Oxidation-reduction potentials general table

Some lines of prokaryote development are shown in Table 6.2 with a guide to oxidation/reduction potential ranges in Table 6.3. In all these and further changes the novel chemistry has to be built into the cooperative whole (see Section 3.9). Note again the necessity that the novel features must become part of a controlled autocatalytic restricted set of reaction paths, which become general to any further evolution. 

CONCLUSIONS DRAWN FROM THE TABLES OF OXIDATION-REDUCTION POTENTIALS From the values of oxidation-reduction potentials we can easily find out whether a particular oxidation-reduction reaction is feasible or not. We have already seen the rules that govern the displacement of metals by one another, and the feasibility of dissolving metals in acid with the liberation of hydrogen. Those conclusions can now be extended and generalized. It can be said that the more positive the oxidation-reduction... 

Oxidation-reduction potentials biochemical species, 7-16 to 18 general table, 8-20 to 29 ion radicals, 8-30 to 31... 

In general, reduction potentials of nucleobases have been studied much less than their oxidation potentials, and in particular water-based data are rather lacking [2, 35]. We therefore listed the available polarographic potentials measured in dimethylformamide and data obtained from pulse radiolysis studies or fluorescence quenching measurements. From the data in Table 1, it is evident that the pyrimidine bases are most easily reduced. The reduction potential of the T=T CPD lesion is close to the estimated value of the undamaged thymine base [34, 36]. 

Type II copper enzymes generally have more positive reduction potentials, weaker electronic absorption signals, and larger EPR hyperfine coupling constants. They adopt trigonal, square-planar, five-coordinate, or tetragonally distorted octahedral geometries. Usually, type II copper enzymes are involved in catalytic oxidations of substrate molecules and may be found in combination with both Type I and Type III copper centers. Laccase and ascorbate oxidase are typical examples. Information on these enzymes is found in Tables 5.1, 5.2, and 5.3. Superoxide dismutase, discussed in more detail below, contains a lone Type II copper center in each of two subunits of its quaternary structure. 

Practically in every general chemistry textbook, one can find a table presenting the Standard (Reduction) Potentials in aqueous solution at 25 °C, sometimes in two parts, indicating the reaction condition acidic solution and basic solution. In most cases, there is another table titled Standard Chemical Thermodynamic Properties (or Selected Thermodynamic Values). The former table is referred to in a chapter devoted to Electrochemistry (or Oxidation - Reduction Reactions), while a reference to the latter one can be found in a chapter dealing with Chemical Thermodynamics (or Chemical Equilibria). It is seldom indicated that the two types of tables contain redundant information since the standard potential values of a cell reaction ( n) can be calculated from the standard molar free (Gibbs) energy change (AG" for the same reaction with a simple relationship... 

Since the potentials in Table XLIX give the free energies of the oxidation reactions, using the term oxidation in its most general sense, they may be called oxidation potentials the potentials for the reverse processes, i.e., with the signs reversed, are then reduction potentials (cf. p. 435). 

Substituted complexes of the type [M (N,N)2XY]" M = Ru, Os, X,Y = halides, CN , 204 , py, en, NH3, etc. show, in general, two doublets of N,N-localized reductions [154-156]. The reduction behavior is complicated by loss of an ancillary ligand X upon the second and, more rapidly, the 3rd bpy-localized reduction. The reduction potentials are only slightly X-dependent. On the other hand, the oxidation potential is highly dependent on X. Extensive tables of oxidation and the first reduction potentials of these complexes are available [15, 28, 74, 157]. Their values can be predicted by use of electrochemical ligand parameters [15, 28, 157]. 

Other important reductants dissolved in water-saturated soils and sediments include ammonia, hydrogen sulfide, Mn, and Fe. Table 11.4 shows that organic carbon (depending on its oxidation state) is generally a stronger reductant on a mole basis than any of these. Organic carbon is also usually more abundant than other potential reductants, particularly in modern aquatic sediments. 

Several investigations of the redox properties of various free base hydroporphyrins and their metal derivatives have been reported. As is typical of many porphyrins and metalloporphyrins, these hydroporphyrins generally show two oxidations and one or more reductions. The reversibility of these redox reactions depends on the nature of the hydroporphyrin and its stereochemistry. For example, the cyclic voltammograms of ris-H2(OEC) and frans-H2(OEC) were superficially alike, although substantial differences existed in the stability of the cation radicals and dications of the cis and trans isomers [85]. The first oxidation of rrans-H2(OEC) was reversible whereas ds-H2(OEC) was not reversible. However, the notable features observed in the redox chemistry of hydroporphyrins is the shift of both oxidation and reduction potentials of hydroporphyrins towards more negative values compared to porphyrins, i.e., they are more easier to oxidise and difficult to reduce [78]. A significant trend was observed in the electrochemistry of free base octaethyl- [86, 87] and tetraphenyl [88,89] hydroporphyrins (Table 2). The porphyrin and chlorin of each series... 

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