03 Fakultät Chemie
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Item Open Access Interphases between alkali metals (Li, Na) and battery electrolytes : ion transport and growth behavior(2022) Lim, Kyungmi; Maier, Joachim (Prof. Dr.)Item Open Access Strukturelle, elektrochemische und spektroskopische Untersuchungen von bioinspirierten Modellkomplexen mit N,S-Liganden(2010) Schnödt, Johannes; Kaim, Wolfgang (Prof. Dr.)Durch die strukturelle Aufklärung der aktiven Zentren von Proteinen und Enzymen hat sich ein interdisziplinäres Forschungsgebiet entwickelt, das versucht entsprechende Modellsysteme als Katalysatoren zu nutzen. Insbesondere Elektronen übertragende Proteine, wie Plastocyanin sowie oxygenierende Enzyme, wie die Peptidylglycin-a-hydroxylierende Monooxygenase, die einen Redoxprozess und einen Sauerstofftransfer verbinden, sind in den Blickpunkt gerückt. In der vorliegenden Dissertation werden die Synthesen und die strukturellen Aufklärungen von bioinspirierten Modellkomplexen mit stickstoff- und schwefelhaltigen Liganden ausführlich beschrieben. Neben den spektroskopischen Eigenschaften dieser Komplexe liegt der Fokus auf den Untersuchungen der elektrochemischen Eigenschaften dieser Redoxsysteme im besonderen Maße im Hinblick auf die Rolle des Schwefels.Item Open Access Experimental and computational phase studies of the ZrO2-based systems for thermal barrier coatings(2006) Wang,Chong; Aldinger, Fritz (Prof.)The ZrO2-based materials are practically important as the thermal barrier coatings (TBC) for high temperature gas turbines, due to their low thermal conductivity, high temperature thermal stability and excellent interfacial compatibility. Studies of the phase equilibira, phase transformation, and thermodynamics of the ZrO2-based systems can provide the necessary basic knowledge to develop the next generation TBC materials. In the thesis, the systems ZrO2 - HfO2, ZrO2 - LaO1.5, ZrO2 - NdO1.5, ZrO2 - SmO1.5, ZrO2 - GdO1.5, ZrO2 - DyO1.5, ZrO2 - YbO1.5 and ZrO2 - GdO1.5 - YO1.5 were experimentally studied. The samples were prepared by the chemical co-precipitation method, with aqueous solutions Zr(CH3COO)4, HfO(NO3)2, and RE(NO3)3×xH2O (RE=La, Nd, Sm, Gd, Dy, Yb) as starting materials. Various experimental techniques, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), differential thermal analysis (DTA), and high temperature calorimetry were employed to study the phase transformation, phase equilibria between 1400 and 1700°C, heat content and heat capacity of the materials. A lot of contradictions in the literature were resolved and the phase diagrams were reconstructed.Item Open Access Synthese und Charakterisierung teilfluorierter Poly(aryl)-Ionomere als Polymerelektrolytmembranen für Brennstoffzellen und ESR-spektroskopische Untersuchung der radikalinduzierten Degradation von Modellverbindungen(2008) Schönberger, Frank; Roduner, Emil (Prof. Dr.)Im ersten Teil dieser Arbeit werden zunächst verschiedene Strategien zum Aufbau sulfonierter teilfluorierter Poly(aryl)e entwickelt und synthetisch umgesetzt. Konzeptionell liegt dabei die Hypothese zugrunde, dass sich teilfluorierte Poly(aryl)-Ionomere gegenüber nichtfluorierten durch eine erhöhte Acidität auszeichnen. Außerdem weisen sie eine höhere Bindungsdissoziationsenergie sowohl der C-F-Bindungen als auch der benachbarten C-H-Bindungen auf, womit ein Gewinn an radikalischer und somit chemischer und thermischer Stabilität einhergeht. Um den Einfluss der chemischen Struktur der jeweiligen (teilfluorierten) Monomerbausteine zu untersuchen, werden zunächst homo-Polymere mit verschiedenen Struktureinheiten (mit aromatischen C-F-Bindungen, C(CF3)2-verbrückten und CF3-substitutierten Phenylenringen) durch Polykondensation synthetisiert und charakterisiert (Elementaranalyse, NMR-Spektroskopie, Gelpermeationschromatographie). Zur gezielten Synthese der Monomere werden bekannte organische Reaktionen, wie die Balz-Schiemann-Reaktion, Suzuki-Reaktion und die Ullmann-Biarylsynthese, angewandt. Nach Sulfonierung der homo-Polymere werden (ionisch-vernetzte) Membranen hergestellt und hinsichtlich Eignung als Polymerelektrolytmembran für Brennstoffzellen charakterisiert (Ionenaustauscherkapazität, Protonenleitfähigkeit, thermische und chemische Stabilität, Wasseraufnahme, Längenänderung). Neben der chemischen Natur der Monomere ist auch deren Anordnung im Polymer bzw. Ionomer für die Eigenschaften der hergestellten Membranen wichtig. Aus diesem Grunde werden mikrophasenseparierte Block-co-Ionomere, ausgehend von hydrophilen (sulfonierten) und hydrophoben (teilfluorierten) telechelen Makromonomeren, synthetisiert und charakterisiert. Dabei werden sowohl der Einfluss der jeweiligen Blocklänge als auch der chemischen Natur der eingesetzten Monomere auf die Membraneigenschaften vergleichend