Reduction rate constants

Taking into account the relationship between the oxidation and reduction rate constants (i.e., kox = kleden with tj = F(E — Ef ) /RT see Sect. 1.7) whatever the kinetic model considered, Eq. (3.4) becomes... 

When the Marcus-Hush treatment is considered, the reduction rate constant is not predicted to increase continuously with the applied potential, but rather a maximum value exists. A simple expression for this value of the rate constant was given in reference [29] ... 

FMN reduction rate constant (sec" ) Heme reduction rate constant (see" ) ... 

Note Data presented as M s"i, 10.0 C, reductate. Rate constants were obtained by plotting the observed rate constant, /cobs, against substrate concentration. /C2610 values were taken from the linear part of these plots, i.e., at low nonsaturating concentrations. 

Oxalate is a tight-binding inhibitor of wild-type LMO. The logarithms of the reduction rate constants for the wild-type and mutant enzymes were linearly correlated with the logarithms of the dissociation constants of oxalate, with a unit slope. Thus, enzymes that bound oxalate tightly also reduced the flavin quickly. This was taken to show that oxalate resembles the carbanion intermediate in the reductive half-reaction. However, oxalate could instead mimic a lactate alkoxide, an intermediate predicted in the hydride-transfer mechanism. ... 

Aminyl radicals are less reactive than carbon radicals, which in turn are less reactive than alkoxy radicals. For dialkylaminyl radicals, the reduction rate constant with tributyltin hydride 5 x 10 M s ) [14] is about ten times lower than for primary alkyl radicals [15] and a thousand times lower than for alkoxy radicals [16]. 

Reduction Rate Constants and Activities for Oj Dismutation of Human SOD and Some of Its Mutants... 

It can be seen that there is a significant decrease in the temperature required for combustion to occur with the hydrophobic catalysts. A detailed kinetic study of the combustion process indicated that the surface reduction rate constant, ki, in the Mars-van Krevelan mechanism increases with temperature faster than the surface re-oxidation rate constant, ks. That is, the surface concentration of adsorbed oxygen (O2) is higher than that of (CnHn-O) at higher temperatures. This occurs in spite of the fact that ki is more sensitive to variations in temperature than ka. The ratio ki/ks for a Pt/hydrophobic catalyst in the combustion of benzene, toluene and xylene at 90-130°C was calculated to be in the range 466-3880, which can be compared to 24-2490 for a conventional hydrophilic catalyst (Pt-Ni/AhOa) in the oxidation of benzene and n-hexane at 140-221°C [34]. 

Pulse radiolysis has been used to collect many data on the reduction rate constants of multivalent ions M +, on the transient absorption spectra of unstable valences M( -i)+, and sometimes on the rate constants of their disproportionation. -" All transition metal ions are reducible by solvated electrons into With long... 

With such laws, when E increases, the oxidation rate constant increases exponentially, whereas the reduction rate constants tend to 0 and vice-versa when E decreases. This behavior corresponds to the variation of the current density with respect to the potential E, such as ... 

TABLE 7.7 Normalized Reduction Rate Constants for 3-Chloronitrobenzene ... 

FIGURE 10.21 First-order Fe(III) reduction rate constants and initial cumulative carbon dioxide and methane production in a wetland soil amended with different amounts of labile organic matter. (Redrawn from Roden and Wetzel, 2002.)... 

Hammett a constants also have been successfully correlated with reduction rate constants. For example, the reduction rate constants of a series of 4-substituted nitrobenzenes in anaerobic sediment-water systems and the Hammett a constants exhibited a positive correlation (Delgado and Wolfe, 1992). The slopes of the linear-free energy plots for a river sediment, pond sediment, and aquifer material were similar, suggesting that reduction was occurring through the same mechanism in each of these systems. 

According to the asymmetric version of the MH model the expressions for the oxidation and reduction rate constants are given by... 

Consequently, k° represents the oxidation and reduction rate constant value at the standard potential E°. 

The dependence of the reduction rate constant on bulk ascorbate concentration was found to be logarithmic in the range of investigated ascorbate concentration (0.005-2 mM) (Figure 10.9). 

Figure 7.13 Arrhenius plots of 02-reduction rate constant vs the reciprocal of temperature at two pH levels. Reprinted...

Xanthine dehydrogenase, XDH [E.C. 1.1.1.204], and the closely related isoenzyme xanthine oxidoreductase, XOR [E.C. 1.1.3.22], are molybdopterin oxidoreductive enzymes. The enzymes catalyze oxidation of a C-substrate atom by two electrons. In human body the enzymes convert the nucleic acid metabolite hypoxanthine into xanthine and xanthine into uric acid. Fig. 10.6 The reductive rate constant of XDH,... 

---