Single isomer cyclodextrins as chiral selectors in capillary electrophoresis

Since decades, cyclodextrins are one of the most powerful selectors in chiral capillary electrophoresis for the enantioseparation of diverse organic compounds. This review concerns papers published over the last decade (from 2009 until nowadays), dealing with the capillary electrophoretic application of single isomer cyclodextrin derivatives in chiral separations.

Journal of Chromatography A 1627 (2020) 461375 Contents lists available at ScienceDirect Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma Single isomer cyclodextrins as chiral selectors in capillary electrophoresis ˝ a, Eszter Kalydi a,b, Milo Malanga b, Gábor Benkovics b, Szabolcs Béni a,∗ Ida Fejos a b ˝ út 26, Hungary Department of Pharmacognosy, Semmelweis University, Budapest, H-1085 Ülloi CycloLab, Cyclodextrin R&D Ltd, Budapest, H-1097 Illatos út 7, Hungary a r t i c l e i n f o Article history: Received 11 May 2020 Revised 24 June 2020 Accepted 28 June 2020 Available online July 2020 Keywords: Capillary electrophoresis Synthesis of single isomer cyclodextrin derivatives Chiral separation Enantiomer migration order Enantiorecognition Supramolecular interactions a b s t r a c t Since decades, cyclodextrins are one of the most powerful selectors in chiral capillary electrophoresis for the enantioseparation of diverse organic compounds This review concerns papers published over the last decade (from 2009 until nowadays), dealing with the capillary electrophoretic application of single isomer cyclodextrin derivatives in chiral separations Following a brief overview of their synthetic approaches, the inventory of the neutral, negatively and positively charged (including both permanently ionic and pH-tunable ionizable substituents) and zwitterionic CD derivatives is presented, with insights to underlying structural aspects by NMR spectroscopy and molecular modeling CE represents an ideal tool to study the weak, non-covalent supramolecular interactions The published methods are reviewed in the light of enantioselectivity, enantiomer migration order and the fine-tuning of enantiodiscrimination by the substitution pattern of the single entity selector molecules, which is hardly possible for their randomly substituted counterparts All the reviewed publications herein support that cyclodextrin-based chiral capillary electrophoresis seems to remain a popular choice in pharmaceutical and biomedical analysis © 2020 The Author(s) Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Introduction The understanding of chiral recognition is not only essential in biology and supramolecular chemistry, but also instructive in stereoselective synthesis and chiral separation The analytical scale separation of chiral analytes is one of the most popular applications in capillary electrophoresis (CE), commonly achieved by adding chiral selectors, most frequently cyclodextrins (CDs) to the background electrolyte (BGE) These popular selectors are composed of (1,4)-linked α -d-glucopyranose units forming a truncated cone shape and contain a hydrophilic outer surface surrounding a rather lipophilic cavity [1] The latter enables inclusion complex formation with a wide variety of small molecules ranging from endogenous bioactive compounds, through agrochemicals, fragrances to oligopeptides, pharmaceuticals to food components The chiral recognition by CDs is mostly based on the different interaction affinities between the selector and the enantiomers of the analyte where diastereomeric host-guest type complexes with subtle structural differences are formed Complexation of the guest molecules ∗ Corresponding author E-mail address: beni.szabolcs@pharma.semmelweis-univ.hu (S Béni) often occurs via their inclusion into the CD cavity either from the narrower or the wider side of the truncated cone, displacing solvent molecules from the cavity, however outer sphere interactions may also contribute to the differential recognition of the enantiomers Van der Waals, hydrophobic and electrostatic interactions as well as hydrogen bonding are considered as driving forces of complex formation besides the steric factors Contrary to chiral separations by liquid or gas chromatography, a successful enantioseparation in CE can still be accomplished in the case of equal binding constants due to different mobilities of the diastereomeric complexes [2] CE represents one of the most powerful analytical techniques not only for the physical separation of enantiomers but also for a better understanding of the molecular basis of (enantioselective) intermolecular interactions [3] A conceptual benefit of CE for the investigation of peculiar stereochemical mechanisms of non-covalent interactions is the cumulative character of this technique CE offers significant advantages compared to other separation methods such as the high efficiency (the high plate numbers) allowing even the observation of weak enantioselective intermolecular interactions, that are invisible to other techniques, the fast separation time, the miniaturization and the amenabil- https://doi.org/10.1016/j.chroma.2020.461375 0021-9673/© 2020 The Author(s) Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, ity to mathematical modeling and “dry-chemistry” optimization [4,5] Capillary electrophoresis also offers an easy, fast and costeffective way to study the enantioselectivity of new chiral selector candidates, as the selector has to be simply added to the background electrolyte A wide range of chiral test compounds could be screened in a short time and due to the high flexibility of chiral capillary electrophoresis (CCE) and the possibility of automation, several parameters influencing the enantioseparation (such as the selector concentration in the BGE or the pH of the running buffer, co-solvents, application of external pressure/vacuum) could be studied Furthermore, no need of selector immobilization and the low consumption of selectors, selectands and running buffers enables the use of rather expensive chiral selectors as well as dual or multiple selector systems Moreover, this technique also carries the possibility of enantiomer migration order (EMO) reversal without affecting the affinity pattern between the selector and the analyte [6] On the other hand, CE suffers from the disadvantage of being incapable to provide any direct structural information about the intermolecular diastereomeric associates involved in chiral recognition/separation The combination of CE and NMR spectroscopy is a powerful tandem for a better understanding of chiral recognition mechanisms, while extending these investigations by state-of-the-art molecular modeling studies, a deeper insight into the pertinent noncovalent host-guest interactions could be achieved [7] The orthogonal techniques of spectroscopy and equilibrium chemistry may help to explain and predict beneficial CCE characteristics, such as opposite migration order of the enantiomers when different CDs are used, or they may assist in development of the optimal conditions for a CCE enantioseparation Single isomer CD derivatives (SIDs) Although cyclodextrins have been known since the end of 19th century [8], their first application in electromigration methods awaited nearly 100 years CDs were originally applied for the separation of achiral compounds [8] Later, specifically in 1988, the first papers on the chiral separation utilizing CDs in CE format were published [9–12] Since that time, a plethora of CD derivatives has been synthesized and employed as chiral selectors Native CDs were historically among the first selectors to be evaluated Their applications may be limited by inadequate aqueous solubility, especially for the most commonly used β -CD, since the optimal CD concentration necessary for the enantiomer separation could not be reached The lack of charged functionalities are also restricting regarding intermolecular interactions, therefore, tailor made synthetic modifications of the native CDs have been extensively performed to provide a large variety of selectors decorated with various substituents, improving water solubility and sometimes also the enantiorecognition towards a specific class of chiral analytes [13,14] The complexity of delicate factors influencing enantiomerselector interactions makes the ab initio prediction or design of a successful enantioseparation particularly difficult There is currently a consensus that no generally applicable model has resulted from the large body of structural studies to predict enantiomeric discrimination, i.e how to design cyclodextrin substitution in order to improve the resolution of enantiomers In order to satisfy the urgent need of structurally diverse selectors in the pharmaceutical, cosmetic and food industries, a wide range of various CD derivatives (such as methylated, sulfated, carboxymethylated, sulfobutylated ones) became commercially available as randomly substituted derivatives [15] Despite the ease of their preparation and their extensive application in CCE, a randomly substituted CD product is in fact a complex mixture of cyclodextrin isomer species, variable both in degrees and position(s) of substitution The manufacturer usually declares only their degree of substitution (DS): the average number of derivatized OH groups While the DS became nowadays synthetically reproducible, the same substitution pattern could not be guaranteed for every lot, resulting potentially in poor reproducibility of CE separation and the failure in method validation by practitioners With a dual aim of gaining a better control on the structural diversity of CD derivatives and a more systematic way to investigate molecular recognition processes, potentially leading to more predictable separations, single isomer CD derivatives have been synthesized for ca 20 years now and characterized both structurally and from the viewpoint of CE separation efficiency [13] Based on several earlier studies of Vigh and co-workers [16–18], the importance of using chemically uniform, better-defined pure isomers as chiral resolving agents from both fundamental and practical points of view was reviewed in 2009 [13] To understand the influence of the substituent moiety, the site and extent of substitution on enantiodiscrimination, CD derivatives with systematically varied substitution patterns are still highly demanded With the help of SIDs both NMR spectroscopic characterization and molecular modeling at the atomic level are feasible contrary to the randomly substituted selectors, where neither theoretical predictions nor accurate explanations of the experimental results are possible The use of single isomer selectors in the studies reviewed herein has been emphasized for two reasons One is to eliminate the drawback of dozens of isomers in commercially available randomly substituted CDs, resulting in selector mixtures illdefined both structurally and in enantiodifferentiation; the other is to provide a solid and comprehensive theoretical framework on the enantiomer migration in electrophoresis and identify the variables in order to predict successful separations [19–21] Typical SIDs are the mono-substituted CDs (having only one substituent per CD molecule in a defined position) and the persubstituted CDs (having all hydroxyl groups substituted in the same positions) Besides the open-chain derivatives, less common SIDs are the capped CD derivatives, bonding a chain to two different points of the rim, forming a bridge (hemispherodextrins, HSDs) 2.1 Synthetic challenges and strategies to obtain single isomer CDs SIDs are generally prepared via multistep synthesis and, when commercially available, are rather expensive products In the following sections we provide a brief overview of the synthetic strategies for the preparation of SIDs 2.1.1 General chemistry of CDs CDs have 18, 21 and 24 free hydroxyl- (OH) groups in case of the α -, β - and γ -CD respectively, one primary and two secondary hydroxyls on each glucopyranose units, where the chemical modifications can take place [22] (see Fig 1) The primary hydroxyl groups (OH-6) are the most basic, most nucleophilic and less hindered By careful selecting a weak base, the primary rim of the CD can be promptly modified with a large variety of electrophiles, even the bulky ones The hydrogen bond between the OH-2 and OH-3 of the adjacent glucopyranose units Fig Cartoon representation of cyclodextrins along with the sites of modification ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, and the neighboring electron-withdrawing anomeric acetal function are responsible for the highest acidity of OH-2 These hydroxyl moieties can be selectively deprotonated, for example, in anhydrous basic conditions The hydroxyl groups at the 3-positions (OH-3) are the less reactive and most hindered Usually, modification of the 3-positions requires extensive use of protective groups, nevertheless, the use of reagents able to strongly interact with the CD cavity can result in direct regioselective substitution of these positions 2.1.2 Persubstitution In persubstituted CDs, all the glucopyranose units are equally modified, either on selected positions or on all the OH groups Per-2,3,6-tri-O-substituted CDs can be prepared in a straightforward manner by utilizing native CDs as starting material In particular, a large variety of per-2,3,6-tri-O-alkyl and -O-aryl substitution has been achieved in anhydrous conditions with polar, aprotic solvents (dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF), mostly) and strong base (mainly hydride) Most recently, efficient and exhaustive alkylation procedures, based on phase transfer catalysis (PTC) have been reported by our group [23] The application of PTC conditions allows the industrial scale-up of a plethora of per-alkylated CDs by utilizing as starting material commercially available partially alkylated CDs Per-2,3,6-tri-O-acylation is also easily achieved from native CDs In this case, organic acid anhydride (for example, acetic anhydride) or mixture of anhydride and the corresponding carboxylic acid (for example, acetic anhydride and acetic acid) are utilized as solvents and the addition of a catalyst (Lewis acid, mostly) allows the exhaustive substitution in reasonable time [24] The use of acyl halide to produce per-2,3,6-tri-O-acylated CDs in inert solvent is also a widely explored strategy Persubstitutions on selected positions are carried out by exploiting the different reactivity of the OH groups The primary hydroxyls, for example, are better nucleophiles than the secondary ones, so they can be selectively modified using a weak base The most important representative of the per-6-substituted family are the per-6-halogenated and the per-6-silylated CDs Per-6halogenated CDs can be prepared by reacting a halogen source, triphenylphosphine (TPP) and DMF (or N-methyl-2-pyrrolidone) in Vilsmeier-Haack-type reaction [25] If a strong halogenating reagent is applied (thionyl chloride/bromide, phosphorous pentachloride/tribromide), then TPP can be omitted According to this classical procedure per-6-chloro-, -bromo- and -iodo-CDs have been prepared in industrial scale The per-6-halo-CDs are fundamental key-intermediates as they can be readily displaced by most nucleophiles, such as azides, amines or thiols The tert-butyldimethylsilyl chloride (TBDMSCl) in DMF with imidazole as a base, or in pyridine, gives access to per-6-O-silylated CDs, the most common primary-side protected CDs [26] These compounds can easily be prepared in kg scale according to the aforementioned synthetic approaches Per-2,3-substitution is generally carried out by using per6-silylated CDs as starting material The exhaustive per-2,3-Oalkylation for example have been achieved by utilizing harsh conditions (hydrides, aprotic solvent, alkylating agent and heating) or, more recently, by applying soft and up-scalable PTC conditions (catalyst, aprotic solvent, alkylating agent, room temperature) Per2-O-alkylation of per-6-O-silylated CDs has been also reported by using aprotic solvent and by carefully selecting a strong base, however, in this case, chromatographic purification is mandatory for the isolation of the corresponding compounds Per-2,6-O-difunctionalization of CDs is also possible Native CDs can be selectively alkylated if barium salts are applied to the mixture By using mixtures of Ba(OH)2 /BaO in polar, aprotic solvents (usually DMSO/DMF in different ratios), several per- 2,6-O-alkylated CDs have been prepared Among these derivatives, per-2,6-O-dimethyl-β -CD (DIMEB) has been prepared in industrial scale Particularly important for this class of compounds are the per-2,6-O-silyl-CDs as they are versatile synthons towards per-3-Osubstitued and per-2-O-substitued CDs Per-2,6-O-silyl-CDs can be effectively prepared in pyridine, with an excess of silylating agent at reflux with a catalytic amount of 4-dimethylaminopyridine (DMAP) Direct per-3,6-O-disubstitution and/or per-3-O-substitution of CDs have not achieved effectively, yet The preparation of these compounds is usually been achieved by applying multistep synthesis based on different protecting groups 2.1.3 Monosubstitution In monosubstituted derivatives, only one glucopyranose unit is modified in a selected position Due to the similar reactivity of the hydroxyl groups, even when a limiting amount of reagent is used, oversubstitution and/or isomer formation is inevitable Mono-6substituted CDs are easily prepared by applying a weak base to the media The most important CDs in this class are the mono-6-tosyl-CDs [27] The β -analogue is classically prepared by reacting β -CD with tosyl-chloride in pyridine and isolated in kg scale without the necessity of chromatography A lot of variations/improvements of this fundamental reaction have been introduced by time to time The α - and the γ -analogues can be prepared in a similar fashion, but chromatography is necessary to achieve a suitable purity Nucleophilic substitution of the tosyl moiety generates the widest variety of CDs Mono-6-halo, azido-, thio-, hydroxylamino, alkylamino CDs have been prepared in this way Treatment of mono-6-tosyl-CDs with aqueous alkaline conditions leads to the formation of peculiar epoxide, the 3,6-anhydro-CD Selective secondary side modification is more challenging due to the higher number of OH groups present, which are forming a H-bond belt making the molecule more rigid and the OH-groups less reactive However, benefiting from the pronounced acidic character of the 2-OH function, by using a controlled amount of a strong base (usually sodium hydride), selective tosylation at the 2-position has been reported In this manner, mono-2-O-alkyl-CDs have been prepared Recently, mono-2-O-propargyl-β -CDs have been prepared in high yield by using lithium hydride in DMSO and propargyl bromide with a catalytic amount of lithium iodide [28] In the CD field, lithium-based hydrides seem more selective compared to the sodium counterparts A more convenient method to obtain selectively 2-OH or 3-OH substituted derivatives is by the exploitation of the inclusion complex forming ability of the CDs When a reagent is used, which forms a stable complex with the CD, then the orientation of the guest will dictate the site of the substitution In this manner, the use of m-nitrophenyl tosylate affords 2-O-tosyl-β -CD in good purity, while the application of 3-nitrobenzenesulfonyl chlorides allows the preparation