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The significance and necessity of separating enantiomers in food, pharmaceuticals, pesticides, and other samples remains constant and unrelenting. The successful chiral separation usually includes the application of a chiral auxiliary compound, known also as a chiral selector (CS), that forms complexes with enantiomers of different physicochemical properties, enabling efficient separation. While both native and substituted cyclodextrins (CDs) are commonly used as CSs, β-CD is undoubtedly the most popular one among them. This review includes recent advancements in the application of β-CD as a CS. While the theoretical background behind the enantioseparation is also part of this work, the main emphasis is put on the factors that affect the efficacy of this process such as temperature, pH, solvent, and the choice of other additives. Also, the different analytical methods: Nuclear Magnetic Resonance (NMR) spectroscopy, Capillary Electrophoresis (CE), fluorescence spectroscopy (FS), High-Performance Liquid Chromatography (HPLC), Isothermal Titration Calorimetry (ITC), and UV-vis spectroscopy, used for enantioseparation with the aid of β-CD as CS, are thoroughly compared. Also, since some of the chiral compounds have been studied in the context of their enantioseparation more than once, those works are compared and critically analyzed. In conclusion, while β-CD can be in most cases used as CS, the choice of the experimental conditions and method of analysis is crucial to achieve the success.

This research focuses on the development and validation of a capillary electrophoresis (CE) method for the chiral separation of three H1-antihistamine drugs chlorcyclizine, norchlorcyclizine, and neobenodine using sulfated β-cyclodextrin (S-β-CD) as the chiral selector. The study explores various factors influencing the separation efficiency, including CD concentration, organic modifier content, voltage application, and buffer pH. Optimal conditions were identified as a 100 mM phosphate buffer (pH 6.0) with 34 mg mL -1 S-β-CD and 40% (v/v) methanol. The method demonstrated excellent linearity in calibration curves, with coefficients of determination exceeding 0.99 for each enantiomer. Precision studies revealed good intra- and inter-day precision for migration times and peak areas. The limits of detection and quantification for the analytes were within the ranges of 5.9-11.4 and 18-34.6 µmol L -1 , respectively. Overall, the developed CE method offers a robust and precise approach for the chiral separation of H1-antihistamine drugs, holding promise for pharmaceutical applications., (© 2024 The Authors. ELECTROPHORESIS published by Wiley‐VCH GmbH.)

The incorporation of phosphorothioate linkages has recently been extensively employed in therapeutic oligonucleotides. For their separation and quality control, new high-efficient and high-sensitive analytical methods are needed. In this work, a new affinity capillary electrophoresis method has been developed and applied for the separation of a potential anticancer drug, 2',3'-cyclic diadenosine diphosphorothioate (R p , R p ) (ADU-S100), and three recently newly synthesized diastereomers of its difluorinated derivative, 3',3'-cyclic di(2'-fluoro, 2'-deoxyadenosine phosphorothioate). The separation was performed in the various background electrolytes (BGEs) within a pH range 5-9 using several native and derivatized cyclodextrins (CDs) as chiral additives of the BGE. Relatively good separations were obtained with β-, γ-, and 2-hydroxypropyl-γ-CDs in some of the BGEs tested. However, the best separation was achieved using the 2-hydroxypropyl-β-CD chiral selector at 43.5 mM average concentration in the BGE composed of 40 mM Tris, 40 mM tricine, pH 8.1. Under these conditions, all the previous four cyclic dinucleotides (CDNs) were baseline separated within 4 min. Additionally, the average apparent binding constants and the average actual ionic mobilities of the complexes of all four CDNs with 2-hydroxypropyl-β-CD in the above BGE were determined. The formed complexes were found to be relatively weak, with the average apparent binding constants in the range of 12.2-94.1 L mol -1 and with the actual ionic mobilities spanning the interval (-7.8 to -12.7) × 10 -9  m 2  V -1  s -1 . The developed method can be applied for the separation, analysis, and characterization of the above and similar CDNs., (© 2024 The Authors. ELECTROPHORESIS published by Wiley‐VCH GmbH.)

The physical and chemical properties of chiral drugs are very similar. However, their pharmacological and toxicological effects vary significantly. For example, one enantiomer may have favorable properties whereas the other may be ineffective or even have toxic side effects. Hence, exploring innovative strategies to improve enantiomeric resolution is of great importance. Metoprolol (MET) is a β -receptor blocker used to treat hypertension, stable angina pectoris, and supraventricular tachyarrhythmia. Establishing chiral separation and analysis methods of MET enantiomers is important for enhancing the quality of chiral drugs. Capillary electrophoresis (CE) has the advantages of a small sample size, simple operation, high separation efficiency, and many alternative modes; therefore it is widely used in the field of chiral drug separation. The chiral selectors commonly used for CE-based chiral separation include cyclodextrin (CD) and its derivatives, polysaccharides, proteins, and macrocyclic antibiotics. CD is one of the most commonly used and effective chiral selectors for CE. The relatively hydrophobic structure inside the cavity and the relatively hydrophilic structure outside the cavity of CD enable it and chiral molecules to form inclusion compounds with different binding constants, thus achieving chiral separation. However, the use of CD alone as a chiral selector does not always yield satisfactory separation results. Hence, the addition of other additives, such as ionic liquids and deep eutectic solvents (DESs) to assist CD-based chiral separation systems has received extensive attention. Previous studies on the enantiomeric separation of MET by CE have focused on the addition of CD and its derivatives alone for separation. Few studies have been conducted on the synergistic addition of auxiliary additives to CD to improve the enantiomeric resolution of MET. In this study, three DESs, namely, choline chloride-D-glucose, choline chloride-D-fructose, and lactate-D-glucose, were used for the CE-based chiral separation of MET for the first time, and the synergistic effect of the DESs on the separation of MET enantiomers by CD-based capillary zone electrophoresis was speculated. For this purpose, an uncoated fused silica capillary with inner diameter of 50 μm, total length of 50 cm and effective length of 41.5 cm was used as the separation column. First, the effects of CD type, CD concentration, buffer pH, and buffer concentration on MET separation were investigated, and the optimal conditions (15 mmol/L carboxymethyl- β -cyclodextrin (CM- β -CD), pH=3.0, and 40 mmol/L phosphate buffer) were obtained. Other CE conditions were as follows: UV detection at 230 nm, applied voltage of 25 kV. All operations were carried out at 20 ℃. Next, three types of DESs were prepared as auxiliary additives via a mixed-heating method. The DESs were mixed in a 50 mL round-bottomed flask at a certain molar ratio and then heated in a water bath at 80 ℃ for 3 h until a clear and transparent liquid was obtained. The effects of different DESs and their mass fraction on chiral separation were subsequently studied. The optimal choline chloride-D-fructose mass fraction was ultimately determined to be 1.5%. The resolution of MET increased from 1.30 without DES to 2.61 with 1.5% choline chloride-D-fructose, thereby achieving baseline separation. Finally, the separation effect and mechanism were speculated. The MET chiral separation method established in this study is of great significance for improving the quality of chiral compounds and ensuring the safety and effectiveness of clinical drugs. Furthermore, it may be useful in the research and development of CE-based chiral separation techniques using CD derivatives with DESs.

