A Water-Soluble Cryptophane Decorated with Aromatic Amine Groups Shows High Affinity for Cesium and Thallium(I)

An anti-cryptophane decorated with three aromatic amine and three phenol groups shows a high affinity for the cesium and thallium cations in LiOH/H₂O (0.1 M). The formation of the complexes was studied by ¹³³Cs NMR and by ²⁰⁵Tl NMR spectroscopy at different temperatures. Characteristic signals for caged cesium and thallium were observed at a high field with respect to the signals of the free cations present in the bulk. Isothermal titration calorimetric experiments performed in LiOH/H₂O (0.1 M) and NaOH/KCl buffer (pH = 13) allowed us to determine the parameter of complexation and to ascertain the high affinity of this cryptophane for cesium and thallium. A comparison with other cryptophanes that bind these two cations shows that the introduction of nitrogen atoms into the cryptophane backbone has an effect on the binding properties. The affinity for cesium and thallium(I) ions is in the following order of substitution: OH > NH₂ > OCH₂COOH. This study paves the way to the design of new efficient host molecules for the extraction of these two cations in aqueous solution.