Ligand Exchange Capillary Electrophoresis Research Articles

Chiral ligand exchange capillary electrophoresis using borate anion as a central ion

Native DL-pantothenic acid, having a 1,3-diol structure, was chirally resolved by ligand exchange capillary electrophoresis using (S)-3-amino-1,2-propanediol as a chiral selector and the borate anion as a central ion. The optimum conditions for both high resolution and short migration time of DL-pantothenic acid were found to be 200 mM (S)-3-amino-1,2-propanediol and 200 mM borate buffer (pH 9.2) containing 15% methanol with an applied voltage of +25 kV at 20 degrees C, using direct detection at 200 nm. With this system, the resolution (Rs) of racemic pantothenic acid was approximately 1.7. When (S)-1,2-propanediol, (S)-1,2,3-propanetriol, (S)-1,3-butanediol or (S)-1-amino-2-propanol were used as chiral ligand instead of (S)-3-amino-1,2-propanediol, DL-pantothenic acid was not enantioseparated. When borate was replaced with Tris or butylborate, no chiral separation was achieved. Therefore, the ionic interaction between the amino and carboxyl groups of the ternary complex may play an important role in the enantioseparation of DL-pantothenic acid by the proposed CE system.

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

The systems that the 3-amino derivative of β-cyclodextrin (CD3NH2) forms with the proton, the copper(II) ion and each of the enantiomers of certain amino acids (alanine, phenylalanine, tyrosine and tryptophan) were investigated. The enantioselectivity shown by the potentiometric measurements carried out on the phenylalanine ternary systems was exploited in capillary electrophoresis by ligand exchange capillary electrophoresis (LECE) to obtain the separation of phenylalanine racemate. The tyrosine racemate was also separated by LECE. The comparison between thermodynamic and capillary electrophoresis (CE) results is discussed, in order to get a better insight into the separation mechanism.

Influence of structure and chirality of the selector on the chiral recognition of amino acids using ligand-exchange capillary electrophoresis.

The dependence of the chiral recognition ability and enantiomer migration order on the structure, substitution pattern and chirality of chiral selectors used in ligand-exchange capillary electrophoresis is investigated. As chiral selectors different N-alkyl derivatives of proline and hydroxyproline as their copper(II) complexes are used. The influence of the position and conformation of the hydroxy group in the hydroxyproline derivatives and of the structure and chirality of the side chain on enantioselectivity is investigated. Furthermore, the effect of surfactants such as sodium dodecyl sulfate and cetyl trimethyl ammonium bromide on resolution and enantiomer migration order is studied. The investigations were carried out with three aromatic amino acids as model compounds.

Chiral separation of underivatized amino acids by ligand-exchange capillary electrophoresis using a copper(II)– l-lysine complex as selector

A ligand-exchange capillary electrophoretic method was explored, with l-lysine as the ligand and copper(II) as the central ion. Its applicability was demonstrated with underivatized aromatic amino acids, namely d,l-phenylalanine, d,l-tryptophan, d,l-tyrosine and d,l-β-phenylserine. Optical resolutions of a single pair of amino acid enantiomers, and of mixed amino acids were obtained with a running buffer of 10 m M NH 4Ac, 6.67 m M Cu(II) and 13.33 m M l-lysine, pH 7.0. Sodium dodecylsulfate (SDS) was shown to be necessary for simultaneous separation of the mixed amino acids. The resolution was found to increase with the concentration of the copper(II) complex at a copper(II)-to-lysine ratio of 1:2. If the total concentration of copper(II) and lysine was kept at 20 m M, decreasing the ratio of copper(II) to lysine caused a resolution loss of tryptophan, but a slight resolution improvement of the other three amino acids. The pH of buffer is another important factor controlling the separations. For all the studied amino acids, the optimum pH was 6.0. An interesting phenomenon was observed in this study. SDS induces precipitation at a concentration below 32 m M at room temperature (16±2 °C), possibly due to the formation of neutral substance from the SDS monomer and the copper(II)–lysine complex.

