The Role of Nonheme Transition Metal-Oxo, -Peroxo, and -Superoxo Intermediates in Enzyme Catalysis and Reactions of Bioinspired Complexes

Transition metals are common cofactors in enzymes and enable catalysis to take place via reaction barriers that are accessible at room temperature. Oxygen-activating metalloenzymes are versatile species in Nature involved in vital processes ranging from biodegradation to biosynthesis. Since oxygen-activating intermediates are not readily amenable to experimental study, research has started to focus on biomimetic model systems that have the active site coordination sphere and structural features, but react in solution. In our research group, we have been involved in computational modeling of heme and nonheme iron dioxygenases as well as biomimetic models of these complexes. In this contribution, an overview is given on recent results of the characterization and reactivity patterns of metal-oxo, metal-peroxo, and metal-superoxo complexes. In particular, in recent studies attempts were made to trap and characterize the short-lived oxygen-bound intermediate in the catalytic cycle of cysteine dioxygenase. Many suggested structures could be ruled out by theoretical considerations, yet these also provided suggestions of possible candidates for the experimentally observed spectra. In addition, we review recent studies on the nonheme iron(III)-hydroperoxo species and how its reactivity patterns with arenes are dramatically different from those found for heme iron(III)-hydroperoxo species. In the final two sections there is a description, with illustrations, of a series of computational studies on manganese(V)-oxo and side-on manganese(III)-peroxo moieties that identify a unique spin-state reactivity pattern with a surprising product distribution.