of 3-O-tosyl-β -CD in good yield The regiospecific 3-O-cinnamylation of CD derivatives has also been reported recently A recent and versatile approach to obtain selectively substituted CDs have been widely applied and it is based on the selective deprotection of persubstituted CDs using diisobutylaluminium hydride (DIBAL) When a permethylated α - or β -CD is treated with DIBAL, the reaction affords permethylated 2A ,3B -dihydroxy α or β -CD and permethylated 6A -hydroxy α - or β -CD in 55% and 20% yields, respectively When a perbenzylated α -, β -, or γ -CD is treated with DIBAL, the reaction leads to perbenzyl-mono-6-OHα /β /γ -CD The deprotected 6-OH position can be further modified and after the removal of the benzyl protection, mono-6-Osubstituted CDs can be prepared in good overall yield ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, Similarly, selective desilylation by DIBAL has also been reported on various per-6-O-tert-butyldimethylsilylated compounds, to afford the corresponding mono-6A -OH or di-6A ,6D -OH derivatives 2.1.4 Disubstitution The selective DIBAL deprotection can be used as starting point for the preparation of new disubstituted CDs This approach is time-consuming and based on extensive chromatography for the purification of the products, however, the achieved regioselectivity is highly remarkable An alternative strategy to get single isomer disubstituted CDs is based on the use of suitable disulfonyl capping agent followed by the subsequent substitution by the desired nucleophile This method can be applied to synthetize 6A , 6B -, 6A , 6C - and 6A , 6D -disubstituted CDs by using 4,6-dimethoxybenzene1,3-disulfonyl chloride, benzophenone-3,3 -disulfonyl chloride or trans-stilbene-4,4 -disulfonyl chloride, respectively The preparation and unambiguous characterization of heterodisubstituted CDs is a challenging task Heterodisubstituted derivatives are usually obtained by the further modification of a mono-substituted SID In case of the β -CD, this approach leads to the formation of three possible pairs of pseudoenantiomers [29] A higher order single isomer multisubstitution is only rarely reported, however, A, C, E-6-O-trisubstitution of α -CD is easily accessible using trityl chloride as a protecting group Trityl chloride is a bulky molecule, therefore has a steric hindering effect, allowing only the substitution of the more accessible primary side, and only every second glucopyranose unit can be accessed The remaining free OH functions can be subsequently modified and the removal of the protecting group results in A, C, E-trisubstituted α CD derivatives SIDs in chiral capillary electrophoresis 3.1 Application of neutral cyclodextrins in CCE Neutral CD derivatives are still frequently used in order to broaden the chiral recognition abilities and fine-tune the physicochemical properties (such as solubility) of the native CDs The methylated CDs are the most common members of this group, composed of selectively mono-, di-, and trimethylated single isomers Even a slight modification in their structure (degree and/or the position of methylation) largely influences their properties such as solubility, complexation ability and enantiorecognition, thus an in-depth characterization of the β -CD derivatives was performed recently by our group [23] In this study, the detailed synthetic procedures clearly indicated that the production of heptakis(2,3,6-tri-O-methyl)-β -CD (TRIMEB or TM-β -CD) was found to be the most straightforward and easily scalable to kilogram scale [23] The syntheses of the per-dimethylated and the per-monomethylated derivatives require multiple steps and extensive use of protecting groups, therefore the industrial scale-up was found to be challenging The introduction of PTC conditions to each alkylating step allowed the production of the methylated derivatives in multi-gram (10–100 g) scale [23] The synthesis of the primary-side homogeneously substituted, heptakis(6-O-methyl)-β -CD (6-MEB or 6-Me-β -CD) has been only described in the pioneering work of Takeo et al (based on extensive chromatographic purification, resulted in low yields) [30] and in the work of Uccello-Barretta et al (using of hazardous reagents) [31] Our proposed method for the efficient synthesis for per-monomethylated heptakis(6-O-methyl)-β -CD (and in general for 6-O-alkylated CDs) is better suited for industrial scale up and completely chromatography-free at each step [32] The enantiorecognition ability of various selectively methylated CDs on several amino acid derivatives has already been inves- tigated previously by Tanaka and his research group [33–38] A study dealing with the influence of the extent of the modification of the CD with a specific substituent on chiral separation has been carried out by Maruszak et al in 2001 [39] They studied three different methylated β -CDs: the randomly methylated β -CD (DS 1.6–2.0), heptakis(2,6-di-O-methyl)-β -CD (DIMEB or DM-β -CD) and heptakis(2,3,6-tri-O-methyl)-β -CD, but no significant differences were found in their separation ability of four neurotransmitters Chankvetadze et al conducted several studies on the EMO reversal in the presence of native β -CD and the fully methylated TMβ -CD [40–42] The effect of degree of methylation on the enantiomer migration order has been shown for peptide enantiomers reviewed by Scriba [43] The separation of the enantiomers depending on the degree of methylation of CDs was reported for medetomidine enantiomers by Krait et al [44] Randomly substituted M-β -CD as well as the trisubstituted TM-β -CD partially resolved the medetomidine enantiomers, while no enantioseparation was observed using the 2,6-disubstituted DM-β -CD The observed enantioseparation in the case of randomly substituted M-β -CD was accomplished by constituent CD species with a substitution pattern differing from that of the 2,6-disubstitution Schmitt et al studied the enantioseparation of several mixture of the single isomer fully methylated TM-β -CD and the native β -CD, comparing with randomly substituted M-β -CD For a robust enantioseparation method development, the application of mixtures of defined single isomer CDs has priority [45] It has been shown recently, that the degree of methylation can also affect the enantiomer migration order as well, independently of the isomeric purity [46] In the case of methylated derivatives, the enantiomer migration order also depended on the substitution pattern of the CD Thus, opposite migration sequence was observed for the enantiomers of certain cyclic β -amino acids when randomly methylated M-β -CD or fully methylated TM-β -CD was used compared to DM-β -CD, regardless of its isomeric purity (50, 75 or 95%) The comparison of chiral recognition abilities of single isomer mono-, di-, and trimethylated CD derivatives with the structurally-related randomly substituted CDs (RAMEB, CRYSMEB, and DIMEB50) was briefly studied by Varga et al [23] In this case the isomeric mixtures were found to be more versatile chiral selectors over the single isomer derivatives As an alternative, the single isomer 2,6-DIMEB showed exceptional enantiorecognition abilities, however, TRIMEB, or 2-MEB could also provide similar advantages 2D ROESY NMR experiments were performed with terbutaline and it was confirmed that 2-O- and 6-O-methylation extends the cavity to accommodate terbutaline in an enantiospecific manner Our study also showed that single isomer 3,6-DIMEB could not be included in the chiral screening study due its low aqueous solubility Several works dealing with the enantioselectivities of permethylated CDs, the applied mono-, di- and trimethylated SIDs are listed in Table Among the per-dimethylated SIDs, the heptakis(2,3-di-O-methyl-6-hydroxy)-β -cyclodextrin (HDM-β -CD) was found to be the most widely studied derivative (see Table 1.) The recent applications of per-trimethylated CDs, hexakis(2,3,6tri-O-methyl)-α -CD (TM-α -CD, TRIMEA), TRIMEB and octakis(2,3,6tri-O-methyl)-γ -CD (TM-γ -CD, TRIMEG) are also summarized in Table Besides the methylated derivatives the less hydrophobic acetyl functionalized CDs were also studied in CCE recently (see Table 1) Salgado studied the impact of acetylation and noticed the enantiomer migration order reversal in the case of clenpenterol with native β -CD and the heptakis(2,3-di-O-acetyl-6-hydroxy)-β cyclodextrin (HDA-β -CD) [47] NMR experiments augmented with molecular modeling and molecular dynamics (MD) simulations provided insight into the structural and energetic determinants of the distinct binding of clenpenterol enantiomers to the two CDs ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, Table Abbreviated names, structures and recent application of neutral SIDs in CCE Substituents are numbered according to Fig Abbreviation Name 2-MEB (HM-β -CD) Heptakis(2-O-methyl)β -CD 25 basic and zwitterionic analytes [56], 27 basic analytes [63] Heptakis(3-O-methyl)- 27 basic analytes [63] 3-MEB Substituents β -CD Analytes separated 6-MEB (6-Me-β -CD) β -CD Heptakis(6-O-methyl)- methylene-dioxypyrovalerone [32], 27 basic analytes [63] 2,6-DIMEB (DM-β -CD) Heptakis(2,6-di-Omethyl)-β -CD 27 basic analytes [63], bicyclic β amino acids [46], medetomidine [44], Tröger’s base derivatives [64], aspartate and glutamate [65], tryptophan methyl ester [66], ephedrine [67], enilconazole [68], terbutaline [69], propranolol [70], norephedrine [71], 6,6 -dibromo-1,1 -binaphthyl-2,2 -diol [72], repaglinide [73], imidazole enantiomers [74], vinpocetine [75], dapoxetine and its impurities [76], warfarin [77], aspartame [78], pregabalin [79], warfarin and its metabolic enantiomers [80], 13 amphetamine-like designer drugs [81], stimulants [82], fluoxetine [83], ofloxacin and its five impurities [84], hydrobenzoin [85], glitazone compounds [86], peptides [87], phenethylamines [88], talinolol [59], fluoxetine and norfluoxetine [89], hirsutine and hirsuteine [90], clemastine and its related substances [91] 2,3-DIMEB Heptakis(2,6-di-Omethyl)-β -CD 25 basic and zwitterionic analytes [56], 27 basic analytes [63] 3,6-DIMEB Heptakis(3,6-di-Omethyl)-β -CD 27 basic analytes [63] TRIMEB (TM-β -CD) Heptakis(2,3,6-tri-Omethyl)-β -CD 27 basic analytes [63], neutral compounds [60], profens [61,92], seven 2-arylpropionic acid nonsteroidal anti-inflammatory drugs [62], ketoprofen [93,94], lipoic acid [95], fluoxetine [83], ketoconazole [65], lercanidipine [96], propranolol [70], carprofen, pentobarbital [97], norephedrine [71], 6,6 -dibromo-1,1 -binaphthyl-2,2 -diol [72], talinolol [59], amphetamine [98], sibutramine [99], ephedrine [67], enilconazole [68], terbutaline [69], three β -blockers [100], cis-β -lactam [83], five antimalarial drugs [101], aspartame [78], pregabalin [79], warfarin [102], asenapine [103], vinpocetine [75], dapoxetine and its impurities [76], six phenoxy acid herbicides [104], fluoxetine and norfluoxetine [89], meptazinol and its three intermediate enantiomers [105], elaidic and vaccenic trans fatty acid isomers [106], coumarin derivatives [107] TRIMEA( TM-α -CD) Hexakis(2,3,6-tri-Omethyl)-α -CD Ketoprofen [93], aspartame [78], pregabalin [79] TRIMEG( TM-γ -CD) Octakis(2,3,6-tri-Omethyl)-γ -CD amine derivaties [108], pregabalin [79], ketoprofen [93], enilconazole [68], terbutaline [69], aspartame [78], HDA-β -CD Heptakis(2,3-di-Oacetyl)-β -CD 25 basic and zwitterionic analytes [56], clenpenterol [47], ephedrine [67], enilconazole [68], norephedrine [71], terbutaline [109] HMA-β -CD Heptakis(2-O-methyl3-O-acetyl)-β -CD 25 basic and zwitterionic analytes [56] and the migration order reversal of their respective inclusion complexes in CCE The research groups of Holzgrabe and Chankvetadze conducted several studies evaluating the application of both HDM-β -CD and HDA-β -CD as a chiral selector in aqueous CE systems [48–55] Our group has investigated the neutral, synthetic precursors of the frequently applied single isomer sulfated CDs in order to determine whether chiral selectivity is associated only with the sulfate group [56] Four neutral single isomer CDs substituted on the secondary side with acetyl and/or methyl functional groups, heptakis(2-O-methyl-3,6-dihydroxy)-β -cyclodextrin (HMβ -CD), HDA-β -CD, HDM-β -CD, heptakis(2-O-methyl-3-O-acetyl6-hydroxy)-β -cyclodextrin (HMA-β -CD), and their sulfated analogues the negatively charged heptakis(2,3-di-O-methyl-6-sulfo)-β - ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, cyclodextrin (HDMS-β -CD) and heptakis(2,3-di-O-acetyl-6-sulfo)β -cyclodextrin (HDAS-β -CD) were investigated by non-aqueous capillary electrophoresis (NACE) for the enantiodiscrimination of various drugs and related pharmaceutical compounds The possibility of extending the applicability of CCE to non-aqueous conditions increases the versatility of method development in CE, especially in the case of sparingly soluble analytes, also opening the floor to chiral selectors with poor aqueous solubility The advantages of non-aqueous BGEs, such as low conductivity, improved compatibility with mass spectrometric detectors, feasibility of ionpair formation in non-aqueous BGEs, reduced adsorption onto the capillary wall, reduced generated electric current and Joule heating etc render this technique a viable extension to aqueous CCE Moreover, NACE gives an opportunity to alternative separation mechanisms: changing the type of the BGE could result in different CDanalyte complex structures, which may manifest as the reversal of the EMO [57–59] This work focused on the chiral selectivity of the neutral derivatives, which are the synthesis intermediates of the sulfated products The chiral recognition experiments proved that among the neutral compounds the HMA-β -CD shows remarkable enantioselectivity towards chiral guests in NACE, while HM-β -CD, HDA-β -CD and HDM-β -CD failed to resolve any of the 25 studied racemates under the applied experimental conditions In order to get deeper insight into the molecular interactions between the studied SIDs and racemic fluoroquinolones (ofloxacin, gatifloxacin and lomefloxacin) and β -blockers (propranolol), H and ROESY NMR experiments were performed The 2-O-methylation in combination with the 3-O-acetylation of the host was evidenced to exclusively carry the essential spatial arrangement necessary for chiral recognition Thus, it was shown that the non-sulfated synthetic precursor HMA-β -CD bears/is responsible to the chiral selectivity prior to the final sulfation step The main drawback of neutral chiral selectors in CE is the lack of self-mobility, therefore enabling the separation of only charged enantiomers Liu et al demonstrated that ionic liquids (ILs) surfactants in conjunction with neutral CDs (TRIMEB) can resolve also neutral enantiomers [60] Ionic liquids are known as organic salts, possessing low melting points close to room temperature These ionic components exhibit beneficial characteristics, such as varying the viscosity, conductivity or miscibility with different solvents Wang et al [61] reported the combined use of the chiral IL-type surfactant N-undecenoxy-carbonyl-L-leucinol bromide (LUCLB) and TM-β -CD as a dual chiral selector system for the simultaneous enantioseparation of profens This MEKC method was optimized regarding the chain length and concentration of the IL surfactant, and could be applied for the quantitative determination of ibuprofen in pharmaceutical tablets A binary system of trimethyl-β -CD and a chiral amino acid ester-based ionic liquid (L-alanine tert-butyl ester lactate, lAlaC4Lac), was developed for the chiral separation of seven 2arylpropionic acid nonsteroidal anti-inflammatory drugs (NSAIDs) by Mavroudi et al [62] Comparing to the system with TM-β -CD as the sole chiral selector, addition of l-lactate as an anion a synergistic effect (improvement in resolution values and in peak efficiency) could be demonstrated 3.2 Negatively charged CDs Semisynthetic CD derivatives bearing ionizable functional groups possess self-electrophoretic mobility The self-mobility of charged CDs makes the enantioseparation of uncharged enantiomers possible and it is also advantageous for charged analytes due to strong ionic interaction between the oppositely charged species [110] All these advantages led to the development of a wide range of various ionic CD derivatives 3.2.1 Persubstituted derivatives 3.2.1.1 Permanently charged derivatives The negatively charged CDs are favorable for the enantioseparation of neutral and cationic compounds Considering the wide application of basic drug molecules, negatively charged CDs have become the most frequently used chiral selectors, especially the sulfate-substituted β CDs This may result from the introduction of sulfate groups carrying the negative charge(s) over the entire pH range studied in CCE This anionic site of the selectors offers an electrostatic-supported interaction with cationic guests, enhancing the enantiorecognition capacity at any pHs This simplifies the CCE method development and helps to predict and understand the enantioseparation process, since the separation selectivity could be determined as a function of the selector concentration and the pH of the BGE This is the basis of the CHARM-model (charged resolving agent migration model) [111] The largest possible enantioselectivities can be achieved by simulations based on measurements in a single lowpH and high-pH BGE as well as varying only the concentration of the chiral selector The synthesis and the application of persubstituted anionic SIDs in CCE was introduced by Vigh et al [16] with the most widely used single isomer resolving agents in CCE, the sulfated CD derivatives Vigh and his group prepared and characterized various families of structurally well-defined sulfated CDs in high isomeric purity In the first generation of these sulfated SIDs, position C-6 was persubstituted with sulfo groups, while the remaining C-2 and C-3 positions of the glucopyranose units were unmodified (as heptakis(6-O-sulfo)-β -CD [HS-β -CD]), or bearing identical acetyl or alkyl substituents (as heptakis(2,3-diacetyl-6-Osulfo)-β -CD [HDAS-β -CD] and heptakis(2,3-dimethyl-6-O-sulfo)-β CD [HDMS-β -CD], respectively) [16–18] Cucinotta et al [13] has already reviewed the first applications of these SIDs, in Table the recent applications are summarized from the last 10 years Several studies compared the enantiorecognition and complexation behavior of the randomly sulfated CD derivatives (with DS of 7–11 or highly sulfated analogs with DS of 12–15) and the 6O-sulfated SID, the HS-β -CD Wang presented examples for both, the superiority of the SIDs (in the case of chlorpheniramine) and the advantage of randomly substituted analogs (in the case of atropine) in enantioseparation [112] Comparative studies on enantioseparation of thioridazine in a citrate buffer at pH 3.0 were performed by dynamic CE, using sulfated-β -CDs with different DS and positions of sulfate substituent, such as randomly sulfated β CD, 18-sulfate-substituted β -CD and heptakis(2,3-dihydroxy-6-Osulfo)-β -CD These studies revealed the role of interactions between chiral selectors and thioridazine in the enantioseparation and enantiomerization of thioridazine [113] Moreover, a substitution pattern-dependent migration order reversal of medetomidine enantiomers was observed in the study of Krait et al in the presence randomly sulfated β -CD (DS~12–15) and heptakis(6-Osulfo)-β -CD [44] Levomedetomidine interacted stronger with the SID, while