Concerted bond switching mechanism coupled with one-electron transfer for the oxygen-oxygen bond formation in the oxygen-evolving complex of photosystem II

Abstract

We here precisely analyzed the electronic structures during the oxygen-oxygen (O-O) bond formation of the oxygen-evolving complex (OEC) in photosystem II (PSII) based on the quantum mechanics/molecular mechanics (QM/MM) calculations. Changes in the spin density and the chemical indices derived from the natural orbitals suggested that the O(5)-O(6) bond formation proceeds with a concerted bond breaking of the Mn4-O(5) coupled with the through-bond one-electron transfer from the O(6) site to the Mn4 site (Mn4(IV) → Mn4(III)). This mechanism can be best described as a Concerted Bond Switching (CBS) mechanism, which is a non-radical reaction of the O(5)-O(6) bond formation.