Importance of the Liquid−Liquid Interface in Assisted Ion Extraction: New Molecular Dynamics Studies of Cesium Picrate Extraction by a Calix[4]arene
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- 作者：Nicolas Sieffert ; Alain Chaumont ; Georges Wipff
- 刊名：Journal of Physical Chemistry C
- 出版年：2009
- 出版时间：June 18, 2009
- 年：2009
- 卷：113
- 期：24
- 页码：10610-10622
- 全文大小：1029K
- 年卷期：v.113,no.24(June 18, 2009)
- ISSN：1932-7455
文摘
We report a molecular dynamics study of key species involved in the liquid−liquid extraction of the cesium picrate salt by an important extractant molecule L (the 1,3-alternate-dimethoxy-calix[4]arene-crown-6) at the chloroform−water interface, with the main aim being to investigate the effect of (i) the explicit representation of polarization effects, (ii) the concentration of the complexes, and (iii) the volume/interfacial area ratio on their distribution at the interface. The outcome of phase separation of randomly mixed systems, consistently simulated with a polarizable force field and with pairwise additive 1−6−12 potentials, is found to be quasi the same, indicating that explicit representation of polarization critically determines neither the formation of the liquid−liquid interface nor the partitioning of the solutes. This is found first at low concentration (3 LCs+ Pic− species per box) in a 1:1 chloroform/water mixture for the complexed and uncomplexed states of the cation, and for a more concentrated mixed system (16 L ligands, 15 LCs+ Pic− complexes, 1 Cs+ Pic− ion pair per box) in a 9:1 chloroform/water mixture. These results confirm that water and chloroform do not mix at the microscopic level and delineate interfaces onto which the extractant molecules 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 investigated by long simulations (80 ns) on biphasic systems with concentrated complexes (27 LCs+ Pic−), showing that increasing the volume/interface ratio promotes the diffusion of complexes to the “bulk” organic phase, leading to an equilibrium between adsorbed and extracted complexes, and between complexed and free ligands.