Exploiting cooperative binding of ion-pair to boost anion recognition in water/acetonitrile mixtures

An L-arginine based compound was designed and prepared as a heteroditopic ion-pair receptor. The cation binding is provided by a sodium selective N-acyl-aza-18-crown-6 subunit whereas for anion complexation, urea and guanidinium groups were introduced. As shown by 1H NMR titrations this receptor is capable of binding sodium halide ion-pairs in solutions containing up to 20% of water. The halide binding is stronger in the presence of co-coordinated sodium cation than in the presence of non-coordinated TBA cation.