| To elucidate the sophisticated mechanisms of biological processes, synthetic porphyrin analogs were used to mimic P450 enzymes. In this study, several oxidative porphyrin-iron-oxo species with different oxidation states were generated chemically and photochemically, the kinetics and mechanistic studies of the oxidants under single-turnover condition provided insight as to the identities and reactivities of the true oxidants in the P450-related catalytic processes.;Those oxidative species include: porphyrin-iron(IV)-oxo species (Compound II), iron(IV)-oxo porphyrin radical cations (Compound I), and putative porphyrin-iron(V)-oxo species. Typical second-order rate constants for epoxidation reaction by these species are in the order of 10-2, 102 and 10 6 M-1 s-1, respectively. Kinetic results suggested a disproportionation mechanism in Compound II oxidation reactions, and relatively small environmental effects in Compound I species when axial ligands, solvents, and porphyrin peripheral structures were modified. On the contrary, the putative porphyrin-iron(V)-oxo transient displayed appropriate level of reactivity for the oxidant in a catalytic process under multiple turnover conditions. |
