摘要
由于电弱力宇称不守恒,氨基酸对映体分子间存在宇称破缺能差,通过Z0粒子的介导,在某临界温度下,氨基酸分子会发生类似于BCS(Bardeen-Cooper-Schrieffer)超导的玻色凝聚,引起二级相变,理论推测相变温度约在250K.本文通过原位测量在240～290K下,D型、L型和DL型缬氨酸晶体的旋光角随温度的变化,发现D型和DL型缬氨酸晶体在270K有旋光角跃变,L型缬氨酸晶体的旋光角基本不变,为Salam预言的二级相变提供了直接证据.
Most biomolecules are chiral, but only one enantiomeric form occurs in nature. Life is based on L-amino acids and D-sugars rather than the D-amino acids and L-sugars. The homochirality is a hallmark of life, which remains a puzzle for theories of the chemical origin of life. This broken symmetry is believed to be a feature of fundamental physics, a result of symmetry breaking by the weak force, which makes one enantiomer slightly more stable than the other. The natural L-amino acids, L-alanine and L-valine were found to be more stable than their D-amino acids. For glyceraldehyde (n = 3), the parent of the higher sugars, the D form is PVED-stabilized by about 10(-17) kT. D-oxyribose is also PVED-stabilized in the C2-endo form found in DNA. It has recently become recognized that homochirality is not just a consequence of life. This is because life and self-organization seem to require polymers and polymerization do not go in racemic solution. It is found that polymerization to give stereoregular biopolymers, in particular poly-D-ribonucleotides and poly-L-peptides, proceeds efficiently only in almost homochiral monomer solutions. In racemic solution, addition of the 'wrong' hand to the growing chain tends to terminate the polymerization. The weak force appears to predict hand whatever came first. For nucleic acids, D-glyceraldehyde and a-D-ribose are more stable and the right-hand helical backbone of DNA is also PVED-stabilized. For proteins, the L-amino acids are more stable. In 1991 Abdus Salam proposed a hypothesis: the subtle energy difference (PVED) of chiral molecules induced by Z(0) interactions combined with Bose condensation may cause homochirality among nineteen amino acids (excluding the achiral glycine). This is a consequence of second-order phase transition at a critical temperature T-c, which is analogous to that of BCS(Bardeen-Cooper-Schrieffer) superconductivity. The value of temperature T-c is estimated to be around 250 K deduced from Ginzberg-Landau equation. To verify the Salam hypothesis, one ma
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2004年第5期540-545,共6页
Acta Physico-Chimica Sinica
基金
国家高技术研究发展规划(863项目
103-13-06-01)
国家自然科学基金(20310202026)资助项目~~
关键词
天然旋光角
双轴晶体
缬氨酸
Salam假说
二级相变
氨基酸
natural optical rotation angle
biaxial crystal
D-L- and DL-valine
Salam hypothesis
second-order phase transition
