手性氨基酸分子的温度诱导相变——自发对称性破缺与复原

运用统计理论热力学函数自由能ΔG、焓ΔH、熵ΔS、平衡常数K与粒子平动、振动、转动配分函数关系, 并通过变温D- 与L-CDBrClF实例计算, 证明在宏观温度变量下, 可以导致手性分子D⇔L平衡中宇称破缺熵差的反号. 根据作者科研组14年来, 采用变温X衍射、中子衍射、比热、直流和交流磁化率、¹H和¹³C固相核磁共振、拉曼光谱、晶体旋光和双折射、超声测定相变等实验方法, 证明Salam假说预言的温度范围(200～250 K)存在温度变量诱导的相变, 产生自发对称性破缺. 在宇称破缺能差(PVED)接近0条件下, 宇称破缺熵差导致D和L分子反向的物理行为, 产生分叉机制(bifurcation mechanism). D和L分子的能量差别, 可能是早期生命起源时, L氨基酸富集的原因. 实验还发现, 在低温变温下自发对称破缺的复原. 由于晶相结构限制分子重排, Salam相变不是D→L的构型相变.

Temperature-induced Phase Transitions in Chiral Amino Acids-- Search of Spontaneous Parity-Breaking and Restoration

The effects of temperature on the parity-violating entropy and energy differences of chiral molecules are investigated both theoretically and experimentally. Statistical thermodynamics calculations indicate the possible occur-rence of sign reversal of parity-violating entropy difference at different temperatures, which is supported by tempera-ture-dependent polarized Raman spectra of D-alanine and L-alanine. An incoherent spontaneous symmetry breaking is proposed to describe the bifurcation mechanism between mirror-image systems at the critical temperature, in which usually violated parity symmetry will be dynamically restored again. An asymmetric double-well potential with a tiny parity-violating energy difference(PVED) in the depths of the two potential wells showed that the presence of PVED can lead to the enrichment of L-form amino acid. Tunneling dynamics of amino acids with PVED provides a plausible mechanism for much faster development of homochirality.