Determination of Binding Affinity for Chenodeoxycholate in Equilibrium with Sulfobutylether-β-Cyclodextrin

A kinetic dialysis technique together with a radiolabeled chenodeoxycholate (CDC) was used to determine the existence of a relationship between the monomer concentration of CDC and the total CDC concentration in different CDC solutions containing 1 or 5 mM sulfobutylether (SBE)-β-cyclodextrin. On the basis of the nature of the relationship and a binding model with binding constants of K1 and K2, the binding affinity for the solutions was quantified at the best curve fitting using a least-squares technique. The very high binding affinity of K1 and the very low (i.e., negligible) binding affinity of K2 indicate the formation of 1:1 inclusion complexes. In addition, the values of K1 and K2 were reasonably interpreted. Similar analysis showed that the formation of 1:2 inclusion complexes and the self-association of the SBE-β-cyclodextrin molecules in the solutions are unlikely. The present study provides a basis for investigating the self-association, quantifying the binding affinity, and interpreting the quantified values. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association