title: Electrocatalytic O2-Reduction by Synthetic Cytochrome c Oxidase Mimics: Identification of a "Bridging Peroxo" Intermediate Involved in Facile 4e(-)/4H(+) O2-Reduction.
abstract: A synthetic heme-Cu CcO model complex shows selective and highly efficient electrocatalytic 4e(-)/4H(+) O2-reduction to H2O with a large catalytic rate (>10(5) M(-1) s(-1)). While the heme-Cu model (FeCu) shows almost exclusive 4e(-)/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-O bond heterolysis is likely to be the rate-determining step (RDS) at the mass transfer limited region. The O-O vibrational frequencies at 819 cm(-1) in (16)O2 (759 cm(-1) in (18)O2) for the FeCu complex and at 847 cm(-1) (786 cm(-1)) 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(-)/1H(+) O2-reduction by the distal Cu where O2 binding to the water bound low spin Fe(II) complex is inhibited.
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science , Jadavpur, Kolkata 700032, India.
authors.forename: Sudipta
authors.initials: S
authors.lastname: Chatterjee
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science , Jadavpur, Kolkata 700032, India.
authors.forename: Kushal
authors.initials: K
authors.lastname: Sengupta
authors.affiliation: Department of Chemistry, Johns Hopkins University , Baltimore, Maryland 21218, United States.
authors.forename: Shabnam
authors.initials: S
authors.lastname: Hematian
authors.affiliation: Department of Chemistry, Johns Hopkins University , Baltimore, Maryland 21218, United States.
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Karlin
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science , Jadavpur, Kolkata 700032, India.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Dey
mesh_terms: D002384:Catalysis; D003576:Electron Transport Complex IV / Q000737:chemistry*; D018716:Molecular Mimicry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*
chemical_list: D003576:Electron Transport Complex IV; D010100:Oxygen