they can have interesting properties such as lower critical solution temperature (LCST) behavior. They are usually synthesized by the ring opening polymerization (ROP) of N-carboxy anhydrides (NCAs), which are produced with the use of toxic compounds (e.g. phosgene) and which are highly sensitive to humidity. In order to avoid the direct synthesis and isolation of the NCAs, N-phenoxycarbonyl-protected N-substituted glycines are prepared, which can yield the NCAs in situ. The conditions for the NCA synthesis and its direct polymerization are investigated and optimized for the simplest N-substituted glycine, sarcosine. The use of a tertiary amine in less than stoichiometric amounts compared to the N-phenoxycarbonyl--sarcosine seems to accelerate drastically the NCA formation and does not affect the efficiency of the polymerization. In fact, well defined polysarcosines that comply to the monomer to initiator ratio can be produced by this method. This approach was also applied to other N-substituted glycines.
Dihydroxyacetone is a sustainable diol produced from glycerol, and has already been used for the synthesis of polycarbonates. Here, it was used as a comonomer for the synthesis of polyesters. However, the polymerization of dihydroxyacetone presented difficulties, probably due to the insolubility of the macromolecular chains. To circumvent the problem, the dimethyl acetal protected dihydroxyacetone was polymerized with terephthaloyl chloride to yield a soluble polymer. When the carbonyl was recovered after deprotection, the product was insoluble in all solvents, showing that the carbonyl in the main chain hinders the dissolution of the polymers. The solubility issue can be avoided, when a 1:1 mixture of dihydroxyacetone/ ethylene glycol is used to yield a soluble copolyester.
Ionizing radiation is used in cancer radiation therapy to effectively damage the DNA of tumors leading to cell death and reduction of the tumor tissue. The main damage is due to generation of highly reactive secondary species such as low-energy electrons (LEE) with the most probable energy around 10 eV through ionization of water molecules in the cells. A simulation of the dose distribution in the patient is required to optimize the irradiation modality in cancer radiation therapy, which must be based on the fundamental physical processes of high-energy radiation with the tissue. In the present work the accurate quantification of DNA radiation damage in the form of absolute cross sections for LEE-induced DNA strand breaks (SBs) between 5 and 20 eV is done by using the DNA origami technique. This method is based on the analysis of well-defined DNA target sequences attached to DNA origami triangles with atomic force microscopy (AFM) on the single molecule level. The present work focuses on poly-adenine sequences (5'-d(A4), 5'-d(A8), 5'-d(A12), 5'-d(A16), and 5'- d(A20)) irradiated with 5.0, 7.0, 8.4, and 10 eV electrons. Independent of the DNA length, the strand break cross section shows a maximum around 7.0 eV electron energy for all investigated oligonucleotides confirming that strand breakage occurs through the initial formation of negative ion resonances. Additionally, DNA double strand breaks from a DNA hairpin 5'-d(CAC)4T(Bt-dT)T2(GTG)4 are examined for the first time and are compared with those of DNA single strands 5'-d(CAC)4 and 5'- d(GTG)4. The irradiation is made in the most likely energy range of 5 to 20 eV with an anionic resonance maximum around 10 eV independently of the DNA sequence. There is a clear difference between σSSB and σDSB of DNA single and double strands, where the strand break for ssDNA are always higher in all electron energies compared to dsDNA by the factor 3. A further part of this work deals with the characterization and analysis of new types of radiosensitizers used in chemoradiotherapy, which selectively increases the DNA damage upon radiation. Fluorinated DNA sequences with 2'-fluoro-2'-deoxycytidine (dFC) show an increased sensitivity at 7 and 10 eV compared to the unmodified DNA sequences by an enhancement factor between 2.1 and 2.5. In addition, light-induced oxidative damage of 5'-d(GTG)4 and 5'-d((CAC)4T(Bt-dT)T2(GTG)4) modified DNA origami triangles by singlet oxygen 1O2 generated from three photoexcited DNA groove binders [ANT994], [ANT1083] and [Cr(ddpd)2][BF4]3 illuminated in different experiments with UV-Vis light at 430, 435 and 530 nm wavelength is demonstrated. The singlet oxygen induced generation of DNA damage could be detected in both aqueous and dry environments for [ANT1083] and [Cr(ddpd)2][BF4]3.
Radical additions to glycals : synthesis and transformations of 2-functionalized carbohydrates
(2009)
The reliance on fossil fuels has resulted in an abnormal increase in the concentration of greenhouse gases, contributing to the global climate crisis. In response, a rapid transition to renewable energy sources has begun, particularly lithium-ion batteries, playing a crucial role in the green energy transformation. However, concerns regarding the availability and geopolitical implications of lithium have prompted the exploration of alternative rechargeable battery systems, such as sodium-ion batteries. Sodium is significantly abundant and more homogeneously distributed in the crust and seawater, making it easier and less expensive to extract than lithium. However, because of the mysterious nature of its components, sodium-ion batteries are not yet sufficiently advanced to take the place of lithium-ion batteries. Specifically, sodium exhibits a more metallic character and a larger ionic radius, resulting in a different ion storage mechanism utilized in lithium-ion batteries. Innovations in synthetic methods, post-treatments, and interface engineering clearly demonstrate the significance of developing high-performance carbonaceous anode materials for sodium-ion batteries. The objective of this dissertation is to present a systematic approach for fabricating efficient, high-performance, and sustainable carbonaceous anode materials for sodium-ion batteries. This will involve a comprehensive investigation of different chemical environments and post-modification techniques as well.
