Dual-ligand 3D lammelar chiral metal-organic framework for capillary electrochromatographic enantioseparations.

Dual-ligand metal-organic frameworks (MOFs) based on tryptophan and camphoric acid were designed and synthesized as the stationary phase of the capillary electrochromatography (CEC) system. This CEC system showed significantly improved enantioseparation ability for nine drugs, compared with the single-ligand MOF stationary phase. Characterization methods such as N adsorption-desorption isotherms and scanning electron microscopy proved that the dual-ligand MOFs possessed excellent 3D spatial structures (ligand ratio is 1:1) which ensured the enantioseparation capability of the CEC system. The influence of ligand types on the chiral selectivity of MOFs was explored using racemic phenylalaninol and its single enantiomers as models. When the chiral type of the ligands is consistent, the enantioseparation ability of the CEC system is better. The chromatographic conditions such as buffer concentration, buffer pH, organic solvent addition ratio, and applied voltage were optimized, and satisfactory repeatability and stability of the CEC system were verified. Additionally, the enantioseparation mechanism of the CEC system was discussed through adsorption kinetic experiments, adsorption isotherm fitting, and thermodynamics.