SYNTHETIC IONOPHORES .13. PYRIDINE-DIAMIDE-DIESTER RECEPTORS - REMARKABLE EFFECT OF AMIDE SUBSTITUENTS ON MOLECULAR-ORGANIZATION AND AG+ SELECTIVITY

The N-Py... HNamide hydrogen bonding within the macrocyclic cavities i n 9, 10, and 13 invokes their symmetrical electron-deficient structure s (H-1 NMR) and consequently bind with water. This results in their po or ionophore characters. The steric requirement of methyl/bentyl subst ituents on am ide N in 11 and 12 takes the substituents out of the cav ity and thus positions the amide 0 toward the cavity (H-1, C-13 NMR an d X-ray analysis). This arrangement of two pyridine N and two amide 0 (C-13 NMR, IR) binding sites provides an appropriate environment for s elective binding toward Ag+ over Pb2+, Tl+, alkali, and alkaline earth cations. The increased spacer length in 14 leads to a lop-sided twist of pyridine rings (X-ray) and disturbs the above arrangement and lead s to its poor binding character.