Decentralized plug and play systems for energy production are the future picture of our society. Artificial photosynthetic systems are used for this purpose. These systems are inspired by natural... Show moreDecentralized plug and play systems for energy production are the future picture of our society. Artificial photosynthetic systems are used for this purpose. These systems are inspired by natural photosynthesis.Chapter 2 illustrates the detailed construction of a three-flash flow cell to study light induced biological reactions, specifically the water oxidation reaction of Photosystem II. This instrument is capable of producing the S2+, S3+ and S0n intermediate states of the Kok cycle. I confirmed these by EPR experiments.In chapter 3, I study the mechanism of the major LHC II involved in conformational switching from light harvesting to the photoprotective state, in which excess light is dissipated as heat. I use MAS NMR as a non-invasive method to understand the structure and environment around Arg residues in Chlamydomonas reinhardtii LHC II. In this approach the Arg amino acid is selectively labeled with 13C isotopesChapter 4 studies the structure of self-aggregated semi synthetic Zn 31 amino chlorin that forms syn-anti parallel stacks according to the solid state NMR data. The small change of removing 33 methyl group of Zn 31 aminomethyl chlorin has significant effect on self-assembly. Finally, chapter 5 provides an outlook on future research. Show less
Solar energy is used by photosynthetic organisms to drive energy required cellular processes. Is absorbed by two groups of pigments, located in the LHCs. These proteins are essential for the... Show moreSolar energy is used by photosynthetic organisms to drive energy required cellular processes. Is absorbed by two groups of pigments, located in the LHCs. These proteins are essential for the performance of photosynthesis, because they are involved in harvesting the light and because they protect the photosynthetic system from excess of light that cause photodamage. I performed in vitro studies mimicking the two functions of LHCII by inserting the protein in nanodiscs and in liposomes. I demonstrate that Chl excitation quenching is dependent on protein-protein interactions. I investigated the specific interactions of LHCII with PsbS. The fluorescence study of our minimal membrane models strongly suggests that the pH-dependent role of PsbS lies in creating membrane rearrangements and supercomplex remodeling that could facilitate LHCII aggregation quenching. I successfully produced 13C lutein-rLhcb1 protein in detergent, mimicking the unquenched state, and protein aggregates, mimicking the quenched state, were biochemically and spectroscopically characterized and further analysed with solid state NMR.Ring current shifts of the lutein head signals indicate that the heads are in close proximity to specific Chls (Chl a610 and Chl a602), providing for the first-time structural information about lutein-Chl interactions in LHCII in its unquenched state. Show less
Zill, J.C.; Kansy, M.; Goss, R.; Alia, A.; Wilhelm, C.; Matysik, J. 2018
Current energy-sources in the form of fossil fuels are quickly being depleted, while the demand of energy by society is increasing. In order to sustain this growth in energy demand, alternatives... Show moreCurrent energy-sources in the form of fossil fuels are quickly being depleted, while the demand of energy by society is increasing. In order to sustain this growth in energy demand, alternatives for the production of energy in a usable form are needed. One of such alternatives is to employ photocatalysis in order to use sunlight for the production of chemical fuels such as for example H2 or methanol. For the production of fuels, electrons are required that can be obtained by oxidizing water, as done by nature in a process called photosynthesis. The work in this thesis was inspired by this natural process; photosensitizers and water-oxidation catalysts were bound to lipid bilayers and their ability to photocatalytically oxidize water was studied in different conditions. The anchoring of compounds to a lipid bilayer leads to large differences in reactivity compared to homogeneous systems. In some cases, even the mechanism of the photocatalytic reaction changed upon membrane-anchoring of the constituents. In general, detailed experiments are described that fully characterize photocatalytic systems, because the mechanism of a reaction involving two different catalytic species is not straight-forward, and cannot be described by a single set of turn-over numbers. Show less
Aim The influence of soil properties on photosynthetic traits in higher plants is poorly quantified in comparison with that of climate.We address this situation by quantifying the unique and joint... Show moreAim The influence of soil properties on photosynthetic traits in higher plants is poorly quantified in comparison with that of climate.We address this situation by quantifying the unique and joint contributions to global leaf-trait variation from soils and climate. Location Terrestrial ecosystems world-wide. Methods Using a trait dataset comprising 1509 species from 288 sites, with climate and soil data derived from global datasets, we quantified the effects of 20 soil and 26 climate variables on light-saturated photosynthetic rate (Aarea), stomatal conductance (gs), leaf nitrogen and phosphorus (Narea and Parea) and specific leaf area (SLA) using mixed regression models and multivariate analyses. Results Soil variables were stronger predictors of leaf traits than climatic variables, except for SLA. On average, Narea, Parea and Aarea increased and SLA decreased with increasing soil pH and with increasing site aridity. gs declined and Parea increased with soil available P (Pavail). Narea was unrelated to total soil N. Joint effects of soil and climate dominated