Radiation-induced radicals in single crystals of N-acetyl-L-cysteine have been studied with ESR spectroscopy. Two different types of radicals were observed. One of these species was identified as a sulfur radical of the type <tex-math>${\rm RCH}_{2}{\rm S}$</tex-math>· with principal g values; <tex-math>$g_{1}=2.214,\ g_{2}=2.006$</tex-math>, and <tex-math>$g_{3}=1.990$</tex-math>. The isotropic hyperfine splitting from the two β-protons were found to be 22.1 and 29.4 G. The sulfur radical was stable at room temperature. However, temperature-broadening effects make it difficult to detect these sulfur radicals at 300 K. The other radical induced at 77 K seems to be the radical product formed by a decarboxylation process.

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