Cryoreduction of the NO-Adduct of Taurine:α-Ketoglutarate Dioxygenase (TauD) Yields an Elusive {FeNO}8 Species

The Fe(II)- and α-ketoglutarate (αKG)-dependent enzymes are a functionally and mechanistically diverse group of mononuclear nonheme-iron enzymes that activate dioxygen to couple the decarboxylation of αKG, which yields succinate and CO2, to the oxidation of an aliphatic C−H bond of their substrates. Their mechanisms have been studied in detail by a combination of kinetic, spectroscopic, and computational methods. Two reaction intermediates have been trapped and characterized for several members of this enzyme family. The first intermediate is the C−H-cleaving Fe(IV)−oxo complex, which exhibits a large deuterium kinetic isotope effect on its decay. The second intermediate is a Fe(II):product complex. Reaction intermediates proposed to occur before the Fe(IV)−oxo intermediate do not accumulate and therefore cannot be characterized experimentally. One of these intermediates is the initial O2 adduct, which is a {FeO2}8 species in the notation introduced by Enemark and Feltham. Here, we report spectroscopic an...