Water-Soluble Molecular Capsule for the Complexation of Cesium and Thallium Cations
Résumé
Binding properties of cesium and thallium cations by an enantiopure cryptophane derivative PP-1 have been investigated in water under basic conditions. The binding process has been evidenced using electronic circular dichroism (ECD), and binding constants of the Cs+@PP-1 and Tl+@PP-1 complexes have been determined from isothermal titration calorimetry (ITC) experiments in LiOH/H2O, NaOH/H2O, and KOH/H2O solutions. In addition, Tl+@PP-1 complex has been characterized for the first time by 205Tl NMR spectroscopy. Cryptophane 1 exhibits an exceptionally high affinity for thallium and cesium cations in a large range of experimental conditions (nature, concentration of the counterion, and temperature). For example, binding constants as high as 2.9 × 109 M–1 and 5.3 × 108 M–1 have been measured by ITC at 298 K in NaOH/H2O (0.1 M) solution, for the Tl+@PP-1 and Cs+@PP-1 complexes, respectively. The high affinity of cryptophane 1 for Cs+ and Tl+ cations is preserved at higher LiOH, NaOH, and KOH concentrations and under extreme basic conditions, revealing the stability and the great selectivity of this supramolecular system toward Li+, Na+, and K+ cations.