Selective decomposition of either enantiomer or aspartic acid irradiated with60Co-γ-rays in the mixed aqueous solution with D- or L-alanine

Abstract

Aqueous solutions of various amino acids were irradiated with60Co-γ-rays, and subsequently the remaining amino acids were analyzed using HPLC. The D37 for the 1 mM glycine and alanine solutions were 1.95×104 and 1.48×104 Gy, respectively. However, when the mixed solutions of glycine and alanine (each in 0.5 mM) were irradiated under the identical condition, the D37 for the glycine decomposition increased to 3.56×104 Gy, while that for alanine decreased to 0.65×104 Gy. A similar phenomenon was observed also in the case of the mixed solutions of aspartic acid and alanine. Namely, aspartic acid was protected from the attack of radiation by the presence of alanine in the solutions. The most interesting finding in this combination experiment is that, when D,L-aspartic acid was irradiated in the presence of L-alanine, the radiation-sensitivity of L-aspartic acid decreased selectively and vice versa. Namely, the asymmetric field induced in the solutions by adding D- or L-alanine might affect the radiodecomposition rate of either aspartic acid. Addition of glycine to D,L-aspartic acid did not bring about the asymmetric decomposition. It seems that some interaction between these amino acid molecules resulted in this effect.