Characterization of the Electronic Properties and Geometric Environment of the Iron Atom in the ‘Myoglobin Hydrogen-Peroxide’ Complex by Soretexcited Resonance Raman Spectroscopy

i’he low temperature (ca. 80 K) Soret-excited resonance Raman spectrum of the ‘myoglobin hydrogen-peroxide’ complex has been obtained and compared to those of Fe(H) and Fe(H) myoglobin. lhe RR spectra suggest that the iron atom in the Znyoglobin hydrogen-peroxide ’ complex is formally in the Fe(IV) state with a t& lowspin configuration. The iron-pyrrole-nitrogen (Fe-N,) and iron-imidazolenitrogen (Fe-N& bond lengths in the Znyoglobin hydrogen-peroxide ’ complex have been estimated from the wavenumbers of the iron-pyrrole and ironimidazole stretching modes around 34.5 and 375 cm-t using the Fe-N, and Fe-Ni,,, distances in Fe(II) myoglobin available from the X-ray crystallographic data in the literature. The distance from the centre of the porphyrin to the pyrrole nitrogen atoms (Ct-N,) was estimated from the position of the anomalously polarized band around 1.560-1590 cm-’ by comparison with data in the literature on model metalloporphyrins. i%e Fe-Nj,,,, Fe-N, and Ct-N, distances for the ‘myoglobin hydrogen-peroxide ’ complex were found to be 2.09, 2.08 and 2.01 A; the distance from the iron atom to the plane of the pyrrole nitrogen atoms was determined by triangulation and found to be 0.53+.ts **I4 A With laser lilumination of 200 m W power, the low-spin t& ‘myoglobin hydrogen-peroxide ’ complex apparently undergoes a two-electron photoreduction, with a rate constant of ca. 2.5 X l@ s’-’ at ea. 80 K, to high spin t&e: Fe(II) myoglobin, since there is no evidence for Fe(III) myoglobin.