Chapter 3: Key Roles of Cavity Portals in Host-Guest Binding Interactions by Cucurbituril Hosts

This chapter summarizes research work showing that electrostatic interactions may have considerable effects on the stability of complexes formed by the cucurbit[n]uril hosts. Focusing primarily on work carried out by the author's research group with the cucurbit[7]uril (CB[7]) molecular receptor, this review highlights the role played by electrostatic interactions involving the host cavity portals, in which considerable negative charge density accumulates due to the carbonyl oxygens lacing the portal rims. Electrostatics are responsible for diminished binding affinities between CB[7] and a number of anionic guests containing one or more carboxylate groups. These electrostatic interactions can be used effectively to control the average location of CB[7] along axle-type guests having terminal -COOH groups as a function of their state of protonation, leading to switchable pseudorotaxane systems. They can also be utilized to advantage to develop favorable lateral interactions between CB[7] and other molecular receptors, which results in systems showing cooperative self-assembly.