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See detailComparative enantioseparation of talinolol in aqueous and non-aqueous capillary electrophoresis and study of related selector-selectand interactions by nuclear magnetic resonance spectroscopy.
Chankvetadze, Lali; Servais, Anne-Catherine ULg; Fillet, Marianne ULg et al

in Journal of Chromatography. A (2012), 1267

The enantiomers of the chiral beta-blocker drug talinolol were separated with two single component sulfated beta-cyclodextrin (CD) derivatives, namely heptakis (2,3-di-O-methyl-6-sulfo)-beta-CD) (HDMS ... [more ▼]

The enantiomers of the chiral beta-blocker drug talinolol were separated with two single component sulfated beta-cyclodextrin (CD) derivatives, namely heptakis (2,3-di-O-methyl-6-sulfo)-beta-CD) (HDMS-beta-CD) and heptakis (2,3-di-O-acetyl-6-sulfo)-beta-CD) (HDAS-beta-CD), in aqueous and non-aqueous capillary electrophoresis (CE). The enantiomer affinity pattern of talinolol toward these two CDs was opposite in both aqueous and non-aqueous CE. However, the enantiomer affinity pattern for a given CD derivative did not change when aqueous buffer was replaced with non-aqueous background electrolyte. The structures of the analyte-selector complexes in both, aqueous and non-aqueous electrolytes were studied using rotating frame nuclear Overhauser effect (ROESY) NMR spectroscopy. Inclusion complex formation between the enantiomers of talinolol and HDAS-beta-CD was confirmed in aqueous buffer, while the complex between the enantiomers of talinolol and HDMS-beta-CD was of the external type. The complex of the talinolol enantiomers with HDAS-beta-CD in non-aqueous electrolyte was also of the external type. In spite of external complex formation excellent separation of the enantiomers was observed in non-aqueous CE. [less ▲]

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See detailOptimization of the LC enantioseparation of chiral pharmaceuticals using cellulose tris(4-chloro-3-methylphenylcarbamate) as chiral selector and polar non-aqueous mobile phases
Dossou, Katina Sourou Sylvestre ULg; Chiap, Patrice ULg; Chankvetadze, Bezhan et al

in Journal of Separation Science (2010), 33

The resolving power of a new commercial polysaccharide-based chiral stationary phase, Sepapak-4, with cellulose tris(4-chloro-3-methylphenylcarbamate) coated on silica microparticles as chiral selector ... [more ▼]

The resolving power of a new commercial polysaccharide-based chiral stationary phase, Sepapak-4, with cellulose tris(4-chloro-3-methylphenylcarbamate) coated on silica microparticles as chiral selector, was evaluated toward the enantioseparation of ten basic drugs with widely different structures and hydrophobic properties, using ACN as the main component of the mobile phase. A multivariate approach (experimental design) was used to screen the factors (temperature, n-hexane content, acidic and basic additives) likely to influence enantioresolution. Then, the optimization was performed using a face-centered central composite design. Complete enantioseparation could be obtained for almost all tested chiral compounds, demonstrating the high chiral discrimination ability of this chiral stationary phase using polar organic mobile phases made up of ACN and containing an acidic additive (TFA or formic acid), 0.1% diethylamine and n-hexane. These results clearly illustrate the key role of the nature of the acidic additive in the mobile phase. [less ▲]

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See detailSeparation of propranolol enantiomers by CE using sulfated beta-CD derivatives in aqueous and non-aqueous electrolytes: Comparative CE and NMR study.
Servais, Anne-Catherine ULg; Rousseau, Anne ULg; Fillet, Marianne ULg et al

in Electrophoresis (2010), 31

Separations using CE employing non-aqueous BGE are already as well established as separations in aqueous buffers. The separation mechanisms in achiral CE with non-aqueous BGEs are most likely similar to ... [more ▼]

