Molecular structure,quadrupole splitting,and magnetic susceptibility of iron in deoxygenated myoglobin and hemoglobin

For three stereo-structural models of deoxymyoglobin (Mb) and deoxyhemoglobin (Hb) we derive electronic configurations and their mutual spin-orbit coupling. From the temperature dependent molecular electric field gradient (EFG) tensor we calculate temperature dependent quadrupole splittings, E_q(T), asymmetry parameters, (T), and orientations of the EFG component V_zz(T) with respect to the heme group. Comparing theoretical and experimental data we find a molecular electronic structure, which then is used to compute temperature dependent magnetic susceptibilities, (T). Theoretical and experimental (T) data are in reasonable agreement. From the consistency of our model calculations with experimental results we conclude that iron in Mb and Hb probably is pentacoordinated and considerably out of the heme plane by 0.4–0.8 Å.Supported in part by Stiftung Volkswagenwerk, by Deutsche Forschungsgemeinschaft, by the European Molecular Biology Organization, by an award from the Biomedical Sciences Support Grant at the University of Utah, and the National Science Foundation.