This dissertation focuses on three main objectives. Firstly, it explores the significance of post-synthetic methods in designing interfaces. A conformal carbon nitride coating is deposited through chemical vapor deposition on a carbon electrode as an artificial solid-electrolyte interface layer, resulting in improved electrochemical performance. The interaction between the carbon nitride artificial interface and the carbon electrode enhances initial Coulombic efficiency, rate performance, and total capacity. Secondly, a novel process for preparing sulfur-rich carbon as a high-performing anode material for sodium-ion batteries is presented. The method involves using an oligo-3,4-ethylenedioxythiophene precursor for high sulfur content hard carbon anode to investigate the sulfur heteroatom effect on the electrochemical sodium storage mechanism. By optimizing the condensation temperature, a significant transformation in the materials’ nanostructure is achieved, leading to improved electrochemical performance. The use of in-operando small-angle X-ray scattering provides valuable insights into the interaction between micropores and sodium ions during the electrochemical processes. Lastly, the development of high-capacity hard carbon, derived from 5-hydroxymethyl furfural, is examined. This carbon material exhibits exceptional performance at both low and high current densities. Extensive electrochemical and physicochemical characterizations shed light on the sodium storage mechanism concerning the chemical environment, establishing the material’s stability and potential applications in sodium-ion batteries.
Wood is used for many applications because of its excellent mechanical properties, relative abundance and as it is a renewable resource. However, its wider utilization as an engineering material is limited because it swells and shrinks upon moisture changes and is susceptible to degradation by microorganisms and/or insects. Chemical modifications of wood have been shown to improve dimensional stability, water repellence and/or durability, thus increasing potential service-life of wood materials. However current treatments are limited because it is difficult to introduce and fix such modifications deep inside the tissue and cell wall. Within the scope of this thesis, novel chemical modification methods of wood cell walls were developed to improve both dimensional stability and water repellence of wood material. These methods were partly inspired by the heartwood formation in living trees, a process, that for some species results in an insertion of hydrophobic chemical substances into the cell walls of already dead wood cells, In the first part of this thesis a chemistry to modify wood cell walls was used, which was inspired by the natural process of heartwood formation. Commercially available hydrophobic flavonoid molecules were effectively inserted in the cell walls of spruce, a softwood species with low natural durability, after a tosylation treatment to obtain “artificial heartwood”. Flavonoid inserted cell walls show a reduced moisture absorption, resulting in better dimensional stability, water repellency and increased hardness. This approach was quite different compared to established modifications which mainly address hydroxyl groups of cell wall polymers with hydrophilic substances. In the second part of the work in-situ styrene polymerization inside the tosylated cell walls was studied. It is known that there is a weak adhesion between hydrophobic polymers and hydrophilic cell wall components. The hydrophobic styrene monomers were inserted into the tosylated wood cell walls for further polymerization to form polystyrene in the cell walls, which increased the dimensional stability of the bulk wood material and reduced water uptake of the cell walls considerably when compared to controls. In the third part of the work, grafting of another hydrophobic and also biodegradable polymer, poly(ɛ-caprolactone) in the wood cell walls by ring opening polymerization of ɛ-caprolactone was studied at mild temperatures. Results indicated that polycaprolactone attached into the cell walls, caused permanent swelling of the cell walls up to 5%. Dimensional stability of the bulk wood material increased 40% and water absorption reduced more than 35%. A fully biodegradable and hydrophobized wood material was obtained with this method which reduces disposal problem of the modified wood materials and has improved properties to extend the material’s service-life. Starting from a bio-inspired approach which showed great promise as an alternative to standard cell wall modifications we showed the possibility of inserting hydrophobic molecules in the cell walls and supported this fact with in-situ styrene and ɛ-caprolactone polymerization into the cell walls. It was shown in this thesis that despite the extensive knowledge and long history of using wood as a material there is still room for novel chemical modifications which could have a high impact on improving wood properties.
The urge of light utilization in fabrication of materials is as encouraging as challenging. Steadily increasing energy consumption in accordance with rapid population growth, is requiring a corresponding solution within the same rate of occurrence speed. Therefore, creating, designing and manufacturing materials that can interact with light and in further be applicable as well as disposable in photo-based applications are very much under attention of researchers. In the era of sustainability for renewable energy systems, semiconductor-based photoactive materials have received great attention not only based on solar and/or hydrocarbon fuels generation from solar energy, but also successful stimulation of photocatalytic reactions such as water splitting, pollutant degradation and organic molecule synthesisThe turning point had been reached for water splitting with an electrochemical cell consisting of TiO2-Pt electrode illuminated by UV light as energy source rather than an external voltage, that successfully pursued water photolysis by Fujishima and Honda in 1972. Ever since, there has been a great deal of interest in research of semiconductors (e.g. metal oxide, metal-free organic, noble-metal complex) exhibiting effective band gap for photochemical reactions. In the case of environmental friendliness, toxicity of metal-based semiconductors brings some restrictions in possible applications. Regarding this, very robust and ‘earth-abundant’ organic semiconductor, graphitic carbon nitride has been synthesized and successfully applied in photoinduced applications as novel photocatalyst. Properties such as suitable band gap, low charge carrier recombination and feasibility for scaling up, pave the way of advance combination with other catalysts to gather higher photoactivity based on compatible heterojunction.
This dissertation aims to demonstrate a series of combinations between organic semiconductor g-CN and polymer materials that are forged through photochemistry, either in synthesis or in application. Fabrication and design processes as well as applications performed in accordance to the scope of thesis will be elucidated in detail. In addition to UV light, more attention is placed on visible light as energy source with a vision of more sustainability and better scalability in creation of novel materials and solar energy based applications.