In this study, a novel supramolecular deep eutectic solvent consisting of sulfated-β-CD and citric acid (S-β-CD-CA) is reported for the first time. This innovative system was evaluated as a sole chiral selector in capillary electrophoresis for the enantioseparation of six fluorine-substituted amphetamine analogs, yielding remarkable outcomes. Baseline separations of all amphetamine analogs under study were achieved in less than 21.00 min using the S-β-CD-CA as the chiral selector. It was observed that the addition of 0.050 % v/v S-β-CD-CA into the background electrolyte resulted in the baseline separation of five out of the six fluorine-substituted amphetamine analogs, while in the case of the para-substituted amphetamine analog, 4-fluoramphetamine (4-FA), a higher percentage (0.15 % v/v) was required to achieve baseline enantioseparation. These findings emphasized the potential of this new supramolecular system in providing a class of solvents with promising chiral recognition properties., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Constantina Kapnissi-Christodoulou reports financial support, administrative support, article publishing charges, equipment, drugs, or supplies, and statistical analysis were provided by University of Cyprus., (Copyright © 2024. Published by Elsevier B.V.)

The thermodynamic properties of molecular recognition in host-guest inclusion complexes can be studied by Taylor dispersion analysis (TDA). Host-guest inclusion complexes have modest size, and it is possible to get convergent results fast, achieving greater certainty for the obtained thermodynamic properties. Cyclodextrins (CDs) and their derivatives can be used as drug carriers that can boost stability, solubility, and bioavailability of physiologically active substances. A simple and effective approach for assessing the binding properties of CD complexes that are critical in the early stages of drug and formulation development is needed to fully understand the process of CD and guest molecules' complex formation. In this work, TDA was successfully used to rapidly determine interaction parameters, including binding constant and stoichiometry, between β-CD and folic acid (FA) along with the diffusivities of the free FA and its complex with β-CD. Additionally, the FA diffusion coefficient obtained by TDA was compared to the results previously obtained by nuclear magnetic resonance. Affinity capillary electrophoresis (ACE) was also used to compare the binding constants obtained by different methods. The results showed that the binding constants obtained by ACE were somewhat lower than those obtained by the two TDA procedures., (© 2023 The Authors. Electrophoresis published by Wiley-VCH GmbH.)

The present contribution describes the application of three single-isomeric cyclodextrin derivatives for the first time - Sugammadex, Subetadex and Sualphadex as chiral selectors. Their recognition ability was investigated by means of chiral capillary electrophoresis, on a pool of cathinone and amphetamine derivatives. The selectors differ in cavity sizes and in the number of ionizable groups which evidently influenced their enantioselectivity performance. Their common feature is their high isomeric purity that enabled the detailed study of the molecular association between the cathinone guest and the cyclodextrin host at the atomic level. With the aid of enantiopure cathinone derivatives, the migration order could also be determined in capillary electrophoresis. As the result of the capillary electrophoresis screening, partial or baseline chiral separation of 19 cathinones and an amphetamine derivative could be achieved, and the systematic study was performed focusing on three different pH conditions pH = 7.0, pH = 5.0 and pH = 2.5 and several different selector concentrations. Among the tested derivatives Subetadex is the best performing chiral selector, especially under acidic pH values for separating enantiomers, proven not only by capillary electrophoresis but also by 1D and 2D NMR measurements., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In this work, a simple, accurate, and rapid capillary electrophoresis with an indirect ultraviolet detection method was developed to simultaneous separate 10 biogenic amines. It was found that β-cyclodextrin and ethylene diamine tetraacetic acid facilitated the separation of tryptamine and tyramine, spermidine and spermine, respectively. The optimized background electrolytes consisted of 20.0 mmol/L imidazole, 8.0 mmol/L β-cyclodextrin, 0.5 mmol/L ethylene diamine tetraacetic acid, and 6.0% methanol (at pH 4.50 adjusted with acetic acid). The total analysis time of this method was less than 11 min with limits of detection in the range of 0.14-1.98 mg/L. The interday relative standard deviation of migration time and peak area were less than 1.36% and 4.44% (n = 6), respectively. To verify the applicability, this method was carried out to analyze biogenic amines in commercial luncheon meat samples. Due to the complex composition of luncheon meat, the real samples were rinsed with deionized water to reduce the influence of matrices. It was found that both storage temperature and protein content of the luncheon meat samples affected the biogenic amines content during storage. The results of this study are instructive for the storage of high-protein meat products., (© 2022 Wiley-VCH GmbH.)

The values of the apparent binding constants for β-cyclodextrin complexes of betulin derivatives determined by mobility shift affinity capillary electrophoresis were found to be independent of the composition of the two background electrolytes used (tetraborate buffer, pH 9.18, and phosphate buffer, pH 8.00, both of them with 20 mM ionic strength). It has been found that if there is not a constant plateau on the binding curve then four independent parameters can be determined: binding constants (also referred to as stability, association, or formation constants) and ionic mobilities of 1:1 and 1:2 complexes. However, at least 10-12 data points in the binding curve should be used to reliably estimate the parameters. For the first time, the apparent binding constants for complexes of ester betulin derivatives with dimethyl-β-cyclodextrin have been determined by mobility shift affinity capillary electrophoresis. The logarithms of the constants for 1:1 and 1:2 complexes at 25°C for betulin 3,28-diphthalate with a 95% confidence interval are 4.98 (4.95-5.01) and 7.52 (7.26-7.68); for betulin 3,28-disulfate, the values are 4.97 (4.89-5.03) and 8.24 (6.82-8.52). It has been found that betulin 3,28-disuccinate forms only a 1:1 complex and the binding constant logarithm is 5.25 ± 0.02., (© 2022 Wiley-VCH GmbH.)

Chiral CE methods were developed for the elucidation of l- or d-configuration of tyrosine residue in antimicrobial dipeptide β-alanyl-tyrosine (β-Ala-Tyr) isolated from the hemolymph of larvae of fleshfly Neobellieria bullata and for the evaluation of enantiopurity of its synthetic isomers (β-Ala-d-Tyr and β-Ala-l-Tyr), and enantiomers of their amidated and acetylated derivatives, β-Ala-d,l-Tyr-NH 2 and N-Ac-β-Ala-d,l-Tyr, respectively. Baseline separations were achieved for all three pairs of enantiomers: (i) for β-Ala-d,l-Tyr in acidic background electrolyte composed of 32/50 mM tris(hydroxymethyl)aminomethane/H 3 PO 4 , pH 2.5, and 20 mg/mL 2-hydroxypropyl-β-cyclodextrin as chiral selector; (ii) for β-Ala-d,l-Tyr-NH 2 enantiomers in acidic background electrolyte consisting of 48/50 mM tris(hydroxymethyl)aminomethane/H 3 PO 4 , pH 3.5, and 30 mg/mL 2-hydroxypropyl-β-cyclodextrin; and (iii) for enantiomers of N-Ac-β-Ala-d,l-Tyr in alkaline background electrolyte composed of 50/49 mM Na 2 B 4 O 7 /NaOH, pH 10.5, and 60 mg/mL 2-hydroxypropyl-β-cyclodextrin. From CE analyses of mixed samples of isolated β-Ala-Tyr and synthetic standards β-Ala-l-Tyr and β-Ala-d-Tyr, it turned out that isolated β-Ala-Tyr was pure l-enantiomer. In addition, the average apparent binding constants, K b , and average actual ionic mobilities of the complexes of β-Ala-d,l-Tyr and its above derivatives with 2-hydroxypropyl-β-cyclodextrin were determined. These complexes were weak, with K b values ranging from 11.2 to 79.1 L/mol. Their cationic mobilities were equal to (5.6-9.2) × 10 -9 m 2 /V/s, and anionic mobilities to (-1.3-1.6) × 10 -9 m 2 /V/s., (© 2022 Wiley-VCH GmbH.)

