Temperature dependence of optical rotation study on parity-violating phase transition of D-, L-, and DL-alanine

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.