Anion surface-inactive

The double-layer structure at the electro-chemically polished and chemically treated Cd(OOOl), Cd(lOlO), Cd(1120), Cd(lOh), and Cd(1121) surface electrodes was studied using cyclic voltammetry, impedance spectroscopy, and chronocoulometry [9, 10]. The limits of ideal polarizahility, Epzc, and capacity of the inner layer were established in the aqueous surface inactive solutions. The values of iipzc decrease, and the capacity of the inner layer increases, if the superficial density of atoms decreases. The capacity of metal was established using various theoretical approximations. The effective thickness of the thin metal layer increases in the sequence of planes Cd(1120) < Cd(lOiO) < Cd(OOOl). It was also found that the surface activity of C104 was higher than that of F anions [10]. 

Fig. 5-2. Schematic representation of the electrically charged double layer when separating surface-inactive anions.

The separation of surface-inactive cations can be interpreted analogously. In this case, lipophilic anions are adsorbed at the resin surface, while the analyte cations are retained in the outer region of the double layer. 

If the ion—metal interaction is completely electrostatic and the squeezing out is absent, the electrolyte is surface-inactive. In the opposite case, specific adsorption takes place, and the corresponding ion is surface-active. Figure 2 shows the electrocapillary curves (dependences of y on electrode potential E) for a mercury electrode in 0.01, 0.1, and 1 M aqueous solutions of a surface-inactive electrolyte (curves 1, 2, and 3) and the corresponding y versus E-curves in solutions containing surface-active anions (1, 2 and 3 ). 

The examples of pzc shifts induced by specific adsorption of anions on mercury in aqueous solutions are presented in Table 1. As demonstrated by Frumkin [13], the specific features of metal-ion interaction can be elucidated by comparing the pzc shifts and the changes of surface potential at the solution/air interface. The adsorption of ion at the latter interface results only from squeezing-out effect. For example, the change of surface potential when going from 0.01 M KCl to 2 M KI solution reaches only 52 mV [14], while the pzc shift for Hg/1 M KI (in comparison with pzc in surface-inactive electrolyte solution) is about 350 mV. 

The combination of Eqs. (13), (14), and (17) make it possible to calculate the dependencies of F and F+ on o from the experimental y. E-curves. Figure 3 shows the corresponding dependencies of FF and FF+ on Eq for 0.1 M solutions of surface-inactive and surface-active electrolytes. The positive adsorption of cations at Eo < 0 and of anions at Eo > 0 in a former solution are induced only by the coulombic attraction of ions to the oppositely charged electrode surface. In contrast, the negative adsorption of cations at >0 and of anions atEo <0 is caused... 

For nonsymmetrical surface-inactive electrolytes, the minimum of C shifts from the pzc. If, in the absolute magnitude the anion charge is higher than the cation charge, the minimum shifts from pzc to more negative values, and vice versa. Specific adsorption of ions also induces a shift of the capacitance minimum from the pzc. Moreover, when the specific adsorption is sufficiently pronounced, no minimum appears in the C, fo Curves,... 

ROH is the fatty acid nonionized molecule RO is the surface-active fatty acid anion //+ is the surface-inactive cation... 

This conclusion is in complete agreement with the experimental results. Figure 6.1 shows the S vs n dependence for different solutions, viz. for a surface-inactive electrolyte, and for solutions to which specifically adsorbed anions and cations have been added. It can be seen that the results for different solutions differ considerably. If, however, we assume, in accordance with the usual equations of the theory of slow discharge[1], that the change in overpotential at a constant concentration of H" " ions is exactly equal to the change in the local -potential (the coefficient (1 - a)/a of the ij -poten-tial is equal to unity, since a = 1/2 in the Tafel regions for the investigated solutions), the displacement of one curve with respect to the other by the difference in overpotentials enables us to... 

The affinity of the polymer-bound catalyst for water and for organic solvent also depends upon the structure of the polymer backbone. Polystyrene is nonpolar and attracts good organic solvents, but without ionic, polyether, or other polar sites, it is completely inactive for catalysis of nucleophilic reactions. The polar sites are necessary to attract reactive anions. If the polymer is hydrophilic, as a dextran, its surface must be made less polar by functionalization with lipophilic groups to permit catalytic activity for most nucleophilic displacement reactions. The % RS and the chemical nature of the polymer backbone affect the hydrophilic/lipophilic balance. The polymer must be able to attract both the reactive anion and the organic substrate into its matrix to catalyze reactions between the two mutually insoluble species. Most polymer-supported phase transfer catalysts are used under conditions where both intrinsic reactivity and intraparticle diffusion affect the observed rates of reaction. The structural variables in the catalyst which control the hydrophilic/lipophilic balance affect both activity and diffusion, and it is often not possible to distinguish clearly between these rate limiting phenomena by variation of active site structure, polymer backbone structure, or % RS. 

Figure 19.4 Schematic view of the surface of the ATP sensing solid M4 showing the possible coordination between the aminoanthracene groups and the ATP anion. Lower left weakly active nonporous material M5. Lower right inactive molecular probe P2.

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