Mössbauer Spectroscopy on Oxygenated Sperm Whale Myoglobin: Evidence for an Fe3+-O2 - Coupling at the Active Center

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Abstract
57Fe Mossbauer spectra of oxygenated sperm whale myoglobin (MbO2) show a well resolved quadrupole doublet with temperature dependent splitting. The temperature dependence of the corresponding electric field gradient tensor (EFG) can be calculated from a Fe3+ term scheme for the Fe at the active center. The Mossbauer spectra as well as the diamagnetic character of the MbO2-complex are then explained by an exchange coupling of the Fe3+ with the O2-. The resulting groundstate is a diamagnetic singlet. In order to keep the whole complex diamagnetic at room temperature, an exchange coupling with