Cytochrome C oxidase
Hyosul Shin, Dong-Heon Lee, Chan Kang, Kenneth D. Karlin, Electrocatalytic four-electron reductions of O2 to H2O with cytochrome c oxidase model compounds, Electrochimica Acta, Volume 48, Issue 27, 30 November 2003, Pages 4077-4082, ISSN 0013-4686, http://dx.doi.org/10.1016/S0013-4686(03)00565-6
Abstract: Three different complexes, heme–Cu ([(6L)FeIICuI]+ (1), 6L=a binucleating ligand having a heme and covalently tethered copper binding tris(2-pyridyl)methylamine tetradentate moiety), heme complex ((6L)FeII (4), (with “empty” tethered chelate)), and the “parent” iron-porphyrinate ((F8TPP)FeII (5), F8TPP=tetrakis(2,6-difluorophenyl)porphyrinate) were employed for the electrocatalytic reduction of O2. Complexes 1 and 4 reduce O2 to water (four-electron reduction) with good efficiency (74 and 59%, respectively), but complex 5 exhibited only an ∼20% efficiency, thus primarily the two-electron reduction to hydrogen peroxide occurred. The results of the present electrochemical O2-reduction studies and the previous studies have elucidated the O2-binding nature of these three complexes, indicating the formation of quite stable FeIII(O22−)CuII (peroxo) or FeIIIO2− (superoxo) species. In line with the thinking of other researchers, the fact that both 1 and 4 can well stabilize FeIIIO2− superoxo species may suggest that the formation of the latter is a key to the pathway favoring four-electron reduction of dioxygen to water.
Keywords: Oxygen reduction; Copper–heme complex; Model compounds; Catalysis; Graphite electrodes