Effect of fabrication strategy on the enantioseparation performance of β-cyclodextrin-functionalized polymethacrylate monoliths: A comparative evaluation

Enantioseparation/Recognition based on nano techniques/materials

Enantiomers show different behaviors in interaction with the chiral environment. Due to their identical chemical structure and their wide application in various industries, such as agriculture, medicine, pesticide, food, and so forth, their separation is of great importance. Today, the term "nano" is frequently encountered in all fields. Technology and measuring devices are moving towards miniaturization, and the usage of nanomaterials in all sectors is expanding substantially. Given that scientists have recently attempted to apply miniaturized techniques known as nano-liquid chromatography/capillary-liquid chromatography, which were originally accomplished in 1988, as well as the widespread usage of nanomaterials for chiral resolution (back in 1989), this comprehensive study was developed. Searching the terms "nano" and "enantiomer separation" on scientific websites such as Scopus, Google Scholar, and Web of Science yields articles that either use miniaturized instruments or apply nanomaterials as chiral selectors with a variety of chemical and electrochemical detection techniques, which are discussed in this article.

Cobalt (II)-Mediated Molecularly Imprinted Polymer as a Monolithic Stationary Phase for Separation of Racemic Citronellal by Liquid Chromatography

A metal-mediated molecularly imprinted polymer (MMIP) monolithic column was prepared as the stationary phase for high-performance liquid chromatography (HPLC) and applied to the enantiomeric separation of rac-citronellal. MMIP column was prepared through in situ copolymerizations with the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate/[BMIM][BF₄] as the primary pore-forming agent and cobalt(II) acetate as the metal pivot. Interactions between polymer components in the synthesized monolith were assessed by FTIR to identify the functional groups. The monolith morphology was characterized with SEM, and the template removal was detected by UV Spectrophotometry at 253 nm. In this study, (R)-(+)-citronellal was used as a template, whereas 4-vinylpyridine (4-VP) was employed as the functional monomer with two monomer crosslinkers, trimethylolpropane trimethacrylate (TRIM), and ethylene glycol dimethacrylate (EDMA). The ternary mixture of porogenic solvent consisted of [BMIM][BF₄], dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) with the applied ratio of 1 : 1:1 (v/v) and 10 : 1:5 (v/v) for the preparation of MMIP using TRIM and EDMA crosslinkers, respectively. Co(II) ion was added to the porogenic solvent before being mixed with the functional monomer and the crosslinker mixtures. Separating the rac-citronellal was achieved on the synthesized MMIP, showing better selectivity than the monolithic metal-mediated nonimprinted polymer (MNIP), nonimprinted polymer (NIP), and molecularly imprinted polymer (MIP).

Rapid preparation and characterization of a bridged bis(β-cyclodextrin) functionalized urea–formaldehyde monolithic column by a “one-pot” approach

A new bridged-CD monolith was prepared by “one-pot” method within 30 minutes. The obtained bridged-CD monolith showed satisfactory enantioselectivity compared to a native-CD monolith.

Preparation of a hydroxypropyl-β-cyclodextrin functionalized monolithic column by one-pot sequential reaction and its application for capillary electrochromatographic enantiomer separation

In this study, a hydroxypropyl-β-cyclodextrin (HP-β-CD) functionalized monolithic capillary column was prepared by one-pot sequential reaction for the first time. The preparation of the HP-β-CD functionalized monolithic column involves two sequential reactions in one pot: (1) the ring opening reaction between HP-β-CD and glycidyl methacrylate (GMA) catalyzed by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU); (2) the copolymerization of GMA-HP-β-CD, ethylene dimethacrylate (EDMA) and 2-acrylamido-2-methyl propane sulfonic acid (AMPS). A series of monolithic columns were successfully prepared by varying the temperature of the ring opening reaction or several copolymerization parameters (the type and composition of porogenic solvents, ratio of GMA-HP-β-CD to EDMA and polymerization temperature). Then, the morphologies and structures of the resulting monolithic stationary phases were characterized by optical microscopy, scanning electron microscopy (SEM) and nitrogen adsorption analysis. Raman spectroscopy clearly indicated the successful bonding of HP-β-CD onto the monolith. When the prepared chiral stationary phase (CSP) was applied for the separation of a set of racemic compounds by capillary electrochromatography (CEC), including racemic anticholinergic drugs, β-adrenergic drugs, meptazinol and its intermediates, satisfactory separation selectivities were obtained. Additionally, the column also showed excellent separation abilities towards four flavanone glycosides epimers. Furthermore, the prepared monolithic columns exhibited satisfactory stability and reproducibilities of retention time, resolution and column efficiency. These results demonstrated the potential and usefulness of the developed one-pot sequential strategy in the preparation of other derivatized CD functionalized monolithic columns.