The mechanism of Mo-/Cu-dependent CO dehydrogenase

Density functional theory computations at the B3LYP/SDDp//B3LYP/Lanl2DZ level were performed on model complexes derived from [(Me(2)C(2)S(2))Mo(O)(2)-S-CuSMe](2-) or its oxo protonated form to gain insight into the reaction steps involved in substrate oxidation of a Mo-/Cu-dependent CO dehydrogenase. Only the bisoxo but not the hydroxo oxo complex was found to oxidize CO exothermically. A thiocarbamate complex structurally characterized as the reaction product of the enzyme with the inhibitor n-butylisonitrile corresponds to a thermodynamic well on the potential energy surface. For the formation of the analogous thiocarbonate complex from CO oxidation, however, we do not find a significant thermodynamic driving force. In the protein matrix of the enzyme this species should be further destabilized, as it requires the metal centers to move apart considerably from each other.