Electronic structure of iron–dioxygen bond in oxy‐Hb‐A and its isolated oxy‐α and oxy‐β chains

A comprehensive study of the temperature dependence of the Mossbauer spectra of oxygenated hemoglobin (oxy‐Hb) and its isolated oxygenated α chains (oxy‐α) and β chains (oxy‐β) has been completed. A model of the iron–dioxygen bond in oxygenated hemoglobin (oxy‐Hb) is proposed where the ground state of the iron ions in oxy‐Hb is assumed to be a quantum mixture of ferrous and ferric states of the Mulliken’s electron‐donor–acceptor type. The temperature dependence of the Mossbauer quadrupole splitting can be explained by anharmonic vibration of the oxygen molecule in the iron ion’s binding potential well. Various previously proposed models and experimental data on the electronic structure of the iron–dioxygen bond in oxy‐Hb are then discussed in terms of this model.