title: DFT investigation of structural, electronic, and catalytic properties of diiron complexes related to the [2Fe](H) subcluster of Fe-only hydrogenases.
abstract: Hydrogenases catalyze the reversible oxidation of dihydrogen to protons and electrons. The structures of two Fe-only hydrogenases have been recently reported [Peters, J. W.; Lanzilotta, W. N.; Lemon, B. J.; Seefeldt, L. C. Science 1998, 282, 1853-1858. Nicolet, Y.; Piras, C.; Legrand, P.; Hatchikian, E. C.; Fontecilla-Camps, J. C. Structure 1999, 7, 13-23], showing that the likely site of dihydrogen activation is the so-called [2Fe](H) cluster, where each Fe ion is coordinated by CO and CN(-) ligands and the two metals are bridged by a chelating S-X(3)-S ligand. Moreover, the presence of a water molecule coordinated to the distal Fe2 center suggested that the Fe2 atom could be a suitable site for binding and activation of H(2). In this contribution, we report a density functional theory investigation of the structural and electronic properties of complexes derived from the [(CO)(CH(3)S)(CN)Fe(II)(mu-PDT)Fe(II)(CO)(2)(CN)](-1) species, which is related to the [2Fe](H) cluster observed in Fe-only hydrogenases. Our results show that the structure of the [2Fe](H) cluster observed in the enzyme does not correspond to a stable form of the isolated cluster, in the absence of the protein. As a consequence, the reactivity of [(CO)(CH(3)S)(CN)Fe(II)(mu-PDT)Fe(II)(CO)(2)(CN)](-1) derivatives in solution may be expected to be quite different from that of the active site of Fe-only hydrogenases. In fact, the most favorable path for H(2) activation involves the two metal atoms and one of the bridging S atoms and is associated with a very low activation energy (5.3 kcal mol(-1)). The relevance of these observations for the catalytic properties of Fe-only hydrogenases is discussed in light of available experimental and theoretical data.
authors.affiliation: Department of Environmental Sciences, University of Milan-Bicocca, Piazza della Scienza 2, I-20156 Milan, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Bruschi
authors.forename: Piercarlo
authors.initials: P
authors.lastname: Fantucci
authors.forename: Luca
authors.initials: L
authors.lastname: De Gioia
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003901:Desulfovibrio / Q000201:enzymology; D006864:Hydrogenase / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D007506:Iron-Sulfur Proteins; D007501:Iron; C118830:iron hydrogenase; D006864:Hydrogenase