A new series of heteroaromatic receptors containing the 1,3-bis(6-oxopyridazin-1-yl)propane unit: their selective transport ability towards NH4+ in relation to Na+, K+ and Ca2+

The synthesis of a new series of heteroaromatic macrocycles containing the 1,3-bis(6-oxopyridazin-1-yl)propane and pyridine units is reported. The acyclic compounds had to be prepared as the intermediates in the synthetic sequence. Evaluation of the ionophoric properties of and shows that and behave as good ammonium ion carriers and exhibit a high selectivity for ammonium with respect to spherically symmetric metallic ions like Na+, K+, and Ca2+. Molecular modelling of the ammonium complexes suggests that the hostʹs oxyimino groups play a more relevant part in effective complexation than the pyridine unit, and that the high complexating efficiency of might be related to the formation of a pseudocavity by intramolecular hydrogen bonding.