MCD spectra of iron-sulfur complexes with or without inorganic sulfur

The magnetic circular dichroism spectra were observed for various iron-sulfur complexes with and without inorganic sulfur as models for rubredoxin and 2-Fe ferredoxin. The MCD band shapes ascribed the bands around 390 and 490 nm to Faraday A terms for mononuclear iron sulfur complexes. These bands are probably assigned to the charge-transfer transitions from the thiol sulfur orbital to the iron t2 and e 3d-orbitals, respectively. The MCD magnitudes decreased by more than one-half for binuclear iron-sulfur complexes with inorganic sulfur in comparison with those for the mononuclear complexes. The low MCD magnitude as well as the possible core symmetry as low as D2d attributed the MCD bands to Faraday B terms. Incorporation of inorganic sulfur produced new MCD bands, some of which can be assigned to the charge-transfer transitions from the inorganic sulfur orbital to the iron t2 and e 3d-orbitals. Among complexes studied here, the bis(o-xylyldithiolato) ferrate(III) monoanion gave the MCD spectrum which resembles that of a rubredoxin. This implies that the MCD spectroscopy also assessed complex as a good rubredoxin model. However the binuclear complex bis[o-xylyldithiolato-micron2-sulfidoferrate(III)] dianion failed to offer the MCD spectrum similar to that of the spinach ferredoxin.