Zur Struktur und Funktion der Typ-3-Kupferproteine sowie der Lichtsammlerkomplexe LHCI und LHCII

In der vorliegenden Arbeit wurden die bioinformatischen Methoden der Homologie-Modellierung und Molekularen Modellierung dazu benutzt, die dreidimensionalen Strukturen verschiedenster Proteine vorherzusagen und zu analysieren. Experimentelle Befunde aus Laborversuchen wurden dazu benutzt, die Genauigkeit der Homologie-Modelle zu erhöhen. Die Ergebnisse aus den Modellierungen wurden wiederum dazu benutzt, um neue experimentelle Versuche vorzuschlagen. Anhand der erstellten Modelle und bekannten Kristallstrukturen aus der Protein-Datenbank PDB wurde die Struktur-Funktionsbeziehung verschiedener Tyrosinasen untersucht. Dazu gehörten sowohl die Tyrosinase des Bakteriums Streptomyces als auch die Tyrosinase der Hausmaus. Aus den vergleichenden Strukturanalysen der Tyrosinasen resultierten Mechanismen für die Monophenolhydroxylase-Aktivität der Tyrosinasen sowie für den Import der Kupferionen ins aktive Zentrum. Es konnte der Beweis geführt werden, daß die Blockade des CuA-Zentrums tatsächlich der Grund für die unterschiedliche Aktivität von Tyrosinasen und Catecholoxidasen ist. Zum ersten Mal konnte mit der Maus-Tyrosinase ein vollständiges Strukturmodell einer Säugetier-Tyrosinase erstellt werden, das dazu in der Lage ist, die Mechanismen bekannter Albino-Mutationen auf molekularer Ebene zu erklären. Die auf der Basis des ermittelten 3D-Modells gewonnenen Erkenntnisse über die Wichtigkeit bestimmter Aminosäuren für die Funktion wurde durch gerichtete Mutagenese an der rekombinant hergestellten Maus-Tyrosinase getestet und bestätigt. Weiterhin wurde die Struktur der Tyrosinase des Krebses Palinurus elephas durch eine niedrigaufgelöste 3D-Rekonstruktion aus elektronenmikroskopischen Bildern aufgeklärt. Der zweite große Themenkomplex umfasst die Strukturanalyse der Lichtsammlerkomplexe LHCI-730 und LHCII. Im Falle des LHCII konnte der Oligomerisierungszustand der LHCMoleküle mit diskreten Konformationen des N-Terminus korreliert werden. Auch hier kam eine Kombination von Homologie-Modellierung und einer experimentellen Methode, der Elektronen-Spin-Resonanz-Messung, zum Einsatz. Die Änderung des Oligomerisierungszustands des LHCII kontrolliert den Energiezufluß zu den Photosystemen PS I und PS II. Des Weiteren wurde ein vollständiges Modell des LHCI-730 erstellt, um die Auswirkungen gerichteter Mutagenese auf das Dimerisierungsverhalten zu untersuchen. Auf Basis dieses Modells wurden die Wechselwirkungen zwischen den Monomeren Lhca1 und Lhca4 evaluiert und potentielle Bindungspartner identifiziert.

Pinning-Effekte kolumnarer Schwerionenspuren in Kuprat-Supraleiter-Dünnschichten

In this work the flux line dynamics in High-Temperature Superconductor (HTSC) thin films in the presence of columnar defects was studied using electronic transport measurements. The columnar defects which are correlated pinning centers for vortices were generated by irradiation with swift heavy ions at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt. In the first part, the vortex dynamics is discussed within the framework of the Bose-glass model. This approach describes the continuous transition from a vortex liquid to a Bose-glass phase which is characterized by the localization of the flux lines at the columnar defects. The critical behavior of the characteristic length and time scales for temperatures in the vicinity of this phase transition were probed by scaling properties of experimentally obtained current-voltage characteristics. In contrast to the predicted universal properties of the critical behavior the scaling analysis shows a strong dependence of the dynamic critical exponent on the experimentally accessible electric field range. In addition, the predicted divergence of the activation energy in the limit of low current densities was experimentally not confirmed.The dynamic behavior of flux lines in spatially resolved irradiation geometries is reported in the second part. Weak pinning channels with widths between 10 µm and 100 µm were generated in a strong pinning environment with the use of metal masks and the GSI microprobe, respectively. Measurements of the anisotropic transport properties of these structures show a striking resemblance to the results in YBCO single crystals with unidirected twin boundaries which were interpreted as a guided vortex motion effect. The use of two additional test bridges allowed to determine in parallel the resistivities of the irradiated and unirradiated parts as well as the respective current-voltage characteristics. These measurements provided the input parameters for a numerical simulation of the potential distribution in the spatially resolved irradiation geometry. The results are interpreted within a model that describes the hydrodynamic interaction between a Bose-glass phase and a vortex liquid. The interface between weakly pinned flux lines in the unirradiated channels and strongly pinned vortices leads to a nonuniform vortex velocity profile and therefore a variation of the local electric field. The length scale of these interactions was estimated for the first time in measuring the local variation of the electric field profile in a Bose-glass contact.Finally, a method for the determination of the true temperature in HTSC thin films at high dissipation levels is described. In this regime of electronic transport the occurrence of a flux flow instability is accompanied by heating effects in the vortex system. The heat propagation properties of the film/substrate system are deduced from the time dependent voltage response to a short high current density pulse of rectangular shape. The influence of heavy ion irradiation on the heat resistance at the film/substrate interface is studied.

