Effect of Chaotropes on the Transfer of Ions and Dyes across the Liquid–Liquid Interface

Abstract

Chaotropes such as urea can break the structure of water, weakening the hydrophobic effect and reducing aggregation. Here, we investigated how the addition of urea affects the transfer of ions and cationic dyes across the interface between immiscible electrolyte solutions, both water-1,2-dichloroethane and water-trifluorotoluene. For most cations, their half-wave potential of transfer shifted toward more negative values, indicating that it is easier to transfer these ions from the aqueous phase with urea to the organic phase, showing that the addition of urea decreases the solvation of ions in the aqueous phase. However, the half-wave potentials for a series of cationic phenothiazine dyes shifted toward more positive potentials, indicating improved solvation in urea solution. The effect of urea was investigated also by differential capacitance and electrocapillary curves, as well as by molecular dynamics simulations. Finally, electrochemistry at liquid–liquid interfaces allows determination of the transfer energies of ions between water and aqueous solutions of urea via a thermodynamic cycle.

On the origin of chaotrope-modulated electrocatalytic activity of cytochrome c at electrified aqueous|organic interfaces

“…Indeed, this cationic behaviour of neutral urea molecules, leading to a negative shift of the PZC, has previously been observed at electrified water|1,2-dichloroethane interfaces. 15 Upon addition of Cyt c to the aqueous phase, the PZC shifted negatively, as expected since Cyt c has a net charge of +9 in its oxidised form at pH 7 (Fig. 1d and Fig.…”

“…Indeed, this cationic behaviour of neutral urea molecules, leading to a negative shift of the PZC, has previously been observed at electrified water|1,2-dichloroethane interfaces. 15 …”

Unexpected Dual Action of Cetyltrimethylammonium Bromide (CTAB) in the Self‐Assembly of Colloidal Nanoparticles at Liquid–Liquid Interfaces

“…[38,39] Moreover, we have previously shown that various organo-ions, from tetrabutyl cations to crown ether-Na + complexes, can transfer from aqueous solution into organic solvents to act as promoters for NP-interfacial selfassembly. [17,18,40] For CTAB, the dissociation into CTA + and Br − in the organic phase is also likely to be aided by the small amount of dissolved water in the DCM. The result is that although at lower concentrations there is insufficient CTAB adsorbed on the surface of Au NPs to induce NP self-assembly by acting as a modifier, there is still sufficient free CTA + in the organic phase, to promote self-assembly through charge-screening on the oil side of the LLI, as shown in Figure 3b.…”

How to polarise an interface with ions: the discrete Helmholtz model

“…Our results thus provide an explanation for the better agreement of the electrocapillary curves with quadratic ttings than with hyperbolic cosine that are predicted by the Gouy-Chapman model. 24,32…”