Dihydrogen has been touted as the future of 'clean energy' since its combustion produces water and it is the most abundant element in the Universe. At the moment, these processes require catalysts for the production and utilization of hydrogen at ambient temperature as in fuel cells. The most efficient electro-catalysts are electrode of noble metals such as platinum. The search for a viable alternative to platinum electrodes leads naturally to the hydrogenase enzymes that contain Fe and Ni and reversibly cleave dihydrogen into protons and electrons.The most studied hydrogenases are [NiFe]-hydrogenases, which consist of a heteronuclear Ni-Fe active site coordinated by cysteines and the biologically unexpected carbonyl and cyanide ligands. It is generally accepted that there are at least seven identifiable states of the [NiFe] complex, called Ni-A, Ni-SU, Ni-B, Ni-SII, Ni-SII, Ni-R and Ni-C. The Ni-A (unready) and Ni-B (ready) oxidize inactive states are paramagnetic (Ni+3, S=1/2), however are distinguished by different g-values and activation rates. The Ni-A requires long incubation under hydrogen to be activated whereas the Ni-B state is rapidly activated under hydrogen atmosphere.In the present study, we have applied density functional theory and implicit solvation model to compute reduction potentials (E0) and proton dissociation constants (pKa) of the prospective intermediates in order to give more insight into the proton reduction process for [NiFe]-hydrogenase.

Activation mechanism for [NiFe]-hydrogenase: A density functional theory study of proton dissociation constants and electrode reduction potentials

246th National Meeting (2013)

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