Use of chiral ionic liquid as additive for synergistic enantioseparation of basic drugs in capillary electrophoresis

Update on chiral recognition mechanisms in separation science

The stereospecific analysis of chiral molecules is an important issue in many scientific fields. In separation sciences, this is achieved via the formation of transient diastereomeric complexes between a chiral selector and the selectand enantiomers driven by molecular interactions including electrostatic, ion-dipole, dipole-dipole, van der Waals or π-π interactions as well as hydrogen or halogen bonds depending on the nature of selector and selectand. Nuclear magnetic resonance spectroscopy and molecular modeling methods are currently the most frequently applied techniques to understand the selector-selectand interactions at a molecular level and to draw conclusions on the chiral separation mechanism. The present short review summarizes some of the recent achievements for the understanding of the chiral recognition of the most important chiral selectors combining separation techniques with molecular modeling and/or spectroscopic techniques dating between 2020 and early 2024. The selectors include polysaccharide derivatives, cyclodextrins, macrocyclic glycopeptides, proteins, donor-acceptor type selectors, ion-exchangers, crown ethers, and molecular micelles. The application of chiral ionic liquids and chiral deep eutectic solvents, as well as further selectors, are also briefly addressed. A compilation of all published literature on chiral selectors has not been attempted.

Fabrication of ionic liquid functionalized silica with different anions and the application in mixed-mode and chiral chromatography

To realize the potential of ionic liquid functionalized silica to prepare mixed-mode and chiral stationary phases, two ionic liquid silane reagents with different anions were synthesized via a high-efficiency click reaction. Then they were decorated onto the surface of silica by a one-step bonding reaction. The functionalized silica was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and elemental analysis (EA). Two stationary phases provided satisfactory performance when compared with a commercial mixed-mode column. Notably, Sil-C10Im-D-BCS with D-3-bromocamphor-8-sulfonate (D-BCS) as anion presented chiral separation capacity towards 1,2,3,4-Tetrahydro-1-naphthol. The separation mechanism was investigated through multiple pathways, and the results revealed that the prepared stationary phases can retain and separate solutes through multiple interactions, like hydrophobic effect, ion exchange, hydrogen-bond interaction, etc. Quantum chemical calculation (QC) was employed to obtain the optimized structures and the binding energy of anions to cations. The results provided some insights into the retention mechanism from a molecular perspective. This work demonstrated the superiority of ionic liquid functionalized silica as mixed-mode stationary phases and the potential of chiral ionic liquid as chiral selectors.