Grafting Metal–Organic Frameworks for Improved Enantioseparation

Chiral metal-organic frameworks (cMOFs) are emerging chiral stationary phases for enantioseparation owing to their porosity and designability. However, a great number of cMOF materials show poor separation performance for chiral drugs in high-performance liquid chromatography (HPLC). The possible reasons might be the irregular shapes of MOFs and the low grafting degree of chiral ligands. Herein, MIL−101−Ppa@SiO[sub.2] was synthesized by a simple coordination post-synthetic modification method using (S)-(+)-2-Phenylpropionic acid and applied as the chiral stationary phase to separate chiral compounds by HPLC. NH[sub.2]−MIL−101−Ppa@SiO[sub.2] prepared via covalent post-synthetic modification was used for comparison. The results showed that the chiral ligand density of MIL−101−Ppa@SiO[sub.2] was higher than that of NH[sub.2]−MIL−101−Ppa@SiO[sub.2], and the MIL−101−Ppa@SiO[sub.2] column exhibited better chiral separation performance and structural stability. The binding affinities between MIL−101−Ppa@SiO[sub.2] and chiral compounds were simulated to prove the mechanism of the molecular interactions during HPLC. These results revealed that cMOFs prepared by coordination post-synthetic modification could increase the grafting degree and enhance the separation performance. This method can provide ideas for the synthesis of cMOFs.