Simulations of Liquid-Liquid Interfaces: A Key Border in Supramolecular Chemistry

Supramolecular Chemistry

2003

According to molecular dynamics (MD) simulations the diprotonated bicyclic 222 2 + cryptand molecules concentrate on the water side of a water-chloroform interface. This is found for its endo-endo and exo-exo isomers and with Cl-, I-or Pic-as counterions. The positively charged interfacial cryptands attract the halide anions which also concentrate at the interface, in spite of their hydrophilic character. The Pic-anions, often used in extraction or transport experiments, display specta· cular stacking arrangements in bulk water, as well as on the aqueous side of the interface. The results are important for the mechanism of assisted cation extraction from water, as well as for electrical prope~ies of the interface. They demonstrate how solvahon at the inherently asymmetrical interface induces bidimensional concentration of charged ,.hydrophobic" solutes.

Section: Discussionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Interfacial Activity of the Diprotonated 222 Cryptand at the Water/"Oil" Interface Revealed by Molecular Dynamics Simulations

Jost

Chaumont

Supramolecular Chemistry

2003

“…After energy minimization, the MD was run at 300 K. Some systems were represented with 3D periodic boundary conditions, while for others periodicity was applied along the X and Y directions only, using a restraining potential at the Z boundaries to avoid evaporation of solvent molecules (see Table 1 and Ref. [36]). Thus, the 3D systems correspond to alternating slabs of water and chloroform separated by one water/chloroform interface, while the 2D systems correspond to a single water/chloroform interface and to two air/liquid interfaces.…”

Section: Methodsmentioning

confidence: 99%

“…The interfacial BPh 4 − ions create a negative potential which attracts somewhat the Na + cations, whose proportion near the interfacial region is about 10%. We suggested that this is an important feature of synergistic effects in extraction systems [34,36,37]. Not only anions of amphiphilic type (e.g.…”

Section: 3mentioning

confidence: 97%

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Distribution of hydrophilic, amphiphilic and hydrophobic ions at a liquid/liquid interface: a molecular dynamics investigation

Berny

Schurhammer

Inorganica Chimica Acta

2000

We report molecular dynamics studies on the interfacial distribution of ionic species of different size, shape and topology at a water/chloroform interface: hydrophilic K + Cl − , K + SCN − and K + Pic − ions, amphiphilic ammonium NTMA + cations and farnesylphosphate FPH − anions, tetrahedral hydrophobic AsPh 4 + and BPh 4 − ions, with different counterions. Contrasted distributions are observed. The K + Cl − and K + SCN − ions sit almost exclusively in the water phase, but SCN − is less 'repelled' than Cl − by the interface. The Pic − anions are partly adsorbed at the interface and dissolved in the water phase where they display remarkable p-stacking interactions. Amphiphilic NTMA + cations or FPH − anions adsorb and dilute at the interface. Less expected is the high surface activity of symmetrical AsPh 4 + and BPh 4 − ions, with marked counterion effects. The two ions fully adsorb at the interface in the AsPh 4 + BPh 4 − salt, while in the Na + BPh 4 − or AsPh 4 + Cl − salts, they display an equilibrium between the organic phase and the interface. Crossed comparisons between the different solutions reveal the important role of counterions on the distribution of a given ionic species. These results are discussed in relation to experimental data.

Macrotricyclic quaternary tetraammonium receptors: Halide anion recognition and interfacial activity at an aqueous interface. A molecular dynamics investigation

Chaumont

2002

J Comput Chem

We report a molecular dynamics study of the halide inclusion complexes X(-) subset L(4+) of a macrotricyclic tetrahedral receptor L(4+) built from four quaternary ammonium sites connected by six (CH(2))(n) chains. The hydrophilic/hydrophobic character of the complexes is investigated at a water/chloroform interface, represented explicitly and, despite their +3 charge and "spherical" shape, they are found to display amphiphilic behavior and to concentrate at the interface. The more lipophilic N-substituted CH(2)phi derivative, as well as less charged models are more surface active than the N-Me substituted host. In relation with the Hofmeister series, I(-) exo neutralizing counterions are compared with Cl(-) anions and are found to sit closer to the interface, which becomes more neutral. The "macrocyclic interfacial effect" is investigated by a comparison of L(4+) complexes with their acyclic counterparts. Finally, we address the question of anion binding selectivity by L(4+) and its L(1) (4+) and L(2) (4+) topological isomers. F(-) is too small for these three hosts, while I(-) is too big. According to free energy perturbation calculations, Cl(-) is preferred to Br(-), but somewhat more by L(1) (4+) than by L(4+).