Binding constant dependency of amphetamines with various commercial methylated beta-cyclodextrins

Cyclodextrins play an important role in enantioselective separations. They represent the major class of chiral selectors used by capillary electrophoresis. Unfortunately, the purity of commercial cyclodextrins is often not well characterized, and similar selectors sold by various suppliers may show totally different enantioselectivities. In this study, the composition of several commercial methylated-beta-cyclodextrins is evaluated by means of previously developed analytical methods. Then, different calculation methodologies, such as graphical determinations, as well as nonlinear or linear regression approaches, are evaluated in order to calculate the binding constants of inclusion complexes formed by some amphetamine derivatives with methylated-beta-cyclodextrins. The nonlinear curve-fitting methodology proves to be the most suitable for these determinations. Comparisons are made between the different selectors and several hypotheses are proposed concerning the formation of the inclusion complex. Finally, enantiomeric resolutions are evaluated for these selectors and conclusions drawn about the knowledge of selector composition.