STUDIES ON PREPARATION OF MIMETICS FOR PHOTOSYSTEM II (PSII) IN PHOTOSYNTHESIS

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This project has been carried out in order to prepare biomimetics for photosystem II in green plants, where water is oxidized to generate dioxygen by cooperation between a tetranuclear manganese cluster (OEC, oxygen-evolving center) and light harvesting antenna chlorophylls. In this study novel manganese complexes have been prepared, characterized and estimated their functions as models for OEC. The results are summarized as follows. 1.The molecular structures of trinuclear manganese(II) complexes with tridentate Schiff base ligands have been determined by X-ray analysis. 2.Amphiphilic manganese(III) complexes with Schiff base ligands bearing both hydrophilic and hydrophobic groups have been prepared. These complexes have been found to decompose H_2O_2 effectively near at critical micelle concentration(CMC) and beyond, which can be explained in terms of concentration effect. 3.Novel dichloromanganese(IV) complexes with Schiff bases having ester groups have been found to generate dioxygen by oxidation of H_2O, which were detected by a DO meter and electrochemical measurements. However, it must be still remained to confirm ^<18>O_2 by MS measurements by using H_2^<18>O. 4.Zinc-chlorins bearing alkyl groups have been prepared and found to be soluble in water in the presence of lecithin and exhibit intense fluorescence. From these results artificial photosynthetic systems (PSII) can be created by combination between oxygen-evolving manganese complexes and Zn-chlorins.