dexmedetomidine formed more stable complexes with randomly sulfated β -CD They investigated the complexation of the enantiomers of medetomidine with various CDs by CE, NMR and molecular modeling However, a complete picture could not be obtained unfortunately by NMR and molecular modeling in the case of the randomly substituted CD since the mixture of positional and substitutional isomers present, highlighting the disadvantage of the random analogs in structural follow-up studies Applying the multiple chiral selector (multi-CS) model, Dubsky demonstrated the difference between the enantiorecognition of single isomer HS-β -CD and randomly substituted, commercial mixture of sulfated CDs [114] He supported the enhanced enantioselectivity of multi-CS systems with an additional, electrophoretic, enantioselective mechanism resulting from different limiting mo- ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, Table Abbreviated names, structures and recent application of negatively charged SIDs in CCE Substituents are numbered according to Fig Abbreviation Name Substituents Analytes separated Permanently charged SIDs per-sulfated β -SIDs HS-β -CD Heptakis(6-O-sulfo)-β -CD Thioridazine [113], propranolol [70], phenolic acids, flavones [167], lorazepam [114], tryptophan methyl ester [66], β -blockers, phenethylamines, anticholinergic agents [112], phenylalanine, 1-phenylethanol, chlorpheniramine, promethazin [168], medetomidine [44], 3-chiral-1,4-benzodiazepines [115], oxazolidinones (tedizolid +precursors) [122], oxazolidinones (radezolid) [123], oxazolidinones (sutezolid+ precursor) [124], ephedrine [67], α -diimine Ru(II) and Fe(II) complexes [139], pindolol [141] HDMS-β -CD Heptakis-(2,3-di-O-methyl-6O-sulfo)-β -CD 10 β -blockers [116], fenbendazole (prochiral), oxfendazole, nonchiral fenbendazole sulfone [120], synthetic intermediate of 3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans [119], 10 basic drugs [143], propranolol [125], carvedilol [57], propranolol [70], bupivacaine and propranolol [126], norephedrine [71], talinolol [59], acebutolol [128], enilconazole [68], terbutaline [69], brombuterol [147], ephedrine [67], 3-chiral-1,4-benzodiazepines [115], oxazolidinones (tedizolid +precursors) [122], oxazolidinones (radezolid) [123], oxazolidinones (sutezolid+ linesolid) [124], β -blocker drugs [127], 25 basic and zwitterionic analytes [56], HDAS-β -CD Heptakis(2,3-di-O-acetyl-6-Osulfo)-β -CD dexamphetamine, 1R,2S(-)norephedrine, 1S,2S(+)norpseudoephedrine [117], 10 β -blockers [116], fenbendazole (prochiral), oxfendazole, nonchiral fenbendazole sulfone [120], synthetic intermediate of 3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans [119], 10 basic drugs [143], propranolol [125], carvedilol [57], propranolol [70], bupivacaine and propranolol [126], alprenolol, bupranolol, terbutaline, tiaprofenic acid, suprofen, flurbiprofen [169], propranolol [58], norephedrine [71], talinolol [59], basic analytes [118], amphetamine [98], acebutolol [128], enilconazole [68], terbutaline [69], brombuterol [147], ephedrine [67], 3-chiral-1,4-benzodiazepines [115], oxazolidinones (tedizolid +precursors) [122], oxazolidinones (radezolid) [123], oxazolidinones (sutezolid+ linesolid) [124], β -blocker drugs [127], 25 basic and zwitterionic analytes [56], α -diimine Ru(II) and Fe(II) complexes [139], phenethylamines [88], Ru(II)- and Fe(II)-polypyridyl associates [170] per-sulfated α - and γ -SIDs HxS-α -CD Hexakis(6-O-sulfo)-α -CD α -diimine Ru(II) and Fe(II) complexes [139] HxDMS-α -CD Hexakis(2,3-di-O-methyl-6-Osulfo)-α -CD – HxDAS-α -CD Hexakis(2,3-di-O-acetyl-6-Osulfo)-α -CD α -diimine Ru(II) and Fe(II) complexes [139], Ru(II)- and OS-γ -CD Octakis(6-O-sulfo)-γ -CD l- and d-amino acids [140], pindolol [141], α -diimine Ru(II) and Fe(II) complexes [139] (continued on next page) Fe(II)-polypyridyl associates [170] ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, Table (continued) Abbreviation Name ODMS-γ -CD Octakis(2,3-di-O-methyl-6-Osulfo)-γ -CD α -diimine Ru(II) and Fe(II) complexes [139] ODAS-γ -CD Octakis(2,3-di-O-acetyl-6sulfo)-γ -CD oxazolidinones (tedizolid+precursors) [122], α -diimine Ru(II) and Fe(II) complexes [139], Ru(II)- and Fe(II)-polypyridyl associates [170] II generation sulfated β -SIDs Substituents Analytes separated HMS-β -CD Heptakis(2-O-methyl-6-Osulfo)-β -CD – HMAS-β -CD Heptakis(2-O-methyl-3-Oacetyl-6-O-sulfo)-β -CD 10 basic drugs [143], non-ionic and weak base analytes [148], carvedilol [57] HMdiSu-β -CD (HMDS) IV generation Heptakis(2-O-methyl-3,6-di-Osulfo)-β -CD Enilconazole [68], terbutaline [69], brombuterol [147], non-ionic and weak base analytes [148] HAMS Heptakis(2-O-sulfo-3-Omethyl-6-O-acetyl)-β -CD non-ionic and weak base analytes [148] DBSB-β -CD Heptakis(2,3-di-O-benzyl-6-Osulfobutyl)-β -CD fluorescent cyanobenzylindole derivatives of d/l–serine [151] DBSB-α -CD Hexakis(2,3-di-O-benzyl-6-Osulfobutyl)-α -CD fluorescent cyanobenzylindole derivatives of d/l–serine [151] 6-(SB)7 -β -CD Heptakis(6-O-sulfobutyl)-β -CD basic and noncharged analytes [152] HDHSA-β -CD Heptakis(2,6-di-O-[2-hydroxy3(sulfoamino)propoxy])-β -CD β -adrenoreceptor agonists [153] III generation sulfoalkylated SIDs (continued on next page) ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, Table (continued) Abbreviation Name Substituents Analytes separated Adjustable anionic charge Per substituted derivatives HDMCM Heptakis(2,3-di-O-methyl-6-Ocarboxymethyl)-β -CD ODMCM 25 noncharged, basic, and zwitterionic analytes [156] Octakis(2,3-di-O-methyl-6-Ocarboxymethyl)-γ -CD Mono substituted derivatives basic analytes [157] 2CMα CD 2A -O-carboxymethyl-α -CD Tryptophan, baclofen, primaquine and Tröger’s bases [159,163] 3CMα CD 3A -O-carboxymethyl-α -CD Tryptophan, baclofen, primaquine and Tröger’s bases [159,163] 6CMα CD 6A -O-carboxymethyl-α -CD Tryptophan, baclofen, primaquine and Tröger’s bases [159,163] 2CMβ CD 2A -O-carboxymethyl-β -CD Tröger’s bases, baclofen, mefloquine, and tryptophan methyl ester [160,163] 3CMβ CD 3A -O-carboxymethyl-β -CD Tröger’s bases, baclofen, mefloquine, and tryptophan methyl ester [160,163] 6CMβ CD 6A -O-carboxymethyl-β -CD Tröger’s bases, baclofen, mefloquine, and tryptophan methyl ester [160] 2CMγ CD 2A -O-carboxymethyl-γ -CD Tröger’s bases, mefloquine, primaquine and tryptophan methyl ester [162,163] 3CMγ CD 3A -O-carboxymethyl-γ -CD Tröger’s bases, mefloquine, primaquine and tryptophan methyl ester [162,163] 6CMγ CD 6A -O-carboxymethyl-γ -CD Tröger’s bases, mefloquine, primaquine and tryptophan methyl ester [162,163] mono-Suc-β CD di-Suc-β -CD tri-Suc-β -CD mono-6A -O-succinyl-β -CD di-6-O-succinyl-β -CD tri-6-O-succinyl-β -CD Catechin [165] SET-β -CD SMHT-β -CD 6A -sulfoethylthio-β -CD 6A -(6-sulfooxy-5,5-bissulfooxymethyl)hexylthio-β CD Basic analytes [166] Basic analytes [166] bilities in the case of chiral selector mixtures It is verified that the two enantiomers of lorazepam under interaction with a mixture of CSs are very likely to differ in their limit mobilities, which is opposite to single CS systems where the two limit mobilities are likely to be the same This additional mechanism generally makes the multi-selector systems more selective than the single selector systems The effect of the sulfation of the primary hydroxy groups of β CD is highlighted: enantiomer migration order reversal could be observed in the case of propranolol enantiomers applying native 10 ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, β -CD (and the partially resolving TM-β -CD) or the 6-O-sulfated analogs, the HS-β -CD (and also in the case of the further substituted HDAS-β -CD and HDMS-β -CD) in aqueous buffer [70] Significant structural differences were also confirmed by 1D ROESY measurements, observed between the complexes of propranolol with native β -CD and its single isomer sulfated analogue, HS-β -CD Inclusion type complexes were formed in both cases, however, the naphthyl moiety entered the cavity from opposite directions and the extent of the penetration into the cavity was also different for the two CDs These significant structural differences between the complexes can be responsible for the opposite migration order of the propranolol enantiomers observed in CE using these two CDs as chiral selectors The molecular mechanisms of enantiorecognition and the opposite enantiomer migration order of ephedrine enantiomers was investigated in the presence of native α - and β -CD, as well as with HDAS-β -CD by CE, NMR and high-resolution MS [67] 1D ROESY experiments prevailed a striking difference between the structures of ephedrine complexes with the native and HDAS-β -CDs Enhanced chiral recognition ability could be observed in the case of HDAS-β -CD towards the enantiomers of ephedrine The EMO were followed for norephedrine enantiomers with native α - and β -CD, as well as with HDAS-β -CD and HDMS-β -CD by CE and NMR [71] The complexes between the enantiomers of norephedrine and the sulfated CDs, HDMS-β -CD, and HDAS-β -CD, were substantially different, however, EMO of norephedrine was identical in the presence of these CDs HDAS-β -CD proved to be the most suitable chiral selector for the enantioseparation of norephedrine Based on 1D ROESY NMR experiments, the interactions with the sulfated CDs occurred through at the primary rim: in the case of HDAS-β -CD, an inclusion complex is formed, whereas only a superficial binding of the analyte is observed for HDMS-β -CD A clear enantiomeric bias could be seen between norephedrine and HDAS-β -CD, as the 1S,2R-isomer seemed to form a stronger complex compared to its 1R,2S counterpart The three 6-O-sulfated CD derivatives, differing in the substituent at C2 and C3 positions: hydroxyl, acetyl and methyl derivatives as HS-β -CD, HDAS-β -CD and HDMS-β -CD respectively, were examined by experimental design for enantioseparation of four chiral benzodiazepines by CE [115] The highest resolution values were obtained with the addition of 5% HS-β -CD and 15% methanol as an organic modifier to 20 mM borate buffer, pH 9.0 The two most widely applied sulfated SIDs, HDAS-β -CD and HDMS-β -CD are both completely sulfated at the primary rim, and additionally substituted at their secondary rims with moderately hydrophobic (acetyl) or hydrophobic (methyl) functional groups Several studies compared these two SIDs in CCE (see Table 2.) Rousseau et al investigated the NACE separation of ten β -blockers with d-optimal design [116] to estimate the effects of the nature of the CD and the BGE anion as well as their concentrations on the enantioseparation A generic NACE system (10 mM ammonium acetate and 40 mM HDAS-β -CD in methanol acidified with 0.75 M formic acid) was able to completely resolve the enantiomers of all β -blockers, with a minimal Rs value of The optimal conditions were compared to the optimal conditions obtained by modeling resolution, mobility difference and selectivity Kokiashvili also found HDAS-β -CD advantageous for the simultaneous determination of the enantiomeric purity of dexamphetamine as well as the analysis of 1R,2S-(−)-norephedrine and 1S,2S-(+)-norpseudoephedrine as potential impurities [117] The validated method was successfully used for the analysis of commercial dexamphetamine sulfate samples where 3–4% of levoamphetamine were detected, indicating the preparation method of amphetamine In comparison with the polarimetric measurements 0.06% of levoamphetamine can be detected by capillary electrophoresis Yao and his group demonstrated the utility of HDAS- β -CD for chiral separation of 12 pairs of basic analyte enantiomers under the optimized conditions (50 mM Tris-H3 PO4 and mM HDAS-β -CD at pH 2.5) [118] Furthermore, a molecular modeling strategy was established with model compounds (clenbuterol, oxybutynin, salbutamol and penehyclidine) to confirm and explain the possible chiral recognition mechanism: the binding energy difference between a pair of enantiomers towards the chiral selector was a significant factor contributing to enantioselectivity Rousseau found the more hydrophobic dimethylated SID, HDMS-β -CD preferable for the analysis of synthetic intermediate of new 3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans in NACE [119] However, high resolution and efficiency values could be achieved only by the addition of a chiral ionic liquid (IL), i.e ethylcholine bis(trifluoromethylsulfonyl)imide (EtChol NTf2 ), to the BGE containing HDMS-β -CD, indicating the synergistic effect of the anionic CD and the chiral IL The validated method permitted the determination of 0.1% of each enantiomer in the presence of its stereoisomer In a further study of this group, a NACE method has been established using the combination of 10 mM HDAS-β CD and 10 mM HDMS-β -CD for the simultaneous determination of a prochiral drug, fenbendazole, and its chiral (oxfendazole) and nonchiral (fenbendazole sulfone) metabolites [120] After the determination of enantiomeric impurity of linezolid by capillary electrophoresis using heptakis-(2,3-diacetyl-6-sulfo)β -cyclodextrin [121], Michalska and her research group investigated the enantioseparation of further oxazolidinones using SIDs in CCE [122–124] During method development for the simultaneous separation of the non-charged tedizolid enantiomers and the weak base linezolid enantiomers, hydrophilic negatively charged single isomer and moderately hydrophobic and hydrophobic CDs were also tested including HS-β -CD, HDAS-β -CD and HDMS-β -CD, respectively [122] Only CDs with acetyl moieties at the C2 and C3 positions (HDAS-β -CD or its gamma analog octakis(2,3-di-Oacetyl-6-sulfo)-γ -CD (ODAS-γ -CD)) provided baseline separation The best enantioseparation of tedizolid (Rs = 4.1) was obtained with HDAS-β -CD in 50 mM formate buffer (pH 4.0) with the addition of acetonitrile The separation mechanism of the more hydrophilic, dibasic radezolid, together with its precursor linezolid was investigated to reveal the relationship between the oxazolidinone structure and the complexation process applying HS-β CD, HDAS-β -CD and HDMS-β -CD [123] The CDs having an acetyl or methyl group at the C2 and C3 positions (HDAS-β -CD and HDMS-β -CD), exhibited partial and baseline separation of enantiomers in a low pH buffer, respectively However, higher temperatures were required for the separation with HDAS-β -CD and acetonitrile addition was required for HDMS-β -CD Some further structure-enantioselectivity relations were also deduced in their study As the further step of the mechanistic investigation of the enantioseparation of oxazolidinones, a NACE method has been developed for the less water-soluble sutezolid enantiomers [124] HSβ -CD, the most hydrophilic selector tested was incompatible with NACE buffers HDAS-β -CD and HDMS-β -CD provided the baseline separation of sutezolid enantiomers, however, with different EMO: a substitution dependent enantiomer migration order reversal occurred Instead, enantiomers of linezolid were separated only by HDMS-β -CD CCE separations in non-aqueous BGEs are as well established as the separations in aqueous buffers While achiral separation mechanisms in NACE are most likely similar to those in aqueous buffers, remarkable differences can exist between the molecular mechanisms of the separation of enantiomers in aqueous and nonaqueous buffers Servais and co-authorss resolved the enantiomers of propranolol using CE in aqueous and non-aqueous methanolic BGEs with the two single isomer sulfated derivatives HDMS-β -CD and HDAS-β -CD [125] The enantiomer migration order of propranolol was reverted when an aqueous BGE was replaced with non- 16 ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, substituted anionic CD derivatives, 6-deoxy-6-monocarboxy-β -CD and 6-monophosphate-β -CD [158] Since in the case of monosubstituted CDs three regioisomers exist, Rezanka and his research group focused on the impact of the position of the CM group on the enantioselectivity of the chiral selector They prepared a complete set of regioisomers of monosubstituted CM-CDs and compared the enantioselectivities of the regioisomers The enantioselectivity of all the three individual regioisomers of the monosubstituted CM-α -CDs was studied and compared with the mixture of the three monosubstituted CM-α -CDs and with native α cyclodextrin [159] Their experiments revealed a significant influence of the location of the carboxymethyl group on the α cyclodextrin skeleton on the enantioselectivity for all the studied analytes Interestingly, the least common 3-O regioisomer provided significantly better resolution than the native α -CD and its monosubstituted carboxymethyl derivatives Comparison of the three monosubstituted carboxymethyl-β -CD regioisomers individually, their 1:1:1 mixture along with the native β -CD, and the commercially available random CM-β -CD (DS~3) [160] indicated that substituent position has a significant influence on the enantioseparation For most of the investigated analytes the commercially available derivative of CD provided better resolutions than the monosubstituted carboxymethyl CD derivatives A complete set of mono-carboxymethylated γ –CDs were also synthesized by the same research group [161] besides the full sets of peracetylated 2-O-, 3-O-, and 6-O-allyl, -propargyl, and -formylmethyl, derivatives of γ -CD 2-O-, 3-O-, and 6-Ocarboxymethyl-γ -CD, as well as the native γ -CD and the random CM-γ -CD analog were studied and the results confirmed that the position of carboxymethyl group influences the enantioseparation efficiency toward all the studied analytes [162] The 2-O-and 3-Oregioisomers provide a significantly better resolution than native γ -CD, while the 6-O-regioisomer gives only a slightly better enantioseparation In general, higher number of carboxymethyl groups led to better resolution A comprehensive study on the position of the carboxymethyl group as well as the cavity size of the individual CD was deeply investigated applying all nine regioisomers of mono- substituted 2-O-, 3-O-, and 6-O-carboxymethyl-α -, β -, and γ -CDs and native α -, β -, and γ -CDs at pH 2.5 [163] Based on CCE data, the apparent stability constants of all CD–Tröger’s base complexes were deduced and a significant influence of the substituent location in the monosubstituted CD as well as the size of the CD cavity on both the chiral separation and the apparent stability constants were found Regarding only the native CDs, the most stable complexes were formed with β -CD, however from all of the studied CD derivatives, the highest apparent stability constants were obtained for 3-O-carboxymethyl-γ -CD and the highest selectivity was achieved for 2-O-CM-β -CD This comparative analysis could serve a basis for development of models aiming to describe chiral separation processes in real case systems The mono-6-O-succinyl-β -CD (CDsuc6) was introduced by Cucinotta [164], and they demonstrated promising chiral recognition ability towards catecholamines in CCE Kim et al synthesized and applied in CCE three kinds of negatively charged Suc-β -CDs with 1, 2, and succinyl moieties at the primary hydroxyl groups of β -CD, the mono-Suc-β -CD, di-Suc-β -CD, and the tri-Suc-β -CD, respectively [165] The effects of nature and concentration of Suc-β -CDs and BGE pH on the migration time and resolution of (±)-catechin are discussed They have concluded that the optimal separation conditions have been reached utilizing monosubstituted CD On the other hand, the