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

The assocn. const., std. Gibbs energy, enthalpy and entropy for formation of inclusion complexes of propranolol, a b-blocker, with various natural and modified cyclodextrins have been detd. by calorimetry at 298 K. Both natural and methyl-modified a-cyclodextrins do not form complexes, while b- and g-cyclodextrins do. Complexing ability of 2-hydroxypropyl-b-cyclodextrin depends on the av. substitution degree. For g-cyclodextrin, hydrophobic interactions play the major role in binding the guest. The assocn. of natural and modified b-cyclodextrins is ruled by van der Waals interactions and hydrogen bonding because of the tighter fit of the guest into the cavity. Decreasing pH dets. increasingly neg. values of the assocn. enthalpies