The effect of hydrogen bonds attaching to sulfur atoms of cysteine ligands on 4Fe-4S cluster is examined by using UB3LYP method. Calculated results indicate that an existence of the hydrogen bonds scarcely changes SOMO-SUMO gap, shapes of Kohn-Sham orbitals, and magnetic interactions between Fe ions, although it stabilizes Kohn-Sham orbital energies of SOMO and SUMO about 1.0 eV. And they also make a reduced state stable in comparison with an oxidized state. In addition, the point charges of +0.1e (e: elementary electric charge) at the position of the hydrogen atoms give almost same results to the hydrogen bonds quantitatively. The results suggest that a positive environment from the hydrogen bonds around the clusters is important for a redox potential of 4Fe-4S clusters. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
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