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Convergent Theoretical Prediction of Reactive Oxidant Structures in Diiron Arylamine Oxygenases AurF and CmlI: Peroxo or Hydroperoxo?

Wang, Chao, Chen, Hui
Journal of the American Chemical Society 2017 v.139 no.37 pp. 13038-13046
carbon-hydrogen bond activation, models, oxidants, oxygen, oxygenases, prediction, quantum mechanics, spectroscopy
AurF and CmlI are currently the only two known diiron arylamine oxygenases. On the basis of extensive quantum mechanical/molecular mechanical (QM/MM) spectroscopic and mechanistic modelings, here we predict that the key oxygenated intermediates in AurF and CmlI, so-called P, are uniformly hydroperoxo species having similar structures. As a basis for mechanistic unification in AurF and CmlI, the proposed diferric-hydroperoxo P is calculated to be able to promote the arylamine N-oxygenation with highly accessible kinetics. This convergent μ-η⁰:η² structural assignment of P’s in AurF and CmlI can rationalize many conundrums for P, including the different Mössbauer spectroscopic parameters, low O–O vibrational frequency, ambiphilic reactivity, and inertness toward C–H activation. In view of the very limited knowledge about hydroperoxo species in diiron enzymes, the novel diferric-hydroperoxo-mediated N-oxygenation mechanism revealed in this work opens up a new avenue for understanding the O₂ activation mode in nature. For elucidating the structures of transient oxidants for diiron enzymes, the promising approach of QM/MM Mössbauer spectroscopic modeling is highlighted as a key problem solver in mechanistic enzymatic research.