How are the ready and unready states of nickel–iron hydrogenase activated by H2? A density functional theory study†
Abstract
We have explored possible mechanisms for the formation of the catalytically active Nia–S state of the enzyme, nickel iron hydrogenase, from the Ni*r (ready) or Ni*u (unready) state, by reaction with H2, using density functional theory calculations with the BP86 functional in conjunction with a DZVP basis set. We find that for the reaction of the ready state, which is taken to have an –OH bridge, the rate determining step is the cleavage of H2 at the Ni3+ centre with a barrier of ∼15 kcal mol−1. We take the unready state to have a –OOH bridge, and find that reaction with H2 to form the Nir–S state can proceed by two possible routes. One such path has a number of steps involving