FORMATION OF INCLUSION COMPLEXES OF CYCLODEXTRINS WITH BILE-SALT ANIONS AS DETERMINED BY NMR TITRATION STUDIES

The interactions between bile acid anions and cyclodextrins (CDs) in a queous solution at room temperature have been studied in detail by the NMR titration method. The conformation adopted by the inclusion compl ex depends on the size of the cavity of the CD: The inclusion complexe s with beta-CD result primarily from interactions with the smaller, hy drophilic side chains of the bile acid anions, while those with gamma- CD, which has a larger cavity, involve interactions with the larger, h ydrophobic end of bile acid anions. The results indicate that hydropho bic interactions between the host CD molecules and the guest bile acid anions are important in the formation of the complexes. Steric hindra nce of certain groups, especially that due to the 12-OH group of the s teroid skeleton, has important effects on the interaction. These resul ts are consistent with additional information derived from molecular m odeling studies.