The product yields in X-irradiated aqueous solutions of glycylglycine (0.05 M and 1.0 M) were measured under deoxygenated conditions. Comparison was made between the results obtained from X- and 60 Co γ-irradiated glycylglycine solutions reported by Garrison, Sokol, and Bennett-Corniea (Radiat. Res. 53, 376-384, 1973). The mechanisms proposed by Garrison et al. were tested by evaluating the stoichiometric relationships. The two intermediate radicals, deamination and H-abstraction radicals, were produced in the initial interactions of glycylglycine with reactive species (<tex-math>$e_{{\rm aq}}^{-}$</tex-math>, OH, H) formed in H 2 O. Although the difference was fairly large at 0.05 M, the production of deamination radicals agreed well with the consumption of the radicals at 1.0 M. The production and the consumption of H-abstraction radicals were within the estimated experimental error in dilute solutions. Among all the products only the G value of aspartic acid decreased with increasing concentration of glycylglycine. This could be attributed to the fact that more acetylglycine is formed at the expense of aspartic acid at 1.0 M than at 0.05 M glycylglycine solutions. Competitive reactions involved with deamination radicals under conditions of homogeneously distributed reactants are discussed to elucidate the radiation chemistry of glycylglycine.

A study has been made of the radiation chemistry of glycylglycine in oxygen-free systems. These include dilute and concentrated solutions as well as the solid state. Detailed reaction stoichiometries for each system are formulated on the basis of product analysis. Specific contributions of radicals, ions, and excited molecules in the formation of products are discussed.

A study has been made of the γ-ray induced reactions of the peptide derivatives N-acetylglycine and glycylglycine in oxygenated solution. In these systems the OH radical is removed through reaction at the C-H position of the main-chain <tex-math>${\rm OH}+{\rm RCONHCH}_{2}{\rm R}\rightarrow {\rm RCONH}\dot{{\rm C}}{\rm HR}+{\rm H}_{2}{\rm O}$</tex-math> to yield the corresponding peroxy radical via <tex-math>${\rm O}_{2}+{\rm RCONH}\dot{{\rm C}}{\rm HR}\rightarrow {\rm RCONNCH}(\dot{{\rm O}}_{2}){\rm R}$</tex-math>. The subsequent chemistry has been examined in detail. The proposed reaction schemes account for the yields of ammonia, glyoxylic acid, formic acid and hydrogen peroxide observed in both systems.

In extending previous studies on the radiation-induced deamination of the simpler α-amino acids in oxygen-free solution, it has been found that reductive deamination by the hydrated electron, <tex-math>${\rm e}_{{\rm aq}}^{-}$</tex-math>, is not confined to the free amino acid configuration. The dipeptides, tripeptides, and other derivatives of glycine, for example, are found to react with <tex-math>${\rm e}_{{\rm aq}}^{-}$</tex-math> (essentially quantitatively) to cleave the N-C bond of the primary amino group. Radiolysis studies of variously substituted amino compounds in solutions containing second solutes which are specific scavengers of H, OH in the one case and of <tex-math>${\rm e}_{{\rm ag}}^{-}$</tex-math> in the other indicates that reductive deamination by <tex-math>${\rm e}_{{\rm aq}}^{-}$</tex-math> requires an unsaturated function at the carbon position α to the amino group. It is suggested that <tex-math>${\rm e}_{{\rm aq}}^{-}$</tex-math> adds to this function and that N-C cleavage then ensues. Observed correlations between rates of reaction of <tex-math>${\rm e}_{{\rm aq}}^{-}$</tex-math> and pK of the amino group are in accord with this formulation. Velocity constants for reaction of <tex-math>${\rm e}_{{\rm aq}}^{-}$</tex-math> with amino acids and derivatives in both acidic and neutral solution were obtained by the method of competition kinetics.