Formation and self-association of host-guest complexes between βCD and nonionic surfactants Brij

Abstract

The thermodynamic study of inclusion complexes formed between cyclodextrin and surfactants gives valuable information about how the hydrophobic/hydrophilic balance affects the complex formation. Although various surfactants have been used with this purpose, there is a lack of thermodynamic data about the formation of complexes between β-cyclodextrin (βCD) and the nonionic Brij surfactants. Moreover, the effect of ionic liquids (IL) on this system has not yet been reported. Isothermal titration calorimetry was used for determining the thermodynamic parameters and stoichiometry of the complexes formed, in the absence and presence of 1-butyl-3-methylimidazolium chloride (C4mimCl). The dynamic light scattering technique was used for complementing the results. Both the tail and head group of the surfactants was included by βCD, and the complexes’ stability followed the order: Brij 78 > Brij 58 ≈ Brij 56 > Brij 76. The standard enthalpy and entropy change were negative for all complexes, indicating the process is enthalpy-driven. The increase of the surfactants’ hydrophilicity didn’t affect the complexes’ stability, while the increase of the hydrophobicity induced the formation of inclusion complex aggregates with 200–270 nm. Finally, the increase of C4mimCl concentration do not affect the complex stability but increase the enthalpy and entropy change associated with the inclusion complex formation.