Reversal behaviors of the enantiomer migration order and the stereo-selectivity of Cu(II) complex with amino acid enantiomers in ligand exchange-micellar electrokinetic chromatography

The dependence of the enantioselectivity and enantiomer migration order (EMO) on the chirality and stereo-conformation of ligands used for the chiral selectors of Cu(II) complexes was investigated. It was interestingly observed that EMOs were reversed not only by a change of the ligand chirality of selector, but also by the trans- or cis-conformation of a 4-hydroxy substituent in 4-hydroxyproline. In the presence of the sodium dodecyl sulfate (SDS) micellar phase, the EMOs were reversed when both the bidentate and tridentate ligands of the proline family were used. The resolution (Rs) of enantiomers decreases when the cis-hydroxy substituent exists in D- or L-hydroxyproline. SDS micellar phase improves the resolution of amino acid enantiomers. The relationships among the EMO, ligand chirality, complex stability and stereo-selectivity are discussed.