chiral selectors with the higher degree of substitution had a broader pH range of (±)-catechin separation when compared with mono-succinyl-β -CD To improve the resolution power of the chiral selector and enantiomeric peak efficiency in CE, single isomer perma- nently negatively charged β -CD derivatives, mono(6-deoxy-6sulfoethylthio)-β -CD (SET-β -CD) bearing one negative charge and mono[6-deoxy-6-(6-sulfooxy-5,5-bis-sulfooxymethyl)hexylthio]-β CD (SMHT-β -CD) carrying three negative charges, were synthesized [166] The apparent binding constants and mobilities of the complexed analytes were determined in order to gain an improved understanding on the effect of the number of negative charges on a given enantioseparation SMHT-β -CD exhibited significantly greater enantioseparation over SET-β -CD at lower concentrations due to its higher number of negative charges providing a wider separation window resulting from an increased countercurrent mobility of the selector and higher binding affinity to the analytes 3.3 Positively charged CDs Positively charged CD-derivatives are less widely used in (chiral) CE applications While they potentially shorten the analyte migration times towards the cathode via complexation, allowing realization of shorter analysis times, their tendency to adsorb to the negatively charged inner surface of the silica capillary may lead to decreased resolution power and reproducibility problems Cationic CDs may hold permanently charged functional groups (strong electrolytes) or nitrogen bases (weak electrolytes), gaining positive charge only upon protonation at suitable pH values of the BGE The first cationic CD synthesized in 1978 was mono-(6A trimethylammonium)-β -cyclodextrin hydrogencarbonate (tma-β CD) [171] This permanently charged derivative was prepared as a simple enzyme model and its ligand-binding and catalytic properties were examined The application of positively charged CD derivatives in CE was first described by Terabe in 1989 [11] He introduced the concept of electrokinetic chromatography (EKC), where a charged (macrocyclic) selector is dissolved in the BGE and functions as a carrier of the analytes The separation is based on the same principle as ordinary chromatography, but the carrier is not immobilized nor form a distinct phase, rather it is homogeneously distributed in the BGE solution forming a quasi-stationary phase When an analyte is added, a certain population of analyte molecules gets incorporated in the carrier through a partition mechanism and transported via the migration of the carrier The unbound fraction of analyte molecules migrates according to its own electrophoretic mobility and the electroosmotic flow As a result, different net migration velocities arise for each analyte, dictated by their affinity towards the carrier host and its molar concentration The application of charged CD as a resolving agent in CE offers special advantages compared to the neutral derivatives Insertion of ionogenic groups may enhance the solubility of the CD itself, but more importantly, neutral molecules lacking an intrinsic electrophoretic mobility also may become resolvable by charged CDs In this pioneering report of EKC [172], Terabe used the negatively charged carboxymethyl-β -CD and the positively charged mono-6A -(2-aminoethylamino)-β -cyclodextrin (AEA-β -CD) to demonstrate the realization of EKC Six enantiomeric dansyl amino acids (DNS-AAs) were resolved by EKC with the cationic AEA-β -CD derivative 3.3.1 pH-adjustable positively charged SID derivatives Weak base CD derivatives can be differentiated according to their substitution degree (mono-, di-, multi- or persubstituted derivatives, where also non-ionizable substituents may be present) or the number of protonable groups (mono-, di- or multivalent [173] derivatives) There are also examples for monosubstituted derivatives holding multiple charges The presence of several basic sites gives the opportunity of more precise tailoring of the pHdependent degree of protonation and overall charge, thus modulating the strength of analyte-selector interaction This dry chemistry- ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, type design of the CE separation would require determination of precise pKa dissociation constants of the CD derivatives, which remain usually unknown Besides mono- [11,174,175] and diamino [176] compounds, their alkylated derivatives [177–183], histamine-modified derivatives [184–187], hemispherodextrins [188–190], a family of hydroxyalkylamino-β -CDs [191–193] and amino-alkylamino-β -CDs [176] were reported between the late 1990s to ca 2010 Comparative screening studies of these selectors provided deeper insights into the intrinsic mechanism of chiral recognition The majority of works in the past decade focused on the extension of previous studies by either introducing a new representative of a previously synthesized family of structurally homologue cationic selectors or explored the applicability of previous successful CD derivatives for enantioresolution of novel families of compounds The simplest form of cationic CDs, mono- and peramino derivatives were studied by several groups for the separation of various Dns-AAs, anionic and ampholytic analytes [11,174–176] In these applications, α -CD and β -CD derivatives were usually functionalized on their primary or secondary side Among the γ -CD derivatives, only mono-6-amino-γ -CD (6NH2 -γ -CD) [174,194] was explored for the chiral separation of Dns-AAs Cucinotta et al used mono-3A -amino-γ -CD (3NH2 -γ -CD) as chiral selector for the separation of Dns-AAs [195] (see Table 3.) In a subsequent study, the same SID was able to separate only eight of the thirteen investigated amino acids as fluorescein isothiocyanate (FITC) derivatives [196], while the mono-3A -amino-β -CD (3NH2 -β -CD) analogue exhibited a better selectivity The cavity size was found to play a key role in the chiral recognition and (compared to Dns-AAs) it was hypothesized that the FITC-moiety of the labelled AAs does not get included into the CD cavity, it solely improves the detection limit Permethyl-mono-6A-amino-β -CD (PMMAB-CD) was proved to be an effective selector to separate pyrethroic acid and profen enantiomers [197], Németh et al used it in 2014 also for the separation of Dns-AAs [101] In the early 20 0s, Cucinotta’s group implemented ligand exchange capillary electrophoresis (LECE) to CE The method relies on the principle that a suitable metal ion is added to the BGE, which can coordinate both the CD derivative and the analyte molecules to form mixed metal-ligand complexes This phenomenon can be exploited to separate enantiomers (chiral LECE, CLECE) Cucinotta et al conducted several studies to explore the exact mechanism of complex formation with copper(II) ion Besides CE, they combined several techniques such as potentiometric titrations, UV/VIS, circular dichroism and NMR spectroscopies to understand the structural influence on enantioseparation on an array of mono- or multivalent cationic CDs, such as amino- or histamine-derivatized CDs, mono-6A -(2-aminoethylamino)-β -CD (AEA-β -CD), and mono-6A [N-(2-methylamino)pyridine)]-β -CD (CDampy), including the different impact of their primary or secondary side modification [190,198–200] The potential of LECE was extended by its coupling to LIF and TOF-MS detection, both yielding similarly low detection limits [201] Moreover, CE-MS proved to be capable of detecting non-UVabsorbing analytes or permitted to use strongly UV-absorbing CD selectors, thus widening the space for chiral LECE method development [202] The researchers demonstrated the suitability of CE-MS by analyzing real-word samples such as transgenic and wild soy and vinegar [202] Although two histamine-modified CDs, mono-6A -N-histaminoβ -CD (CD-hm) and mono-6A -[4-(2-aminoethyl)imidazolyl]-β -CD (CD-mh) were among the first published members of cationic CD selectors [184–187], a new histamine derivative of β -CD, functionalized at the secondary rim (CDhm3) was applied in chiral LECE towards the enantiomeric pairs of certain AAs only more than twenty years later [176] Comparing the structures of the success- 17 fully applied CD derivatives revealed that the factor to determine the EMO of AAs is the presence of histamine and not the position of derivatization on the CD Recently, the AEA-β -CD derivative was also used successfully for the achiral separation of hirsutine and hirsutein, two pharmacologically active ingredients of Uncaria rhynchophylla, applied in the therapy of mental and cardiovascular diseases [90] Mono-6-hydroxyalkylamino-β -CD derivatives are a family of well-characterized chiral CE selectors, reported by Iványi et al [192], tested for the resolution of mandelic acids, pyrethroic acids and profens as model compounds Jakó et al used the mono-6A -(3-hydroxy)propylamino-β -CD (HPA-β -CD) to develop a method for quantitative determination of amino acid neurotransmitters and neuromodulators using CELIF hyphenation [203] The analytes determined were aspartate and glutamate enantiomers, derivatized with the fluorophore 4fluoro-7-nitro-2,1,3-benzoxadiazole The method was validated on animal brain samples The enantioselectivity could further be increased by addition of DIMEB to the BGE The potential of HPA-β CD was further demonstrated in the validated CE-LIF method targeting also D–serine in mice brain samples [204] These examples illustrate that in spite of the underutilization of positively charged CD derivatives as chiral selectors in CE, they can be successfully applied for AA enantiomer analysis even in complex biological matrices In 2014, Yu et al investigated the applicability of a previously unreported derivative, mono-6A -piperidine-β -CD (Pip-β -CD) both alone and together with neutral CDs (β -CD, TRIMEB and HP-β CD) for the enantioseparation of meptazinol and its three enantiomeric intermediates [105] It turned out that Pip-β -CD alone performed well for intermediate II, while the dual system with β -CD provided the best enantioseparation for intermediate III In addition, the Pip-β -CD/HP-β -CD dual system excelled at the chiral resolution of meptazinol and intermediates III and IV in a single run Pip-β -CD was successfully applied to separate folinic acid diastereomers, where computational techniques were also used to model the separation mechanism [205] The results identified electrostatic interactions as the decisive factor for the enantioseparation Three years later the same SID was compared by Zhu et al to five other CD derivatives: cyclohexylamine-β -CD (CHA-β -CD), dimethyl- and hydroxypropyl-β -CD, carboxymethyl- and sulfatedβ -CD for the enantiomeric separation of ofloxacin and its five related substances [84] No enantioresolution could be achieved with the cationic CDs, since in the investigated pH range of 2.5–4.5, both the analyte carboxylic acids and the selectors were protonated, disabling the attractive electrostatic forces to aid enantiorecognition Pip-β -CD augmented with DIMEB and sodium cholate as micellar modifier in the BGE lead to a twofold increase in resolution Besides the further utilization of previously reported SID cationic selectors, a few attempts have been made to synthesize novel derivatives to further broaden the portfolio of adjustable cationic SIDs A unique multicationic CD, mono-6A -((2S,3S)-(1)−2,3-Oisopropylidene-1,4-tetramethylenediamine)-β -CD (MIPTACD) has been synthesized in 2010 by Liu et al [206] Ten Dns-AAs racemates and N-acetylphenylalanine served as model compounds for this aminoalkylamino derivative, holding a sidechain with two additional chiral centers MIPTACD showed excellent chiral recognition towards the 11 mentioned amino acid derivatives Although this pioneering application was promising, no additional chiral CE study appeared using MIPTACD, presumably due to its 7-step synthesis compared to the less laborious preparation of simpler cationic derivatives Hemispherodextrins, synthesized by Cucinotta et al., represent a special class of disubstituted CDs: a saccharidic unit is attached to the primary side of the CD, connecting the oppo- 18 Table Abbreviated names, structures and recent application of positively charged SIDs in CCE Substituents are numbered according to Fig Abbreviation Name Substituents Analytes separated Adjustable cationic charge mono-3A -amino-β -CD FITC-AAs [196], AAs [202] 3NH2 -γ -CD mono-3A -amino-γ -CD FITC-AAs [196,195] PMMAB-CD Permethyl-mono-6A -amino-β -CD Dns-AAs [230] CDhm3 (C3-histamine-substitutedβ -CD) mono-3A -deoxy-3A -[2-(4imidazolyl)ethylamino]-β -CD AAs [176] HPA-β -C mono-6A -(3-hydroxypropylamino)-β -CD Amino acid neurotransmitters [204,203] Pip-β -CD mono-6A -piperidine-β -CD Meptadizol and synthetic intermediates [105] Folinic acid diastereomers [205] Ofloxacine and its related compounds [84] CHA-β -CD mono-6A -cyclohexylamine-β -CD Ofloxacine and its related compounds [84] AEA-β -CD (CDen) mono-6A -(2-aminoethylamino)-β CD AAs [202] Hirsutine and hirsuteine [90] MIPTACD mono-6A -[(2S,3S)-(1)−2,3-OIsopropylidene-1,4tetramethylenediamine]-β -CD Dns-amino acids, N-acetylphenylalanine [206] THLYSH (Lysine bridged HSD) Di-6A ,6D -[6,6 -dideoxy-6,6 diLysamino-α ,α ’-trehalose]-β -CD Terbutaline and non-steroidal anti-inflammatory drugs [207] HEtAMCD mono-6A -(2-hydroxyethyl-1ammonium)-β -CD chloride Acidic and ampholytic racemates [191,212] (continued on next page) ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, 3NH2 -β -CD Table (continued) Name Substituents Analytes separated MPrAMCD mono-6A -(3methoxypropylammonium)-β -CD chloride Dns-amino acids, α -hydroxyl and carboxylic acids [210,212] MEtAMCD mono-6A -(2methoxyethylammonium)-β -CD chloride ampholytic and acidic racemates [211,212] MBuAMCD mono-6A -(4methoxybutylammonium)-β -CD chloride 16 acidic racemates including three Dns-amino acids [231] HPrAMCD mono-6A -(3-hydroxypropyl-1ammonium)-β -CD chloride AA neurotransmitters and neuromodulators [203,204,212] HBuAMCD mono-6A -(4-hydroxybutyl-1ammonium)-β -CD chloride Carboxylic acids [212] BHEtAMCD mono-6A -[bis(2-hydroxyethyl)−1ammonium]-β -CD chloride Carboxylic acids [212] THEtAMCD mono-6A -[tris(2-hydroxyethyl)−1ammonium]-β -CD chloride Carboxylic acids [212] BMEtAMCD mono-6A -[bis(2-methoxyethyl)−1ammonium]-β -CD chloride Carboxylic acids [212] ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, Abbreviation (continued on next page) 19 20 Table (continued) Name Substituents Analytes separated dhypy-CDCl mono-6A -(3R,4Rdihydroxypyrrolidinium)-β -CD Dns-AAs, anionic and ampholytic acids [213] pyCDCl mono-6A -pyrrolidinium-β -CD chloride Dns-amino acids, α -hydroxyl and carboxylic acids [214] N-CH3 -pyCDCl mono-6A -(N-methylpyrrolidinium)-β -CD chloride Dns-amino acids, α -hydroxyl and carboxylic acids [214] N-EtOH- pyCDCl mono-6A -(N-(2-hydroxyethyl)pyrrolidinium)-β -CD chloride Dns-amino acids, α -hydroxyl and carboxylic acids [214] mono-6A -(2-hydroxymethylpyrrolidinium)-β -CD chloride Permanently cationic derivatives Dns-amino acids, α -hydroxyl and carboxylic acids [214] PEMEDA-β -CD mono-6A -(N,N,N’,N’,N’pentamethylethylenediammonium)-β -CD dichloride Anionic, weak-acids and neutral analytes [216] PEMPDA-β -CD mono-6A -(N,N,N’,N’,N’pentamethyl-propylene-1,3diammonium)-β -CD dichloride Anionic, weak-acids and neutral analytes [216] mono-6A -(3-methylimidazolium)- Tetracyclines [220] 2-MeOH-pyCDCl MIMCDOTs β -CD tosylate (continued on next page) ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, Abbreviation Table (continued) Substituents Analytes separated PrIMCD mono-6A -(propylimidazolium)-β CD chloride Dns-AAs [221] MPrIMCD mono-6A -(3methoxypropylimidazolium)-β -CD chloride Dns-AAs [221] AllIm-β -CD mono-6A -(1-allylimidazolium)-β CD chloride Kynurenine [222] 4-ATMCDCl mono-6A -(4-amino-1,2,4triazolium)-β -CD chloride Dansyl-AAs, Naproxen [223] AMBuIMCD mono-6A -[3-(4-ammoniumbutyl)imidazol-1-ium]-β -CD chloride Dns-AAs, acidic racemates [232] AMBIMCD 6A -Ammonium-6C butylimidazolium-β -CD chloride Dns-amino acids, α -hydroxyl and carboxylic acids [226,227] HEtTrMEtIm-β -CD 6A -(4-Hydroxyethyl-1,2,3triazole)−6C -(2methoxyethylimidazolium)-β -CD chloride Dns-AAs [228] HEtTrMPrIm-β -CD 6A -(4-Hydroxyethyl-1,2,3triazole)−6C -(3methoxypropylimidazolium)-β -CD chloride Dns-AAs [228] HEtTrMPrAm-β -CD 6A -(4-Hydroxyethyl-1,2,3triazole)−6C -(3methoxypropylammonium)-β -CD chloride Acidic racemates [229] 21 Name ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, Abbreviation 22 ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, site sides of the rim as a bridge, forming a hemispherical saccharidic system The first representatives, di-6A ,6D -(6,6 -diaminoα ,α ’-trehalose)-β -CD (THAMH) [188,190], Di-6A ,6D -[6,6 -dideoxy6,6 -di(S-cysteamine)-α ,α ’-trehalose]-β -CD (THCMH) [189] and di6A ,6D -N-[6,6 -di-(β -alanylamido)−6,6 -dideoxy- α ,α ’-trehalose]-β CD (THALAH) [188,190] were successfully applied for the separation of phenoxy acids, profens and DNS-AAs They were followed in 2017 by di-6A ,6D -[6,6 -dideoxy-6,6 diLys-amino-α ,α ’-trehalose]β -CD (THLYSH or lysine-bridged HSD), which was used to separate terbutaline and non-steroidal anti-inflammatory drugs, in both chiral and achiral separations [207] Chiral separations could be achieved by the lysine-bridged HSD without addition of another CD derivative, which was not the case for the earlier HSDs In contrary to their negative counterparts, the family of weak base-type CD derivatives contains relatively few persubstituted members, reported around 20 0 or earlier The first representatives was the per-6-hydroxyalkylamino-derivative [208], followed by per-6-amino-β -CD in 2004 [173] The resolving power of persubstituted weak bases has a pronounced pH-dependence, as their degree of protonation can be varied sensitively in a larger pH interval The charge repulsion of the substituents can alter the shape of the CD cavity, influencing complexation, selectivity and affecting enantiomeric resolution as well [209] Moreover, at acidic pH values, the multiple positive charges present on the selector molecule promote its adsorption propensity to the capillary wall, leading to limited reproducibility These factors may be the reason of the scarcity of studies with persubstituted cationic CDs Although primary, secondary and tertiary amine functionalized CDs (with n-alkyl or cycloalkyl moieties on the nitrogen) not possess a pH-independent positive charge over the entire pH range, at pH was achieved in certain cases at 3.0 mM CD The hydrogen-bond-enhanced enantioseparation was supported by auxiliary NMR spectroscopic studies (see Fig 5) Both the number and the length of the alkyl substituents on the nitrogen turned out to influence significantly the chiral separation in a later study [212] Mono-6A -bis(2-hydroxyethyl)-1-ammoniumβ -CD chloride (BHEtAMCD), Mono-6A -tri(2-hydroxyethyl)-1ammonium-β -CD chloride (THEtAMCD), and mono-6A -bis(2methoxyethyl)-1-ammonium-β -CD chloride (BMEtAMCD) were first described as chiral selectors in CE Six carboxylic acid racemates were chosen as test analytes at different concentrations The results demonstrated, that with the increasing number of hydroxylalkyl groups at the N-atom, the chiral resolving power significantly declined, as the aqueous solubility of the derivatives deteriorated The best enantioseparation was achieved by mono6A -(3-hydroxypropyl)-1-ammonium-β -CD chloride (HPrAMCD) and MPrAMCD These CD derivatives