High-frequency EPR study of the ferrous ion in the reduced rubredoxin model.
High-frequency (94-371 GHz) EPR data are reported for powdered samples of [PPh4]2[Fe(SPh)4], an accurate model for the reduced site of rubredoxins. This is the first HFEPR investigation of an S = 2 ferrous complex, illustrating the utility of this technique for the investigation of integer-spin systems. A full-matrix diagonalization approach is used to simulate spectra over the 94-371 GHz frequency range, providing the spin-Hamiltonian parameters g, D, and E. It is observed that g is anisotropic, characterized by gx = gy = 2.08 and gz = 2.00, and that D = +5.84 cm(-1) and E = +1.42 cm(-1), where the uncertainty in each parameter is estimated as +/- 2%. The spin-Hamiltonian for [PPh4]2[Fe(SPh)4] is related to fundamental properties, such as the crystal-field splitting and the spin-orbit coupling of Fe2+. It is shown that the conventional spin-Hamiltonian accurately represents the electronic structure of the Fe2+ ion in this molecule. Through a comparison with Fe(SPh)4(PPh4)2, the zero-field splitting of the Fe2+ site in reduced rubredoxin is estimated to be D = +5.3 cm(-1) and E = +1.5 cm(-1). This is one of the few HFEPR investigations of a rhombic, high-spin system; as such, it is a step toward the eventual investigation of similar Fe2+ sites in proteins.
Knapp
M J
MJ
Department of Chemistry and Biochemistry-0358, University of California at San Diego, La Jolla 92093, USA.
Krzystek
J
J
Brunel
L C
LC
Hendrickson
D N
DN
D004578:Electron Spin Resonance Spectroscopy; D005296:Ferrous Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D012416:Rubredoxins / Q000737:chemistry*
D005296:Ferrous Compounds; D012416:Rubredoxins