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+ O2s

详细信息    查看全文

• 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<sup>鈥?/sup>/4H<sup>+sup> O<sub>2sub>-reduction to H<sub>2sub>O with a large catalytic rate (>10<sup>5sup> M<sup>鈥?sup> s<sup>鈥?sup>). While the heme-Cu model (FeCu) shows almost exclusive 4e<sup>鈥?/sup>/4H<sup>+sup> reduction of O<sub>2sub> to H<sub>2sub>O (detected using ring disk electrochemistry and rotating ring disk electrochemistry), when imidazole is bound to the heme (Fe(Im)Cu), this same selective O<sub>2sub>-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 O<sub>2sub>-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<sup>鈥?sup> in <sup>16sup>O<sub>2sub> (759 cm<sup>鈥?sup> in <sup>18sup>O<sub>2sub>) for the FeCu complex and at 847 cm<sup>鈥?sup> (786 cm<sup>鈥?sup>) for the Fe(Im)Cu complex, indicate the formation of side-on and end-on bridging Fe-peroxo-Cu intermediates, respectively, during O<sub>2sub>-reduction in an aqueous environment. These data suggest that side-on bridging peroxide intermediates are involved in fast and selective O<sub>2sub>-reduction in these synthetic complexes. The greater amount of H<sub>2sub>O<sub>2sub> production by the imidazole bound complex under fast electron transfer is due to 1e<sup>鈥?/sup>/1H<sup>+sup> O<sub>2sub>-reduction by the distal Cu where O<sub>2sub> binding to the water bound low spin Fe<sup>IIsup> complex is inhibited.