Extraction and complexation of lanthanide ions by dihomooxacalix[4]arene and calix[4]arene tetraketone derivatives: An experimental and molecular dynamics investigation
Résumé
Lanthanide cation binding by tetraketone derivatives of p-tert-butyldihomooxacalix[4]arene (methyl 1a, tert-butyl 1b, adamantyl 1c and phenyl 1d) and of p-tert-butylcalix[4]arene (methyl 2a, adamantyl 2c and phenyl 2d), in the cone conformation, was investigated. These properties were assessed by extraction experiments of the metal picrates from water to dichloromethane and by stability constant measurements in acetonitrile by UV-vis absorption spectrophotometry. Proton NMR titrations with La3+, Eu3+ and Yb3+ cations were also performed to obtain information on the binding sites. Molecular dynamics (MD) simulations and potential of mean force (PMF) free energy calculations were carried out for ligands 1d and 2d in pure solvents and at a CH2Cl2/water interface to add further information on the complexation and extraction processes. Comparison between dihomooxacalix[4]arene and calix[4]arene ketone derivatives showed that the former are better extractants, displaying the highest percentages of extraction for Gd3+ and Yb3+ cations. Concerning complexation, all ligands studied presented high affinities for the lanthanide ions. Ligands 1b and 1d showed preference for the light La3+, while 2d displayed the strongest affinity for the heavy and smaller Yb3+. These results were also corroborated by MD simulations, which revealed specificities of ligands 1d and 2d in the binding of lanthanide cations.