Benzene—water interfaces, ITIES

Monte Carlo and molecular dynamics calculations of the density profile of model system of benzene-water [70], 1,2-dichloroethane-water [71], and decane-water [72] interfaces show that the thickness of the transition region at the interface is molecu-larly sharp, typically within 0.5 nm, rather than diffuse (Fig. 4). A similar sharp density profile has been reported also at several liquid-vapor interfaces [73, 74]. The sharpness of interfaces thus seems to be a general characteristic of the boundary between two stable phases and it is likely that the presence of supporting electrolytes would not significantly alter the thickness of the transition region at an ITIES. The interfacial mixed solvent layer [54, 55], if any, would probably have a thickness comparable with this thin inner layer. 

The kf versus [lipid] dependencies for Fe(CN)s are different. Although the ET rate decreases markedly with increasing concentration of lipid, it does not approach zero at higher concentrations, but reaches the limiting value at about 50 /xM. This saturation suggests the formation of a complete phospholipid monolayer at the ITIES. The formation of compact phospholipid monolayers at similar lipid concentrations was observed at water/nitro-benzene (40a) and water/dichloroethane (40b) interfaces. 

FIGURE 1.32 (a) Schematic diagram of the application of SECM in the feedback mode measurement of the kinetics of ET between ZnPor in benzene and RufCN) " in water. Electroneutrality maintained by distribution of perchlorate ions across the interface. (b) Dependence of the effective heterogeneous rate constant on potential drop across the ITIES at 5 mM concentrations of RufCN) ". The value A ( ) is expressed in terms of log[ClCf ]. Potential dependence of an effective bimolecular rate constant k) k f/[Ru(CN)g ] (M cm-s" ). (Tsionsky, M., A. J. Bard, and M. V. Mirkin, 1996, J Phys Chem-US, Vol. 100, p. 17881. Used with permission.)... 

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