宇称与手性──丙氨酸(缬氨酸)对映体宇称破缺能差的实验探索

From Parity to Chirality-Experimental Search for Parity-viola-ting Energy Difference of Alanine and Valine Enantiomers

为什么构成生命的蛋白质全由Ｌ型氨基酸组成（ＤＮＡ和ＲＮＡ全由Ｄ核糖组成），这是至今未解的科学之谜．由Ｚ°玻色子介导的弱中性流宇称破缺被认为是造成生命分子手性起源的主要原因．１９９１年Ｓａｌａｍ提出由于Ｚ°相互作用，电子与电子或电子与核子耦合形成库柏对，在其临界低温下玻色凝聚，有可能引起氨基酸由Ｄ型向Ｌ型的二级相变，并理论预测相变温度为２５０Ｋ．本文用差分绝热连续加热量热法测定了１００～３００ Ｋ下 Ｄ－缬氨酸（丙氨酸）和Ｌ－缬氨酸（丙氨酸）的Ｃｐ－Ｔ图，实验发现在２７０Ｋ有明显的λ型二级相变．用量子磁强计测定了正向与反向１万高斯下直流磁化率行为，显示出Ｄ和Ｌ型氨基酸不同电子手征性密度特征．利用毛细管手性柱气相色谱分析否定了Ｓａｌａｍ预言的氨基酸由Ｄ型到Ｌ型相变的可能性．本文在实验中发现的相变，虽然不是Ｄ型到Ｌ型相变，但检测出了电弱力宇称不守恒能差在分子水平上的反映．

The first unifying principle in biochemistry is that the key molecules have the same handedness or chirality. The parity violating of electroweak neutral current (mediated by the Z(0) boson) is suggested as the main force inducing the observed homochirality. After exposing D-/L-alanine and valine crystals to temperatures ranging from 300 K to 100 K, we observed a second order phase transition by differential scanning calorimetry and DC magnetic susceptibilities measurement. No configuration change was found by chirasil-Val capillary column gas chromatography thus failing to validate Salam's predicted parity-violating energy difference (PVED) induced D-->L phase transition. The present studies show the experimental evidence provided by quantitative and apparently reliable estimates of PVED in phase transition of D- / L-alanine and valine crystals.