Amino-substituted β-cyclodextrin copper(II) complexes for the electrophoretic enantioseparation of dansyl amino acids: Role of dual chelate–inclusion interaction and mechanism

The four amino-substituted β-cyclodextrins were synthesized and used as the chiral ligands to form the copper(II) complexes, respectively. CDen copper(II) complex was applied as the model selector to optimize the electrophoresis conditions and all the selected chiral dansyl amino acids were baseline separated under the proposed method, the optimum experimental conditions were 10 mmol/L CDen, 10 mmol/L CuSO4·5H2O, 5.0 mg/mL PEG20000 and 1.5% (v/v) tertbutyl alcohol, pH 4.2. By comparing the enantioselectivity of the copper(II) copmplexes of four amino-substituted β-CDs, the cooperation between the inclusion and chelate interaction was demonstrated to be the key factor to obtain satisfactory chiral discrimination ability. Fluorescence experiments were carried out to investigate microenvironment of the chiral recognition process, which indicated that the order of penetration depth of dansyl group into the host cavity is CD > CDen copper(II) complex > CDdien copper(II)complex, and the molecular bulk of derivatization reagents has great effect on the chiral separation.