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

The association constant, standard Gibbs energy, enthalpy and entropy for formation of inclusion complexes of propranolol, a β-blocker, with various natural and modified cyclodextrins have been determined by calorimetry at 298 K. Both natural and methyl-modified α-cyclodextrins do not form complexes, while β- and γ-cyclodextrins do. Complexing ability of 2-hydroxypropyl-β-cyclodextrin depends on the average substitution degree. For γ-cyclodextrin, hydrophobic interactions play the major role in binding the guest. The association of natural and modified β-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.