Separations using CE employing non-aqueous BGE are already as well established as separations in aqueous buffers. The separation mechanisms in achiral CE with non-aqueous BGEs are most likely similar to those in aqueous buffers. However, for the separation of enantiomers involving their interaction with chiral buffer additives, the interaction mechanisms might be very different in aqueous and non-aqueous BGEs. While the hypothesis regarding distinct mechanisms of enantiomer separations in aqueous and non-aqueous BGEs has been mentioned in several papers, no direct proof of this hypothesis has been reported to date. In the present study, the enantiomers of propranolol were resolved using CE in aqueous and non-aqueous methanolic BGEs with two single isomer sulfated derivatives of beta-CD, namely heptakis (2,3-diacetyl-6-sulfo)-beta-CD and heptakis (2,3-dimethyl-6-sulfo)-beta-CD. The enantiomer migration order of propranolol was inverted when an aqueous BGE was replaced with non-aqueous BGE in the case of heptakis (2,3-dimethyl-6-sulfo)-beta-CD but remained the same in the case of heptakis (2,3-diacetyl-6-sulfo)-beta-CD. The possible molecular mechanisms leading to this reversal of enantiomer migration order were studied by using nuclear overhauser effect spectroscopy in both aqueous and non-aqueous BGEs. [less ▲]

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See detailCapillary electrophoretic and nuclear magnetic resonance studies on the opposite affinity pattern of propranolol enantiomers towards various cyclodextrins
Servais, Anne-Catherine ULg; Rousseau, Anne ULg; Fillet, Marianne ULg et al

in Journal of Separation Science (2010), 33

In the present study the migration order of the propranolol enantiomers with various native CDs and neutral and charged CD derivatives was examined in capillary electrophoresis (CE). The reversal of the ... [more ▼]

In the present study the migration order of the propranolol enantiomers with various native CDs and neutral and charged CD derivatives was examined in capillary electrophoresis (CE). The reversal of the enantiomer migration order was observed due to sulfation of β-CD on its primary hydroxy groups. The structures of intermolecular selector-selectand temporary diastereomeric associates in solution were elucidated based on 1D rotating frame nuclear Overhauser effect spectroscopy (1D ROESY) experiments. Major structural differences were observed between the propranolol complexes with native β-CD and heptakis(6-O-sulfo)-β-CD. [less ▲]

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See detailEnantioresolution of basic pharmaceuticals using cellulose tris(4-chloro-3-methylphenylcarbamate) as chiral stationary phase and polar organic mobile phases.
Dossou, Katina Sourou Sylvestre ULg; Chiap, Patrice ULg; Chankvetadze, Bezhan et al

in Journal of Chromatography. A (2009), 1216(44), 7450-5

A polysaccharide-based chiral stationary phase (Sepapak-4), with cellulose tris(4-chloro-3-methylphenylcarbamate) as chiral selector, has been investigated in liquid chromatography (LC). Its ... [more ▼]

A polysaccharide-based chiral stationary phase (Sepapak-4), with cellulose tris(4-chloro-3-methylphenylcarbamate) as chiral selector, has been investigated in liquid chromatography (LC). Its enantioresolution power was evaluated towards 13 basic amino-drugs with widely different structures and polarities, using polar organic mobile phases. After preliminary experiments, acetonitrile was selected as the main mobile phase component, to which a low concentration of diethylamine (0.1%) was systematically added in order to obtain efficient and symmetrical peaks. Different organic solvents were first added in small proportions (5-10%) to acetonitrile to modulate analyte retention. Polar organic modifiers were found to decrease retention and enantioresolution while hexane had the opposite effect, indicating normal-phase behaviour under these conditions. The addition of an organic acid (formic, acetic or trifluoroacetic acid) was found to strongly influence the retention of the basic amino drugs in these nonaqueous systems. The nature and proportion of the acidic additive in the mobile phase had also deep impact on enantioresolution. Therefore, the studied compounds could be subdivided in three groups in respect to the acidic additive used. All analytes could be enantioseparated in relatively short analysis times (10-20min) using these LC conditions. [less ▲]

