Cyclodextrin-assisted capillary electrophoretic resolution of 1,1'-bi-2-naphthol atropisomers

Native beta- and gamma-cyclodextrin (CD), neutral beta-CD derivatives and ethylcarbonate derivatives of beta- and gamma-CD were used as stereoselective additives for CD-capillary zone electrophoresis (CZE) resolution of atropisomers of 1,1'-bi-(2-naphthol) (BN). CZE experiments at variable CD concentration allowed calculating binding constants from electrophoretic mobility data, corrected for electroosmotic flow (EOF) and running buffer viscosity variations. The CDs were chosen on the basis of geometric examination of molecular models of BN and CDs that suggested the possibility of inclusion complexes formation. Optimum concentrations, with aqueous 25 mM phosphate running buffer at pH 10.5, 36 cm x 50 microm capillary and 10 kV applied potential, were 3.6, 3.9, 2.1, 2.2, 1.9 mM for beta-CD, gamma-CD, ethylcarbonate-beta-CD, methyl-beta-CD and hydroxypropyl-beta-CD, respectively.