Thermodynamics of the interaction between hydroxypropyl-α-cyclodextrin and alkanols in aqueous solutions

The interactions of hydroxvpropyl-alpha-cyclodextrin (HP-alpha-CD) with 1-alkanols and with some alpha,omega-alkanediols have been studied by calorimetric titration at 298.15 K. This technique enables the determination of the enthalpy and association constant for the complex formation, from which Gibbs energy and entropy can be derived. The results are compared to those reported for the complex formation between the native alpha-cyclodextrin (alpha-CD) and 1-alkanols or alpha,omega-alkanediols in the literature. Thermodynamic parameters corresponding to the transfer process of the alkanol from the native to the modified alpha-CD are also calculated. The results clearly show that the hydrophobic interactions are important in this process, but there are other effects like the size of the alkanol that are also of some importance. (C) 2003 Elsevier Science B.V. All rights reserved.