A number of optically active amino acids, both in the solid state and as sodium or hydrochloride salts in aqueous solution, have been exposed to ionizing radiation from a 3000 Ci60Co γ-ray source to see if radioracemization might accompany their well-known radiolysis. γ-Ray doses causing 55-68% radiolysis of solid amino acids typically engendered 2-5% racemization, while aqueous solutions of the sodium salts of amino acids which underwent 53-66% radiolysis showed 5-11% racemization. Amino acid hydrochloride salts in aqueous solution, on the other hand, showed little or no radioracemization accompanying their radiolysis. Both radiolysis, and radioracemization were roughly proportional to γ-ray dose in the range studied (1-36×106 rads). Mechanisms for the radioracemization of amino acids in the solid state and as aqueous sodium salts are discussed, and the absence of radioracemization for aqueous hydrochloride salts is rationalized. Isovaline, a non-protein amino acid which has been isolated from the Murchison meteorite, contains no α-hydrogen atom and is therefore incapable of racemization via the chemical mechanisms by which ordinary amino acids racemize. Nevertheless, isovaline suffers radioracemization in the solid state to an extent comparable to that shown by ordinary amino acids, as do its sodium and hydrochloride salts in the solid state. The sodium salt of isovaline in aqueous solution, however, fails to racemize during its radiolysis. Several implicaitons of the newly described phenomenon of radiomization are pointed out for the fields of geochemistry and cosmochemistry.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Environmental Science(all)
- Agricultural and Biological Sciences (miscellaneous)
- Earth and Planetary Sciences(all)