The need to reduce humankind reliance on fossil fuels by exploiting sustainably the planet renewable resources is a major driving force determining the focus of modern material research. For this reason great interest is nowadays focused on finding alternatives to fossil fuels derived products/materials. For the short term the most promising substitute is undoubtedly biomass, since it is the only renewable and sustainable alternative to fossil fuels as carbon source. As a consequence efforts, aimed at finding new synthetic approaches to convert biomass and its derivatives into carbon-based materials, are constantly increasing. In this regard, hydrothermal carbonisation (HTC) has shown to be an effective means of conversion of biomass-derived precursors into functional carbon materials. However the attempts to convert raw biomass, in particular lignocellulosic one, directly into such products have certainly been rarer. Unlocking the direct use of these raw materials as carbon precursors would definitely be beneficial in terms of HTC sustainability. For this reason, in this thesis the HTC of carbohydrate and protein-rich biomass was systematically investigated, in order to obtain more insights on the potentials of this thermochemical processing technique in relation to the production of functional carbon materials from crude biomass. First a detailed investigation on the HTC conversion mechanism of lignocellulosic biomass and its single components (i.e. cellulose, lignin) was developed based on a comparison with glucose HTC, which was adopted as a reference model. In the glucose case it was demonstrated that varying the HTC temperature allowed tuning the chemical structure of the synthesised carbon materials from a highly cross-linked furan-based structure (T = 180oC) to a carbon framework composed of polyaromatic arene-like domains. When cellulose or lignocellulosic biomass was used as carbon precursor, the furan rich structure could not be isolated at any of the investigated processing conditions. These evidences were indicative of a different HTC conversion mechanism for cellulose, involving reactions that are commonly observed during pyrolytic processes. The evolution of glucose-derived HTC carbon chemical structure upon pyrolysis was also investigated. These studies revealed that upon heat treatment (Investigated temperatures 350 – 900 oC) the furan-based structure was progressively converted into highly curved aromatic pre-graphenic domains. This thermal degradation process was observed to produce an increasingly more hydrophobic surface and considerable microporosity within the HTC carbon structure. In order to introduce porosity in the HTC carbons derived from lignocellulosic biomass, KOH chemical activation was investigated as an HTC post-synthesis functionalisation step. These studies demonstrated that HTC carbons are excellent precursors for the production of highly microporous activated carbons (ACs) and that the porosity development upon KOH chemical activation is dependent on the chemical structure of the HTC carbon, tuned by employing different HTC temperatures. Preliminary testing of the ACs for CO2 capture or high pressure CH4 storage yielded very promising results, since the measured uptakes of both adsorbates (i.e. CO2 and CH4) were comparable to top-performing and commercially available adsorbents, usually employed for these end-applications. The combined use of HTC and KOH chemical activation was also employed to produce highly microporous N-doped ACs from microalgae. The hydrothermal treatment of the microalgae substrate was observed to cause the depletion of the protein and carbohydrate fractions and the near complete loss (i.e. 90%) of the microalgae N-content, as liquid hydrolysis/degradation products. The obtained carbonaceous product showed a predominantly aliphatic character indicating the presence of alkyl chains presumably derived from the lipid fractions. Addition of glucose to the initial reaction mixture was found out to be extremely beneficial, because it allowed the fixation of a higher N amount, in the algae derived HTC carbons (i.e. 60%), and the attainment of higher product yields (50%). Both positive effects were attributed to Maillard type cascade reactions taking place between the monosaccharides and the microalgae derived liquid hydrolysis/degradation products, which were in this way recovered from the liquid phase. KOH chemical activation of the microalgae/glucose mixture derived HTC carbons produced highly microporous N-doped carbons. Although the activation process led to a major reduction of the N-content, the retained N-amount in the ACs was still considerable. These features render these materials ideal candidates for supercapacitors electrodes, since they provide extremely high surface areas, for the formation of electric double-layer, coupled to abundant heteroatom doping (i.e. N and O) necessary to obtain a pseudocapacitance contribution.
The present thesis is to be brought into line with the current need for alternative and sustainable approaches toward energy management and materials design. In this context, carbon in particular has become the material of choice in many fields such as energy conversion and storage. Herein, three main topics are covered: 1)An alternative synthesis strategy toward highly porous functional carbons with tunable porosity using ordinary salts as porogen (denoted as “salt templating”) 2)The one-pot synthesis of porous metal nitride containing functional carbon composites 3)The combination of both approaches, enabling the generation of highly porous composites with finely tunable properties All approaches have in common that they are based on the utilization of ionic liquids, salts which are liquid below 100 °C, as precursors. Just recently, ionic liquids were shown to be versatile precursors for the generation of heteroatom-doped carbons since the liquid state and a negligible vapor pressure are highly advantageous properties. However, in most cases the products do not possess any porosity which is essential for many applications. In the first part, “salt templating”, the utilization of salts as diverse and sustainable porogens, is introduced. Exemplarily shown for ionic liquid derived nitrogen- and nitrogen-boron-co-doped carbons, the control of the porosity and morphology on the nanometer scale by salt templating is presented. The studies within this thesis were conducted with the ionic liquids 1-Butyl-3-methyl-pyridinium dicyanamide (Bmp-dca), 1-Ethyl-3-methyl-imidazolium dicyanamide (Emim-dca) and 1 Ethyl 3-methyl-imidazolium tetracyanoborate (Emim-tcb). The materials are generated through thermal treatment of precursor mixtures containing one of the ionic liquids and a porogen salt. By simple removal of the non-carbonizable template salt with water, functional graphitic carbons with pore sizes ranging from micro- to mesoporous and surface areas up to 2000 m2g-1 are obtained. The carbon morphologies, which presumably originate from different onsets of demixing, mainly depend on the nature of the porogen salt whereas the nature of the ionic liquid plays a minor role. Thus, a structural effect of the porogen salt rather than activation can be assumed. This offers an alternative to conventional activation and templating methods, enabling to avoid multiple-step and energy-consuming synthesis pathways as well as employment of hazardous chemicals for the template removal. The composition of the carbons can be altered via the heat-treatment procedure, thus at lower synthesis temperatures rather polymeric carbonaceous materials with a high degree of functional groups and high surface areas are accessible. First results suggest the suitability of the materials for CO2 utilization. In order to further illustrate the potential of ionic liquids as carbon precursors and to expand the class of carbons which can be obtained, the ionic liquid 1-Ethyl-3-methyl-imidazolium thiocyanate (Emim-scn) is introduced for the generation of nitrogen-sulfur-co-doped carbons in combination with the already studied ionic liquids Bmp-dca and Emim-dca. Here, the salt templating approach should also be applicable eventually further illustrating the potential of salt templating, too. In the second part, a one-pot and template-free synthesis approach toward inherently porous metal nitride nanoparticle containing nitrogen-doped carbon composites is presented. Since ionic liquids also offer outstanding solubility properties, the materials can be generated through the carbonization of homogeneous solutions of an ionic liquid acting as nitrogen as well as carbon source and the respective metal precursor. The metal content and surface area are easily tunable via the initial metal precursor amount. Furthermore, it is also possible to synthesize composites with ternary nitride nanoparticles whose composition is adjustable by the metal ratio in the precursor solution. Finally, both approaches are combined into salt templating of the one-pot composites. This opens the way to the one-step synthesis of composites with tunable composition, particle size as well as precisely controllable porosity and morphology. Thereby, common synthesis strategies where the product composition is often negatively affected by the template removal procedure can be avoided. The composites are further shown to be suitable as electrodes for supercapacitors. Here, different properties such as porosity, metal content and particle size are investigated and discussed with respect to their influence on the energy storage performance. Because a variety of ionic liquids, metal precursors and salts can be combined and a simple closed-loop process including salt recycling is imaginable, the approaches present a promising platform toward sustainable materials design.
