The electronic structure of the catalytic intermediate Ni-C in [NiFe] and [NiFeSe] hydrogenases

The catalytic intermediate Ni-C in the heterolytic cleavage of molecular hydrogen is studied using relativistic DFT calculations. The difference between the [NiFe] and [NiFeSe] hydrogenases is investigated and it is found that structural modifications lead to changes in the electronic structure, manifested by g-values and hyperfine interactions. The sulfur to selenium substitution leads to small changes in the structural parameters and the spin density distribution. The g-tensor principal values are changed but the g-tensor orientation is retained in both enzymes. The hyperfine parameters show small but systematic changes. Participation of the terminal cysteine Cys530 in the reaction mechanism is discussed.