Several model systems for nonheme iron-sulfur proteins

Abstract

The stability and unusual electronic properties of the sulfur coordinated iron atoms in nonheme iron-sulfur proteins appear to be related to the nature of iron-sulfur bonding involving the sulfhydryl groups of the proteins and sometimes the inorganic sulfides. The iron(III) chromophore of rubredoxins has only Fe-SR bonds but ferredoxins and other nonheme iron-sulfur proteins have both Fe-SR and Fe-S-Fe bonds. Model complexes containing either of these two bonds were spectrophotometrically studied. The models were made with the assumption that multidentate ligands such as HEDTA, EDTA and other related aminocarboxylic acids chelate with iron(III) to form a hard core primary coordination polyhedron around iron, leaving at least one coordination position not coordinated or weakly coordinated which can subsequently be occupied by a strong nucleophilic ligand. These iron(III) chelates react with mercaptans or hydrogen sulfide to form iron(III) chelate-sulfide complexes. The model complex formed by the action of mercaptan appears to have one iron-sulfur bond, and the complex formed by hydrogen sulfide appears to have a Fe-S-Fe bridging bond. ...