Electron Spin Resonance of a γ-Irradiated Single Crystal of N-Acetyl Methionine

Free radicals produced by γ irradiation of single crystals of N-acetyl methionine have been investigated through their electron spin resonance patterns for different orientations in the magnetic field. Two chemically different free radicals have been found, both relatively stable at room temperature. One of them has an ESR pattern very similar to that of cystine dihydrochloride. Analysis of this resonance shows that the electron spin density is concentrated mainly on the S in a free radical which probably has the chemical form[Complex chemical formula]The g tensor for this radical is anisotropic with principal values 2.004, 2.029, and 2.064. An isotropic doublet hyperfine structure of 9.5-G spacing is observed. The second resonance has a complex, incompletely resolved, hyperfine structure with a total spread of about 26 G. Its almost isotropic g tensor with principal values from 2.002 to 2.005 indicates that the electron spin density is concentrated on a carbon. The free radical is believed to have the form[Complex chemical formula]but this structure is not proved.