Chiral Selector In Capillary Electrophoresis Research Articles

Study on the separation of ofloxacin enantiomers by hydroxyl-propyl-β-cyclodextrin as a chiral selector in capillary electrophoresis: a computational approach

Hydroxypropyl-β-cyclodextrin (HPβCD) has been used successfully as a chiral additive to separate ofloxacin (OFL) enantiomers in a capillary electrophoresis system. Using electrospray-mass spectrometry (ESI–MS) it was revealed that OFL forms an inclusion complex with HPβCD at 1:1 stoichiometry. The interaction of the enantiomers with the host was further investigated by molecular modeling using molecular mechanics dockings, PM7 semiempirical calculations and molecular dynamics simulations. Calculations using PM7 semiempirical methods indicated that the separation is brought about by a large difference in the binding energies (∆∆E) of 15 kcal mol−1 between R-OFL-HPβCD and S-OFL-HPβCD inclusion complexes. S-OFL was predicted to be eluted first by the PM7 method which corroborates the experimental results. Moreover, the molecular dynamic simulations show that the formation of stable R-OFL-HPβCD is because it is more deeply inserted into the cavity of the host. The study also revealed the absence of the role of strong hydrogen bonding in the enantioseparations.

Molecular dynamics simulation and NMR investigation of the association of the β-blockers atenolol and propranolol with a chiral molecular micelle

Molecular dynamics simulations and NMR spectroscopy were used to compare the binding of two β-blocker drugs to the chiral molecular micelle poly-(sodium undecyl-(L)-leucine-valine). The molecular micelle is used as a chiral selector in capillary electrophoresis. This study is part of a larger effort to understand the mechanism of chiral recognition in capillary electrophoresis by characterizing the molecular micelle binding of chiral compounds with different geometries and charges. Propranolol and atenolol were chosen because their structures are similar, but their chiral interactions with the molecular micelle are different. Molecular dynamics simulations showed both propranolol enantiomers inserted their aromatic rings into the molecular micelle core and that (S)-propranolol associated more strongly with the molecular micelle than (R)-propranolol. This difference was attributed to stronger molecular micelle hydrogen bonding interactions experienced by (S)-propranolol. Atenolol enantiomers were found to bind near the molecular micelle surface and to have similar molecular micelle binding free energies.

Quantitative prediction of enantioseparation using β-cyclodextrin derivatives as chiral selectors in capillary electrophoresis.

β-Cyclodextrin derivatives as chiral selectors are becoming increasingly important for enantioseparations in capillary electrophoresis (CE). Nevertheless, there are some enormous challenges in choosing effective selectors from a variety of compounds, and up to now no systematic quantitative studies for predicting the possibility of enantiomeric separation before CE experiments have been reported. In this paper, in order to resolve previous confusions, we investigated the enantioseparations of ten chiral drugs using a method of combining experiments with theoretical calculations. MMFF, PM3, DFT and ONIOM2 methods were simultaneously utilized during the course of our computer simulations. The results indicated that a specific value of greater than or approximately equal to 6 kJ mol(-1) for the interaction energy difference (ΔΔE) between a pair of enantiomers with a selector is required in order to achieve enantiomeric separation. This discovery offers a meaningful reference to predict enantiomeric separations, so as to design and synthesize some more efficient chiral selectors.

Combination of poly(diallyldimethylammonium chloride) and hydroxypropyl-γ-cyclodextrin for high-speed enantioseparation of phenothiazines by capillary electrophoresis

