ISSN:0173-0835    

DOI:10.1002/elps.1150180602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

ISSN:0173-0835    

DOI:10.1002/elps.1150180603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

ISSN:0173-0835    

DOI:10.1002/elps.1150180604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractThe separation of enantiomer pairs of eight biogenic amines by capillary zone electrophoresis (CZE) was investigated with heptakis (2,6‐di‐O‐methyl)‐β‐cyclodextrin as the chiral selector at temperatures ranging from −20° to 40°C by using a commercial electrophoresis unit retrofitted with an external thermostated refrigerated circulating bath in order to assist the original cooling system. Sodium phosphate in both neat aqueous and methanolic media at pH 2.5, as measured by the glass pH electrode, were used with the fused silica capillary from 1.5° to 40°C and −20° to 40°C, respectively. The effect of temperature on enantioselectivity was found to depend on the number of phenolic hydroxyl groups in the molecule. Upon lowering the temperature from 40° to −20°C, the chiral selectivity of the system, as measured by the relative mobility difference, increased tenfold for the amines with two vicinal phenolic hydroxyls, whereas the increase was insignificant for those having no phenolic hydroxyl groups. The complex formation constants of three amines which have the same molecular structure but the number of phenolic hydroxyl groups were determined at different temperatures and the thermodynamic parameters as well as compensation temperatures for the process were evaluated. Whereas the compensation temperature was 690 K for the amine without phenolic hydroxyl group, it was<400 K for the amines with one or two phenolic hydroxyl groups. The difference in the compensation temperatures indicates that the intrinsic mechanisms of their complexation with the chiral selector are not the same; this may account for the discrepancies observed in the temperature dependency of the chiral selectivity. The enthalpy change per phenolic hydroxyl group was 2.5 kcal mol−1, which compares favorably with the typical value for a single hydrogen bond. Therefore, when the amines have phenolic hydroxyl groups, the strong increase in chiral selectivity with decreasing temperature may be due to enhanced H‐bonding between the cyclodextrin and the phenolic hydroxyls under the condi

ISSN:0173-0835    

DOI:10.1002/elps.1150180605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractThree different capillary electrochromatographic methods for the enantiomer separation of β‐adrenergic antagonists (acebutolol, alprenolol, atenolol, metoprolol, pindolol, prenalterol, and propranolol) were applied using different cyclodextrins (β‐cyclodextrin, carboxymethyl‐β‐cyclodextrin and dimethyl‐β‐cyclodextrin) added to the electrolyte, a cross‐linked protein‐gel (cellobiohydrolase I) and a molecularly imprinted ((R)‐enantiomer of propranolol) superporous polymer as chiral selectors. Through use of these different separation strategies, all the β‐adrenergic antagonists studied could be resolved into their enantiomers, although the three methods were carried out without extensive optimization. The protein and molecularly imprinted phases gave the highest selectivities whereas employing cyclodextrins resulted in the highest separation efficiency. Proteins and cyclodextrins are primarily natural products, albeit the cyclodextrins can be derivatized. In contrast, the molecularly imprinted chiral stationary phase can be highly

ISSN:0173-0835    

DOI:10.1002/elps.1150180606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractThe purity and enantioselectivity of a novel chiral agent, the zwitterionic mono‐(6‐δ‐glutamylamino‐6‐deoxy)‐β‐cyclodextrin (β‐CD‐Glu), were studied by capillary electrophoresis. Chiral separation of the enantiomers of chlorthalidone was obtained at pH 2.3, a pH at which β‐CD‐Glu is partially protonated. Comparison with the cationic mono‐(6‐amino‐6‐deoxy)‐β‐cyclodextrin (β‐CD‐NH2) enantioselectivity clearly shows that the greater the difference in mobility between the free analyte and the analyte‐cyclodextrin complex, the better the resolution. Hydrobenzoin enantiomers were separated at pH 11.2, a pH at which β‐CD‐Glu is anionic. Under these conditions, the migration order was opposite to that observed in the presence of β‐CD‐NH2 at pH 2.3. When no separation was obtained directly with β‐CD‐Glu, a dual cyclodextrin system was developed. Carprofen enantiomers were resolved at pH 2.3 in the presence of a β‐CD‐Glu/trimethyl‐β‐cyclodextrin (TM‐β‐CD) system in which the charged CD confers a non

