High magnetic field Mössbauer studies of deoxymyoglobin, deoxyhemoglobin, and synthetic analogues: Theoretical interpretations

Mössbauer spectra of deoxymyoglobin, deoxyhemoglobin, and the synthetic analogues, iron (ii) 2-methylimidazole meso-tetraphenylporphyrin, and iron (ii) 1,2-dimethylimidazole meso-tetraphenylophorphyrin, observed in high magnetic fields and over a wide range of temperature, have been examined theoretically in an effort to correlate them with known susceptibility data, and a search for a satisfactory model within the 5D term has been carried out. It is shown in a general way that any solution within 5D would demand the use of magnetic hyperfine coupling constants about half as large as the smallest previously observed. Even allowing this anomaly we have failed to find a solution within 5D. An interesting result is that the myoglobin appears to have a singlet ground state while the 2-methyl substituted model has a nearly degenerate ground doublet, approximately describable as Sz=±2. Yet the hyperfine fields of these materials are very similar at elevated temperatures. It appears that the introduction of low lying states of different spin multiplicity will be needed to accommodate this behavior and to provide the observed magnitude of magnetic hyperfine coupling.