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

Abstract

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.

On the Importance of the Aqueous Interface in the Multiphasic Rhodium Catalyzed Hydroformylation of Propene: a Molecular Dynamics Study

“…As discussed previously, 14 the surface activity of these species can be understood from the fact that they are quite bulky and possess hydrophobic moietes, and tend to be expelled out of water in order to avoid paying the price for their high cavitation energy in water, 37 while still enjoying as much as possible the hydrophilic solvation of their polar moieties. The results are consistent with other computational results, [38][39][40] surface spectroscopy, 41 surface tension measurements at aqueous interfaces, 42 and with the interpretation of kinetic data on assisted anion extraction 43 that support the view that bulky charged species, even lacking the classical amphiphilic topology (e.g., "spherical" cryptates, 44,45 tetrahedral ions like AsPh 4 + and BPh 4 -, 46 or even +3 charged symmetrical complexes like Eu(BTP) 3 3+ where BTP is a 2,6-di(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine ligand), 9 can be surface active. In the case of the studied catalytic reaction, there should be therefore an equilibrium between the bulk aqueous phase where the anionic ligands and their complexes are diluted, and the aqueous interface, where they are more concentrated, without necessarily fully covering the aqueous surface, though.…”

The Unique Molecular Behavior of Water at the Chloroform—Water Interface

“…[38][39][40] Jedlovszky and co-workers investigated the structure of some of these liquid-liquid interfaces by utilizing Monte Carlo simulation methods in a similar manner to the studies by Hore et al 35,36 The chloroform-water interface has been used by Wipff and coworkers as a model oil-aqueous interface for studying liquidliquid extraction phenomena and partitioning of ions via numerous simulation studies. [41][42][43][44][45] Vibrational sum-frequency spectroscopy has been shown to be a powerful technique for studying buried interfaces, and liquid-liquid interfaces are no exception. 29 In the current VSFS study, isotopic mixtures of H 2 O and D 2 O are employed in the aqueous phase to assist in understanding the general types of bonding between interfacial molecules in the VSF spectrum.…”