Interaction of 6-p-toluidinylnaphthalene-2-sulphonate with beta-cyclodextrin.

The present study examines the complexation of beta-cyclodextrin (beta-CD) with 6-p-toluidinylnaphthalene-2-sulfonate (TNS), a fluorescent probe for exploring hydrophobic regions of several biological substances. The complexation was monitored in aqueous solution by ultraviolet spectrophotometry. At first, the stoichiometry of the formed complex was examined by applying the continuous variation (Job plot) method. Next, the kinetic of the complex formation as well as the determination of the stability constant were calculated by monitoring the spectrophotometric properties of TNS in the presence of increasing concentrations of beta-CD applying both linear and nonlinear models. The results suggested that TNS forms a stable complex with beta-CD with a stability constant of 1109 M(-1) and 1:1 molar ratio, at least at the examined concentrations.