High-speed capillary electrophoresis (CE) enables the simple, rapid, and inexpensive analysis of large sets of chiral samples in the pharmaceutical industry. Hence, we developed a novel method for separating enantiomers of d,l-phenothiazines simply and rapidly, based on using poly(diallyldimethylammonium chloride) (PDDAC) as an additive and hydroxypropyl-γ-cyclodextrin (Hp-γ-CD) as a chiral selector in capillary electrophoresis. Adding 0.9% PDDAC to the background electrolyte generated a stable, high, and reversed electroosmotic flow (EOF). Hp-γ-CD not only worked as a complexing agent to increase the chiral resolution between d,l-phenothiazines but also decreased the effective electrophoretic mobility of these drugs. Combining PDDAC and Hp-γ-CD as buffer additives enabled CE to achieve a high-speed enantioseparation of five pairs of d,l-phenothiazines. A decrease in capillary length and an increase in the intensity of the electric field further shortened the separation time. When the background electrolyte contained 0.9% PDDAC, 5mM Hp-γ-CD, and 75mM formic acid (pH 3.0), enantioseparation of the d,l-phenothiazines was attained within 230s by applying a capillary length of 32.5cm and an electric field of 292Vcm−1. The limit of detection (LOD) of the d,l-phenothiazines at a signal-to-noise ratio of 3 ranged from 2 to 8μM. We demonstrated the feasibility of this method by detecting the five pairs of d,l-phenothiazines in urine samples.

Combined use of chiral ionic liquid surfactants and neutral cyclodextrins: Evaluation of ionic liquid head groups for enantioseparation of neutral compounds in capillary electrophoresis

Cyclodextrins (CDs) are most commonly used chiral selectors in capillary electrophoresis (CE). Although the use of neutral CDs and its derivatives have shown to resolve plethora of charged enantiomers, they cannot resolve neutral enantiomers. The use of ionic liquids (ILs) surfactants forming successful complex with CDs present itself an opportunity to resolve neutral enantiomers. In this work, the effect of IL head groups and their complexation ability with heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CD) was studied for the separation of neutral enantiomers by CE. First, cationic IL type surfactants with different chiral head groups were synthesized. Physicochemical properties such as critical micelle concentration were determined by surface tension, whereas aggregation and polarity were determined by fluorescence spectroscopy. The complexation ability of ILs with TM-β-CD was characterized in the gas phase by CE-mass spectrometry. The influence of the type of ILs head group and its concentration on chiral resolution, resolution per unit time and selectivity were investigated for four structurally diverse neutral compounds. The binding constants of the neutral analytes to the IL–CD complex were estimated by y-reciprocal method. The hydrophobicity of the side chain of the IL head group displayed significant effect on the binding constants and enantioseparations.

Combined use of [TBA][L-ASP] and hydroxypropyl-β-cyclodextrin as selectors for separation of Cinchona alkaloids by capillary electrophoresis

In this paper, a new capillary electrophoresis (CE) separation and detection method was developed for the chiral separation of the four major Cinchona alkaloids (quinine/quinidine and cinchonine/cinchonidine) using hydroxypropyl-β-cyclodextrin (HP-β-CD) and chiral ionic liquid ([TBA][L-ASP]) as selectors. Separation parameters such as buffer concentrations, pH, HP-β-CD and chiral ionic liquid concentrations, capillary temperature, and separation voltage were investigated. After optimization of separation conditions, baseline separation of the three analytes (cinchonidine, quinine, cinchonine) was achieved in fewer than 7min in ammonium acetate background electrolyte (pH 5.0) with the addition of HP-β-CD in a concentration of 40mM and [TBA][L-ASP] of 14mM, while the baseline separation of cinchonine and quinidine was not obtained. Therefore, the first-order derivative electropherogram was applied for resolving overlapping peaks. Regression equations revealed a good linear relationship between peak areas in first-order derivative electropherograms and concentrations of the two diastereomer pairs. The results not only indicated that the first-order derivative electropherogram was effective in determination of a low content component and of those not fully separated from adjacent ones, but also showed that the ionic liquid appeared to be a very promising chiral selector in CE.

Application of maltodextrin as chiral selector in capillary electrophoresis for quantification of amlodipine enantiomers in commercial tablets.