In this work, the development of a new molecular building block, based on synthetic peptides derived from decorin, is presented. These peptides represent a promising basis for the design of polymer-based biomaterials that mimic the ECM on a molecular level and exploit specific biological recognition for technical applications. Multiple sequence alignments of the internal repeats of decorin that formed the inner and outer surface of the arch-shaped protein were used to develop consensus sequences. These sequences contained conserved sequence motifs that are likely to be related to structural and functional features of the protein. Peptides representative for the consensus sequences were synthesized by microwave-assisted solid phase peptide synthesis and purified by RP-HPLC, with purities higher than 95 mol%. After confirming the desired masses by MALDI-TOF-MS, the primary structure of each peptide was investigated by 1H and 2D NMR, from which a full assignment of the chemical shifts was obtained. The characterization of the peptides conformation in solution was performed by CD spectroscopy, which demonstrated that using TFE, the peptides from the outer surface of decorin show a high propensity to fold into helical structures as observed in the original protein. To the contrary, the peptides from the inner surface did not show propensity to form stable secondary structure. The investigation of the binding capability of the peptides to Collagen I was performed by surface plasmon resonance analyses, from which all but one of the peptides representing the inner surface of decorin showed binding affinity to collagen with values of dissociation constant between 2•10-7 M and 2.3•10-4 M. On the other hand, the peptides representative for the outer surface of decorin did not show any significant interaction to collagen. This information was then used to develop experimental demonstration for the binding capabilities of the peptides from the inner surface of decorin to collagen even when used in more complicated situations close to possible appications. With this purpose, the peptide (LRELHLNNN) which showed the highest binding affinity to collagen (2•10-7 M) was functionalized with an N-terminal triple bond in order to obtain a peptide dimer via copper(I)-catalyzed cycloaddition reaction with 4,4'-diazidostilbene-2,2'-disulfonic acid. Rheological measurements showed that the presence of the peptide dimer was able to enhance the elastic modulus (G') of a collagen gel from ~ 600 Pa (collagen alone) to ~ 2700 Pa (collagen and peptide dimer). Moreover, it was shown that the mechanical properties of a collagen gel can be tailored by using different molar ratios of peptide dimer respect to collagen. The same peptide, functionalized with the triple bond, was used to obtain a peptide-dye conjugate by coupling it with N-(5'-azidopentanoyl)-5-aminofluorescein. An aqueous solution (5 vol% methanol) of the peptide dye conjugate was injected into a collagen and a hyaluronic acid (HA) gel and images of fluorescence detection showed that the diffusion of the peptide was slower in the collagen gel compared to the HA gel. The third experimental demonstration was gained using the peptide (LSELRLHNN) which showed the lower binding affinity (2.3•10-4 M) to collagen. This peptide was grafted to hyaluronic acid via EDC-chemistry, with a degree of functionalization of 7 ± 2 mol% as calculated by 1H-NMR. The grafting was further confirmed by FTIR and TGA measurements, which showed that the onset of decomposition for the HA-g-peptide decreased by 10 °C compared to the native HA. Rheological measurements showed that the elastic modulus of a system based on collagen and HA-g-peptide increased by almost two order of magnitude (G' = 200 Pa) compared to a system based on collagen and HA (G' = 0.9 Pa). Overall, this study showed that the synthetic peptides, which were identified from decorin, can be applied as potential building blocks for biomimetic materials that function via biological recognition.
The needs for sustainable energy generation, but also a sustainable chemistry display the basic motivation of the current thesis. By different single investigated cases, which are all related to the element carbon, the work can be devided into two major topics. At first, the sustainable synthesis of “useful” carbon materials employing the process of hydrothermal carbonisation (HC) is described. In the second part, the synthesis of heteroatom - containing carbon materials for electrochemical and fuel cell applications employing ionic liquid precursors is presented. On base of a thorough review of the literature on hydrothermolysis and hydrothermal carbonisation of sugars in addition to the chemistry of hydroxymethylfurfural, mechanistic considerations of the formation of hydrothermal carbon are proposed. On the base of these reaction schemes, the mineral borax, is introduced as an additive for the hydrothermal carbonisation of glucose. It was found to be a highly active catalyst, resulting in decreased reaction times and increased carbon yields. The chemical impact of borax, in the following is exploited for the modification of the micro- and nanostructure of hydrothermal carbon. From the borax - mediated aggregation of those primary species, widely applicable, low density, pure hydrothermal carbon aerogels with high porosities and specific surface areas are produced. To conclude the first section of the thesis, a short series of experiments is carried out, for the purpose of demonstrating the applicability of the HC model to “real” biowaste i.e. watermelon waste as feedstock for the production of useful materials. In part two cyano - containing ionic liquids are employed as precursors for the synthesis of high - performance, heteroatom - containing carbon materials. By varying the ionic liquid precursor and the carbonisation conditions, it was possible to design highly active non - metal electrocatalyst for the reduction of oxygen. In the direct reduction of oxygen to water (like used in polymer electrolyte fuel cells), compared to commercial platinum catalysts, astonishing activities are observed. In another example the selective and very cost efficient electrochemical synthesis of hydrogen peroxide is presented. In a last example the synthesis of graphitic boron carbon nitrides from the ionic liquid 1 - Ethyl - 3 - methylimidazolium - tetracyanoborate is investigated in detail. Due to the employment of unreactive salts as a new tool to generate high surface area these materials were first time shown to be another class of non - precious metal oxygen reduction electrocatalyst.
