The T - alence and Spin State of Iron in Oxyhemoglobin as Inferred from Resonance

A comparative study of the resonance Raman spectra of a number of hemoproteins with excitation in the Soret region reveals features that characterize the valence and spin state of the iron. (a) The frequency of the strongest band in the spectra for reduced (ferrous) hemoproteins always occurs between 1356 and 1361 cm-l, whereas for oxidized (ferric) proteins it occurs between 1370 and 1378 cm-l. (b) In all cases studied there is a band in the conjugated double bond stretching region, with principal component at 1584 and 1566 cm-’ for the low and high spin configurations, respectively. Since the strongest band of oxyhemoglobin occurs at 1375 cm-l and the 1584 cm-l band dominates the conjugated double bond stretching region, the present results strongly support the assignment of a low spin ferric structure to the iron ion in oxyhemoglobin.