Role of the Photosystem II as an Environment in the Oxidation Free Energy of the Mn Cluster from S1 to S2

Hideaki Takahashi, Daiki Suzuoka, Shun Sakuraba, Akihiro Morita

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

The manganese cluster (CaMn4O5) in the photosystem II (PSII) is the reaction center of the light-driven oxidation reaction, which generates the molecular oxygen. In this paper, we address the issue of the effect of the environment on the free energy associated with the oxidation of the Mn cluster in S1 state by conducting the large-scale quantum mechanical/molecular mechanical simulations, which involve the whole of the PSII monomer. It was found by the simulations at the level of the B3LYP functional that the environment surrounding the Mn cluster reduces the vertical oxidation free energy δμvrt by 64.8 kcal/mol. A decomposition analysis of the free energy δμvrt revealed that the system composed of peptide chains, ligands, lipids, and potassium ions contributes to lowering of δμvrt by -98.0 kcal/mol, whereas the solvent water makes an opposite contribution of 38.9 kcal/mol. Reduction of the vertical oxidation free energy directly leads to the lowering of the activation free energy δGac for the electron transfer reaction from the Mn cluster in S1 state to the neighboring Tyrz+. Consequently, the electron transfer rate was found to be enhanced by a factor of 1012 by virtue of the influence of the environment.

Original languageEnglish
Pages (from-to)7081-7091
Number of pages11
JournalJournal of Physical Chemistry B
Volume123
Issue number33
DOIs
Publication statusPublished - 2019 Aug 22

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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