were further investigated by NMR experiments using mandelic acid as a guest, proving that besides the inclusion complex formation, electrostatic attraction and hydrogen bonded interactions are also present as additional chiral driving forces A series of mono-6-pyrrolidinium-β -CD derivatives have been characterized as chiral selectors by Xiao et al [213,214] Originally, they have been synthesized to overcome analyte detection limit problems caused by the UV absorption of imidazoliumderivatized CDs A non-planar pyrrolidine ring or its derivative was attached to the primary side of β -CD [213] The first synthesized SID was mono-6A -(3R,4R-dihydroxypyrrolidinium)-β -CD chloride (dhypy-CDCl) for the enantioseparation of anionic and ampholytic acids A baseline resolution could be achieved for a mixture of five enantiomer pairs Although its analogue mono-6A -pyrrolidine-β CD chloride (pyCDCl) holds achiral center sidechain, it surprisingly ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, showed a higher selectivity and resolution The authors proposed the explanation that the two hydroxyl groups on the side-chain might produce a steric hindrance during chiral recognition, thus lowering the degree of complexation and the binding constant In another study, mono-6A -pyrrolidinium-β -CD chloride (pyCDCl), mono-6A -(N-methyl-pyrrolidinium)-β -CD chloride (N-CH3 pyCDCl), mono-6A -(N-(2-hydroxyethyl)-pyrrolidinium)-β -CD chloride (N-EtOH-pyCDCl), mono-6A -(2-hydroxymethyl-pyrrolidinium)β -CD chloride (2-MeOH-pyCDCl) were synthesized and explored for the enantioresolution of carboxylic acids, hydroxycarboxylic acids and Dns-AAs [214] Interestingly, the unsubstituted pyCDCl performed best The other three cationic CDs with N-alkyl substituents afforded higher anionic effective mobilities but much lower selectivity and resolution for most of the analytes Exceptions were Dns-Asp- and Dns-Glu, due the role of the carboxylic group in chiral recognition 3.3.2 Permanently positively charged SID derivatives In certain chiral CE separations, the appropriate protonation state of the analyte dictates the pH of the BGE In these cases, application of a permanently positively charged CD irrespective of pH may be beneficial during method development The permanently cationic derivatives can be categorized according to their charge numbers or the number of substituents The simplest and most widely employed members are the monosubstituted, monocationic CDs Additional charge can be either introduced on the same substituent, constituting the group of monosubstituted, dually cationic (or even multiple charged) derivatives or onto a different substituent forming the disubstituted, dicationic members In the recent literature, there is a trend for the synthesis of the latter group of SID selectors The ever-growing variety of cationic CD selectors is mainly built up of alkylimidazolium-derivatives, various types of alkyltriazolium derivatives and quaternary ammonium-CD derivatives Their counterion is generally chloride, coming synthetically from either a strong cation-exchanger resin or HCl salt formation, and this anion does not interfere with the detection In the literature of disubstituted cationic SIDs, a permanently cationic substituent is typically combined either with a protonable side-chain or with a non-basic substituent A series of permanently positively charged, novel SI α /β /γ CDs were synthesized by Popr et al., introducing one, two or three tetraalkylammonium groups on the primary side of the rim [215] However, only two of the prepared compounds were reported, the mono-6A -(N,N,N,N,N-pentamethyl-ethylene1,2-diammonium)-β -CD dichloride (PEMEDA-BCD) [216], which was previously prepared by Nzeadibe et al [217] and the newly synthesized mono-6A− (N,N,N,N,N-pentamethylpropylene-1,3diammonium)-β -CD (PEMPDA-BCD) [216] Both derivatives are dicationic compounds, bearing two quaternary ammonium groups in their sidechain They were tested as additives in BGE systems, including also an organic modifier Fourteen analytes including native amino acids, N-protected amino acids and profens were tested Both chiral selectors enabled the enantioseparation of N-Boc-D,Ltryptophan due to an favorable ionic interaction In the past few years, ionic-liquid functionalized CDs raised more attention in the field of enantioseparation Tang and Ong et al introduced a new family of mono-6-substituted-CDs as permanently positively charged chiral selectors in CE They synthesized and characterized the series of IL-functionalized SIDs, mono6A -(3-alkylimidazolium)-β -CDs with different chain-length CDs with a shorter alkyl chain (R = Cn H2 n +1, n ≤ 4) demonstrated a better resolution during the enantioseparation of Dns-AAs [218,219] In a recent study, Zhou et al used mono-6A -(3methylimidazolium)-β -CD tosylate (MIMCDOTs) for the separation and quantification of tetracyclines at the same time [220] (see 23 Table 3.) The cationic CD served simultaneously as electroosmotic flow modifier by coating the capillary wall and also as a resolving agent via inclusion complex formation with tetracyclines After the successful enhancement of chiral resolution of amino acids and hydroxyl acids by MPrAMCD compared to the PrAMCD exploiting the extra interaction provided by the methoxy group [210], mono-6A -methoxypropylimidazolium-β -CD chloride (MPrIMCD) and mono-6A -propylimidazolium-β -CD chloride (PrIMCD) were compared for the separation of eight Dns-AAs [221] The novel single isomer CD enhanced the interactions between the CD and the amino acids to afford better chiral resolutions in case of all the investigated AAs As a novel chiral selector, mono-6A -(1-allylimidazolium)-β -CD chloride (AllIm-β -CD) was introduced by Rizvi et al [222] Along with the native α -CD, β -CD and the randomly substituted HPBCD the derivative was investigated for the chiral separation of kynurenin from biological samples like urine and serum Both enantiomers have a role in the development of neurological diseases The authors revealed the synergetic effect of allIm-β -CD and α -CD leading to baseline separation, while these two CDs alone afforded no or only partial separation at lower concentration The cooperative effect was confirmed by molecular modeling (see Fig 6) The benefit of the dual system was outstanding at 7.4, when the dual system provided resolution of the two constituents In the study of Li et al., a novel IL amino triazolium functionalized SID, mono-6A -(4-amino-1,2,4-triazolium)-β -CD chloride (4ATMCDCl) was synthesized to separate dansyl amino acids and naproxen [223] Besides its permanent positive charge on the triazole ring, the amino substituent adds an adjustable positive charge to the selector A molecular modeling method was additionally applied, which demonstrated that amino triazolium could provide more additional interactions, such as π -π stacking, π -cation and hydrogen bonding, increasing the enantioselectivity towards the analytes A similar class of cationic CDs were synthesized by Boffa et al [224] They combined the advantages of CDs and ILs using the copper—catalyzed azide-alkyne cycloaddition applicability in CE was not explored, only one of the prepared compounds was investigated as a stationary phase in a later chiral GC study Similarly to 4-ATMCDCl, mono-6A -[3-(4-ammoniumbutyl)imidazol-1-ium]-β -CD chloride (AMBuIMCD) [225], reported by Zhou et al bears an additional adjustable charge besides its permanently positive imidazolium moiety, providing high aqueous solubility irrespectively to pH This SID provided good enantiomeric recognition towards Dns-AAs and acidic analytes, deprotonated at pH of the BGE Synthesis of two different sets of structurally analogous dicationic derivatives have also been reported mono-6A -[3-(4-ammoniumalkyl)-imidazol-1-ium]-β -CD chlorides and mono-6A -[3-(3-imidazolalkyl)-ammonium]-β -CD chlorides, with the chain lengths between and 6) The last decade witnesses a trend to synthesize multisubstituted SIDs for chiral CE separations Dai et al prepared a series of SID dicationic AC regioisomer CDs: mono-6A -ammonium-6C alkylimidazolium-β -CD chlorides [226] Although four derivatives with chain-lengths of 1–4 have been synthesized, only mono-6A ammonium-6C -butylimidazolium-β -CD chloride (AMBIMCD) was evaluated as a chiral selector towards Dns-AAs and acidic racemates [226,227] Seven out of eighteen studied analytes were baseline separated at 0.5 mM CD concentration At the same separation conditions, these dicationic CDs displayed better enantioseparations than their mono-imidazolium and mono-ammonium counterpart CDs In 2014 Tang et al synthesized two AC-regioisomer SIDs of β -CD, functionalized with methoxyalkylimidazolium and 4-(2-hydroxyethyl)-1,2,3-triazole to form mono-6A -4(2-hydroxyethyl)-1,2,3-triazole-6C -methoxyethylimidazolium-β -CD ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, 24 Fig (A) Separation of D, l-kynurenin (KYN) in α -CD/AllIm-β -CD dual selector system BGE: 50 mM borax borate buffer, pH 9.0 CE conditions: 15 kV, 50 mbar × s, 25 °C, λ= 226 nm, d-KYN, l-KYN 10 0 nM each (B) Synergetic effect of α -CD/AllIm-β -CD on the chiral separation of D,L-kynurenin Right: l-KYN/ α -CD/AllIm-β -CD Left: l-KYN/ α -CD/AllIm-β -CD The details of the separation mechanism were revealed by molecular docking and molecular mechanics Figure redrawn from Ref [222] chloride (HEtTrMEtIm-β -CD) and mono-6A -4-(2-hydroxyethyl)1,2,3-triazole-6C -methoxypropylimidazolium-β -CD chloride (HEtTrMPrIm-β -CD) [228] mono-6A -4-(2-hydroxyethyl)-1,2,3triazole-6C -3-methoxypropylimidazolium β -CD chloride was shown to separate Dns-amino acids and acidic enantiomers Compared to the aforementioned AC-regioisomers, the latter SID could achieve satisfactory enantioseparation in shorter time The third type of SID AC-regioisomer positively charged CD was reported by Zhou et al [229] As a new member of the AC disubstituted SID, mono-6A -4-(2-hydroxylethyl)-1,2,3-triazole6A -3-methoxypropylamino-β -CD (HETz-MPrAMCD) was compared to its monosubstituted counterpart, MPrAMCD, showing better enantioseparations for dansyl AAs at low concentrations 3.4 Zwitterionic CDs A new, inner-salt type 6-O-(2-hydroxyl-3-betainyl-propyl)- β -cyclodextrin (6-HBP-β -CD) was prepared by a ‘‘synthesis- deprotection one pot’’ method and this zwitterionic CD was found to be an efficient chiral selector in CCE comparing with native β CD and 2-HP-β -CD for drug racemates including chlorphenamine [233] An amino acid modified single isomer CD derivative, heptakis{2,6-di-O-[3-(1,3-dicarboxyl propylamino)−2hydroxypropyl]}-β -cyclodextrin (glutamic acid-β -cyclodextrin, glu-β -CD) was synthesized and used as a chiral selector in CE for the enantioseparation of 12 basic drugs [234] Glu-β -CD switches its charge state at the isoelectric point of the glutamic acid (pH 3.2), thus the effect of the BGE pH and the selector concentration was studied during the method optimization To confirm and explain the possible chiral recognition mechanism computational modeling strategy was used with three antihistamines Concluding remarks CCE has become an established and powerful analytical scale separation for enantiomers in pharmaceutical, agrochemical, cosmetic and food industries The multitude of experimental variables along with the possibility of solid physicochemical modeling of electromigration phenomena with predictive outcome makes this technique particularly attractive for easy and fit-for-purpose method development The most versatile and commonly used supramolecular selectors for the discrimination of enantiomers remain to be cyclodextrins, available now in a plethora of derivatives varying in positions, degrees and types of functionalization The structurally uniform single isomer cyclodextrins offer unique opportunities for in-depth, systematic studies of the structural aspects of the selector-analyte interactions in particular with NMR spectroscopy and molecular modeling, contributing to better understanding and experimental design of chiral CE separations Reviewing the past decade of this field emphasized the importance of CD structure-enantioresolution relationships to achieve previously unattained separations, including also specific combinations of CDs (dual systems), ligand-exchange metal-ion complexation, ionic liquids or micelles Capillary electrophoresis as the youngest member of the separation science family is flourishing for chiral separations, which is clearly attributed to the synthetic efforts leading to the huge variety of CD-based selectors reviewed herein ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, Declaration of Competing Interest None CRediT authorship contribution statement Ida Fejos: ˝ Writing - original draft, Supervision, Writing - review & editing Eszter Kalydi: Writing - review & editing, Visualization Milo Malanga: Writing - review & editing Gábor Benkovics: Writing - review & editing Szabolcs Béni: Conceptualization, Funding acquisition, Writing - review & editing Acknowledgements This work was partially supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences and by the Bolyai+ New National Excellence Program (grant number: ÚNKP19-4-SE-53) of the Ministry of Human Capacities References [1] J Szejtli, Introduction and general overview of cyclodextrin chemistry, Chem Rev 98 (1998) 1743–1753 https://doi.org/10.1021/cr970022c [2] B Chankvetadze, Separation selectivity in chiral capillary electrophoresis with charged selectors l, J Chromatogr A 792 (1997) 269–295 https://doi.org/10 1016/S0 021-9673(97)0 0752-8 [3] B Chankvetadze, Capillary Electrophoresis in Chiral Analysis, John Wiley, 1997 [4] S Fanali, B Chankvetadze, Some thoughts about enantioseparations in capillary electrophoresis, Electrophoresis 40 (2019) 2420–2437 https://doi.org/10 10 02/elps.20190 0144 [5] J.M Saz, M.L Marina, Recent advances on the use of cyclodextrins in the chiral analysis of drugs by capillary electrophoresis, J Chromatogr A 1467 (2016) 79–94 https://doi.org/10.1016/j.chroma.2016.08.029 [6] B Chankvetadze, Enantiomer migration order in chiral capillary electrophoresis, Electrophoresis 23 (2002) 4022–4035 https://doi.org/10.1002/ elps.20 0290 016 [7] A Salgado, B Chankvetadze, Applications of nuclear magnetic resonance spectroscopy for the understanding of enantiomer separation mechanisms in capillary electrophoresis, J Chromatogr A 1467 (2016) 95–144 https://doi.org/ 10.1016/j.chroma.2016.08.060 [8] A.V.-C.R.A Sci, undefined 1891, Sur la fermentation de la fécule par l’action du ferment butyrique, (n.d.) [9] E Gassmann, J.E Kuo, R.N Zare, Electrokinetic separation of chiral compounds, Science 230 (1985) 813–814 https://doi.org/10.1126/science.230.4727 813 [10] S Fanali, Separation of optical isomers by capillary zone electrophoresis based on host-guest complexation with cyclodextrins, J Chromatogr A 474 (1989) 441–446 https://doi.org/10.1016/S0021-9673(01)93941-X [11] S Terabe, Electrokinetic chromatography: an interface between electrophoresis and chromatography, Trends Anal Chem (1989) 129–134 https://doi org/10.1016/0165- 9936(89)85022- [12] J Snopek, I Jelínek, E Smolková-Keulemansová, Use of cyclodextrins in isotachophoresis IV The influence of cyclodextrins on the chiral resolution of ephedrine alkaloid enantiomers, J Chromatogr A 438 (1988) 211–218 https: //doi.org/10.1016/S0 021-9673(0 0)90251-6 [13] V Cucinotta, A Contino, A Giuffrida, G Maccarrone, M Messina, Application of charged single isomer derivatives of cyclodextrins in capillary electrophoresis for chiral analysis, J Chromatogr A 1217 (2010) 953–967 https: //doi.org/10.1016/j.chroma.2009.11.094 [14] B Chankvetadze, Separation of enantiomers with charged chiral selectors in CE, Electrophoresis 30 (2009) 211–221 https://doi.org/10.1002/elps 20 090 0102 [15] Q Zhu, G.K.E Scriba, Advances in the use of cyclodextrins as chiral selectors in capillary electrokinetic chromatography: fundamentals and applications, Chromatographia 79 (2016) 1403–1435 https://doi.org/10.1007/ s10337- 016- 3167- [16] J Bryan Vincent, A.D Sokolowski, T.V Nguyen, G Vigh, A family of singleisomer chiral resolving agents for capillary electrophoresis Heptakis(2,3diacetyl-6-sulfato)-β -cyclodextrin, Anal Chem 69 (1997) 4226–4233 https: //doi.org/10.1021/ac970252r [17] J.B Vincent, D.M Kirby, T.V Nguyen, G Vigh, A family of single-isomer chiral resolving agents for capillary electrophoresis Hepta-6-sulfatoβ -cyclodextrin, Anal Chem 69 (1997) 4419–4428 https://doi.org/10.1021/ ac970418o [18] H Cai, T.V Nguyen, G Vigh, A family of single-isomer chiral resolving agents for capillary electrophoresis Heptakis(2,3-dimethyl-6-sulfato)β -cyclodextrin, Anal Chem 70 (1998) 580–589 https://doi.org/10.1021/ ac970822n 25 [19] B.M Busby, G Vigh, Synthesis of heptakis(2-O-methyl-3-O-acetyl-6-O-sulfo)cyclomaltoheptaose, a single-isomer, sulfated β -cyclodextrin carrying nonidentical substitutents at all the C2, C3, and C6 positions and its use for the capillary electrophoretic separation of enantio, Electrophoresis 26 (2005) 1978–1987 https://doi.org/10.10 02/elps.20 050 057 [20] S Li, G Vigh, Single-isomer sulfated α -cyclodextrins for capillary electrophoresis Part Hexakis(6-O-sulfo)-α -cyclodextrin: synthesis, analytical characterization, and initial screening tests, Electrophoresis 25 (2004) 1201– 1210 https://doi.org/10.10 02/elps.20 0405863 [21] J.B Vincent, G Vigh, Nonaqueous capillary electrophoretic separation of enantiomers using the single-isomer heptakis(2,3-diacetyl-6-sulfato)-β cyclodextrin as chiral resolving agent, J Chromatogr A 816 (1998) 233–241 https://doi.org/10.1016/S0 021-9673(98)0 0489-0 [22] J Szejtli, Cyclodextrins and Their Inclusion Complexes, Akadémiai Kiadó, Budapest, 1982 [23] E Varga, G Benkovics, A Darcsi, B Várnai, T Sohajda, M Malanga, S Béni, Comparative analysis of the full set of methylated β -cyclodextrins as chiral selectors in capillary electrophoresis, Electrophoresis 40 (2019) 2789–2798 https://doi.org/10.10 02/elps.20190 0134 [24] L Jicsinszky, K Martina, M Caporaso, P Cintas, A Zanichelli, G Cravotto, Complexes of peracetylated cyclodextrin in a non-aqueous aprotic medium: the role of residual water, Phys Chem Chem Phys 17 (2015) 17380–17390 https://doi.org/10.1039/c5cp02379c [25] L Jicsinszky, M Caporaso, K Martina, E.C Gaudino, G Cravotto, Efficient mechanochemical synthesis of regioselective persubstituted cyclodextrins, Beilstein J Org Chem 12 (2016) 2364–2371 https://doi.org/10.3762/bjoc.12 230 [26] P Fügedi, Synthesis of heptakis(6-O-tert-butyldimethylsilyl)cyclomaltoheptaose and octakis(6-O-tert-butyldimethylsilyl)cyclomalto-octaose, Carbohydr Res 192 (1989) 366–369 https://doi.org/10.1016/0 08- 6215(89)85197- ˇ [27] M Rezanka, Monosubstituted Cyclodextrins as Precursors for Further Use, 2016, pp 5322–5334 https://doi.org/10.10 02/ejoc.20160 0693 [28] J Casas-solvas, M Malanga, A Vargas-Berenguel, Synthesis of 2I-Opropargylcyclomaltoheptaose and its peracetylated and hepta(6-O-silylated) derivatives, in: 2019 [29] G Benkovics, M Bálint, É Fenyvesi, E Varga, S Béni, K Yannakopoulou, M Malanga, Homo- and hetero-difunctionalized β -cyclodextrins: short direct synthesis in gram scale and analysis of regiochemistry, Beilstein J Org Chem 15 (2019) 710–720 https://doi.org/10.3762/bjoc.15.66 [30] K Takeo, H Mitoh, K Uemura, Selective chemical modification of cyclomaltooligosaccharides via tert-butyldimethylsilylation, Carbohydr Res 187 (1989) 203–221 