Maltodextrin was investigated as a chiral selector in capillary electrophoresis (CE) analysis of amlodipine (AM) enantiomers. For development of a stereoselective CE method, various effective parameters on the enantioseparation were optimized. The best results were achieved on an uncoated fused silica capillary at 20 °C using phosphate buffer (100 mM, pH 4) containing 10% w/v maltodextrin (dextrose equivalent value 4-7). The UV detector was set at 214 nm and a constant voltage of 20 kV was applied. The range of quantitation was 2.5-250 µg/mL (R(2) > 0.999) for both enantiomers. Intra- (n = 5) and interday (n = 3) relative standard deviation (RSD) values were less than 7%. The limits of quantitation and detection were 1.7 µg/mL and 0.52 µg/mL, respectively. Recoveries of R(+) and S(-) enantiomers from tablet matrix were 97.2% and 97.8%, respectively. The method was applied for the quantification of AM enantiomers in commercial tablets. Also, the enantioseparation capability of heparin was evaluated and the results showed that heparin did not have any chiral selector activity in this study.

Evaluation of ionic liquids-coated carbon nanotubes modified chiral separation system with chondroitin sulfate E as chiral selector in capillary electrophoresis

Nanoparticles (NPs) and ionic liquids (ILs) have been extensively studied and have aroused considerable interest in separation science; however, the employment of ILs-dispersed NPs as buffer modifiers for CE chiral separation has not been previously studied. In this work, we describe a new CE method using ILs dispersed multi-walled carbon nanotubes (ILs-MWNTs) as a modifier for enantioseparation with a polysaccharide, chondroitin sulfate E (CSE), as the chiral selector. As observed, significantly improved separations, including better enantioselectivity and improved peak shapes, were obtained in the ILs-MWNTs modified separation system for all drug enantiomers compared to the single CSE system. Several parameters affecting the enantioseparation, such as the choice of ILs and carbon nanoparticles, ILs-MWNTs concentration, chiral selector concentration, buffer pH and applied voltage, were systematically investigated. Satisfactory separations were achieved when 2.4μg/mL ILs-MWNTs were introduced into the 20mM Tris/H3PO4 buffer solution containing 2.5% CSE at pH 2.8–3.4 with a 15kV applied voltage. A brief mechanism of the enhanced enantioseparation capability of the ILs-MWNTs modified chiral separation system was also discussed.

Investigation of chondroitin sulfate D and chondroitin sulfate E as novel chiral selectors in capillary electrophoresis

Various chiral selectors have been utilized successfully in capillary electrophoresis (CE); however, the number of polysaccharides used as chiral selectors is still small and the mechanism of enantiorecognition has not been fully elucidated. Chondroitin sulfate D (CSD) and chondroitin sulfate E (CSE), belonging to the group of glycosaminoglycans, are linear, sulfated polysaccharides with large mass. In this paper, they were investigated for the first time for their potential as chiral selectors by CE. The effect of buffer composition and pH, chiral selector concentration, and applied voltage were systematically examined and optimized. A variety of drug enantiomers were resolved in the buffer pH range of 2.8-3.4 using 20mM Tris/H3PO4 buffer with 5.0% CSD or CSE and 20kV applied voltage. A central composite design was used to validate the optimized separation parameters and satisfactory uniformity was obtained. As observed, CSE allowed satisfactory separation of the enantiomers of amlodipine, laudanosine, nefopam, sulconazole, and tryptophan methyl ester, as well as partial resolution of citalopram, duloxetine, and propranolol under the optimized conditions. CSD allowed partial or nearly baseline separation of amlodipine, laudanosine, nefopam, and sulconazole. The results indicated that CSE has a better enantiorecognition capability than CSD toward the tested drugs.

Penicillin G as a novel chiral selector in capillary electrophoresis

The penicillin sub-class of β-lactam antibiotics has not been examined for its enantiodiscriminating abilities in capillary electrophoresis (CE) until date. The present work was therefore designed to evaluate penicillin G potassium salt (PenG) as an ion-pair chiral selector (CS) using CE for its several attributes, namely, high solubility in water and lower alcohols, structure allowing multiple interactions with analytes and cost-effectiveness. Systematic experiments were performed to investigate the effect of composition of background electrolyte, applied voltage and capillary temperature on chiral separation. Baseline resolutions of enantiomers of five basic chiral drugs (namely, darifenacin, citalopram, sertraline, propranolol and metoprolol) were attained using a background electrolyte composed of water:methanol (90:10, v/v) and consisting of 10.7 or 16.1mM CS at 20°C using an applied voltage of 5kV.

