Mimicking the Mn4CaO5-Cluster in Photosystem II

Abstract

The oxygen-evolving center (OEC) in photosystem II (PSII) is a unique biocatalyst that splits water into electrons, protons, and dioxygen. Recent crystallographic studies of PSII have revealed that the structure of the OEC is an asymmetric Mn4CaO5-cluster, while the detailed mechanism for the O=O bond formation is still elusive mainly due to the complexity of the large protein environment and structural uncertainty of the OEC during the catalytic reaction. To understand the structure-function relationship and the catalytic mechanism of this natural Mn4CaO5-cluster, as well as to develop efficient man-made water-splitting catalysts in artificial photosynthesis, precise mimics of the OEC are highly required. It is of a great challenge to precisely mimic the structure and function of the OEC in the laboratory. However significant advances have recently been achieved. One of the most important advances is the synthesis of a series of the artificial Mn4CaO4-clusters that closely mimics both the geometric and electronic structures of the OEC, which provides a structurally well-defined chemical model to investigate the structure-function relationship of the natural Mn4CaO5-cluster, and sheds new insights into the mechanism of the water-splitting reaction in PSII. The artificial Mn4CaO4-cluster and its variants may open new avenues to develop efficient artificial catalysts for the water-splitting reaction by using earth-abundant and nontoxic chemical elements in the future.