https://doi.org/10.1016/0 08-6215(89)80 04-7 [31] G Uccello-Barretta, G Sicoli, F Balzano, P Salvadori, NMR spectroscopy: a powerful tool for detecting the conformational features of symmetrical persubstituted mixed cyclomaltoheptaoses (β -cyclodextrins), Carbohydr Res 340 (2005) 271–281 https://doi.org/10.1016/j.carres.2004.11.022 [32] M Bálint, A Darcsi, G Benkovics, E Varga, M Malanga, S Béni, Synthesis of the chiral selector heptakis(6-O-methyl)-β -cyclodextrin by phase-transfer catalysis and hydrazine-mediated transfer-hydrogenation, Electrophoresis 40 (2019) 1941–1950 https://doi.org/10.10 02/elps.20190 065 [33] M Yoshinaga, M Tanaka, Use of selectively methylated β -cyclodextrin derivatives in chiral separation of dansylamino acids by capillary zone electrophoresis, J Chromatogr A 679 (1994) 359–365 https://doi.org/10.1016/ 0021- 9673(94)80579- [34] M Yoshinaga, M Tanaka, Enantiomeric separation of dansylamino acids by capillary zone electrophoresis with selectively methylated γ -cyclodextrin derivatives, Anal Chim Acta 316 (1995) 121–127 https://doi.org/10.1016/ 0 03-2670(95)0 0341-V [35] M Miura, K Funazo, M Tanaka, Chiral separation of several naphthalenesulfonylamino acids by capillary zone electrophoresis with selectively methylated cyclodextrin derivatives, Anal Chim Acta 357 (1997) 177–185 https: //doi.org/10.1016/S0 03-2670(97)0 0586-2 [36] M Miura, K Kawamoto, K Funazo, M Tanaka, Chiral separation of several amino acid derivatives by capillary zone electrophoresis with selectively acetylated β -cyclodextrin derivatives, Anal Chim Acta 373 (1998) 47–56 https://doi.org/10.1016/S0 03-2670(98)0 0396-1 [37] M Miura, Y Terashita, K Funazo, M Tanaka, Chiral separation of naphthoylamino acids by capillary zone electrophoresis with selectively methylated cyclodextrin derivatives, Anal Sci 15 (1999) 299–302 https://doi.org/10.2116/ analsci.15.299 [38] M Miura, Y Terashita, K Funazo, M Tanaka, Separation of phenoxy acid herbicides and their enantiomers in the presence of selectively methylated cyclodextrin derivatives by capillary zone electrophoresis, J Chromatogr A 846 (1999) 359–367 https://doi.org/10.1016/S0 021-9673(99)0 0285-X ´ [39] W Maruszak, M Trojanowicz, M Margasinska, H Engelhardt, Application of carboxymethyl-β -cyclodextrin as a chiral selector in capillary electrophoresis for enantiomer separation of selected neurotransmitters, J Chromatogr A 926 (2001) 327–336 https://doi.org/10.1016/S0021-9673(01)01076-7 [40] B Chankvetadze, N Burjanadze, G Pintore, D Strickmann, D Bergenthal, G Blaschke, Chiral recognition of verapamil by cyclodextrins studied with capillary electrophoresis, NMR spectroscopy, and electrospray ionization mass spectrometry, Chirality 11 (1999) 635–644 https://doi.org/10.1002/(SICI)1520-636X(1999)11:83.0.CO;2-D [41] B Chankvetadze, N Burjanadze, G Pintore, D Bergenthal, K Bergander, C Mühlenbrock, J Breitkreuz, G Blaschke, Separation of brompheniramine enantiomers by capillary electrophoresis and study of chiral recog- 26 [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, nition mechanisms of cyclodextrins using NMR-spectroscopy, UV spectrometry, electrospray ionization mass spectrometry and X-ray crystallography, J Chromatogr A 875 (20 0) 471–484 https://doi.org/10.1016/S0 021-9673(0 0) 00153-9 B Chankvetadze, G Pintore, N Burjanadze, D Bergenthal, K Bergander, J Breitkreuz, C Mühlenbrock, G Blaschke, Mechanistic study of opposite migration order of dimethindene enantiomers in capillary electrophoresis in the presence of native β -cyclodextrin and heptakis(2,3,6-tri-O-methyl)-β cyclodextrin, J Chromatogr A 875 (20 0) 455–469 https://doi.org/10.1016/ S0 021-9673(0 0)0 0146-1 G.K.E Scriba, Recent advances in enantioseparations of peptides by capillary electrophoresis, Electrophoresis 24 (2003) 4063–4077 https://doi.org/10 10 02/elps.20 0305657 S Krait, A Salgado, B Chankvetadze, F Gago, G.K.E Scriba, Investigation of the complexation between cyclodextrins and medetomidine enantiomers by capillary electrophoresis, NMR spectroscopy and molecular modeling, J Chromatogr A 1567 (2018) 198–210 https://doi.org/10.1016/j.chroma.2018.06.010 U Schmitt, M Ertan, U Holzgrabe, Chiral capillary electrophoresis: facts and fiction on the reproducibility of resolution with randomly substituted cyclodextrins, Electrophoresis 25 (2004) 2801–2807 https://doi.org/10.1002/ elps.200405932 H Harnisch, I Ilisz, F Fülöp, Z Szakonyi, L Kiss, A Péter, G.K.E Scriba, Cyclodextrin-mediated capillary electrophoresis enantioseparation of dansylated β -amino acids with bicyclo[2.2.2]octane, bicyclo[3.1.1]heptane and cyclopenta[d][1,2]oxazole core structures, Electrophoresis 40 (2019) 1931–1940 https://doi.org/10.10 02/elps.20180 0492 A Salgado, E Tatunashvili, A Gogolashvili, B Chankvetadze, F Gago, Structural rationale for the chiral separation and migration order reversal of clenpenterol enantiomers in capillary electrophoresis using two different β cyclodextrins, Phys Chem Chem Phys 19 (2017) 27935–27939 https://doi org/10.1039/c7cp04761d B Chankvetadze, K Lomsadze, N Burjanadze, J Breitkreutz, G Pintore, M Chessa, K Bergander, G Blaschke, Comparative enantioseparations with native β -cyclodextrin, randomly acetylated β -cyclodextrin and heptakis-(2,3di-O-acetyl β -cyclodextrin in capillary electrophoresis, Electrophoresis 24 (2003) 1083–1091 https://doi.org/10.10 02/elps.20 0390126 S.K Branch, U Holzgrabe, T.M Jefferies, H Mallwitz, M.W Matchett, Chiral discrimination of phenethylamines with β -cyclodextrin and heptakis(2,3di-O-acetyl)β -cyclodextrin by capillary electrophoresis and NMR spectroscopy, J Pharm Biomed Anal 12 (1994) 1507–1517 https://doi.org/10 1016/0731-7085(94)0 080-8 S.K Branch, U Holzgrabe, T.M Jefferies, H Mallwitz, F.J.R Oxley, Effect of β cyclodextrin acetylation on the resolution of phenethylamines with capillary electrophoresis and nuclear magnetic resonance spectroscopy, J Chromatogr A 758 (1997) 277–292 https://doi.org/10.1016/S0 021-9673(96)0 0734-0 M Thunhorst, Y Otte, T.M Jefferies, S.K Branch, U Holzgrabe, Effect of various cyclodextrin derivatives on the resolution of fencamfamine isomers with capillary electrophoresis and nuclear magnetic resonance, J Chromatogr A 818 (1998) 239–249 https://doi.org/10.1016/S0 021-9673(98)0 0562-7 M Wedig, U Holzgrabe, Resolution of ephedrine derivatives by means of neutral and sulfated heptakis(2,3-di-O-acetyl)β -cyclodextrins using capillary electrophoresis and nuclear magnetic resonance spectroscopy, Electrophoresis 20 (1999) 2698–2704 https://doi.org/10.1002/ (SICI)1522-2683(19990901)20:133.0.CO;2-N C Hellriegel, H Händel, M Wedig, S Steinhauer, F Sörgel, K Albert, U Holzgrabe, Study on the chiral recognition of the enantiomers of ephedrine derivatives with neutral and sulfated heptakis(2,3-O-diacetyl)-β -cyclodextrins using capillary electrophoresis, UV, nuclear magnetic resonance spectroscopy and mass spectrometry, J Chromatogr A 914 (2001) 315–324 https://doi.org/ 10.1016/S0 021-9673(0 0)01015-3 U Schmitt, J Bojarski, U Holzgrabe, Enantioseparation of chiral thiobarbiturates using cyclodextrin-modified capillary electrophoresis, Electrophoresis 22 (2001) 3237–3242 https://doi.org/10.1002/ 1522-2683(200109)22:153.0.CO;2-N F Süß, C Kahle, U Holzgrabe, G.K.E Scriba, Studies on the chiral recognition of peptide enantiomers by neutral and sulfated β -cyclodextrin and heptakis-(2,3-di-O-acetyl)-β -cyclodextrin using capillary electrophoresis and nuclear magnetic resonance, Electrophoresis 23 (2002) 1301–1307 https:// doi.org/10.1002/1522-2683(200205)23:93.0.CO;2-7 ˝ E Varga, G Benkovics, A Darcsi, M Malanga, É Fenyvesi, T SohaI Fejos, jda, L Szente, S Béni, Comparative evaluation of the chiral recognition potential of single-isomer sulfated beta-cyclodextrin synthesis intermediates in non-aqueous capillary electrophoresis, J Chromatogr A 1467 (2016) 454–462 https://doi.org/10.1016/j.chroma.2016.07.033 A.C Servais, M Fillet, R Mol, A Rousseau, J Crommen, G.W Somsen, G.J De Jong, Influence of the BGE composition on analyte response in CD-mediated NACE-MS, Electrophoresis 31 (2010) 1157–1161 https://doi.org/10.1002/elps 20 090 0649 K Lomsadze, A Salgado, E Calvo, J Antonio López, B Chankvetadze, Comparative NMR and MS studies on the mechanism of enantioseparation of propranolol with heptakis(2,3-diacetyl-6-sulfo)-β -cyclodextrin in capillary electrophoresis with aqueous and non-aqueous electrolytes, Electrophoresis 32 (2011) 1156–1163 https://doi.org/10.1002/elps.201000672 L Chankvetadze, A.C Servais, M Fillet, A Salgado, J Crommen, B Chankvetadze, Comparative enantioseparation of talinolol in aqueous and nonaqueous capillary electrophoresis and study of related selector-selectand in- [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] teractions by nuclear magnetic resonance spectroscopy, J Chromatogr A 1267 (2012) 206–216 https://doi.org/10.1016/j.chroma.2012.08.063 Y Liu, S.A Shamsi, Combined use of chiral ionic liquid surfactants and neutral cyclodextrins: evaluation of ionic liquid head groups for enantioseparation of neutral compounds in capillary electrophoresis, J Chromatogr A 1360 (2014) 296–304 https://doi.org/10.1016/j.chroma.2014.07.047 B Wang, J He, V Bianchi, S.A Shamsi, Combined use of chiral ionic liquid and cyclodextrin for MEKC: Part I Simultaneous enantioseparation of anionic profens, Electrophoresis 30 (2009) 2812–2819 https://doi.org/10.1002/ elps.20 080 0851 M.C Mavroudi, C.P Kapnissi-Christodoulou, Combined use of l-alanine tert butyl ester lactate and trimethyl-β -cyclodextrin for the enantiomeric separations of 2-arylpropionic acids nonsteroidal anti-inflammatory drugs, Electrophoresis 36 (2015) 2442–2450 https://doi.org/10.10 02/elps.20150 0143 E Varga, G Benkovics, A Darcsi, B Várnai, T Sohajda, M Malanga, S Béni, Comparative analysis of the full set of methylated β -cyclodextrins as chiral selectors in capillary electrophoresis, 40 (2019) 2789–2798 https://doi.org/ 10.10 02/elps.20190 0134 ˇ P Rezanka, D Sýkora, M Novotný, M Havlík, V Král, Nonaqueous capillary electrophoretic enantioseparation of water insoluble tröger’s base derivatives using β -cyclodextrin as chiral selector, Chirality 25 (2013) 810–813 https:// doi.org/10.1002/chir.22220 W.A.W Ibrahim, S.R Arsad, H Maarof, M.M Sanagi, H.Y Aboul-Enein, Chiral separation of four stereoisomers of ketoconazole drugs using capillary electrophoresis, Chirality 27 (2015) 223–227 https://doi.org/10.1002/chir.22416 P Dubský, M Ưrdưgová, M Malý, M Riesová, CEval: all-in-one software for data processing and statistical evaluations in affinity capillary electrophoresis, J Chromatogr A 1445 (2016) 158–165 https://doi.org/10.1016/j.chroma.2016 04.004 E.D Vega, K Lomsadze, L Chankvetadze, A Salgado, G.K.E Scriba, E Calvo, J.A López, A.L Crego, M.L Marina, B Chankvetadze, Separation of enantiomers of ephedrine by capillary electrophoresis using cyclodextrins as chiral selectors: comparative CE, NMR and high resolution MS studies, Electrophoresis 32 (2011) 2640–2647 https://doi.org/10.1002/elps.20110 015 A Gogolashvili, E Tatunashvili, L Chankvetadze, T Sohajda, J Szeman, A Salgado, B Chankvetadze, Separation of enilconazole enantiomers in capillary electrophoresis with cyclodextrin-type chiral selectors and investigation of structure of selector-selectand complexes by using nuclear magnetic resonance spectroscopy, Electrophoresis 38 (2017) 1851–1859 https://doi.org/10 10 02/elps.20170 078 A Gogolashvili, E Tatunashvili, L Chankvetadze, T Sohajda, J Szeman, M Gumustas, S.A Ozkan, A Salgado, B Chankvetadze, Separation of terbutaline enantiomers in capillary electrophoresis with cyclodextrin-type chiral selectors and investigation of structure of selector-selectand complexes, J Chromatogr A 1571 (2018) 231–239 https://doi.org/10.1016/j.chroma.2018.08.012 A.C Servais, A Rousseau, M Fillet, K Lomsadze, A Salgado, J Crommen, B Chankvetadze, Capillary electrophoretic and nuclear magnetic resonance studies on the opposite affinity pattern of propranolol enantiomers towards various cyclodextrins, J Sep Sci 33 (2010) 1617–1624 https://doi.org/10.1002/ jssc.2010 0 040 K Lomsadze, E.D Vega, A Salgado, A.L Crego, G.K.E Scriba, M.L Marina, B Chankvetadze, Separation of enantiomers of norephedrine by capillary electrophoresis using cyclodextrins as chiral selectors: comparative CE and NMR studies, Electrophoresis 33 (2012) 1637–1647 https://doi.org/10.1002/ elps.20120 062 H Krajian, N Mofaddel, D Villemin, P.L Desbène, A new example of reversal of the order of migration of enantiomers, as a function of cyclodextrin concentration and pH, by cyclodextrin-modified capillary zone electrophoresis: enantioseparation of 6,6-binaphthyl-2,2-diol, Anal Bioanal Chem 394 (2009) 2193–2201 https://doi.org/10.10 07/s0 0216-0 09-2925-3 C Li, Y Jiang, Analysis of repaglinide enantiomers in pharmaceutical formulations by capillary electrophoresis using 2,6-di-o-methyl-β -cyclodextrin as a chiral selector, J Chromatogr Sci 50 (2012) 739–743 https://doi.org/10.1093/ chromsci/bms064 W.A Wan Ibrahim, S.M Abd Wahib, D Hermawan, M.M Sanagi, H.Y AboulEnein, Separation of selected imidazole enantiomers using dual cyclodextrin system in micellar electrokinetic chromatography, Chirality 25 (2013) 328– 335 https://doi.org/10.1002/chir.22156 W.A.W Ibrahim, S.M.A Wahib, D Hermawan, M.M Sanagi, H.Y Aboul-Enein, Chiral separation of vinpocetine using cyclodextrin-modified micellar electrokinetic chromatography, Chirality 24 (2012) 252–254 https://doi.org/10 1002/chir.21990 H Harnisch, G.K.E Scriba, Capillary electrophoresis method for the determination of (R)-dapoxetine, (3S)-3-(dimethylamino)-3-phenyl-1-propanol, (S)-3amino-3-phenyl-1-propanol and 1-naphthol as impurities of dapoxetine hydrochloride, J Pharm Biomed Anal 162 (2019) 257–263 https://doi.org/10 1016/j.jpba.2018.09.039 M Wang, Z Cai, L Xu, Coupling of acetonitrile deproteinization and saltingout extraction with acetonitrile stacking in chiral capillary electrophoresis for the determination of warfarin enantiomers, J Chromatogr A 1218 (2011) 4045–4051 https://doi.org/10.1016/j.chroma.2011.04.067 T Sohajda, S Béni, E Varga, R Iványi, Á Rácz, L Szente, B Noszál, Characterization of aspartame-cyclodextrin complexation, J Pharm Biomed Anal 50 (2009) 737–745 https://doi.org/10.1016/j.jpba.2009.06.010 S Béni, T Sohajda, G Neumajer, R Iványi, L Szente, B Noszál, Separation and characterization of modified pregabalins in terms of cyclodextrin com- ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] plexation, using capillary electrophoresis and nuclear magnetic resonance, J Pharm Biomed Anal 51 (2010) 842–852 https://doi.org/10.1016/j.jpba.2009 10.010 Y.T Chang, Z.R Wang, M.M Hsieh, Sensitive determination of warfarin and its metabolic enantiomers in body fluids via capillary electrophoresis combined with ultrasound-assisted dispersive liquid-liquid microextraction and online sample stacking, Microchem J 146 (2019) 1276–1284 https://doi.org/10.1016/ j.microc.2019.02.065 L Burrai, M Nieddu, M.A Pirisi, A Carta, I Briguglio, G Boatto, Enantiomeric separation of 13 new amphetamine-like designer drugs by capillary electrophoresis, using modified–cyclodextrins, Chirality 25 (2013) 617–621 https: //doi.org/10.1002/chir.22185 T Mantim, D Nacapricha, P Wilairat, P.C Hauser, Enantiomeric separation of some common controlled stimulants by capillary electrophoresis with contactless conductivity detection, Electrophoresis 33 (2012) 388–394 https: //doi.org/10.1002/elps.201100370 M Cârcu-Dobrin, M Buda˘ u, G Hancu, L Gagyi, A Rusu, H Kelemen, Enantioselective analysis of fluoxetine in pharmaceutical formulations by capillary zone electrophoresis, Saudi Pharm J 25 (2017) 397–403 https://doi.org/10 1016/j.jsps.2016.09.007 B Zhu, S Xu, X Guo, L Wei, J Yu, T Wang, Use of various β -cyclodextrin derivatives as chiral selectors for the enantiomeric separation of ofloxacin and its five related substances by capillary electrophoresis, J Sep Sci 40 (2017) 1784–1795 https://doi.org/10.1002/jssc.201601403 J Svobodová, P Dubský, E Tesarˇová, M Beneš, B Gaš, Methods for determination of all binding parameters in systems with simultaneous borate and cyclodextrin complexation, J Chromatogr A 1218 (2011) 7211–7218 https: //doi.org/10.1016/j.chroma.2011.07.088 B Jamali, I Bjørnsdottir, C Cornett, S.H Hansen, Investigation of a dual CD chiral CE system for separation of glitazone compounds, Electrophoresis 30 (2009) 2853–2861 https://doi.org/10.1002/elps.200800812 M Hammitzsch-Wiedemann, G.K.E.E Scriba, Effect of urea on analyte complexation by 2,6-dimethyl-β -CD in peptide enantioseparations by CE, Electrophoresis 30 (2009) 3764–3771 https://doi.org/10.1002/elps.200900384 C Borst, U Holzgrabe, Comparison of chiral electrophoretic separation methods for phenethylamines and application on impurity analysis, J Pharm Biomed Anal 53 (2010) 1201–1209 https://doi.org/10.1016/j.jpba.2010.06.025 Z.R Wang, M.M Hsieh, Ultrasound-assisted dispersive liquid–liquid microextraction coupled with field-amplified capillary electrophoresis for sensitive and quantitative determination of fluoxetine and norfluoxetine enantiomers in biological fluids, Anal Bioanal Chem (2020) 1–11 https://doi.org/10.1007/ s00216- 020- 02441- x M Wang, J Guo, Z Wang, G Zhang, H Yu, R Chang, A Chen, Simultaneous separation and determination of hirsutine and hirsuteine by cyclodextrinmodified micellar electrokinetic capillary chromatography, Phytochem Anal 31 (2020) 112–118 https://doi.org/10.1002/pca.2871 F Melani, I Giannini, B Pasquini, S Orlandini, S Pinzauti, S Furlanetto, Evaluation of the separation mechanism of electrokinetic chromatography with a microemulsion and cyclodextrins using NMR and molecular modeling, Electrophoresis 32 (2011) 3062–3069 https://doi.org/10.1002/elps.201100263 M Riesová, J Svobodová, K Ušelová, Z Tošner, I Zusková, B Gaš, Determination of thermodynamic values of acidic dissociation constants and complexation constants of profens and their utilization for optimization of separation conditions by Simul Complex, J Chromatogr A 1364 (2014) 276–288 https://doi.org/10.1016/j.chroma.2014.08.070 S Samakashvili, A Salgado, G.K.E Scriba, B Chankvetadze, Comparative enantioseparation of ketoprofen with trimethylated α -, β -, and γ -cyclodextrins in capillary electrophoresis and study of related selector-selectand interactions using nuclear magnetic resonance spectroscopy, Chirality 25 (2013) 79–88 https://doi.org/10.1002/chir.22111 J Petr, P Ginterová, J Znaleziona, R Knob, M Lošåáková, V Maier, J Ševcˇ ík, Separation of ketoprofen enantiomers at nanomolar concentration levels by micellar electrokinetic chromatography with on-line electrokinetic preconcentration, Cent Eur J Chem 11 (2013) 335–340 https://doi.org/10.2478/ s11532- 012- 0177- S Kodama, A Taga, S Aizawa, T Kemmei, Y Honda, K Suzuki, A Yamamoto, Direct enantioseparation of lipoic acid in dietary supplements by capillary electrophoresis using trimethyl-β -cyclodextrin as a chiral selector, Electrophoresis 33 (2012) 24412445 https://doi.org/10.1002/elps.201100531 Luciana Pereira Lourenỗo, Fernando Armani Aguiar, Anderson Rodrigo Moraes de Oliveira, Cristiane Masetto de Gaitani, Quantitative determination of lercanidipine enantiomers in commercial formulations by capillary electrophoresis, J Anal Methods Chem (2015) https://pubmed.ncbi.nlm.nih.gov/ 25821632/ (accessed May 9, 2020) A.C Servais, M Fillet, Application of dual cyclodextrin systems in capillary electrophoresis enantioseparations, Methods Mol Biol 970 (2013) 289–295 https://doi.org/10.1007/978- 1- 62703- 263- 6_18 L Müllerová, P Dubský, M Ưrdưgová, B Gaš, Determination of relative enantiomer migration order using a racemic sample, J Chromatogr A 1424 (2015) 139–143 https://doi.org/10.1016/j.chroma.2015.10.058 Y.J Lee, S Choi, J Lee, N.T Nguyen, K Lee, J.S Kang, W Mar, K.H Kim, Chiral discrimination of sibutramine enantiomers by capillary electrophoresis and proton nuclear magnetic resonance spectroscopy, Arch Pharm Res 35 (2012) 671–681 https://doi.org/10.1007/s12272-012-0411-5 Y Jin, C Chen, L Meng, J Chen, M Li, Z Zhu, Simultaneous and sensitive capillary electrophoretic enantioseparation of three β -blockers with the combi- [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] 27 nation of achiral ionic liquid and dual CD derivatives, Talanta 89 (2012) 149– 154 https://doi.org/10.1016/j.talanta.2011.12.005 K Németh, G Tárkányi, E Varga, T Imre, R Mizsei, R Iványi, J Visy, J Szemán, L Jicsinszky, L Szente, M Simonyi, Enantiomeric separation of antimalarial drugs by capillary electrophoresis using neutral and negatively charged cyclodextrins, J Pharm Biomed Anal 54 (2011) 475–481 https: //doi.org/10.1016/j.jpba.2010.09.020 ˝ G Tárkányi, K Németh, R Mizsei, O Toke, J Visy, M Simonyi, L Jicsinszky, J Szemán, L Szente, Structure and stability of warfarin-sodium inclusion complexes formed with permethylated monoamino-β -cyclodextrin 2, n.d Z.I Szabó, G Tóth, G Vưlgyi, B Komjáti, G Hancu, L Szente, T Sohajda, S Béni, D.L Muntean, B Noszál, Chiral separation of asenapine enantiomers by capillary electrophoresis and characterization of cyclodextrin complexes by NMR spectroscopy, mass spectrometry and molecular modeling, J Pharm Biomed Anal 117 (2016) 398–404 https://doi.org/10.1016/j.jpba.2015 09.022 N Casado, J.M Saz, M.