Remarkable Boosting of the Binding of Ion-Paired Organic Salts by Binary Host Systems The authors thank MURST (PRIN 2000 project) for financial support of this work.

Confinement of the charged constituents of ion-paired organic salts within the complementary cavities of suitably chosen pairs of cation and anion receptors to form supramolecular systems, as shown for the complexation of Nα-Ac-L-Lys-OMe⋅HCl by a calix[5]arene/calix[6]pyrrole combination, results in a remarkable (up to 104-fold) enhancement of the binding ability of the binary host systems compared to that of either receptor taken individually.