Oxidation-reduction, potential reagents

Cleland (1964) showed that DTT and DTE are superior reagents in reducing disulfide bonds in proteins (see previous discussion, this section). DTT and DTE have low oxidation-reduction potential and are capable of reducing protein disulfides at concentrations far below that required with 2-mercaptoethanol. However, even these reagents have to be used in approximately 20-fold molar excess in order to get close to 100 percent reduction of a protein. 

Swain and Goldstein (6, 7) noted a rather large difference in the molar color yield from different phenols with the Folin-Denis reagent. They attributed this to differences in relative oxidation-reduction potentials of the different phenols, but under their conditions pyrogallol gave about half the color of catechol and more than resorcinol. However, they also reported that the molar absorptivity produced by a flavonoid was approximately equal to the sum of the values for the separate phenolic moieties which it contained. 

Oxidation-Reduction Potentials of Chemical Reagents for Water and Wastewater Treatment... 

Copper acetate-benzidine acetate test (DANGER THE REAGENT IS CARCINOGENIC.) This reaction takes place because the oxidation-reduction potential of the copper(II)-copper(I) couple is increased if copper(I) ions are removed by cyanide ions. 

The most of chemical reactions accompanied by electron transfer from an atom of one reagent (reducer) to an atom of another reagent (oxidizer). Each element can have some oxidation states. The standard oxidation-reduction potential between two oxidation states of element is bonded with standard thermodynamic free energy of the transition from one state to another by the following equation ... 

That oxidation-reduction potentials are related to equilibrium constants may be used to underscore the fact that they apply to (theoretically) reversible reactions. The oxidized member of any couple will reduce some of the reduced member of any other couple, provided a reaction mechanism exists. The potentials of the two couples permit an estimation only of the possible extent of the reaction nothing can be predicted about the rate, or indeed, whether the reaction will occur at all. In determining the extent of any reaction, actual concentrations of all reagents must be considered, since the actual equilibrium is important, not the equilibrium of an ideal 1 M solution that might be calculated from AE or AFo values. 

As discussed previously, cytochrome c is reduced by several flavo-proteins. On enzymatic reduction or reaction with hydrosulfite, ascorbic acid, or any of several other reducing reagents, the typical spectrum of reduced cytochrome c is produced. The band at 550 m/ is usually used to assay reduced cytochrome c. The reduction causes a change in the iron from the ferric to the ferrous state. The oxidation-reduction potential of the couple, ferric3rtochrome Jerrocytochrome at neutral pH values (5-8) is -H0.256 volts. ... 

The standard reduction potential of Cr " (Table 2) shows that this ion is a strong reducing agent, and Cr(II) compounds have been used as reagents in analytical chemistry procedures (26). The reduction potential also explains why Cr(II) compounds are unstable in aqueous solutions. In the presence of air, the oxidation to Cr(III) occurs by reaction with oxygen. However, Cr(II) also reacts with water in deoxygenated solutions, depending on acidity and the anion present, to produce H2 and Cr(III) (27,28). 

Radical cations can be generated by many chemical oxidizing reagents, including Brpnsted and Lewis acids, the halogens, peroxide anions or radical anions, metal ions or oxides, nitrosonium and dioxygenyl ions, stable aminium radical cations, semiconductor surfaces, and suitable zeolites. In principle, it is possible to choose a reagent with a one-electron redox potential sufficient for oxidation-reduction, and a two-electron potential insufficient for oxidation-reduction of the radical ion. 

By international agreement, the algebraic sign of E° for a half-cell is chosen to be the same as its electrical sign relative to the SHE. This means, in effect, that we must write the half-reactions with the electrons on the left-hand side in other words, E° values are taken to be reduction potentials. Consequently, a reagent such as chlorine that is more oxidizing than aqueous H+ (— H2) under standard conditions will have a positive E°... 

In summary, the triplet (do po) excited states of the d -d metal dimers [Ir(p-pz)(C0D)]2 and Pt2(pop)4 " undergo a variety of photochemical reactions. Electron transfer to one-electron quenchers such as pyridinium cations or halocarbons readily occurs with acceptors that have reduction potentials as negative as -2.0 V. With the latter reagents, net two-electron, photoinduced electron transfer yields d -d oxidative addition products. Additionally, the triplet (da pa) excited state of Pt2(pop)4 apparently is able to react by extracting a hydrogen atom from a C-H bond of an organic substrate. 

The lowest energy level of the conduction band defines the reduction potential of the photoelectrons, while the highest one of the valence band determines the oxidizing power of the photoholes, respectively. When the reagents spread on the catalyst surface they are adsorbed on the active site and they can participate in redox reactions. 

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