title: Electronic, Magnetic, and Redox Properties of [MFe(3)S(4)] Clusters (M = Cd, Cu, Cr) in Pyrococcus furiosus Ferredoxin.
abstract: The ground- and excited-state properties of heterometallic [CuFe(3)S(4)](2+,+), [CdFe(3)S(4)](2+,+), and [CrFe(3)S(4)](2+,+) cubane clusters assembled in Pyrococcus furiosus ferredoxin have been investigated by the combination of EPR and variable-temperature/variable-field magnetic circular dichroism (MCD) studies. The results indicate Cd(2+) incorporation into [Fe(3)S(4)](0,-) cluster fragments to yield S = 2 [CdFe(3)S(4)](2+) and S = (5)/(2) [CdFe(3)S(4)](+) clusters and Cu(+) incorporation into [Fe(3)S(4)](+,0) cluster fragments to yield S = (1)/(2) [CuFe(3)S(4)](2+) and S = 2 [CuFe(3)S(4)](+) clusters. This is the first report of the preparation of cubane type [CrFe(3)S(4)](2+,+) clusters, and the combination of EPR and MCD results indicates S = 0 and S = (3)/(2) ground states for the oxidized and reduced forms, respectively. Midpoint potentials for the [CdFe(3)S(4)](2+,+), [CrFe(3)S(4)](2+,+), and [CuFe(3)S(4)](2+,+) couples, E(m) = -470 +/- 15, -440 +/- 10, and +190 +/- 10 mV (vs NHE), respectively, were determined by EPR-monitored redox titrations or direct electrochemistry at a glassy carbon electrode. The trends in redox potential, ground-state spin, and electron delocalization of [MFe(3)S(4)](2+,+) clusters in P. furiosus ferredoxin are discussed as a function of heterometal (M = Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Tl).
authors.affiliation: Departments of Chemistry and Biochemistry & Molecular Biology and Center for Metalloenzyme Studies, University of Georgia, Athens, Georgia 30602.
authors.forename: Christopher R.
authors.initials: CR
authors.lastname: Staples
authors.forename: Ish K.
authors.initials: IK
authors.lastname: Dhawan
authors.forename: Michael G.
authors.initials: MG
authors.lastname: Finnegan
authors.forename: Derek A.
authors.initials: DA
authors.lastname: Dwinell
authors.forename: Zhi Hao
authors.initials: ZH
authors.lastname: Zhou
authors.forename: Heshu
authors.initials: H
authors.lastname: Huang
authors.forename: Marc F. J. M.
authors.initials: MF
authors.lastname: Verhagen
authors.forename: Michael W. W.
authors.initials: MW
authors.lastname: Adams
authors.forename: Michael K.
authors.initials: MK
authors.lastname: Johnson