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See detailComparative study on the enantioseparation of glutethimide using dual cyclodextrin systems and cyclodextrin modified MEKC in capillary electrophoresis
Abushoffa, Adel M.; Burjanadze, Naira; Blaschke, Gottfried et al

in Journal of Separation Science (2002), 25(1-2), 10-16

In order to critically evaluate the potential of dual cyclodextrin (CD) systems in CE, enantioseparation of the neutral chiral analyte glutethimide (GT) was performed using: a) charged CDs; b ... [more ▼]

In order to critically evaluate the potential of dual cyclodextrin (CD) systems in CE, enantioseparation of the neutral chiral analyte glutethimide (GT) was performed using: a) charged CDs; b) combinations of charged and neutral CDs (dual CD systems), and c) CD-modified micellar electrokinetic chromatography (CD-MECK). The results of this comparative study indicate that properly designed dual CD systems may in certain cases represent a valuable alternative to CD-MEKC and electrokinetic chromatography involving charged CDs for enantioseparation of neutral analytes. [less ▲]

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See detailEnantioseparation of aminoglutethimide with cyclodextrins in capillary electrophoresis and studies of selector-selectand interactions using NMR spectroscopy and electrospray ionization mass spectrometry.
Chankvetadze, Bezhan; Fillet, Marianne ULg; Burjanadze, N. et al

in Enantiomer (2000), 5(3-4), 313-22

The enantiomers of aminoglutethimide [2-(p-aminophenyl)-2-ethylglutarimide, AGT] can be resolved in CE using all of three most commonly used native cyclodextrins (CD): alpha-, beta-, and gamma-CDs. The ... [more ▼]

The enantiomers of aminoglutethimide [2-(p-aminophenyl)-2-ethylglutarimide, AGT] can be resolved in CE using all of three most commonly used native cyclodextrins (CD): alpha-, beta-, and gamma-CDs. The migration order of the enantiomers was opposite using beta-CD compared to alpha- and gamma-CDs as chiral selectors. In order to examine some underlying mechanisms of the chiral recognition the interaction of AGT with the chiral selectors was studied with one- and two-dimensional NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). The Job's and Scott's plots constructed based on the complexation-induced chemical shifts (CICS) observed in NMR spectra provided some preliminary information on the stoichiometry of the intermolecular complexes but did not seem to be absolutely reliable perhaps because the self-association of the analyte molecules and the formation of multiple type selectand-selector complexes. Therefore, an attempt was made to characterize the complexes using ESI-MS. This technique provided information on the stoichiometry and relative affinity constants of selector-selectand complexes. The information on the structure of complexes in the solution was obtained using one-dimensional rotating frame nuclear Overhauser enhancement (1D-ROESY) NMR spectroscopic studies. Significant differences were observed between the structures of the AGT complexes with beta- and gamma-CD. [less ▲]

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See detailDesigned combination of chiral selectors for adjustment of enantioseparation selectivity in capillary electrophoresis.
Fillet, Marianne ULg; Chankvetadze, Bezhan; Crommen, Jacques ULg et al

in Electrophoresis (1999), 20(13), 2691-7

In this study an attempt has been made to explain the reasons for changing the enantioseparation selectivity in some dual cyclodextrin (CD) systems compared to the use of single chiral selectors in ... [more ▼]

In this study an attempt has been made to explain the reasons for changing the enantioseparation selectivity in some dual cyclodextrin (CD) systems compared to the use of single chiral selectors in capillary electrophoresis (CE). An explanation for selectivity changes is proposed based on the effect of the chiral selector on the mobility of the analyte. In order to support the proposed mechanism, several dual systems were designed on the basis of the known recognition pattern of enantiomers for individual CDs. In most cases the separation selectivity could be adjusted in a designed way. There was no experimental evidence for simultaneous binding of a given chiral analyte with both chiral selectors or of chiral recognition of an analyte complex with one CD by another CD. [less ▲]

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