Hydrogenases are a group of enzymes specialized in the reversible catalytic conversion of protons plus electrons into dihydrogen (H2).1, 2 Our Density Functional Theory (DFT) investigations on the Hydrogen Evolution Reaction (HER) followed by [NiFe] hydrogenases disclose that H2 is produced through the ‘singlet multiplicity’ pathway. The two non-spontaneous H+/e– additions to the sulfur atom of the active site demonstrate to be the limiting steps of the whole reaction. While the proton transfers toward the metal center of the active site to form the bridging hydride and the H2 molecule at the Ni-C and I2 steps are spontaneous processes.3 Our DFT results investigated the role of the ligands attached to both the Ni and Fe centers. For the cysteine ligands bound to Ni, the spatially confined cysteine ligands model shows lower reaction energies for HER than the unconfined model, in which ligand carbons are able to freely adjust. As for the inorganic ligands on Fe, larger changes on the energy profile can be seen on replacing the [CN]– and CO ligands on the Fe center by each other. These results may guide materials synthesis efforts towards optimized HER catalysts.4

Unraveling the role of ligands in the hydrogen evolution mechanism catalyzed by [NiFe] hydrogenases

253rd National Meeting (2017)

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