Cation transfer, water-nitrobenzene interfac

The effect of temperature on ion transfer across the water-nitrobenzene interface was studied for a series of six quaternary ammonium and phosphonium cations and two anions using cyclic voltammetry and equilibrium impedance measurements [115]. Standard entropies (A S ) and enthalpies (A iT ) of ion transfer have been evaluated from the experimentally accessible reversible half-wave potential ( "572 and standard Gibbs energy of transfer (A G ),... 

These processes are quite rapid with an apparent rate constant which exceeds lO" cm s" [5,6] The only example of electron transfer reaction which has been observed was between the hydrophobic ferro-cinium - ferrocene redox couple in nitrobenzene and the hydrophilic hexacyanoferrate redox couple in water [9]. A more complex mechanism is involved in the case of ion transfer facilitated by an iono-phore[10]. This is the case, for example in the transfer of the alkali and alkaline earth metal cations across a water/nitrobenzene interface facilitated by synthetic neutral cyclic or acyclic iono-phores derived from 3,6-dioxaoctanedicarboxylic acid [11]. 

Samec, Z., V. Marecek, and D. Homolka, Charge transfer between two immiscible electrolyte solutions. Part 9. Kinetics of the transfer of choline and acetylcholine cations across the water-nitrobenzene interface, J Electroanal Chem, Vol. 158, (1983) p. 25. 

Gulaboski, R., V. Mirceski, and R Scholz, Determination of the standard Gibbs energies of transfer of cations and anions of amino acids and small peptides across the water nitrobenzene interface. Amino Acids, Vol. 24, (2003) p. 149. 

While most comparisons of the free energy profile between experiments and simulations have been limited to just the net free energy of transfer. X-ray reflectivity measurements can probe the total ionic density across the interface between two immiscible electrolyte solutions and can be used to make a comparison with the full PMF. The PMF of Br and tetra butyl ammonium cation (TBA+) across the water/nitrobenzene interface, calculated by MD, have been used to derive the ionic density distribution. The total distribution was found to agree well with the measured one over a wide range of bulk electrolyte concentration.2 " This contrasts with the predictions of the continuum electrostatic Gouy-Chapman theory, where ionic density distributions vary substantially from the X-ray reflectivity measurements, and this underscores the importance of molecular-scale structure at the interface. 

Scholz, R, R. Gulaboski, and K. Caban, The determination of standard Gibbs energies of transfer of cations across the nitrobenzene I water interface using a three-phase electrode, Electmchem Commun, Vol. 5, (2003) p. 929. 

On the assumption that = 2, the theoretical values of the ion solvation energy were shown to agree well with the experimental values for univalent cations and anions in various solvents (e.g., 1,1- and 1,2-dichloroethane, tetrahydrofuran, 1,2-dimethoxyethane, ammonia, acetone, acetonitrile, nitromethane, 1-propanol, ethanol, methanol, and water). Abraham et al. [16,17] proposed an extended model in which the local solvent layer was further divided into two layers of different dielectric constants. The nonlocal electrostatic theory [9,11,12] was also presented, in which the permittivity of a medium was assumed to change continuously with the electric field around an ion. Combined with the above-mentioned Uhlig formula, it was successfully employed to elucidate the ion transfer energy at the nitrobenzene-water and 1,2-dichloroethane-water interfaces. 

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