@article {2376,
	title = {Ligand K-edge X-ray absorption spectroscopy and DFT calculations on [Fe3S4]0,+ clusters: delocalization, redox, and effect of the protein environment},
	journal = {J Am Chem Soc},
	volume = {126},
	number = {51},
	year = {2004},
	note = {<p>0002-7863 (Print)0002-7863 (Linking)Journal ArticleResearch Support, U.S. Gov{\textquoteright}t, Non-P.H.S.Research Support, U.S. Gov{\textquoteright}t, P.H.S.</p>
},
	month = {Dec 29},
	pages = {16868-78},
	abstract = {<p>Ligand K-edge XAS of an [Fe3S4]0 model complex is reported. The pre-edge can be resolved into contributions from the mu(2)S(sulfide), mu(3)S(sulfide), and S(thiolate) ligands. The average ligand-metal bond covalencies obtained from these pre-edges are further distributed between Fe(3+) and Fe(2.5+) components using DFT calculations. The bridging ligand covalency in the [Fe2S2]+ subsite of the [Fe3S4]0 cluster is found to be significantly lower than its value in a reduced [Fe2S2] cluster (38\% vs 61\%, respectively). This lowered bridging ligand covalency reduces the superexchange coupling parameter J relative to its value in a reduced [Fe2S2]+ site (-146 cm(-1) vs -360 cm(-1), respectively). This decrease in J, along with estimates of the double exchange parameter B and vibronic coupling parameter lambda2/k(-), leads to an S = 2 delocalized ground state in the [Fe3S4]0 cluster. The S K-edge XAS of the protein ferredoxin II (Fd II) from the D. gigas active site shows a decrease in covalency compared to the model complex, in the same oxidation state, which correlates with the number of H-bonding interactions to specific sulfur ligands present in the active site. The changes in ligand-metal bond covalencies upon redox compared with DFT calculations indicate that the redox reaction involves a two-electron change (one-electron ionization plus a spin change of a second electron) with significant electronic relaxation. The presence of the redox inactive Fe(3+) center is found to decrease the barrier of the redox process in the [Fe3S4] cluster due to its strong antiferromagnetic coupling with the redox active Fe2S2 subsite.</p>
},
	keywords = {Binding Sites, Ferredoxins/chemistry, Iron-Sulfur Proteins/*chemistry, Iron/chemistry, Models, Chemical, Models, Molecular, Oxidation-Reduction, Spectrometry, X-Ray Emission, Sulfur/chemistry, Thermodynamics},
	url = {http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve\&db=PubMed\&dopt=Citation\&list_uids=15612726 },
	author = {Dey, A. and Glaser, T. and Moura, J. J. and Holm, R. H. and Hedman, B. and Hodgson, K. O. and Solomon, E. I.}
}
