[NiFe]ヒドロゲナーゼの反応機構に関する計算化学的解析
The catalytic mechanism of [NiFe] hydrogenase, which reversibly converts molecular hydrogen into protons and electrons, was examined using multiple computational approaches. Structural geometries were derived from QM/MM calculations, while energetics were refined through large-scale QM computations encompassing 819 atoms. Free energies were estimated via QM/MM thermodynamic cycle perturbation, and electronic structures of intermediate states were characterized by DMRG-CASSCF methods. The results indicate that the Ni-L intermediate does not participate in the catalytic cycle. Rather, one-electron reduction of the Ni-C state triggers transfer of the bridging hydride to the sulfur of Cys546 as a proton, with simultaneous two-electron transfer to the Ni center. This step constitutes the rate-determining barrier at 58 kJ/mol, consistent with the experimentally measured rate of 750 ± 90 s⁻¹ (~52 kJ/mol). H–H bond cleavage proceeds with a comparatively low barrier of 33 kJ/mol. Reaction energies were found to depend on QM region size, basis set selection, and the choice of density functional.
Following one-electron reduction of the Ni-C state, the bridging hydride transfers as a proton to Cys546 sulfur while two electrons migrate to the Ni ion; this constitutes the rate-limiting step at 58 kJ/mol. H–H bond cleavage occurs with a lower barrier of 33 kJ/mol.
The delivery route is not clearly identifiable from this paper. For hydrogen intake, inhalation is the most efficient route; inhalation, however, carries explosion risk (empirical LFL of 10%; high-concentration devices are not recommended).
See also:
https://h2-papers.org/en/papers/30500163