Coreceptor–substrate binding. Crystal structures of a macrotricyclic ligand and of its molecular cryptate with the cadaverine dication

The structure of the complex formed by the macrotricycle (1) with the cadaverine dication is a mononuclear-dihapto molecular cryptate-{+H3N–[CH2]5–NH3+⊂(1)}, (2), in which the substrate is held inside the coreceptor molecule by simultaneous binding to the macrocyclic subunits; the preferential complexation of this dication results from the structural complementarity between the receptor and the substrate.