Toshiyuki Hobo

Simultaneous separation of sixteen positional and optical isomers of the tryptophan family by ligand-exchange micellar electrokinetic chromatography

SummaryLigand-exchange micellar electrokinetic chromatography has been used for the simultaneous separation of 16 positional and optical isomers of the tryptophan family. The Cu(II) complex with L-hydroxyproline was used as the chiral selector. Two groups of anionic surfactant, linear alkylbenzenesulfonates (LAS) and straight-chain alkyl sulfates such as sodiumn-decyl sulfate (SDeS), sodium dodecyl sulfate (SDS) and sodiumn-tetradecyl sulfate (STS), were used for simultaneous separation. The best result was obtained by use of SDS. The influence of SDS concentration and of pH on the separation was investigated. The separation behavior in the absence of the Cu(II) complex with L-hydroxyproline was also examined. Use of organic modifiers causes the resolution to decrease. Relationships between the logarithm of the octanol-water partition coefficient (logPOW) and resolution, and between logPOW and migration time are discussed.

Determination of critical micelle concentrations of anionic surfactants based on ligand exchange micellar electrokinetic chromatography

Abstract A new method for determining the critical micelle concentration (CMC) of anionic surfactants by ligand exchange-micellar electrokinetic chromatography (LE-MEKC) has been developed. In the separation of amino acid enantiomers by LE-MEKC using a copper complex with l -hydroxyproline as a chiral selector, it has been noted that the addition of anionic surfactants to the electrolyte causes the reversal of the enantiomer migration order EMO. The point of reversal is correlated with the CMC. Resolution (Rs) decreases with the addition of surfactant below the CMC and increases above the CMC. The inflection point at which Rs equals zero was used for the calculation of the CMC. Based on this fact, the CMCs of anionic surfactants sodium n -decyl sulphate, sodium dodecyl sulfate and sodium n -tetradecyl sulphate in 25xa0mM CuSO 4 , 50xa0mM l -hydroxyproline at pH 4 have been determined. The CMCs in the presence of 2.5% acetonitrile were also determined. Results show that the CMCs of anionic surfactants increased with the addition of acetonitrile.

Separation behavior of amino acid enantiomers in ligand exchange micellar electrokinetic chromatography

The separation of amino acid enantiomers using a Cu(II) complex with l-hydroxyproline as a chiral selector has been investigated by ligand exchange micellar electrokinetic chromatography. It was found that anionic surfactants like sodium dodecyl sulfate (SDS), sodium n-decyl sulfate, and sodium n-tetradecyl sulfate can not only improve the resolution of d,l-enantiomers, but also can change their migration orders. The migration order of o-, m-, and p-positional isomers of fluorophenylalanine and tyrosine was reversed when the concentration of SDS exceeded a certain concentration. Tween 20 improved the separation efficiency, but the migration time became longer. Cetyltrimethylammonium bromide can change the direction of electroosmotic flow, but it has no significant improvement on resolution. Organic modifiers cause the decline of resolution, but not the reversal of enantiomer migration order (EMO). A possible mechanism of the reversal of EMO is presented.xa0©1999 John Wiley & Sons, Inc.xa0J Micro Sep 11: 534–540, 1999

Enantioseparations of dansyl amino acids by capillary electrophoresis using Cu(II) complexes with L-amino acylamides as chiral selectors in electrolytes

Enantioseparations of dansyl amino acids using Cu(II) complexes with L-amino acylamides as the chiral selectors in the electrolyte solution were investigated by capillary electrophoresis. It has been demonstrated that the Cu(II) complexes with L-amino acylamides such as L-phenylalaninamide, L-prolinamide, and L-alaninamide are suitable for use as chiral selectors for enantioseparations of dansyl amino acids. The optimal separation conditions were examined. The employed chiral ligands exhibited different enantioselectivities and enantiomer migration orders. The enantiomer migration orders are discussed by using three different chiral selectors. L-enantiomers migrate faster than D-enantiomers when Cu(II)-L-phenylalaninamide and Cu(II)-L-alaninamide are used as chiral selectors, but D-enantiomers faster than their (--counterparts in the Cu(II)-L-prolinamide system.

Enantioseparation Of Aromatic Dipeptides Using Carboxymethyl-β-Cyclodextrin Polymer As Chiral Selector By Capillary Electrophoresis

ABSTRACT Chiral separation of peptides is of interest because of the different biological activity of enantiomers. In this report, several underivatized dipeptides with benzene moieties were optically resolved by employing carboxymethyl-β-cyclodextrin polymer(CM-β-CD polymer) as chiral selector. The effects of different cyclodextrin types, selector concentration, buffer pH, and organic additive were examined. Selector concentration and buffer pH played significant roles in resolution. Enantioseparation was found to be negatively influenced by adding the organic additive into running buffer and even completely lost at the organic additive content of 16%. It was also noted that the dipeptides with short chain in the vicinity of the second chiral carbon atom showed better chiral resolution by using CM-β-CD polymer than by using either carboxyethyl-β-CD or succinylated-β-CD. Simultaneous chiral separation of a mixture of DL-Ala-DL-Phe and DL-Leu-DL-Phe was also obtained using 27 mg/ml CM-β-CD polymer in the running buffer at pH5.12.

Separation selectivity in micellar electrokinetic chromatography using different anionic surfactants as pseudo-stationary phases

SummaryMicellar electrokinetic chromatography (MEKC) and ligand exchange-MEKC have been widely used for the separation of achiral and chiral compounds. For the separation of different compounds, one expects to obtain the desired different separation selectivity by choosing different surfactants as pseudo-stationary phases. This paper describes a comparative study on the separation selectivity in MEKC and LE-MEKC using different anionic surfactants such as sodium dodecyl sulfate (SDS), sodium alkyl polyoxyethylene sulfate (AES-Na) and sodium α-sulfonated fatty acid methyl esters (α-SF-Na). Different selectivities were observed with these anionic surfactants. For the separation of aromatic derivatives by MEKC, better selectivity was obtained by using AES-Na than SDS micellar phases. For the simultaneous separation, of positional enantiomers ofo-, m- andp-fluoro-DL-phenylalanine by LE-MEKC, the SDS micellar phase provided the best selectivity among these anionic surfactants. Furthermore, the critical micelle concentrations (CMC) of these surfactants were also estimated by LE-MEKC.