Oxidation of ferrocyanide

Comparison of Interfacial Density Differences Resulting from the Deposition of Copper, the Cathodic Reduction of Ferricyanide, and the Anodic Oxidation of Ferrocyanide at the Limiting Current Density (7" = 25°C)... 

For forced-convection studies, the cathodic reaction of copper deposition has been largely supplanted by the cathodic reduction of ferricyanide at a nickel or platinum surface. An alkaline-supported equimolar mixture of ferri- and ferrocyanide is normally used. If the anolyte and the catholyte in the electrochemical cell are not separated by a diaphragm, oxidation of ferrocyanide at the anode compensates for cathodic depletion of ferricyanide.3... 

Oxidation of ferrocyanide, although used occasionally, offers no advantages relative to reduction of ferricyanide. Because the potential for oxygen liberation in alkaline solutions is close to the oxidation potential of the ferrocyanide couple, the limiting-current plateaus obtained in this case are quite narrow (El). 

Another mode of SOD prooxidant activity has been proposed by Offer et al. [9]. In 1973, Rotilio et al. [10] showed that SOD can readily oxidize ferrocyanide. Offer et al. [9] found that low SOD concentrations inhibited superoxide-induced oxidation of ferrocyanide, but SOD becomes prooxidative at higher concentrations. As this reaction did not require hydrogen peroxide, it was suggested that the prooxidant effect of enhanced SOD concentrations might be explained by decreasing the steady state of superoxide and the direct oxidation of ferrocyanide by SOD. 

A new development is that electrochemical oxidation of ferrocyanide to ferricyanide can be coupled with AD to give a very efficient electrocatalytic process [37]. Under these conditions, the amount of potassium ferricyanide needed for the reaction becomes catalytic and Eqs. 6D.6 and 7 can be added following Eq. 6D.4. Summation of Eq. 6D.1-6D.4, 6D.6, and 6D.7 gives 6D.8, showing that only water in addition to electricity is needed for the conversion of olefins to asymmetric diols and that hydrogen gas, released at the cathode, is the only byproduct of this process. In practice, sodium ferrocyanide is used in the reaction and the amount of this reagent used in comparison with the potassium ferricyanide method mentioned above has been reduced from 3.0 equiv. to 0.15 equiv. (relative to an equivalent of olefin). 

Potassium ferricyanide 1 can be produced by the electrolytic oxidation of ferrocyanide. 

The standard equilibrium potential at the anode related to reaction (XXIV-7 is 7c° = 0.356 V. As oxygen is evolved owing to overvoltage from neutral solutions as late as the potential is about 1.2 V and from alkaline solution at about 0.8 V, the oxidation of ferrocyanide to ferricyanide can proceed with a 100 per... 

It will be seen that even the total ourrent efficiency at the oomplete oxidation of ferrocyanide increases inversely in proportion to the current density. 

Results with Theory for Voltage and Controlled Potential Scanning, Controlled Potential Electrolysis and Chronopotentiometric Techniques. Oxidation of Ferrocyanide and o-Dianisidin at Boron Carbide Electrode. Anal. Chim. Acta 25, 482 (1961). 

Several papers compare the properties of sulfobetaine (meth)acrylic polymers. NMR spectra and solution properties of 23a and 23b [59,60] are correlated with data from the corresponding polycarbobetaines [26]. The photophysical and solution properties of pyrene-labeled 23c were studied in terms of fluorescence emission. Addition of surfactants induces the formation of mixed micelles in aqueous solution [61]. Excluded volume effects of the unlabeled polymer were measured by light scattering [62], its adsorption on silica was studied by adsorbance measurement and ellipsometry [62,63], and the electrostimulated shift of the precipitation temperature was followed at various electric held intensities [64]. Polysulfobetaines may accelerate interionic reactions, e.g., oxidation of ferrocyanide by persulfate [65]. The thermal and dielectric properties of polysulfobetaines 23d were investigated. The flexible lateral chain of the polymers decreased Tg, for which a linear relationship with the number of C atoms was shown [66,67]. 

Complex Cyanides of Iron. Cyanide ion added to a solution of ferrous or ferric ion forms precipitates, which dissolve in excess cyanide to produce the complexes. Yellow crystals of potassium ferrocyanide, K4Fe(CN)(./3H20, are made by heating organic material, such as dried blood, with iron filings and potassium carbonate. The mass produced by the heating is extracted with warm water, and the crystals are made by evaporation of the solution. Potassium ferricyanide, K3Fe(CN), is made as red crystals by oxidation of ferrocyanide. 

Exainple 2. To what extent would the oxidation of ferrocyanide ion by an equivalent amount of ferric ion proceed (Neglect the effect of the precipitation of Prussian blue.)... 

In contrast with the three halide ions, the specific adsorption is certainly involved in the photoanodic oxidation of ferrocyanide, Fe(CN)g , which has been observed to be strongly attached to the Ti02 surface ° . However, this case does not permit any definitive conclusion with regard to the mechanism of the Fe(CN)6 photo-oxidation, as the actual high current efficiency for this reaction is, in fact, expected from the position of the standard potential of the Fe(CN) /Fe(CN)6 couple (0.36 V). 

