Redox theories

Students preconcepts are particularly addressed through the well-known formation of rust, conflicts between everyday language and modern redox theory readily occur. Luckily, 56% of the students chose the correct answer... 

Conway EJ. A redox theory of hydrochloric acid production by the gastric mucosa. Irish J Med Sci 288 801-804, 1949, p 802. 

Figure 14 A proposed mechanism for O2 sensing. The redox theory of HPV suggests that AOS are produced in proportion to PO2 hy O2 sensors, likely complexes I and III of the mitochondrial ETC, and possibly also cytochrome-hased vascular oxidases. The changes in AOS production alter the gating and open probability of the effectors of HPV, the O2- and redox-sensitive Kv channels, such as Kvl.5 and Kv2.1.

Thus these results are inconsistent with the simple redox theory, while they are easily explained by postulating the utilization of an energy source such as ATP. They do not exclude, however, the possibility of a coupling between a redox system and the hydrolysis of ATP. 

The literature [14] on electrochemical kinetics is extensive and specialized. Figure 2-4 shows a J(rjj) curve of a redox reaction according to Eq. (2-9) with activation and diffusion polarization. It follows from theory [4, 10] for this example ... 

J Li, MR Nelson, CY Peng, D Bashford, L Noodleman. Incorporating protein environments in density functional theory A self-consistent reaction field calculation of redox potentials of [2Ee2S] clusters in feiTedoxm and phthalate dioxygenase reductase. J Phys Chem A 102 6311-6324, 1998. 

Even when they have a partial crystallinity, conducting polymers swell and shrink, changing their volume in a reverse way during redox processes a relaxation of the polymeric structure has to occur, decreasing the crystallinity to zero percent after a new cycle. In the literature, different relaxation theories (Table 7) have been developed that include structural aspects at the molecular level magnetic or mechanical properties of the constituent materials at the macroscopic level or the depolarization currents of the materials. 

Contrary to theory the value of y oo depends on the concentration ration of the redox components with values ranging from 34. 3 Solution saturated with benzene. 

The conspicuous separation between the cathodic and anodic peak potentials was initially interpreted in terms of the simple theory for redox polymers as a kinetic effect of slow heterogeneous charge transfer the thermodynamic redox potential of the whole systems was calculated from the mean value between Ep and Ep ... 

A general theory based on the quantitative treatment of the reaction layer profile exists for pure redox catalysis where the crucial function of the redox mediator is solely electron transfer and where the catalytic activity largely depends only on the redox potential and not on the structure of the catalyst This theory is consistent... 

Theories neglect that catalysts usually have limited turnover numbers due to destructive side reactions. This may not be so obvious in analytical experiments but it has severe consequences for large scale applications. A simple calculation can illustrate this problem if a redox polymer with a monomer molecular weight of 400 Da and a density of 1 g cm " is considered with all redox centers addressable from the electrode and accessible to the substrate with a turnover number of 1000, then, to react 1 nunol of substrate at a 1 cm electrode surface, at least 5 pmol of active catalyst centers corresponding to 2 mg of polymer, or a dry film thickness of 20 pm are required. This is 20 times more than the calculated optimum film thickness for rather favorable conditions... 

EPR studies on electron transfer systems where neighboring centers are coupled by spin-spin interactions can yield useful data for analyzing the electron transfer kinetics. In the framework of the Condon approximation, the electron transfer rate constant predicted by electron transfer theories can be expressed as the product of an electronic factor Tab by a nuclear factor that depends explicitly on temperature (258). On the one hand, since iron-sulfur clusters are spatially extended redox centers, the electronic factor strongly depends on how the various sites of the cluster are affected by the variation in the electronic structure between the oxidized and reduced forms. Theoret-... 

The rate of peroxide decomposition and the resultant rate of oxidation are markedly increased by the presence of ions of metals such as iron, copper, manganese, and cobalt [13]. This catalytic decomposition is based on a redox mechanism, as in Figure 15.2. Consequently, it is important to control and limit the amounts of metal impurities in raw rubber. The influence of antioxidants against these rubber poisons depends at least partially on a complex formation (chelation) of the damaging ion. In favor of this theory is the fact that simple chelating agents that have no aging-protective activity, like ethylene diamine tetracetic acid (EDTA), act as copper protectors. 

Here we mention as an example that in the coordination-chemistry field optical MMCT transitions between weakly coupled species are usually evaluated using the Hush theory [10,11]. The energy of the MMCT transition is given by = AE + x- Here AE is the difference between the potentials of both redox couples involved in the CT process. The reorganizational energy x is the sum of inner-sphere and outer-sphere contributions. The former depends on structural changes after the MMCT excitation transition, the latter depends on solvent polarity and the distance between the redox centres. However, similar approaches are also known in the solid state field since long [12]. 

FIG. 21 Plot of log ki2 vs. AEi/2 showing the dependence of ET rate on the driving force for the reaction between ZnPor and four aqueous reductants. The difference between the half-wave potentials for an aqueous redox species and ZnPor, AE-i/2 = AE° + A°0, where AE° is the difference in the formal potentials of the aqueous redox species and ZnPor and A° is the potential drop across the ITIES. The solid line is the expected behavior based on Marcus theory for X = 0.55 eV and a maximum rate constant of 50 cm s M . (Reprinted from Ref. 49. Copyright 1999 American Chemical Society.)... 

The ET reaction between aqueous oxidants and decamethylferrocene (DMFc), in both DCE and NB, has been studied over a wide range of conditions and shown to be a complex process [86]. The apparent potential-dependence of the ET rate constant was contrary to Butler-Volmer theory, when the interfacial potential drop at the ITIES was adjusted via the CIO4 concentration in the aqueous phase. The highest reaction rate was observed with the smallest concentration of CIO4 in the aqueous phase, which corresponded to the lowest driving force for the oxidation process. In contrast, the ET rate increased with driving force when this was adjusted via the redox potential of the aqueous oxidant. Moreover, a Butler-Volmer trend was found when TBA was used as the potential-determining ion, with an a value of 0.38 [86]. 

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