Département de chimie moléculaire

The authors report a mol. dynamics study of key species involved in the liq.-liq. extn. of the cesium picrate salt by an important extractant mol. L (the 1,3-alternate-dimethoxy-calix[4]arene-crown-6) at the chloroform-water interface, with the main aim being to study the effect of (i) the explicit representation of polarization effects, (ii) the concn. of the complexes, and (iii) the vol./interfacial area ratio on their distribution at the interface. The outcome of phase sepn. of randomly mixed systems, consistently simulated with a polarizable force field and with pairwise additive 1-6-12 potentials, is quasi the same, indicating that explicit representation of polarization critically dets. neither the formation of the liq.-liq. interface nor the partitioning of the solutes. This is found 1st at low concn. (3 LCs+ Pic- species per box) in a 1:1 chloroform/water mixt. for the complexed and uncomplexed states of the cation, and for a more concd. mixed system (16 L ligands, 15 LCs+ Pic- complexes, 1 Cs+ Pic- ion pair per box) in a 9:1 chloroform/water mixt. Water and chloroform do not mix at the microscopic level and delineate interfaces onto which the extractant mols. and their complexes adsorb, favoring a complexation process right at interface. Counterions play a key role, as shown by the comparison of picrate to nitrate as counterion. The nature of the interfacial layer is further studied by long simulations (80 ns) on biphasic systems with concd. complexes (27 LCs+ Pic-), showing that increasing the vol./interface ratio promotes the diffusion of complexes to the bulk org. phase, leading to an equil. between adsorbed and extd. complexes, and between complexed and free ligands. [on SciFinder(R)]