Redox cations

B. Limoges, C. Degrand, and P.J. Brassier, Redox cationic or procationic labeled drugs detected at a perfluorosulfonated ionomer film-coated electrode. J. Electroanal. Chem. 402, 175-187 (1996). 

Unfortunately, the use of TS1 (as well as TS2 discovered in 1990 by the group of Ratnasamy (27)) in catalytic oxidations is restricted to the relatively small substrates able to enter the pores of these zeolites (apertures 0.55 nm). Therefore, many research groups attempted to incorporate titanium in large pore molecular sieves BEA zeolites, mesoporous molecular sieves MCM41 and MCM48. Other transition metal zeolites were also synthesized and tested in oxidation one of the main problems of these systems is the release of redox cations in liquid phase (24). Progress remains to be made to develop molecular sieves catalyzing the oxidation... 

This different behaviour with respect to the direct decomposition could be still related to a redox mechanism if one considers the comparable fraction of Cu reduced by the treatment with CO instead of the fraction reduced by He in Cu-HZSM5 and Cu-NaY. (Table 2). Tlie alternative explanation is that a redox cation is not essential for the reduction of NOx with hydrocarbons [6, 14]. The marked dependence of the CO conversion on the type of zeolite and on the... 

If the semiconductor-solution interface involves simple redox cations (a Fe + Fe A-e type of situation), then the surface states which exist on the surface of the semiconductor will consist of the first two kinds and may be small in number. In this case the ideal Schottky barrier case probably obtains. However, in such a situation the adsorbed H2O may also give rise to surface states. 

Voltammetry at modified electrodes has also heen used to investigate the interactions of redox-active DNA-hinding agents with immohilized DNA. Examples include the survey done hy Hashimoto and coworkers [211], an investigation of methylene hlue [214], a comparison of interactions of redox cations with surface-hound and solution DNA [215], and an investigation of the kinetics and mechanism of mitoxantrone... 

Mariaulle P, Sinapi F, Lamberts L, Walcarius A (2001) Application of electrodes modified with ion-exchange polymers for the amperometric detection of non-redox cations and anions in combination to ion chromatography. Electrochim Acta 46 3543-3553... 

The carbonium ion is stabilized by the presence of a counterion. Recently, a redox cationic-initiator system based on ascorbyl 6-hexadecanoate and diaryliodonium salts in the presence of catalytic amounts of a copper compound has been described in the literature. 

Kennedy, J. P. and E. G. M. Tornquist (eds.), Polymer Chemistry of Synthetic Elastomers , Interscience, New York, 1968 and 1969 (2 parts). A collection of treatises showing various aspects of the chemistry involved in the formation of common elastomers by different mechanisms—redox, cationic, anionic, condensation, alkali metal catalysts. A history and status of synthetic elastomers, and the structure-property relationship for elastomer materials is also presented High Polym., vol. 23). 

Chemical expansion studies were reported for a variety of other perovskite materials with different B-site redox cations such as Cr [93], Co [81], Mn [94] or Ni [82] and combinations of different redox cations [75, 76, 95]. A summary of chemical expansion results (Asc/A<5) is shown in Fig. 7. Differences in this variety of perovskite materials are far from trivial and should not be underestimated. 

Fig. 7 Correlation between the chemical expansion coefficient and tolerance factor of representative ABO3 pevoskites containing redox susceptible B-site species (Cr, Mn, Fe, Co, Ni) (from [75, 76, 81, 82,93-96]). Closed squares correspond to tolerance factor based on 3+ B-site redox cations with CN = 6, and open squares for 2+ B-site redox cations with CN = 6. Other open symbols are for Fe with CN = 4 (O), CN = 5 (o) or equal fractions of CN = 4 and CN = 6 (A)...

The data in Tables 4.2 and 4.3 refer to ions in aqueous acid solution for cations, this means effectively [MlHjO), ]" species. However, we have already seen that the hydrated cations of elements such as aluminium or iron undergo hydrolysis when the pH is increased (p. 46). We may then assume (correctly), that the redox potential of the system... 

When the water ligands around a cation are replaced by other ligands which are more strongly attached, the redox potential can change dramatically, for example for the cobalt(II)-cobalt(III) system we have... 

Electroanalytical chemistry is one of the areas where advantage of the unique properties of SAMs is clear, and where excellent advanced analytical strategies can be utilized, especially when coupled with more complex SAM architectures. There are a number of examples where redox reactions are used to detect biomaterials (357,358), and where guest—host chemistry has been used to exploit specific interactions (356,359). Ion-selective electrodes are an apphcation where SAMs may provide new technologies. Selectivity to divalent cations such as Cu " but not to trivalent ions such as Fe " has been demonstrated (360). 

For solvent extraction of a tetravalent vanadium oxyvanadium cation, the leach solution is acidified to ca pH 1.6—2.0 by addition of sulfuric acid, and the redox potential is adjusted to —250 mV by heating and reaction with iron powder. Vanadium is extracted from the blue solution in ca six countercurrent mixer—settler stages by a kerosene solution of 5—6 wt % di-2-ethyIhexyl phosphoric acid (EHPA) and 3 wt % tributyl phosphate (TBP). The organic solvent is stripped by a 15 wt % sulfuric acid solution. The rich strip Hquor containing ca 50—65 g V20 /L is oxidized batchwise initially at pH 0.3 by addition of sodium chlorate then it is heated to 70°C and agitated during the addition of NH to raise the pH to 0.6. Vanadium pentoxide of 98—99% grade precipitates, is removed by filtration, and then is fused and flaked. 

For vanadium solvent extraction, Hon powder can be added to reduce pentavalent vanadium to quadrivalent and trivalent Hon to divalent at a redox potential of —150 mV. The pH is adjusted to 2 by addition of NH, and an oxyvanadium cation is extracted in four countercurrent stages of mixer—settlers by a diesel oil solution of EHPA. Vanadium is stripped from the organic solvent with a 15 wt % sulfuric acid solution in four countercurrent stages. Addition of NH, steam, and sodium chlorate to the strip Hquor results in the precipitation of vanadium oxides, which are filtered, dried, fused, and flaked (22). Vanadium can also be extracted from oxidized uranium raffinate by solvent extraction with a tertiary amine, and ammonium metavanadate is produced from the soda-ash strip Hquor. Fused and flaked pentoxide is made from the ammonium metavanadate (23). 

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