Photografted methacrylate-based monolithic columns coated with cellulose tris(3,5-dimethylphenylcarbamate) for chiral separation in CEC

Polydopamine Coating Doped with Graphene Oxide Enhances Enantioseparation of Capillary Column

How to improve the enantiomer separation efficiency of drugs is a hot topic. In this paper, polydopamine (PDA) coating doped with graphene oxide (GO) by physical adsorption was used to modify the capillary column to enhance the enantioseparation efficiency of the drugs. In the capillary electrochromatography (CEC) system, the novel capillary column with carboxymethyl-β-cyclodextrin (CM-β-CD) as a chiral selector has completed the enantioseparation of four basic drugs (propranolol, metoprolol, amlodipine and chlorpheniramine). The optimum separation conditions were obtained by optimizing the pH of the buffer, the concentration of organic modifier, the concentration of the chiral selector and the voltage, and the resolution and peak shape were significantly improved compared with uncoated bare-fused column. The stability and reproducibility of the new capillary column were satisfactory and the relative standard deviation of intra-day and inter-day was <3.2%, and of column-to-column was <4.8%. The rich functional groups of GO are key factors to improve the enantioseparation efficiency, which also indicates that nanomaterials with easy modification of functional groups and large specific surface area are excellent resources for capillary modification applications.

Chiral covalent organic framework incorporated organic polymer monolithic capillary column for enantioseparations

A chiral covalent organic framework was synthesized, characterized, and incorporated into organic polymer monolithic capillary columns to provide chiral stationary phases for enantioseparations. The prepared monolithic capillary columns were characterized by scanning electron microscopy and elemental analysis. To obtain better enantioseparations, the columns' preparation conditions, and enantioseparation conditions were optimized. Baseline resolutions of several chiral compounds were obtained with good reproducibility and stability. Furthermore, the mechanism of chiral recognition was investigated using molecular docking with AutoDock. Docking results showed that the enantioselectivity factor rather than resolution is correlated with the binding free energy difference between enantiomers with the chiral covalent organic framework. And abundant acetoxy and nitrile groups as well as benzene rings in the chiral covalent organic framework are responsible for the enantioseparation ability of the chiral monolithic capillary columns.

Poly(carboxyethyl acrylate-co-ethylene glycol dimethacrylate) precursor monolith with bonded (S)-(-)-1-(2-naphthyl) ethylamine ligands for use in chiral and achiral separations by capillary electrochromatography

In this research report, the previously developed poly(carboxyethyl acrylate-co-ethylene glycol dimethacrylate) precursor monolith (referred to as carboxy monolith) is further exploited in the preparation of a chiral stationary phase for enantiomeric separations. The carboxy monolith precursor was subjected to post polymerization functionalization (PPF) with the chiral selector (S)-(-)-1-(2-naphthyl) ethylamine (NAS) at room temperature in the presence of N, N´-dicyclohexylcarbodiimide (DCC) in chloroform. The DCC, which is an organic soluble carbodiimide, permits the linkage for the amine functionality of the chiral ligand NAS to the carboxy group of the monolithic surface forming a stable amide linkage. The NAS column thus obtained allowed not only enantiomeric separations in the RP mode via its chiral site but also the separation of nonpolar species via its achiral functionality offering both hydrophobic and π-π interactions for aromatic compounds such toluene derivatives and polyaromatic hydrocarbons. The dual interaction sites (e.g., chiral, and achiral) of the NAS present a convenient column for the separations of slightly polar and nonpolar chiral and achiral solutes in the RP mode.

Recent developments of monolithic and open-tubular capillary electrochromatography (2017-2019)

Capillary electrochromatography, which combined the high selectivity of high-performance liquid chromatography and the high separation efficiency of capillary electrophoresis, is an attractive separation tool. In this review, the developments on monolithic and open tubular capillary electrochromatography during 2017 to August 2019 are summarized. Considering the development of novel stationary phases is the most active research field in capillary electrochromatography, monolithic capillary electrochromatography is classified according to the polymer-based and hybrid monolithic columns, while open-tubular capillary electrochromatography is categorized by cyclodextrin, silica, polymer, nanomaterials, microporous materials, and biomaterials-based open tubular columns.

Helical poly(phenyl isocyanide)s grafted selectively on C-6 of cellulose for improved chiral recognition ability

Cellulose graft copolymers are an effective way to endow new properties to cellulose substrate, as well the rigidity, regularity, and helicity of the cellulose backbone could induce the self-assembly of supramolecular structures. In this work, right-handed helical poly(phenyl isocyanide)s (PPI_n) were grafted selectively onto C-6-cellulose. Alkyne-terminated PPI_n was synthesized by living polymerization of right-handed phenyl isocyanide monomer using an alkyne-terminated palladium(II) complex as an initiator/catalyst, and were grafted onto the C-6 of the cellulose backbone (Cell-6-g-PPI_n) at various chain lengths using copper-catalyzed alkyne-azide cycloaddition (CuAAC) "click" chemistry. We confirmed the successful grafting by liquid ¹H NMR and ¹³C NMR, as well as solid ¹³C NMR, FTIR, and GPC. After grafting onto cellulose, the right-handed chirality of PPI_n was significantly increased by 111.2%. Additionally, the Cell-6-g-PPI_n exhibited better chiral recognition of L-Phe-DNSP than PPI_n alone. Therefore, the helical cellulose backbone has enhanced effect on preferred helix of PPI_n.

An organic polymer monolith modified with an amino acid ionic liquid and graphene oxide for use in capillary electrochromatography: application to the separation of amino acids, β-blockers, and nucleotides

The preparation of an organic polymer monolithic column modified with an amino acid ionic liquid and graphene oxide (AAIL-GO) and its application to capillary electrochromatography (CEC) was described. The AAIL tetramethylammonium-L-arginine was bonded to a monolithic column that was previously modified with graphene oxide by using an hydrochloride/N-hydroxysuccinimide coupling reaction. The morphology of a poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith was examined by scanning electron microscopy. The incorporation of AAIL and graphene oxide was detected by infrared spectroscopy and elemental analysis. The resulting monolithic column produced a strong and stable electroosmotic flow from the anode to the cathode in the pH range from 3 to 9. Compared with a column modified with AAIL or graphene oxide only, the AAIL-GO-modified column has a better separation ability for amino acids, β-blockers, and nucleotides (the resolution of three amino acids: 2.231 and 2.036, β-blockers: 2.779 and 2.470 and nucleotides: 8.345 and 3.321). Molecular modeling was applied to demonstrate the separation mechanism of small molecules which showed a good support for experimental results. Graphical abstract Schematic representation of capillary electrochromatography (CEC) systems with an amino acid ionic liquid-graphene oxide modified organic polymer monolithic column as stationary phases for separation of amino acids, β-blockers, and nucleotides.

Novel approaches for biomolecule immobilization in microscale systems

This manuscript reviews novel approaches applied for biomolecule immobilization in microscale systems.

A protein-based mixed selector chiral monolithic stationary phase in capillary electrochromatography

A mixed selector CSP combines the enantioselectivities of both individual proteins, thus expanding their application range practically.