| Research Abstract |
In chiral ligand exchange capillary electrophoresis(CLECE), copper(II) complexes with amino acids or their derivatives have been widely used as chiral selectors for the enantioseparation of amino acids, their derivatives, and α-hydroxy acids, where the ternary copper(II) complexes are formed by the ligand-exchange reaction of the chiral selector with the racemate. On the other hand, borate anion interacts with cis-1, 2- and cis-1, 3-diols to form monocyclic complex, and spirocyclic complex, which coexist in aqueous solution. Recently, we have found that native DL-pantothenic acid(DL-PTA) was enantioseparated by CLECE using borate as a central ion and(S)-3-amino-1, 2-propanediol(SAP) as a chiral selector. In this study, we studied (1) the mechanism of enantioseparation of DL-PTA in CLECE using a diol-borate system and (2) the application of CLECE for the enantioseparation of other diols and polyols. (3) In order to apply the proposed CLECE to real samples, we also studied covalent modif
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ication procedures to obtain capillary that gives reproducibile migration times for CE.
(1) Using ^<13>C and^<11>B NMR, it was confirmed that the binary complexes and the ternary complexes coexist at equilibrium in the ternary system. Thermodynamic experiments by variable temperature ^<11>B NMR revealed that the ternary complex, [B(SAP)(D-PTA)]^-, was entropically more stable than [B(SAP)(L-PTA)]^-. Two geometrical isomers are possible for the respective ternary complexes, senuempmcal molecular orbital calculations indicated that(5) isomer is more probable for the respective ternary complexes with D^- and L-PTA. In the optimized structure of(S)-[B(SAP)(D-PTA)]^- in water, the SAP and D-PTA ligands were oppositely oriented to form a rather linear structure, while the diastereomer, (5)-[B(SAP)(L-PTA)]^-, have a folded structure. Because such a difference in the solvated structure of the ternary complexes can give different electrophoretic velocity in capillary electrophoresis, the enantioseparation of DL-PTA in CE is reasonably attributed to a difference in the observed electrophoretic mobility for the equilibrated ternary systems containing the respective ternary complexes.
(2) We found that three compounds having 1, 2-diol structure(1-phenyl-1, 2-ethanediol, 3-phenoxy-1, 2-propanediol and 3-benzyloxy-1, 2-propanediol) were enantioseparated by ligand exchange micellar electrokinetic chromatography using(1S, 2S, 3R, 5S)-pinanediol as a chiral selector and borate anion as a central ion together with sodium dodecyl sulfate and that six reducing monosaccharides(mannose, galactose, fucose, glucose, xylose, and arabinose), which were derivatized with 8-aminonaphtalene-1, 3, 6-trisufonate, were simultaneously enantioseparated by CLECE using borate as a central ion and SAP as a chiral selector.
(3) Sulfonated groups were chemically introduced to an inner wall of untreated fused silica capillary with 2-(4-chlorosulfonylphenyl) ethyltrichlorosilane. The sulfona Less
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