Nanostructured inorganic materials are routinely synthesized by the use of templates. Depending on the synthesis conditions of the product material, either “soft” or “hard” templates can be applied. For sol-gel processes, usually “soft” templating techniques are employed, while “hard” templates are used for high temperature synthesis pathways. In classical templating approaches, the template has the unique role of structure directing agent, in the sense that it is not participating to the chemical formation of the resulting material. This work investigates a new templating pathway to nanostructured materials, where the template is also a reagent in the formation of the final material. This concept is described as “reactive templating” and opens a synthetic path toward materials which cannot be synthesised on a nanometre scale by classical templating approaches. Metal nitrides are such kind of materials. They are usually produced by the conversion of metals or metal oxides in ammonia flow at high temperature (T > 1000°C), which make the application of classical templating techniques difficult. Graphitic carbon nitride, g-C3N4, despite its fundamental and theoretical importance, is probably one of the most promising materials to complement carbon in material science and many efforts are put in the synthesis of this material. A simple polyaddition/elimination reaction path at high temperature (T = 550°C) allows the polymerisation of cyanamide toward graphitic carbon nitride solids. By hard templating, using nanostructured silica or aluminium oxide as nanotemplates, a variety of nanostructured graphitic carbon nitrides such as nanorods, nanotubes, meso- and macroporous powders could be obtained by nanocasting or nanocoating. Due to the special semi-conducting properties of the graphitic carbon nitride matrix, the nanostructured graphitic carbon nitrides show unexpected catalytic activity for the activation of benzene in Friedel-Crafts type reactions, making this material an interesting metal free catalyst. Furthermore, due to the chemical composition of g-C3N4 and the fact that it is totally decomposed at temperatures between 600°C and 800°C even under inert atmosphere, g-C3N4 was shown to be a good nitrogen donor for the synthesis of early transition metal nitrides at high temperatures. Thus using the nanostructured carbon nitrides as “reactive templates” or “nanoreactors”, various metal nitride nanostructures, such as nanoparticles and porous frameworks could be obtained at high temperature. In this approach the carbon nitride nanostructure played both the role of the nitrogen source and of the exotemplate, imprinting its size and shape to the resulting metal nitride nanostructure.
Molecules are often naturally embedded in a complex environment. As a consequence, characteristic properties of a molecular subsystem can be substantially altered or new properties emerge due to interactions between molecular and environmental degrees of freedom. The present thesis is concerned with the numerical study of quantum dynamical and stationary properties of molecular vibrational systems embedded in selected complex environments.
In the first part, we discuss "strong-coupling" model scenarios for molecular vibrations interacting with few quantized electromagnetic field modes of an optical Fabry-Pérot cavity. We thoroughly elaborate on properties of emerging "vibrational polariton" light-matter hybrid states and examine the relevance of the dipole self-energy. Further, we identify cavity-induced quantum effects and an emergent dynamical resonance in a cavity-altered thermal isomerization model, which lead to significant suppression of thermal reaction rates. Moreover, for a single rovibrating diatomic molecule in an optical cavity, we observe non-adiabatic signatures in dynamics due to "vibro-polaritonic conical intersections" and discuss spectroscopically accessible "rovibro-polaritonic" light-matter hybrid states.
In the second part, we study a weakly coupled but numerically challenging quantum mechanical adsorbate-surface model system comprising a few thousand surface modes. We introduce an efficient construction scheme for a "hierarchical effective mode" approach to reduce the number of surface modes in a controlled manner. In combination with the multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) method, we examine the vibrational adsorbate relaxation dynamics from different excited adsorbate states by solving the full non-Markovian system-bath dynamics for the characteristic relaxation time scale. We examine half-lifetime scaling laws from vibrational populations and identify prominent non-Markovian signatures as deviations from Markovian reduced system density matrix theory in vibrational coherences, system-bath entanglement and energy transfer dynamics.
In the final part of this thesis, we approach the dynamics and spectroscopy of vibronic model systems at finite temperature by formulating the ML-MCTDH method in the non-stochastic framework of thermofield dynamics. We apply our method to thermally-altered ultrafast internal conversion in the well-known vibronic coupling model of pyrazine. Numerically beneficial representations of multilayer wave functions ("ML-trees") are identified for different temperature regimes, which allow us to access thermal effects on both electronic and vibrational dynamics as well as spectroscopic properties for several pyrazine models.
As climate change worsens, there is a growing urgency to promote renewable energies and improve their accessibility to society. Here, solar energy harvesting is of particular importance. Currently, metal halide perovskite (MHP) solar cells are indispensable in future solar energy generation research. MHPs are crystalline semiconductors increasingly relevant as low-cost, high-performance materials for optoelectronics. Their processing from solution at low temperature enables easy fabrication of thin film elements, encompassing solar cells and light-emitting diodes or photodetectors. Understanding the coordination chemistry of MHPs in their precursor solution would allow control over the thin film crystallization, the material properties and the final device performance.
