Selective Chiral Symmetry Breaking during Crystallization: Parity Violation or Cryptochiral Environment in Control?

Abstract

We have attempted to check experimentally whether the parity violating energy difference (PVED) between enantiomers is ultimately responsible for any bias in the final homochirality of crystals, after suitable autocatalytic amplification. When two equivalent (50-50) chiral populations of L- and D-crystals (of either NaClO3 or NaBrO3) generated independently are mixed and undergo dissolution-crystallization, one of the chiral populations disappears randomly in an irreversible autocatalytic competition process that nurtures the other population. If enough experiments are carried out with this 50-50 mixture of chiral crystals, a random distribution of solutions with final L- or D- crystals is obtained in total. However, when the two populations of L- and D-crystals are generated together in the same solution and undergo a dissolution-crystallization process, a nonrandom distribution of the final handedness among different homochiral solutions is obtained. This selective symmetry breaking is sporadic although always in the same direction; thus, we discard any explanation based on PVED effects. We conclude that the result represents an experimental demonstration of selective chiral symmetry breaking on a macrocopic level brought about by cryptochiral environmental impurity.