In another study, the application of a weak ultrasonic field (0.3 W/cm2 25 kHz) during the electrochemical oxidation of ferrocyanide ions on Pb anodes at 20 °C and at a fixed cd (2.5-15 mA/cm2) markedly increased the reaction rate and the current, while the polarization was substantially decreased [146a], The effects, which were most pronounced at the beginning of the electrolysis and at low current densities, were attributed to a considerable thinning of the diffusion layer on the anode in the presence of ultrasound. 

The oxidized form of superoxide reductase formed in this reaction is reduced back by rubredoxin, dependent ultimately on reduced pyridine nucleotides via intermediate electron carriers [65]. The reaction of SOR with superoxide is also very fast, the reaction rate constant being of an order of 10 M s. It has been demonstrated that CuZnSOD can also function as superoxide reductase reducing superoxide at the expense of oxidation of ferrocyanide, or as superoxide oxidase, oxidizing superoxide at the expense of reducing ferricyanide [66]. Both ferri- and ferrocyanide are unphysiological substrates but the enzyme can also act as superoxide reductase with nitroxyl anion oxidizing it to nitric oxide [67]. 

In most amperometric cytochrome b2 electrodes the reaction is followed by anodic oxidation of ferrocyanide at a potential of +0.25 V or above. The first of such sensors was assembled by Williams et al. (1970), who immobilized the enzyme (from baker s yeast) physically at the tip of a platinum electrode within a nylon net of 0.15 mm thickness. The large layer thickness resulted in a response time of 3-10 min. Owing to the low specific enzyme activity used, the sensor was kinetically controlled. Therefore the linear measuring range extended only up to 0.1 Km-A similar sensor has been applied by Durliat et al. (1979) to continuous lactate analysis. The enzyme was contained in a reaction chamber of 1 pi volume in front of the electrode. This principle has also been employed in the first commercial lactate analyzer using an enzyme electrode (Roche LA 640, see Section 5.2.3.3X With a sensor stability of 30 days and a C V below 5%, 20-30 samples/h can be processed with this device. 

Laccase also catalyzes the 02-dependent oxidation of ascorbic acid, ferrocyanide, iodide, and uric acid. These reactions have been utilized to eliminate electrochemical interferences in amperometric hydrogen peroxide detection at membrane-covered enzyme electrodes (Wollen-berger et al., 1986). The capacity of the laccase membrane to oxidize ferrocyanide has been characterized by anodic oxidation of ferrocyanide at +0.4 V (Fig. 62). When a fresh enzyme membrane is used, a current signal appears only at substrate concentrations above 5 mmolA the current increases linearly with increasing concentration. This threshold concentration decreases with increasing membrane age until the remaining enzyme activity is too low for complete substrate oxidation. 

Aromatic amines are activators of horseradish peroxidase. Kulys and Vidziunaite (1983) adsorbed HRP together with GOD on a carbon electrode and crosslinked the enzymes with glutaraldehyde to assemble a sensor for aromatic amines. H2O2 is produced in the presence of glucose, acting as cosubstrate in the HRP-catalyzed oxidation of ferrocyanide. The ferricyanide formed was reduced back to ferrocyanide at an electrode potential of +10 mV vs SCE, the current being limited by the... 

An immunostirrer for the determination of creatine kinase (CK) isoenyzme MB based on alkylamine glass-immobilized anti-IgG antibody has been proposed by Yuan et al. (1981). By binding of creatine kinase to antibody, only the CK-M subunit but not the CK-B subunit is inhibited. The remaining CK-B activity was measured by electrochemical oxidation of ferrocyanide formed in the following coupled reaction ... 

FIG. 28 Dissolution rate image of the (010) surface of potassium ferrocyanide trihydrate recorded in the same area of the crystal as the topographic image shown in Figure 27. The tip was held at a potential to establish the diffusion-controlled oxidation of ferrocyanide and scanned at a speed of 50 gm s... 

These observations are readily explained in terms of reactions of the aquo salts and it would appear that the usually accepted rapid oxidation of ferrocyanide by hydrogen peroxide is misleading. The fact that this is a very slow reaction means that although the ferricyanide reduction is fairly rapid there is no possibility of appreciable catalytic decomposition of the peroxide by the compensating reactions mechanism. 

Reactions involving the ferrocyanide/ferricyanide couple are of current interest. The oxidation of ferrocyanide ion by OH radicals has been studied in detail by both pulse radiolysis (5,34) and steady-state methods (23, 25, 30, 35). The reaction, which involves electron transfer to OH can be followed conveniently by directly observing the buildup of the ferricyanide ion... 

Kinetic studies of reactions of horseradish peroxidase (HRP) using stopped-floiv and temperature-jump techniques are summarized. The reactions were studied intensively as a function of pH to establish the presence or absence of pH-dependences in the reaction rates. Minimum mechanisms are presented which cannot he proven to be correct. However, simpler mechanisms will not fit the data within experimental error. The reactions which have been studied are fluoride and cyanide binding by (dissociation from) HRP and the oxidation of ferrocyanide to ferricyanide by HRP Compounds I and II. From the pH profiles of the reaction rates, the pK values of acid groups which influence the rates are deduced. Trends in pK values can be explained qualitatively in terms of electrostatic effects. 

These studies led us to begin kinetic investigations of the enzymatic reaction of HRP the first of these is the oxidation of ferrocyanide. 

---