Calix[6]azacryptand-based receptors

Abstract

The calix[6]azacryptands present a grid-like nitrogenous cap that closes the small rim of a calix[6]arene core and rigidifies it into a cone open to the solvent, at the large rim. These macrocycles behaves as heteroditopic receptors, displaying remarkable binding properties toward either neutral guests, zwitterions, anions, contact ion-pairs or metal ions. Despite this versatility, they are highly selective within each class of guests. Furthermore, their channel-like calixarene cavity controls the access to the polyaza recognition site and they are efficient in competitive media (polar and/or coordinating solvents). Their flexibility allows induced-fit processes and their hosting properties can be allosterically controlled by the addition of acids and bases. All these recognition properties are highly reminiscent of the binding processes operating in natural systems.