ISSN:0173-0835    

DOI:10.1002/elps.1150180607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

Abstractβ‐Cyclodextrin, 1, can act as a chiral buffer additive in capillary zone electrophoresis (CZE) owing to its ability to form diastereomeric complexes with the enantiomers of ionic compounds. Reaction of 1 with 2,3‐epoxy‐propyltrimethylammonium chloride gave preponderantly 6‐O‐(2‐hydroxy‐3‐trimethyl‐ammoniopropyl) derivatives (2) of varying degrees of substitution (d.s.). Analogous reaction of 1 with 1,3‐propanesultone yielded 6‐O‐(sulfo‐n‐propyl) derivatives (SPE‐β‐CD, 3) of varying d.s. The purity and the d.s. of 2 and 3 were determined by1H NMR and electrospray ionization mass spectrometry (ESI‐MS). These charged β‐cyclodextrin derivatives were used for the chromatographic enantiomer separation of a series of neutral barbiturates, of chlorthalidone, terbutaline, warfarin, salbutamol and brompheniramine by cyclodextrin electrokinetic chromatography (CD‐EKC). During the separation of chlorthalidone with 3 as chiral additive, a reversible interconversion of the enantiomers (enantiomerization)

ISSN:0173-0835    

DOI:10.1002/elps.1150180608

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractTwo novel monosubstituted β‐cyclodextrins (CD) bearing the histamine moiety linked to the upper CD rim, either through the amino group or the imidazole nitrogen1N, CD‐hm and CD‐mh, were successfully used as chiral selectors in capillary electrophoresis for the enantiomeric discrimination of dansyl (Dns)‐amino acids. Good results were obtained by using low concentrations of the selectors (1–3 mM). The effect of pH on the chiral discrimination was studied in order to modulate the number and the position of the positive charges. By increasing the pH from 5 to 7.5, chiral discrimination decreased along with the deprotonation of the imidazolyl moiety. Inversion of the migration order was observed with the two CDs, depending on the relative position of the charged moieties on the upper rim. Ion pair interaction coupled to inclusion complexation seems to account for the discrimination process. The effects of the temperature, CD concentration and capillary length on chiral resolution were als

ISSN:0173-0835    

DOI:10.1002/elps.1150180609

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractThree alkylglycoside surfactants, namelyn‐octyl‐β‐D‐glucopyranoside (OG),n‐nonyl‐β‐D‐glucopyranoside (NG), andn‐octyl‐β‐D‐maltopyranoside (OM), were compared in the enantiomeric separation of dansyl amino acids, binaphthyl phosphate, bupivacaine and warfarin. While only OM exhibited an enantioselectivity toward warfarin, bupivacaine, and dansyl tryptophan, all three surfactants were effective in the enantiomeric resolution of napthyl phosphate and other dansyl amino acids. With the exception of naphthyl phosphate, which could be resolved enantiomerically with OM at surfactant concentrations below the CMC, all solutes required surfactant concentrations greater than the CMC value. This was attributed to the strong hydrophobic association of napthyl phosphate with the OM monomers and to the presence of maltoside residue in the OM surfactant. In general, the optimum surfactant concentration needed for maximum enantiomeric resolution was an inverse function of the hydrophobic character of the solute. Under a given set of conditions, the enantiomeric resolution exhibited by the alkylglycoside surfactants was largely influenced by the extent and loci of solute solubilization into the micelle, and by the nature of the chiral sugar he

ISSN:0173-0835    

DOI:10.1002/elps.1150180610

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractThe use of nonaqueous background electrolytes in capillary electrophoresis (CE) is a promising new trend which should widen the scope of this technique. We demonstrate the chiral separation of dansyl‐amino acids (Dns‐AAs) inN‐methylformamide (NMF) using β‐cyclodextrin (β‐CD) as chiral selector. The solubility of β‐CD is much better in NMF than in water, allowing high concentration of the chiral selector and successful enantioseparation despite the weak host‐guest interaction between the Dns‐AAs and β‐CD. The association constants for the complexation between Dns‐AAs and β‐CD could be calculated from the electrophoretic mobilities, with attention paid to the change in viscosity of the electrolyte upon addition of β‐CD. The association constant

ISSN:0173-0835    

DOI:10.1002/elps.1150180611

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY