Substituent effects on the driving force for inclusion complexation of α- and β-cyclodextrin with monosubstituted benzene derivatives

The association constant values, K-a, for the inclusion of alpha- and beta-CD with monosubstituted benzene derivatives were determined by means of UV-vis and fluorescence spectroscopy. The stability of the complexes is influenced by the properties of the substituents of the guest compounds. Regression analysis was used to create a set of inclusion models with the experimental association constant In K-a and the corresponding substituent molar refraction R-m, hydrophobic constant pi and Hammett sigma constant of the benzene derivatives. The In K-a value mainly correlated with R-m for alpha-CD and with both R-m and pi for beta-CD complexes. The association constants predicted by the models are in good agreement with the experimentally determined data. This suggests that the inclusion complexation of benzene derivatives with alpha-CD is predominantly driven by van der Waals force and with beta-CD mainly by van der Waals force and hydrophobic interactions.