Spin-lattice relaxation in Mössbauer spectra of metmyoglobin: investigation of crystals, water and water-glycerol solutions Original Research Article

Mössbauer spectra of a polycrystalline metmyoglobin sample, metmyoglobin dissolved in 0.1 M phosphate buffer at pH = 6.8 and metmyoglobin in a water-glycerol solution have been measured. An extended theoretical approach is offered to describe the relaxation changes. The spectra are fitted in the temperature interval 4.2–40 K with due regard for the contributions both from the high spin (HS) state and low spin (LS) state of the Fe(III) ion to the hyperfine structure. It is shown that even a small amount of the LS compound affects significantly the resultant spectra. The relaxation behavior of the hyperfine spectra of the HS species is governed by the one-phonon direct processes, and the set of two relaxation constants for each sample is reported. In the case of the water-glycerol solution, the drastic reduction of the vibrations of the nearest-heme environment, described by the first relaxation parameter, is related to the influence of glycerol.