title: Homogeneous catalytic O2 reduction to water by a cytochrome c oxidase model with trapping of intermediates and mechanistic insights.
abstract: An efficient and selective four-electron plus four-proton (4e(-)/4H(+)) reduction of O(2) to water by decamethylferrocene and trifluoroacetic acid can be catalyzed by a synthetic analog of the heme a(3)/Cu(B) site in cytochrome c oxidase ((6)LFeCu) or its Cu-free version ((6)LFe) in acetone. A detailed mechanistic-kinetic study on the homogeneous catalytic system reveals spectroscopically detectable intermediates and that the rate-determining step changes from the O(2)-binding process at 25 °C room temperature (RT) to the O-O bond cleavage of a newly observed Fe(III)-OOH species at lower temperature (-60 °C). At RT, the rate of O(2)-binding to (6)LFeCu is significantly faster than that for (6)LFe, whereas the rates of the O-O bond cleavage of the Fe(III)-OOH species observed (-60 °C) with either the (6)LFeCu or (6)LFe catalyst are nearly the same. Thus, the role of the Cu ion is to assist the heme and lead to faster O(2)-binding at RT. However, the proximate Cu ion has no effect on the O-O bond cleavage of the Fe(III)-OOH species at low temperature.
authors.affiliation: Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Zakaria
authors.initials: Z
authors.lastname: Halime
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kotani
authors.forename: Yuqi
authors.initials: Y
authors.lastname: Li
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Karlin
mesh_terms: D055162:Biocatalysis; D001696:Biomechanical Phenomena; D003576:Electron Transport Complex IV / Q000378:metabolism*; D004583:Electrons; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D003576:Electron Transport Complex IV; D010100:Oxygen