Theoretical elucidation of the Si(i=0-3) intermediates and transition state (S4) in the Kok cycle for photosynthetic water oxidation; comparisons with the serial femtosecond crystallography (SFX)
K. Yamaguchia,b, M. Shojic, H. Isobed, K. Miyagawab, T. Kawakamib,e and T. Nakajimab
a Riken Center for Computational Science (R-CCS), Kobe, Hyogo, 659-0047, Japan,
b The Institute for Scientific and Industrial Research, Osaka University, Japan,
c Center of Computational Sciences, Tsukuba University, Tsukuba, Ibaraki, Japan,
d Research Institute for Interdisciplinary Science, Okayama University, Japan,
e Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
Abstract
Large-scale quantum-mechanics (QM)1 and QM/molecular mechanics (MM)2 calculations were performed for theoretical elucidation of the intermediates in the Si (i=0-3) states and the transition state (S4) of the Kok cycle for water oxidation in the oxygen evolving complex (OEC) of photosystem II (PSII). Fully optimized geometrical structures of the CaMn4Ox (x=5, 6) clusters in the Si (i=0-3) states by the QM1 and QM/MM2 were compared with recent experimental results by the serial femtosecond crystallography (SFX) at about 2.1 Å resolution.3 The computational results by the QM1 and QM/MM2 were found to be wholly compatible with the experiments by SFX3, providing the whole Kok cycle involving the S4 state responsible for the Ca(II)-assisted concerted bond switching (CBS) process4,5 for the O-O bond formation of water oxidation reaction in OEC of PSII.
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