物理化学学报 >> 2004, Vol. 20 >> Issue (11): 1345-1351.doi: 10.3866/PKU.WHXB20041112

研究论文 上一篇    下一篇

手性分子中的宇称破缺:D-和L-丙氨酸的变温中子结构研究

王文清;刘轶男;龚   

  1. 北京大学化学与分子工程学院, 应用化学系,北京 100871
  • 收稿日期:2004-05-17 修回日期:2004-07-01 发布日期:2004-11-15
  • 通讯作者: 王文清 E-mail:wangwq@chem.pku.edu.cn

Parity Violations on Molecular Chirality: Neutron Crystal-Structure of D- and L-alanine

Wang Wen-Qing;Liu Yi-Nan;Gong Yan   

  1. Department of Applied Chemistry , College of Chemistry and Chemical Engineering, Peking University, Beijing 100871
  • Received:2004-05-17 Revised:2004-07-01 Published:2004-11-15
  • Contact: Wang Wen-Qing E-mail:wangwq@chem.pku.edu.cn

摘要: 利用单晶的中子衍射研究295 K和60 K时丙氨酸对映体的结构特征以及由D到L构型转变的可能性.中子衍射数据揭示了变温过程中产生的晶格扭曲和的扭转. 通过分析宇称破缺能差EPV随二面角及扭角的变化,肯定了D-丙氨酸能量高于L-丙氨酸的结论.降温过程中D-和L-丙氨酸的弱氢键的行为的差异表明,可能是由于电弱相互作用宇称不守恒所引起.丙氨酸中子结构再次证实Cα-H…O氢键的存在.然而,比较295 K和60 K(高于和低于丙氨酸相变温度250 K)的中子衍射结构数据,表明并没有发生D型到L型的构型转化,这意味着Salam相变不是传统意义的结构相变.

关键词: 宇称破缺, 分子手性, 中子衍射, D-和L-丙氨酸

Abstract: The role of chirality determines the origin of life that almost all amino acids utilized in living systems are of the L-type. Starting from Z0 interactions, Salam speculated on an explanation in terms of quantum mechanical cooperative and condensation phenomena where the electron-nucleon system has the same status as Cooper-pairing, which could give rise to second-order phase transitions(including D to L transformations) below a critical temperature Tc(~250 K). Neutron diffraction of single crystal D- and L-alanine was performed to look for the characteristic structural feature above and below the Tc (295 K and 60 K) and the possibility of D- to L-type transformation. Data analysis of the temperature effect on the crystal lattice together with the NH3+ torsional motion, parity-violating energy difference (ΔEPV) as a function of dihedral angle (ω), the CO2(θ) and NH3(ψ)torsion angles and the contribution of Cα-H…O=C hydrogen bond is discussed. Observation of the behavior of weak hydrogen bonding during the cooling process threw a light on the distinction between D- and L-alanine, which could be attributed to the parity-violating weak interactions. Measurements of the neutron crystal-structure of D-alanine rule out the possibility of configuration transition to L-alanine, which means that Salam phase transition is not a conventional structure transition.

Key words: Parity violation, Molecular chirality, Neutron diffraction, D- and L-alanine