The Acid-Base Properties, Hydrolytic Mechanism, and Susceptibility to O(2) Oxidation of Fe(4)S(4)(SR)(4) Clusters.
The iron-sulfur cluster compounds Fe(4)S(4)(SR)(4) (-2) [where -SR = -SCH(3), -S-C(CH(3))(3), and -S- CH(2)-CH(CH(3))(2)] have been found to represent the base species of weak acids of pK(a) comparable to that of carboxylic acids. The acid species Fe(4)S(4)(SR)(4)H(-) is most subject to reaction with O(2) and to acid-catalyzed solvolysis, while the base species Fe(4)S(4)(SR)(4) (-2) most readily undergoes ligand exchange. The kinetics for hydrolysis of the isobutyl mercaptide cluster salt has been investigated in detail and a mechanism involving the stepwise process [Formula: see text] has been proposed. The importance of the acid-base equilibria in determining the reactivity of the iron-sulfur clusters and its possible importance as a factor in the determination of the potentials of ferredoxins and high potential iron protein are discussed.
Department of Chemistry, University of California, Santa Barbara, Calif. 93106.
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