untersucht. Auf der Grundlage der in diesem Teil der Arbeit gewonnen Erkenntnisse werden die Vor- und Nachteile teilfluorierter Ionomermembranen analysiert und diskutiert. Der zweite Teil der Arbeit befasst sich mit der ESR-spektroskopischen Untersuchung der radikalinduzierten Degradation von Modellverbindungen, denen Struktureinheiten einiger im ersten Teil der Arbeit hergestellten Poly(aryl)-Ionomere entsprechen. Diese Modellverbindungen werden in einer Durchflusszelle Hydroxyl- und Hydroperoxylradikalen ausgesetzt, welche direkt im Hohlraumresonator eines ESR-Spektrometers durch Photolyse von Wasserstoffperoxid erzeugt werden. Mit diesem Aufbau können verschiedene Parameter (wie die Hydroxylradikal- und Monomerkonzentration, die Durchflussrate und der pH-Wert) gezielt variiert werden und so deren Einflüsse in Bezug auf die Produktbildung der aromatischen Modellverbindungen mit den Hydroxylradikalen abgeschätzt werden. Aus diesen Untersuchungen lassen sich Rückschlüsse auf mögliche Radikalreaktionen des Poly(aryl)-Ionomers ziehen und damit Aussagen in Bezug auf zu vermeidende strukturelle Merkmale (z.B. Art der Endgruppen der Ionomere) und zu vermeidende Bedingungen (z.B. pH-Wertschwankungen in der Membran) treffen.Item Open Access Die alpha-Amylase aus Bacillus amyloliquefaciens: Verbesserung der Alkaliaktivität und Steigerung der spezifischen Aktivität mittels gerichteter Evolution(2002) Bessler, Cornelius; Schmid, Rolf D. (Prof. Dr.)Amylasen werden häufig in Waschmitteln eingesetzt. Diese Anwendung werden Amylasen benötigt, die eine hohen Stabilität und Aktivität bei alkalischem pH besitzen. Zudem ist eine hohe spezifische Aktivität wünschenswert, da so Enzymmenge und dadurch Kosten gespart werden können. Ziel dieser Arbeit war die Etablierung und Anwendung von Methoden der gerichteten Evolution auf die Amylase aus Bacillus amyloliquefaciens (BAA) zur Steigerung der spezifischen Aktivität und der Alkaliaktivität. Die Gene für die BAA sowie zwei Punktmutanten derselben wurden durch Error-prone PCR mutagenisiert und durch Gen-Shuffling rekombiniert. Zur Durchmusterung der Mutantenbibliotheken wurde ein Hochdurchsatz-Test auf Basis des kommerziell erhältlichen Phadebas(r)-Tests entwickelt. Das pH-Optimum von Mutante 42 ist um eine pH-Einheit zu höheren pH-Werten verschoben und liegt bei pH 7. Dies führt zusammen mit einer um den Faktor fünf höheren Aktivität bei pH 10 zu einem verbreiterten pH-Profil. Außerdem stieg die Aktivität in den Periplasmafraktionen um den Faktor vier und die spezifische Aktivität um den Faktor 1,5 als beim Wildtyp. Eine weitere Mutante, Mutante 29 zeigt das pH-Profil des Wildtyps. Allerdings liegen Aktivität der Periplasmafraktionen und spezifische Aktivität um den Faktor 40 beziehungsweise um den Faktor 9 höher als beim Wildtyp. Mutante B1, die durch Error-prone PCR mit der Mutante 29 erzeugt wurde zeigt ebenfalls das pH-Profil des Wildtyps. Zudem ist ihre spezifische Aktivität niedriger als die der Mutante 29, aber immerhin noch um den Faktor 4,2 höher als die des Wildtyps. Durch Vergleich der Aminosäuresequenzen der Mutanten mit dem Wildtyp und mit homologen Amylasen konnte der Einfluss der einzelnen Mutationen erklärt werden.Item Open Access Mechanistic studies on the DNA methyltransferases DNMT3A and DNMT3B(2021) Dukatz, Michael; Jeltsch, Albert (Prof. Dr.)In this work, both regulatory and catalytic mechanisms of de novo methyltransferases were investigated, which include interactions with other proteins and the specific recognition of the substrate sequence. Another part of this work strived to elucidate how enzymatic generation of 3-methylcytosine by DNMT3A can occur.Item Open Access Using spin polarised positive muons for studying guest molecule partitioning in soft matter structures(2007) Martyniak-Stronczek, Aleksandra; Roduner, Emil (Prof. Dr.)The intention of this thesis is to explore the effect of guest molecules on the structure of diverse soft matter architectures, and thus the stability of the entire systems. More specifically, we focus on the determination of the factors that affect partitioning of fragrance components in emulsions and microemulsions, including various lyotropic liquid crystalline mesophases of cationic and anionic surfactants. It is well known that the most common fragrance materials are created based on the mixtures of aliphatic alcohols or/and phenyl alcohols. Until recently, however, qualitative and quantitative studies of the guest molecule partitioning into the surfactant membrane have been performed mostly for short, medium and long chain aliphatic alcohols. In consequence, in the literature arose a gap of information on the distribution of alcohols containing an aromatic group into colloidal surfactant dispersions. Hence, to fill at least partly this gap, the probes used