Département de chimie moléculaire

The authors report a mol. dynamics (MD) study of the effect of a fluorinated lipophilic alc. (referred to as "cs3" by Delmau et al, Solvent Extr. Ion Exch., 2005, 23, 23) used as a phase modifier in the solvent extn. of Cs+ NO3- by a calix[4]arene. It is shown that adding cs3 to a chloroform phase improves the solvation of all partners of the extn. system, i.e. dimethoxycalixarene-crown L, its LCs+ complex and its counterion. This effect is most pronounced for the NO3- anion that is H-bonded to the -OH and terminal -CF2H protons of cs3. On the av., the dissocd. nitrate interacts with 2 to 4 cs3 mols., whereas the assocd. nitrate (LCs+NO3- complex) interacts with one cs3 dimer. The remaining modifier mols. are mainly dissolved in the soln. as dimers or trimers and, to a lesser extent, as monomers and tetramers. Insights into the question of ion pairing in the org. phase are obtained via free energy perturbation (FEP) calcns., showing that the LCs+NO3- paired complex is more stable than its analog with the dissocd. anion. Furthermore, the nitrate dissocn. energy is ca. twice as small in the cs3-modified soln. than in a pure chloroform phase. The authors also simulated chloroform/cs3/water ternary systems, showing that the modifiers are surface active and stabilize the formation of water nanodroplets, while other modifier mols. drag some water to the org. phase. Calixarene complexes also adsorb at the aq. interface in the presence of modifiers, confirming the importance of interfacial phenomena in the assisted cation extn. process. The microscopic insights obtained by the simulations are consistent with exptl. results and allow better understanding why the extn. is enhanced after addn. of modifiers to the org. phase. [on SciFinder(R)]