The monooxygenation of polycyclic aromatic hydrocarbons (PAH) by cytochrome P450 is an important biological reaction, responsible for activation of PAH to ultimate carcinogenic forms. Nevertheless, this reaction has received only limited attention in model studies employing porphinatoiron catalysts designed to mimic cytochrome P450 activity. The overall aim of work proposed in this study is to gain insight into the cytochrome P450-mediated oxidations by investigating a series of model oxidations employing PAH, porphinatoiron catalysts and peroxyacid monooxygen donors. The action of peroxyacids on porphinatoiron complexes can generate oxoferryl porphyrin cation radicals (formally iron (V) complexes). This species has been implicated in heme-mediated oxidations in both model and enzymic systems, but only one oxoferryl porphyrin cation radical complex has been characterized to-date. Therefore an initial specific objective is to characterize a series of oxoferryl porphyrin cation radicals derived from bifacially hindered phorphinatioiron (III) complexes spanning a range of high and low oxidation potentials. Both weakly and strongly coordinating anionic ligands will further modulate reactivity of the iron(V) intermediates. Correlation of physico-chemical parameters obtained by UV-vis, 1HNMR and Mossbauer spectroscopy will provide information on electronic structure and the electronic effects of varying axial ligands and phorphyrin ring substitutents. Once conditions have been optimized for the generation of oxoferryl porphyrin cation radicals, a second specific objective will be to determine the role of charge transfer in porphinatoiron-mediated PAH oxidations. The oxidation of benzo(a)pyrene, benz(k)- acephenanthrylene and cyclopenta(cd)pyrene will be studied. Charge transfer pathways are expected to result in oxidation of the meso positions of benzo(a)pyrene and benz(k)acephenanthrylene, while the 5-membered rings of benz(k)acephenanthrylene and cyclopenta- (cd)pyrene are reactive towards oxidation by electrophilic attack.
