Inclusion of Quaternary Ammonium Compounds by Calixarenes

In weakly polar solvents, strong association occurs between calixarene anions and tetraalkylammonium cations, with the magnitude of the observed equilibrium constants depending upon the charge on the anion, the solvent, the ring size of the calixarene and the nature of the alkyl group of the cation. Large upfield shifts of the methyl resonances of the [(CH3)(4)N](+) cation in solutions of [(CH3)(4)N](2) [p-t-butylcalix[6]arene - 2H] indicate cation inclusion in a structure which is possibly identical with that found for the solid 'salt' by X-ray crystallography. This shows one of the cations to be included within a partial cone structure of a 'hinged 3-up, 3-down' conformation of the calixarene. The functionalised tetramethylammonium ions, choline and acetyl choline, are also strongly included by various calixarene anions but attempts to detect significant modification of the reactivity of acetyl choline resulting from inclusion have not been successful.