Amino acid radicals produced chemically in aqueous solutions. Electron spin resonance spectra and relation to radiolysis products

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Abstract
Amino acid radicals were generated by the reaction of titanium trichloride with hydrogen peroxide in the presence of an amino acid, and were identified by electron spin resonance spectroscopy. An amino acid analyzer was used to show that the products of this reaction were the same as those of the corresponding γ-irradiated, oxygenated aqueous amino acid solution. Cysteine, cystine, and homocystine gave identical spectra which were attributed to [Formula: see text]·radicals, whereas penicillamine gave [Formula: see text]·radicals. Most other amino acid radicals were formed by the abstraction of a hydrogen atom from the C2 position (numbered from the amino group). This was true for dl-α-alanine, β-alanine, taurine, dl-aspartic acid, γ-aminoisobutyric acid, dl-serine, and dl-valine, although with valine a lower concentration of the radical resulting from the removal of a hydrogen atom from C3 was also observed. Abstraction from the C3 position also occurred with dl-threonine. These facts are consistent with the view that the strong negative inductive effect of the NH3+ group deactivates the neighboring C—H bond towards attack by the electrophilic hydroxyl radical. Glycine formed one radical by the loss of a hydrogen atom from the C1 position, and a second by deamination.

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