Neutral interface found

A selective solvent will be solubilized preferentially into one subdomain. The difference between the solvent densities between subdomains increases as the selectivity increases, but the density within each one is nearly constant. The solvent density difference between subdomains can easily be greater than the solvent excess at the interface found in neutral solvents. 

ESI operating in the negative ion mode has been the interface most widely used for the analysis of anionic perfluorinated surfactants. In addition, ESI has also been optimized for the determination of neutral compounds such as the sulfonamides perfluorooctanesulfonamide (PFOSA), perfluorooctanesulfonami-doacetate (A-EtFOSAA), and t-Bu-PFOS. The use of APPI has been explored in few works [126-128], Takino et al. [126] found as the main advantage of this technology, the absence of matrix effects, but the LODs were considerably higher than those obtained by LC-ESI-MS-MS. 

There are also several papers describing adsorption of quinoline. Sawamoto [143] have studied adsorption and reorientation of quinoline molecules at Hg electrodes by recording differential capacity-potential and differential capacity-time plots using the flow-injection method. Adsorption of quinoline was found reversible at any potential, with the possibility of reorientation of the molecules at the interface. Ozeld etal. [144] have studied adsorption, condensation, orientation, and reduction of quinoline molecules at pure Hg electrode from neutral and alkaline solutions, applying electrochemistry and Raman microprobe spectroscopy. The adsorbed quinoline molecules changed their orientation from the flat at —0.1 V > E > —0.3 V, to the upright at < —0.5 V. At potentials —0.3 V > > —0.5 V, both orientations were observed. Later, Ozeld et al. [145] have extended the studies on reorientation of quinolinium ions at the Hglacidic aqueous solution interface. For these conditions, the specific adsorption of quinoline was not observed. 

The curvature correction can be important when K is small, R is small, and/or a is large. With regard to this aspect, Hirotsu has recently found strong size-dependence of the first-order transition temperature and proposed that a can be much larger in ionized gels than in neutral gels due to the presence of an electric double layer at the interface [31]. 

In ISFETS utilizing polymeric ion-selective membranes, it has been always assumed that these membranes are hydrophobic. Although they reject ions other than those for which they are designed to be selective, polymeric membranes allow permeation of electrically neutral species. Thus, it has been found that water penetrates into and through these membranes and forms a nonuniform concentration gradient just inside the polymer/solution interface (Li et al., 1996). This finding has set the practical limits on the minimum optimal thickness of ion-selective membranes on ISFETS. For most ISE membranes, that thickness is between 50-100 jttm. It also raises the issue of optimization of selectivity coefficients, because a partially hydrated selective layer is expected to have very different interactions with ions of different solvation energies. 

Bebawy et al. [186] demonstrated that CPZ (9) and vinblastine inhibited each other s transport in a human lymphoblastic leukemia cell line (CCRF-CEM/VLBioo). CPZ (9) reversed resistance to vinblastine but not to fluores-cently labeled colchicine and it increased resistance to colchicine. Colchicine was supposed to be transported from the inner leaflet of the membrane and vinblastine from the outer leaflet. CPZ (9) was assumed to be located in the inner membrane leaflet where it interacts with anionic groups of phospholipids and it may inhibit vinblastine transport via allosteric interactions. The authors concluded that transport of P-gp substrates and its modulation by CPZ (9) (or verapamil (79)) are dependent on substrate localization inside the membrane. Contrary to CPZ (9) location in the inner leaflet of the membrane, other modulators and substrates of P-gp were proved to be rather localized within the interface region of the membrane. The location of seven P-gp substrates and two modulators within neutral phospholipid bilayers was examined by NMR spectroscopy by Siarheyeva et al. [129]. The substrates and the modulators of P-gp were found in the highest concentrations within the membrane interface region. The role of drug-lipid membrane interactions in MDR and its reversal was reviewed in detail elsewhere [53,187]. 

Since local space-charge neutrality does not hold at the oxide interfaces, the above expression for the current is restricted to the interior zone [28] where local space charge neutrality has been found [46] to be a good approximation. This is illustrated for the case of cation vacancy (or anion interstitial) and electron-hole diffusion by Fig. 17. Thus, the domain of validity is not 0 but instead is 5 < [Pg.75]

---