  Chiral molecules are characterized by a specific optical rotation angle. An
experimental method was presented to dissect the temperature dependence of the
optical rotation angle with the molecular chirality of D-alanine, L-alanine and
DL-alanine crystals. Salam hypothesis predicted that quantum mechanical
cooperative and condensation phenomena may give rise to a second order phase
transition below a critical temperature linking the transformation of D-amino
acids to L-amino acids due to parity-violating energy difference. The
temperature- dependent measurement of the optical rotation angle of D-, L- and
DL-alanine crystals provided the direct evidence of the phase transition, but
denied the configuration change from D-alanine to L-alanine. New views on Salam
hypothesis are presented to demonstrate its importance in the application of
low temperature enantiomeric separation and the origin of biochirality.
