Large calixarenes

This chapter deals with those members of the calix[n]arene family having a number n of aryl rings ranging from 7 to 20, which have been defined as the "large" calixarenes. In particular, their synthesis, chemical modification, and supramolecular properties are here reviewed. Notwithstanding their unfavorable common features (the lack of efficient large-scale syntheses, an intricate chemistry, a high conformational mobility, which imply many possible regioisomers with floppy threedimensional shapes) they can be considered useful platforms to construct large hosts for medium-sized organic molecules or metal clusters, or to prepare di- or polytopic receptors, which may present cooperativity or allostery typical of biological systems. The research work here reviewed demonstrates that very interesting results have been already obtained, with recognition properties towards metal and organic cations and different biomolecular targets. Additional applications regard their ability to act as wheels for pseudorotaxane complexes, to stabilize metal clusters, and to give rise to peculiar supramolecular architectures.