A tetraguanidinium macrocycle for the recognition and cavity expansion of calix[4]arene tetraoxoanions

Molecular containers have raised an increased interest over the last decade. These supramolecular architectures have found applications in catalysis, molecular sensing or as insulators for key intermediates, among others. In this study, we describe the synthesis and binding properties of a tetraguanidinium macrocycle which forms robust complexes with diverse calix[4]arene tetraoxoanions through hydrogen bonding and electrostatic interactions. The binding behaviour and affinity strength of these constructs have been measured by NMR and isothermal titration calorimetry. Besides, VT NMR experiments show that this novel cyclic tetracation is able to stabilise the cone conformation of these calix[4]arenes. Preliminary NMR-binding experiments between a tetraguanidinium calix[4]arenate and quinolinium or isoquinolinium salts suggest an effective increase in the cavity volume of these supramolecular constructs.