Redox potential determinant

Various methods have been used to determine the redox potentials (Table XI). Very commonly, EPR-monitored chemical redox titration is performed, which can be used to measure the redox potential not only in isolated complexes but also in membrane preparations. In general, there is good agreement between redox potentials determined in membranes, isolated complexes, or isolated Rieske proteins or fragments the only exception is the water-soluble Rieske fragment from spinach bef complex where differences of more than 50 mV have been observed by the same group but using different methods (31). 

Fig. 18. pH dependence of the oxidized Rieske fragment from bovine heart mitochondria (ISF). (a) Redox potential determined by cyclic voltammetry. The line was fitted to the data points, giving = 7.6 and pi a, x2 = 9-2. (b) CD intensity of the oxidized... 

To sum up, oxyanions are liable to accommodate an additional electron on interaction with e aq, if the central atom has an available orbital This parameter, not the redox potential, determines the reactivity toward e aq. In all cases investigated AO n yielded AO (w+l) which occasionally may lose H20 to give AO (n l). 

Increasing the sweep rate increases the sensitivity and the precision of the capacity measurement, but time-dependent phenomena may interfere with the measurement at higher sweep rate, especially resistive (in relation with the current intensity), electron transfer kinetics, and diffusion phenomena. Capacity measurements and redox potentials determination should be independent of the sweep rate. 

First dark redox potential, determined with sodium dithionite. 

Although the ratio of reduced to oxidized forms of species j affects its redox potential [Ej = EfH - (RT/qF)ln(reduced))(oxidized)) Eq. 6.9], the actual activities of the two forms are usually not known in vivo. Moreover, the value of the local pH (which can affect h7) is also usually not known. Consequently, midpoint (standard) redox potentials determined at pH 7 are usually compared to predict the direction for spontaneous electron flow in the lamellar membranes of chloroplasts. We will assume that free energy is required to transfer electrons to a compound with a more negative midpoint redox potential, whereas electrons spontaneously flow toward higher midpoint redox potentials. 

Kolling, M., 2000. Comparison of Different Methods for Redox Potential Determination in Natural Waters. In Schuring et al. (Eds.) Redox - Fundamentals, Processes and Applications. Springer, Berlin, Heidelberg etc., pp. 42-54. 

The redox potential determined for both iron sites of Rr is over 200 mV, which is too high for Rr to be involved in electron transfer reactions in the cytoplasm of Desulfovibrio. The much higher redox potential of the Rr Rd-like center in comparison to those exhibited by rubredoxins (around OmV) is intriguing if one considers the similar spectroscopic characteristics of both centers [58]. 

Principle of redox potential determination of transient species... 

The saliva of blood-sucking insects contains a variety of components that counteract blood clotting and vasoconstriction. A nitric oxide binding heme protein, ni-trophorin 1 (NPl), was studied by UV-vis and FTIR spectroelectrochemistry. In the absence of NO, the spectroelectrochemistry of the Fe / process was clear. However, in the presence of NO, the changes were small for the Fe NO and Fe NO forms, and there was a larger than usual error ( 5 mV rather than 1 to 2 mV) on the redox potentials determined from Nemst plots [246]. 

The chemical redox potentials determined the order of the chemical advances that shaped history. On any replicate Earth, gold and silver should be the currencies of trade, the Bronze Age should come before the Iron Age, and magnesium and aluminum should not be found by the early empires. Chemistry determines the order in which metals will be discovered and used. 

A large number of redox potential determinations were carried out on freshly manufactured polymer dispersions using a silver/silver chloride electrode and the results compared with isothiazolin-3-one analyses by HPLC. The conclusions from this work are displayed in Table 15 and confirm the expected finding that CIT/MIT has better stability at positive redox potential values whereas the reverse is generally the case for BIT. 

Desilylative coupling of cinnamyltrimethylsilane results in 3,6-diphenyl-1,5-hexadiene as shown in Scheme 2.60. The cross-coupling reaction of silyl enol ethers and allylic silanes proceeds chemoselectively to give Y,8-unsaturated ketones, in which the oxovanadium(V) oxidatively desilylates the more readily oxidizable organosilicon compound [126], Their redox potentials determine whether they will act as a radical generator or acceptor. These redox potentials can be predicted from calculated ionization potentials. VO(OR)Cl2 is a versatile oxidant, which can induce chemoselective coupling via the oxidative desilylation of a variety of organosilicon compounds under controlled conditions, as shown in Scheme 2.61. 

The reaction with hydrogen is usually less interesting than that with some other oxidant or reductant. The difference in redox potentials determines the change of free energy. To convert one to the other, we use the expression ... 

For the reasons mentioned above, differential titration and redox potential determinations cannot be used to determine the nature of the heme-linked groups. Under such conditions it seems impossible to solve the whole question of the heme-linked groups of catalases by the aid of the methods we have at our immediate disposal. Some amino acid analyses have been carried out, but these cannot yet contribute to our knowledge of the heme-linked groups. However, some information has been obtained from magnetometric observations, from spectrophotometric studies of different catalase compounds with inhibitors, and from activity determinations in solutions of different pH values and varying concentrations of inhibiting anions. 

Berr MJ, Wagner P, Fischbach S, Vaneski A, Schneider J, Susha AS, Rogach AL, Jackel F, Feldmann J (2012) Hole scavenger redox potentials determine quantum efficiency and stability of Pt-decorated CdS nanorods for photocatalytic hydrogen generation. AppI Phys Lett 100 223903... 

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