Selectivity and Cooperativity in the Binding of Multiple Guests to a Pillar[5]arene-Crown Ether Fused Tricyclic Host.

A novel tricylic host molecule 1 that consists of two pillar[5]arene units and a crown ether ring was found to selectively bind two kinds of guest molecules with different shapes, sizes, and electronic constitutions, namely 1,4-dicyanobutane G1 and paraquat G2, with its two macrocyclic subunits, to form a four-component complex 2G1⊂1⊃G2. An (1)H NMR study of stepwise bindings of G1 and G2 to host 1 in CDCl3/DMSO-d6 revealed that the strength of the association between complex 2G1⊂1 and guest G2 was only one-fourth of that between free 1 and G2, demonstrating a negative heterotropic cooperativity of G1 in the binding of G2 to host 1.