Volumetric study on the inclusion complex formation of α- and β-cyclodextrin with 1-alkanols at different temperatures

The partial molar volumes (Va) of 1-alkanols (carbon number, m=5, 6, 7) in α- and β-cyclodextrin (CD) solutions at 5.00 mmol kg−1 have been determined as a function of alkanol concentration (Ca) between 293.2 and 308.2 K by using a dilatometer. It has been observed that with an increase in Ca, Va increased in α-CD solution but decreased in β-CD solution, asymptotically to a value of Va in CD-free water. The dependence of Va on Ca provided the binding constant (K) of 1:1 complex, the volume change in complex formation, and the partial molar volume of complex itself. The complex formation mechanism has been discussed on the basis of these values and their carbon number dependences in the respect of geometric behavior, hydrophobic interaction, and van der Waals interaction. It is concluded that the CD cavity in water is not rigid but flexible for fitting in nicely with guest molecule.