DFT calculations of the electronic structure of the paramagnetic states Ni-A, Ni-B and Ni-C of [NiFe] hydrogenase

Structural parameters and atomic spin densities of the active centre of [NiFe] hydrogenases in the paramagnetic states Ni-A, Ni-B and Ni-C are reported. The DFT (BLYP/DZVP) calculated spin density distribution is found to be in good agreement with experimental data when the bridging ligand is OH- in the Ni-B and O2- in the Ni-A states of the enzyme. For the reduced enzyme (Ni-C) it is postulated that a hydride ligand bridges the Ni and Fe atoms. The atomic spin densities for the proposed paramagnetic states are in good agreement with experimental electron magnetic resonance data. Based on the deduced composition of the states Ni-A, Ni-B and Ni-C a model for the reaction mechanism is proposed.