In this work, we elaborate on the key parameters to manipulate the precursor solution with the long-term objective of enabling systematic process control. We focus on the nanostructural characterization of the initial arrangements of MHPs in the precursor solutions. Small-angle scattering is particularly well suited for measuring nanoparticles in solution. This technique proved to be valuable for the direct analyzes of perovskite precursor solutions in standard processing concentrations without causing radiation damage. We gain insights into the chemical nature of widely used precursor structures such as methylammonium lead iodide (MAPbI3), presenting first insights into the complex arrangements and interaction within this precursor state. Furthermore, we transfer the preceding results to other more complex perovskite precursors. The influence of compositional engineering is investigated using the addition of alkali cations as an example. As a result, we propose a detailed working mechanism on how the alkali cations suppress the formation of intermediate phases and improve the quality of the crystalline thin film. In addition, we investigate the crystallization process of a tin-based perovskite composition (FASnI3) under the influence of fluoride chemistry. We prove that the frequently used additive, tin fluoride (SnF2), selectively binds undesired oxidized tin (Sn(IV)) in the precursor solution. This prevents its incorporation into the actual crystal structure and thus reduces the defect density of the material. Furthermore, SnF2 leads to a more homogeneous crystal growth process, which results in improved crystal quality of the thin film material.
In total, this study provides a detailed characterization of the complex system of perovskite precursor chemistry. We thereby cover relevant parameters for future MHP solar cell process control, such as (I) the environmental impact based on concentration and temperature (II) the addition of counter ions to reduce the diffuse layer surrounding the precursor nanostructures and (III) the targeted use of additives to eliminate unwanted components selectively and to ensure a more homogeneous crystal growth.
Design and development of novel three color-FRET systems in synthetic peptides and oligonucleotides
(2012)
Hybrid nanomaterials offer the combination of individual properties of different types of nanoparticles. Some strategies for the development of new nanostructures in larger scale rely on the self-assembly of nanoparticles as a bottom-up approach. The use of templates provides ordered assemblies in defined patterns. In a typical soft-template, nanoparticles and other surface-active agents are incorporated into non-miscible liquids. The resulting self-organized dispersions will mediate nanoparticle interactions to control the subsequent self-assembly. Especially interactions between nanoparticles of very different dispersibility and functionality can be directed at a liquid-liquid interface.
In this project, water-in-oil microemulsions were formulated from quasi-ternary mixtures with Aerosol-OT as surfactant. Oleyl-capped superparamagnetic iron oxide and/or silver nanoparticles were incorporated in the continuous organic phase, while polyethyleneimine-stabilized gold nanoparticles were confined in the dispersed water droplets. Each type of nanoparticle can modulate the surfactant film and the inter-droplet interactions in diverse ways, and their combination causes synergistic effects. Interfacial assemblies of nanoparticles resulted after phase-separation. On one hand, from a biphasic Winsor type II system at low surfactant concentration, drop-casting of the upper phase afforded thin films of ordered nanoparticles in filament-like networks. Detailed characterization proved that this templated assembly over a surface is based on the controlled clustering of nanoparticles and the elongation of the microemulsion droplets. This process offers versatility to use different nanoparticle compositions by keeping the surface functionalization, in different solvents and over different surfaces. On the other hand, a magnetic heterocoagulate was formed at higher surfactant concentration, whose phase-transfer from oleic acid to water was possible with another auxiliary surfactant in ethanol-water mixture. When the original components were initially mixed under heating, defined oil-in-water, magnetic-responsive nanostructures were obtained, consisting on water-dispersible nanoparticle domains embedded by a matrix-shell of oil-dispersible nanoparticles.
Herein, two different approaches were demonstrated to form diverse hybrid nanostructures from reverse microemulsions as self-organized dispersions of the same components. This shows that microemulsions are versatile soft-templates not only for the synthesis of nanoparticles, but also for their self-assembly, which suggest new approaches towards the production of new sophisticated nanomaterials in larger scale.
In recent years, the aim of supramolecular syntheses is not only the creation of particular structures but also the introduction of specific functions in these supramolecules. The present work describes the use of the ionic self-assembly (ISA) route to generate nanostructured materials with integrated functionality. Since the ISA strategy has proved to be a facile method for the production of liquid-crystalline materials, we investigated the phase behaviour, physical properties and function of a variety of ISA materials comprising a perylene derivative as the employed oligoelectrolyte. Functionality was introduced into the materials through the use of functional surfactants. In order to meet the requirements to produce functional ISA materials through the use of functional surfactants, we designed and synthesized pyrrole-derived monomers as surfactant building blocks. Owing to the presence of the pyrrole moiety, these surfactants are not only polymerizable but are also potentially conductive when polymerized. We adopted single-tailed and double-tailed N-substituted pyrrole monomers as target molecules. Since routine characterization analysis of the double-tailed pyrrole-containing surfactant indicated very interesting, complex phase behaviour, a comprehensive investigation of its interfacial properties and mesophase behavior was conducted. The synthesized pyrrole-derived surfactants were then employed in the synthesis of ISA complexes. The self-assembled materials were characterized and subsequently polymerized by both chemical and electrochemical methods. The changes in the structure and properties of the materials caused by the in-situ polymerization were addressed. In the second part of this work, the motif investigated was a property rather than a function. Since chiral superstructures have obtained much attention during the last few years, we investigated the possibility of chiral ISA materials through the use of chiral surfactants. Thus, the work involved synthesis of novel chiral surfactants and their incorporation in ISA materials with the aim of obtaining ionically self-assembled chiral superstructures. The results and insights presented here suggest that the presented synthesis strategy can be easily extended to incorporate any kind of charged tectonic unit with desired optical, electrical, or magnetic properties into supramolecular assemblies for practical applications.
