Nucleophilic Attack of Hydroxide on a Mn~v Oxo Complex: A Model of the O-O Bond Formation in the Oxygen Evolving Complex of Photosystem II

摘要

In photosynthesis by green plants, water is the source of the electrons that are finally used to convert carbon dioxide into biomass. In this process, which takes place in the oxygen evolving complex (OEC) of photosystem II, water is oxidized to molecular oxygen. The catalytic center of the OEC consists of a tetranuclear manganese cluster. Despite numerous experimental and theoretical model studies, the actual mechanism for the formation of molecular oxygen is not clear.rnIn principle, three different mechanisms have been suggested for the formation of the O-O bond: (a) nucleophilic attack of water or hydroxide on a formally Mn~V species, (b) radical coupling of two Mn~V oxo species, and (c) radical coupling of water (or hydroxide) with a bridging oxygen in the manganese cluster.