Theory of chemical bonds in metalloenzymes XX: Magneto-structural correlations in the CaMn4O5 cluster in oxygen-evolving complex of photosystem II

K. Yamaguchi, Hiroshi Isobe, M. Shoji, S. Yamanaka, M. Okumura

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13 Citations (Scopus)

Abstract

Magneto-structural correlations in oxygen-evolving complex (OEC) of photosystem II (PSII) have been elucidated on the basis of theoretical and computational results in combination with available electron paramagnetic resonance (EPR) experimental results, and extended x-ray absorption fine structure (EXAFS) and x-ray diffraction (XRD) results. To this end, the computational methods based on broken-symmetry (BS) UB3LYP solutions have been developed to elucidate magnetic interactions in the active manganese catalyst for water oxidation by sunlight. The effective exchange interactions J for the CaMn(III)Mn(IV)3O5(H2O)3Y(Y = H2O or OH-) cluster (1) model of OEC of PSII have been calculated by the generalised approximate spin projection (GAP) method that eliminates the spin contamination errors of the BS UB3LYP solution. Full geometry optimisations followed by the zero-point energy (ZPE) correction have been performed for all the spin configurations of 1 to improve the J values that are compared with accumulated EPR in the S2 state of Kok cycle and magnetic susceptibility results of Christou model complex Ca2Mn(IV) 3O4 (2). Using the calculated J values, exact diagonalisation of the spin Hamiltonian matrix has been carried out to obtain excitation energies and spin densities of the ground and lower excited states of 1. The calculated excitation energies are consistent with the available experimental results. The calculated spin densities (projection factors) are also compatible with those of the EPR results. The calculated spin densities have been used to calculate the isotropic hyperfine (Aiso) constants of 55Mn ions revealed by the EPR experiments. Implications of the computational results are discussed in relation to the structural symmetry breaking (SSB) in the S1, S2 and S3 states, spin crossover phenomenon induced by the near-infrared excitation and the right- and left-handed scenarios for the O-O bond formation for water oxidation.

Original languageEnglish
Pages (from-to)519-546
Number of pages28
JournalMolecular Physics
Volume114
Issue number3-4
DOIs
Publication statusPublished - Feb 16 2016

Keywords

  • BS UB3LYP
  • magneto-structural correlations
  • oxygen-evolving complex
  • PSII
  • spin Hamiltonian model

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Condensed Matter Physics
  • Biophysics
  • Molecular Biology

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