10.1021/ja061581g.s001 Sam P. de Visser Sam P. de Visser Propene Activation by the Oxo-Iron Active Species of Taurine/α-Ketoglutarate Dioxygenase (TauD) Enzyme. How Does the Catalysis Compare to Heme-Enzymes? American Chemical Society 2006 oxygenation heme bond state surface 10 kcal mol complex TauD catalyst 2006-08-02 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Propene_Activation_by_the_Oxo_Iron_Active_Species_of_Taurine_Ketoglutarate_Dioxygenase_TauD_Enzyme_How_Does_the_Catalysis_Compare_to_Heme_Enzymes_/3067426 Density functional calculations on the oxygenation reaction of propene by a model for taurine/α-ketoglutarate dioxygenase (TauD) enzyme are presented. The oxo-iron active species of TauD is shown to be a powerful and aggressive oxidant, which is able to hydroxylate C−H bonds and epoxidize CC bonds with low barriers. In the case of propene oxygenation, the hydroxylation and epoxidation mechanisms are competitive on a dominant quintet spin state surface. We have compared the mechanism and thermodynamics of TauD with oxo-iron heme catalysts, such as the cytochromes P450, and found some critical differences. The TauD model is found to be much more reactive toward oxygenation of substrates than oxo-iron complexes in a heme environment with much lower reaction barriers. We have analyzed this and assigned this to the strength of the O−H bond formed after hydrogen abstraction from a substrate, which is at least 10 kcal mol<sup>-1</sup> stronger in five-coordinated oxo-iron nonheme complexes than in six-coordinated oxo-iron heme complexes. Since, the metal in TauD enzymes is five-coordinated, whereas in heme-enzymes it is six-coordinated there are some critical differences in the valence molecular orbitals. Thus, in oxo-iron heme catalysts one of the antibonding π* orbitals is replaced by a low-lying nonbonding δ orbital resulting in a lower overall spin state. Moreover, heme-enzymes have an extra oxidation equivalent located on the heme, which is missing in non-heme oxo-iron catalysts. As a result, the oxo-iron species of TauD reacts via single-state reactivity on a dominant quintet spin state surface, whereas oxo-iron heme catalysts react via two-state reactivity on competing doublet and quartet spin states.