Oxidation-reduction potentials, table

The diversity in oxidation-reduction potentials (Table 9) can not be accounted for as iron environmental differences among these non-heme iron proteins, since the fundamental structures of iron coordination must be identical (Section III-A and B). Therefore, it is of interest that the secondary environmental effect causes such a great variety in oxidation-reduction potentials. 

They are the basis of many products and processes, from batteries to photosynthesis and respiration. You know redox reactions involve an oxidation half-reaction in which electrons are lost and a reduction half-reaction in which electrons are gained. In order to use the chemistry of redox reactions, we need to know about the tendency of the ions involved in the half-reactions to gain electrons. This tendency is called the reduction potential. Tables of standard reduction potentials exist that provide quantitative information on electron movement in redox half-reactions. In this lab, you will use reduction potentials combined with gravimetric analysis to determine oxidation numbers of the involved substances. 

Table 3.5 Standard oxidation-reduction potentials. (From the CRC Handbook of Chemistry and Physics)... 

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. 

Theoretically, according to the mechanism of biological azo dye reduction, the processes of biological decolorization are oxidation-reduction reactions, in which transfer of electrons match with the proton flow by the help of coenzymes, such as NADPH/NADP+ and NADH/NAD+. The oxidation-reduction potentials of the couples of NADPH/NADP+ and NADH/NAD+ are -324 and -320 mV, respectively [25, 46]. The least AGo value of the conversion NADPH/NADP+ and NADH/NAD+ is 44 kJ [47]. Therefore, —93 mV, which is obtained from (1), could be considered as a rough limited ORP value for ordinary primary electron donors of the third mechanism of biological azo dye reduction. This was demonstrated by the results of many researches (Table 1). Hence, the observed failure of cyanocobala-min [30] and ethyl viologen [48] to act as a mediator is most probably due to their too low Ed values 530 and —480 mV, respectively. 

Find the values of the standard oxidation-reduction potentials of the indicated systems (see Appendix 1, Table 21). Write the Nernst equation. 

Table 4. Oxidation-reduction potentials for the redox centers of xanthine oxidase (mV)...

Here n represents the number of electrons transferred in the reaction. With this equation we can calculate the free-energy change for any oxidation-reduction reaction from the values of E" in a table of reduction potentials (Table 13-7) and the concentrations of the species participating in the reaction. 

The oxidation-reduction potential of a pyridine nucleotide coenzyme system is determined by the standard redox potential for the free coenzyme (Table 6-8) together with the ratio of concentrations of oxidized to reduced coenzyme ([NAD+] / [NADH], Eq. 6-64). If these concentrations are known, a redox... 

However, these experiments may not have established a mechanism for natural flavoprotein catalysis because the properties of 5-deazaflavins resemble those of NAD+ more than of flavins.239 Their oxidation-reduction potentials are low, they do not form stable free radicals, and their reduced forms don t react readily with 02. Nevertheless, for an acyl-CoA dehydrogenase the rate of reaction of the deazaflavin is almost as fast as that of natural FAD.238 For these enzymes a hydride ion transfer from the (3 CH (reaction type D of Table 15-1) is made easy by removal of the a-H of the acyl-CoA to form an enolate anion intermediate. 

Table 20.2 lists standard potentials E° for oxidation of first-series transition metals. Note that these potentials are the negative of the corresponding standard reduction potentials (Table 18.1, page 775). Except for copper, all the E° values are positive, which means that the solid metal is oxidized to its aqueous cation more readily than H2 gas is oxidized to H+(aq). 

At the present time, tables of E° values use reduction half reactions called standard reduction potentials. Because the value of E° is affected by the concentration of the electrolyte solution, these values are given for 1 molar solutions. On a table of standard reduction potentials, we would find the E° value for zinc to be -0.76 V, the negative value resulting because the zinc oxidation half reaction must be reversed for a reduction potential table When the half reaction is reversed, the sign must also be reversed. Some standard reduction potential half reactions include the following ... 

