Boyd M. Weeks

Radiolysis of aqueous solutions of glycine.

A detailed mechanism for the radiolysis of the glycine-water system is developed. The treatment is based on the various literature sources and on new experimental findings which are described. It is proposed that the indirect action of radiation on glycine in oxygenfree solution results in formation of the free-radical intermediates CH/sub 2/COOH and NH/sub 2/CHCCOH. Although most of these ultimately yield acetic acid and glyoxylic acid, respectively, it is concluded that some undergo radical-radical reaction to yield succinic acid, aspartic acid, and diaminosuccinic acid. Effects of oxygen, glycine concentration, and pH are discussed. (auth)

Radiation Chemistry of Compounds Containing the Peptide Bond

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.

Some effects of heavy-particle irradiation of aqueous acetic acid.

In the preceding papers of this symposium, consideration has been given to the problem of determining the mechanism of the decomposition of water by highenergy radiation. Formation of the chemically reactive radicals H and OH and the decomposition products H2 and H202 have been critically investigated in the light of available evidence. According to present concepts (1-5) of the mechanism of the indirect action of radiation on solutes, the preliminary chemical effect is the dissociation, by ionization and excitation, of water molecules to give the H and OH radicals. The observed chemical changes in irradiated solutions are attributed to subsequent reactions of H and OH radicals with one another and with solute molecules. The relative amounts of those radicals that combine to form H2 and H202 and of those that are available for reaction with added solute depend upon the ionization density of the effective radiation. Radiation chemical reactions in dilute solution have been discussed in the previous papers in some detail, primarily however, from the standpoint of determining the yields of free H and OH. In studies of this type, in which the principal objective is the determination of the mechanism of water decomposition, the use of relatively simple solute systems is advantageous because the complete mechanism of the over-all reaction must be determined. Radiolysis of most aquo-organic systems, however, usually results in the formation of a spectrum of reaction products many of which may be formed in amounts which are difficult, if not impossible, to determine by classical analytical procedures. The development of radiometric and chromatographic techniques during the last few years has made it possible to study quantitatively many of the systems which were previously not amenable to investigation. Recently, as part of a general investigation (6-8) of radiation-induced reactions of organic substances in aqueous solution, we have applied these techniques to a study of the products formed in aqueous acetic acid by heavy-particle irradiation. Some of the methods and results are described in the present paper.

Water Decomposition Yields in the Radiolysis of Aqueous Formic Acid‐Oxygen Solutions by Cyclotron‐Produced Radiations

Water decomposition yields in the radiolysis of aqueous formic acid-- oxygen solutions by cyclotron-produced protons and neutrons are reported. Two primary processes occur, (1) H/sub 2/O = H + OH and (2) H/sub 2/O + 1/2H/sub 2/0/ sub 2/. The absolute yields of reactions 1 and 2 are essentially independent of pH over the corresponding range and, to a first approximation, are related to the yields of observed products by the equations G(l) = G(CO/sub 2/) = -G(0/sub 2/), G(2) = 2G(H/sub 2/), and G(1) + 0.5 G(2) = G(H/sub 2/0/sub 2/). The values G(l) = 2.39 plus or minus 0.05 and G(2) = 1.26 plus or minus 0.18 were obtained for 10Mev protons. The value G(1)/G(2) = 2.73 plus or minus 0.10 was obtained from the neutron data. (L.T.W.)