Acta Phys. -Chim. Sin. ›› 2005, Vol. 21 ›› Issue (07): 774-781.doi: 10.3866/PKU.WHXB20050715

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Temperature Effect on Molecular Chirality:X-ray Diffraction and Neutron Diffraction Studies of D-alanine

WANG Wen-qing; GONG Yan; YAO Nan   

  1. Department of Applied Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871
  • Received:2004-11-12 Revised:2005-02-28 Published:2005-07-15
  • Contact: WANG Wen-qing

Abstract: The results of X-ray diffraction of single crystal D- and L-alanine at 300, 270, 250 K and neutron diffraction of D-alanine at 300, 260, 250, 240 K were presented to look for the static and dynamical structure feature of Salam phase transition. No change in the space group P212121 symmetry was observed. The data rule out the hypothesis of a conventional structural phase transition and reveal a subtle and continuous symmetry breaking that occurs below ~250 K. A vibrationally generated electronic ring current model was explained the temperature effect on magnetic susceptibilities and opposite optical rotation phenomena related to the bond lengths of αC-H(2), N(1)-H(1), N(1)-H(4), and N(1)-H(6) lengthening (or contraction). A picture of dynamic disorder due to the protonic motion was presented in the intermolecular hydrogen bonds between the NH3+ group and the CO2- group. Salam predicted the enhancement of parity-violating energy difference (PVED) due to temperature-induced phase transition. Tunneling dynamics of amino acids with PVED may provide a bifurcation mechanism for much faster development of homochirality.

Key words: Temperature effect, Phase transition, X-ray diffraction, Neutron diffraction, D-alanine single crystal, Parity-violating energy difference