Models of the oxygen-evolving complex of photosystem II

Abstract

Structural and mechanistic understanding of the biol. site of water oxidn.-the oxygen-evolving complex (OEC) of photosystem II-has gradually developed over the last 30 years based on the highly collaborative work of biochemists, biophysicists, spectroscopists, inorg. chemists and computational chemists, culminating in the current proposal: a Mn_4CaO_5 heterometallic cluster, proposed to contain a Mn-_3CaO_4 cubane / open cubane unit with a fourth, dangling Mn bridged to the cubane through two oxido ligands. Our group joined this collaborative tradition in aims to synthesize accurate Mn_4Ca models. In past work we synthesized a Mn_3CaO_4 cubane supported by three acetates and a 1,3,5-triarylbenzene framework contg. six pyridines and three alkoxides. More recently, incorporation of a fifth metal center has been targeted to complete the Mn_4Ca stoichiometry. A desymmetrized Mn_3CaO_4 complex has been made with reactivity complementary to the parent, sym. complex; synthetic strategies from this desymmetrized complex toward more accurate Mn_4Ca models of the OEC will be discussed. Redox and acid/base reactivity will also be discussed, as both are relevant to the mechanism of water oxidn.