A calix[6]arene receptor rigidified by a self-assembled triammonium cap: X-ray and NMR characterization of the binding of polar neutral guests

A calix[6]arene has been rigidified by three primary ammonium arms self-assembled with the counter anions. This supramolecular edifice provides a well-defined conic hydrophobic cavity closed at the narrow rim by a tricationic site. X-ray and NMR analyses show that the resulting polarized host behaves as a remarkable endoreceptor for small molecules such as amides, alcohols and even nitriles. This study highlights the efficiency of a system that associates a cationic site with a hydrophobic cavity to host dipolar neutral molecules.