Molecular mechanism of the cesium and rubidium selective binding to the calix[4]arene revealed by Born–Oppenheimer molecular dynamics simulation and electron density analysis

Born–Oppenheimer molecular dynamics simulations with PBE-D3/GTH-DZVP potentials were utilized to explore molecular mechanism of alkali metal cation binding to the calix[4]arene. The calculated standard Gibbs free energy decreased to the higher extent upon binding in case of Cs⁺ and Rb⁺ compared to Li⁺, Na⁺ and K⁺. The experimentally observed selectivity was attributed to the stronger coordination shells of Cs⁺ and Rb⁺ in the calixarene-bound state compared with the water-coordinated complexes as revealed by electron density analysis.