276 Abstracts Journal of Inorganic Biochemistry

K03 DIOXYGEN ACTIVATION BY IRON "PICKET-FENCE" PORPHYRIN COMPLEXES

Ravmond W¢i8~, Dominique Mandon

Laboratoire de Cristallochimie et de Chimie Structurale (UA-CNRS 424) Institut Le Bel, Universit6 Louis Pasteur 4, Rue B. Pascal 67070 STRASBOURG (France)

The major steps which are assumed to occur in the mechanism by which the P- 450 cytochromes activate molecular oxygen include : (i) reduction of the heme- iron to the ferrous state, binding of 02 and reduction to a peroxidic intermediate (ii) heterolytic cleavage of the O-O bond and transformation into an iron(IV)-oxo porphyrin species having incorporated two oxidizing equivalents relative to the ferric resting state and (iii) oxygen transfer to the organic substrate (concomitant with or following step (ii)). The high-valent iron(IV)-oxo porphyr in intermediate, with two supplementary oxidizing equivalents relative to the ferric resting state of the enzymes, remains to date the most attractive candidate for the active oxygen donating species of the P-450 cytochromes. Reduction of the 02 adduct of iron(II)"picket-fence"porphyrin by an aluminium hydride yields in THF a peroxidic-iron(III) "picket-fence" porphyrin species, i FeIno2(tpivpp) i-. 1 To see, if an iron(IV)-oxo porphyrin ~-cation radical forms by

protonation of such a peroxidic iron(III) derivative, we have studied its protonation in THF or toluene or methylene chloride with the tetrafluoroboric acid - diethyl ether adduct HBF4.O(C2H5)2 .2 We have shown by UV-Vis, M6ssbauer and EXAFS spectroscopy that this reaction yields a high-valent iron- oxo "picket-fence" porphyrin species which contains two supplementary oxidizing equivalents relative to the ferric state. However, this species does not show the typical spectroscopic and magnetic properties of the iron(IV)-oxo porphyrin ~-cation radical derivatives that one can obtain in toluene, methylene chloride or butyronitrile by oxidation with m-CPBA of iron(III) complexes of sterically hindered porphyrins such as H2tmp, H2tdcpp etc .... A species displaying identical spectroscopic properties is obtained by m-CPBA oxidation of the triflato-iron(III) "picket-fence" porphyrin complex. We have now established the nature and structure of this high-valent iron-oxo porphyrin species obtained by protonation of the peroxo-iron(III) "picket-fence" porphyrin derivative. The corresponding results will be presented and discussed.

1. M. Schappacher, R. Weiss, R. Montiel-Montoya, A.X. Trautwein, A. Tabard J. Am. Chem. Soc. 107, 3736 (1985) 3. D. Mandon, R. Weiss, M. Franke, E. Bill, A.X. Trautwein Angew. Chem. Int. Ed. 28, 1709 (1989)