Synthetic ditopic receptors

A small. but emerging field of topical interest in supramolecular chemistry is ion-pair recognition, in which a host simultaneously binds both cationic and anionic guests. Details of these receptors. which combine, for example, crown ethers and calixarenes for cation complexation, with Lewis acid centers, pyrroles, amides or urea groups for anion recognition, will be discussed. The predicate of this approach, successfully achieved in certain instances, is that the binding of one guest ion can induce electrostatic and conformational changes in the host, thereby enhancing the complexation of the counter ion