Artificial Mimicking Of The Water-splitting Catalytic Center In Photosynthesis

The oxygen-evolving center(OEC)in photosystem II(PSII)of photosynthetic biology is the unique biological catalyst,which utilizes solar energy to split thermodynamically stable water efficiently and safely,releasing oxygen,electrons and protons.The mimicking of the structure and function of the OEC is of great scientific significance for understanding its natural principle,which is also significantly important for potential application in artificial photosynthesis in future.Recently,the structure of biological OEC has been revealed.OEC core is composed by four Mn and one Ca ions bridged by five ?-O,forming an asymmetric Mn4CaO5-cluster.The peripheral ligands of the OEC consist of six carboxyl groups,one imidazole and four water molecules.This structure provides a blueprint for the synthesis of artificial water-splitting catalysts.Based on previous work on water-splitting catalysts from our group in both natural photosynthesis and artificial photosynthesis,we have carried out further investigations and got following results:i)Two novel compounds containing Mn4-clusters have been synthesized.Their structures,redox properties and catalytic properties were characterized.Compared with the structure and properties of previous Mn4Ca-cluster reported recently,we could conclude that Ca ion may play key roles to stabilize the high valence manganese ions in the Mn4Ca-cluster.Therefore,these two new compounds may act as good reference model to study both natural and artificial Mn4Ca-cluster in future.ii)Two Mn2YO compounds containing rare earth metal yttrium ion,have been prepared.Their structures and catalytic capability have been characterized,which provides useful clue for the synthesis of artificial OEC containing rare earth ions in future.iii)One Mn6Dy2O9 compound has been synthesized for the first time,and its structure and spectral properties were characterized.The Mn6Dy2O9-cluster in this compound is very similar to the Mn6Ca2O9-cluster reported recently.This work provides important information to synthesize the artificial water-splitting catalyst containing lanthanide elements in future.iv)From the synthetic system of the artificial Mn4Ca-cluster,we have isolated four new compounds:MngO9OH(ButCO2)11(C5H5N)2,Mn4O2(ButCO2)8(C5H5N)2,Mn6O2(ButCO2)10 and Mn(ButCO2)4·(Bun4N).Among of them,the high reactive species,the four-coordinated Mn(?)complex,has never been reported in literatures.The isolation of these new complexes provides important clue to understand the synthetic mechanism of the Mn4Ca-cluster reported recently,and also provides experimental evidence to optimize the artificial water-splitting catalyst in future.