Photosynthesis in plants, algae and cyanobacteria releases oxygen and is referred to as oxygenic photosynthesis. Among all the photosynthetic reaction centers only PSII provides a redox potential... Show morePhotosynthesis in plants, algae and cyanobacteria releases oxygen and is referred to as oxygenic photosynthesis. Among all the photosynthetic reaction centers only PSII provides a redox potential sufficiently strong for water oxidation. While the electron flow in PSII is strictly asymmetric, in PSI different levels of bidirectionality indicate functional flexibility of this complex. Photo-CIDNP is non-Boltzmann nuclear magnetization caused by photochemical reactions and can be observed by NMR spectroscopy as strongly enhanced absorptive or emissive signals. In this thesis photo-CIDNP solid state NMR with selective isotope labeling is applied to get direct access to the heart of large PSII and PSI photosynthetic complexes in intact and isolated systems of Spirodela oligorrhiza and Synechocyctis. For the first time the direct observation of selective atoms within the heart of the PSII and PSI complexes by experiment s on entire plants and whole cells is reported. In this way the conservation of the electronic structure of the PSII electron donor at various levels of biological preparations have been addressed and the electron spin density (ρi) in the active cofactors of PSI has been constructed. In addition the functional heterogeneity of the PSI electron donor among different plant species was probed. Show less
Photosynthetic reaction centers (RCs) from plants, heliobacteria and green sulphur bacteria has been investigated with photochemically induced dynamic nuclear polarization (photo-CIDNP) MAS NMR. In... Show morePhotosynthetic reaction centers (RCs) from plants, heliobacteria and green sulphur bacteria has been investigated with photochemically induced dynamic nuclear polarization (photo-CIDNP) MAS NMR. In photosystem (PS) I of spinach, all signals appear negative which is proposed by a predominance of the three spin mixing (TSM) over the differential decay (DD) mechanism. There are contrasting magnetic-field dependence of photo-CIDNP of PSI and PSII. For PSII the optimal NMR enhancement factor of ~5000 is observed at 4.7 T, while the strongest light-induced signals of PSI are at 9.4 T. The simulations indicate that difference between bacterial RCs and plant PS I can be due to an increase of the exchange coupling between the donor and acceptor radicals. In the RCs of Chlorobium tepidum the spectra appear negative and can be tentatively assigned to two bacterio chlorophyll a molecules of the donor. The spectral pattern obtained from membrane fragments of Heliobacillus mobilis at 4.7 T, appear to be both positive and negative, which is similar to the pattern observed in the RCs of plant PSII and RCs of Rhodobacter sphaeroides R-26. However, unlike the other RCs, in this system, at 17.6 T, the positive signals undergo a sign change and appear negative. 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
