Acta Phys. -Chim. Sin. ›› 2004, Vol. 20 ›› Issue (11): 1345-1351.doi: 10.3866/PKU.WHXB20041112

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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

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