Preparation of novel optically active polyamide@silica hybrid core-shell nanoparticles and application for enantioselective crystallization

A kind of hybrid core-shell nanoparticles (NPs) based on a novel chiral polyamide for the application in enantioselective crystallization was studied in this work. First, the optically active polyamide (PA11DT) derived from bio-based D-tartaric acid and 1,11-undecanediamine was synthesized. Fantastically, the aliphatic polyamide with low chiral atom content in the backbone showed rather strong optical activity. Particularly, PA11DT in solid state displayed more intense optical activity than that in solution, which is due to its more regular helical aggregation in solid state. Second, the core-shell structural NPs consisting of PA11DT and SiO2 were designed to make sure its stable helical structure in practice. The PA11DT@SiO2 NPs with the core-shell structure and a uniform diameter were successfully achieved in a preformed aqueous microemulsion system through an in-situ approach. The obtained nanoparticles mantained strong optical activity and displayed more thermostable chirality. The core-shell nanospheres can be used as a specific chiral additive to induce enantioselective crystallization of racemic alanine. As a result, D-alanine was crystallized preferentially with an e.e. value to 63% after 48 h crystallization.