Oxygen, addition effect redox potential

In addition to effects on the concentration of anions, the redox potential can affect the oxidation state and solubility of the metal ion directly. The most important examples of this are the dissolution of iron and manganese under reducing conditions. The oxidized forms of these elements (Fe(III) and Mn(IV)) form very insoluble oxides and hydroxides, while the reduced forms (Fe(II) and Mn(II)) are orders of magnitude more soluble (in the absence of S( — II)). The oxidation or reduction of the metals, which can occur fairly rapidly at oxic-anoxic interfaces, has an important "domino" effect on the distribution of many other metals in the system due to the importance of iron and manganese oxides in adsorption reactions. In an interesting example of this, it has been suggested that arsenate accumulates in the upper, oxidized layers of some sediments by diffusion of As(III), Fe(II), and Mn(II) from the deeper, reduced zones. In the aerobic zone, the cations are oxidized by oxygen, and precipitate. The solids can then oxidize, as As(III) to As(V), which is subsequently immobilized by sorption onto other Fe or Mn oxyhydroxide particles (Takamatsu et al, 1985). 

The static trans effect of L on the CO-stretching frequencies in [30a-30g] does not show any correlations to the Osn/Osm redox potentials (see Table 10), which range between 0.48 and 0.56 V irrespective of L, with the exception of the species [30c], [30i], and [30k] where L contains an imidazole skeleton in the latter compounds, they are about 0.1 V lower than the mean value of the others. As this deviation has no parallel with the optical spectra, it is assumed that this low redox potential indicates an additional rr-donor effect of the imidazole moiety. As this additional 7r-donor effect is also ascribed to the oxygen donors, e.g., DMF and THF, the latter should also show low redox potentials. However, their potentials fall into the normal range. This may be due to the fact that they have a different a-rr-donor 7r-acceptor balance, the oxygen donors acting as weaker a-donors and not at all as 7r-acceptors. For this reason, their w-donor function becomes very effective in the fixation of... 

The redox potentials of various oxidants derived from nitric oxide and peroxynitrite are summarized in Table 4. Clearly, as the adducts of molecular oxygen and nitric oxide become more reduced, they form substantially stronger oxidizing agents. In effect, addition of one electron makes these nitrogen oxides more ready to accept the next. The precise pathway of decomposition followed is influenced by what types of target molecules come in contact with peroxynitrite and is... 

Some additional insight as to possible mechanisms of the photocorrosion process can be gained from a more detailed consideration of the effects of pH on the band levels in SrTiC>3 and on the redox potentials of oxygen formation and the photo-Kolbe reaction. These data, along with the band levels for Ti02, are shown in Figure 5. It is important to remember that the photocorrosion process occurs in com-... 

In addition to direct toxic effects of substances, whether to hnmans or more generally in the environment, other environmental effects may also need to be taken into account. Natural gas, for example, is toxic only to the extent that it carries traces of substances such as the carcinogen benzene. However, if released nnderground, it can lead to the displacement of oxygen, with adverse effects on roots and soil microorganisms. Accompanying changes in soil conditions such as pH and redox potentials can also lead to the mobilization of heavy metals. 

In agreement with calculations, cyclovoltammetric data on selected thiophene-5,5-dioxides and -5-oxides showed that the addition of oxygen atoms to sulfur has a dramatic effect on redox potentials and hence on the HOMO and LUMO position and energy gap [12], Table 4.1 illustrates this effect, comparing the redox potentials of 2,5-bis(trimethylsilyl)thiophene with that of the corresponding 5-oxide and 5,5-dioxide. 

In addition, bromide can serve as a redox mediator. The potential of Brj/Br" couple allows the oxidation of Br by oxygen and oxidation of Pd(0) by generated bromine. This may explain the absolutely crucial role of a bromide salt, which is superior to other halides, in DPC synthesis. Nonadditive effect (positive or negative) of two or more cocatalysts confirms the hypothesis of formation of mixed-metal complexes in DPC catalytic system. 

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