Determination of thermodynamic and kinetic parameters of inclusion complex formation of 2-mercaptobenzothiazole with beta-cyclodextrin

The inclusion of 2-mercaptobenzothiazole by beta-cyclodextrin was studied by spectrophotometry. The absorbance of inclusion complex decreased when beta-cyclodextrin was dissolved in water and the complex was diluted with ethanol. The same result was obtained by using water as the solvent and diluent. The absorbance decrease in ethanol was greater than that in water. The absorbance increased with the increase of the content of beta-cyclodextrin when DMSO was used both as the solvent and diluent. Although the absorbance of the complex was higher than that of the guest when beta-cyclodextrin was dissolved in DMSO and inclusion complex was diluted with water, the absorption decreased when the concentration of beta-cyclodextrin was increased. Stability constants of the inclusion complex in different solvents changed in the order K-DMSO < KH2O < K-EtOH. Further studies showed that formation of the inclusion complex was spontaneous and exothermic. Thermodynamic parameters and the rate constants of the inclusion reaction were determined.