Oxidant-reductant pair

Although FEP is mostly useful for binding type of simulations rather than chemical reactions, it can be valuable for reduction potential and pKa calculations, which are of interest from many perspectives. For example, prediction of reliable pKa values of key groups can be used as a criterion for establishing a reliable microscopic model for complex systems. Technically, FEP calculation with QM/MM potentials is complicated by the fact that QM potentials are non-seperable [78], When the species subject to perturbation (A B) differ mainly in electronic structure but similar in nuclear connectivity (e.g., an oxidation-reduction pair), we find it is beneficial to use the same set of nuclear geometry for the two states [78], i.e., the coupling potential function has the form,... 

Equations 3-40 and 3-41 differ from those (Eqs. 3-31 and 3-32) discussed previously in that the factor of 2 is absent from the expression for R, since typically only one radical is produced per oxidant-reductant pair. 

Oxazone fluoride, see Tetraoxygen difluoride Oxidant-reductant pair charge transfer process, 21 189 linked, 21 194, 195... 

Thus, the Franck-Condon barrier for the oxidant-reductant pair is given by... 

By linked pairs we denote oxidant-reductant pairs that are joined by a chain of atoms serving to fix the mutual distance between certain limits but not interacting electronically with either of the reacting centers, as exemplified in structures I to IV. 

In this reaction metallic sodium is the reducing agent. Metallic sodium and sodium ion are called an oxidation-reduction pair, or oxidation-reduction. cpuple. The interconversion of metallic sodium and sodium ion by an electron reaction can be expressed by a single equation, with a double arrow ... 

An example of the reversal of an electron reaction involving an oxidation-reduction pair is the bromine-bromide ion pair ... 

The table can be extended to include also many other oxidation-reduction pairs. An extended table is given in Chapter 32, in which its use is discussed. 

Simultaneous occurrence of oxidation and reduction in a chemical reaction. Oxidizing agent reducing agent oxidation-reduction pair (couple). 

Define an oxidation-reduction pair, and write an electron equation in illustration. 

Qtdnhydrone Electrode. The quinhydrone electrode is an important hydrogen-ion electrode, and is perhaps typical of a whole class of such electrodes which function as pH sensors owing to a reversible organic oxidation-reduction pair involving protons. Quinhydrone (an equimolar compound of benzoquinone and hydroquinone) is only slightly soluble in water. The reversible oxidation-reduction couple... 

The standard reference point in the EMF series is the hydrogen electrode, which consists of gaseous hydrogen at 1 atm bubbling over a platinum electrode in an acidic solution with activity 1 for the hydrogen ion (Figure 11-6). Similar electrodes can be made for some other non-metallic elements, and a few of these elements are included in the table, as well as some other oxidation-reduction pairs. 

Figure 31.10 The same principle as in Figure 31.9, demonstrated for an oxidation/reduction pair in one pot.

In a complexation reaction, a Lewis base donates a pair of electrons to a Lewis acid. In an oxidation-reduction reaction, also known as a redox reaction, electrons are not shared, but are transferred from one reactant to another. As a result of this electron transfer, some of the elements involved in the reaction undergo a change in oxidation state. Those species experiencing an increase in their oxidation state are oxidized, while those experiencing a decrease in their oxidation state are reduced, for example, in the following redox reaction between fe + and oxalic acid, H2C2O4, iron is reduced since its oxidation state changes from -1-3 to +2. 

Because the breadth of chemical behavior can be bewildering in its complexity, chemists search for general ways to organize chemical reactivity patterns. Two familiar patterns are Br< )nsted acid-base (proton transfer) and oxidation-reduction (electron transfer) reactions. A related pattern of reactivity can be viewed as the donation of a pair of electrons to form a new bond. One example is the reaction between gaseous ammonia and trimethyl boron, in which the ammonia molecule uses its nonbonding pair of electrons to form a bond between nitrogen and boron ... 

Subsequent ion exchange of the metal cation with the quaternary ammonium ion catalyst provides a lipophilic ion pair (step 2), which either reacts with the requisite alkyl electrophile at the interface (step 3) or is partitioned into the electrophile-containing organic phase, whereupon alkylation occurs and the catalyst is reconstituted. Enantioselective PTC has found apphcation in a vast number of chemical transformations, including alkylations, conjugate additions, aldol reactions, oxidations, reductions, and C-X bond formations." ... 

Many half-reactions of interest to biochemists involve protons. As in the definition of AG °, biochemists define the standard state for oxidation-reduction reactions as pH 7 and express reduction potential as E °, the standard reduction potential at pH 7. The standard reduction potentials given in Table 13-7 and used throughout this book are values for E ° and are therefore valid only for systems at neutral pH Each value represents the potential difference when the conjugate redox pair, at 1 m concentrations and pH 7, is connected with the standard (pH 0) hydrogen electrode. Notice in Table 13-7 that when the conjugate pair 2ET/H2 at pH 7 is connected with the standard hydrogen electrode (pH 0), electrons tend to flow from the pH 7 cell to the standard (pH 0) cell the measured E ° for the 2ET/H2 pair is -0.414 V... 

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. 

As we learned in Chapter 9, chemicals that react with one another are called reactants. In the process of reacting, the reactants form new chemicals known as products. In most acid-base reactions, a proton is transferred from one reactant to the lone pair of another reactant. In this chapter we look at a class of reactions in which an electron or a series of electrons are transferred from one reactant to another.These types of reactions are called oxidation-reduction reactions. 

We live under a blanket of the powerful oxidant 02. By cell respiration oxygen is reduced to H20, which is a very poor reductant. Toward the other end of the scale of oxidizing strength lies the very weak oxidant H+, which some bacteria are able to convert to the strong reductant H2. The 02 -H20 and H+ - H2 couples define two biologically important oxidation-reduction (redox) systems. Lying between these two systems are a host of other pairs of metabolically important substances engaged in oxidation-reduction reactions within cells. 

If there are three or more -SH groups in a chain some incorrect pairing may, and often does, occur. Tire protein disulfide isomerases break these bonds and allow new ones to form.92 The active sites of these isomerases contain pairs of -SH groups which can be oxidized to internal -S-S- bridges by NAD+-dependent enzymes. These enzymes and their relatives thioredoxin and glutaredoxin are discussed further in Box 15-C. Glutathione and oxidation-reduction buffering are considered in Box 11-B. 

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