Ferricyanide reduction kinetics

Fig. 3. (a) Typical galvanostatic limiting-current curve for copper deposition at a copper disk in acidified CuS04 solution. The circles indicate the experimental curve. The solid curves were calculated using kinetic parameters as indicated, (b) Typical galvanostatic limiting current curve for ferricyanide reduction at a nickel electrode in equimolar ferri ferrocyanide solution with excess NaOH. [From Selman (S8).]... 

The reaction may be characterized by slow surface kinetics, leading to shortening of the plateau. Compare, for example, ferricyanide reduction and copper deposition at a rotating disk (shown in Fig. 3a and b). 

Steady-state kinetic experiments indicate that the rate of ferricyanide reduction by the enzyme is essentially independent of ferricyanide concentration in the range 0.2-3.0 mM. This is another reason... 

Ertl P, Unterladstaetter B, Bayer K, Mikkelsen SR (2000) Ferricyanide reduction by escherichia coli kinetics, mechanism, and application to the optimization of recombinant fermentations. Anal Chem 72(20) 4949-4956. doi 10.1021/ac000358d... 

Similar kinetics are reported for the reduction of several quinones by ferro-cyanide, but the rate coefficients, k are affected by added ferricyanide , viz. 

The kinetics of oxidation and reduction of [4Fe-4S] proteins by transition metal complexes and by other electron-transfer proteins have been studied. These reactions do not correlate with their redox potentials.782 The charge on the cluster is distributed on the surface of HiPIP through the hydrogen bond network, and so affects the electrostatic interaction between protein and redox agents such as ferricyanide, Co111 and Mnin complexes.782 783 In some cases, limiting kinetics were observed, showing the presence of association prior to electron transfer.783... 

As ice crystals grow in the freezing system, the solutes are concentrated. In addition to increased ionic strength effects, the rates of some chemical reactions—particularly second order reactions—may be accelerated by freezing through this freeze-concentration effect. Examples include reduction of potassium ferricyanide by potassium cyanide (2), oxidation of ascorbic acid (3), and polypeptide synthesis (4). Kinetics of reactions in frozen systems has been reviewed by Pincock and Kiovsky (5). 

Reoxidation of the enzyme-pyridine nucleotide complex by ferricyanide takes place in two one-electron steps. The rate of the first step is too rapid to measure and the rate of the second step can be measured only if NADPH is used to prereduce the enzyme. In this case the complex with NADP+ is virtually nonexistent and the changes measured are those of uncomplexed enzyme. These observations demonstrate that a species is formed within the mixing time and that it decays rapidly (78 sec", 0°). Repetition at 10 nm intervals generates the spectrum of the intermediate which is that of the neutral semiquinone. The fact that both steps in the reoxidation of the enzyme-pyridine nucleotide complexes (i.e., when NADH is the reductant) are complete in less than 2 msec demonstrates that they meet the kinetic requirements of an intermediate, rapid formation and reoxidation 3S5). 

The physiological pathway of electron transfer in flavocytochrome is from bound lactate to FMN, then FMN to 52-heme, and finally 52-heme to cytochrome c (Fig. 9) (2,11, 80,102). The first step, oxidation of L-lactate to pyruvate with concomitant electron transfer to FMN, is the slowest step in the enzyme turnover (103). With the enzyme from S. cerevisiae, a steady-state kinetic isotope effect (with ferricyanide as electron acceptor) of around 5 was obtained for the oxidation of dl-lactate deuterated at the C position, consistent with the major ratedetermining step being cleavage of the C -H bond (103). Flavocytochrome 52 reduction by [2- H]lactate measured by stopped-flow spectrophotometry resulted in isotope effects of 8 and 6 for flavin and heme reduction, respectively, indicating that C -H bond cleavage is not totally rate limiting (104). 