Á García, M.L Marina, Modeling-based optimization of the simultaneous enantiomeric separation of multicomponent mixtures of phenoxy acid herbicides using dual cyclodextrin systems by Capillary Electrophoresis, J Chromatogr A 1610 (2019) 460552 https://doi.org/10.1016/j chroma.2019.460552 J Yu, Y Zhao, J Song, X Guo, Enantioseparation of meptazinol and its three intermediate enantiomers by capillary electrophoresis using a new cationic β -cyclodextrin derivative in single and dual cyclodextrin systems, Biomed Chromatogr 28 (2014) 868–874 https://doi.org/10.1002/bmc.3187 T.L Amorim, L.M Duarte, H.F Dos Santos, M.A.L de Oliveira, Screening method for simultaneous detection of elaidic and vaccenic trans fatty acid isomers by capillary zone electrophoresis, Anal Chim Acta 1048 (2019) 212– 220 https://doi.org/10.1016/j.aca.2018.10.057 ´ M Wozniakiewicz, M Gładysz, P.M Nowak, J Kedzior, ˛ P Kos´ cielniak, Separation of 20 coumarin derivatives using the capillary electrophoresis method optimized by a series of Doehlert experimental designs, Talanta 167 (2017) 714–724 https://doi.org/10.1016/j.talanta.2017.02.017 M Lecoeur-Lorin, R Delépée, P Morin, Sensitivity improvement by using contactless conductivity rather than indirect UV detection for the determination of enantiomeric purity of amines by CE, Electrophoresis 30 (2009) 487–498 https://doi.org/10.10 02/elps.20 080 0316 A Gogolashvili, L Chankvetadze, N Takaishvili, A Salgado, B Chankvetadze, Separation of terbutaline enantiomers in capillary electrophoresis with neutral cyclodextrin-type chiral selectors and investigation of the structure of selector-selectand complexes using nuclear magnetic resonance spectroscopy, Electrophoresis (2020) elps.2020 0 010 https://doi.org/10.1002/elps 2020 0 010 B Chankvetadze, Separation of enantiomers with charged chiral selectors in CE, Electrophoresis 30 (2009) https://doi.org/10.10 02/elps.20 090 0102 B.A Williams, G Vigh, Dry look at the CHARM (charged resolving agent migration) model of enantiomer separations by capillary electrophoresis, J Chromatogr A 777 (1997) 295–309 https://doi.org/10.1016/S0021-9673(97) 00424-X Z Wang, Q Zhang, L Luo, T Sun, X Guo, Comparison of three S-β -CDs with different degrees of substitution for the chiral separation of 12 drugs in capillary electrophoresis, Chirality 29 (2017) 558–565 https://doi.org/10.1002/chir 22731 C.E.C.H Lin, T.C Ko, C.M Kuo, O Trapp, W.Y Lin, C.E.C.H Lin, J.C Wu, Y.C Liu, Determination of enantiomerization barrier of thioridazine by dynamic capillary electrophoresis using sulfated cyclodextrins as chiral selectors, Electrophoresis 30 (2009) 3071–3078 https://doi.org/10.1002/elps.200900160 P Dubský, J Svobodová, E Tesarˇová, B Gaš, Enhanced selectivity in CZE multi-chiral selector enantioseparation systems: proposed separation mechanism, Electrophoresis 31 (2010) 1435–1441 https://doi.org/10.1002/elps 20 090 0742 M.G Vargas-Martínez, G Ramírez-Galicia, Molecular modeling and chiral separation of benzodiazepines by capillary electrophoresis using highly sulfated cyclodextrins, J Mex Chem Soc (2018) 62 https://doi.org/10.29356/jmcs v62i2.413 A Rousseau, P Chiap, R Oprean, J Crommen, M Fillet, A.C Servais, Effect of the nature of the single-isomer anionic CD and the BGE composition on the enantiomeric separation of β -blockers in NACE, Electrophoresis 30 (2009) 2862–2868 https://doi.org/10.10 02/elps.20 080 0824 N.G Kokiashvili, S Wongwan, C Landgraf, K Michaelis, M HammitzschWiedemann, G.K.E Scriba, Profiling of levoamphetamine and related substances in dexamphetamine sulfate by capillary electrophoresis, J Pharm Biomed Anal 50 (2009) 1050–1053 https://doi.org/10.1016/j.jpba.2009.06 018 Y Yao, P Song, X Wen, M Deng, J Wang, X Guo, Chiral separation of 12 pairs of enantiomers by capillary electrophoresis using heptakis-(2,3-diacetyl6-sulfato)-β -cyclodextrin as the chiral selector and the elucidation of the chiral recognition mechanism by computational methods, J Sep Sci 40 (2017) 2999–3007 https://doi.org/10.1002/jssc.201700137 A Rousseau, X Florence, B Pirotte, A Varenne, P Gareil, D Villemin, P Chiap, J Crommen, M Fillet, A.C Servais, Development and validation of a nonaqueous capillary electrophoretic method for the enantiomeric purity determination of a synthetic intermediate of new 3,4-dihydro-2,2-dimethyl-2H-1benzopyrans using a single-isomer anionic cyclodextrin derivative and an, J Chromatogr A 1217 (2010) 7949–7955 https://doi.org/10.1016/j.chroma.2010 07.005 28 ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, [120] A Rousseau, F Gillotin, P Chiap, J Crommen, M Fillet, A.C Servais, Association of two single-isomer anionic CD in NACE for the chiral and achiral separation of fenbendazole, its sulphoxide and sulphone metabolites: application to their determination after in vitro metabolism, Electrophoresis 31 (2010) 1482–1487 https://doi.org/10.10 02/elps.20 090 0723 [121] K Michalska, G Pajchel, S Tyski, Determination of enantiomeric impurity of linezolid by capillary electrophoresis using heptakis-(2,3-diacetyl-6-sulfato)β -cyclodextrin, J Chromatogr A 1180 (2008) 179–186 https://doi.org/10.1016/ j.chroma.2007.11.110 [122] K Michalska, E Gruba, J Cielecka-Piontek, E Bednarek, Chiral separation of tedizolid using charge single isomer derivatives of cyclodextrins by capillary electrokinetic chromatography, J Pharm Biomed Anal 120 (2016) 402–412 https://doi.org/10.1016/j.jpba.2015.11.022 [123] K Michalska, E Gruba, W Bocian, J Cielecka-Piontek, Enantioselective recognition of radezolid by cyclodextrin modified capillary electrokinetic chromatography and electronic circular dichroism, J Pharm Biomed Anal 139 (2017) 98–108 https://doi.org/10.1016/j.jpba.2017.01.041 [124] K Michalska, W Bocian, E Bednarek, B Pałys, J Cielecka-Piontek, Enantioselective recognition of sutezolid by cyclodextrin modified non-aqueous capillary electrophoresis and explanation of complex formation by means of infrared spectroscopy, NMR and molecular modelling, J Pharm Biomed Anal 169 (2019) 49–59 https://doi.org/10.1016/j.jpba.2019.02.033 [125] A.C Servais, A Rousseau, M Fillet, K Lomsadze, A Salgado, J Crommen, B Chankvetadze, Separation of propranolol enantiomers by CE using sulfated β -CD derivatives in aqueous and non-aqueous electrolytes: comparative CE and NMR study, Electrophoresis 31 (2010) 1467–1474 https://doi.org/10.1002/ elps.20 090 0738 [126] A.C Servais, A Rousseau, G Dive, M Frederich, J Crommen, M Fillet, Combination of capillary electrophoresis, molecular modelling and nuclear magnetic resonance to study the interaction mechanisms between single-isomer anionic cyclodextrin derivatives and basic drug enantiomers in a methanolic background electrolyte, J Chromatogr A 1232 (2012) 59–64 https://doi.org/ 10.1016/j.chroma.2011.10.010 [127] Y Feng, T Wang, Z Jiang, B Chankvetadze, J Crommen, Comparative enantiomer affinity pattern of β -blockers in aqueous and nonaqueous CE using single-component anionic cyclodextrins, Electrophoresis 36 (2015) 1358–1364 https://doi.org/10.10 02/elps.20140 0462 [128] J Guo, J Wang, H Lin, Y Feng, H Shen, R Huang, L Liu, Z Zhao, Combination of capillary electrophoresis and molecular modeling to study the enantiomer affinity pattern between β -blockers and anionic cyclodextrin derivatives in a methanolic and water background electrolyte, J Sep Sci 42 (2019) 1077– 1087 https://doi.org/10.10 02/jssc.20180 0884 [129] S Li, G Vigh, Synthesis, analytical characterization and initial capillary electrophoretic use in acidic background electrolytes of a new, single-isomer chiral resolving agent: hexakis (2,3-di-O-acetyl-6-O-sulfo)-α -cyclodextrin, Electrophoresis 24 (2003) 2487–2498 https://doi.org/10.10 02/elps.20 0305509 [130] S Li, G Vigh, Single-isomer sulfated α -cyclodextrins for capillary electrophoresis: hexakis(2,3-di-O-methyl-6-O-sulfo)-α -cyclodextrin, synthesis, analytical characterization, and initial screening tests, Electrophoresis 25 (2004) 2657–2670 https://doi.org/10.1002/elps.200405839 [131] C.E Lin, S.L Lin, I.J Fang, W.S Liao, C.C Chen, Enantioseparations of hydrobenzoin and structurally related compounds in capillary zone electrophoresis using heptakis(2,3-dihydroxy-6-O-sulfo)-β -cyclodextrin as chiral selector and enantiomer migration reversal of hydrobenzoin with a dual cyclodextrin system in the presence of borate complexation, Electrophoresis 25 (2004) 2786–2795 https://doi.org/10.10 02/elps.20 0405968 [132] W Zhu, G Vigh, A family of single-isomer, sulfated γ -cyclodextrin chiral resolving agents for capillary electrophoresis: octa(6-O-sulfo)-γ -cyclodextrin, Electrophoresis 24 (2003) 130–138 https://doi.org/10.1002/elps.200390005 [133] W Zhu, G Vigh, Capillary electrophoretic separation of enantiomers in a high-pH background electrolyte by means of the single-isomer chiral resolving agent octa(6-O-sulfo)-γ -cyclodextrin, J Chromatogr A (2003) 459–466 https://doi.org/10.1016/S0021-9673(02)01822-8 [134] W Zhu, G Vigh, A family of single-isomer, sulfated γ -cyclodextrin chiral resolving agents for capillary electrophoresis Octakis(2,3-diacetyl-6sulfato)-γ - cyclodextrin, Anal Chem 72 (20 0) 310–317 https://doi.org/10 1021/ac991039t [135] W Zhu, G Vigh, Capillary electrophoretic separation of the enantiomers of weak acids in a high pH background electrolyte using the new, single-isomer, octakis(2,3-diacetyl-6-sulfato)-γ -cyclodextrin as chiral resolving agent, J Microcolumn Sep 12 (20 0) 167–171 https://doi.org/10.1002/(SICI)1520-667X(2000)12:33.0.CO;2-L [136] W Zhu, G Vigh, Enantiomer separations by nonaqueous capillary electrophoresis using octakis(2,3-diacetyl-6-sulfato)-γ -cyclodextrin, J Chromatogr A 892 (20 0) 499–507 https://doi.org/10.1016/S0 021-9673(0 0) 00387-3 [137] M.B Busby, P Lim, G Vigh, Synthesis, analytical characterization and use of octakis(2,3-di-O-methyl-6-O-sulfo)-γ -cyclodextrin, a novel, single-isomer, chiral resolving agent in low-pH background electrolytes, Electrophoresis 24 (2003) 351–362 https://doi.org/10.1002/elps.200390045 [138] M.B Busby, O Maldonado, G Vigh, Electrophoretic enantiomer separations at high pH using the new, single-isomer octakis(2,3-dimethyl-6-O-sulfo)-γ cyclodextrin as chiral resolving agent, J Chromatogr A (2003) 63–73 https: //doi.org/10.1016/S0021-9673(02)01797-1 [139] P Sázelová, D Koval, L Severa, F Teplý, V Kašicˇ ka, Chiral analysis of α diimine Ru(II) and Fe(II) complexes by capillary electrophoresis using sul- [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155] [156] [157] [158] [159] fated cyclodextrins as stereoselectors, Electrophoresis 38 (2017) 1913–1921 https://doi.org/10.10 02/elps.20170 077 I Fradi, A.C Servais, C Lamalle, M Kallel, M Abidi, J Crommen, M Fillet, Chemo- and enantio-selective method for the analysis of amino acids by capillary electrophoresis with in-capillary derivatization, J Chromatogr A 1267 (2012) 121–126 https://doi.org/10.1016/j.chroma.2012.05.098 L Kanizsová, M Ansorge, I Zusková, P Dubský, Using single-isomer octa(6O-sulfo)-γ -cyclodextrin for fast capillary zone electrophoretic enantioseparation of pindolol: determination of complexation constants, software-assisted optimization, and method validation, J Chromatogr A 1568 (2018) 214–221 https://doi.org/10.1016/j.chroma.2018.07.020 M.B Busby, G Vigh, Synthesis of a single-isomer sulfated β -cyclodextrin carrying nonidentical substituents at all of the C2, C3, and C6 positions and its use for the electrophoretic separation of enantiomers in acidic aqueous and methanolic background electrolytes, Part 2:„, Electrophoresis 26 (2005) 3849–3860 https://doi.org/10.10 02/elps.20 050 0191 A Rousseau, F Gillotin, P Chiap, E Bodoki, J Crommen, M Fillet, A.C Servais, Generic systems for the enantioseparation of basic drugs in NACE using single-isomer anionic CDs, J Pharm Biomed Anal 54 (2011) 154–159 https://doi.org/10.1016/j.jpba.2010.08.004 D.K Maynard, G Vigh, Synthesis and analytical characterization of the sodium salt of heptakis(2-O-methyl-3,6-di-O-sulfo)cyclomaltoheptaose, a chiral resolving agent candidate for capillary electrophoresis, Carbohydr Res 328 (20 0) 277–285 https://doi.org/10.1016/S0 08-6215(0 0)0 0114-2 D.K Maynard, G Vigh, Heptakis(2-O-methyl-3,6,di-O-sulfo)-β -cyclodextrin: a single-isomer, 14-sulfated β -cyclodextrin for use as a chiral resolving agent in capillary electrophoresis, Electrophoresis 22 (2001) 3152–3162 https://doi.org/10.1002/1522-2683(200109)22:153.0.CO ;2-I B Chankvetadze, N Burjanadze, D.M Maynard, K Bergander, D Bergenthal, G Blaschke, Comparative enantioseparations with native β -cyclodextrin and heptakis-(2-0-methyl-3,6-di-O-sulfo)-β -cyclodextrin in capillary electrophoresis, Electrophoresis 23 (2002) 3027–3034 https://doi.org/10.1002/1522-2683(200209)23:173.0.CO ;2-V A Gogolashvili, E Tatunashvili, L Chankvetadze, T Sohajda, M Gumustas, S.A Ozkan, A Salgado, B Chankvetadze, Separation of brombuterol enantiomers in capillary electrophoresis with cyclodextrin-type chiral selectors and investigation of structure of selector-selectand complexes using nuclear magnetic resonance spectroscopy, Electrophoresis 40 (2019) 1904–1912 https: //doi.org/10.10 02/elps.20190 062 E Tutu, G Vigh, Synthesis, analytical characterization and initial capillary electrophoretic use in an acidic background electrolyte of a new, singleisomer chiral resolving agent: heptakis(2-O-sulfo-3-O-methyl-6-O-acetyl)-β cyclodextrin, Electrophoresis 32 (2011) 2655–2662 https://doi.org/10.1002/ elps.201100104 D.L Kirschner, T.K Green, Nonaqueous synthesis of a selectively modified, highly anionic sulfopropyl ether derivative of cyclomaltoheptaose (β cyclodextrin) in the presence of 18-crown-6, Carbohydr Res 340 (2005) 1773–1779 https://doi.org/10.1016/j.carres.2005.04.012 D Kirschner, M Jaramillo, T Green, F Hapiot, L Leclercq, H Bricout, E Monflier, Fine tuning of sulfoalkylated cyclodextrin structures to improve their mass-transfer properties in an aqueous biphasic hydroformylation reaction, J Mol Catal A Chem 286 (2008) 11–20 https://doi.org/10.1016/j.molcata.2008 01.038 J.A McKee, T.K Green, Synthesis of 2,3-O-dibenzyl-6-O-sulfobutyl-α and β cyclodextrins: new chiral surfactants for capillary electrophoresis, Tetrahedron Lett 56 (2015) 4451–4454 https://doi.org/10.1016/j.tetlet.2015.05.057 ˝ E Varga, G Benkovics, A Darcsi, J Szemán, S Béni, M Malanga, I Fejos, Synthesis, analytical characterization and capillary electrophoretic use of the single-isomer heptakis-(6-O-sulfobutyl)-beta-cyclodextrin, J Chromatogr A 1514 (2017) 127–133 https://doi.org/10.1016/j.chroma.2017.07.069 L Li, C Wu, Y Ma, S Zhou, Z Li, T Sun, Effectively enhancing the enantioseparation ability of β -cyclodextrin derivatives by: de novo design and molecular modeling, Analyst 142 (2017) 3699–3706 https://doi.org/10.1039/c7an00986k S.A.C Wren, R.C Rowe, Theoretical aspects of chiral separation in capillary electrophoresis I Initial evaluation of a model, J Chromatogr A 603 (1992) 235–241 https://doi.org/10.1016/0021- 9673(92)85366- T Kraus, M Budeˇ šínský, J Závada, A simple synthesis of hexakis(6-Ocarboxymethyl-2,3-di-O-methyl) cyclomaltohexaose and heptakis(6-Ocarboxymethyl-2,3-di-O-methyl) cyclomaltoheptaose, Carbohydr Res 304 (1997) 81–84 https://doi.org/10.1016/S0 08-6215(97)0 0216-4 ˝ E Varga, G Benkovics, M Malanga, T Sohajda, J Szemán, S Béni, I Fejos, Characterization of a single-isomer carboxymethyl-beta-cyclodextrin in chiral capillary electrophoresis, Electrophoresis 38 (2017) 1869–1877 https://doi org/10.10 02/elps.20170 0 04 ˝ A Darcsi, E Varga, M Malanga, É Fenyvesi, T SohaG Benkovics, I Fejos, jda, L Szente, S Béni, J Szemán, Single-isomer carboxymethyl-γ -cyclodextrin as chiral resolving agent for capillary electrophoresis, J Chromatogr A 1467 (2016) 445–453 https://doi.org/10.1016/j.chroma.2016.06.083 B Chankvetadze, G Schulte, D Bergenthal, G Blaschke, Comparative capillary electrophoresis and NMR studies of enantioseparation of dimethindene with cyclodextrins, J Chromatogr A 798 (1998) 315–323 https://doi.org/10.1016/ S0 021-9673(97)0 0999-0 ˇ ˇ M Rezanka, P Rzanka, D Sýkora, J Jindrˇich, V Král, Impact of substituent position in monosubstituted α -cyclodextrins on enantioselectivity in capil- ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, [160] [161] [162] [163] [164] [165] [166] [167] [168] [169] [170] [171] [172] [173] [174] [175] [176] [177] [178] [179] [180] [181] lary electrophoresis, J Sep Sci 35 (2012) 811–815 https://doi.org/10.1002/ jssc.201101034 ˇ ˇ K Navrátilová, P Rezanka, M Rezanka, D Sýkora, J Jindrˇich, V Král, The study of enantioselectivity of all regioisomers of mono-carboxymethyl- β cyclodextrin used as chiral selectors in CE, J Sep Sci 36 (2013) 1270–1274 https://doi.org/10.1002/jssc.201201144 ˇ M Bláhová, E Bednáˇrová, M Rezanka, J Jindrˇich, Complete sets of monosubstituted γ -cyclodextrins as precursors for further synthesis, J Org Chem 78 (2013) 697–701 https://doi.org/10.1021/jo301656p ˇ ˇ ˇ P Rezanka, L Rokosová, K Rezanková, M Bláhová, M Rezanka, D Sýkora, J Jindrˇich, V Král, The influence of the substituent position in monocarboxymethyl-γ -cyclodextrins on enantioselectivity in capillary electrophoresis, J Sep Sci 37 (2014) 2779–2784 https://doi.org/10.10 02/jssc.20140 0604 ˇ ˇ P Rezanka, K Rezanková, H Sedláˇcková, J Mašek, L Rokosová, M Bláhová, ˇ M Rezanka, J Jindrˇich, D Sýkora, V Král, Influence of substituent position and cavity size of the regioisomers of monocarboxymethyl-α -, β -, and γ cyclodextrins on the apparent stability constants of their complexes with both enantiomers of Tröger’s base, J Sep Sci 39 (2016) 980–985 https: //doi.org/10.1002/jssc.201500845 V Cucinotta, A Giuffrida, G Maccarrone, M Messina, A Puglisi, A Torrisi, G