Hydrophobic interactions in the formation of a complex between a polycationic water-soluble oxacalix[4]arene and a neutral aromatic guest

Polycationic oxacalix[4]arene 1 center dot 4HCl was found to be able to recognise, in water, the neutral pi-rich aromatic guest 2,7-dihydroxynaphthalene, despite earlier studies indicating that the binding cleft of the oxacalixarene is pi rich in nature. H-1 NMR titrations at different pH values demonstrate that the tricationic receptor 1 center dot 3H(+) displays the highest affinity towards DHN. According to a combination of NMR data and semiempirical (PM6) calculations, hydrophobic interactions play a prominent role in the formation of the complex.