Can Non-Photochemical Laser induced Nucleation be a stereoselective Process?

International audienceChirality means that a system cannot be superimposed on its image in a mirror. Chirality exists in molecules and can be generated in crystals by a specific arrangement of chiral or even achiral molecules. The latest is known as supramolecular chirality. The challenge with chirality is to separate the stereoisomers called enantiomers for molecules and enantiomorphs for crystals. Therefore, many crystallisation processes have been developed to produce enantiopure compounds such as Viedma ripening, deracemization or preferential crystallization.In 1996, Garetz et al1 discovered a new crystallization process in which nucleation is triggered in supersaturated solutions by high energy laser nanosecond pulses. This process is called Non-Photochemical Laser Induced Nucleation (NPLIN) because is not based on an absorption mechanism. Since, NPLIN has been applied to many compounds: organic molecules2,3, inorganic salts4,5, and proteins6. It was in particular found out that it is possible to control polymorphism2,3,7,8 with NPLIN. Logically, attempt to control the stereoselectivity by changing the polarization of light was also tested. To date, attempts were not successful for sodium chlorate9,10 nor 4,4‘-dimethylchalcone11 two compounds exhibiting supramolecular chirality. In this communication, Ethylenediamine sulfate (EDS) has been crystallized by exposure to laser light with linear, right circularly and left circularly polarized light. EDS is achiral but it was chosen because the main crystallographic direction exhibits a fourfold screw axis running clockwise (41) or anticlockwise (43), and this feature could favour a stereoselective interaction with the right or left handed circular laser polarization. We will thus report the main results obtained and try to answer the question “can NPLIN be stereoselective?”. This aims at improving the understanding of the NPLIN mechanism that is still not fully understood