We report a theoretical study on the liquid−liquid interfacial behavior 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 LCs+ and LCs+ Pic- complexes, and uncomplexed L. Based on molecular dynamics simulations, we calculated the free energies changes for migration from the interface into the aqueous and the organic phases, respectively. For free L and for the LCs+ complex, with or without Pic- counterion, an energy minimum is found close to the interface, on the chloroform side, showing that these species behave as surfactants. This contrasts with the uncomplexed Cs+, which diffuses spontaneously from the interface to water and displays no energy minimum. A remarkable counterion 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 synergistic effects in assisted cation transfer through the liquid−liquid interface between immiscible liquids are discussed from the interfacial point of view.

Using molecular dynamics simulations, we compare the solvation of uranyl and strontium nitrates and uranyl chlorides in two room-temperature ionic liquids (ILs): [BMI][PF(6)] based on 1-butyl-3-methylimidazolium(+),PF(6)(-) and [EMI][TCA] based on 1-ethyl-3-methylimidazolium(+),AlCl(4)(-). Both dissociated M(2+),2NO(3)(-) and associated M(NO(3))(2) states of the salts are considered for the two cations, as well as the UO(2)Cl(2) and UO(2)Cl(4)(2)(-) uranyl complexes. In a [BMI][PF(6)] solution, the "naked" UO(2)(2+) and Sr(2+) ions are surrounded by 5.8 and 10.1 F atoms, respectively. The first-shell PF(6)(-) anions rotate markedly during the dynamics and are coordinated, on the average, monodentate to UO(2)(2+) and bidentate to Sr(2+). In an [EMI][TCA] solution, UO(2)(2+) and Sr(2+) coordinate 5.0 and 7.4 Cl atoms of AlCl(4)(-), respectively, which display more restricted motions. Four Cl atoms sit on a least motion pathway of transfer to uranyl, to form the UO(2)Cl(4)(2)(-) complex. The free NO(3)(-) anions and the UO(2)Cl(4)(2)(-) complex are surrounded by imidazolium(+) cations ( approximately 4 and 6-9, respectively). The first shell of the M(NO(3))(2) and UO(2)Cl(2) neutral complexes is mostly completed by the anionic components of the IL, with different contributions depending on the solvent, the M(2+) cation, and its counterions. Insights into energy components of solvation are given for the different systems.

In recent years, molecular dynamic simulations on choline chloride based deep eutectic solvents (DES) have flourished. Most of these studies point to the fact that in order to accurately reproduce dynamical properties of the latter using a fixed-charge atomistic force field (FF) one has to resort to charge scaling. In this work, we propose an alternative to charge scaling and show that the sole refinement of the Lennard-Jones parameters of the oxygen and hydrogen of the hydroxyl function in the GAFF v2.11 FF enables an accurate description of static, dynamical, and structural properties of two commonly used DES, namely, ethaline (1:2 mixture of choline chloride and ethylene glycol) and glyceline (1:2 mixture of choline chloride and glycerol). Various computed physicochemical properties for both mixtures with our modified version of the GAFF v2.11 FF are found in good agreement with experimental data. Most importantly, however, is the fact that self-diffusion coefficients for the various components of both ethaline and glyceline are found within a maximum deviation of 33% from experimental values, which is at least as good if not better than current scaled-charge FF. Finally, computed radial distribution functions match with those reported in the literature.