title: Synthetic Ionophores. 13. Pyridine-Diamide-Diester Receptors: Remarkable Effect of Amide Substituents on Molecular Organization and Ag(+) Selectivity.
abstract: The N(Py).HN(amide) hydrogen bonding within the macrocyclic cavities in 9, 10, and 13 invokes their symmetrical electron-deficient structures ((1)H NMR) and consequently bind with water. This results in their poor ionophore characters. The steric requirement of methyl/benzyl substituents on amide N in 11 and 12 takes the substituents out of the cavity and thus positions the amide O toward the cavity ((1)H, (13)C NMR and X-ray analysis). This arrangement of two pyridine N and two amide O ((13)C NMR, IR) binding sites provides an appropriate environment for selective binding toward Ag(+) over Pb(2+), 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 leads to its poor binding character.
authors.affiliation: Departmento de Cristalografia, Instituto de Quimica Fisica, Rocasolano, Serrano-119, E-28006, Madrid, Spain.
authors.forename: Subodh
authors.initials: S
authors.lastname: Kumar
authors.forename: Maninder Singh
authors.initials: MS
authors.lastname: Hundal
authors.forename: Navneet
authors.initials: N
authors.lastname: Kaur
authors.forename: Rajinder
authors.initials: R
authors.lastname: Singh
authors.forename: Harjit
authors.initials: H
authors.lastname: Singh
authors.forename: Geeta
authors.initials: G
authors.lastname: Hundal Nee Sood
authors.forename: Martin Martinez
authors.initials: MM
authors.lastname: Ripoll
authors.forename: Juliana Sanz
authors.initials: JS
authors.lastname: Aparicio