Hydroxyethylammonium monosubstituted cyclodextrin as chiral selector for capillary electrophoresis

A novel cationic cyclodextrin, mono-6A-(2-hydroxyethyl-1-ammonium)-6A-β-cyclodextrin chloride (HEtAMCD) has been successfully synthesized and applied as chiral selector in capillary electrophoresis. The NMR study revealed this chiral selector has three recognition sites: β-CD, ammonium cation and hydroxy group in the sidearm to contribute three corresponding driving forces including inclusion complexation, electrostatic interaction and hydrogen bonding. The effect of buffer pH and HEtAMCD concentration (2.5–10mM) on enantioselectivity, chiral resolution as well as effective mobility of analytes was investigated. This elegantly designed CD exhibits outstanding enantioselectivities toward the studied hydroxyl acids and ampholytic racemates in CE with the aid of extra hydrogen bonding. Under optimum pH 6.0, chiral resolutions over 5 can be readily obtained for hydroxy acids with CD concentration below 5mM. The comparison study between HEtAMCD and our earlier reported ammonium CDs indicates the hydroxyethylammonium group of HEtAMCD significantly increased the enantioselective capability.

Synthesis and application of a chiral ionic liquid functionalized β‐cyclodextrin as a chiral selector in capillary electrophoresis

A novel chiral ionic liquid functionalized β-cyclodextrin, 6-O-2-hydroxpropyltrimethylammonium-β-cyclodextrin tetrafluoroborate ([HPTMA-β-CD][BF4]), was synthesized and used as a chiral selector in capillary electrophoresis. [HPTMA-β-CD][BF4] not only increased the solubility in aqueous buffer in comparison with the parent compound, but also provided a stable reversal electroosmotic flow, and the enantioseparation of eight chiral drugs was examined in phosphate buffer containing [HPTMA-β-CD][BF4] as the chiral selector. The effects of the [HPTMA-β-CD][BF4] concentration and the background electrolyte pH were studied. Moreover, the chiral separation abilities of β-CD and [HPTMA-β-CD][BF4] were compared and possible mechanisms for the chiral recognition of [HPTMA-β-CD][BF4] are discussed.

Analysis of Repaglinide Enantiomers in Pharmaceutical Formulations by Capillary Electrophoresis Using 2,6-Di-o-methyl- -cyclodextrin as a Chiral Selector

This study used the general applicability of 2,6-didi-o-methyl-β-cyclodextrin (DM-β-CD) as the chiral selector in capillary electrophoresis for fast and efficient chiral separation of repaglinide enantiomers. A systematic study of the parameters affecting separation was performed with UV detection at 243 nm. The optimum conditions were determined to be 1.25% (w/v) DM-β-CD in 20 mM sodium phosphate (pH 2.5) as the running buffer and separation voltage at 20 kV. DM-β-CD had the best enantiomer resolution properties under the tested conditions, whereas other β-cyclodextrins showed inferior performances or no performance. The proposed method had a linear calibration curve in the concentration range of 12.5-400 µg/mL. The limit of detection was 100 ng/mL. The intra-day and inter-day precisions were 2.8 and 3.2%, respectively. Recoveries of 97.9-100.9% were obtained. The proposed method was fast and convenient, and was determined to be efficient for separating enantiomers and applicable for analyzing repaglinide enantiomers in quality control of pharmaceutical production.

