Reversal of enantiomer elution order in capillary electrophoresis using charged and neutral cyclodextrins

Chankvetadze, Bezhan; Schulte, Georg; Blaschke, Gottfried

doi:10.1016/0021-9673(95)01245-1

Cited by 83 publications

(72 citation statements)

References 11 publications

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“…In fact, many works have thrown light on the reversal of the EMO. 14,15,[18][19][20][21][22] Our previous work involved the separation behavior of amino acid enantiomers in LE-MEKC, 23 in which we discussed the reversal of EMO of amino acids and o-, m-and p-order of enantiomers with the introduction of micellar phases. In this paper we focus our study on the influence of ligand chirality, trans-and cis-conformation of 4-hydroxy group in hydroxyproline and the SDS micellar phase on the separation behavior when using different ligands of the proline family in LE-MEKC.…”

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confidence: 99%

Reversal Behaviors of the Enantiomer Migration Order and the Stereo-selectivity of Cu(II) Complex with Amino Acid Enantiomers in Ligand Exchange-Micellar Electrokinetic Chromatography

et al. 2000

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Since the pioneering work of Terabe et al. 1,2 micellar electrokinetic chromatography (MEKC) has become a powerful technique for the analysis of both neutral and charged samples. 3 Many researchers focus their work on the development of novel methods concerning MEKC by using modifiers. For example, cyclodextrin-modified MEKC (CD-MEKC) 4-7 borate-complex EKC 8,9 and ion-exchange EKC 10,11 have been reported. Each of these methods has extended the application of MEKC to the analysis of various types of compounds. The mechanism of the ligand exchange was reported for the separation of dansyl amino acid enantiomers by liquid chromatography 12,13 and subsequently capillary electrophoresis. 13,14 Ligand exchange-micellar electrokinetic chromatography (LE-MEKC), a hybrid technique of the ligand exchange mechanism and MEKC, has been receiving increasing attention, because it offers the possibility of the simultaneous separation of optical isomers with the differences in the positional structure, such as o-, m-, p-enantiomers of amino acids, which contain a phenyl ring with different substituents 16 as well as positional and optical isomers of the tryptophan family. 17 Based on the ligand exchange mechanism, it is the difference in the stability constants that give the chiral separation of enantiomers. In other words, the EMO depends on the stability of the complex. Therefore, EMO can be predicted based on the stability of the complex. Conversely, the EMO can be applied in a study of complex stability.In order to explore the mechanism of LE-MEKC and to provide some scientific evidence for predicting and controlling the EMO or for studying the complex stability of a ternary Cu(II) complex with different amino acid enantiomers, it is significant to study the separation behavior of enantiomers in LE-MEKC. In fact, many works have thrown light on the reversal of the EMO. 14,15,18-22 Our previous work involved the separation behavior of amino acid enantiomers in LE-MEKC, 23 in which we discussed the reversal of EMO of amino acids and o-, m-and p-order of enantiomers with the introduction of micellar phases. In this paper we focus our study on the influence of ligand chirality, trans-and cis-conformation of 4-hydroxy group in hydroxyproline and the SDS micellar phase on the separation behavior when using different ligands of the proline family in LE-MEKC. Experimental InstrumentationThe CE instrumental setup involves a HEL5-30P2-TTu high voltage power supply (Matsusada Precision Devices Inc., Japan), a CE-971 UV detector (Jasco Corporation, Japan) and a C-R6A Chromatopac Recorder (Shimadzu, Japan). Separations were carried out in fused-silica capillaries (0.050 mm i.d.×0.375 mm o.d.) from GL Sciences Inc. (Japan) with a total length of 56 cm and an effective length of 40 cm. ChemicalsAll of the chemicals were of reagent grade and were used as Hachioji, Japan The dependence of the enantioselectivity and enantiomer migration order (EMO) on the chirality and stereo-conformation of ligands used for the chiral selectors of Cu(...

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Reversal Behaviors of the Enantiomer Migration Order and the Stereo-selectivity of Cu(II) Complex with Amino Acid Enantiomers in Ligand Exchange-Micellar Electrokinetic Chromatography

et al. 2000

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“…Besides, organic solvents generally cause a decrease of analyte complexation with the CD due to the analyte-organic solvent competition in fitting the hydrophobic chiral selector cavity. However, in several cases, improvement of enantiomer resolution was observed [39][40][41][42]. By adding an organic solvent, the interaction between baclofen and HS-b-CD was reduced and migration times increased.…”

Section: Effect Of Organic Solventmentioning

confidence: 99%

“…4). As mentioned by Chankvetadze et al [42], the reversal of the enantiomeric migration order (EMO), using CD with opposite chiral recognition ability, is a powerful technique. Furthermore, in the analysis of nonracemic mixtures of enantiomers, it is desirable to detect the minor component before the major one since the peak tailing does not allow the detection of enantiomeric impurity as the second peak even at high percentages [43].…”

Section: Migration Ordermentioning

confidence: 99%

Enantioseparation of baclofen with highly sulfated β‐cyclodextrin by capillary electrophoresis with laser‐induced fluorescence detection

Kavran-Belin

Rudaz

Veuthey

2005

J of Separation Science

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Enantioseparation of baclofen with highly sulfated b-cyclodextrin by capillary electrophoresis with laser-induced fluorescence detectionThe enantioseparation of baclofen (4-amino-3-p-chlorophenylbutyric acid) was achieved by CE-LIF with highly sulfated b-CD (HS-b-CD) as chiral selector. Naphthalene-2,3-dicarboxaldehyde was used for the derivatization of nonfluorescent baclofen. HS-b-CD (2%) containing 50 mM borate buffer at pH 9.5 was chosen as the optimal running electrolyte and applied to the analysis of baclofen enantiomers in human plasma. The linearity of calibration curves (R 2 F 0.998) for R-( -) and S-(+)-baclofen was in the 0.1-2.0 lM concentration range. After a simple ACN-protein precipitation, the LOD of baclofen in plasma sample was found as low as 50 nM.

