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Aqueous solutions of tetraalkylammonium halides: ion hydration, dynamics and ion-ion interactions in light of steric effects

Abstract : Molecular simulations have allowed us to probe the atomic details of aqueous solutions of tetramethylammonium (TMA) and tetrabutylammonium (TBA) bromide, across a wide range of concentrations (0.5 to 3-4 molal). We highlight the space-filling (TMA(+)) versus penetrable (TBA(+)) nature of these polyatomic cations and its consequence for ion hydration, ion dynamics and ion-ion interactions. A well-established hydration is seen for both TMA(+) and TBA(+) throughout the concentration range studied. A clear penetration of water molecules, as well as counterions, between the hydrocarbon arms of TBA(+), which remain in an extended configuration, is seen. Global rotation of individual TBA(+) points towards isolated rather than aggregated ions (from dilute up to 1 m concentration). Only for highly concentrated solutions, in which inter-penetration of adjacent TBA(+)s cannot be avoided, does the rotational time increase dramatically. From both structural and dynamic data we conclude that there is absence of hydrophobicity-driven cation-cation aggregation in both TMABr and TBABr solutions studied. The link between these real systems and the theoretical predictions for spherical hydrophobic solutes of varying size does not seem straightforward.
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https://hal.sorbonne-universite.fr/hal-01484087
Contributor : Olivier Bernard <>
Submitted on : Monday, March 6, 2017 - 5:48:24 PM
Last modification on : Friday, March 5, 2021 - 3:01:01 PM

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Debsindhu Bhowmik, Natalie Malikova, Guillaume Mériguet, Olivier Bernard, José Teixeira, et al.. Aqueous solutions of tetraalkylammonium halides: ion hydration, dynamics and ion-ion interactions in light of steric effects. Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2014, 16 (26), pp.13447. ⟨10.1039/c4cp01164⟩. ⟨hal-01484087⟩

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