Ammonium Calixarene Complexes

Calixarenes are macrocyclic compounds that form complexes with ions and neutral molecules. Association with ammonium cations and calixarenes is directed by coulombic forces, hydrogen bonding, N+-C-H---π interactions and van der Waals interactions. Calixarenes are stronger acids than corresponding phenols and react with aliphatic amines by proton-transfer and the ammonium cations can be placed as exo or endo-calix. The type of aggregate and the association constants are related to the branching of the chain, the basic character of amine, and the size of the calix. Trimethylammonium cations, like choline, bind sulfonate calix[4 and 6]arenes and calix[6]arenes by coulombic and N+-C-H---π interactions. Interaction of calixarenes and ammonium cations has been used for biological sensors for neurotransmitters and peptide hormones.