Vecchio, The 6-derivative of β -cyclodextrin with succinic acid: a new chiral selector for CD-EKC, J Pharm Biomed Anal (2005) 1009–1014 https: //doi.org/10.1016/j.jpba.2004.08.023 H Kim, Y Choi, J Lim, S.R Paik, S Jung, Chiral separation of catechin by capillary electrophoresis using mono-, di-, tri-succinyl-β -cyclodextrin as chiral selectors, Chirality 21 (2009) 937–942 https://doi.org/10.1002/chir.20696 J Boonleang, J.F Stobaugh, New single isomer negatively charged β cyclodextrin derivatives as chiral selectors in capillary electrophoresis, Electrophoresis 34 (2013) 1232–1240 https://doi.org/10.10 02/elps.20120 0591 ˇ P Cesla, J Fischer, P Jandera, Separation of phenolic acids and flavone natural antioxidants by two-dimensional method combining liquid chromatography and micellar electrokinetic capillary chromatography, Electrophoresis 31 (2010) 2200–2210 https://doi.org/10.10 02/elps.20 090 0689 X Wang, Y Fan, Y Zhuang, L Luo, T Wang, Enantioseparation of pharmaceuticals by capillary electrophoresis using per-(6-sulfo-6-deoxy)-β -cyclodextrin as chiral selector, Asian J Chem 27 (2015) 2951–2954 https://doi.org/10 14233/ajchem.2015.18327 A.C Servais, M Fillet, Enantioseparations in nonaqueous capillary electrophoresis using charged cyclodextrins, Methods Mol Biol 970 (2013) 297– 305 https://doi.org/10.1007/978- 1- 62703- 263- 6_19 P Sázelová, D Koval, L Severa, F Teplý, G Vigh, V Kašicˇ ka, Determination of binding constants of multiple charged cyclodextrin complexes by ACE using uncorrected and ionic strength corrected actual mobilities of the species involved, Electrophoresis (2019) https://doi.org/10.10 02/elps.20190 0352 Y Matsui, K Ogawa, S Mikami, M Yoshimoto, K Mochida, Binding and Catalytic Properties of Charged β -Cyclodextrins, Bull Chem Soc Jpn 60 (1987) 1219–1223 https://doi.org/10.1246/bcsj.60.1219 S Terabe, H Ozaki, K Otsuka, T Ando, Electrokinetic chromatography with 2-O-carboxymethyl-β -cyclodextrin as a moving “stationary” phase, J Chromatogr A 332 (1985) 211–217 https://doi.org/10.1016/S0021-9673(01) 83299-4 N Budanova, E Shapovalova, S Lopatin, V Varlamov, O Shpigun, Heptakis(6amino-6-deoxy)-β -cyclodextrin as a chiral selector for the separation of anionic analyte enantiomers by capillary electrophoresis, Electrophoresis 25 (20 04) 2795–280 https://doi.org/10.10 02/elps.20 0405970 W Tang, S Ng, Facile synthesis of mono-6-amino-6-deoxy- a -, b -, c - cyclodextrin hydrochlorides for molecular recognition, chiral separation and drug delivery, Nat Protocols (2008) 691–697 https://doi.org/10.1038/nprot 2008.37 W Tang, I.W Muderawan, S.C Ng, H.S.O Chan, Enantiomeric separation of hydroxy, 10 carboxylic and dansyl amino acids by mono(6-amino-6-deoxy)β -cyclodextrin in capillary electrophoresis, Anal Chim Acta 554 (2005) 156– 162 https://doi.org/10.1016/j.aca.2005.08.034 A Giuffrida, V Cucinotta, G Maccarrone, M Messina, E Rizzarelli, G Vecchio, Coordination properties of 3-functionalised β -cyclodextrins: thermodynamic stereoselectivity of copper(ii) complexes of the 3-histamine derivative and its exploitation in ligand-exchange capillary electrophoresis, Eur J Inorg Chem 2014 (2014) 377–383 https://doi.org/10.1002/ejic.201301015 A Nardi, A Eliseev, P Bocˇ ek, S Fanali, Use of charged and neutral cyclodextrins in capillary zone electrophoresis: enantiomeric resolution of some 2hydroxy acids, J Chromatogr A 638 (1993) 247–253 https://doi.org/10.1016/ 0021- 9673(93)83435- U W Tang, I.W Muderawan, T.T Ong, S.C Ng, A family of single-isomer positively charged cyclodextrins as chiral selectors for capillary electrophoresis: mono-6A-butylammonium-6A-deoxy-β -cyclodextrin tosylate, Electrophoresis 26 (2005) 3125–3133 https://doi.org/10.1002/elps.200500018 W Tang, S.C Ng, Monosubstituted positively charged cyclodextrins: synthesis and applications in chiral separation, J Sep Sci 31 (2008) 3246–3256 https: //doi.org/10.10 02/jssc.20 080 0357 W.H Tang, I.W Muderawan, T.T Ong, S.C Ng, Enantioseparation of dansyl amino acids by a novel permanently positively charged single-isomer cyclodextrin: mono-6-N-allylammonium-6-deoxy-β - cyclodextrin chloride by capillary electrophoresis, Anal Chim Acta 546 (2005) 119–125 https://doi org/10.1016/j.aca.2005.05.013 W Tang, I.W Muderawan, T.T Ong, S.C Ng, Enantioseparation of acidic enantiomers in capillary electrophoresis using a novel single-isomer of posi- [182] [183] [184] [185] [186] [187] [188] [189] [190] [191] [192] [193] [194] [195] [196] [197] [198] [199] [200] [201] 29 tively charged β -cyclodextrin: mono-6 A-N- pentylammonium-6A-deoxy-β cyclodextrin chloride, J Chromatogr A 1091 (2005) 152–157 https://doi.org/ 10.1016/j.chroma.2005.07.045 W Tang, I.W Muderawan, S.C Ng, H.S.O Chan, Enantioselective separation in capillary electrophoresis using a novel mono-6A-propylammoniumβ -cyclodextrin as chiral selector, Anal Chim Acta 555 (2006) 63–67 https: //doi.org/10.1016/j.aca.2005.08.064 P Mikuš, D Kaniansky, Capillary zone electrophoresis resolutions of 2,4dinitrophenyl labeled amino acids enantiomers by N-methylated aminoβ -cyclodextrins, Anal Lett 40 (2007) 335–347 https://doi.org/10.1080/ 0 03271060 0867705 R.P Bonomo, V Cucinotta, F D’Alessandro, G Impellizzeri, G Maccarrone, G Vecchio, E Rizzarelli, Conformational features and coordination properties of functionalized cyclodextrins Formation, stability, and structure of proton and copper(II) complexes of histamine-bearing beta.-cyclodextrin in aqueous solution, Inorg Chem 30 (1991) 2708–2713 https://doi.org/10.1021/ ic0 013a0 03 G Impellizzeri, G Maccarrone, E Rizzarelli, G Vecchio, R Corradini, R Marchelli, 6-Deoxy&6-N-histamino-β -cyclodextrin copper(ii) complex, a new enantioselective receptor for aromatic amino acids, Angew Chemie Int Ed English 30 (1991) 1348–1349 https://doi.org/10.1002/anie.199113481 G Galaverna, R Corradini, A Dossena, R Marchelli, Histamine-modified cationic β -cyclodextrins as chiral selectors for the enantiomeric separation of hydroxy acids and carboxylic acids by capillary electrophoresis, Electrophoresis (1999) https://doi.org/10.1002/(SICI)1522-2683(19990901)20: 13 2619::AID-ELPS2619 3.0.CO;2-X V Cucinotta, A Giuffrida, G Grasso, G Maccarrone, G Vecchio, Ligand exchange chiral separations by cyclodextrin derivatives in capillary electrophoresis, Analyst 128 (2003) 134–136 https://doi.org/10.1039/b210 03g V Cucinotta, A Giuffrida, G Grasso, G Maccarrone, A Mazzaglia, G Vecchio, New cyclodextrin derivatives as chiral selectors in capillary electrophoresis, Anal Bioanal Chem 370 (2001) 363–366 https://doi.org/10.1039/ cs9962500141 V Cucinotta, A Giuffrida, G Grasso, G Maccarrone, M Messina, Simultaneous separation of different enantiomeric pairs in capillary electrophoresis by mixing different hemispherodextrins, a very versatile class of receptors, J Chromatogr A 979 (2002) 137–145 https://doi.org/10.1016/S0021-9673(02) 01437-1 V Cucinotta, A Giuffrida, G Grasso, G Maccarrone, M Messina, G Vecchio, High selectivity in new chiral separations of dansyl amino acids by cyclodextrin derivatives in electrokinetic chromatography, J Chromatogr A 1155 (2007) 172–179 https://doi.org/10.1016/j.chroma.20 07.02.0 06 J Zhou, F Ai, B Zhou, J Tang, S.C Ng, W Tang, Hydroxyethylammonium monosubstituted cyclodextrin as chiral selector for capillary electrophoresis, Anal Chim Acta 800 (2013) 95–102 https://doi.org/10.1016/j.aca.2013.09.021 R Iványi, L Jicsinszky, Z Juvancz, N Roos, K Otta, J Szejtli, Influence of (hydroxy)alkylamino substituents on enantioseparation ability of single-isomer amino-β -cyclodextrin derivatives in chiral capillary electrophoresis, Electrophoresis 25 (2004) 2675–2686 https://doi.org/10.1002/elps.200406030 I Fradi, A.C Servais, M Pedrini, P Chiap, R Iványi, J Crommen, M Fillet, Enantiomeric separation of acidic compounds using single-isomer amino cyclodextrin derivatives in nonaqueous capillary electrophoresis, Electrophoresis 27 (2006) 3434–3442 https://doi.org/10.1002/elps.200500643 W Tang, I.W Muderawan, T.T Ong, S.C Ng, Facile synthesis of positively charged monosubstituted α - and γ -cyclodextrins for chiral resolution of anionic racemates, Tetrahedron Asymmetry 18 (2007) 1548–1553 https://doi org/10.1016/j.tetasy.2007.06.017 A Giuffrida, A Contino, G Maccarrone, M Messina, V Cucinotta, The 3amino-derivative of γ -cyclodextrin as chiral selector of Dns-amino acids in electrokinetic chromatography, J Chromatogr A 1216 (2009) 3678–3686 https://doi.org/10.1016/j.chroma.2008.12.035 A Giuffrida, R Caruso, M Messina, G Maccarrone, A Contino, A Cifuentes, V Cucinotta, Chiral separation of amino acids derivatised with fluorescein isothiocyanate by single isomer derivatives 3-monodeoxy-3-monoamino-β and γ -cyclodextrins: the effect of the cavity size, J Chromatogr A 1269 (2012) 360–365 https://doi.org/10.1016/j.chroma.2012.08.034 R Iványi, L Jicsinszky, Z Juvancz, Chiral separation of pyrethroic acids with single isomer permethyl monoamino β -cyclodextrin selector, Electrophoresis 22 (2001) 3232–3236 https://doi.org/10.1002/1522-2683(200109) 22:15 3232::AID- ELPS3232 3.0.CO;2- G A Contino, V Cucinotta, A Giuffrida, G Maccarrone, M Messina, A Puglisi, G Vecchio, Synthesis and characterisation of the 3-amino-derivative of c cyclodextrin, showing receptor ability and metal ion coordination properties, 49 (2008) 4765–4767 https://doi.org/10.1016/j.tetlet.2008.05.093 V Cucinotta, A Giuffrida, G Maccarrone, M Messina, G Vecchio, Ligand exchange capillary electrophoresis by cyclodextrin derivatives, a powerful tool for enantiomeric separations, Electrophoresis 27 (2006) 1471–1480 https: //doi.org/10.10 02/elps.20 050 0755 V Cucinotta, A Giuffrida, D La Mendola, G Maccarrone, A Puglisi, E Rizzarelli, G Vecchio, 3-Amino derivative of β -cyclodextrin: thermodynamics of copper(II) complexes and exploitation of its enantioselectivity in the separation of amino acid racemates by ligand exchange capillary electrophoresis, J Chromatogr B 800 (2004) 127–133 https://doi.org/10.1016/j.jchromb.2003.08 040 A Giuffrida, A Contino, G Maccarrone, M Messina, V Cucinotta, Mass spectrometry detection as an innovative and advantageous tool in ligand exchange capillary electrophoresis, Electrophoresis 32 (2011) 1176–1181 https: //doi.org/10.1002/elps.201000570 30 ˝ E Kalydi and M Malanga et al / Journal of Chromatography A 1627 (2020) 461375 I Fejos, [202] A Giuffrida, C León, V García-Cas, V Cucinotta, A Cifuentes, Modified cyclodextrins for fast and sensitive chiral-capillary electrophoresis-mass spectrometry, Electrophoresis 30 (2009) 1734–1742 https://doi.org/10.1002/elps 20 080 0333 [203] T Jakó, E Szabó, T Tábi, G Zachar, A Csillag, É Szöko, Chiral analysis of amino acid neurotransmitters and neuromodulators in mouse brain by CE-LIF, Electrophoresis 35 (2014) 2870–2876 https://doi.org/10.10 02/elps.20140 0224 ˝ Chiral separation [204] Z Wagner, T Tábi, T Jakó, G Zachar, A Csillag, É Szöko, and determination of excitatory amino acids in brain samples by CE-LIF using dual cyclodextrin system, Anal Bioanal Chem 404 (2012) 2363–2368 https: //doi.org/10.10 07/s0 0216- 012- 6384- x [205] J Yu, X Liang, Z Wang, X Guo, T Sun, X Guo, Separation of folinic acid diastereomers in capillary electrophoresis using a new cationic β -cyclodextrin derivative, PLoS ONE (2015) 10 https://doi.org/10.1371/journal.pone.0120216 [206] P Liu, W He, X.Y Qin, X.L Sun, H Chen, S.Y Zhang, Synthesis and application of a novel single-isomer mono-6-deoxy-6-((2S,3S)-(+)-2,3-Oisopropylidene-1,4-tetramethylenediamine)-β -cyclodextrin as chiral selector in capillary electrophoresis, Chirality 22 (2010) 914–921 https://doi.org/10 1002/chir.20859 [207] V Cucinotta, M Messina, A Contino, G Maccarrone, S Orlandini, A Giuffrida, Chiral separation of terbutaline and non-steroidal anti-inflammatory drugs by using a new lysine–bridged hemispherodextrin in capillary electrophoresis, J Pharm Biomed Anal 145 (2017) 734–741 https://doi.org/10.1016/j.jpba.2017 07.041 [208] F O’Keeffe, S.A Shamsi, R Darcy, P Schwinté, I.M Warner, A persubstituted cationic β -cyclodextrin for chiral separations, Anal Chem 69 (1997) 4773– 4782 https://doi.org/10.1021/ac970370e [209] D Lee, S.A Shamsi, Chiral separation of anionic and neutral compounds using a hepta-substituted cationic β -cyclodextrin as a chiral selector in capillary electrophoresis, Electrophoresis 23 (2002) 1314–1319 https://doi.org/10.1002/1522-2683(200205)23:93.0.CO;2-O [210] Y Dai, S Wang, J Zhou, Y Liu, D Sun, J Tang, W Tang, Cationic cyclodextrin as versatile chiral selector for enantiomeric separation in capillary electrophoresis, J Chromatogr A 1246 (2012) 98–102 https://doi.org/10.1016/j chroma.2012.02.065 [211] S Wang, Y Dai, J Wu, J Zhou, J Tang, W Tang, Methoxyethylammonium monosubstituted β -cyclodextrin as the chiral selector for enantioseparation in capillary electrophoresis, J Chromatogr A 1277 (2013) 84–92 https://doi org/10.1016/j.chroma.2012.12.045 [212] Y Wang, J Zhou, Y Liu, J Tang, W Tang, Evaluation of the chiral separation ability of single-isomer cationic β -cyclodextrins in capillary electrophoresis, Electrophoresis 35 (2014) 2744–2751 https://doi.org/10.10 02/elps.20140 0198 [213] Y Xiao, T.T Ong, T.T.Y Tan, S.C Ng, Synthesis and application of a novel single-isomer mono-6-deoxy-6-(3R,4R-dihydroxypyrrolidine)-β -cyclodextrin chloride as a chiral selector in capillary electrophoresis, J Chromatogr A 1216 (2009) 994–999 https://doi.org/10.1016/j.chroma.2008.12.015 [214] Y Xiao, Y Wang, T.T Ong, L Ge, S.N Tan, D.J Young, T.T.Y Tan, S.C Ng, Chiral capillary electrophoresis with cationic pyrrolidinium-β - cyclodextrin derivatives as chiral selectors, J Sep Sci 33 (2010) 1797–1805 https://doi.org/10 10 02/jssc.20 090 0732 [215] M Popr, S Hybelbauerová, J Jindrˇich, A complete series of 6-deoxymonosubstituted tetraalkylammonium derivatives of α -, β -, and γ cyclodextrin with 1, 2, and permanent positive charges, Beilstein J Org Chem 10 (2014) 1390–1396 https://doi.org/10.3762/bjoc.10.142 [216] M Havlikova, Z Bosakova, G Benkovics, J Jindrich, M Popr, P Coufal, Use of 6-O-mono-substituted derivatives of β -cyclodextrin-bearing substituent with two permanent positive charges in capillary electrophoresis, Chem Pap 70 (2016) 1144–1154 https://doi.org/10.1515/chempap- 2016- 0053 [217] K Nzeadibe, G Vigh, Synthesis of mono-6-deoxy-6-N,N,N ,N ,N pentamethylethylenediammonio-cyclomaltoheptaose, a single-isomer, monosubstituted, permanently dicationic β -CD and its use for enantiomer separations by CE, Electrophoresis 28 (2007) 2589–2605 https://doi.org/10.10 02/elps.20 070 028 [218] T.T Ong, W Tang, W Muderawan, S.C Ng, H.S.O Chan, Synthesis and application of single-isomer 6-mono(alkylimidazolium)-β -cyclodextrins as chiral selectors in chiral capillary electrophoresis, Electrophoresis 26 (2005) 3839– 3848 https://doi.org/10.10 02/elps.20 050 0189 [219] W Tang, T.T Ong, I.W Muderawan, S.C Ng, Effect of alkylimidazolium substituents on enantioseparation ability of single-isomer alkylimidazolium-β cyclodextrin derivatives in capillary electrophoresis, Anal Chim Acta 585 (2007) 227–233 https://doi.org/10.1016/j.aca.2006.12.041 [220] C Zhou, J Deng, G Shi, T Zhou, β -cyclodextrin-ionic liquid polymer based dynamically coating for simultaneous determination of tetracyclines by capillary electrophoresis, Electrophoresis 38 (2017) 1060–1067 https://doi.org/10 10 02/elps.20160 0229 [221] J Tang, Y Lu, Y Wang, J Zhou, W Tang, Novel methoxypropylimmidazolium β -cyclodextrin for improved enantioseparation of amino acids, Talanta 128 (2014) 460–465 https://doi.org/10.1016/j.talanta.2014.06.006 [222] A.S Rizvi, G Murtaza, M Irfan, Y Xiao, F Qu, Determination of kynurenine enantiomers by alpha-cyclodextrin, cationic-β eta-cyclodextrin and their synergy complemented with stacking enrichment in capillary electrophoresis, J Chromatogr A (2020) 461128 https://doi.org/10.1016/j.chroma.2020.461128 [223] J Li, T Yu, G Xu, Y Du, Z Liu, Z Feng, X Yang, Y Xi, J Liu, Synthesis and application of ionic liquid functionalized β -cyclodextrin, mono-6-deoxy-6-(4amino-1,2,4-triazolium)-β -cyclodextrin chloride, as chiral selector in capillary electrophoresis, J Chromatogr A 1559 (2018) 178–185 https://doi.org/10.1016/ j.chroma.2017.11.068 [224] L Boffa, E.C Gaudino, K Martina, L Jicsinszky, G Cravotto, A new class of cationic cyclodextrins: synthesis and chemico-physical properties, New J Chem 34 (2010) 2013–2019 https://doi.org/10.1039/c0nj0 021c [225] J Zhou, Y Dai, S Wang, E Zhu, J Hai, Y Liu, J Tang, W Tang, Monosubstituted dually cationic cyclodextrins for stronger chiral recognition, RSC Adv (2012) 5088–5093 https://doi.org/10.1039/c2ra20086d [226] Y Dai, S Wang, J Zhou, J Tang, W Tang, A family of single-isomer, dicationic cyclodextrin chiral selectors for capillary electrophoresis: mono6A-ammonium-6C-butylimidazolium-β -cyclodextrin chlorides, Electrophoresis 34 (2013) 833–840 https://doi.org/10.10 02/elps.20120 0473 [227] Y Dai, S Wang, J Wu, J Tang, W Tang, Dicationic AC regioisomer cyclodextrins: mono-6A-ammonium-6 C-alkylimidazolium-β -cyclodextrin chlorides as chiral selectors for enantioseparation, RSC Adv (2012) 12652– 12656 https://doi.org/10.1039/c2ra21940a [228] J Zhou, Y Liu, Y Lu, J Tang, W Tang, Clicked AC regioisomer cationic cyclodextrins for enantioseparation, RSC Adv (2014) 54512–54516 https://doi org/10.1039/c4ra06279e [229] J Zhou, Y Wang, Y Liu, J Tang, W Tang, Methoxypropylamino β -cyclodextrin clicked AC regioisomer for enantioseparations in capillary electrophoresis, Anal Chim Acta 868 (2015) 73–79 https://doi.org/10.1016/j.aca.2015.02.013 [230] K Németh, C Domonkos, V Sarnyai, J Szemán, L Jicsinszky, L Szente, J Visy, Cationic permethylated 6-monoamino-6-monodeoxy-β -cyclodextrin as chiral selector of dansylated amino acids in capillary electrophoresis, J Pharm Biomed Anal 99 (2014) 16–21 https://doi.org/10.1016/j.jpba.2014.06.028 [231] S Wang, Y Wang, J Zhou, Y Lu, J Tang, W Tang, Mono-6A-(4methoxybutylamino)-6A-β -cyclodextrin as a chiral selector for enantiomeric separation, J Sep Sci 37 (2014) 2056–2061 https://doi.org/10.1002/jssc 201400248 [232] J Zhou, Y Dai, S Wang, E Zhu, J Hai, Y Liu, J Tang, W Tang, Monosubstituted dually cationic cyclodextrins for stronger chiral recognition, RSC Adv (2012) 5088–5093 https://doi.org/10.1039/c2ra20086d [233] H Sun, A Hao, Y Yang, C Zhu, J Li, J Shen, M Yin, New cyclodextrin derivative 6-O-(2-hydroxyl-3-betainylpropyl)-β -cyclodextrin: preparation and its application for enantiomer separation of drugs by capillary electrophoresis, J Incl Phenom Macrocycl Chem 65 (2009) 427–430 https://doi.org/10 1007/s10847- 009- 9587- [234] Y Liu, M Deng, J Yu, Z Jiang, X Guo, Capillary electrophoretic enantioseparation of basic drugs using a new single-isomer cyclodextrin derivative and theoretical study of the chiral recognition mechanism, J Sep Sci 39 (2016) 1766–1775 https://doi.org/10.1002/jssc.201501026 ... -cyclodextrins as chiral selectors in capillary electrophoresis, Electrophoresis 40 (2019) 2789–2798 https://doi.org/10.10 02/elps.20190 0134 [24] L Jicsinszky, K Martina, M Caporaso, P Cintas,... Dns-AAs [221] The novel single isomer CD enhanced the interactions between the CD and the amino acids to afford better chiral resolutions in case of all the investigated AAs As a novel chiral. .. H.S.O Chan, Synthesis and application of single- isomer 6-mono(alkylimidazolium)-β -cyclodextrins as chiral selectors in chiral capillary electrophoresis, Electrophoresis 26 (2005) 3839– 3848 https://doi.org/10.10