One-electron oxidation of vinylidene-carbene complexes of iron porphyrins. Isolation of complexes spectrally analogous to catalase and horseradish peroxidase compounds I

Further Studies on the Oxidation State of Iron in μ-Oxo Dimeric Phthalocyanine Complexes

The reaction with sodium cyanide of the μ-oxo-bridged complex of tetra-4-tert-butyl-substituted iron phthalocyanine (form ‘690’) and that of the product of its treatment with organic bases such as Py, Im, etc. (form ‘627’) result in the formation of the same ferrous bis-cyanide complex Na 2[ Pc t Fe II ( CN )2] which can be readily oxidized to the analogous ferric complex Na [ Pc t Fe III ( CN )2]. Form ‘690’ has been oxidized to the corresponding ferric μ-oxo complex (form ‘630’). Data for all μ-oxo-bridged complexes (chemical behavior; electronic, NMR, Mössbauer, X-ray photoelectron and ESR spectra; magnetic susceptibility) are discussed, and based on them, the following structures are proposed: ( HPc t Fe II )2 O (form ‘690’), H 2[( LPc t Fe II )2 O ] (form ‘627’) and ( Pc t Fe III )2 O (form ‘630’).

Biodehalogenation: reactions of cytochrome P-450 with polyhalomethanes

The products, stoichiometry, and kinetics of the oxidation of the enzyme cytochrome P-450 cam by five polyhalomethanes and chloronitromethane are described. The reactivity of the enzyme is compared with that of deuteroheme and with the enzyme in its native cell, Pseudomonas putida (PpG-786). In all cases, the reaction entails hydrogenolysis of the carbon-halogen bond: 2FeIIP + RCXn----2FeIIIP + RCHXn-1 (P = porphyrin or P-450 cam in vitro and in vivo). Trichloronitromethane was the fastest reacting substrate, and chloroform was the slowest. The results establish that P. putida is a valid whole cell model for the reductase activity of the P-450 complement in these reactions. The reactions of cytochrome P-450 with polyhaloalkanes proceed in a manner quite analogous to other iron(II) proteins in the G conformation. The chemistry observed for the enzyme parallels that of its iron(II) porphyrin active site. Iron-bonded carbenes are not intermediates, and hydrolytically stable iron alkyls are not products of these reactions.

Evidence for heme pi cation radical species in compound I of horseradish peroxidase and catalase

Magnetic circular dichroism spectra are reported for the compound I species of beef liver catalase (hydrogen-peroxide: hydrogen-peroxide oxidoreductase, EC 1.11.1.6) and horseradish peroxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) and the pi cation radical derivatives of porphyrins that have been suggested as models of the electronic configuration of the heme in the compound I species of these enzymes. Comparison of the magnetic circular dichroism spectra of the compound I species with the spectra of [Co(octaethylporphyrin)]2Br and [Co(octaethylporphyrin)]2ClO4 indicates that in both the intermediate enzyme species the heme has been oxidized to a pi cation radical. While there is a clear distinction between the magnetic circular dichroism spectra of the 2A2u porphyrin [Co(III)octaethylporphyrin]2ClO4, and the 2A1u porphyrin, [Co(III)octaethylporphyrin]2Br, such specific differences are not observed in the spectra of the two enzymes. Analysis of our data suggests that the ground states in the two enzymes are far more similar than the ground states in the two model porphyrins.