Sulfur K-Edge X-ray Absorption Spectroscopy and Density Functional Theory Calculations on Monooxo MoIV and Bisoxo MoVI Bis-dithiolenes: Insights into the Mechanism of Oxo Transfe

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• 作者：Yang Ha ; Adam L. Tenderholt ; Richard H. Holm ; Britt Hedman ; Keith O. Hodgson ; Edward I. Solomon
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：June 25, 2014
• 年：2014
• 卷：136
• 期：25
• 页码：9094-9105
• 全文大小：689K
• ISSN：1520-5126

文摘

Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations have been used to determine the electronic structures of two complexes [Mo^IVO(bdt)₂]^{2鈥?/sup> and [MoVIO₂(bdt)₂]2鈥?/sup> (bdt = benzene-1,2-dithiolate(2鈭?) that relate to the reduced and oxidized forms of sulfite oxidase (SO). These are compared with those of previously studied dimethyl sulfoxide reductase (DMSOr) models. DFT calculations supported by the data are extended to evaluate the reaction coordinate for oxo transfer to a phosphite ester substrate. Three possible transition states are found with the one at lowest energy, stabilized by a P鈥揝 interaction, in good agreement with experimental kinetics data. Comparison of both oxo transfer reactions shows that in DMSOr, where the oxo is transferred from the substrate to the metal ion, the oxo transfer induces electron transfer, while in SO, where the oxo transfer is from the metal site to the substrate, the electron transfer initiates oxo transfer. This difference in reactivity is related to the difference in frontier molecular orbitals (FMO) of the metal鈥搊xo and substrate鈥搊xo bonds. Finally, these experimentally related calculations are extended to oxo transfer by sulfite oxidase. The presence of only one dithiolene at the enzyme active site selectively activates the equatorial oxo for transfer, and allows facile structural reorganization during turnover.}