Visible and near-infrared magnetic circular dichroism spectra of high spin iron(III) complexes of protoporphyrin-IX-dimethylester. Characterization of charge-transfer bands of high spin heme [Fe(III)

Abstract

Magnetic circular dichroism (MCD) spectra for several five-coordinated heme [Fe(III)] complexes were observed from the near-ultraviolet to the near-infrared (IR) regions (300 ∼ 1200 nm) to characterize the nature of the MCD bands especially in the visible and near-infrared regions (500 ∼ 1200 nm). The MCD spectra reveal that the wavelengths and magnitudes of the visible and near-IR MCD bands depend critically on the nature of the axial ligand. The dependence can be explained on the basis of a qualitative molecular orbital theory by using the previously proposed assignment that these bands are attributable to the in-plane porphyrin π to metal charge-transfer transitions. The observed effects of solvent and environment on the MCD patterns and magnitudes of the model heme complexes give some implications about the heme environments of native hemoproteins.