Relationship Between Structure of Nitrogenous Compounds and their Sensitivity to X-Rays

Abstract

IN previous investigations, the dependence of sensitivity to X-radiation on molecular structure has been examined for various compounds1. One of our more recent, unpublished, results is the deamination of amino-acids by X-radiation, which has been reported independently by Stein and Weiss2. On the basis of our experimental results however, some difficulties exist concerning the mechanism of the reaction. Weiss3 has put forward the hypothesis that the reaction of ionizing radiations is due to the formation of radicals formed by the splitting of water molecules. This simple mechanism should give an ionic yield of not more than unity if one OH radical is involved in the deamination of one mono-amino-mono-carboxylic acid molecule, and this appears to be the yield reported by these authors. We have, however, found that the ionic yield of the deamination of glycine rises gradually with its concentration to a value of three for 0·2 gm./ml. (see ). This ionic yield exceeding unity means, when interpreted in terms of radicals, that one OH radical can affect more than one amino-acid molecule, which is unlikely, or that one ion pair can give rise to more than one OH radical, or that some of the radiation energy can form radicals by excitation rather than by ionization. In general, therefore, one would always expect an ionic yield exceeding unity in relatively concentrated solutions, independent of the nature of the solute, with perhaps the exception of very big molecules. A further possibility, but remote in the case of deamination, would be a chain reaction of some sort.