over their unique effects on Narea and Parea, while unique effects of soils dominated for Aarea and gs. Path analysis indicated that variation in Aarea reflected the combined independent influences of Narea and gs, the former promoted by high pH and aridity and the latter by low Pavail. Main conclusions Three environmental variables were key for explaining variation in leaf traits: soil pH and Pavail, and the climatic moisture index (the ratio ofprecipitation to potential evapotranspiration). Although the reliability of global soil datasets lags behind that of climate datasets, our results nonetheless provide compelling evidence that both can be jointly used in broad-scale analyses, and that effects uniquely attributable to soil properties are important determinants of leaf photosynthetic traits and rates. A significant future challenge is to better disentangle the covarying physiological, ecological Show less
In the project described in this thesis we studied a simple bio-electronic device for solar energy conversion by surface-assembly of photosynthetic pigment-protein complexes on a bare gold... Show moreIn the project described in this thesis we studied a simple bio-electronic device for solar energy conversion by surface-assembly of photosynthetic pigment-protein complexes on a bare gold-electrode. Optical excitation of the photosynthetic pigments gives rise to charge separation in the so-called reaction center complex. Energy conversion is completed by subsequent electron transfer to the electrode, generating a light-induced electric current. The efficiency of the initial steps of charge separation is very high, the challenge lies in interfacing the protein complexes with conducting surfaces in an efficient manner to exploit the larger part of the harvesting energy. We have interfaced photosynthetic proteins with the Gold electrode by different techniques namely, simple incubation from solution, 2D crystallization and Langmuir-Blodgett deposition and measured photocurrent and current-voltage characteristics of these complexes. We conclude that Langmuir-Blodgett deposition gives a uniformly oriented mono-layer of protein complexes, which enhance the electron transfer efficiency between the electrode and proteins, resulting in highest ever photo-current density and internal quantum efficiency of a mono-layer of protein complexes. 2D crystals of photosynthetic proteins provide native like environment which is desirable for any application of the proteins.2D crystal packing of proteins seem to compete the excitation quenching by the gold electrode Show less
This PhD thesis focuses on fundamental aspects of protein-protein interactions. A multidisciplinary methodology for the detection and visualization of transient, lowly-populated encounter protein... Show moreThis PhD thesis focuses on fundamental aspects of protein-protein interactions. A multidisciplinary methodology for the detection and visualization of transient, lowly-populated encounter protein complexes is described. The new methodology combined paramagnetic NMR spectroscopy with computational methods (ensemble docking approach and Monte Carlo simulations) to provide a new model to describe the formation of a protein complex on the basis of the physical forces involved in the process, namely electrostatic and hydrophobic interactions. The formation of a productive protein complex is a stepwise process, in which the free components evolve to the final complex passing through a transient, lowly-populated encounter state. For a long time the first step of association was thought to be exclusively driven by long-range electrostatic interactions. Experimental evidences and theoretical studies questioned this assumption and suggested also a role of hydrophobic interactions in protein association. To study the contribution of the different forces we study the highly dynamic complex formed by plastocyanin and cytochrome f, two redox partners in oxygenic photosynthesis, for which both electrostatic and hydrophobic interactions were shown to contribute to the stabilization of the final complex. Through the combination of paramagnetic relaxation enhancement NMR techniques and computational methods we were able to visualize the presence of hydrophobic interactions in the encounter state and to elucidate the contribution of either electrostatic or hydrophobic forces to the formation of the encounter complex. Show less
The interfacing of biomolecules to nanostructures, electrode surfaces and/or optical components constitutes the new discipline of bioelectronics. It is based on electron transfer between a protein... Show moreThe interfacing of biomolecules to nanostructures, electrode surfaces and/or optical components constitutes the new discipline of bioelectronics. It is based on electron transfer between a protein and an electrode, and can be monitored by amperometric techniques. The integration of biomolecules with electronics has strong potential for applications in a variety of functional devices, ranging from biosensors to solar cells. In this thesis we explore the possibilities of constructing a bio-electronic device for solar energy conversion by surface-assembly of photosynthetic pigment-protein complexes on a gold electrode. Optical excitation of the photosynthetic pigments gives rise to charge separation in the so-called reaction center complex. Energy conversion is completed by subsequent electron transfer to the electrode, generating a light-induced electric current. The data shows that light-harvesting complexes can be immobilized directly on a gold surface and on various SAM surfaces whilst retaining their full optical functionality. All energy transferring reactions still take place and are similar to those observed for the detergent-solubilized proteins. Furthermore it is shown that LH1 complexes exhibit a remarkable photostability, even under ambient conditions. These findings demonstrate the possibility of interfacing a fully functional energy transferring protein complex to a conducting substrate in the presence of oxygen, with the capacity of converting light into electrical energy. Show less
