Molecular recognition involving multiple cation–π interactions: the inclusion of the acetylcholine trimethylammonium moiety in resorcin[4]arene

X-Ray analysis of the molecular complex formed between the neurotransmitter acetylcholine (ACh) and resorcin[4]arene, ACh + .resorcinarene.Cl - .H 2 O shows that the ACh molecule is captured by the macrocyclic resorcinol tetramer through multiple cation–π interactions between the quaternary trimethylammonium group of ACh and the four π-rings of the cavitand.