Mössbauer spectroscopic studies of ferric myoglobin single crystals in a small applied magnetic field

• Published in: The Journal of chemical physics 1979-01, Vol.71 (3), p.1309-1318
• Main Author: Harami, T.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.438431

Mössbauer experiments on single crystals of some ferric myoglobin (Mb) compounds which include high spin compounds (S=5/2), metMb and MbF, and a low spin compound (S=1/2), MbN3, have been done in the presence of a small external magnetic field perpendicular to the γ rays at liquid He temperature. The Mössbauer spectra of these compounds were analysed by a spin Hamiltonian formalism. For metMb and MbF, saturation fields of 480±5 and 510±5 kOe and quadrupole interactions eOVzz/2 of 1.10±0.05 and 0.70±0.05 mm sec−1 were obtained, respectively. The value of a hyperfine coupling constant Az was determined from spectra obtained with the applied field nearly along the a axis. The difference between Az and A⊥ was less than 5% and 4% for metMb and MbF, respectively. For MbN3 the following Mössbauer parameters were obtained: an asymmetry parameter η=0.4±0.1, the quadrupole interaction eQVzz/2 =−2.10±0.05 mm sec−1 and an isomer shift=0.30±0.05 mm sec−1. The axis of the largest component of an electric field gradient is rather close to the heme plane and deviates by 32° from one of four Fe–N directions. Taking the results of EPR into account, it was found that the environment around the heme iron is lower than orthorhombic symmetry, being almost monoclinic symmetry.