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