The measurements of water quality parameters (oxidation-reduction potential, pH, temperature, conductivity, dissolved oxygen, and turbidity) and the collection of field screening data with field portable instruments and test kits constitute a substantial portion of field work. Field measurements, such as pH, stand on their own as definitive data used for the calculations of solubility of chemical species and chemical equilibrium in water, whereas others serve as indicators of well stabilization or guide our decision-making in the field. Table 3.8 shows the diversity of field measurement... 

Variations Between Lakes. Results of a study to evaluate sulfide production variation with water depth is given in Table V. In this experiment, samples were taken from five different sediment depths over a two-day period at each lake in early October. At both lakes sulfate reduction exceeded putrefaction by a factor of approximately 2 with overall mean rates of 0.55 and 0.29 mg S L-kH1 respectively. Sulfate reduction exceeded cysteine decomposition in all samples except one collected from Third Sister Lake at 17 m. Results of this study snow a good correlation at Third Sister Lake between percent hydrogen sulfide production attributable to putrefaction and depth of sampling station (r=0.94) and oxidation-reduction potential (r=0.98). This correlation was not observed at Frains Lake. A possible factor m differences observed may be the physical nature of the sediment at Frains which was less dense and more flocculent than thatofTliird Sister. 

Table 2. Oxidation-reduction potential for metals in various oxidation states...

The data of Table 11 compare the properties of certain non-heme iron proteins with ferredoxin. While there are certain similarities and differences between these proteins, it is stressed that the main feature which uniquely distinguishes ferredoxin from the others and from spectrally similar proteins from mammalian sources Kimura and Suzuki 60) Omura et al. (77)) is its low oxidation-reduction potential. This feature of ferredoxin renders it capable of fulfilling its recently recognized roles in cellular metabolism. These are dealt with in the final section of this chapter. 

Because oxidation is simply the opposite of reduction, it is only necessary to create a table of one of the values. By convention, the reduction potential is used in tables, and the values are typically given for the standard reduction potential, E°, also written E°red, in units of volts, V. Because oxidation takes place at the anode, this is the value that will need to be reversed (since oxidation potential = -reduction potential). Therefore, we can rearrange Equation 18.1 so we can use values from the reduction potential tables in Equation 18.2 ... 

Table 8.8 Oxidation-reduction potential for various compounds.10...

The factors that influence corrosion of steels in soils are the type of soil moisture content and the position of the water table soil resistivity and soluble ion content soil pH oxidation-reduction potential and the role of microbes present in soil. The exposure of a buried pipe to the soil environment is illustrated in Figure 4.2. The steel pipe is exposed to both meteoric water passing through ground surface and the water in the ground. The meteoric water may be acidic due to the presence of carbon dioxide and sulfur dioxide in the atmosphere. The soil water may be acidic in addition to some dissolved minerals. The steel pipe is partially above the water table with the rest below the water. The pH and the dissolved ions in the ground water provide a corrosive environment. 

The corrosivity of soils also depends upon the oxidation-reduction potential as classified by Booth et al.15 The classification scheme of the corrosivity of soils is given in Table 4.4b. Macrogalvanic cells are formed in underground pipelines due to foreign structure the combination of new and old pipe dissimilar metals (stainless steel and carbon steel) differential aeration dissimilar soils and stray currents. All these lead to localized corrosion of underground pipelines. 

Table 4,4b Soil corrosivity Based on Oxidation-Reduction Potential...

Table III. Oxidation—Reduction Potentials for Manganese (IV) Gluconate and for H2O-O2 Half-Reactions (66, 67)...

By the loss of 4f electrons, La attains a stable electronic configuration giving rise to a trivalent oxidation state. Other oxidation states, such as two and four in some lanthanides, are possible when electronic configurations 4/°, 4 f1 and 4/14 are attained. The oxidation states and the oxidation-reduction potentials of some couples are given in Table 6.1. The lanthanides in 4+ oxidation state are strong oxidizing agents and an example is Ce4+. 

Table 1.17 Standard oxidation-reduction potentials of simple redox systems at 2S°C...

Table 1.18 Standard oxidation-reduction potentials of combined redox and acid-base systems at 25°C...

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... 

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