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Theory of chemical bonds in metalloenzymes. XVII. Symmetry breaking in manganese cluster structures and chameleonic mechanisms for the OO bond formation of water splitting reaction
Author(s) -
Saito Toru,
Shoji Mitsuo,
Kanda Keita,
Isobe Hiroshi,
Yamanaka Shusuke,
Kitagawa Yasutaka,
Yamada Satoru,
Kawakami Takashi,
Okumura Mitsutaka,
Yamaguchi Kizashi
Publication year - 2012
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.23255
Subject(s) - diradical , chemistry , singlet state , symmetry breaking , triplet state , electron transfer , chemical physics , photochemistry , computational chemistry , molecule , excited state , atomic physics , physics , organic chemistry , quantum mechanics
Abstract Symmetry breaking in cluster structures of manganese oxides by doping of Ca(II) ion is examined in relation to chameleonic mechanisms of water splitting reaction. The orbital and spin correlation diagrams have been depicted to clarify one‐electron transfer and electron‐pair transfer mechanisms for the reaction. The spin‐polarized molecular orbital models have been applied to elucidate correspondence between magnetic‐coupling mode and reaction mechanism of the oxygen–oxygen (OO) bond formation and oxygen evolution catalyzed by multicenter Ca(II) manganese oxides and related systems. The present UB3LYP calculations followed by the natural orbital analyses have been performed to elucidate electronic structures of the key intermediates and the transition state structure for the OO bond formation. The results indicate that the reaction proceeds through the continuous diradicaloid mechanism without discreet free radical fragments and/or electron‐pair transfer mechanism induced by symmetry breaking with Ca(II) in the pure low‐spin singlet state. The computational results are compatible with local singlet and triplet diradical‐coupling mechanisms for the OO bond formation in the low‐ and high‐spin states, respectively. Thus, magnetic (exchange) coupling modes in the oxygen evolution complex are directly related to the local singlet and triplet diradical mechanisms as in the case of soluble methane monooxygenase. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012