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Cu(II) complexed amino acid ionic liquid, Cu(II)-[1-butyl-3-methylimidazolium][L-Pro] (Cu(II)-[BMIm][L-Pro]), was successfully adopted as chiral ligand to improve the enantioseparation efficiency in high speed counter-current chromatography (HSCCC). For the enantioseparation of intractable naringenin (NRG) racemic mixtures, Cu(II)-[BMIm][L-Pro] coupled with hydroxypropyl-β-cyclodextrin (HP-β-CD) was successfully applied as dual chiral selectors in HSCCC. The influence of important parameters, including the concentration of the chiral selectors, the pH value, and the temperature were investigated. Under optimal conditions, 4.5 mg of (+)-NRG and 4.1 mg of (−)-NRG were successfully separated from 10 mg NRG racemic mixtures with the purity of 98%. The chiral recognition mechanism of dual chiral selectors was illuminated by the UV–vis and NMR spectra, suggesting that the enantioseparation was upon the difference of the thermodynamic stability of the quaternary complexes of Cu(II), [BMIm][L-Pro], HP-β-CD, and NRG. The results illustrated that the developed HSCCC system, based on the synergistic mechanism of Cu(II)-[BMIm][L-Pro] and HP-β-CD, exhibited better performance on enantioseparation and had great application potential in preparative chiral separation of natural products. [ABSTRACT FROM AUTHOR]

The use of a dinuclear Cu 2 (II)-β-cyclodextrin complex (Cu 2 -β-CyD) as a chiral selector (CS) was successfully applied to chiral high speed counter-current chromatography (HSCCC) for the enantioseparation of aromatic α-hydroxycarboxylic acids. α-cyclohexylmandelic acid (CHMA) as a case was studied to optimize the separation temperature, the pH value of the aqueous phase, and the concentration of the chiral selector, which were comparatively studied between Cu 2 -β-CyD and native β-cyclodextrin (β-CyD) as CSs. The thermodynamic parameters of the formation of the complex between the enantiomers and the CSs were obtained, and the complex formation constants between the enantiomers and Cu 2 -β-CyD or β-CyD were determined using induced circular dichroism technology. The results indicate that Cu 2 -β-CyD can remarkably improve the enantioseparation compared with β-CyD, mainly due to the ion-pairing interactions between the deprotonation of carboxyl group of CHMA and the Cu(II) ion of Cu 2 -β-CyD. Five of other aromatic α-hydroxycarboxylic acids were also enantioseparated successfully by HSCCC using Cu 2 -β-CyD as a CS. [ABSTRACT FROM AUTHOR]