Water oxidation chemistry of photosystem II

Photosystem II (PSII) uses light energy to split water into protons, electrons and O-2. In this reaction, nature has solved the difficult chemical problem of efficient four-electron oxidation of water to yield O-2 without significant amounts of reactive intermediate species such as superoxide, hydrogen peroxide and hydroxyl radicals. In order to use nature's solution for the design of artificial catalysts that split water, it is important to understand the mechanism of the reaction. The recently published X-ray crystal structures of cyanobacterial PSII complexes provide information on the structure of the Mn and Ca ions, the redox-active tyrosine called Y-Z and the surrounding amino acids that comprise the O-2-evolving complex (OEC). The emerging structure of the OEC provides constraints on the different hypothesized mechanisms for O-2 evolution. The water oxidation mechanism of PSII is discussed in the light of biophysical and computational studies, inorganic chemistry and X-ray crystallographic information.