title: Chemical activity of iron in [2Fe-2S]-protein centers and FeS2(100) surfaces.
abstract: Iron atoms bonded to sulfur play an important role in proteins, heterogeneous catalysts, and gas sensors. First-principles density functional calculations were used to investigate the structure and chemical activity of a unique [2Fe-2S] center in the split-Soret cytochrome c (Ssc) from Desulfovibrio desulfuricans. In agreement with a previously proposed structural model [Abreu et al., J. Biol. Inorg. Chem. 2003, 8, 360], it is found that the [2Fe-2S] cluster is located in a surface pocket of the Ssc and bonded to only three cysteines. The [2Fe-2S] center in the Ssc is nonplanar and somewhat distorted with respect to canonical [2Fe-2S] centers seen in proteins where the iron-sulfur unit is bonded to four cysteines. In the Ssc, the lack of one Fe-cysteine bond is partially compensated by the separation between the cysteines that minimizes electrostatic repulsion among these ligands. The unique structure of the [2Fe-2S] center in the Ssc makes the center more chemically active than canonical [2Fe-2S] centers in proteins, (RS)(4)[2Fe-2S] inorganic complexes, and an FeS2(100) surface. A [2Fe-2S] center in the Ssc interacts efficiently with electron acceptors (O2, NO, CO) and poorly with a Lewis base such as H2O. The interaction with molecular oxygen is so strong that eventually oxidatively destroys the [2Fe-2S] unit. The bonding energy of the ligands to the [2Fe-2S] centers and FeS2(100) surface increases following the sequence: H2O << CO < NO < O2. The higher the electron affinity of the ligand, the larger its bonding energy. A relatively large positive charge on the Fe cations in FeS2(100) makes this sulfide surface less reactive toward O2, CO, and NO than the [2Fe-2S] centers in proteins and inorganic complexes.
authors.affiliation: Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973-5000, USA. rodriguez@bnl.gov
authors.forename: José A
authors.initials: JA
authors.lastname: Rodriguez
authors.forename: Isabel A
authors.initials: IA
authors.lastname: Abreu
mesh_terms: D002627:Chemistry, Physical / Q000379:methods; D045285:Desulfovibrio desulfuricans / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D007501:Iron / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D010100:Oxygen / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D013499:Surface Properties
chemical_list: D007506:Iron-Sulfur Proteins; D008024:Ligands; D007501:Iron; D010100:Oxygen