Standard reduction potential biological

Table 3.1 Biological Standard Reduction Potentials (E ) for a Series of Antioxidant Compounds and Flavonoids and Biological Standard Free Energy Variation (AG" ) for the Reactions between These Compounds and Oxygen Free Radicals... 

The redox couple C02/CH3C00 has a biological standard reduction potential (see Exercise 109) of - 0.29 V. The redox couple O2/H2O has a biological standard reduction potential of 0.82 V. 

Standard Reduction Potentials for Several Biological Reduction Half-Reactions ... 

TABLE 13-7 Standard Reduction Potentials of Some Biologically Important Half-Reactions, at pH 7.0 and 25°C (298 K)... 

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

Table 7.5. Standard reduction potentials of some biologically important half-reactions (25°C, pH = 7)...

Cob(III)alamins undergo ligand exchange reactions typical of cobalt(III) complexes, most of which are not directly relevant to biological function. One-electron reduction to cob(II)alamin and two-electron reduction to cob(I)alamin are biologically relevant. The standard reduction potentials are +200 and —610 mV, respectively, for the base-on Cob(III)/Cob(II) and Cob(II)/Cob(I) couples, referenced to the normal hydrogen electrode. ... 

For biological systems this tendency is expressed by the standard reduction potential, Eq, defined as the electromotive force (emf) in volts given by a half-cell in which the reductant and oxidant species are both present at 1.0 M concentration unit activity, at 25°C and pH 7.0 in equilibrium with an electrode which can reversibly accept electrons from the reductant species, according to the equation ... 

The standard reduction potentials of a number of biologically important redox couples are given in Table 12. Systems having a more negative standard reduction potential than the H2-2H couple have a greater tendency to lose electrons than hydrogen those with a more positive potential have a lesser tendency to lose them. 

The standard reduction potentials of various biological oxidation-reduction systems allow us to predict the direction of flow of electrons from one redox couple to another under standard conditions. Furthermore, we can calculate the final equilibrium resulting when electrons flow from one redox system of known standard potential to another of known potential, as well as the free-energy changes during such reactions which will be discussed later. 

Table 18.6 lists formal potentials for common protein electron transfer reactions in biologically related systems. Table 18.7 lists standard reduction potentials for biochemical reduction reactions. 

Though accelerating effect of redox mediators is proved, differences in electrochemical factors between mediator and azo dye is a limiting factor for this application. It was reported that redox mediator applied for biological azo dye reduction must have redox potential between the half reactions of the azo dye and the primary electron donor [37], The standard redox potentials for different azo dyes are screened generally between -430 and -180 mV [47],... 

The standard redox potential El (standard conditions for the biochemist are 1M oxidant, 1M reductant, 10-7 M [H+], i.e. pH 7 and 25 °C) for most biological redox couples are known. Remember that in this context El refers to the partial reaction written as ... 

The midpoint potential of a half-reaction E, is the value when the concentrations of oxidized and reduced species are equal, [Aox] = [Aredl- In biological systems the standard redox potential of a compound is the reduction/oxidation potential measured under standard conditions, defined at pH = 7.0 versus the hydrogen electrode. On this scale, the potential of 02/water is +815 mV, and the potential of water/H2 is 414 mV. A characteristic of redox reactions involving hydrogen transfer is that the redox potential changes with pH. The oxidation of hydrogen H2 = 2H + 2e is an m = 2 reaction, for which the potential is —414 mV at pH 7, changing by 59.2 mV per pH unit at 30°C. 

The reduction-oxidation potential (typically expressed in volts) of a compound or molecular entity measured with an inert metallic electrode under standard conditions against a standard reference half-cell. Any oxidation-reduction reaction, or redox reaction, can be divided into two half-reactions, one in which a chemical species undergoes oxidation and one in which another chemical species undergoes reduction. In biological systems the standard redox potential is defined at pH 7.0 versus the hydrogen electrode and partial pressure of dihydrogen of 1 bar. 

The standard potential for a redox reaction is defined for a galvanic cell in which all activities are unity. The formal potential is the reduction potential that applies under a specified set of conditions (including pH, ionic strength, and concentration of complexing agents). Biochemists call the formal potential at pH 7 E° (read "E zero prime"). Table 14-2 lists E° values for various biological redox couples. 

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