in this work are muoniated cyclohexadienyl radicals derived from five different phenyl alcohols: 2-Phenylethan-1-ol (n = 2), 3-Phenylpropan-1-ol (n = 3), 4-Phenylbutan-1-ol (n = 4), 5-Phenylpentan-1-ol (n = 5) und Para-propyl-2-phenylethan-1-ol (n = 2 + 3). The variation of their hydrocarbon chain length (distinguished by the number, n, of CH2 groups in their hydrocarbon chain) changes their hydrophobicity, and this is expected to affect their partitioning between the aqueous and the hydrocarbon moiety of the surfactant dispersion, which is the main focus of the present study. Furthermore, a detailed understanding of solvation thermodynamic properties and reorientational dynamics of the chosen species, including Heisenberg spin exchange in order to confirm the interpretation of particular aspects, is also presented here. Common methods for the investigation of a variety of soft matter structures, such as spherical micelles, vesicles, lamellar, rectangular, hexagonal and cubic phases or bi-continuous sponge type structures include light, X-ray and neutron scattering, and measurements of calorimetric and rheological properties. Nuclear magnetic resonance is a powerful tool for the study of the dynamics of specific molecules or groups, or also of the entire structures. For the same purpose but with higher sensitivity, fluorescent dye molecules or spin labels are introduced as guests or bound to the amphiphile in specific positions, permitting optical spectroscopy (UV-Vis) or electron spin resonance studies, respectively. Technical applications may require other types of guest molecules to be introduced into these structures. Prominent examples are drug molecules for their delivery to specific sites in the body, or skin care, dyes and fragrance molecules in day care products or additives to food. They are often needed in low concentrations (because of the limited solubility or high toxicity, etc.) that makes it difficult to monitor them with conventional methods at a molecular level. For these reasons we used here a special experimental technique which permits highly sensitive spectroscopy, the Avoided Level Crossing Muon Spin Resonance (ALC-mSR). ALC-mSR relies on a unique property of the positive muon, i.e. where it becomes attached to a C=C double bond or phenyl group via addition of the muonium atom (Mu), which can be regarded as a light hydrogen isotope. Mu addition to unsaturated molecules produces radicals that contain the muon as a fully polarized spin label which reveals information about the structure, kinetics, distribution and solvation thermodynamics of such radicals even under extremely dilute conditions in different colloidal dispersions. Moreover, the high spin polarisation and the single particle counting technique make the muon an exceptionally sensitive probe. It has been already shown that ALC-mSR has so far found applications for the investigation of muonium-substituted free radicals in various environments, for example in the gas phase, in polymers, in liquid crystals, in zeolites, and also for Mu in semiconductors and for muons in metals. This time, however, to prove that this method is also suitable to apply in more complex (multicomponent) systems than described above, the ALC-mSR serves here as a tool for sensitive monitoring of the local environment and reorientational dynamics of muoniated radicals (kept at very low concentrations) in ternary and quaternary surfactant mixtures. Thus, it is a successive challenge of these studies to show that the muoniated radical can be treated as a spectator of the changes in the properties of diverse surfactant systems at a molecular level.Item Open Access In-situ radiation grafting of polymer films and degradation studies of monomers for applications in fuel cell membranes(2007) Mitov, Svetlin; Roduner, Emil (Prof. Dr.)The present work consists of three parts which deal with the optimization of the properties of polymers finding application as proton exchange membranes in PEMFCs. The focus is the oxidative and photochemical stability of non-fluorinated polymer membranes, as well as the radiation-induced grafting of commercially available fluoropolymer films. The use of the ESR technique is common for the first two parts of the dissertation. The third part comprises the results and discussions of DFT calculations for non-fluorinated and fluorinated fragments. In order to predict hydroxyl radical initiated degradation of new proton conducting polymer membranes based on sulfonated polyetherketones and polysulfones, five non-fluorinated aromatics (4,4'-sulfonyldiphenol, bisphenol A, 4,4'-diphenol, 4,'-dihydroxybenzophenone and sulfonated 4,4'-dichlorodiphenylsulfone) are chosen as model compounds for ESR experiments, aiming at the identification of products of HO· radical reactions