Redox potential definition

In general, no matter what the route, certain characteristics will predispose a material to have local effects (and, by definition, if not present, tend to limit the possibility of local effects). These factors include pH, redox potential, high molar concentration, and the low flexibility and sharp edges of certain solids. These characteristics will increase the potential for irritation by any route and, subsequent... 

In chloroform solvent, the platinum dithiolene complexes Pt(S2C2R2)2 are photooxidized between 300 and 350 nm, providing the complexes used are those for which the R groups result in redox potentials in the 0.1 to 0.5 V (vs SCE) range. The results are consistent with the reaction shown in equation (534).1849 Further work on this system identifies the fact that several excited states are probably photoreactive in this process,1850 and no definitive answer on the excited state reactivities is yet available. Very recently, however, highly structured solid-state emissions have been observed for Pt S2C2(CN)2 P(OR)3 2, and this data may help resolve some of these questions.1851... 

As the data for the above two complexes indicate, there exists a definite correlation of the redox potentials with substituent inductive effects. This is further illustrated in a plot of the potentials for all the Mn(III)(R2Dtc)3/ Mn(IV)(R2Dtc)3 couples versus the potentials of the Mn(II)(R2Dtc)3/ Mn(IIlXR2 Dtc)3 couples. The plot is very nearly linear, with a slope A/(recl/ AZTox = 1.1, and clearly indicates that substituents that stabilize Mn(IV) destabilize Mn(II) and vice versa. 

In this connection, it is essential to discuss the reduction potentials E of oxygen derived reactive species and of several other intermediates that are important in AOPs (Tab. 6-1). For a viable definition of the term reduction potential , which should be used instead of the obsolete oxidation potential or of the ambiguous redox potential the reader is referred to Wardman s (1989) comprehensive review and data collection. The reduction potentials E of couples M/M refer to reactions described by Eq. 6-1 or Eq. 6-2. 

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. 

However, there is no definite correlation between the polymerization rate and the redox potential, partly because a higher concentration of the radical species may lead to a higher probability of bimolecu-lar termination and a higher concentration of persistent radical species.54-261 Another possibility of side reaction is due to the reduction of the radical into an anion with metal complexes with extremely low redox potential. An appropriate range for the redox potential of the metal catalysts was suggested between —0.3 and +0.6 V (versus NHE) for living radical polymerization.54... 

The tendency for a specific substance to lose or gain electrons is called its redox or reduction potential. The redox potential of a conjugate redox pair is measured in an electrochemical cell against a reference standard, usually a standard hydrogen electrode. The redox potential of the standard hydrogen electrode is 0.0 V at 1 atm, by definition. Substances with a more negative... 

Acenes, definition in terms of graphite translational periodicity axes, 369 Aggregation, effect on redox potentials, 16-21... 

Electrochemical studies indicate that biological cubane-type [3Fe-4S] clusters have accessible l-f, 0, and 2— redox states. However, only the [3Fe-4S]+ ° couple appears to be used to mediate biological electron transport and redox potentials for this couple span a range from -1-90 to —460 mV (Figure 4). The midpoint potential for the two-electron [3Fe-4S]° couple is —700 mV at pH 7, and is strongly pH dependent with reduction to the [3Fe-4S] state involving the net uptake of three protons. Protonation of the [3Fe-4S]° clusters in some 7Fe Fds has also been observed with a pKa 7.5. Although the protonation sites of reduced clusters have yet to be definitively established, the three /X2 -S atoms are the most likely candidates. ... 

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