Protonation structure of the photosynthetic water oxidizing complex in the S0state as revealed by normal mode analysis using quantum mechanics/molecular mechanics calculations

Masao Yamamoto, Shin Nakamura, Takumi Noguchi

研究成果: Contribution to journalArticle査読

4 被引用数 (Scopus)

抄録

Photosynthetic water oxidation takes place through the light-driven cycle of five intermediates (S0-S4) of the water oxidizing complex (WOC), which consists of the Mn4CaO5 cluster and surrounding amino acid residues in photosystem II. Clarifying the protonation structures of the Mn4CaO5 cluster and its water ligands (W1-W4) is essential for understanding the molecular mechanism of water oxidation. Here, we performed normal mode analysis of WOC in the S0 and S1 states using quantum mechanics/molecular mechanics calculations and simulated an S1-minus-S0 infrared difference spectrum focusing on the symmetric COO- stretching (νsCOO-) region. The calculated spectrum by an S0 model, in which O4 of the Mn4CaO5 cluster is protonated and W2 is H2O, and a corresponding S1 state with deprotonated O4 best reproduced the νsCOO- features of the experimental spectrum, whereas models with protonated O5 showed poor agreement. In addition, comparison of the calculated coordination distances of the water ligands with the experimental data by X-ray diffraction analysis indicates that W2 is most probably not OH- but H2O both in the S0 and S1 states. The present calculations thus strongly suggest that the S0 state has a protonation structure of O4-H and W2 = H2O. The O4-H structure in the S0 state supports the view that this proton is released through the O4-water chain immediately after electron transfer during the S0 → S1 transition.

本文言語英語
ページ(範囲)24213-24225
ページ数13
ジャーナルPhysical Chemistry Chemical Physics
22
42
DOI
出版ステータス出版済み - 11 14 2020
外部発表はい

All Science Journal Classification (ASJC) codes

  • 物理学および天文学(全般)
  • 物理化学および理論化学

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