Recognition of Ammonium Ions and Related Substrates

A great variety of macrocyclic polyethers have been shown to bind R-NH3+ molecules with structural and chiral selectivity [2.100-2.103, 2.107]. Extensive 

Varying the side groups X in 27b affects both the stability and selectivity of the complexes (lateral discrimination), and allows the receptor-substrate interactions in biological systems to be modelled, for instance, the interaction between nicotinamide and tryptophan [2.109b]. One may attach to 27b amino acid residues (leading to parallel peptides [2.109] as in 27c), nucleic acid bases or nucleosides, saccharides, etc. The structural features of 27 and its remarkable binding properties make it an attractive unit for the construction of macropolycyclic multisite receptors, molecular catalysts, and carriers for membrane transport. Such extensions require sepa- 

Gas phase studies reveal size selective effects on binding of ammonium cations to crown ethers and acyclic analogs [2.111]. 

---