title: A theoretical study of spin states in Ni-S4 complexes and models of the [NiFe] hydrogenase active site.
abstract: We have applied density functional theory, using both pure (BP86) and hybrid (B3LYP and B3LYP*) functionals, to investigate structural parameters and reaction energies for nickel(II)-sulfur coordination compounds, as well as for small cluster models of the Ni-SI and Ni-R redox state of [NiFe] hydrogenases. Results obtained investigating experimentally well-characterized complexes show that BP86 is well suited to describe the structural features of this class of compounds. However, the singlet-triplet energy splitting and even the computed ground state are strongly dependent on the applied functional. Results for the cluster models of [NiFe] hydrogenases lead to the conclusion that in the reduced protein structures characterized by X-ray diffraction a hydride bridges the two metal centres. The energy splitting of the singlet and triplet states in Ni-R and Ni-SI models is calculated to be very small and may be overcome at room temperature to allow a spin crossover. Moreover, the relative stability of the Ni-SI and Ni-R structures adopted in the present investigation is fully compatible with their involvement in the reversible heterolytic cleavage of H(2).
authors.affiliation: Department of Environmental Science, University of Milano-Bicocca, Piazza della Scienza 1, 20126 Milan, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Bruschi
authors.forename: Luca
authors.initials: L
authors.lastname: De Gioia
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Zampella
authors.forename: Markus
authors.initials: M
authors.lastname: Reiher
authors.forename: Piercarlo
authors.initials: P
authors.lastname: Fantucci
authors.forename: Matthias
authors.initials: M
authors.lastname: Stein
mesh_terms: D001665:Binding Sites; D045286:Desulfovibrio gigas / Q000201:enzymology; D006864:Hydrogenase / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D010084:Oxidation-Reduction; D013455:Sulfur / Q000737:chemistry*
chemical_list: D013455:Sulfur; D009532:Nickel; C043296:nickel-iron hydrogenase; D006864:Hydrogenase