Paramagnetic Resonance Spectrum of Irradiated Single Crystals of L-Cystine Dihydrochloride

The principal absorption in the ESR spectrum of single crystals of cystine dihydrochloride irradiated at 77°K is attributed to the free radical ([–S–CH2–CH(NH3+Cl−)COOH]2)+in which the unpaired electron is localized primarily on the sulfur atoms. The principal values of the g tensor are 2.017, 2.018, and 2.002. Each of the four CH2 protons contributes a nearly isotropic hyperfine splitting of approximately 8.5 G.