Photosynthesis is the physico-chemical process by which plants, algae and photosynthetic bacteria use light energy to drive the synthesis of organic compounds. Light-induced electron transfer in... Show morePhotosynthesis is the physico-chemical process by which plants, algae and photosynthetic bacteria use light energy to drive the synthesis of organic compounds. Light-induced electron transfer in photosynthetic reaction centers (RCs) is highly efficient, having a quantum yield close to unity. In RCs of Rhodobacter (R.) sphaeroides wild type (WT), the primary electron donor is a bacteriochlorophyll a (BChl) dimer, called the Special Pair P, comprising two dimer halves PL and PM. Two additional BChl cofactors called accessory BChls (BA and BB), two bacteriopheophytins (_A and _B), two quinones and a non-heme iron are organized into two pseudo-symmetric branches named A and B. After the photo excitation the electron is transferred only via the active __A__ branch. On the other hand, in structurally similar RCs, as that of photosystem I, the electron transfer occurs equally over both branches. Neither the reason for the high efficiency nor that of the directionality of the electron transfer has been elucidated so far. To solve these questions, the solid-state photo-chemically induced nuclear polarization (photo-CIDNP) effect with its dramatic enhancement of local NMR signals provides an analytical tool especially suited for studying electron transfer in photosynthetic RCs. In fact, photo-CIDNP MAS NMR has been applied to explore electronic structures of the electron donors and acceptors in RCs Show less
Photochemically induced dynamic nuclear polarization (photo-CIDNP) is non-Boltzmann nuclear magnetization which can be observed by magic angle spinning NMR spectroscopy as enhanced absorptive or... Show morePhotochemically induced dynamic nuclear polarization (photo-CIDNP) is non-Boltzmann nuclear magnetization which can be observed by magic angle spinning NMR spectroscopy as enhanced absorptive or emissive signals. In solids, photo-CIDNP has been observed since its discovery in 1994 in various photosynthetic reaction centers. In natural photosynthetic charge separation, electron-electron interactions are fine-tuned to lead to highly efficient electron transfer. Nanosecond laser-flash photo-CIDNP magic-angle spinning NMR allows for determination of the nuclear polarizations and hyperfine interactions with atomic selectivity and with a resolution of a few microseconds. The build-up of nuclear polarization in reaction centers of Rhodobacter sphaeroides is found to depend on the presence and lifetimes of the molecular triplet states of the donor and carotenoid. Time-resolved 13C photo-CIDNP MAS NMR spectroscopy is used to map the electronic structure of the donor. In the dark state, maximum electron density is localized in the center of the special pair. In contrast, in the light state, the maximum of the electron spin density is localized at the periphery of the two cofactors. The balance of electron spin density between the two bacteriochlorophyll cofactors is shifted in favor of the L branch of the protein by the ratio of 7:3. We show that the asymmetry is induced by both geometric differences between the two cofactors and non-covalent interactions with the protein. Show less
Photosynthesis is the process through which plants and photosynthetic organisms convert solar energy into chemical energy. The fundamental primary reaction of photosynthesis is charge separation... Show morePhotosynthesis is the process through which plants and photosynthetic organisms convert solar energy into chemical energy. The fundamental primary reaction of photosynthesis is charge separation which takes place in the photosynthetic reaction centers. Among all photosynthetic reaction centers, the oxidized electron donor of photosystem II is the strongest oxidizing agent known in living nature, based on this capability, water splitting and production of atmospheric oxygen is possible. Despite decades of research, the origin of this oxidizing power is not yet fully understood. Photo-CIDNP (Photochemically induced dynamic nuclear Polarization) MAS (Magic-angle spinning) NMR proves to be a valuable technique to gain information on the primary step of photosynthesis. The work revealed advantages of the technique in the area of solid-state NMR, such as faster scanning and spectral editing by applying it to various types of photosynthetic reaction centers. In addition, studies on isotope labeled photosystems from spinach enabled to generate a model for the donor of photosystem II addressing the origin of the high redox potential. Show less
Light harvesting (LH) lies at the basis of photosynthesis, the process in which energy from the sun is stored by a photochemical reaction. The photophysics of light absorption and energy transfer... Show moreLight harvesting (LH) lies at the basis of photosynthesis, the process in which energy from the sun is stored by a photochemical reaction. The photophysics of light absorption and energy transfer is the key to a detailed understanding of the first steps in this process. This thesis describes the investigation of four types of LH systems that are expressed by bacteria, depending on light conditions. All systems have been studied by optical single-particle spectroscopy in order to eliminate the averaging effects that are typical for ensemble measurements. In this way, the spectral details of the individual systems are reveiled, allowing for a better understanding of the photodynamics that are associated with their spatial structures. Show less
