Jm. Harrowfield et al., INCLUSION OF QUATERNARY AMMONIUM-COMPOUNDS BY CALIXARENES, Journal of inclusion phenomena and molecular recognition in chemistry, 19(1-4), 1994, pp. 257-276
In weakly polar solvents, strong association occurs between calixarene
anions and tetraalkylammonium cations, with the magnitude of the obse
rved 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-butylcal
ix[6]arene - 2H] indicate cation inclusion in a structure which is pos
sibly identical with that found for the solid 'salt' by X-ray crystall
ography. This shows one of the cations to be included within a partial
cone structure of a 'hinged 3-up, 3-down' conformation of the calixar
ene. The functionalised tetramethylammonium ions, choline and acetyl c
holine, are also strongly included by various calixarene anions but at
tempts to detect significant modification of the reactivity of acetyl
choline resulting from inclusion have not been successful.