Phototropic microalgae have a large potential for producing valuable substances for the feed, food, cosmetics, pigment, bioremediation, and pharmacy industries as well as for biotechnological processes. Today it is estimated that the microalgal aquaculture worldwide production is 5000 tons of dry matter per year (not taking into account processed products) making it an approximately $1.25 billion U.S. per year industry. In this work, several spectroscopic techniques were utilized for the investigation of microalgae cells. Specifically, photondensity wave spectroscopy was applied as a technique for the on-line observation of the culture. For effective evaluation of the photosynthetic growth processes, fast and non-invasive sensor systems that analyze the relevant biological and technical process parameters are preferred. Traditionally, the biomass in a photobioreactor is quantified with the help of turbidimetry measurements, which require extensive calibration. Another problem frequently encountered when using spectral analysis for investigating solutions is that samples of interest are often undiluted and highly scattering and do not adhere to Beer-Lambert's law. Due to the fluorescence properties of chlorophyll, fluorescence spectroscopy techniques including fluorescence lifetime imaging and single photon counting could be applied to provide images of the cells as well as determine the effects of excitation intensity on the fluorescence lifetime, which is an indicator of the condition of the cell. A photon density wave is a sinusoidally intensity-modulated optical wave stemming from a point-source of light, which propagates through diffuse medium and exhibits amplitude and phase variations. Light propagation though strongly scattering media can be described by the P1 approximation to the Boltzmann transport equation. Photon density wave spectroscopy enables the ability to differentiate between scattered and absorbed light, which is desired so that an independent determination of the reduced scattering and absorption coefficients can be made. The absorption coefficient is related to the pigment content in the cells, and the reduced scattering coefficient can be used to characterize physical and morphological properties of the medium and was here applied for the determination of the average cell size.
Solar photocatalysis is the one of leading concepts of research in the current paradigm of sustainable chemical industry. For actual practical implementation of sunlight-driven catalytic processes in organic synthesis, a cheap, efficient, versatile and robust heterogeneous catalyst is necessary. Carbon nitrides are a class of organic semiconductors who are known to fulfill these requirements.
First, current state of solar photocatalysis in economy, industry and lab research is overviewed, outlining EU project funding, prospective synthetic and reforming bulk processes, small scale solar organic chemistry, and existing reactor designs and prototypes, concluding feasibility of the approach.
Then, the photocatalytic aerobic cleavage of oximes to corresponding aldehydes and ketones by anionic poly(heptazine imide) carbon nitride is discussed. The reaction provides a feasible method of deprotection and formation of carbonyl compounds from nitrosation products and serves as a convenient model to study chromoselectivity and photophysics of energy transfer in heterogeneous photocatalysis.
Afterwards, the ability of mesoporous graphitic carbon nitride to conduct proton-coupled electron transfer was utilized for the direct oxygenation of 1,3-oxazolidin-2-ones to corresponding 1,3-oxazlidine-2,4-diones. This reaction provides an easier access to a key scaffold of diverse types of drugs and agrochemicals.
Finally, a series of novel carbon nitrides based on poly(triazine imide) and poly(heptazine imide) structure was synthesized from cyanamide and potassium rhodizonate. These catalysts demonstrated a good performance in a set of photocatalytic benchmark reactions, including aerobic oxidation, dual nickel photoredox catalysis, hydrogen peroxide evolution and chromoselective transformation of organosulfur precursors.
Concluding, the scope of carbon nitride utilization for net-oxidative and net-neutral photocatalytic processes was expanded, and a new tunable platform for catalyst synthesis was discovered.
The Reversible Addition Fragmentation Chain Transfer (RAFT) process using the new RAFT agent benzyldithiophenyl acetate is shown to be a powerful polymerization tool to synthesize novel well-defined amphiphilic diblock copolymers composed of the constant hydrophobic block poly(butyl acrylate) and of 6 different hydrophilic blocks with various polarities, namely a series of non-ionic, non-ionic comb-like, anionic and cationic hydrophilic blocks. The controlled character of the polymerizations was supported by the linear increase of the molar masses with conversion, monomodal molar mass distributions with low polydispersities and high degrees of end-group functionalization. The new macro-surfactants form micelles in water, whose size and geometry strongly depend on their composition, according to dynamic and static light scattering measurements. The micellization is shown to be thermodynamically favored, due to the high incompatibility of the blocks as indicated by thermal analysis of the block copolymers in bulk. The thermodynamic state in solution is found to be in the strong or super strong segregation limit. Nevertheless, due to the low glass transition temperature of the core-forming block, unimer exchange occurs between the micelles. Despite the dynamic character of the polymeric micellar systems, the aggregation behavior is strongly dependent on the history of the sample, i.e., on the preparation conditions. The aqueous micelles exhibit high stability upon temperature cycles, except for an irreversibly precipitating block copolymer containing a hydrophilic block exhibiting a lower critical solution temperature (LCST). Their exceptional stability upon dilution indicates very low critical micelle concentrations (CMC) (below 4∙10<sup>-4 g∙L<sup>-1). All non-ionic copolymers with sufficiently long solvophobic blocks aggregated into direct micelles in DMSO, too. Additionally, a new low-toxic highly hydrophilic sulfoxide block enables the formation of inverse micelles in organic solvents. The high potential of the new polymeric surfactants for many applications is demonstrated, in comparison to reference surfactants. The diblock copolymers are weakly surface-active, as indicated by the graduate decrease of the surface tension of their aqueous solutions with increasing concentration. No CMC could be detected. Their surface properties at the air/water interface confer anti-foaming properties. The macro-surfactants synthesized are surface-active at the interface between two liquid phases, too, since they are able to stabilize emulsions. The polymeric micelles are shown to exhibit a high ability to solubilize hydrophobic substances in water.
