Oxidation-reduction reactions characteristics

In the majority of cases both the primary and the induced reactions are oxidation-reduction reactions. In such reactions the actor can have either reducing or oxidizing properties. The chemical characteristics of the inductor and acceptor are always identical and opposite to that of the actor. When the latter is a reducing agent the acceptor and inductor are oxidants and vice versa. 

Indicine IV-oxide (169) (Scheme 36) is a clinically important pyrrolizidine alkaloid being used in the treatment of neoplasms. The compound is an attractive drug candidate because it does not have the acute toxicity observed in other pyrrolizidine alkaloids. Indicine IV-oxide apparently demonstrates increased biological activity and toxicity after reduction to the tertiary amine. Duffel and Gillespie (90) demonstrated that horseradish peroxidase catalyzes the reduction of indicine IV-oxide to indicine in an anaerobic reaction requiring a reduced pyridine nucleotide (either NADH or NADPH) and a flavin coenzyme (FMN or FAD). Rat liver microsomes and the 100,000 x g supernatant fraction also catalyze the reduction of the IV-oxide, and cofactor requirements and inhibition characteristics with these enzyme systems are similar to those exhibited by horseradish peroxidase. Sodium azide inhibited the TV-oxide reduction reaction, while aminotriazole did not. With rat liver microsomes, IV-octylamine decreased... 

One easily demonstrated electrical characteristic of moist soil is seen in the production of electricity when two different metals, namely, copper and zinc, are inserted into it. This is not unexpected because any salt-containing solution adsorbed in media, such as paper or cloth, and placed between these same two electrodes will cause a spontaneous reaction that produces electricity. The source of this flow of electrons is an oxidation-reduction reaction, represented as two half-reactions as shown in Figure 9.1 for copper and zinc. 

Biological oxidation-reduction reactions can be described in terms of two half-reactions, each with a characteristic standard reduction potential, E °. 

Redox pairs Oxidation (loss of electrons) of one compound is always accompanied by reduction (gain of electrons) of a second substance. For example, Figure 6.11 shows the oxidation of NADH to NAD+ accompanied by the reduction of FAD to FADH2. Such oxidation-reduction reactions can be written as the sum of two halfreactions an isolated oxidation reaction and a separate reduction reaction (see Figure 6.11). NAD+ and NADH form a redox pair, as do FAD and FADH2. Redox pairs differ in their tendency to lose electrons. This tendency is a characteristic of a particular redox pair, and can be quantitatively specified by a constant, E (the standard reduction potential), with units in volts. 

Combustion is an oxidation-reduction reaction between a nonmetallic material and molecular oxygen. Combustion reactions are characteristically exothermic (energy releasing). A violent combustion reaction is the formation of water from hydrogen and oxygen. As discussed in Section 9.5, the energy from this reaction is used to power rockets into space. More common examples of combustion include the burning of wood and fossil fuels. The combustion of these and other carbon-based chemicals forms carbon dioxide and water. Consider, for example, the combustion of methane, the major component of natural gas ... 

The various oxidation-reduction reactions in the Black Sea occur in narrow layers of water of similar density and form features that are characteristic of the hydrochemical structure (e.g., maxima and minima, onset points). The position of these features in the density field is very stable [17-20] and it is possible to name this feature chemotropic [21] the connection between the water density and properties of the chemical structure (by analogy with barotropic—the connection between density and pressure). In Table 1 we summarize the correspondence of the key features of the chemical structure with the density values. These values have served as a benchmark for subsequent cruises to evaluate the stability of the characteristic features. 

Sobel, R. E. and W. Lovenberg Characteristics of Clostridium pasteurianum ferredoxin in oxidation-reduction reactions. Biochemistry 5, 6—13 (1966). 

L-Ascorbic acid is also added to food in essentially a non-nutrient capacity such as a preservative or oxygen acceptor, as an acidulant, as a stabilizer of cured meat color, or as a flour improver. Because of the ene-diol group, it has a marked inhibitory influence on the oxidation-reduction reactions responsible for undesirable color, flavor, and odor development. Its mechanism of action is dependent upon the characteristics of the food or food ingredient, the associated environments, the processing technology, and the storage expectancy of the product. 

Note that chlorine steals electrons from bromide ions to become chloride ions. When the bromide ions lose their extra electrons, the two bromine atoms form a covalent bond with each other to produce Br2 molecules. The result of this reaction, the characteristic color of elemental bromine in solution, is shown in Figure 20-2. The formation of the covalent bond by sharing of electrons also is an oxidation-reduction reaction. 

What is the main characteristic of oxidation-reduction reactions (20.1)... 

As we have just seen, system for oxidation/reduction titration is usually independent of dilution. Consequently, titration curves for oxidation/reduction reactions are usually independent of analyte and reagent concentrations. This characteristic is in distinct contrast to that observed in the other types of titration curves we have encountered. 

Standard substances in clinical chemistry include primary standards, which can be obtained sufficiently pure to be used for the preparation of solutions by weighing or by reference to other definable physical characteristics (e.g., constant-boiling hydrochloric acid). Primary standard chemicals are available for acid-base reactions, precipitation reactions, oxidation-reduction reactions, etc. (V3), and are used in these various categories of analytical determination to validate the preparation of solutions of other chemical substances which cannot be obtained in a form suitable to meet the criteria demanded for a primary standard. Following their calibration in terms of a primary standard, these other chemieals can act as secondary standards. 

On May 4, 1923, the Dutch chemical journal Receueildes Travaux Chim-iques des Pays-Bas (42 718) received a paper from Bronsted on existing concepts of acids and bases. In this paper Bronsted demonstrated how useful it was to define an acid as a proton donor and a base as a proton acceptor. In the Bronsted scheme, acid-base reactions are proton transfer reactions. Every acid is related to a conjugate base, and every base to a conjugate acid. Also in this paper he pointed out that there is an analogy between the proton transfer that is characteristic of acid-base reactions and the electron transfer that is characteristic of oxidation-reduction reactions. 

Oxidation States The Characteristics of Oxidation-Reduction Reactions... 

Unique characteristics of ferromanganese nodules and associated oxidation-reduction reactions have been used by soil scientists as morphological indicators to help identify hydric soils (see Chapter 3). These characteristics are termed by soil scientists as redoximorphic features however, various terms such as redox concentrations, redox depletions, and reduced matrix are synonymously used for the oxidation-reduction of iron and manganese and their respective concentrations. We prefer not to define these characteristics as redoximorphic features because oxidation-reduction reactions not only involve iron and manganese but also a range of elements that support biotic communities in the biosphere. 

Most of this discussion of electrochemistry has dealt with effects involving a how of electrical current. It has been seen that chemical reactions can be used to produce an electrical current. It has also been seen that the flow of an electrical current through an electrochemical cell can be used to make a chemical reaction occur. Another characteristic of electricity is its voltage, or electrical potential, which was discussed as E and ° values above as a kind of driving force behind oxidation-reduction reactions. 

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