Thiol-ene click synthesis of silica-immobilized chiral metal-organic cage for high-performance liquid chromatographic enantioseparation.

Abstract

Metal-organic cages (MOCs), as emerging supramolecular porous materials, have become a research focus in the field of separation due to their unique structures and excellent solubility. In this study, a novel chiral composite, denoted as MOC-SH-(R)-(+)-α-All@SiO2, was fabricated by constructing chiral MOC-SH-(R)-(+)-α-All via thiol-ene click reaction between (R)-(+)-α-allylalanine and thiol-functionalized MOC (MOC-SH), followed by covalent immobilization of the resultant chiral MOC molecules onto the surface of aminated silica microspheres. This composite material was used as a new chiral separation medium for HPLC enantioseparation. Baseline resolution was achieved for more than two-thirds of the chiral analytes including alcohols, esters, carboxylic acids, and phenols on the MOC-SH-(R)-(+)-α-All@SiO2-packed column, with the maximum resolution up to 6.67. The effects of injection mass and mobile phase composition on the separation performance were examined. The relative standard deviation (RSD) values of retention time and peak area obtained by multiple separations of ethyl mandelate were less than 1.0 %, indicating that this chiral column has good reproducibility and stability. In addition, the chiral column exhibits good complementarity with commercial chromatographic columns (Chiralpak AD-H and Chiralcel OD-H columns) as well as the previously reported MOC-based chiral column. This study demonstrates that MOC-SH-(R)-(+)-α-All@SiO2, as a new HPLC separation medium, has great application potential in the field of enantioseparation.