Assignment of the μ_4-O5 atom in catalytic center for water oxidation in photosystem Ⅱ  

作　　者：WANG YaNan ZHANG ChunXi WANG Luan ZHAO JingQuan 

机构地区：[1]Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences

出　　处：《Chinese Science Bulletin》2013年第26期3213-3216,共4页

基　　金：supported by the National Natural Science Foundation of China (20973186 and 31070216) and Chinese Academy of Sciences

摘　　要：The detailed structure of catalytic center of water oxidation, Mn4Ca-cluster, in photosystem ⅡI (PSII) has been reported recently. However, due to the radiation damage induced by X-ray and the complexity of the Mn4Ca-cluster, the assignment of the μ4-O5 atom coordinated by three Mn and one Ca2+ ions is still lack of essential evidences. In this article, we synthesized one Mn complex containing two μ4-O atoms. It is found that the lengths of all μ4-O-Mn bonds in this Mn complex are in the range of 1.89-2.10 , which are significantly shorter than 2.40-2.61 distance of μ4-O5-Mn bonds in Mn4Ca-cluster observed in the crystal structure of PSII. In addition, DFT calculations have been carried out on the Mn4Ca-cluster. It is found that the O atom of μ4-O or μ4-OH always trends to deviate from the center position of four metal ions, resulting in unequal bond lengths of four μ4-4-M (M=Mn or Ca), which is obviously different with larger and nearly equal distances between μ4-O and four metal ions observed in the crystal structure. Based on these results, we suggest that the μ4-atom in Mn4Ca-cluster of PSII is unlikely to be a μ4-O, μ4-OH or μ4-OH2 , and its assignment is still an open question.The detailed structure of catalytic center of water oxidation, Mn4Ca-cluster, in photosystem II （PSII） has been reported recently. However, due to the radiation damage induced by X-ray and the complexity of the Mn4Ca-cluster, the assignment of the μ4-O5 atom coordinated by three Mn and one Ca2＋ ions is still lack of essential evidences. In this article, we synthesized one Mn complex containing two μ4-O atoms. It is found that the lengths of all μ4-O-Mn bonds in this Mn complex are in the range of 1.89-2.10 A, which are significantly shorter than 2.40--2.61 A distance of μ4-O5-Mn bonds in MnaCa-cluster observed in the crystal structure of PSII. In addition, DFT calculations have been carried out on the MnnCa-cluster. It is found that the O atom of μ4-O or μ4-OH always trends to deviate from the center position of four metal ions, resulting in unequal bond lengths of four μ4-O-M （M=Mn or Ca）, which is obviously different with larger and nearly equal distances between μ4-O and four metal ions observed in the crystal structure. Based on these results, we suggest that the μ4-atom in Mn4Ca-cluster of PSII is unlikely to be a μ4-O, μ4-on or μ4-OH2, and its assignment is still an open question.

关 键 词：光系统II 氧化催化 水氧化 原子 分配 PSII 晶体结构 金属离子 

分 类 号：O643.32[理学—物理化学]