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

Abstract

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NH+3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.

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 (△ EPV) as a gen 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.