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

Mössbauer spectra of deoxymyoglobin, deoxyhemoglobin, and the synthetic analogues, iron (II) 2-methylimidazole meso-tetraphenylporphyrin, and iron (II) 1,2-dimethylimidazole meso-tetraphenylporphyrin have been observed in high magnetic fields and over a wide range of temperature. At temperatures greater than 20 K all materials exhibit remarkably similar spectra, with anisotropic internal magnetic fields decreasing as 1/T. All have negative quadrupole interaction, and both this and the magnetic anisotropy imply that the orbital of the odd electron is prolate in the ground quintet, with little unquenched orbital angular momentum. At 4.2 K the spectra differ, suggesting different detailed structure within the quintet. In contrast to the proteins, the 2-methyl model exhibits spectra at 4.2 K which imply that the lowest spin state has high susceptibility in a single direction.