光学活性起源的研究Ⅶ．^（60）Coγ射线对D，L－亮氨酸γ辐解立体选择的研究

THE INQUIRY ON THE SOURCE OF OPTICAL ACTIVITY Ⅶ.STUDY ON THE STEREOSELECTIVE GAMMA RADIOLYSIS OF LEUCINEENANTIOMERS

以Ｄ－、Ｌ－、和Ｄ，Ｌ－亮氨酸为研究对象，研究￣（６０）Ｃｏ的非极化γ射线对亮氨酸异构体辐解时的立体选择性。实验通过毛细管手性柱气相色谱法测得Ｄ－和Ｌ－亮氨酸的相对含量，并测定了其辐解气体产物Ｈ＿２、ＣＯ＿２和ＮＨ＿３相对产率。结果表明非极化的γ射线对Ｄ，Ｌ－亮氨酸的辐解是随机的，无立体选择性。

?irradiation of D,L-amino acids introducing the stereoselective radiolysis is an openquestion concerning origin of optical activity.Merwitz(1976)reported that the rate of theγ-ray induced solid state decarboxylation of ￣(14)C labeled D-phenylalanine was 2.7 timesgreater than that of L-phenylalanine. Norden(1985)reported that the decarboxylation ofsublimed D-and L-leucine by nonpolarized γ-rays gave different yields ,with a A_D/A_L for￣(12)CO_2 cleavage ratio of 2.Since impurities have significant effect on the stop or the enhance-ment of chain reaction,the conclusion from the separatively purified amino acids is howeverdubious. In the paper,sublimed D-,L-leucine and the D,L-racemate are irradiated by ￣(60)Coγ-ray under strictly controlled condition. Chirasil-val capillary column gas chromatography isused to determine the peak ratios of D,L-leucine,D-and L- leucine. From the results ofTable 1 and 2, the changes of G values with dose are nearly the same. The relative yields ofthe radiolysis gas products(H_2,CO_2,NH_3)of D-and L-leucine are detected.The experimen-tal data show that γ-irradiation induced degradations of D-and L-leucine give generally equalamount of gas H_2,CO_2,and NH_3, indicating no stereoselective effects observed.