C-N bond cleavage reactions on the radiolysis of amino-containing organic compounds and their derivatives in aqueous solutions

Abstract

Purpose : To investigate regularities observed in the course of reactions involving cleavage of C-N bonds on the radiolysis of amino-containing organic compounds and their derivatives in aqueous solutions. Materials and methods : Aqueous solutions of amino-containing compounds, saturated with Ar or O 2, were exposed to γ-radiation from a 137 Cs source. The absorbed dose-rate was 0.33 Gy s −1, the absorbed dose range was 0.1-7.5 kGy. Analyses for ammonia and amino-containing organic compounds were performed using an amino acid analyser, and analyses for other radiolysis products were made by gas-liquid chromatography. Results : The presence of a hydroxyl group in the β-position to the amino group promotes deamination of amino alcohols, amino acids, di- and tripeptides, these processes being associated with the possible occurrence of monomolecular fragmentation of the respective radicals. Oxygen inhibits the deamination of α, β-amino alcohols and hydroxyl-containing amino acids. The presence of alkyl substituents in the amino group favours C-N bond cleavage on the radiolysis of amino alcohols, whereas the presence of an acyl group sharply suppresses this process. Replacement of the hydroxyl group in molecules of the initial amino alcohols by a hydrogen atom (i.e. a changeover to alkylamines) or by a methoxy group decreases the efficiency of deamination sharply. The presence of hydroxyl groups in side residues of di- and tripeptides promotes destruction of the peptide chain with formation of amides of amino acids, while suppression of deamination and main chain destruction processes in these compounds is observed in the presence of oxygen. Conclusions : The most effective processes leading to the C-N bond cleavage on the radiolysis of aqueous solutions of amino-containing organic compounds are those in which the key role is played by reactions of monomolecular decomposition of radicals of the initial compounds.