Molecular dynamics study of dicarbollide anions in nitrobenzene solution and at its aqueous interface. Synergistic effect in the Eu(iii) assisted extraction

Abstract

We report a molecular dynamics study of chlorinated cobalt bis(dicarbollide) anions [(B(9)C(2)H(8)Cl(3))(2)Co](-)"CCD(-)" in nitrobenzene and at the nitrobenzene-water interface, with the main aim to understand the solution state of these hydrophobic species and why they act as strong synergists in assisted liquid-liquid extraction of metallic cations. Neat nitrobenzene is found to well solubilize CCD(-), Cs(+) salts in the form of diluted pairs or oligomers, without displaying aggregation. In biphasic nitrobenzene-water systems, CCD(-) anions mainly partition to the organic phase, thus attracting Cs(+) or even more hydrophilic counterions like Eu(3+) into that phase. The remaining CCD(-) anions adsorb at the interface, but are less surface active than at the chloroform interface. Finally, we compare the interfacial behavior of the Eu(BTP)(3)(3+) complex in the absence and in the presence of CCD(-) anions and extractant molecules. It is found that in the absence of CCDs, the complex is trapped at the interface, while when the CCDs are concentrated enough, the complex is extracted to the nitrobenzene phase. These results are compared to those obtained with chloroform or octanol as organic phase and discussed in the context of synergistic effect of CCDs in liquid-liquid extraction, pointing to the importance of dual solvation properties of nitrobenzene or octanol to solubilize the CCD(-) salts as well as the extracted complex.

Amphiphiles without Head-and-Tail Design: Nanostructures Based on the Self-Assembly of Anionic Boron Cluster Compounds

“…Later, computational studies conducted by the Wipff group showed that COSAN accumulates at the water/organic solvent interface. Simultaneously, small COSAN aggregates were predicted by computer simulation. ,, Subsequently, experimental evidence of COSAN aggregation supported these self-assembly predictions (first reported by Matejicek et al). ,, However, COSAN hydrophobicity, amphiphilicity, and surface activity remain controversial topics, as shown by the discrepant explanations that have been published in the literature.…”

An octanol hinge opens the door to water transport

“…Importantly, there is a strong correlation between the calculated interfacial tension and the associated solubility of water in octanol. [40][41][42] The GROMOS54A7/SPC-E set was observed to reproduce the correct solubility and interfacial tension, with excellent agreement being observed for the interfacial structure, Table 1 Summary of intermolecular interactions, mole fraction solubility of water in octanol, and interfacial tension of the liquid/liquid interface predicted with different octanol/water models. CG-MARTINI is the coarse-grained model from Ndao et al 34 as described in Section 3.1, and based upon the associated intermolecular pairwise interactions (Table S3).…”

“…Prior work using polarizable octanol and water has also predicted a semi-organized second layer of octanol relative to the instantaneous surface, 35 while most non-polarizable force fields predict a monolayer under equilibrium conditions and mixing/demixing studies sometimes predict a semi-bilayer structure that is dependent upon system configuration. 40,61 We compared several classical force field representations (Tables 1 and S3) and analyzed the associated intermolecular pairwise interactions which indicated that strong interactions of the water and octanol hydroxyl group have a dual effect of causing the correct water solubility, and stabilizing water rich octanol islands in the semi-bilayer.…”

Nonclassical Hydrophobic Effect in Micellization: Molecular Arrangement of Non‐Amphiphilic Structures

“…[20] In the former case, closely apposed pairs of COSAN molecules accompanied by two Na + counterions bind in the HIV protease active site. [17] The latter application of metallacarboranes is underlaid by their unique solution behavior which led to the computational prediction [21][22][23] and the experimental evidence [24,25] that they behave as surfactants. Various substituted forms (Me, Cl, Br) and the parental cobalt bis(dicarbollide) anions coupled with several counterions (Na + , K + , Cs + , H 3 O + , UO 2 2+ , Eu 3+ ) showed surface activity.…”