Thermodynamics of the interaction between antihistamines with native and hydroxypropyl-cyclodextrin derivatives in aqueous solutions

The interactions of native and hydroxypropyl-cyclodextrin derivatives with pheniramine, (+/-)-brompheniramine, (+)-brompheniramine, (+/-)-chlorpheniramine, (+)-chlorpheniramine, carbinoxamine maleate salts and doxylamine succinate salt have been studied by isothermal titration calorimetry at T = 298.15 K in aqueous solution. The enthalpies and association constants for the complex formation were obtained, from which the Gibbs energy and entropy changes were derived. The thermodynamic parameters corresponding to the transfer process of the guest from the native to the modified CD are also calculated. The results show that the hydrophobic interactions are important in this process, but the size of the guest and the nature of the substituent are also of some importance. (c) 2013 Elsevier Ltd. All rights reserved.