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 1H 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.