Enantioseparation of dansyl amino acids by ligand-exchange capillary electrophoresis with zinc(II)-L-phenylalaninamide complex.

A novel method of chiral ligand-exchange CE was developed with L-amino acylamides as a chiral ligand and zinc(II) as a central ion. It has been demonstrated that these chiral complexes, such as Zn(II)-L-alaninamide, Zn(II)-L-prolinamide, and Zn(II)-L-phenylalaninamide, are suitable for use as chiral selectors for the enantioseparation of either individual pair of or mixed dansyl amino acids. The optimal separation running buffer consisted of 5 mM ammonium acetate, 100 mM boric acid, 4 mM ZnSO(4) x 7 H(2)O, and 8 mM L-amino acylamides at pH 8.2. The experiments showed that apart from the effect of the concentration of the complexes on the resolution and the migration time, the buffer pH also had a sharp influence on resolution. The employed chiral ligands exhibited different enantioselectivities and enantiomer migration orders. D-amino acids migrate faster than L-amino acids when Zn(II)-L-alaninamide and Zn(II)-L-phenylalaninamide are used as chiral selectors, but it was observed that the migration order is reversed when Zn(II)-L-prolinamide is used as the chiral selector. Furthermore, the amount of dansylated amino acids is found to be highly dependent on the labeling temperature.