Ferricyanide is the most commonly used electron acceptor in steady-state kinetic experiments on flavocytochrome 62. How is ferricyanide reduced by the enzyme Ogura and Nakamura suggested that ferricyanide could accept electrons only from the 62 heme (79). This is clearly incorrect, because dehemoflavocytochrome 62 and the isolated flavode-hydrogenase domain can still function as ferricyanide reductases, though at somewhat lower efficiency 51, 126). These results imply that ferricyanide can accept electrons from both flavohydroquinone and flavosemiquinone as well as heme. In heme-free cleaved enzyme from S. cerevisiae it was calculated that ferricyanide was reduced around 20 times faster by flavosemiquinone than by flavohydroquinone 126). This would mean that in the holoenzyme, reduction of ferricyanide would occur rapidly from heme and flavosemiquinone. The fact that ferricyanide is reduced by both 62 heme and flavosemiquinone, and that cytochrome c is reduced only by 62 heme, might be an explanation for the observation that specific activities of the enzyme determined with cytochrome c are usually somewhat lower than those determined with ferricyanide. 

Many redox reactions by colloidal nanoparticles have been reported. Three of the most-studied reactions are (1) the catalyzed electron transfer between ferricyanide and thiosulfate [8,19-21], (2) the catalytic reduction of fluorescent dyes by sodium borohydride [22, 23], and (3) the catalytic reduction of organic compounds (e.g., nitro-aryls [9] and alcohols [24]). These reactions have been studied extensively because they are easy to follow spectroscopically allowing for straightforward measurement of reaction kinetics. The third set of reactions has enormous industrial significance, where nitro compounds are reduced to their less toxic nitrate or amine counterparts [25, 26] and the electrooxidation of methanol is utilized for methanol fuel cells [27, 28]. 

X 10 M s and was 3.1 x 10 M s" at 25°C, pH 7.0 and ionic strength of 1.0 . Kinetic data was interpreted in terms of a mechanism of electron transfer from chromium(II) involving attack of Cr(II) adjacent to the Fe(III) center Analysis of the one-to-one chromium(III) cytochrome c complex revealed that the chromium(III) cross-linked two peptide fragments located in the heme.crevice by binding to tyrosine 67 and asparagine 52 The chromium(III) bound to reduced cytochrome c did not affect the ability of the protein to be reoxidized with ferricyanide and then to be reduced with dithionite . The chromium complex was oxidized by cytochrome oxidase at the same rate as the untreated ferrocytochrome c, however, the rate of reduction of the chromium complex by bovine heart submitochondrial particles was slower than that of untreated ferricytochrome c Thus, the binding of chromium(III) to cytochrome c appears to selectively inhibit its function in certain electron transfer reactions. 

Nitroxides have been used to study the membranes of macrophages and also to investigate some of the oxidative intermediates that are produced by macrophages as part of their mechanism of cell killing. As in other cell lines, the reduction of lipophilic nitroxides, which spontaneously localise in membranes, is not preceded by active internalisation and cytoplasmic reduction and does not occur by penetration of external ascorbic acid into the lipid bilayer. The reduction is enzymatic and can be described by first-order kinetics it can be reversed by potassium ferricyanide, decreased by disulphides, and increased by NO2 (Rowlands et al. 1978). 

The kinetics of formation of nitrosyl complexes of iron(n) from the reaction between ferric anide and nitric and nitrous acid in strongly acidic solution have been reported. These reactions involve reduction of iron(m) to iron(n) and oxidation of cyanide ion to cyanate ion. The ferricyanide is attacked by NOj which is formed from the following rapid equilibria ... 

There has been considerable recent interest in the reductions of [Fe(CN)6]. The electron exchange with A -propyl-l,4-dihydronicotinamide is catalyzed by alkali metal ions. The increase in reaction rate is attributed to the polarizability of M and the observed linear free energy relationship is discussed. An outer-sphere mechanism is postulated in the oxidation of phenothiazines. A free radical mechanism involving the alcohol anion is invoked in the reaction of 1-and 2-propanol in aqueous alkaline media, the kinetic order being unity for [Fe(CN)6], OH, and alcohol concentrations. Catalysis by metal ions has also been observed in the presence of copper(II) and ruthenium(III) complexes. In the oxidation of a-hydroxypropionic acid in alkaline media,a Cu(II)-ligand complex is formed which is oxidized slowly to a copper(III) species. Alkaline ferricyanide oxidizes butanol, the process being catalyzed by chlororuthenium complexes.The rate law is consistent with oxidation of the alcohol by the Ru(III) followed by reoxidation of the catalyst by [Fe(CN)6]. The rate law is of the form ... 

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