Thermodynamics of inclusion complexes of natural and modified cyclodextrins with propranolol in aqueous solution at 298 K

The association constant, standard Gibbs energy, enthalpy and entropy for formation of inclusion complexes of propranolol, a beta-blocker, with various natural and modified cyclodextrins have been determined by caloritnetry at 298 K. Both natural and methyl-modified alpha-cyclodextrins do not form complexes, while beta- and gamma-cyclodextrins do. Complexing ability of 2-hydroxypropyl-beta-cyclodextrin depends on the average Substitution degree. For gamma-cyclodextrin, hydrophobic interactions play the major role in binding the guest. The association of natural and modified P-cyclodextrins is ruled by van der Waals interactions and hydrogen bonding because of the tighter fit of the guest into the cavity. Decreasing pH determines increasingly negative Values of the association enthalpies. (c) 2006 Elsevier Ltd. All rights reserved.