Binding forces contributing to the complexation of organic molecules with β-cyclodextrin in aqueous solution

Abstract

Formation constants of weak inclusion complexes between β-cyclodextrin (CD) and a number of organic solutes in aqueous solution were measured by the spectrophotometric measurement of the inhibitory effect of the solutes on the complexation of CD with phenolphthalein. Types and relative strengths of various intermolecular forces between CD and the guest affecting the stability of inclusion complexes were studied based upon the linear solvation energy relationship (LSER). It was found that increasing guest molecular size stabilizes the complex by virtue of increasing dispersive interactions between the hydrophobic interior of the CD cavity and the guest whereas increasing guest dipolarity and hydrogen bond (HB) acceptor basicity lead to a decrease in the stability of the complex due to the stronger dipolar and hydrogen bonding interactions with water, which is more dipolar and HB acidic than CD.