Cyclodextrins and their derivatives have been used for chiral high-performance liquid chromatography selectors, while they are costly to use as mobile phase additives in high-performance liquid chromatography. Here, we report application of phenyl column coated permanently with methylated β-cyclodextrin for chiral high-performance liquid chromatography. A 0.1% (v/v) phosphoric acid solution containing 1 M NaCl and 0.5% (w/v) methylated β-cyclodextrin was subjected to a phenyl column at a flow rate of 0.5 mL/min at 30°C for 2 h. Using the precoating phenyl column, all the enantiomers of the four phenethylamines (norepinephrine, epinephrine, octopamine, and synephrine) were successfully separated simultaneously by high-performance liquid chromatography with a mobile phase without methylated β-cyclodextrin at a flow rate of 0.2 mL/min at 30°C. The enantioseparation ability was retained for successive analyses during 1 week. It is suggested that inclusion complex of methylated β-cyclodextrin with a phenyl group on the surface of the stationary phase could be formed and that the inclusion complex could form the ternary complex with the injected analytes. The longer retention time of (S)-enantiomers of analytes than corresponding (R)-enantiomers for high-performance liquid chromatography could be explained from the higher stability of the methylated β-cyclodextrin complexes with (S)-enantiomers, which were confirmed by capillary electrophoresis and 1 H NMR spectroscopy experiments., (© 2021 Wiley-VCH GmbH.)

Molecular modeling (MM) results for tedizolid and radezolid with heptakis-(2,3-diacetyl-6-sulfo)-β-cyclodextrin (HDAS-β-CD) are presented and compared with the results previously obtained for linezolid and sutezolid. The mechanism of interaction of chiral oxazolidinone ligands belonging to a new class of antibacterial agents, such as linezolid, tedizolid, radezolid, and sutezolid, with HDAS-β-CD based on capillary electrokinetic chromatography (cEKC), nuclear magnetic resonance (NMR) spectroscopy, and MM methods was described. Principles of chiral separation of oxazolidinone analogues using charged single isomer derivatives of cyclodextrin by the cEKC method were presented, including the selection of the optimal chiral selector and separation conditions, complex stoichiometry, and binding constants, which provided a comprehensive basis for MM studies. In turn, NMR provided, where possible, direct information on the geometry of the inclusion complexes and also provided the necessary structural information to validate the MM calculations. Consequently, MM contributed to the understanding of the structure of diastereomeric complexes, the thermodynamics of complexation, and the visualization of their structures. The most probable mean geometries of the studied supramolecular complexes and their dynamics (geometry changes over time) were determined by molecular dynamics methods. Oxazolidinone ligands have been shown to complex mainly the inner part of cyclodextrin, while the external binding is less privileged, which is consistent with the conclusions of the NMR studies. Enthalpy values of binding of complexes were calculated using long-term molecular dynamics in explicit water as well as using molecular mechanics, the Poisson-Boltzmann or generalized Born, and surface area continuum solvation (MM/PBSA and MM/GBSA) methods. Computational methods predicted the effect of changes in pH and composition of the solution on the strength and complexation process, and it adapted the conditions selected as optimal during the cEKC study. By changing the dielectric constant in the MM/PBSA and MM/GBSA calculations, the effect of changing the solution to methanol/acetonitrile was investigated. A fairly successful attempt was made to predict the chiral separation of the oxazolidinones using the modified cyclodextrin by computational methods.

A new capillary electrophoresis method was applied to chiral separation of three amino acids, including D,L-tryptophan, D,L-tyrosine and D,L-phenylalanine. The chiral resolution was attained in an untreated fused-sillica capillary using a dual chiral selector, which was made up of Cu(II)-L-histidine complex and β-cyclodextrin (CD). The cardinal factors influencing its separation efficiency, such as chiral selectors, buffer pH and applied voltage, were optimized. Best results were acquired by using a buffer consisting of 10 mmol/L Cu(II), 13 mmol/L L-histidine, 8 mmol/L β-CD, 5 mmol/L phosphate adjusted to pH 5.0 and 15 kV applied voltage. All enantiomers were entirely resolved within 20 min with high resolutions of 3.6~6.1. The analysis method was verified through the determination of D,L-tryptophan in terms of linearity, precision and accuracy. And the robustness of this method was proved. The Limit of Detection and Limit of Quantification for both enantiomers were 2.5 and 5 μg/mL, respectively. The method was perfectly applied to the determination of the enantiomeric purity of L-tryptophan. Furthermore, the interaction between Cu(II)-L-histidine complex and β-CD was also studied using Ultraviolet-visible and 1H NMR spectroscopy to explain the synergistic effect involved. The results illustrated that Cu(II)-L-histidine complex and β-CD played a synergistic role in the enantiomeric separation of chiral drugs, with good prospects for application., (© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

We present high resolution fast, cost-effective and sensitive Capillary zone electrophoresis (CZE) methods for determination of enantiomeric compounds of Kynurenine pathway, i.e. D, L-Kynurenine (KYN), in human serum and urine samples by cationic-β-CD and its synergistic dual chiral selector system (SD-CSs) with α-CD in 50 mM borax borate buffer (pH 9.0) as BGE. Acid-mediated stacking enrichment by HCl delivered 15 nM limit of detection (LOD) and 50 nM limit of quantification (LOQ). The methods gave advantages of linearity in the concentration range of 50 nM-1000 nM, reproducibility (RSD ≤ 3.35), selectivity against interfering amino acids, and remarkable recoveries. SD-CSs delivered resolution of D, L-KYN twice that of individual chiral selectors (CSs) under similar conditions. The binding constants (Kb) and electrophoretic mobilities (µeff) of D, L-KYN with different concentrations of CSs were calculated to find the migration order of enantiomers. The chiral recognition mechanism was investigated by molecular docking and molecular mechanics, which revealed strong hydrogen bonding between Kynurenine enantiomers and the SD-CSs as compared to individual CS as the key player in binding, formation of stable complexes which led to the ultimate separation., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflict of interest., (Copyright © 2020. Published by Elsevier B.V.)

The major goal of this study was to determine the affinity pattern of the terbutaline (TB) enantiomers toward α-, β-, γ-, and heptakis(2,3-di-O-acetyl)-β-cyclodextrins and using NMR spectroscopy for the understanding of the fine mechanisms of interaction between the cyclodextrins (CD) and TB enantiomers. It was shown once again that CE in combination with NMR spectroscopy represents a sensitive tool to study the affinity patterns and structure of CD complexes with chiral guests. Opposite affinity patterns of TB enantiomers toward native α- and β-CDs were associated with significant differences between the structure of the related complexes in solution. In particular, the complex between TB enantiomers and α-CD was of the external type, whereas an inclusion complex was formed between TB enantiomers and β-CD. One of the possible structures of the complex between TB and heptakis(2,3-di-O-acetyl)-β-CD (HDA-β-CD) was quite similar to that of TB and β-CD, although the chiral recognition pattern and enantioselectivity of TB complexation with these two CDs were very different., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The chiral separation ability of the full library of methylated-β-cyclodextrins towards pharmacologically significant racemic drugs including basic compounds was studied by chiral CE. The syntheses of all the methylated, single isomer β-cyclodextrins were revised and optimized and the aqueous solubility of the derivatives was unambiguously established. The three most relevant commercially available methylated isomeric mixtures were also included in the screening, so a total of ten various methylated CDs were investigated. The effects of the selector concentration on the enantiorecognition properties at acidic pH were investigated. Among the dimethylated β-cyclodextrins, the heptakis (2,6-di-O-methyl)-β-cyclodextrin isomer (2,6-DIMEB) resulted to be the most versatile chiral selector. Terbutaline was selected as a model compound for the in-depth investigation of host-guest enantiodiscrimination ability. The association constants between the two terbutaline enantiomers and 2,6-DIMEB were determined in order to support that the enantioseparation is driven by differences is host-guest binding. The migration order of the enantiomers was confirmed by performing spiking experiments with the pure enantiomers. 1D and 2D NMR spectroscopy was applied to the 2,3-, and 2,6-DIMEB/terbutaline systems to rationalize at molecular level the different enantioseparation ability of the dimethylated β-cyclodextrin selectors., (© 2019 The Authors. Electrophoresis published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

