Results water-nitrobenzene interface

Koryta et al. [48] first stressed the relevance of adsorbed phospholipid monolayers at the ITIES for clarification of biological membrane phenomena. Girault and Schiffrin [49] first attempted to characterize quantitatively the monolayers of phosphatidylcholine and phos-phatidylethanolamine at the ideally polarized water-1,2-dichloroethane interface with electrocapillary measurements. The results obtained indicate the importance of the surface pH in the ionization of the amino group of phosphatidylethanolamine. Kakiuchi et al. [50] used the video-image method to study the conditions for obtaining electrocapillary curves of the dilauroylphosphatidylcholine monolayer formed on the ideally polarized water-nitrobenzene interface. This phospholipid was found to lower markedly the surface tension by forming a stable monolayer when the interface was polarized so that the aqueous phase had a negative potential with respect to the nitrobenzene phase [50,51] (cf. Fig. 5). 

In both cases, the half-wave potential shifts by RT/ ziF)vaN per pH unit, and a typical example of such a behavior is given in Fig. 9 for the transfer of two acidic fi-diketones at the water-nitrobenzene interface. These results were unexpected, since a current wave is measured at a pH where the compound of interest is by a very large majority neutral, but they in fact represent the typical behavior of ionizable compounds at the ITIES and prove that the interfacial potential and the transfer of protons plays a key role for the distribution in biphasic systems. 

As to results for the water-oil interface, fig. 4.22 gives a charge-potential curve for the water-nitrobenzene interface. These results were obtained by Samec et al. who solved the polarization problem by adding LiCl to the water and tetrabufylam-monlum tetraphenylborate (TBATPB) to the nitrobenzene. The former electrol5de... 

The impedance plots for the water/nitrobenzene interface are illustrated in Fig. 5. At frequencies approaching 5 kHz, the correction was made for the phase shift of the measured signal caused by the potentiostat itself. Sometimes a semicircular arc appears on the impedance plot frequencies and low electrolyte concentrations [23, 35], but suchn behaviour is probably due to the unsuitable cell construction or the potentiostat failure. The results of the analysis of the impedance plots shown in Fig. 5 are summarized in Table 1. With the increasing frequency co, the parameter X increases and its evaluation from the equation ... 

Fig. 13. Potential difference across the inner layer Ao

Very little has been done regarding the kinetic study of assisted ion transfer reactions. Senda et studied the transfer of sodium at the water-nitrobenzene interface facilitated by dibenzo-18 Crown-6 in order to elucidate the mechanism of the transfer, and concluded that the transfer occured by a TIC mechanism. Recently, Shao revisited this system at the water-1,2-dichloroethane interface. The results obtained for the following charge transfer reactions are illustrated in Fig. 16. 

Dynamic surface tension has also been measured by quasielastic light scattering (QELS) from interfacial capillary waves [30]. It was shown that QELS gives the same result for the surface tension as the traditional Wilhelmy plate method down to the molecular area of 70 A. QELS has recently utilized in the study of adsorption dynamics of phospholipids on water-1,2-DCE, water-nitrobenzene and water-tetrachloromethane interfaces [31]. This technique is still in its infancy in liquid-liquid systems and its true power is to be shown in the near future. 

Concluding Remarks on Potentiometry. Due to the unique characteristics of the liquid-liquid interface system, factors in addition to the concentration of analyte ion must be considered in potentiometric studies. These factors include the nature and concentration of the supporting electrolytes and the relative volume of the phases in contact. Numerical solutions of the theoretical relationship derived by Hung (15) are useful to predict the effect of such factors as volume of the phases and concentration of added ions. Experimental results with an oxacyanine dye in a water-nitrobenzene system show a linear response in the 10 3-10 5-mol/L concentration range, which corresponds to a 120-mV dynamic range of these dyes for use as potential sensors. This response agrees with measurements on biological... 

The possibility of determination of the difference of surface potentials of solvents, see Scheme 18, among others, has been used for the investigation of Ajx between mutually saturated water and organic solvent namely nitrobenzene [57,58], nitroethane and 1,2-dichloroethane (DCE) [59], and isobutyl methyl ketone (IB) [69]. The results show a very strong influence of the added organic solvent on the surface potential of water, while the presence of water in the nonaqueous phase has practically no effect on its x potential. The information resulting from the surface potential measurements may also be used in the analysis of the interfacial structure of liquid-liquid interfaces and their dipole and zero-charge potentials [3,15,22]. 

Small LL interfaces have been used by Girault and co-workers (33-38) and by Senda et al. (39, 40). We have used a small hole formed in a thin glass wall (41-43). Figure 16 shows the voltammetric response of lauryl sulfate anion transport between water and nitrobenzene. Recent analytical applications of these microinterfaces have resulted in construction of gel-solidified probes. The advantage of such a modification is ease of handling (44-47). The immobilization can be extended further to studies of frozen interfaces, or even to solid electrolytes. Significantly, ITIES theory also applies to interfaces that are encountered in ion-doped, conductive, polymer-coated electrodes. 

Oil/water interfaces are classified into the ideal-polarized interface and the nonpolarized interface. The interface between a nitrobenzene solution of tetrabutylam-monium tetraphenylborate and an aqueous solution of lithium chloride behaves as an ideal-polarized interface in a certain potential range. Electrocapillary curves of the interface were measured. The results are analyzed using the electrocapillary equation of the ideal-polarized interface and the Gouy-Chapman theory of diffuse double layers. The electric double layer structure consisting of the inner layer and the two diffuse double layers on each side of the interface is discussed. Electrocapillary curves of the nonpolarized oil/water interface are discussed for two cases of a nonpolarized nitrobenzene/water interface. 

The values of surface charge density obtained by numerical differentiation of the electrocapillary curve agreed well with those obtained by numerical integration of the differential capacity curve [17,29] (Fig. 3). These results indicate that the interface between a nitrobenzene solution of TBATPB and an aqueous solution of LiCl actually behaves as an ideal-polarized interface in a certain potential range and also that the differential capacity measurements should give essentially the same information on the electrocapillarity and the double layer structure of nitrobenzene/water interfaces as the electrocapillary curve measurements, provided that their electrocapillary maximum potential which is now equal to the potential of zero charge (pzc) and interfacial tension at the pzc (y J known. 

They analyzed their results using a thermodynamic approach based on the Gibbs adsorption equation and the main conclusion of their work was that relative surface excesses of the ionic species were well described by the Gouy-Chapman theory. They adopted the MVN model of the ideally polarized interface stating that the compact layer is an ion-free layer consisting of laminated layers of water and nitrobenzene sandwiched between two diffuse layers. The potential difference across this inner layer was estimated to be about 20 mV at the PZC but was found to vary with the surface charge density. 

The first electrochemical observation of a facilitated ion transfer reaction was reported in 1979 by Koryta et al They studied the transfer of potassium from water to nitrobenzene, facilitated by the crown ether ionophore dibenzo-18-crown-6. This original publication has heralded an important part of the field of electrochemistry at liquid-liquid interfaces. The Prague group at the Heyrovsky Institute dedicated a lot of attention to this particular subject, resulting in a large number of publications. The ionophores investigated included nonactin, monensin, calcium ionophore, dibenzo-18-crown-6, tetracycline, valinomycin, and nigericin. ... 

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