Influence of terminal substituents on the halide anion binding of foldamer-based receptors

Foldamers 1-4 incorporating different terminal substituents have been designed and synthesized for binding halide anions. ¹H NMR titration experiments carried out in DMSO-d₆/CDCl₃ (15/85, v/v) demonstrated that the short oligo(aryltriazole)s backbone 1 could not bind halide anions unless that amide H-bond donors were incorporated at the termini of the oligomer. Terminal substituents on oligo(aryltriazoleamide)s foldamers 2-4 display a considerable influence on the binding affinities of the foldamers for halide anions. Large steric hindrance of the terminal substituents was found to be unfavorable for binding halide anions, but aromatic π-π interactions between two terminal substituents are capable of stabilizing the conformation of foldamers thus giving rise to an enhancement in the binding strengths. However, the terminal substituents were found to hardly affect the binding selectivity in the studied cases.