Modeling Near-Edge Fine Structure X-ray Spectra of the Manganese Catalytic Site for Water Oxidation in Photosystem II
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- 作者：Barbara Brena ; Per E. M. Siegbahn ; Hans 脜gren
- 刊名：The Journal of the American Chemical Society
- 出版年：2012
- 出版时间：October 17, 2012
- 年：2012
- 卷：134
- 期：41
- 页码：17157-17167
- 全文大小：461K
- 年卷期：v.134,no.41(October 17, 2012)
- ISSN：1520-5126
文摘
The Mn 1s near-edge absorption fine structure (NEXAFS) has been computed by means of transition-state gradient-corrected density functional theory (DFT) on four Mn4Ca clusters modeling the successive S0 to S3 steps of the oxygen-evolving complex (OEC) in photosystem II (PSII). The model clusters were obtained from a previous theoretical study where they were determined by energy minimization. They are composed of Mn(III) and Mn(IV) atoms, progressing from Mn(III)3Mn(IV) for S0 to Mn(III)2Mn(IV)2 for S1 to Mn(III)Mn(IV)3 for S2 to Mn(IV)4 for S3, implying an Mn-centered oxidation during each step of the photosynthetic oxygen evolution. The DFT simulations of the Mn 1s absorption edge reproduce the experimentally measured curves quite well. By the half-height method, the theoretical IPEs are shifted by 0.93 eV for the S0 鈫?S1 transition, by 1.43 eV for the S1 鈫?S2 transition, and by 0.63 eV for the S2 鈫?S3 transition. The inflection point energy (IPE) shifts depend strongly on the method used to determine them, and the most interesting result is that the present clusters reproduce the shift in the S2 鈫?S3 transition obtained by both the half-height and second-derivative methods, thus giving strong support to the previously suggested structures and assignments.