Speed of Sound, Density, and Molecular Modeling Studies on the Inclusion Complex between Sodium Cholate and β-Cyclodextrin

The system sodium cholate (NaC) + β-cyclodextrin (β-CD) in water has been studied by speed of sound and density measurements to obtain the corresponding apparent and partial molar volumes and adiabatic compressibilities. For pure NaC the values for the micellization volumes and compressibilities have been obtained, as well as the transference properties due to the complexation for the ternary system. When the β-CD is present, a shift in the critical micelle concentration of the surfactant equivalent to the amount of β-CD added is observed, due to the complex formation between solutes that delays the micellization. At infinite dilution, there is a marked change in the compressibility of the surfactant, although it is not appreciable in the volume. A detailed molecular modeling study has been carried out to elucidate, together with 1 H NMR data, the microscopic structure of the complex.