Mimicking the oxygen evolution center: Making a synthetic analog of plant photosynthesis is a key goal for exploiting solar energy and replacing fossil fuels. Zhang et al. synthesized a manganese-calcium cluster that looks and acts like the oxygen evolution center in photosystem II (see the Perspective by Sun). The mimic structurally resembles the biological complex, with the notable exception of bridging protein ligands and water-binding sites on a dangling Mn atom. Functionally, however, the cluster's metal center readily undergoes four redox transitions, which contribute to splitting water into oxygen. This and other synthetic mimics will pave the way for developing more efficient catalysts for artificial photosynthesis. Science , this issue p. 690 ; see also p. 635

A novel family of heteronuclear Mn^IVCa–oxido complexes containing Mn^IVCa–oxido cuboidal moieties and reactive water molecules on Ca²⁺ have been synthesized and characterized to mimic the oxygen-evolving complex (OEC) of photosystem II (PSII) in nature.

The oxygen-evolving center (OEC) in photosystem II (PSII) of plants, algae and cyanobacteria is a unique natural catalyst that splits water into electrons, protons and dioxygen. The crystallographic studies of PSII have revealed that the OEC is an asymmetric Mn₄CaO₅-cluster. The understanding of the structure-function relationship of this natural Mn₄CaO₅-cluster is impeded mainly due to the complexity of the protein environment and lack of a rational chemical model as a reference. Although it has been a great challenge for chemists to synthesize the OEC in the laboratory, significant advances have been achieved recently. Different artificial complexes have been reported, especially a series of artificial Mn₄CaO₄-clusters that closely mimic both the geometric and electronic structures of the OEC in PSII, which provides a structurally well-defined chemical model to investigate the structure-function relationship of the natural Mn₄CaO₅-cluster. The deep investigations on this artificial Mn₄CaO₄-cluster could provide new insights into the mechanism of the water-splitting reaction in natural photosynthesis and may help the development of efficient catalysts for the water-splitting reaction in artificial photosynthesis.