Investigation of interactions between drug enantiomers and flavoprotein as a chiral selector by affinity capillary electrophoresis

Interactions between drug enantiomers and flavoprotein as a pseudo chiral stationary phase were investigated by using affinity capillary electrophoresis (CE) in order to avoid the effects of nonspecific interactions that occur in chiral HPLC. Circular dichroism (CD) measurement was used to monitor changes of the secondary structure of flavoprotein under various analysis conditions in affinity CE. The chiral discrimination region for ketoprofen on the flavoprotein surface was concluded to consist of α- helix structure, and the decrease of chiral separation ability with increase of methanol content in the electrophoretic buffer was directly related to conformational change of the α-helix. Studies with chemically modified flavoprotein indicated that two types of interaction at the chiral discrimination region are required for chiral separation: π-π interaction of a tryptophan residue with the aromatic ring of ketoprofen, and ionic interaction of the carboxyl group of ketoprofen with an amino group and a carboxyl group of the protein.