Lanthanide cationextraction by malonamideligands: from liquid–liquid interfaces to microemulsions. A molecular dynamics study

Abstract

According to molecular dynamics simulations, uncomplexed malonamide ligands L and their neutral Eu(NO₃)₃L₂ or charged EuL₄³⁺ complexes are surface active and adsorb at a water–“oil” interface, where “oil” is modeled by chloroform. Aqueous solvation at the interface is found to induce a trans to gauche rearrangement of the carbonyl groups, i.e. to preorganize the chelating L ligands for complexation. The interface also induces a larger proportion of extended amphiphilic forms, of EE-gauche type. The effect of increased oil/water ratio is also investigated. It shown that the system evolves from a well-defined interface between immiscible phases to water-in-oil cylindrical micelles and micro-droplets, onto which L ligands and the lanthanide complexes adsorb, while other ligands are extracted in organic phase. Two electrostatic models of the complexes are compared and, in no case is the neutral or charged complex fully extracted to the organic phase. These features allow us to better understand synergistic and solvation effects in the assisted liquid–liquid extraction of lanthanide or actinide cations.