Study on the use of boromycin as a chiral selector in capillary electrophoresis

The first application of boromycin as a chiral selector in capillary electrophoresis is described. Given boromycin's insolubility in water, a non-aqueous background electrolyte based on methanol was used for enantiomeric discrimination of selected chiral primary amines (α-methylbenzylamine, R,S-tryptophanol, R,S-norepinephrine, R,S-octopamine, R,S-p-hydroxynorephedrine and R,S-2-amino-1-phenylethanol). A basic study of experimental conditions including the influence of boromycin concentration, the composition and concentration of background electrolyte and also the influence of different organic solvents was performed. The best separation condition was 75mM Tris/50mM boric acid in methanol, pHws 9.0, with a positive separation voltage. The enantiomeric separation of the primary amines was achieved within 14min with resolution values greater than 1.5 for the majority of the studied analytes.

Cationic cyclodextrin as versatile chiral selector for enantiomeric separation in capillary electrophoresis

A novel cationic cyclodextrin, mono-6A-(3-methoxypropan-1-ammonium)-6A-β-cyclodextrin chloride, has been developed and used as chiral selector in capillary electrophoresis (CE). This chiral selector has three recognition sites: β-CD, ammonium cation and methoxy group in the sidearm to contribute three corresponding driving forces including inclusion complexation, electrostatic interaction and hydrogen bonding. This elegantly designed CD exhibits outstanding enantioselectivities in CE for a wide range of acidic and ampholytic racemates due to the extra hydrogen bonding for the chiral recognition. Under optimum pH 6.0, chiral resolutions over 10 can be readily achieved for acidic racemates with CD concentration below 10mM. This cationic CD exhibits great potential for versatile chiral separation in CE. The finding in this study may be applied to construct new host–guest systems for practical applications.

Synthesis and application of clindamycin succinate as a novel chiral selector for capillary electrophoresis

A novel chiral selector, clindamycin succinate, was synthesized and first used as a chiral selector in capillary electrophoresis (CE). The chiral resolution ability of this kind of clindamycin derivation was studied by CE using some racemic drugs as model analytes. From the experimental results, it was found that both resolution and selectivity of the selector were dependent on the following parameters: concentration of chiral selectors, pH of the running buffer, temperature of the capillary column, applied voltage and organic modifier used. The results show that the chiral selector possesses high resolution toward some racemic drugs, including ofloxacin, chlorphenamine, tryptophan, propranolol, sotalol and metoprolol. Excellent chiral resolution of these tested drugs was achieved under the optimal conditions of 50 mM clindamycin succinate, 10% MeOH v/v, 50 mM Tris buffer, pH 4.0, at 22 kV and 20 °C within 25 min.

Evaluation of clarithromycin lactobionate as a novel chiral selector for enantiomeric separation of basic drugs in capillary electrophoresis

Nowadays, macrocyclic antibiotics are presenting an increasing number of enantioseparation applications. The macrocyclic antibiotics used as chiral selectors in capillary electrophoresis (CE) include the ansamycins and the glycopeptides. The macrolides, another important class of macrocyclic antibiotics, have been reported as a new type of chiral selectors recently. In this study, clarithromycin lactobionate (CL), belonging to the group of macrolide antibiotics, was first investigated for its potential as a novel chiral selector in CE for enantiomeric separation of several basic drugs. As observed, CL allowed excellent separation of the enantiomers of metoprolol, atenolol, propranolol, bisoprolol, esmolol, ritodrine, and amlodipine, as well as partial enantioresolution of labetalol and nefopam. In addition, CL possesses advantages such as high solubility and low viscosity in the solvent and very weak UV absorption. In the course of this study, it was found that both migration times and enantioseparation of the basic drugs were influenced by several experimental parameters, e.g. selector concentration, the composition and pH of the BGE, the type and concentration of organic modifier, and applied voltage. Thus, the effects of these factors were systematically investigated, and satisfactory enantioseparations of the studied drugs were achieved at the buffer pH range of 7.3-7.5 using 12.5 mM borax buffer with 50% v/v methanol, 60 mM CL, and 20 kV applied voltage. Moreover, comparison of the influences of the studied parameters was further investigated by means of Statistical Product and Service Solutions (SPSS) in this article.

