Chiral Breaking In Crystallization Induced By Amino Acid

Chiral symmetry breaking of crystals represented by sodium chlorate has been a hot spot in scientific research and academic discussion.Changes of physical and chemical factors can bring chiral symmetry breaking in the crystallization process of sodium chlorate aqueous solution,besides,some chiral additives which are called chiral inducer,such as amino acids and glucose,may also result in directed symmetry breaking of sodium chlorate crystals.At present,there are great differences on whether chiral inducers can direct chiral symmetry breaking,and what's more,scientists who hold a positive view can't agree on the mechanism of the induction.To figure out the above questions,investigation of the influence of chiral amino acid additives on the chiral symmetry breaking during crystallization is carried out in the article,and the mechanism of chiral symmetry breaking induced by amino acids was discussed meanwhile.Keeping the supersaturation,temperature and crystalline time in the same degree,we studied the influence of the different space structure of the following chiral amino acids additives,including L-Glycine,L-Alanine,L-Aspartic acid,L-Glutamic acid,L-Arginine,L-Tyrosine and L-Proline,on the chiral symmetry breaking of sodium chlorate crystals during crystallization.The crystal enantiomeric excess can be measured by CEE.Results show that the CEE of sodium chlorate aqueous solution crystallization induced by L-Arginine shows an obvious difference with the regular crystallization,producing a directed enantiomer amplification of D crystals.However,the CEE of the rest amino acids additives doesn't perform a significant result as the regular crystallization.The above results indicate that only L-Arginine is enantioselective.Meanwhile,the above results indicate that specific chiral additive can indeed direct chiral symmetry breaking.Due to the idea that only the space structure of chiral additive molecular can exert a significant influence on the induction process,we propose a mechanism based on size effect to explain the phenomenon that L-Arginine has a chiral induction effect during the crystallization of sodium chlorate aqueous solution.The chiral induction mechanism proposed by us thinks the matching of L-Arginine molecule and sodium chlorate crystal in the space structure can reduce the surface energy exists in nucleation process.Therefore,sodium chlorate molecules or molecular clusters are more likely to generate D crystals when they are nucleated with L-arginine as template,which results in the number of D crystals that are more than L crystals.It's obvious that the chiral induction mechanism based on size effect can explain our experimental results reasonably,to support the mechanism,we make the L-Arginine to induce the sodium bromate crystal which have the same space structure with the sodium chlorate crystal,The results show that L-Arginine also has a chiral induction effect on the crystallization of sodium bromate solution,which proves the correctness of the chiral induction mechanism based on size effect.To make the crystallization of sodium chlorate induced by L-Arginine achieve directional complete chiral breaking,L-Arginine is added into the solution containing excess sodium chlorate solute crystals,and abrasion-grinding is used to try to achieve directional complete chiral symmetry breaking.In the process,the effects of the content of L-Arginine,the amount of glass balls and the stirring speed on the symmetry breaking of sodium chlorate crystal system are investigated.The results show that L-Arginine has a strong chiral induction effect,even when the mole ratio of L-Arginine to sodium chlorate is 1:1350(the corresponding concentration of L-Arginine is only about 0.008 mol/L),the crystal system of sodium chlorate still achieve directional and highly chiral symmetry breaking.With the increase of L-Arginine content,the time to achieve the same degree of chiral symmetry breaking will be shortened,but the final degree of chiral symmetry breaking is not enhanced,the optical purity of D crystal which meanwhile represent the CEE of the system will stop at around 94%.However,when the ratio increase to 1:400(the corresponding concentration of L-Arginine is about 0.026 mol/L),the system is difficult to achieve a high degree of chiral symmetry breaking instead,it is probably because higher concentration of L-Arginine destroys the normal crystallization system of sodium chlorate;Similarly,increasing the amount of glass balls or the stirring speed can only shorten the system to achieve the same degree of chiral symmetry breaking,but unable to improve the final chiral symmetry breaking degree of the system,the optical purity of D crystal which meanwhile represent the CEE of the system will stop at the same level-around 94%.