Redox buffer system

It is important not to confuse the reactions of Eq. 17-42 as they occur in an aerobic cell with the tightly coupled pair of redox reactions in the homolactate fermentation (Fig. 10-3 Eq. 17-19). Tire reactions of steps a and c of Eq. 17-42 are essentially at equilibrium, but the reaction of step b may be relatively slow. Furthermore, pyruvate is utilized in many other metabolic pathways and ATP is hydrolyzed and converted to ADP through innumerable processes taking place within the cell. Reduced NAD does not cycle between the two enzymes in a stoichiometric way and the "reducing equivalents" of NADH formed are, in large measure, transferred to the mitochondria. The proper view of the reactions of Eq. 17-42 is that the redox pairs represent a kind of redox buffer system that poises the NAD+/NADH couple at a ratio appropriate for its metabolic function. 

The significance of the redox control to molten salt transmuter systems with uranium-free fuel is that in some cases where the fuel is, e.g., PUF3, the Pu(III)/ Pu(IV) redox couple is too oxidizing to present satisfactory redox buffered system. In this case as it was proposed by ORNL redox control could be accomplished by including an HF/H2 mixture to the inert cover gas sparge which will not only set the redox potential, but will also serve as the redox indicator if the exit HF/H2 stream is analyzed relative to inlet [44]. 

Hydrogen chloride, 203,562-563 Hydrogen fluoride, 183,562-563 Hydrogen ion acceptors, donors of, 353 and balancing redox equations, 88-89 in buffer systems, 387-390 and hydroxide ion, 354—355 and indicator color, 391-393 and pH, 355... 

The obtained results on the reaction mechanism can be summarized as follows The metal silicides form cluster structures which represent electron buffer systems. They can be oxidized or reduced easily by surface reactions. The adsorption of SiCl4 molecules at the cluster surface is immediately followed by an electron transfer from the cluster to the silicon atom of SiCl4, the cluster is oxidized. As a result of such a process a silylene species is formed at the surface of the catalyst. Chloride ions act as counter ions to the positive cluster, supporting the redox step (Eq. 4). 

Note that at pH > 7 the redox potentials vary only slightly. The H2S-S0-H2O system behaves as a redox buffer. This effect can be of importance in waters where sulfide and polysulfide are found. 

In practical developers there is usually an excess of the reduced form of the developing agent with a small and variable amount of the oxidized form. Except for certain cases, such as in Lith development, the oxidation products are not allowed to accumulate. This means that the redox potentials are uncertain because the system is not in equilibrium. Redox buffers are solutions which are in equilibrium and contain definite amounts of oxidized and reduced forms. Many organic developing agents have oxidized forms which undergo side reactions, particularly in alkaline solution, which prevent them from being used as redox buffers for that reason, metal ion couples are used instead. 

Fe " /Fe +, so if air is excluded from the system a range of redox buffers can be made with definite potentials by adjusting this ratio. The complexing agent C can be oxalate [83], citrate, tartrate, ethylenediamine tetraacetate (EDTA), DTPA, or other amino carboxylic acids. 

The poising (buffering) of a redox system against a pe change can be defined—similarly as in acid-base systems—as a redox-buffer or poising intensity... 

Since LAW and H2LAW are present at much lower concentrations than hydrogen sulfide, the redox potential, (pH) of the system is essentially determined by Eq. 21 with [H2S]T = 5x 10 3M. Hence, in analogy to a pH buffer for proton-transfer reactions, the H2S/S(s) couple is used as a redox buffer for electron transfer. 

Lacking GSH-dependent peroxidases, Plasmodium spp. rely on a Prx-linked detoxification for hydroperoxides and reduced GSH acts primarily as the principal redox buffer. It is also important in detoxification reactions as a co-factor for GST and glyoxalase and has been shown to be involved in the breakdown of free ferriprotoporphyrin IX. The lack of two major antioxidants present in other cells (catalase and GSH peroxidase) suggests that malaria parasites would be vulnerable to disturbances in their anti-oxidant systems. As a consequence, pro-oxidant drugs such as the artemisinins, which increase the oxidative stress, are efficient antimalarials. It has been proposed that a novel approach to malaria chemotherapy would be to develop drugs that disrupt the anti-oxidant and redox system of Plasmodium (Muller, 2004 Nickel et al., 2006 Rahlfs and Becker, 2005). 

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