Cation transference

C Cation transfer membrane A Anion transfer membrane... 

FIG. 1 Cyclic voltammogram of acetylcholine cation transfer from water to DCE. The liquid-liquid interface was supported at a 20/xm-diameter hole formed in the 12/xm-thick polyester film. The sweep rate was lOmV/s. (Reprinted with permission from Ref. 3a. Copyright 1989 Elsevier Science S.A.)... 

More recently, Manzanares et al. [17] presented additional experimental evidence of the enhanced cation transfer across a hemispherical water-1,2-DCE interface covered with DSPC by using a syringe experimental set up described elsewhere [9,28]. Figure 7 shows the cyclic voltammograms measured in the cell [17],... 

The theory presented above accounts for the electrostatic effects on the apparent rate constant for ion transfer by relating the observed changes in to changes in c"(0), or equivalently to 0(0). In the following, we present the simulated electrical potential distributions and the corresponding enhancement factors for a cation transferring from the aqueous phase across the water-l,2-DCE interface (s" = 78.39, s° = 10.36). The rela-... 

A theoretical approach based on the electrical double layer correction has been proposed to explain the observed enhancement of the rate of ion transfer across zwitter-ionic phospholipid monolayers at ITIES [17]. If the orientation of the headgroups is such that the phosphonic group remains closer to the ITIES than the ammonium groups, the local concentration of cations is increased at the ITIES and hence the current observed due to cation transfer is larger than in the absence of phospholipids at the interface. This enhancement is evaluated from the solution of the PB equation, and calculations have been carried out for the conditions of the experiments presented in the literature. The theoretical results turn out to be in good agreement with those experimental studies, thus showing the importance of the electrostatic correction on the rate of ion transfer across an ITIES with adsorbed phospholipids. 

CATION TRANSFERENCE NUMBERS AND EQUIVALENT CONDUCTIVITIES (fi cm2 equiv.-1) IN AQUEOUS SOLUTIONS AT 25° C... 

Subsequently, the rapid unimolecular (mesolytic) fragmentation of the resulting pinacol cation radical followed by proton (or trimethylsilyl cation) transfer to quinone anion radical (within the solvent cage) yields the retropinacol products in equations (55) and (56) (equation 58). 

As shown in Fig. 7-1, the electrode reaction in which a particle of negative charge (electron or anion) transfers finm an electrode to an electrol3de (aqueous solution) is called the cathodic reaction-, and the electrode reaction in which a particle of positive charge (hole or cation) transfers from an electrode to an electrolyte is called the anodic reaction. Further, the electrode at which the cathodic reaction takes place is called the cathode and the electrode at which the anodic reaction takes place is called the anode. 

From neutrality requirement, the anodic current of cation transfer equals the cathodic current of anion transfer. The transfer rate of cations and the transfer... 

Mauritz and Gray analyzed the IR continuous absorption of hydrated Na OH - and K OH -imbibed Nafion sulfonate membranes for the purpose of correlating this phenomenon to the current efficiency (cation transference number) of chlor-alkali electrochemical cells.In this case, the similar issue of OH ( defect proton ) conductivity is important. A distinct continuous absorption appeared in the spec-... 

Another analytically useful phenomenon in electrolysis at ITIES is ion transfer faciUtated by ionophores present in the non-aqueous phase [8]. If the ionophore is present at a low concentration in the non-aqueous phase and the aqueous phase contains a large concentration of the cation that is bound in a complex with the ionophore (for example as a component of the base electrolyte), then a voltammetric wave controlled by diffusion of the ionophore toward the ITIES or by diffusion of the complex formed away from the ITIES into the bulk of the organic phase appears at a potential lower than the potential of simple cation transfer. The peak height of this wave is proportional to the ionophore concentration in the solution and can be used for the determination (fig. 9.8). This effect has been observed with valinomycin, nonactin, cycUc polyethers and other substances [2,3,23]. The half-wave potential of these waves is... 

Dietz, M. L., Dzielawa, J. A., Ion-exchange as a mode of cation transfer into room-temperature ionic liquids containing crown ethers Implications for the "greenness" of ionic liquids as diluents in liquid-liquid extraction, Chem. Commun., 2124-2125, 2001. 

The experimental values for kp and h , at different temperatures are summarized in Table 1. In every case hj, is much lower than kp and kp . Moreover, with temperature, the polymerization rates increase and simultaneously kp/hm becomes greater for both cations. Transfer reactions to monomer are more numerous at lower temperatures and also when I.i+ is used At - 40 C, the values of the kp/hm ratio are 47 for Li+ and 140 for Na+. 

Are the mechanisms described here applicable to cells operating in nonaque-ous environments It is conceivable that the sequence described by Eqs. (12)-( 14) occurs under certain conditions. The more complex sequence involving coupled electron and cation transfer probably does not. Although Li+ (the electrolyte cation most often used in Gratzel-type cells) is known to intercalate into high-area metal oxide semiconductors [49,90,108-111], the rate is probably too slow to be coupled to injection and back ET in the same way that aqueous proton uptake and release are coupled to these processes. The ability to use water itself as a proton source means that solution-phase diffusional limitations on proton uptake are absent. Alkali metal ion uptake from nonaqueous solutions, on the other hand, clearly is subject to diffusional limitations. 

A series of synthetic 32-membered ring macrotetrolides related to the actins have been prepared and show cation transfer ability. The K+/Na+ selectivity is however inferior to that of the actins and cyclic polyethers.563... 

Equation (8.14) demonstrates once more that the cation flux caused by the oxygen potential gradient consists of two terms 1) the well known diffusional term, and 2) a drift term which is induced by the vacancy flux and weighted by the cation transference number. We note the equivalence of the formulations which led to Eqns. (8.2) and (8.14). Since vb = jv - Vm, we may express the drift term by the shift velocity vb of the crystal. Let us finally point out that this segregation and demixing effect is purely kinetic. Its magnitude depends on ft = bB/bA, the cation mobility ratio. It is in no way related to the thermodynamic stability (AC 0, AG go) of the component oxides AO and BO. This will become even clearer in the next section when we discuss the kinetic decomposition of stoichiometric compounds. 

Table 12. Cation transference numbers of aqueous solutions of EuClt in various concentration ranges at 25° C...

Electrical conductance, cation transference number and activity coefficient of the halide systems are discussed on page 37. 

Artificial cation channels could give fundamental information on the mechanism of cation flow and channel conduction [6.69, 6.70]. A solid-state model of cation transfer inside a channel is provided by the crystal structure of the KBr complex of 27c (Y = Y = CH3), which contains stacks of macrocycles with cations located alternately inside and above a macrocyclic unit, like a frozen picture of cation propagation through the channel defined by the stack [6.71]. 

Kanoh, S. Nishimura, T. Naka, M. Motoi, M. Unusual cyclodimerization of small cyclic ethers via neighboring carbonyl-group participation and cation transfer. Tetrahedron 2002, 58, 7065-7074. 

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