Effect of Hydrogen Binding on Selective Recognition of Halide Anions

Abstract

AbstractThe interplay of molecular rigidity enforced by interior or exterior hydrogen bonding and affinity for binding halide anions is described to demonstrate the effect of intramolecular hydrogen bonding in anion recognition process. To this end pyridine‐2,6‐dicarboxamides 1 and 2, and aromatic oligoamides 3 and 4 containing intramolecular hydrogen bonds were explored for their ability in associating with tetrabutylammonium halide (Cl−, Br−, and I−). Binding constants in chloroform solution were calculated using nonlinear curve‐fitting method based on 1H NMR titration experiments. The trimeric amide 3, which adopts a crescent conformation as revealed by single‐crystal X‐ray diffraction analysis, strongly binds chloride anion with binding constant as high as 379 L·mol−1. This is more than 6 times greater than the binding constant for the control receptor 2 with a backbone that is only partially rigidified. The comparative data provided supportive information for rationalizing the observed affinity difference in binding halide anions in terms of local preorganization effected by interior or exterior hydrogen bonding.