with these monomers. Direct photolysis of aqueous solutions of H2O2 was chosen as the source of HO· radicals. In order to distinguish HO· radical attack from direct photolysis of the monomers, experiments were carried out in the presence and absence of H2O2. In the second part of the present work three different electron beam irradiated fluoropolymers - poly(ethylene-alt-tetrafluoroethylene), poly(tetrafluoroethylene-co-hexafluoropropylene) and poly(vinylidenefluoride), as well as their grafting reactions with styrene, 25% styrene in benzene and 25% styrene in ethanol are investigated by means of ESR. Firstly, it was possible to compare the radiation chemistry of the three fluoropolymers that have been irradiated using the same irradiation source, doses and atmospheres. Secondly, it was possible to compare the decay of radicals in the different fluoropolymers by carrying out in-situ ESR measurements in a similar systematic manner during the radiation grafting process, aiming at an understanding of the influence of the irradiation atmosphere and of the diluent. In addition, in the radiation grafting of polymer films with styrene for fuel cell applications it is important to control whether the polystyrene chain is grafted onto a peroxy or a carbon centered radical. Thus thermodynamic properties of small alkyl and alkyl-peroxy radicals are studied to model primary, secondary and tertiary radicals in non-fluorinated and perfluorinated polymers and a comparative DFT study is conducted. Furthermore, it is shown based on DFT calculations that pronounced spin polarization effects lead to unexpected behavior of the hyperfine anisotropy. This is demonstrated by comparison of the parameters of CF3·CF2, both in its fully optimized non-planar and in a forced planar conformation, with those of the analogous non-fluorinated and essentially planar CH3·CH2 radical. A B3LYP or UB3LYP hybrid functional and 6-311+G** or EPR-II basis sets are used, and all calculations are performed with the Gaussian package.Item Open Access Kationische Wolfram-Alkylidin-N-Heterozyklische-Carben-Komplexe und deren Reaktionen zu Wolfram-Oxo- und Sulfido-Alkyliden-Komplexen(2022) Hauser, Philipp M.; Buchmeiser, Michael R. (Prof. Dr.)Item Open Access Gelled bicontinuous microemulsions : a new type of orthogonal self-assembled systems(2013) Laupheimer, Michaela; Stubenrauch, Cosima (Prof. Dr.)In this work a new type of orthogonal self-assembled systems, namely a gelled bicontinuous microemulsion, was investigated with a set of complementary physico-chemical methods. Orthogonal self-assembly means that different structures self-assemble simultaneously in a system and coexist independently. In the chosen model system H2O – n-decane / 12-hydroxyoctadecanoic acid (12-HOA) – tetraethylene glycol monodecyl ether (C10E4) the organogelator 12-HOA forms a network which is surrounded by bicontinuous microemulsion domains. This was proved by comparing characteristic properties and the microstructure of the gelled bicontinuous microemulsion with those of the two ‘base systems’, i.e. the non-gelled bicontinuous microemulsion H2O – n-decane – C10E4 and the binary gel n-decane / 12-HOA. Firstly, phase studies were carried out which showed that the microemulsion phase boundaries are maintained upon gelation, merely shifted by about 6 K to lower temperatures. Likewise, a sol-gel transition occurs in the gelled microemulsion just as in the binary gel. Differential scanning calorimetry and temperature-dependent oscillating shear rheometry measurements revealed that the sol-gel transition temperature is about 20 K lower when a microemulsion, instead of pure n-decane, surrounds the gelator network. This reflects that part of the surface-active 12-HOA molecules adsorb at the water-oil interface instead of forming gelator fibers when a microemulsion is present. Accordingly, studying the linear viscoelastic range and the frequency-dependence of the storage and the loss modulus it was found that the gelator network is somewhat weaker in the gelled bicontinuous microemulsion than in the binary gel, although both systems are strong gels. In the following the focus turned to the microstructure of the gelled bicontinuous microemulsion. To begin with, the bicontinuity of the microemulsion domains in the middle of the one-phase region was verified determining the relative self-diffusion coefficients of water and n-decane with Fourier transform pulsed-gradient spin-echo 1H-NMR measurements. Subsequently, the coexistence of the bicontinuous microemulsion domains and the gelator network in the gelled bicontinuous microemulsion was evidenced by means of small angle neutron scattering. Finally, a visualization of the coexisting microstructures with freeze-fracture transmission electron microscopy complemented the work.