CD-CZE methods were developed for complete stereoisomeric separations of a series of six γ-lactam analogues, of which some were neutral, or cationic depending on the background electrolyte nature. The tested cyclodextrin was the versatile sulfobutylether- β-CD, used either in a phosphate buffer using capillaries dynamically coated with polyethylene oxide or in a borate buffer using uncoated capillaries. Long-end and short-end modes and concentration variations of chiral selectors allowed finding conditions of complete separation of four out of the six derivatives (i.e., 1, 2, 3, and 4) in short run times, confirming their broad range of applications. To separate the two last compounds, the highly sulfated- γ-CD was examined as chiral selector in acidic phosphate conditions. The enantiomers of the γ-lactam analogues 5 and 6 were baseline resolved with 5.5 and 4%, respectively as concentration in the buffer., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The exhaustive primary-side alkylation of cyclodextrins has never been achieved directly. The undesired and simultaneous derivatization of the secondary hydroxyl moieties generates intricate isomeric mixtures that are challenging to purify, analyse and characterize. The aim of this study was to develop a chromatography-free and up-scalable strategy towards the preparation of per-6-O-methylated cyclodextrin and to test the compound as potential chiral selector. The target molecule was prepared according to a five-step synthesis by using methyltriphenylphosphonium bromide as catalyst under heterogeneous conditions. The removal of benzyl moieties, used as temporary secondary-side protecting groups, was attained by applying hydrazine-carbonate in the presence of Pd/C. All the intermediates were obtained in high yields, thoroughly characterized and their purity was assessed by ad-hoc developed HPLC methods. The per-6-O-methylated β-cyclodextrin showed promising chiral recognition ability as background electrolyte additive in cyclodextrin-modified capillary electrophoresis using the recreational drug methylene-dioxypyrovalerone as model compound. Additionally, a model for the inclusion geometry between the single isomer host and the selected drug was developed based on the extensive 2D NMR analysis. The versatility of the proposed synthetic strategy opens the way to the industrial production of homogeneously primary-alkylated cyclodextrins and to their wide application in chiral separation of various drugs., (© 2019 The Authors. Electrophoresis published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The enantioseparation of chiral drugs via CE was first investigated using β-CD as chiral additive and deep eutectic solvents (DESs) as auxiliary additive. The results showed that improved separation of tested chiral drugs was obtained in the presence of DESs and β-CD compared to the single β-CD separation system. With the optimized condition, resolutions of DESs applied β-CD separation system for rac-Zopiclone, rac-Salbutamol, and rac-Amlodipine increased 3-4.2 times as single β-CD separation system. The resolutions reached 4.74, 6.37, and 9.67, respectively. The results demonstrate that DESs are viable additives to CD system in CE for the separation of the chiral drugs., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Pressure-assisted stereospecific capillary electrophoresis method was developed for the determination of enantiomeric purity of the antiparkinsonian agent (R)-rasagiline. The optimized method, 50 mM glycine-HCl buffer pH 2, supplied with 30 mM sulfobutylether-β-cyclodextrin, at 35°C, applying 12 kV in reversed polarity, and -8 mbar pressure (vacuum), short-end injection with -25 mbar × 2 s, was successful for baseline separation of rasagiline enantiomers (R s = 3.5 ± 0.1) in a short analysis time. The method was validated according to current guidelines and proved to be reliable, linear, precise and accurate for determination of 0.15% S-enantiomer as chiral impurity in R-rasagiline sample, as well as quantification of the eutomer. Method application was tested on a commercial tablet formulation. Determination of spatial structure of diastereomeric associates was based on 1 H and 2D ROESY NMR, indicating that the aromatic moiety of the molecule can enter the cyclodextrin cavity. NMR titration and molecular modeling revealed that S-rasagiline formed a more stable inclusion complex with sulfobutylether-β-cyclodextrin, than its antipode, which is in agreement with electrophoretic results., (© 2019 The Authors. Electrophoresis published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

For the first time, capillary electrophoresis has been successfully employed for the fast and highly efficient separations of a novel type of stereoisomers - planar rotamers (planamers) of four newly synthesized 5-nitrosopyrimidine derivatives. These derivatives can form two rotamers differing in the orientation of nitroso group due to strong intramolecular hydrogen bonds. Partial separation of rotamers of two 5-nitrosopyrimidines was achieved in alkaline 50 mM sodium tetraborate, pH 9.3, and in acidic 18.5/42 mM Tris/phosphate, pH 2.3, background electrolytes (BGEs) free of stereoselectors. To improve the separation of these rotamers and to attain the baseline or better separation of rotamers of other two 5-nitrosopyrimidines, various BGEs and different cyclodextrins-based stereoselectors were tested. The most effective, i.e. the fastest and baseline or better separations of rotamers of all analyzed 5-nitrosopyrimidines were achieved within a short time, 3.7-9.3 min, in the above alkaline or acidic BGEs using β-cyclodextrin (β-CD) or carboxymethyl-β-CD as stereoselectors. Moreover, since the experiments with β-CD resulted in good separations of rotamers of all the investigated 5-nitrosopyrimidines, the apparent binding constants of their complexes with this selector were determined from the dependence of their effective mobilities on the β-CD concentration in the BGEs. The examined complexes were found to be relatively weak, with the apparent binding constants in the range 11.3-153.0 L/mol., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Methcathinone (ephedrone), 4-methylmethcathinone (mephedrone), and 3-methylmethcathinone (metaphedrone) are toxicologically-important cathinone derivatives used commonly as designer drugs. In this work we show the first method allowing to separate simultaneously all these molecules in a chiral medium, ensuring good resolution between all enantiomers. Eight cyclodextrins have been tested as potential chiral selectors, the best results were obtained with 2-hydroxyethyl-β-cyclodextrin, unreported so far for efficient separation of cathinones. After optimization, the method was calibrated and validated with and without the use of internal standard. The addition of standard improved an overall repeatability and precision, the use of electrophoretic mobility ratio was especially favorable (RSD < 1%). It was demonstrated that the method may be easily extended by introducing the additional cathinone-related drugs to the sample, maintaining satisfactory separation efficiency., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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 compounds by capillary electrophoresis (CE). In this paper, chondroitin sulfate D-based dual-selector system (CSD/CM-β-CD) was firstly established and investigated for the enantioseparation of six basic racemic drugs in capillary electrophoresis. Compared to the single-selector systems, synergistic effect and significantly improved separations for all tested analytes were observed in CSD/CM-β-CD system. The effect of several parameters, such as buffer pH, chiral selector concentration, and applied voltage, was systematically optimized. Meanwhile, to investigate the possible chiral recognition mechanisms in CSD/CM-β-CD synergistic system, we tried to apply the molecular docking method to simulate the host-guest binding procedures of the polysaccharide-based dual system for the first time. The difference in binding free energy was found to correspond to the chiral selectivity factor. The existence of CSD-CM-β-CD complex may give rise to a higher discriminatory ability against the enantiomers, indicating the synergistic effect in CSD/CM-β-CD system. Graphical abstract ᅟ.