Direct chiral resolution of tartaric acid in food products by ligand exchange capillary electrophoresis using copper(II)– d-quinic acid as a chiral selector

Chiral resolution of native dl-tartaric acid was performed by ligand-exchange capillary electrophoresis using copper(II)– d-quinic acid as a chiral selector. Factors affecting chiral resolution, migration time, and peak area of tartaric acid were studied. The running conditions for optimum separation of tartaric acid were found to be 1 m M copper(II) sulfate–10 m M d-quinic acid (pH 5.0) with an effective voltage of −15 kV at 30°C, using direct detection at 250 nm, and resolution of racemic tartaric acid was approximately 1.3. With this system, chiral resolution of dl-tartaric acid in food products was conducted successfully.

Direct chiral resolution of malic acid in apple juice by ligand-exchange capillary electrophoresis using copper(II)-L-tartaric acid as a chiral selector.

Chiral resolution of native DL-malic acid was achieved by ligand-exchange capillary electrophoresis using copper(II)-L-tartrate as a chiral selector. Factors affecting chiral resolution, migration time, and peak area of malic acid were studied. The running conditions for optimum separation of malic acid were found to be 1 mM copper(II) sulfate-1 mM L-tartrate (pH 5.1) with an effective voltage of -20 kV at 30 degrees C, using direct detection at 280 nm, and resolution (Rs) of racemic malic acid was approximately 4. With this system, D- and L-malic acids in apple juice were analyzed successfully.

Application of ligand-exchange capillary electrophorersis to the chiral separation of α-hydroxy acids and β-blockers

The application of the principle of ligand-exchange capillary electrophoresis to two substance classes is described. As chiral selector N-(2-hydroxyoctyl)- l-4-hydroxyproline–copper(II) complex was used. This principle was applied to the chiral separation of α-hydroxy acids and drugs containing amino alcohol structure such as β-blockers. The enantioselectivity was found to be strongly dependent on pH corresponding to the optimal conditions for complex formation for each structure class.

Chiral separation of sympathomimetics by ligand exchange capillary electrophoresis.

A rapid and simple approach to the chiral separation of sympathomimetic drugs with amino alcohol structure by ligand exchange capillary electrophoresis is described. An N-(2-hydroxyoctyl)-L-4-hydroxyproline/copper(II) complex is used as chiral selector. Thirteen sympathomimetics were resolved, nine with baseline resolution. The influence of pH and composition of the electrolyte on resolution was investigated. The optimal pH for complexation of these amino alcohols was found to be 12.

Chiral separation of sympathomimetics by ligand exchange capillary electrophoresis

Chiral separation of sympathomimetics by ligand exchange capillary electrophoresis

Enantiomeric separation of amino acids by copper (II)-L-arginine ligand exchange capillary zone electrophoresis

A novel method for the separation of amino acid enantiomers by ligand exchange capillary zone electrophoresis (CZE) using a chiral Cu(II)-L-arginine ligand was developed in this paper. The effects of the buffer concentration, pH, the molar ratio of L-arginine to Cu(II), and the total concentrations of Cu(II) and L-arginine on the migration times and resolutions of chiral amino acids were investigated. The optimum experimental conditions were 40 mmol/L of NH4OAc, pH 7.0, the 2:1 concentration ratio of L-arginine to Cu(II), 1 mmol/L CuSO4 x 5H2O and 2 mmol/L L-arginine. Using the proposed method, six different dansyl-amino acids were separated successfully with the resolution ranging from 1.1 to 2.3 in less than 15 min.

Enantioseparation of α-amino acids and dipeptides by ligand-exchange capillary electrophoresis of various l-4-hydroxyproline derivatives

The principle of ligand exchange has been applied to the enantioseparation of underivatized aromatic and aliphatic amino acids as well as dipeptides. Two non commercially available N-alkyl- l-4-hydroxyproline derivatives were compared to underivatized l-4-hydroxyproline for their ability to resolve α-amino acids and dipeptides. N-(2-hydroxyoctyl)- l-4-hydroxyproline and N-(2-hydroxypropyl)- l-4-hydroxyproline were used as their copper(II) complexes as chiral selectors. With these selectors, several aliphatic amino acids and dipeptides, in addition to aromatic amino acids, were resolved. The pH optimum was found to be 4.3 for amino acids and 6.0 for dipeptides.