A Chiral Hierarchical Helical Covalent Organic Framework for Enantiomeric Separation

Abstract

Helical covalent organic frameworks (HeliCOFs) are a special type of organic framework material that successfully integrates molecular chirality, channel chirality, and morphological chirality into a single crystalline entity. In this study, a novel P-heliCOF@SiO₂ core–shell composite with uniform particle size and shell thickness was prepared based on an in situ growth synthesis strategy. The shell thickness of the P-heliCOF@SiO₂ microspheres was adjusted by altering the concentration of the catalyst (acetic acid) and the ratio of reactants. The P-heliCOF@SiO₂ microspheres packed column was applied for the resolution of various racemates by HPLC. The P-heliCOF@SiO₂ core–shell composite exhibited excellent resolution performance for 25 pairs of enantiomers such as alcohols, esters, amines, epoxides, ethers, ketones, and organic acids. The effects of sample mass, column temperature, mobile phase composition, and different batches of chromatographic columns on the separation performance were investigated. Compared with the commercial Chiralcel OD-H and Chiralpak AD-H columns, the enantioseparation performance of the P-heliCOF@SiO₂ column shows good complementarity with that of these two widely used commercial columns for these chiral compounds. This chiral column also showed good reproducibility and stability for HPLC enantiomeric separation. This work develops a HeliCOF with hierarchical chirality as a novel chromatographic medium, which will push forward the applications of CCOFs in the field of chiral separation.