Synthetic Ionophores. 13. Pyridine-Diamide-Diester Receptors: Remarkable Effect of Amide Substituents on Molecular Organization and Ag(+) Selectivity.
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.
Kumar
Subodh
S
Departmento de Cristalografia, Instituto de Quimica Fisica, Rocasolano, Serrano-119, E-28006, Madrid, Spain.
Hundal
Maninder Singh
MS
Kaur
Navneet
N
Singh
Rajinder
R
Singh
Harjit
H
Hundal Nee Sood
Geeta
G
Ripoll
Martin Martinez
MM
Aparicio
Juliana Sanz
JS