[UV spectroscopic characterization of the inclusion interaction of beta-cyclodextrin and sym-diphenyl-thiourea and sym-diphenyl-urea].

The inclusion interaction of beta-cyclodextrin and sym-diphenyl-thiourea and sym-diphenyl-urea was studied by UV spectra. The stoichiometry ratio for the formation of the inclusion complexes was determined by Hildebrand-Benesi equation linear analysis and molar ratio method. The standard molar Gibbs energies, enthalpies, and entropies were derived for the inclusion process by Ks at different temperatrues. The result showed that the host:guest ratio of inclusion complex between the two diphenyl compounds and beta-CD is 2 : 1, the stability constant (Ks) of 2 : 1 inclusion complexes was higher than that of 1 : 1 inclusion complexes due to cooperative binding in the close two hydrophobic cyclodextrin cavities, and the association of the guest molecule with beta-CD was favored by enthalpy changes, proving that the Van der Waals interaction and the dipole-dipole interaction were main binding forces of cyclodextrin inclusion complex.