In the context of a global artificial photosynthesis (GAP) project, we review our current work on nature's water splitting catalyst. In a recent report (Cox et al. 2014 Science 345, 804-808 (doi:10.1126/science.1254910)), we showed that the catalyst-a Mn4O5Ca cofactor-converts into an 'activated' form immediately prior to the O-O bond formation step. This activated state, which represents an all Mn(IV) complex, is similar to the structure observed by X-ray crystallography but requires the coordination of an additional water molecule. Such a structure locates two oxygens, both derived from water, in close proximity, which probably come together to form the product O2 molecule. We speculate that formation of the activated catalyst state requires inherent structural flexibility. These features represent new design criteria for the development of biomimetic and bioinspired model systems for water splitting catalysts using first-row transition metals with the aim of delivering globally deployable artificial photosynthesis technologies.
Keywords: H2 production; photosynthesis; photosystem II; water splitting.