Interaction of 8-Anilino-1-naphthalenesulfonate with Heptakis(2, 3, 6-tri-O-methyl)-[beta]-cyclodextrin

The interaction of 8-anilino-1-naphtalenesulfonate (ANS) with heptakis(2, 3, 6-tri-O-methyl)-β-cyclodextrin (TOM-β-CD) was investigated in a 0.1 M phosphate buffer at pH 7.4 by fluorescence spectrophotometry. Utilizing the fact that the fluorescence intensity of ANS increases in the presence of TOM-β-CD, the thermodynamic parameters for inclusion complex formation were determined as follows : δG°=-8.95kJ·mol-1 at 25°C, δH°=-10.9kJ·mol-1, δS°=-6.3J·mol-1·K-1. The main driving force for the inclusion complex was considered to be the van der Waals-London dispersion forces, while the contributions of the hydrophobic interaction was small. Also, from the measurements of proton nuclear magnetic resonance spectra and studies with Corey Pauling Koltun models, the probable structure of the complex was determined. Further, the effects of permethylation on inclusion complex formation were discussed.