Azithromycin as a new chiral selector in capillary electrophoresis

In capillary electrophoresis (CE), separation of enantiomers of a chiral compound can be achieved through the chiral interactions and/or complex formation between the chiral selector and the enantiomeric analytes on leaving their diastereomeric forms with different stability constants and hence different mobilities. A great number of chiral selectors have been employed in CE and among them macrocyclic antibiotics exhibited excellent enantioselective properties towards a wide number of racemic compounds. The use of azithromycin (AZM) as a chiral selector has not been reported previously. This work reports the use of AZM as a chiral selector for the enantiomeric separations of five chiral drugs and one amino acid (tryptophan) in CE. The enantioseparation is carried out using polar organic mixtures of acetonitrile (ACN), methanol (MeOH), acetic acid and triethylamine as run buffer. The influences of the chiral selector concentration, ACN/MeOH ratio, applied voltage and capillary temperature on enantioseparation are investigated. The results show that AZM is a viable chiral selector in CE for the enantioseparation of the type of chiral drugs investigated.

Evaluation of the enantioselectivity of glycogen-based dual chiral selector systems towards basic drugs in capillary electrophoresis

Several chiral reagents including cyclodextrins (CDs) and derivatives, crown ethers, proteins, chiral surfactants and polymers have been involved in dual selector systems for enantioseparation of a series of chiral compounds by capillary electrophoresis (CE). In comparison to the chiral reagents above-mentioned, there is no report concerning the use of polysaccharides in dual chiral CE system. In this paper we first investigate the enantioselectivity of polysaccharide-based dual selector systems towards some chiral drugs. During our recent work, glycogen belonging to the class of branched polysaccharides has been used as a novel chiral selector in CE. In this study, three glycogen-based dual chiral CE systems have been established for enantiomeric separations of several racemic basic drugs consisting of duloxetine, cetirizine, citalopram, sulconazole, laudanosine, amlodipine, propranolol, atenolol and nefopam. These three dual systems combined glycogen (neutral polysaccharide) with chondroitin sulfate A (CSA, ionic polysaccharide), β-CD and HP-β-CD, respectively. It was found that the dual system of glycogen/CSA exhibited good enantioselective properties toward the tested drugs. More importantly, compared to the single selector systems, synergistic effect was observed when glycogen was used with CSA for most of the analytes. This indicated the enhancement of enantioseparation observed for these analytes in glycogen/CSA system might be due to some favorable interaction effects between glycogen and CSA. Moreover, in order to evaluate the stereoselectivity of glycogen/CSA, the influences of buffer pH and selector concentration on enantioseparation of the studied drugs were also investigated.

Chiral capillary electrophoresis with cationic pyrrolidinium‐β‐cyclodextrin derivatives as chiral selectors

New single-isomer, cationic beta-cyclodextrins, including mono-6-deoxy-6-pyrrolidine-beta-cyclodextrin chloride (pyCDCl), mono-6-deoxy-6-(N-methyl-pyrrolidine)-beta-cyclodextrin chloride (N-CH(3)-pyCDCl), mono-6-deoxy-6-(N-(2-hydroxyethyl)-pyrrolidine)-beta-cyclodextrin chloride (N-EtOH-pyCDCl), mono-6-deoxy-6-(2-hydroxymethyl-pyrrolidine)-beta-cyclodextrin chloride (2-MeOH-pyCDCl) were synthesized and used as chiral selectors in capillary electrophoresis for the enantioseparation of carboxylic and hydroxycarboxylic acids and dansyl amino acids. The unsubstituted pyCDCl exhibited the greatest resolving ability. Most analytes were resolved over a wide range of pH from 6.0 to 9.0 with this chiral selector. In general, increasing pH led to a decrease in resolution. The effective mobilities of all the analytes were found to decrease with increasing CD concentration. The optimal concentration for most carboxylic acids and dansyl amino acid was in the range 5-7.5 mM and >15 mM for hydroxycarboxylic acids. (1)H NMR experiments provided direct evidence of inclusion in the CD cavity.