In this work, the nonaqueous synthesis of binary and ternary metal oxide nanoparticles is investigated for a number of technologically important materials. A strong focus was put on studying the reaction mechanisms leading to particle formation upon solvothermal treatment of the precursors, as an understanding of the formation processes is expected to be crucial for a better control of the systems, offering the potential to tailor particle size and morphology. The synthesis of BaTiO3 was achieved by solvothermal reaction of metallic barium and titanium isopropoxide in organic solvents. Phase-pure, highly crystalline particles about 6 nm in size resulted in benzyl alcohol, whereas larger particles could be obtained in ketones such as acetone or acetophenone. In benzyl alcohol, a novel mechanism was found to lead to BaTiO3, involving a C–C coupling step between the isopropoxide ligand and the benzylic carbon of the solvent. The resulting coupling product, 4-phenyl-2-butanol, is found in almost stoichiometric yield. The particle formation in ketones proceeds via a Ti-mediated aldol condensation of the solvent, involving formal elimination of water which induces formation of the oxide. These processes also occurred when reacting solely the titanium alkoxide with ketones or aldehydes, leading to highly crystalline anatase nanoparticles for all tested solvents. In ketones, also the synthesis of nanopowders of lead zirconate titanate (PZT) was achieved, which were initially amorphous but could be crystallized by calcination at moderate temperatures. Additionally, PZT films were prepared by simply casting a suspension of the powder onto Si substrates followed by calcination.Solvothermal synthesis however is not restricted to alkoxides as precursors but is also achieved from metal acetylacetonates. The use of benzylamine as solvent proved particularly versatile, making possible the synthesis of nanocrystalline In2O3, Ga2O3, ZnO and iron oxide from the respective acetylacetonates. During the synthesis, the acetylacetonate ligand undergoes a solvolysis under C–C cleavage, resulting in metal-bound enolate ligands which, in analogy to the synthesis in ketones, induce ketimine and aldol condensation reactions. In the last section of this work, surface functionalization of anatase nanoparticles is explored. The particles were first capped with various organic ligands via a facile in situ route, which resulted in altered properties such as enhanced dispersibility in various solvents. In a second step, short functional oligopeptide segments were attached to the particles by means of a catechol linker to achieve advanced self-assembly properties.
This thesis provides a novel view on the early stage of crystallization utilizing calcium carbonate as a model system. Calcium carbonate is of great economical, scientific and ecological importance, because it is a major part of water hardness, the most abundant Biomineral and forms huge amounts of geological sediments thus binding large amounts of carbon dioxide. The primary experiments base on the evolution of supersaturation via slow addition of dilute calcium chloride solution into dilute carbonate buffer. The time-dependent measurement of the Ca2+ potential and concurrent pH = constant titration facilitate the calculation of the amount of calcium and carbonate ions bound in pre-nucleation stage clusters, which have never been detected experimentally so far, and in the new phase after nucleation, respectively. Analytical Ultracentrifugation independently proves the existence of pre-nucleation stage clusters, and shows that the clusters forming at pH = 9.00 have a proximately time-averaged size of altogether 70 calcium and carbonate ions. Both experiments show that pre-nucleation stage cluster formation can be described by means of equilibrium thermodynamics. Effectively, the cluster formation equilibrium is physico-chemically characterized by means of a multiple-binding equilibrium of calcium ions to a ‘lattice’ of carbonate ions. The evaluation gives GIBBS standard energy for the formation of calcium/carbonate ion pairs in clusters, which exhibits a maximal value of approximately 17.2 kJ mol^-1 at pH = 9.75 and relates to a minimal binding strength in clusters at this pH-value. Nucleated calcium carbonate particles are amorphous at first and subsequently become crystalline. At high binding strength in clusters, only calcite (the thermodynamically stable polymorph) is finally obtained, while with decreasing binding strength in clusters, vaterite (the thermodynamically least stable polymorph) and presumably aragonite (the thermodynamically intermediate stable polymorph) are obtained additionally. Concurrently, two different solubility products of nucleated amorphous calcium carbonate (ACC) are detected at low binding strength and high binding strength in clusters (ACC I 3.1EE-8 M^2, ACC II 3.8EE-8 M^2), respectively, indicating the precipitation of at least two different ACC species, while the clusters provide the precursor species of ACC. It is proximate that ACC I may relate to calcitic ACC –i.e. ACC exhibiting short range order similar to the long range order of calcite and that ACC II may relate to vateritic ACC, which will subsequently transform into the particular crystalline polymorph as discussed in the literature, respectively. Detailed analysis of nucleated particles forming at minimal binding strength in clusters (pH = 9.75) by means of SEM, TEM, WAXS and light microscopy shows that predominantly vaterite with traces of calcite forms. The crystalline particles of early stages are composed of nano-crystallites of approximately 5 to 10 nm size, respectively, which are aligned in high mutual order as in mesocrystals. The analyses of precipitation at pH = 9.75 in presence of additives –polyacrylic acid (pAA) as a model compound for scale inhibitors and peptides exhibiting calcium carbonate binding affinity as model compounds for crystal modifiers- shows that ACC I and ACC II are precipitated in parallel: pAA stabilizes ACC II particles against crystallization leading to their dissolution for the benefit of crystals that form from ACC I and exclusively calcite is finally obtained. Concurrently, the peptide additives analogously inhibit the formation of calcite and exclusively vaterite is finally obtained in case of one of the peptide additives. These findings show that classical nucleation theory is hardly applicable for the nucleation of calcium carbonate. The metastable system is stabilized remarkably due to cluster formation, while clusters forming by means of equilibrium thermodynamics are the nucleation relevant species and not ions. Most likely, the concept of cluster formation is a common phenomenon occurring during the precipitation of hardly soluble compounds as qualitatively shown for calcium oxalate and calcium phosphate. This finding is important for the fundamental understanding of crystallization and nucleation-inhibition and modification by additives with impact on materials of huge scientific and industrial importance as well as for better understanding of the mass transport in crystallization. It can provide a novel basis for simulation and modelling approaches. New mechanisms of scale formation in Bio- and Geomineralization and also in scale inhibition on the basis of the newly reported reaction channel need to be considered.