An ESR study of radical kinetics in L-alpha-amino-n-butyric acid hydrochloride containing L-cysteine hydrochloride.

On annealing at temperatures near 100°C, carbon-centered radicals migrate to sulfur-centered radicals in X-irradiated crystals of L-α-amino-n-butyric acid hydrochloride, ${\rm CH}_{3}{\rm CH}_{2}{\rm CH}({\rm NH}_{3}{\rm Cl}){\rm COOH}$, containing L-cysteine hydrochloride, ${\rm SHCH}_{2}{\rm CH}({\rm NH}_{3}{\rm Cl}){\rm COOH}$. Samples containing 0, 0.5, 1.0, and 1.5% L-cysteine hydrochloride were studied. When no cysteine is present, the carbon-centered radical formed by X irradiation, ${\rm CH}_{3}{\rm CH}_{2}\dot{{\rm C}}{\rm HOOH}$, decays according to a second-order diffusion-controlled rate equation. In samples containing cysteine, the same carbon-centered radicals are formed, but on annealing, they migrate to cysteine, where a perthiyl radical, RSṢ, is formed. The transfer of carbon-centered radicals to perthiyl radicals follows a pseudo first-order rate equation with an activation energy of 1.15 eV. A decrease in the initial concentration of the carbon-centered radicals or an increase in the in...