Degree of Supersaturation-Regulated Chiral Symmetry Breaking in One Crystal

Abstract

This paper aimed at studying chiral symmetry-breaking phenomena in one crystal. Preferential crystallization of racemic asparagines was carried out in nonseeded stagnant solutions through slow cooling. By varying the supersaturation, only one transparent crystal could be obtained at enough low supersaturation of dl-asparagine, and the crystal was not pure enantiomer with crystal enantiomeric excess increasing inversely with the degree of supersaturation. Crystal enantiomeric excess can amount up to 85% in one transparent crystal. Because no secondary nucleation occurred except for stochastic primary nucleation, we suggest that primary nucleation and competition between l- and d-nuclei were considered to be a mechanism for asymmetry amplification. High-performance capillary electrophoresis coupled with laser-induced fluorescence was used to separate and quantify l- and d-asparagine and the enantiomeric excess value can be calculated according to their concentration.