Solvent effect on MCD of Fe(III) heme complexes: Magnetic circular dichroism spectra of five-coordinated high-spin iron(III) protoporphyrin-IX-dimethylester in the visible region and their environmental effect. A characterization of the visible electronic transitions in Fe(III) high-spin porphyrins

Abstract

Magnetic circular dichroism (MCD) spectra were observed to characterize the nature of the visible bands for high-spin Fe(III) protoheme derivatives with p-nitrothiophenolate, p-nitrophenolate, and methoxy anion as the fifth ligands in several solvents. The visible MCD bands for p-nitrophenolate heme were very sensitive to the solvent polarity, but that those for p-nitrothiophenolate heme and methoxy heme were not dependent on solvent polarity. Thus, both the two visible MCD band positions and the magnitudes were dependent on E Tr value (a solvent polarity parameter) in the former complex, but not in the latter two complexes. The results are consistent with previously proposed electronic structures of high-spin Fe(III) heme complexes.