Quantification of short-range effects in the special pair of photosystem II: The non-conservative nature of the circular dichroism spectrum of the reaction center
Sprache des Vortragstitels:
Englisch
Original Kurzfassung:
Photosystem II is able to extract electrons from water. Although all photosynthetic reaction centers (RCs) show a similar structure, a critical difference between the RC of purple bacteria and that of PSII is that the wavefunction overlap between the two central pigments, known as special pair, is decreased in PSII-RC by a slight mutual tilt of pigment planes. Probably, this tilt contributes to the high redox potential needed for the splitting of water. We investigated the remaining short-range effects in the PSII-RC by combining QM/MM calculations for the geometry of the special pair with quantum chemical calculations and a diabatization technique to parameterize the Frenkel exciton-charge transfer state Hamiltonian of the special pair and combine it with the Hamiltonian of the whole RC to calculate otical spectra and compare with experiment. The calculations reveal that 45% of the excitonic coupling in the special pair of PSII-RCS is due to superexchange type coupling via CT states and that direct electron exchange leads to a large increase of the intrinsic (non-excitonic) circular dichroism (CD) of the special pair that explains the strong non-conservativity of the CD spectrum of PS-RCs.
Forschungs-