Radiation chemistry of compounds containing the peptide bond.

Abstract

A few years ago we proposed that major aspects of the radiation chemistry of a wide diversity of organic nitrogenous compounds both in the solid state and in aqueous solution could be correlated and generalized in terms of a common locus of reaction (1-4). These earlier considerations of mechanism are consistent with the point of view that the formation of free radical intermediates and molecular products from compounds of the type R2N-CH(R)2 can be characterized in terms of chemical changes involving the aliphatic carbon atom adjacent to the nitrogen function. Subsequent applications of this concept to the radiation chemistry of primary amines, secondary amines, N-alkyl amides, and peptides have been made, and in a more recent report we have given detailed chemical evidence of the validity of this approach to the study of the indirect action of ionizing radiation on the variously substituted N-C bonds of protein in oxygenated solution (5). In the present paper we are concerned more specifically with radiation-induced reactions of the peptide bond in simpler chemical compounds, both in solution and in the solid state. The N-acylamino acids provide a convenient model for such studies. The chemical and physical properties of the acetylated amino acids are fairly well defined, and, in addition, there is considerable literature on analytical methods for the separation and determination of this particular class of peptide. In fact, the techniques of partition chromatography were originally developed by Martin and Synge (6) for the express purpose of analyzing protein hydrolyzates after acetylation. Cleavage of the N-C Bond The radiation-induced oxidation of peptides in oxygenated solution can be represented (5) in terms of reactions 1 and 2. The relative importance of these reactions I This work was performed under the auspices of the U. S. Atomic Energy Commission.