Single-turnover intermolecular reaction between a Fe(III)-superoxide-Cu(I) cytochrome c oxidase model and exogeneous Tyr244 mimics.

An Fe(III)-superoxide-Cu(I) cytochrome c oxidase model reacts intermolecularly with hindered phenols leading to phenoxyl radicals, as was observed in the enzyme and evidence for the formation of an Fe(IV)-oxo is presented.

Synthesis and characterization of Rh(III) corroles: unusual reactivity patterns observed during metalation reactions.

A new approach to the synthesis of Rh(III) corrole complexes is developed and an unusual activation of C-C and C-N bonds is disclosed.

Electrocatalytic reduction of ROOH by iron porphyrins.

Electrocatalytic reduction of a series of chemical oxidants of different power (tert-butyl hydroperoxide, potassium peroxomonosulfate, peracetic acid, and m-chloroperbenzoic acid) at iron-porphyrin-modified graphite electrodes is studied in buffered aqueous solutions by rotating disk and ring-disk voltammetry. Both ferric and ferrous porphyrins are catalytically active. Turnover of ferric catalysts is slower than that of the ferrous analogues and involves competing catalytic reduction and disproportionation.

Spectroscopic evidence for a heme-superoxide/Cu(I) intermediate in a functional model of cytochrome c oxidase.

A superstructured tetraphenylporphyrin with a covalently attached proximal imidazole axial base and three distal imidazole pickets has been developed as a model for the active site of terminal oxidases such as cytochrome c oxidase. The oxygen adduct of the Fe-only heme (at low temperature) has a diamagnetic NMR and is EPR silent, which taken together with a resonance Raman oxygen isotope sensitive band (nuFe-O) at 575/554 cm-1 (16O2/18O2) indicates formation of a six-coordinate heme-superoxide complex. Unexpectedly, the Fe/Cu complex, where the copper is in a trisimidazole environment approximately 5 A above the heme plane, displays similar characteristics: a diamagnetic NMR, EPR silence, and nuFe-O at 570/544 cm-1.

Nonideal electrochemical behavior of biomimetic iron porphyrins: interfacial potential distribution across multilayer films.

The electrochemical behavior of multilayer films formed by iron porphyrins deposited on an edge plane graphite electrode has been examined under anaerobic conditions. In the scan rate interval (1-250 mV/s) where the electrode reaction is reversible, CV diagrams of these films demonstrate substantial deviations from ideality in broadening and separation of the peaks. A model that describes the observed behavior is proposed by taking into account the potential distribution at the electrode/film interface and the concentration dependence of surface activity coefficients.

Distal metal effects in cobalt porphyrins related to CcO.

Cobalt(II) porphyrins were studied to determine the influence of distal site metalation and superstructure upon dioxygen reactivity in active site models of cytochrome c oxidase (CcO). Monometallic, Co(II)(P) complexes when ligated by an axial imidazole react with dioxygen to form reversible Co-superoxide adducts, which were characterized by EPR and resonance Raman (RR). Unexpectedly, certain Co porphyrins with Cu(I) metalated imidazole pickets do not form mu-peroxo Co(III)/Cu(II) products even though the calculated intermetallic distance suggests this is possible.

Functional analogues of the dioxygen reduction site in cytochrome oxidase: mechanistic aspects and possible effects of Cu(B).

Catalytic reduction of O(2) and H(2)O(2) by new synthetic analogues of the heme/Cu site in cytochrome c and ubiquinol oxidases has been studied in aqueous buffers. Among the synthetic porphyrins yet reported, those employed in this study most faithfully mimic the immediate coordination environment of the Fe/Cu core. Under physiologically relevant conditions, these biomimetic catalysts reproduce key aspects of the O(2) and H(2)O(2) chemistry of the enzyme.

Electrochemical metalloporphyrin-catalyzed reduction of chlorite.

We measured the redox stoichiometry and rate constants for the electrochemical reduction of ClO(2)(-) at pH 7, catalyzed by a series of metalloporphyrins of Mn, Fe, and Co with different proximal and distal environments. A clean four-electron reduction was observed. The catalytic activity correlates well with that observed in reduction of H(2)O(2).

Biomimetic studies of terminal oxidases: trisimidazole picket metalloporphyrins.

Three biomimetic models for the binuclear Fe/Cu (heme/trisimidazole) active site of terminal oxidases, such as cytochrome c oxidase and related enzymes, have been prepared. Based upon a tetrakis(aminophenyl)porphyrin core, these models possess a single covalently linked imidazole-bearing tail on one side of the porphyrin and three imidazole "pickets" on the opposite side of the porphyrin ring. Three different imidazole picket motifs are characterized in free base, Fe, Zn, Fe/Cu, and Zn/Cu forms.