Oxido-reduction reaction

Metabolism of the major fuels, described above, generates hydrogen atoms or electrons. These are oxidised, not directly, but via a series of oxidations and reductions (oxido-reduction reactions or, alternatively, redox reactions) that... 

The catalytic properties of copper during polyols conversion in aqueous phase may be drastically modified by some additives. Metals having a standard oxido-reduction potential higher than that of copper (Ir, Rh, Ru, Pd, Pt, Au) can be deposited on it by oxido-reduction reaction. The first atoms of second metal deposited exchange with hydroxylated... 

The second system involves numerous hydrophilic or lipophilic molecules like ascorbic acid (AH-) (vitamin C) and a-tocopherol (aT-OH) (vitamin E). These low-molecular-weight antioxidants (LMWA) reduce ROS by oxido-reduction reactions ... 

Other antioxidant species are synthesized by cells like uric acid, ubiquinol or thiols (cystein, homocystein, etc.). In addition, many compounds found in food display antioxidant properties retinol (vitamin A) and its precursor /(-carotene, and polyphenols (flavonoids, etc.). Figure 8.2 shows the apparent standard potential of some LMWA and ROS explaining the spontaneous oxido-reduction reactions at the origin of the antioxidant protection system. 

Some microorganisms can catalyze certain oxido-reduction reactions like the oxidation of iron and manganese in water, the oxidation of sulfur compounds, and oxidation-reduction of nitrogen compounds. Aerobic autotrophic bacteria of the type Thiobacillus can release soluble iron, copper, and sulfuric acid as sulphates into water. These organisms can be found everywhere in nature wherever an acidic environment is maintained in the presence of sulfide-containing minerals. 

For each of the redox couples, the potential can be calculated using the Nernst equation. This equation correlates Gibb s free energy, known as AG, and the electromotive force provided by an oxido-reduction reaction (such a reaction acts as a galvanic cell). Given the following equation due to a chemical reaction ... 

Equation (12.10) is known as the Nernst equation, where R is the gas constant (8.314 J mol K ), T the temperature in Kelvin, Q the reaction quotient as defined in Eq. (12.8), T the Faraday constant (9.65 x 10" C mol ) and n being the number of electrons involved during the oxido-reduction reaction. By using log (to the base 10) instead of the natural logarithm, replacing the variables with their numerical values and fixing the temperature at 25 °C (298 K), the Nernst equation becomes ... 

All these results are related to observations and measurements in the field as well as from oxalotrophic bacterial cultures in the laboratory (Braissant et al, 2004). There is no theoretical model available to explain the oxalate-carbonate transformation and its consequences on the soil solution properties, i.e. alkalinization facilitating precipitation of calcium carbonate (CaCOs) and CO2 release into the atmosphere. This kind of model should be able to explain the process of oxido-reduction reactions, pH regulation and the evolution of the various phase concentrations involved in the system, i.e. oxalate, carbonate, water and CO2. This is the aim of the next section. 

A theoretical analysis of oxalate-carbonate transformation The objective of this theoretical approach is to try to compare the equilibrium diagrams of the CaCOs—CaC204—CO2—H2O system with the biogeochemical data available on the oxalate-carbonate transformation. The initial hypothesis is that the oxido-reduction reaction of oxalate-carbonate occurs biochemically, i.e. due to bacterial activity. In other words, activation energy is present and high enough to initiate the reactions. The theoretical system studied is defined by three different phases present ... 

A peculiar oxido-reductive reaction takes place when p-aminotoluene is heated with sodium polysulfide the product is p-aminobenzaldehyde [505]. 

All the parameters influencing the rate of oxido-reduction reactions (e.g., temperature, pressure, concentrations of additives, and complexing agents) have to be very carefully controlled to achieve the desirable thickness and/or properties of the deposit. 

Consider following oxido-reduction reaction involving the charge transfer of z electrons ... 

Additionally it should be remembered that nicotine metabolites still retain a pyridyl moiety and this functional group can release nicotinamide from NADPH and generate an analogue of the coenzyme via a glycohydrolase. As these analogues may not be able to participate in the normal oxido/reduction reactions of intermediary metabolism certain pathways may be inhibited leading to accumulation of substrates e.g. glucose-6-phosphate and diminution of availability of products e.g. ribose, and thereby affect purine, pyrimidine and nucleic acid biosynthesis. 

It has been evidenced that among the various unsaturated hydrocarbons, alkynes show the largest inhibiting effect on all oxido-reduction reactions occuring on a PtRh catalyst, i.e. non-alkyne hydrocarbons, CO and NO are not converted until alkynes are eliminated,... 

If an oxido-reduction reaction occurs between species O and R, with concentra-... 

Balancing numerous chemical reactions often involves exchanges of electrons between different species. These reactions are called oxidation-reduction reactions, oxido-reduction reactions, or redox reactions. They can take place in a homogeneous phase, specifically within a solution. They can also take place in a heterogeneous medium, on the surface of electrodes. In the first case, we simply speak of redox reactions (it is understood in solution). In the second, we speak of electrochemical reactions. 

In the Mulliken, Hudson and Klopman quantum treatments, the degree of charge transfer may take any value. Consequently, they apply not only to Lewis-type acid-base reactions, in which, strictly speaking, an electron pair is shared, but also to oxido-reduction reactions ... 

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