Immobilization of 3,5-dimethylphenylcarbamates of cellulose and amylose onto silica gel using (3-glycidoxypropyl)triethoxysilane as linker.

The 3,5-dimethylphenylcarbamates of cellulose and amylose were effectively immobilized onto plain silica gels as chiral packing materials (CPMs) for HPLC by means of intermolecular polycondensation of triethoxysilyl groups introduced with (3-glycidoxypropyl)triethoxysilane. The immobilization and chiral recognition abilities of the obtained CPMs prepared with different amounts of (3-glycidoxypropyl)triethoxysilane were investigated. In addition, the solvent compatibilities of the immobilized-type CPMs were examined with eluents containing chloroform and THF. When these eluents were used, for most of the tested racemates, the chiral resolving abilities of the obtained CPMs were improved.

Immobilization of cellulose phenylcarbamate onto silica gel via in termolecular polycondensation of triethoxysilyl groups introduced with (3-glycidoxypropyl)triethoxysilane.

Cellulose 3,5-dimethylphenylcarbamate was successfully immobilized onto bare silica gel for HPLC through the intermolecular polycondensation of triethoxysilyl groups, which were introduced onto the cellulose derivative via epoxide ring-opening reaction under acidic conditions. The immobilized-type chiral packing material (CPM) exhibited high chiral recognition ability and could be used with various eluents, which are incompatible with the conventional CPMs prepared by coating the derivative onto silica gel.

Facile preparation of a stable and functionalizable hybrid monolith via ring-opening polymerization for capillary liquid chromatography.

An organic-inorganic hybrid monolith was prepared by a single-step ring-opening polymerization of octaglycidyldimethylsilyl polyhedral oligomeric silsesquioxane (POSS) with poly(ethylenimine) (PEI). The obtained hybrid monoliths possessed high ordered 3D skeletal microstructure with dual retention mechanism that exhibits reversed-phase (RP) mechanism under polar mobile phase and hydrophilic-interaction liquid chromatography (HILIC) retention mechanism under less polar mobile phase. The high column efficiencies of 110,000N/m can be achieved for separation of alkylbenzenes in capillary reversed-phase liquid chromatography (cLC). Due to the robust property of hybrid monolith and the rich primary and secondary amino groups on its surface, the resulting hybrid monolith was easily modified with γ-gluconolactone and physically coated with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC), respectively. The former was successfully applied for HILIC separation of neutral, basic and acidic polar compounds as well as small peptides, and the latter for enantioseparation of racemates in cLC. The high column efficiencies were achieved in all of those separations. These results demonstrated that the hybrid monolith (POSS-PEI) possessed high stability and good surface tailorbility, potentially being applied for other research fields.

Hybrid monolithic columns coated with cellulose tris(3,5-dimethylphenyl-carbamate) for enantioseparations in capillary electrochromatography and capillary liquid chromatography.

A hybrid monolithic capillary column synthesized with (3-chloropropyl)-trimethoxysilane (CPTMS) and tetramethoxysilane (TMOS) via sol-gel chemistry was in situ coated with cellulose tris(3,5-dimethylphenyl-carbamate) (CDMPC) for enantioseparations in capillary electrochromatography (CEC) and capillary liquid chromatography (CLC). Prior to coating, the prepared CP-silica hybrid monolith was straightforwardly modified with diethylenetriamine (DETA) to introduce NH(2) functionalities via the nucleophilic substitution reaction, which generate the stronger EOF for CEC. The coating condition was optimized to obtain a stable and reproducible chiral stationary phase for enantioseparation. The results indicated that racemic benzoin was baseline separated on the resulting hybrid monolith coated with 30 mg/mL CDMPC in CEC, while several racemates were successfully enantioseparated on the resulting CP-silica hybrid monolithic column coated with 60 mg/mL CDMPC in CLC with RP and NP modes.

[Preparation and evaluation of amylose and cellulose tris (3-trifluoromethylphenylcarbamates)-based chiral stationary phases].

To broaden the category of polysaccharide-based chiral stationary phases (CSPs), coated CSPs based on tris (3-trifluoromethylphenylcarbamates) of amylose and cellulose were prepared for enantioseparation in high performance liquid chromatography. Their performances were evaluated by eight racemates using hexane-isopropanol as mobile phase. Compared with the most widely used, commercially available polysaccharide-based CSPs, Chiralpak AD and Chiralcel OD, utilizing tris (3,5-dimethylphenylcarbamates) of amylose and cellulose as the chiral selector, respectively, the obtained CSPs exhibited lower enantioseparation abilities. However, cellulose tris(3-trifluoromethylphenylcarbamate)-based CSP exhibited characteristic enantioseparation and some chiral compounds were better resolved on this CSP than on Chiral-cel OD. The chiral recognition abilities of the obtained CSPs were increased with the decrease of the portion of isopropanol in the mobile phase and relatively high enantioseparation was obtained with the mobile phase of hexane-isopropanol (95: 5, v/v). The obtained amylosic phase demonstrated slightly higher chiral resolving ability than the cellulosic one for the test racemates. In addition, it was revealed that the enantioseparations of the cellulosic and amylosic CSPs were complementary.

Application of cross-linked beta-cyclodextrin polymer for adsorption of aromatic amino acids.

Beta-cyclodextrin (beta-CyD) was cross-linked by hexamethylene diisocyanate and the polymer was investigated for adsorption of aromatic amino acids (AAA) from phosphate buffer. High adsorption rates were observed at the beginning and the adsorption equilibrium was then gradually achieved in about 45 min. The adsorption of AAA decreased with the increase of initial concentration and also temperature. Under the same conditions, the adsorption efficiencies of AAA were in the order of L-tryptophan (L-Trp) > L-phenylalanine (L-Phe) > L-tyrosine (L-Tyr). Much higher adsorption values, up to 52.4 and 43.0 mg/g for L-Trp and L-Phe, respectively, at 50 mmol/L and 3.2 mg/g for L-Tyr at 2 mmol/L, were obtained with the beta-CyD polymer at 37 degrees C. It was shown that the adsorption of AAA on the beta-CyD polymer was consistent with the Freundlich isotherm equation. The adsorption of mixed aromatic amino acids and branched-chain amino acids (BCAA) showed that AAA were preferentially adsorbed with adsorption efficiencies 10-24%, while those of BCAA were lower than 2%. It seems that the structure and hydrophobicity of amino acid molecules are responsible for the difference in adsorption, by influencing the strength of interactions between amino acid molecule and the polymer.

Chiral separation of 1,1'-bi-2-naphthol and its analogue on molecular imprinting monolithic columns by HPLC.

Two molecular imprinting polymer (MIP) monolithic columns with (S)-(-)-1,1'-bi-2-naphthol and (R)-(+)-5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol as the templating molecules, respectively, have been prepared by in situ polymerization using 4-vinylpyridine and ethylene dimethacrylate as functional monomer and cross-linker, respectively. The columns with good flow-through properties were obtained by changing the molar ratio of the functional monomer and the template molecule. The effects of mobile-phase composition on separation of enantiomers were systematically investigated. The results indicate that hydrophobic interaction in aqueous solution and hydrogen-bonding interaction in ACN between the enantiomers and polymers could play important roles in the retention and resolution. The effects of chromatographic conditions, such as flow rate, column temperature, sample loading, on the enantioseparation were also studied. Further, these two MIP columns show a cross-reactivity.