The uncatalyzed reactions of O2 (S = 1) with organic substrates (S = 0) are thermodynamically favorable but kinetically slow because they are spin-forbidden and the one-electron reduction potential of O2 is unfavorable. In nature, many of these important O2 reactions are catalyzed by metalloenzymes. In the case of mononuclear non-heme iron enzymes, either FeII or FeIII can play the catalytic role in these spin-forbidden reactions. Whereas the ferrous enzymes activate O2 directly for reaction, the ferric enzymes activate the substrate for O 2 attack. The enzyme-substrate complex of the ferric intradiol dioxygenases exhibits a low-energy catecholate to FeIII charge transfer transition that provides a mechanism by which both the Fe center and the catecholic substrate are activated for the reaction with O2. In this Perspective, we evaluate how the coupling between this experimentally observed charge transfer and the change in geometry and ligand field of the oxidized metal center along the reaction coordinate can overcome the spin-forbidden nature of the O2 reaction.
|Original language||English (US)|
|Number of pages||8|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Nov 20 2007|