Head-column field-amplified sample stacking of cations from a low conductivity sample followed by enantiomeric separation using negatively charged chiral selectors was studied experimentally and with computer simulation. Aspects investigated include the direct electrokinetic injection of the analytes into the background electrolyte, the use of a selector free buffer plug, the contribution of complexation within the buffer plug and the application of an additional water plug between sample and buffer plug. Attention was paid for changes of ionic strength which is known to have a significant impact on complexation and thus effective mobility. Racemic methadone was selected as a model compound, randomly substituted sulfated β-cyclodextrin as chiral selector and phosphate buffers (pH 6.3) for the background electrolyte and the buffer plug. Results confirm that the buffer plug is providing a spacer between cationic analytes and the negatively charged selector during electrokinetic injection. Simulation predicts the required length and composition of the plug for a given injection time to avoid an interference with the selector. A short water plug added between the low conductivity sample and a high conductivity buffer plug is demonstrated to provide best conditions to achieve high sensitivity in enantioselective drug assays with sulfated cyclodextrins as selectors., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The enantiomeric separation of methadone in the presence of multiple isomer mixtures of sulfated β-cyclodextrin (S-β-CD) was studied experimentally with CZE and theoretically using computer simulation. Experiments were performed over many years with several lots of S-β-CD from the same manufacturer with a specified degree of substitution of 7-11. Large differences in the migration patterns were observed between certain lots and it was concluded that the extent of labelling in lots released after a transition time was higher than originally specified. The migration pattern was observed to be associated with (i) the ionic strength increase resulting from using S-β-CDs with a higher charge state and (ii) differences in buffer composition. Apparent binding constants between methadone and the S-β-CD and complex mobilities were determined for different lots of S-β-CD at varying ionic strength using phosphate and 3-morpholino-2-hydroxypropanesulfonic acid buffers. The obtained values were used as input for simulations. For a given ionic strength, agreement between predicted and experimentally observed behavior was obtained for different buffers. R-methadone has a stronger interaction with S-β-CD than S-methadone. For any given configuration there is a distinct S-β-CD concentration range which results in the cationic migration of S-methadone while the migration direction of R-methadone is reversed. This configuration was demonstrated to be applicable for micropreparative CZE separations., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The aim of the study was to develop an alternative capillary zone electrophoresis (CZE) for simultaneous determination of phillyrin ( 1 ), phillygenin ( 2 ), epipinoresinol-4- O -β-glucoside ( 3 ), pinoresinol-4- O -β-glucoside ( 4 ), lariciresinol ( 5 ), pinoresinol ( 6 ), isolariciresinol ( 7 ) and vladinol D ( 8 ) in Forsythia suspensa . The structural types of lignans 1 - 8 could be attributed to bisepoxylignans ( 1 - 4 and 6 ), monoepoxylignans ( 5 and 8 ) and cyclolignan ( 7 ). The major difficulties in the CZE separation of 1 - 8 could be summarization as the simultaneous presence of free lignans ( 1 , 2 and 5 - 8 ) and lignan glucosides ( 3 and 4 ) and simultaneous occurrence of two pairs of isomers ( 3 and 4 as well as 5 and 7 ). Without the addition of β-CD and methanol, the resolution of these analytes was quite poor. However, in this study, compounds 1 - 8 were excellently separated from each other within 15 min under optimized conditions with a borax running buffer (40 mM borax, pH 10.30) containing 2 mM β-CD and 5% methanol ( v / v ) at the voltage of 20 kV, temperature of 35 °C and detection wavelength of 234 nm. Validation of the method included tests of linearity, precision, repeatability, stability and accuracy. In addition, the method offered inherent advantages such as lower analytical cost, no need of specific columns and use of small amounts of organic solvents and reagents. Finally, this green and economic CZE was successfully applied for the determination of these bioactive components 1 - 8 in F. suspensa fruits and its commercial extracts., Competing Interests: The authors declare no conflict of interest.

Herein we present the enantioseparation of 10 cardiovascular agents and six bronchiectasis drugs including propranolol, carteolol, metoprolol, atenolol, pindolol, esmolol, bisoprolol, bevantolol, arotinolol, sotalol, clenbuterol, procaterol, bambuterol, tranterol, salbutamol and terbutaline sulfate using carboxymethyl-β-cyclodextrin (CM-β-CD) as chiral selector. To our knowledge, there is no literature about using CM-β-CD for separating carteolol, esmolol, bisoprolol, bevantolol, arotinolol, procaterol, bambuterol and tranterol. During the course of work, changes in pH, CM-β-CD concentration, buffer type and concentration were studied in relation to chiral resolution. Excellent enantiomeric separations were obtained for all 16 compounds, especially for procaterol. An impressive resolution value, up to 17.10, was obtained. In particular, most of them achieved rapid separations within 20 min. Given the fact that enantioseparation results rely on analytes' structural characters, the possible separation mechanisms were discussed. In addition, in order to obtain faster separation for propranolol enantiomers in practical application, the effective length of capillary was innovatively shortened from 45 to 30 cm. After the validation, the method was successfully applied to the enantiomeric purity determination of propranolol in the formulation of drug substances., (Copyright © 2017 John Wiley & Sons, Ltd.)

This contribution reports the synthesis, characterization and capillary electrophoretic application of heptakis-(6-O-sulfobutyl-ether)-β-cyclodextrin sodium salt, (6-(SB) 7 -β-CD). The compound was obtained through a five-steps synthesis and it represents the first example of single-isomer sulfobutylated cyclodextrin that carries the negatively charged functions exclusively on its primary side and it is unmodified on the lower rim. The purity of each intermediate was determined by appropriate liquid chromatographic methods, while the isomeric purity of the final product was established by an ad-hoc developed HPLC method based on a CD-Screen-IEC column. The structural identification of 6-(SB) 7 -β-CD was carried out by 1D, 2D NMR spectroscopy and ESI-MS. The chiral separation ability of 6-(SB) 7 -β-CD was studied by chiral capillary electrophoresis using the single-isomer host as a background electrolyte additive to separate the enantiomers of a representative set of pharmacologically significant model compounds such as verapamil, dapoxetine, ondansetron, propranolol, atenolol, metoprolol, carvedilol, terbutaline, amlodipine and tadalafil. The enantiomer migration order and the effects of the selector concentration on the enantiorecognition properties were investigated. NMR spectroscopy was applied to deepen and further confirm the host-guest interactions and in the case of the model compound dapoxetine a potential representation for the supramolecular assembly was developed based on the dataset collected by the extensive 2D NMR analysis. This single-isomer chiral selector offers a new alternative to the widely applied randomly sulfobutylated- and sulfated-beta-cylodextrins as well as to the single-isomer sulfated and carboxymethylated derivatives in chiral separations., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Three kinds of sulfated β-cyclodextrin (S-β-CD), including a single isomer, heptakis-6-sulfato-β-cyclodextrin (HS-β-CD), degree of substitution (DS) of 7, which was synthesized in our laboratory and another two commercialized randomly substituted mixtures, a sulfated β-cyclodextrin with DS of 7 to 11, as well as a highly sulfated-β-cyclodextrin with DS of 12 to 15, were used for the enantioresolution of 12 drugs (the β-blockers, phenethylamines, and anticholinergic agents) in capillary electrophoresis. The enantioseparation under varying concentrations of S-β-CD and background electrolyte pH were systematically investigated and compared. Based on the experimental results, the effect of the nature of S-β-CD and analyte structure on the enantioseparation is discussed., (© 2017 Wiley Periodicals, Inc.)

