Electronic, Magnetic, and Redox Properties of [MFe(3)S(4)] Clusters (M = Cd, Cu, Cr) in Pyrococcus furiosus Ferredoxin

Christopher R. Staples; Ish K. Dhawan; Michael G. Finnegan; Derek A. Dwinell; Zhi Hao Zhou; Heshu Huang; Marc F. J. M. Verhagen; Michael W. W. Adams; Michael K. Johnson

doi:10.1021/ic970200k

Electronic, Magnetic, and Redox Properties of [MFe(3)S(4)] Clusters (M = Cd, Cu, Cr) in Pyrococcus furiosus Ferredoxin

Inorg Chem. 1997 Dec 3;36(25):5740-5749. doi: 10.1021/ic970200k.

Authors

Christopher R. Staples¹, Ish K. Dhawan, Michael G. Finnegan, Derek A. Dwinell, Zhi Hao Zhou, Heshu Huang, Marc F. J. M. Verhagen, Michael W. W. Adams, Michael K. Johnson

Affiliation

¹ Departments of Chemistry and Biochemistry & Molecular Biology and Center for Metalloenzyme Studies, University of Georgia, Athens, Georgia 30602.

PMID: 11670195
DOI: 10.1021/ic970200k

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).