Structure and Spectra of Ferrous Dioxygen and Reduced Ferrous Dioxygen Model Cytochrome P450

The optimized geometries of the stable ferrous dioxygen and transient reduced ferrous dioxygen forms of a methylmercaptate porphine model of the cytochrome P450 heme system were calculated using nonlocal density functional theoretical (DFT) methods. The optimized geometry of the ferrous dioxygen form is in good agreement with the structure of a model compound of this species and the calculated diamagnetic singlet ground state is consistent with the reported lack of ESR spectrum of this species. The calculated ground state of the reduced ferrous dioxygen species is a low-spin (doublet) state, in agreement with the reported ESR signature of this species in P450cam. The dioxygen ligand in the reduced form is shown to preferentially bind to the heme iron in an asymmetric “end-on” geometry. The most pronounced structural effects of the reduction of the ferrous dioxygen species are the elongation of the Fe−O and Fe−S bonds. This bond lengthening is due to the addition of an electron into a molecular orbital of ...