Multicomponent Ugi reaction as a tool for fast and easy preparation of stationary phases for hydrophilic interaction liquid chromatography. Part I: The influence of attachment and spacing of the functional ligand obtained via the Ugi reaction

Preparation of small peptoid-modified zwitterion-exchange/reversed-phase mixed-mode chromatography stationary phases for the separation of arenes and antibiotics

In this study, three small peptoids with different structures, named Sil-peptoids, were developed to improve the separation selectivity of zwitterion-exchange/reversed-phase mixed-mode chromatography stationary phases for multi-component complex drugs. Nonpolar, amphoteric, and alkaline drugs were used as test samples to demonstrate their retention behaviors in reversed-phase, ionic, and mixed-mode interactions. It was observed that different carboxyl anions in the small peptoids of the Sil-peptoids had vast differences in their stereo-selectivity. The stereo-selectivity and the influence of Sil-peptoids on the retention behavior of complex drugs and their interaction mechanism for the drug molecules were effectively evaluated through the combination of chromatographic analysis and molecular modeling. Finally, a mixture of drugs consisting of two polar and six non-polar drugs was used to obtain a separation effect with a resolution >1.5. Two other groups of polar antibiotics were used to verify the separation ability of the Sil-peptoids. The results indicated that the Sil-peptoids could separate multiple substances simultaneously. These novel stationary phases can be applied to the analysis of complex multi-component drugs.

Development of an approach to determining enzymatic activity of ribonucleoside hydrolase c using hydrophilic interaction liquid chromatography

Ribonucleoside hydrolase C (RihC, EC 3.2.2.1-3.2.2.3, 3.2.2.7, 3.2.2.8) belongs to the family of ribonucleoside hydrolases that catalyze the cleavage of both purine and pyrimidine ribonucleosides to nitrogenous bases and ribose. Its most efficient reaction is the cleavage of uridine with the highest reaction rate. The reaction cannot be detected by a simple spectrophotometric method because of the same absorption maximum for the substrate and reaction product or requires time- and labor-consuming sample preparation for ribose. Reversed-phase HPLC is currently used to register enzymatic activity, where the time of one chromatographic run takes about 10 min. Since a large number of analyses is required to measure the kinetics of an enzymatic reaction, the total time is significant. In this work, we obtained new recombinant RihC from Limosilactobacillus reuteri by gene cloning and expression in E.coli cells. We proposed a new approach for determining the enzymatic activity of the new RihC using hydrophilic interaction liquid chromatography (HILIC). The novel column was developed for this procedure providing the determination of uracil and uridine with high efficiency and retention times of 0.9 and 1.7 min, respectively. Kinetic parameters for RihC uridine cleavage were determined. The proposed approach provided significant rapidity for measurement of the enzyme kinetics being 5 times faster as compared to reversed-phase HPLC.

Separation of Panax notoginseng saponins on modified rosin ester-bonded silica stationary phase and its mechanism

A column prepared using a unique three-membered phenanthrene skeleton of rosin has complementary selectivity to a C18 column for some separation tasks. In this study, propylene pimaric acid (16-hydroxyethyl acrylate-34-n-butyl) ester (BRB) and propylene pimaric acid (16-hydroxyethyl acrylate-34-dodecyl) ester (BRLA) were used as functional ligands to prepare two novel stationary phases, namely BRB@SiO₂ and BRLA@SiO₂, through a "thiol-ene" click chemistry reaction. The characterization results of Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption-desorption measurements, and contact angle tests showed that the BRB@SiO₂ and BRLA@SiO₂ stationary phases were successfully prepared. In addition, the performance of the columns was evaluated using the Tanaka test and hydrophobic subtraction model, which showed that the stationary phases exhibited typical reversed-phase chromatography performance and good hydrophobicity, hydrophobic selectivity, and steric selectivity. The changes in the retention of Panax notoginseng saponins on a column under different chromatographic conditions (acetonitrile content, flow rate, and column temperature) were investigated. The separation effect of BRB@SiO₂ and BRLA@SiO₂ columns on P. notoginseng saponins was better than that of the C18 column and the BRLA@SiO₂ column could replace the C18 column for the detection of P. notoginseng saponins.

Effect of phenyl numbers in polyphenyl ligand on retention properties of aromatic stationary phases

Aromatic phase, as one type of reversed-phase stationary phases, shows complementary selectivity to the n-alkyl counterparts especially for certain challenging separation tasks. However, effect of phenyl numbers in aromatic ligands on retention behaviors has rarely been addressed compared with the alkyl stationary phases. To illustrate the issue, a series of polyphenyl stationary phases were facially prepared via the coupling chemistry of isocyanate with amine, including aniline (π¹), 4-aminobiphenyl (π²), 4-amino-p-terphenyl (π³) and [1,1':4',1'':4'',1'''-quaterphenyl]-4-amine (π⁴), respectively. The chromatographic behaviors of the new stationary phases as well as the traditional C18 were systematically compared in terms of retention mode, hydrophobic and aromatic selectivity, shape selectivity and π-π interaction by various analytes, including alkylbenzenes, polycyclic aromatic hydrocarbons congeners and substituted benzenes with electron-withdrawing groups. Due to the homologous structure of four polyphenyl ligands, the hydrophobic selectivity, aromatic selectivity and shape selectivity of stationary phases increase with phenyl numbers in the bonded polyphenyl ligands, whereas the increment becomes insignificant from U-π³ to U-π⁴. This phenomenon is explained by the insertion degree of analytes in the polyphenyl ligand brushes. Compared with the homemade C18, the polyphenyl phases indicate insignificant changes of shape selectivity with temperature. Notably, the new polyphenyl phases demonstrate the great selective separation towards the electron-deficient compounds through the π-π interaction. These findings make up for the understanding of the retention behavior of aromatic stationary phases.