A selenolate-ligated P450 compound I (SeP450-I) intermediate was recently shown to be more reactive towards C-H bonds than its wild type counterpart. To determine how the selenolate axial ligand influences the reactivity of compound I, we investigated the electronic structure of the SeP450-I intermediate using variable temperature Mossbauer (VTM) spectroscopy. The VTM data reveal that electronic spin relaxation rates are significantly slower in SeP450-I than in P450-I. Analyses of these and other data in terms of a standard ligand field model indicate that excited state mixing within the ferryl moiety plays an important role in determining electronic properties of compound I species. For SeP450-I, P450-I, and chloroperoxidase compound I, we find that electronic relaxation times correlate with the magnitude of the exchange coupling and track with reactivity towards C-H bonds.

Electronic relaxation data and the importance of excited state mixing in determining the properties of compound I

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