Electronic energy transfer processes in pi-conjugated polymers

Currently pi-conjugated polymers are considered as technologically interesting materials to be used as functional building elements for the development of the new generation of optoelectronic devices. More specifically during the last few years, poly-p-phenylene materials have attracted considerable attention for their blue photoluminescence properties. This Thesis deals with the optical properties of the most representative blue light poly-p-phenylene emitters such as poly(fluorene), oligo(fluorene), poly(indenofluorene) and ladder-type penta(phenylene) derivatives. In the present work, laser induced photoluminescence spectroscopy is used as a major tool for the study of the interdependence between the dynamics of the probed photoluminescence, the molecular structures of the prepared polymeric films and the presence of chemical defects. Complementary results obtained by two-dimensional wide-angle X-ray diffraction are reported. These findings show that the different optical properties observed are influenced by the intermolecular solid-state interactions that in turn are controlled by the pendant groups of the polymer backbone. A significant feedback is delivered regarding the positive impact of a new synthetic route for the preparation of a poly(indenofluorene) derivative on the spectral purity of the compound. The energy transfer mechanisms that operate in the studied systems are addressed by doping experiments. After the evaluation of the structure/property interdependence, a new optical excitation pathway is presented. An efficient photon low-energy up-conversion that sensitises the blue emission of poly(fluorene) is demonstrated. The observed phenomenon takes place in poly(fluorene) derivatives hosts doped with metallated octaethyl porphyrins, after quasi-CW photoexcitation of intensities in the order of kW/cm2. The up-conversion process is parameterised in terms of temperature, wavelength excitation and central metal cation in the porphyrin ring. Additionally the observation of the up-conversion is extended in a broad range of poly-p-phenylene blue light emitting hosts. The dependence of the detected up-conversion intensity on the excitation intensity and doping concentration is reported. Furthermore the dynamics of the up-conversion intensity are monitored as a function of the doping concentration. These experimental results strongly suggest the existence of triplet-triplet annihilation events into the porphyrin molecules that are subsequently followed by energy transfer to the host. After confirming the occurrence of the up-conversion in solutions, cyclic voltammetry is used in order to show that the up-conversion efficiency is partially determined from the energetic alignment between the HOMO levels of the host and the dopant.

Electronic energy transfer processes and charge carrier transport in pi-conjugated polymers

Conjugated polymers have attracted tremendous academical and industrial research interest over the past decades due to the appealing advantages that organic / polymeric materials offer for electronic applications and devices such as organic light emitting diodes (OLED), organic field effect transistors (OFET), organic solar cells (OSC), photodiodes and plastic lasers. The optimization of organic materials for applications in optoelectronic devices requires detailed knowledge of their photophysical properties, for instance energy levels of excited singlet and triplet states, excited state decay mechanisms and charge carrier mobilities. In the present work a variety of different conjugated (co)polymers, mainly polyspirobifluorene- and polyfluorene-type materials, was investigated using time-resolved photoluminescence spectroscopy in the picosecond to second time domain to study their elementary photophysical properties and to get a deeper insight into structure-property relationships. The experiments cover fluorescence spectroscopy using Streak Camera techniques as well as time-delayed gated detection techniques for the investigation of delayed fluorescence and phosphorescence. All measurements were performed on the solid state, i.e. thin polymer films and on diluted solutions. Starting from the elementary photophysical properties of conjugated polymers the experiments were extended to studies of singlet and triplet energy transfer processes in polymer blends, polymer-triplet emitter blends and copolymers. The phenomenon of photonenergy upconversion was investigated in blue light-emitting polymer matrices doped with metallated porphyrin derivatives supposing an bimolecular annihilation upconversion mechanism which could be experimentally verified on a series of copolymers. This mechanism allows for more efficient photonenergy upconversion than previously reported for polyfluorene derivatives. In addition to the above described spectroscopical experiments, amplified spontaneous emission (ASE) in thin film polymer waveguides was studied employing a fully-arylated poly(indenofluorene) as the gain medium. It was found that the material exhibits a very low threshold value for amplification of blue light combined with an excellent oxidative stability, which makes it interesting as active material for organic solid state lasers. Apart from spectroscopical experiments, transient photocurrent measurements on conjugated polymers were performed as well to elucidate the charge carrier mobility in the solid state, which is an important material parameter for device applications. A modified time-of-flight (TOF) technique using a charge carrier generation layer allowed to study hole transport in a series of spirobifluorene copolymers to unravel the structure-mobility relationship by comparison with the homopolymer. Not only the charge carrier mobility could be determined for the series of polymers but also field- and temperature-dependent measurements analyzed in the framework of the Gaussian disorder model showed that results coincide very well with the predictions of the model. Thus, the validity of the disorder concept for charge carrier transport in amorphous glassy materials could be verified for the investigated series of copolymers.

Numerical coupling of thermal-electric network models and energy-transport equations including optoelectronic semiconductor devices

In this work the numerical coupling of thermal and electric network models with model equations for optoelectronic semiconductor devices is presented. Modified nodal analysis (MNA) is applied to model electric networks. Thermal effects are modeled by an accompanying thermal network. Semiconductor devices are modeled by the energy-transport model, that allows for thermal effects. The energy-transport model is expandend to a model for optoelectronic semiconductor devices. The temperature of the crystal lattice of the semiconductor devices is modeled by the heat flow eqaution. The corresponding heat source term is derived under thermodynamical and phenomenological considerations of energy fluxes. The energy-transport model is coupled directly into the network equations and the heat flow equation for the lattice temperature is coupled directly into the accompanying thermal network. The coupled thermal-electric network-device model results in a system of partial differential-algebraic equations (PDAE). Numerical examples are presented for the coupling of network- and one-dimensional semiconductor equations. Hybridized mixed finite elements are applied for the space discretization of the semiconductor equations. Backward difference formluas are applied for time discretization. Thus, positivity of charge carrier densities and continuity of the current density is guaranteed even for the coupled model.