Mössbauer spectroscopic determination of the electronic structure of highly oxidized iron in hemoproteins

Mössbauer spectra have been obtained from the hydrogen peroxide compounds of peroxidase and met-myoglobin, in the presence of an applied magnetic field. The magnetically perturbed spectra and the temperature dependence of the quadrupole splittings have been analyzed with a low symmetry ligand field approximation and spin–orbit coupling. The electronic structure of heme-iron in peroxidase Compound II and met-myoglobin H2O2 compound is ascribed to a low-spin (t2g)4 S=1 paramagnetic configuration. The axial and rhombic field parameters are determined to be 624 and ?312 cm−1, respectively. The lowest state is characterized by a spin-singlet Sz=0 in a 3A2 multiplet. The covalency parameter indicates the large expansion of radial charge-distribution of the t2g orbitals in these compounds.