Electrocatalytic O2-Reduction by Synthetic Cytochrome c Oxidase Mimics: Identification of a 鈥淏ridging Peroxo鈥?Intermediate Involved in Facile 4e鈥?/sup>/4H+ O2
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- 作者：Sudipta Chatterjee ; Kushal Sengupta ; Shabnam Hematian ; Kenneth D. Karlin ; Abhishek Dey
- 刊名：Journal of the American Chemical Society
- 出版年：2015
- 出版时间：October 14, 2015
- 年：2015
- 卷：137
- 期：40
- 页码：12897-12905
- 全文大小：664K
- ISSN：1520-5126
文摘
A synthetic heme鈥揅u CcO model complex shows selective and highly efficient electrocatalytic 4e鈥?/sup>/4H+ O2-reduction to H2O with a large catalytic rate (>105 M鈥? s鈥?). While the heme-Cu model (FeCu) shows almost exclusive 4e鈥?/sup>/4H+ reduction of O2 to H2O (detected using ring disk electrochemistry and rotating ring disk electrochemistry), when imidazole is bound to the heme (Fe(Im)Cu), this same selective O2-reduction to water occurs only under slow electron fluxes. Surface enhanced resonance Raman spectroscopy coupled to dynamic electrochemistry data suggests the formation of a bridging peroxide intermediate during O2-reduction by both complexes under steady state reaction conditions, indicating that O鈥揙 bond heterolysis is likely to be the rate-determining step (RDS) at the mass transfer limited region. The O鈥揙 vibrational frequencies at 819 cm鈥? in 16O2 (759 cm鈥? in 18O2) for the FeCu complex and at 847 cm鈥? (786 cm鈥?) for the Fe(Im)Cu complex, indicate the formation of side-on and end-on bridging Fe-peroxo-Cu intermediates, respectively, during O2-reduction in an aqueous environment. These data suggest that side-on bridging peroxide intermediates are involved in fast and selective O2-reduction in these synthetic complexes. The greater amount of H2O2 production by the imidazole bound complex under fast electron transfer is due to 1e鈥?/sup>/1H+ O2-reduction by the distal Cu where O2 binding to the water bound low spin FeII complex is inhibited.