In this work, the synthesis, characterization, and chiral capillary electrophoretic study of heptakis-(2,3-di-O-methyl-6-O-carboxymethyl)-β-CD (HDMCM), a single-isomer carboxymethylated CD, are presented. The pH-dependent and selector concentration-dependent enantiorecognition properties of HDMCM were investigated and discussed herein. The enantioseparation was assessed applying a structurally diverse set of noncharged, basic, and zwitterionic racemates. The increase in the selector concentration and gross negative charge of HDMCM improved the enantioseparation that could be observed in the majority of the cases. HDMCM was also successfully applied as BGE additive in NACE using a methanol-based system in order to prove the separation selectivity features and to highlight the broad applicability of HDMCM. Over 25 racemates showed partial or baseline separation with HDMCM under the conditions investigated, among which optimal enantiomer migration order was found for the four stereoisomers of tadalafil, tapentadol, and dapoxetine, offering the possibility of a chiral CE method development for chiral purity profiling of these drugs., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Capillary electrophoresis (CE) is an extremely effective technique in many kinds of separations, including separation of enantiomers. Some additional techniques may be necessary to determine the enantiomer migration order (EMO) and also the mechanism involved in chiral recognition. This paper reports the development and optimization of a CE method for enantioseparation of racemic mixture of both R- and S-stereoisomers of tramadol (TRM) with a computational contribution for the EMO determination and the responsible mechanisms for chiral distinction. Parameters such as composition and concentration of background electrolyte (BGE) and type and concentration of cyclodextrins (CD) were evaluated. For calculations, a sequential methodology was used, resorting to semiempirical Parametric Model 3 (PM3) followed by calculations accomplished using density functional theory. The best results were obtained with sulfated-β-CD (s-β-CD) and carboxymethyl-β-cyclodextrin (cm-β-CD) as chiral selector. Calculations show that the inclusion of TRM is not a probable process due to the shape of the TRM molecule and the size CDs cavities. Therefore, the chiral recognition process occurs by the formation of association complexes between modified β-CD and groups of TRM molecules. The structural analysis of the fragments of complexes at a pH of 10 and a thermodynamic analysis of the complexes' formation process allows determining the EMO. Comparing results obtained experimentally and computationally, it seems that the developed method is adequate for separation of TRM enantiomers and the computational methodology is also adequate to get a sense of the system at a molecular level., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The racemic N-methyl-d-aspartate receptor antagonist ketamine is used in anesthesia, analgesia and the treatment of depressive disorders. It is known that interactions of hydroxylated norketamine metabolites and 5,6-dehydronorketamine (DHNK) with the α 7 -nicotinic acetylcholine receptor and the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor are responsible for the antidepressive effects. Ketamine and its first metabolite norketamine are not active on these receptors. As stereoselectivity plays a role in ketamine metabolism, a cationic capillary electrophoresis based method capable of resolving and analyzing the stereoisomers of four hydroxylated norketamine metabolites, norketamine and DHNK was developed. The assay is based on liquid/liquid extraction of the analytes from the biological matrix, electrokinetic sample injection across a buffer plug and analysis of the stereoisomers in a phosphate background electrolyte (BGE) at pH 3 comprising a mixture of sulfated β-cyclodextrin (5 mg/mL) and highly sulfated γ-cyclodextrin (0.1%). The method was used to analyze samples of an in vitro study in which ketamine was incubated with equine liver microsomes and in plasma samples of dogs and horses that were collected after an i.v. bolus injection of racemic ketamine., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Capillary electrophoresis frontal analysis (CE-FA) can be used to determine binding affinity of molecular interactions. However, its current data processing method mandate specific requirement on the mobilities of the binding pair in order to obtain accurate binding constants. This work shows that significant errors are resulted when the mobilities of the interacting species do not meet these requirements. Therefore, the applicability of CE-FA in many real word applications becomes questionable. An electrophoretic mobility-based correction method is developed in this work based on the flux of each species. A simulation program and a pair of model compounds are used to verify the new equations and evaluate the effectiveness of this method. Ibuprofen and hydroxypropyl-β-cyclodextrinare used to demonstrate the differences in the obtained binding constant by CE-FA when different calculation methods are used, and the results are compared with those obtained by affinity capillary electrophoresis (ACE). The results suggest that CE-FA, with the mobility-based correction method, can be a generally applicable method for a much wider range of applications., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Tetracyclines are a group of broad spectrum antibiotics widely used in animal husbandry to prevent and treat diseases. However, the improper use of tetracyclines may result in the presence of their residues in animal tissues or waste. Recently, great attention has been drawn towards the green solvents ionic liquids. Ionic liquids have been employed as a coating material to modify the electroosmotic flow in capillary electrophoresis. In this study, a functionalized ionic liquid, mono-6-deoxy-6-(3-methylimidazolium)-β-cyclodextrin tosylate, was synthesized and used for the simultaneous separation and quantification of tetracyclines by capillary electrophoresis. Good separation efficiency could be achieved due to the multiple functions of β-cyclodextrin derived ionic liquid, including the electrostatic interaction, the hydrogen bonding, and the cavity structure in β-cyclodextrin ionic liquid which can entrap the tetracyclines to form inclusion complex. After optimization, baseline separation achieved in 25 min with the running buffer consisted of 10 mmol/L, pH 7.2 phosphate buffer and 20 mmol/L β-cyclodextrin ionic liquid. The satisfied result demonstrated that the β-cyclodextrin ionic liquid is an ideal background electrolyte modifier in the separation of tetracyclines with high stability and good reproducibility. And it is an effective strategy to design and synthesize specific ILs as additive applied in separation., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

