MIGRATION OF IONOPHORES AND SALTS THROUGH A WATER CHLOROFORM LIQUID-LIQUID INTERFACE - MOLECULAR DYNAMICS-POTENTIAL OF MEAN FORCE INVESTIGATIONS

We report a theoretical study on the liquid-liquid interfacial behavio r of the species involved in the extraction of Cs+ by a calix[4]arene- crown6 ionophore (L): the free Cs+ Pic(-) and Cs+ Cl- salts, the LCsand LCs+ Pic(-) complexes, and uncomplexed L. Based on molecular dynam ics simulations, we calculated the free energies changes for migration from the interface into the aqueous and the organic phases, respectiv ely. For free L and for the LCs+ complex, with or without Pie-counteri on, an energy minimum is found close to the interface, on the chlorofo rm side, showing that these species behave as surfactants. This contra sts with the uncomplexed Cs+, which diffuses spontaneously from the in terface to water and displays no energy minimum. A remarkable counteri on effect is found with Pic(-) which displays a high affinity for the interface, while Cl- prefers the bulk aqueous phase. The questions of ion extraction by ionophores, counterions, concentration and synergist ic effects in assisted cation transfer through the liquid-liquid inter face between immiscible liquids are discussed from the interfacial poi nt of view.