Production of Pyrazine Derivatives in the Radiolysis of Aqueous Solutions of the Cyclic Dipeptides

Abstract

RADIATION-INDUCED reactions in aqueous solutions of amino-acids, peptides, and related compounds have been treated in a number of reports from this Laboratory¹. In connexion with this work, we have had occasion to examine the effects of γ-irradiation on the ultra-violet absorption spectra of solutions of various simple peptides. The measurements reveal that solutions of the cyclic dipeptides under specific conditions exhibit pronounced and characteristic post-irradiation changes. If, for example, an oxygen-free solution of alanine anhydride is irradiated and examined spectrophotometrically, the differential spectrum (read against unirradiated solution) shows negligible absorption above 2600 Å. so long as the solution is not exposed to the atmosphere. However, if oxygen is introduced, an absorption maximum in the longer wave-length region slowly appears. This post-irradiation change is accelerated by addition of either acid or base. In neutral and basic solution the absorption maximum is at about 320 mµ ; in acid solution the maximum shifts to 340 mµ. This shift is reversible, and the evidence is that the final yield of the absorbing species is essentially independent of the pH of the solution during the post-irradiation oxidation. Solutions of glycine anhydride exhibit quite similar properties except that the wavelength of maximum absorption (320 mµ) is independent of pH. It is also to be noted that these post-irradiation changes are not observed if oxygen is present during irradiation.