To optimize chiral separation conditions and to improve the knowledge of enantioseparation, it is important to know the binding constants K between analytes and cyclodextrins and the electrophoretic mobilities of the temporarily formed analyte-cyclodextrin-complexes. K values for complexes between eight phenethylamine enantiomers, namely ephedrine, pseudoephedrine, methylephedrine and norephedrine, and four different β-cyclodextrin derivatives were determined by affinity capillary electrophoresis. The binding constants were calculated from the electrophoretic mobility values of the phenethylamine enantiomers at increasing concentrations of cyclodextrins in running buffer. Three different linear plotting methods (x-reciprocal, y-reciprocal, double reciprocal) and nonlinear regression were used for the determination of binding constants with β-cyclodextrin, (2-hydroxypropyl)-β-cyclodextrin, methyl-β-cyclodextrin and 6-O-α-maltosyl-β-cyclodextrin. The cyclodextrin concentration in a 50 mM phosphate buffer pH 3.0 was varied from 0 to 12 mM. To investigate the influence of the binding constant values on the enantioseparation the observed electrophoretic selectivities were compared with the obtained K values and the calculated enantiomer-cyclodextrin-complex mobilities. The different electrophoretic mobilities of the temporarily formed complexes were crucial factors for the migration order and enantioseparation of ephedrine derivatives. To verify the apparent binding constants determined by capillary electrophoresis, a titration process using ephedrine enantiomers and β-cyclodextrin was carried out. Furthermore, the isothermal titration calorimetry measurements gave information about the thermal properties of the complexes., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This work reported that ionic liquid (IL) ([Bmim] [PF 6 ]) and sulfobutylether-β-CD (SBE-β-CD) were used as electrolyte additives for the separation and determination of camptothecin (CPT) alkaloids by CZE. Separation parameters such as the buffer type, pH, and concentration of the running buffer, the concentration of SBE-β-CD and IL, temperature, and separation voltage were all investigated in order to achieve the maximum possible resolution. The four analytes were baseline separated within 10 min in capillary at the separation voltage of 15 kV with a running buffer consisting of 20 mM borate buffer, 20 mM IL, and 100 mM SBE-β-CD at pH 9.0. Under such conditions, good linearity about two orders of magnitudes of peak areas was achieved for the investigated CPT alkaloids with the correlation coefficients ranging from 0.9946 to 0.9985. For all analytes, detection limits (S/N = 3) and quantitation limits (S/N = 10) range from 0.05 to 0.92 μg/mL and 0.17 to 3.06 μg/mL, respectively. The proposed method has not only been successfully applied to the separation and determination of CPT alkaloids but also showed that IL seemed to be a promising additive in CZE separation., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The study on sulfated beta-cyclodextrin binding to uranyl ion helps to get a better understanding of uranyl compounds' intermolecular interaction mechanism and facilitates the structure-based design of uranyl binding molecules. Here we investigated the electromigration of the inclusion complex by using affinity capillary electrophoresis in acidic solution. The binding constant was determined to be logK = 2.96 ± 0.02 (R 2 = 0.996) through nonlinear regression approach. The possible configurations and structural features of the inclusion complex were further studied by molecular dynamics simulation. The results suggest the distinctions of coordination environment and hydration compared with bare uranyl ion in aqueous solution. Thus, two water oxygen atoms coordinated with uranyl in the first hydration shell at 2.55 angstrom instead of five in the same distance range. The binding free energy was calculated as -12.10 ± 1.46 kcal/mol by means of thermodynamic perturbation method. The negative value indicates that the process of S-β-CD capture uranyl ion in the aqueous media is spontaneous., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This work focuses on the characterization of the rosmarinic acid (RA)-β-cyclodextrin (CD) complex in aqueous solution by (1)H NMR (1D- and 2D-ROESY), completed with studies by capillary electrophoresis (CE). From the (1)H NMR data, the stoichiometry of the complex was determined by a Job's plot and the binding constant was estimated from a linear regression (Scott's method). At pH 2.9, the results showed that RA binds CD with a 1:1 stoichiometry and a binding constant Kb of 445 (±53) M(-1) or 465 (±81) M(-1) depending on the CD protons (H-5 or H-3) selected for the evaluation. The Kb value was also calculated from the CD-induced chemical shifts of each RA proton in order to collect information on the structure of the complex. The pH dependence of Kb revealed that the RA carboxylic form displays the highest affinity for CD. An investigation by capillary electrophoresis fully confirmed these results. 2D ROESY analysis provided detailed structural information on the complex and showed a strong correlation between H-3 and H-5 of CD and most RA protons. In conclusion, RA, an efficient phenolic antioxidant from rosemary with a marketing authorization, spontaneously forms a relatively stable inclusion complex with CD in water., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A novel dispersive micro-SPE method with trace poly-β-CD wrapped multiwalled carbon nanotubes as sorbents was applied to extract flavonoids in honey samples. The analytes were then determined by CE with LED-induced fluorescence detection. The influencing parameters, such as the sorbent concentration, extraction time, and eluent type, were properly optimized. The established method had the advantages of simplicity, low consumption of sorbent amount (0.009 mg) and organic solvent (100 μL), and high sensitivity, meeting the principle of green chemistry. Under the optimum conditions, the sorbents allowed the extraction and preconcentration of the flavonoids with enrichment factors in the range from 78 to 166. The recovery study performed at two different fortification levels provided an average recovery >91%. LODs for all the compounds ranged from 0.07 to 17.99 ng/mL. These results demonstrated that the proposed method could be used as a convenient and efficient extraction technique for analysis of flavonoids in different honey matrices., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Capillary electrophoresis methods were developed for the enantiomeric separation of 27 citalopram analogues. Sulfated β-cyclodextrin was the most broadly selective and useful chiral selector. The separations of most of the citalopram analogue compounds reported in this work have not been reported previously. Excellent enantiomeric separations were obtained for 26 out of 27 compounds, and most of the separations were achieved within 10 min. The effects of chemical parameters such as chiral selector types, buffer types, chiral selector and buffer concentrations, buffer pH and organic modifiers on the separation were investigated. The influence of analyte structure on separation also was examined and discussed., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The enantiomers of asenapine maleate (ASN), a novel antipsychotic against schizophrenia and mania with bipolar I disorder have been separated by cyclodextrin (CD) modified capillary zone electrophoresis for the first time. 15 different CDs were screened as complexing agents and chiral selectors, investigating the stability of the inclusion complexes and their enantiodiscriminating capacities. Although initially, none of the applied chiral selectors gave baseline separation, β-CD proved to be the most effective chiral selector. In order to improve resolution, an orthogonal experimental design was employed, altering the concentration of background electrolyte, organic modifier, pH, capillary temperature and applied voltage in a multivariate manner. The developed method (160 mM TRIS-acetate buffer pH 3.5, 7 mM β-CD, at 20 °C, applying 15 kV) was successful for baseline separation of ASN enantiomers (R(s)=2.40±0.04). Our method was validated according to ICH guidelines and proved to be sensitive, linear, accurate and precise for the chiral separation of ASN. Properties of the inclusion complexes, such as stoichiometry, atomic level intermolecular host-guest connections are proposed on the basis of ROESY NMR measurement, ESI-MS spectrometry and molecular modeling studies. It was found that the ASN-β-CD complex is of 1:1 composition, and either of the aromatic rings can be accommodated in the β-CD cavity., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Affinity capillary electrophoresis (ACE) has been applied to estimation of apparent binding constant of complexes of (R,S)-enantiomers of selected acyclic nucleoside phosphonates (ANPs) with chiral selector β-cyclodextrin (βCD) in aqueous alkaline medium. The noncovalent interactions of five pairs of (R,S)-enantiomers of ANPs-based antiviral drugs and their derivatives with βCD were investigated in the background electrolyte (BGE) composed of 35 or 50 mM sodium tetraborate, pH 10.0, and containing variable concentration (0-25 mM) of βCD. The apparent binding constants of the complexes of (R,S)-enantiomers of ANPs with βCD were estimated from the dependence of effective electrophoretic mobilities of (R,S)-enantiomers of ANPs (measured simultaneously by ACE at constant reference temperature 25°C inside the capillary) on the concentration of βCD in the BGE using different nonlinear and linear calculation methodologies. Nonlinear regression analysis provided more precise and accurate values of the binding constants and a higher correlation coefficient as compared to the regression analysis of the three linearized plots of the effective mobility dependence on βCD concentration in the BGE. The complexes of (R,S)-enantiomers of ANPs with βCD have been found to be relatively weak - their apparent binding constants determined by the nonlinear regression analysis were in the range 13.3-46.4 L/mol whereas the values from the linearized plots spanned the interval 12.3-55.2 L/mol., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this study, a new CE method, employing a binary system of trimethyl-β-CD (TM-β-CD) and a chiral amino acid ester-based ionic liquid (AAIL), was developed for the chiral separation of seven 2-arylpropionic acid nonsteroidal anti-inflammatory drugs (NSAIDs). In particular, the enantioseparation of ibuprofen, ketoprofen, carprofen, indoprofen, flurbiprofen, naproxen, and fenoprofen was improved significantly by supporting the BGE with the chiral AAIL l-alanine tert butyl ester lactate (l-AlaC4 Lac). Parameters, such as concentrations of TM-β-CD and l-AlaC4 Lac, and buffer pH, were systematically examined in order to optimize the chiral separation of each NSAID. It was observed that the addition of the AAIL into the BGE improved both resolution and efficiency significantly. After optimization of separation conditions, baseline separation (Rs >1.5) of five of the analytes was achieved in less than 11 min, while the resolution of ibuprofen and flurbiprofen was approximately 1.2. The optimized enantioseparation conditions for all analytes involve a BGE of 5 mM sodium acetate/acetic acid (pH 5.0), an applied voltage of 30 kV, and a temperature of 20°C. In addition, the results obtained by computing the %-RSD values of the EOF and the two enantiomer peaks, demonstrated excellent run-to-run, batch-to-batch, and day-to-day reproducibilities., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Curcuminoids have received great attention in the past decades due to their health benefit properties. The aim of this study is to develop a very simple, rapid, and sensitive capillary zone electrophoresis technique coupled with a laser induced fluorescence detector (LIF) for the simultaneous determination of three major curcuminoids of turmeric, namely, curcumin, demethoxy curcumin (DMC), and bisdemethoxy curcumin (BDMC). Background electrolyte was selected as borate at pH 9.6 and (2-hydroxypropyl)-β-cyclodextrin (2-HP-β-CD) was added to prevent rapid alkali degradation of curcuminoids in buffer and to increase fluorescence intensities of molecules. With the addition of 2-HP-β-CD to the separation electrolyte, the fluorescence signal intensities of curcuminoids were enhanced considerably by 30, 40, and 54 fold for curcumin, DMC, and BDMC, respectively. The three curcuminoids of turmeric were fully separated and quantified in less than 4.5 min. The repeatability of the peak areas of curcuminoids for intra-day and inter-day experiments was in the satisfactory range of 2.26 and 2.55%, respectively. The LOD and LOQ values for the developed method were equal to or less than 0.081 and 0.270 μg/mL, respectively, for all curcuminoids. The developed method was successfully applied to find curcuminoids amount in turmeric samples and herbal supplements., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A method for the separation of folinic acid diastereomers by capillary electrophoresis in chiral separation media was developed. Aiming to achieve a good separation of the anionic analytes, a newly synthesized cationic β-cyclodextrin derivative, mono-6-deoxy-6-piperdine-β-cyclodextrin, was applied as the chiral selector. The effect of background electrolyte pH, the concentration of the cyclodextrin additive, and organic modifier on the separation was investigated. A good separation of folinic acid diastereomers was obtained with 30 mmol/L phosphate buffer at pH 6.50 containing 6.0 mmol/L of mono-6-deoxy-6-piperdine-β-cyclodextrin in 10% acetonitrile. Based on the capillary electrophoresis data, the binding constants of each diastereomer with mono-6-deoxy-6-piperdine-β-cyclodextrin were determined. Moreover, a computational modeling study, using the semi-empirical PM3 method, was used to discuss the possible mechanism of separation of folinic acid with mono-6-deoxy-6-piperdine-β-cyclodextrin.

