Title of article :
Density Functional Theory Investigation of the Active Site of [Fe]-Hydrogenases: Effects of Redox State and Ligand Characteristics on Structural, Electronic, and Reactivity Properties of Complexes Related to the [2Fe]H Subcluster
Author/Authors :
Bruschi، Maurizio نويسنده , , Fantucci، Piercarlo نويسنده , , Gioia، Luca De نويسنده ,
Abstract :
The effects of redox state and ligand characteristics on structural, electronic, and reactivity properties of complexes related to the [2Fe]H subcluster of [Fe]-hydrogenases have been investigated by DFT calculations and compared with experimental and theoretical data obtained investigating both the enzyme and synthetic model complexes. Our results show that FeIIFeII species characterized by OH or H2O groups terminally coordinated to the iron atom distal to the terminal sulfur ligand (Fed) are less stable than corresponding (mu)-OH or (mu)-H2O species, suggesting that the latter are destabilized or kinetically inaccessible in the enzyme. In addition, results obtained investigating FeIFeI and FeIIFeI complexes show that structure and relative stability of species characterized by a (mu)-CO group are significantly affected by the electronic properties of the ligands coordinated to the iron atoms. The investigation of reaction pathways for H2 activation confirms and extends a previous hypothesis indicating that H2 can be cleaved on FeIIFeII species. In particular, even though [Fe]-hydrogenases are proposed to bind and activate H2 at a single iron center, the comparison of our data with experimental results obtained studying synthetic complexes (Zhao, X.; Georgakaki, I. P.; Miller, M. L.; Mejia-Rodriguez, R.; Chiang, C.-Y.; Darensbourg, M. Y. Inorg. Chem. 2002, 41, 3917) suggests that activation paths involving both metal ions are also possible. Moreover, (mu)-H FeIIFeI complexes are predicted to correspond to stable species and might be formed in the enzyme catalytic cycle.