Sharpness, ITIES

Girault and Schiffrin [4] proposed an alternative model, which questioned the concept of the ion-free inner layer at the ITIES. They suggested that the interfacial region is not molecularly sharp, but consist of a mixed solvent region with a continuous change in the solvent properties [Fig. 1(b)]. Interfacial solvent mixing should lead to the mixed solvation of ions at the ITIES, which influences the surface excess of water [4]. Existence of the mixed solvent layer has been supported by theoretical calculations for the lattice-gas model of the liquid-liquid interface [23], which suggest that the thickness of this layer depends on the miscibility of the two solvents [23]. However, for solvents of experimental interest, the interfacial thickness approaches the sum of solvent radii, which is comparable with the inner-layer thickness in the MVN model. 

When a monolayer of phospholipids is adsorbed at the ITIES, there must be a modification of the electrical structure of the interface [60]. Since we aim at describing the effect of this monolayer on the rate of ion transfer in a simple way, we assume a sharp interface also in the presence of phospholipids. The hydrophobic tails are located in the organic phase (negative x region), and the hydrophilic headgroups are located in the aqueous phase (positive X region). 

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. 

Of more relevance to ITIES work is the interrogation of the interface between pure water and DCE via the same nonlinear spectroscopic techniques The less distinct sum-frequency spectral features were taken as evidence of a rougher, less structured interface compared to interfaces between water and nonpolar organic solvents, consistent with the fluorescent anisotropy work [39]. The transition from a sharp to a blurred interface could be induced by a progressive increase in the mole fraction of DCE in a CC14-DCE mixture. Subsequent MD calculations have been used to gain structural information on... 

The maximum electrical potential in the compact layer A < - includes a dipolar potential which is shown schematically as a narrow region at the sharp interface. A dipolar layer can be located not only in the compact layer but can also occupy part of the diffuse layer. The amplitude and sign of isPpg can differ from the total interfadal potential. Figure 4 illustrates four possibilities for potential distribution at ITIES. Generally, the dipolar potential depends on the total interfadal potential A <. ... 

In addition, switching the catalyst simply from Pd(OAc>2 to RhCl(PPh3)3 leads to a sharp reversal of regioselectivity in the addition of PhSH to alkynes, providing fl/iti-Markovnikov-type vinylic sulfides with the trans configuration. In this reaction, a 5yn-hydrorhodation process (not iyn-thiorhodation process) is operative. 

---