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.

A practical chiral CE method, using sulfated-β-CD as chiral selector, was developed for the enantioseparation of glycopyrrolate containing two chiral centers. Several parameters affecting the separation were studied, including the nature and concentration of the chiral selectors, BGE pH, buffer type and concentration, separation voltage, and temperature. The separation was carried out in an uncoated fused-silica capillary of (effective length 40 cm) × 50 μm id with a separation voltage of 20 kV using 30 mM sodium phosphate buffer (pH 7.0, adjusted with 1 M sodium hydroxide) containing 2.0% w/v sulfated-β-CD at 25°C. Finally, the method for determining the enantiomeric impurities of RS-glycopyrrolate was proposed. The method was further validated with respect to its specificity, linearity range, accuracy and precision, LODs, and quantification in the expected range of occurrence for the isomeric impurities (0.1%)., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this study, a rapid chiral separation of 12 cathinones analogs has been developed and validated using cyclodextrin-assisted CE with UV and TOF-MS detection. Optimum separation was obtained on a 57.5 cm × 50 μm capillary using a buffer system consisting of 10 mM β-cyclodextrin (β-CD) in a 100 mM phosphate buffer for CE-UV, and 0.6% v/v highly sulfated-γ-cyclodextrin (HS-γ-CD) in a 50 mM phosphate buffer for CE-MS. In the CE-MS experiment, a partial filling technique was employed to ensure that a minimum amount of cyclodextrin entered the mass spectrometer. All analytes were separated within 18 min in the CE-UV separation and identified by TOF-MS. Ten compounds were enantiomerically separated using β-CD in the UV mode and an additional two more were enantiomerically separated using HS-γ-CD in the MS mode. Detection limits down to 1.0 ng/mL were obtained. The method was then applied to examine seized drugs., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Successful simultaneous diastereomeric separation and sensitive determination of two pairs of triterpenoidal saponins have been achieved by capillary electrophoresis (CE) using β-cyclodextrin (β-CD) as a stereoselective agent to cooperate with borate complexation. A usual technique for isolation and group separation of saponins was developed as an appropriate purification step prior to the determination of individual saponins by CE. Soyasaponin I ( S1: ), azukisaponin V ( S2: ), bersimoside I ( S3: ) and bersimoside II ( S4: ) could be well separated within 14 min in a fused-silica capillary (60 cm long to the detector with an additional 10 cm to the cathode; 75 µm i.d.). The background electrolyte was borate buffer (80 mM, pH 10), containing 24 mM β-CD. The separation voltage was 14 kV with a detection wavelength of 195 nm. The sample was electrokinetically injected using a voltage of 16 kV for 12 s. Methanol (70%) was used as the diluent for field-amplified sample stacking after hydrodynamic injection of short water plug (5 cm, 4 s). The method was partially validated for linearity, repeatability, reproducibility, limits of detection and limits of quantification. The correlation coefficients of the calibration curves were all >0.998, and the recoveries were from 98.23 to 96.21%., (© The Author [2013]. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

In this paper we determine acid dissociation constants, limiting ionic mobilities, complexation constants with β-cyclodextrin or heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin, and mobilities of resulting complexes of profens, using capillary zone electrophoresis and affinity capillary electrophoresis. Complexation parameters are determined for both neutral and fully charged forms of profens and further corrected for actual ionic strength and variable viscosity in order to obtain thermodynamic values of complexation constants. The accuracy of obtained complexation parameters is verified by multidimensional nonlinear regression of affinity capillary electrophoretic data, which provides the acid dissociation and complexation parameters within one set of measurements, and by NMR technique. A good agreement among all discussed methods was obtained. Determined complexation parameters were used as input parameters for simulations of electrophoretic separation of profens by Simul 5 Complex. An excellent agreement of experimental and simulated results was achieved in terms of positions, shapes, and amplitudes of analyte peaks, confirming the applicability of Simul 5 Complex to complex systems, and accuracy of obtained physical-chemical constants. Simultaneously, we were able to demonstrate the influence of electromigration dispersion on the separation efficiency, which is not possible using the common theoretical approaches, and predict the electromigration order reversals of profen peaks. We have shown that determined acid dissociation and complexation parameters in combination with tool Simul 5 Complex software can be used for optimization of separation conditions in capillary electrophoresis., (Copyright © 2014 Elsevier B.V. All rights reserved.)