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“…Among the diverse ways of EMO reversal developed, suppressing or reversing the direction of electroosmotic flow has been most widely used. 9,[12][13][14][15][16] In our recent report, simultaneous EMO reversal of nine chiral profens was achieved in the normal polarity and reversed polarity modes. 16 The most certain and easy method of EMO reversal might be, however, the use of two chiral selectors with the opposite chiral recognition ability, like (+)-18C6H 4 and (−)-18C6H 4 when employing crown ether-modified CE systems.…”

mentioning

confidence: 99%

“…8 The surest way of the accurate chiral discrimination is the reversal of enantiomer migration order (EMO). [9][10][11][12][13][14][15][16] It is especially desirable when peak tailing, fronting or overlapping is observed. Among the diverse ways of EMO reversal developed, suppressing or reversing the direction of electroosmotic flow has been most widely used.…”

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Chiral Discrimination of Aromatic Amino Acids by Capillary Electrophoresis in (+)- and (-)-(18-Crown-6)-2,3,11,12-tetracarboxylic Acid Selector Modes

2003

Bulletin of the Korean Chemical Society

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Optically active (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18C6H 4 ) ( Figure 1) has been successfully employed as a chiral selector in enantioseparations of diverse amino acids and chiral primary amines in capillary electrophoresis (CE). 1-7The host-guest complexation mechanisms for the chiral recognition of crown ethers toward chiral amines have been well established. 2,6 The accurate chiral discrimination of each separated analyte has become an important task for their optical purity control and stereoselective pharmacokinetic studies in chiral drug development. The migration order of separated enantiomers is mainly determined by co-electrophoresis with enantiomerically pure standards and matching its migration time or relative migration time (RMT) with that of the reference. However, crosschecking two RMT sets measured with two chiral selectors of different enantioselectivities could enhance confidence in the identification of CE peaks and the chiral discrimination as well. Based on this concept, simultaneous chiral discrimination of 15 racemic aromatic amino acids was achieved with chiral CE in neutral and charged cyclodextrin modes in our previous report. 8 The surest way of the accurate chiral discrimination is the reversal of enantiomer migration order (EMO).9-16 It is especially desirable when peak tailing, fronting or overlapping is observed. Among the diverse ways of EMO reversal developed, suppressing or reversing the direction of electroosmotic flow has been most widely used. 9,[12][13][14][15][16] In our recent report, simultaneous EMO reversal of nine chiral profens was achieved in the normal polarity and reversed polarity modes. 16 The most certain and easy method of EMO reversal might be, however, the use of two chiral selectors with the opposite chiral recognition ability, like (+)-18C6H 4 and (−)-18C6H 4 when employing crown ether-modified CE systems. However, no attempt to exploit the crosschecking each EMO measured in these two selector modes has been made in chiral CE of amino acids to date. The present study was undertaken to investigate EMO reversal by crown ether modified-CE system in the two selector modes with (+)-18C6H 4 and (−)-18C6H 4 for the chiral discrimination of nine aromatic amino acids. When (+)-18C6H 4 was added at 5 mM to 20 mM Triscitric acid buffer (pH 2.50), each enantiomeric pairs of nine aromatic amino acids studied were baseline-resolved with similar enantioselectivity and resolution factor except for 3-hydroxyphenylglycine (Table 1). 3-Hydroxyphenylglycine showed much stronger interaction with the selector than other analytes, thereby yielding a very large separation factor (1.684) and resolution factor (21.99). In good agreement with the previous reports, 1,2,4 each D-enantiomer migrated slower than the corresponding L-isomer, indicating that the D-isomers were bound more strongly with (+)-18C6H 4 in CE. The (R)-baclofen migrated ahead of the (S)-enantiomer. When (+)-18C6H 4 was replaced in the same buffer condition with its antipode, (−)-18C6H 4 (Figure 1), ...

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Reversal of enantiomer elution order in capillary electrophoresis using charged and neutral cyclodextrins

Cited by 83 publications

References 11 publications

Reversal Behaviors of the Enantiomer Migration Order and the Stereo-selectivity of Cu(II) Complex with Amino Acid Enantiomers in Ligand Exchange-Micellar Electrokinetic Chromatography

Reversal Behaviors of the Enantiomer Migration Order and the Stereo-selectivity of Cu(II) Complex with Amino Acid Enantiomers in Ligand Exchange-Micellar Electrokinetic Chromatography

Enantioseparation of baclofen with highly sulfated β‐cyclodextrin by capillary electrophoresis with laser‐induced fluorescence detection

Chiral Discrimination of Aromatic Amino Acids by Capillary Electrophoresis in (+)- and (-)-(18-Crown-6)-2,3,11,12-tetracarboxylic Acid Selector Modes

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