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Jingwu Kang

Publications and source records attributed to Jingwu Kang.

7 recordsLinked to original sources
PubMed2005

Enantioseparation of chiral allenic acids by micellar electrokinetic chromatography with cyclodextrins as chiral selector.

Enantioseparation of chiral aryl allenic acids by micellar electrokinetic chromatography (MEKC) with cyclodextrins (CDs) as chiral selectors was described. The screen of chiral selectors (beta-CD, gamma-CD, and hydroxypropyl (HP)-gamma-CD) showed that the enantioseparation was not only dependent on the type of CD but also the presence of 2-propanol in the buffer. In order to optimize the operational parameters, the effect of the concentration of CDs, sodium dodecyl sulfate (SDS), and 2-propanol, as well as the buffer ionic strength and pH on enantioseparation were studied. It was proved that the concentration of CDs, 2-propanol, and the buffer ionic strength were the critical parameters. Under optimal conditions, baseline separations of all seven allenic acid enantiomers were achieved. Furthermore, the method validation in terms of repeatability, linearity, limit of detection (LOD), and limit of quantitation (LOQ) were performed. Using the present method, the optical purity of a nonracemic sample with the enantiomeric excess (e.e.%) value of 99.65% was determined.

2-Propanol↗
PubMed2004

A mechanistic study of enantiomeric separation with vancomycin and balhimycin as chiral selectors by capillary electrophoresis. Dimerization and enantioselectivity.

The role of the sugar moiety of glycopeptide antibiotics in chiral recognition was investigated with capillary electrophoresis. Two glycopeptide antibiotics, vancomycin and balhimycin, were employed as models since they possess the same aglycon and almost identical sugar moieties, however, with different attachment sites to the aglycon. The observed enantioselectivity of balhimycin for dansylated alpha-amino acids is 2.6 times higher than that of vancomycin. Blocking of the sugar amino group of balhimycin by N-carbamoylation reaction with KOCN led to a significantly decreased enantioselectivity compared to vancomycin, which remained almost the same upon carbamoylation. These results suggest a major role of the amino sugar together with its site of attachment to the aglycon. A dimerization-based mechanism is proposed to explain this phenomenon due to the fact that the dimerization properties of glycopeptides are similarly related to their glycosylation patterns; e.g., the dimerization constant of balhimycin is 78 times higher than that of vancomycin. Furthermore, the dimerization of glycopeptides promotes their affinity to carboxyl-containing ligands via cooperativity effects between the dimerization and the formation of glycopeptide-ligand complexes. The higher dimer stability probably leads to a more favorable conformation for chiral recognition. Thus, it is concluded that a weakened dimerization of N-carbamoylated balhimycin results in a decreased enantioselectivity.

Amino Acids↗
PubMed2004

Evaluation of balhimycin as a chiral selector for enantioresolution by capillary electrophoresis.

The glycopeptide antibiotic balhimycin and its haloanalogue bromobalhimycin were evaluated as chiral selectors for enantioresolution by capillary electrophoresis. In order (i) to eliminate the adsorption of the glycopeptide antibiotics on the capillary wall, (ii) to shorten the separation time and (iii) to improve the detection sensitivity, a combined approach of the dynamic surface coating technique, the co-electroosmotic flow electrophoresis technique and the partial filling technique was employed for the enantioresolution of 16 acidic racemates. The effect of experimental parameters (plug length of the partial filling solution containing the chiral selector, selector concentration and buffer pH) on enantiorecognition was investigated. Furthermore, the enantiorecognition ability imparted by balhimycin, bromobalhimycin and vancomycin were compared. For most tested compounds, the highest enantiorecognition was obtained with balhimycin as chiral selector. Only in the case of the enantioresolution of tiaprofenic acid, vancomycin showed a superior enantiorecognition.

Anti-Bacterial Agents↗
PubMed2003

Fast enantiomeric separation with vancomycin as chiral additive by co-electroosmotic flow capillary electrophoresis: increase of the detection sensitivity by the partial filling technique.

A fast and sensitive method is described by using vancomycin as a chiral additive for enantiomeric separation by capillary electrophoresis (CE). In order to overcome disadvantages associated with use of vancomycin as chiral additive in CE, several strategies including the dynamic coating technique, the co-electroosmotic flow technique, and the partial filling technique were employed sequentially in this method. Using the polycationic polymer hexadimethrine bromide (HDB) as a buffer additive, the capillary wall was dynamically coated with a thin film formed by the adsorbed HDB. Consequently, the adsorption of vancomycin onto the capillary wall was minimized via electrostatic repulsion between the coating of the capillary wall and the vancomycin molecule. In addition, the reversed electroosmotic flow (from cathode to anode) produced by the positively charged capillary wall migrates in the same direction of negatively charged analytes (co-electroosmotic flow electrophoresis). Thereby the electrophoretic mobility of negatively charged analytes were drastically accelerated leading to a short separation time of less than 3.4 min. The separation time was further reduced by the use of a short-end-injection technique. For example, the analysis time was achieved by as short as 55 s for a baseline separation of dansyl-alpha-amino-n-butyric acid. Concurrently, the partial filling technique was used to avoid the loss of detection sensitivity caused by the presence of vancomycin in the running buffer. The effect of several parameters, such as HDB concentration, buffer pH, plug length of the chiral selector, concentration of the chiral selector and applied voltage, on enantioselectivity were investigated toward optimization. Besides the advantage of a very short separation time, the method is characterized by high detection sensitivity, high selectivity, and high efficiency.

Amino Acids↗
PubMed2002

A silica monolithic column prepared by the sol-gel process for enantiomeric separation by capillary electrochromatography.

A method for the preparation of a silica monolithic capillary electrochromatography (CEC) column for the separation of enantiomers has been developed. The porous silica monolith was fabricated inside a fused-silica capillary column by using the sol-gel process. After gelation for 24 h, hydrothermal treatment at 100 degrees C for 24 h was performed to prevent the sol-gel matrix from cracking. The prepared monolith was then coated with Chirasil-beta-Dex which represents a chiral polymer prepared by grafting permethyl-beta-cyclodextrin to polymethylsiloxane with an octamethylene spacer. Immobilization of Chirasil-beta-Dex was performed by heat treatment at 120 degrees C for 48 h to give a nonextractable coating. The column performance was evaluated by using racemic hexobarbital as a model compound. The efficiency of 9.2 x 10(4) theoretical plates/m for the first eluted enantiomer of hexobarbital was obtained at an optimal flow rate of the mobile phase. The effect of mobile phase composition on enantiomeric separation of hexobarbital was also investigated. The column proved to be stable for more than one hundreds of runs during a two-months period. The enantiomers of several neutral and negatively charged chiral compounds were baseline separated on this column.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2002

Recent progress in enantiomeric separation by capillary electrochromatography.

Recent progress in enantiomeric separations by capillary electrochromatography (CEC) is reviewed. The development of simple and robust CEC column technologies plays an important role for popularization of CEC. During the last several years, various approaches for the preparation of enantioselective columns have been reported. Currently, the monolithic column technology (continuous beds) represents the most advanced approach for the preparation of CEC columns. The development of new chiral stationary phase used for CEC is another important issue in this field. Fundamental investigations on electrochromatographic behaviors of various CSPs are necessary in order to understand the separation mechanism and thus improve the separation performance. Some chiral stationary phases performed better under nonaqueous CEC conditions than reversed-phase conditions. Coupling CEC with mass spectrometry (MS) provides a powerful tool for enantiomeric separation. Finally, some applications of enantiomeric separation by CEC are summarized.

Chromatography↗