Orbital tuning of electron donor in photosystem II: A combined photo-CIDNP MAS NMR and theoretical study

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The photosynthetic reaction center (RC) of Photosystem II (PS2) of plants allows for light-driven electron transfer (ET) with quantum efficiency close to unit. The oxidation potential of up to 1.4V, necessary for water oxidation, is the highest in living nature. The cofactor arrangement in the PS2 RC shows a strong similarity to that found in bacterial RCs of purple bacteria but the operational mechanism is clearly distinguished. The origin of the exceptional high redox potential, the orbital architecture and the role of the protein matrix are still not entirely understood. Here we aim to understand the factors controlling orbital energies. Advanced photochemically induced dynamic nuclear polarization (photo-CIDNP) magic-angle spinning (MAS) NMR methods will be applied to study the cofactors and their environment with atomic resolution. Local electronic structures and local mobility will be obtained. Experimental results will be interpreted in close collaboration with theoretical modelling by methods employing density functional theory (DFT), both in the Kohn-Sham and in the subsystem DFT variant. Concepts on the electronic architecture and control will inspire artificial photosynthesis.