SURFACE-TENSION AND H-1-NMR STUDIES ON INCLUSION COMPLEXES OF BETA-CYCLODEXTRIN WITH SODIUM ALKYL SULFONATE

The inclusion complexes of beta-CD with sodium octyl sulfonate (C8As), sodium dodecyl sulfonate (C12As), and sodium hexadecyl sulfonate (C16 As) in aqueous solutions have been studied by surface tension measurem ent at the air/water interface and H-1 NMR spectroscopy at 323 K. At f ixed concentrations of the surfactants, the surface tensions first inc rease with the increase of beta-CD concentrations, then they attain a maximum. The surface tension curves of the surfactants in the presence of beta-CD are higher than those in the absence of beta-CD. The value s increase with increasing beta-CD concentrations for each surfactant. The apparent critical micelle concentrations (CMC) of the surfactants vary linearly with beta-CD concentrations. A H-1 NMR study shows that the signals of the inner H-3 and H-5 of beta-CD shift upfield upon ad dition of the surfactants. The magnitude of the chemical shift changes (Delta delta = delta(CD) - delta(obs)) varies as a function of the co ncentrations of the surfactants. From the relationships between the ch emical shift changes of H-3 or H-5 inside the beta-CD cavity and guest /host molar ratios, a 1:1 stoichiometry for each inclusion complex is assumed. The association constants of the inclusion complexes have bee n determined by H-1 NMR spectroscopy.