Ferrocyanide peroxide

Subsequent work (84) confirmed these ideas. The addition of oxidized aquo salt to ferrocyanide-peroxide mixtures has the same effect as the same concentration of the reduced form, as it should. Further, addition of cyanide, nitrite, or nitrosobenzene to both illuminated ferrocyanide solutions and to ferrocyanide containing aquopentacyanoferrate, suppresses the catalytic decomposition. This effect is due to the reversal of the equilibrium (I) by a higher cyanide concentration, and to the removal of aquo salt by nitrite and nitrosobenzene to form the complex ions [Fe(CN)5N02]"" and [Fe(CN)6ONPh],/, respectively, reactions which are known to occur readily. It is also suggested (85) that even the catalytic decomposition by ferrocyanide in the dark is due to a small amount of aquopentacyanoferrite in purely thermal (as opposed to photochemical) equilibrium with ferrocyanide according to (I). 

A wide variety of enzymes have been used in conjunction with electrochemical techniques. The only requirement is that an electroactive product is formed during the reaction, either from the substrate or as a cofactor (i.e. NADH). In most cases, the electroactive products detected have been oxygen, hydrogen peroxide, NADH, or ferri/ferrocyanide. Some workers have used the dye intermediates used in classical colorimetric methods because these dyes are typically also electroactive. Although an electroactive product must be formed, it does not necessarily have to arise directly from the enzyme reaction of interest. Several cases of coupling enzyme reactions to produce an electroactive product have been described. The ability to use several coupled enzyme reactions extends the possible use of electrochemical techniques to essentially any enzyme system. 

Other solutions to dealing with interferences in the detection of H O have included the use of a copperfll) diethyldithiocarbamate precolumn to oxidize the sample before it reaches the immobilized enzyme, as well as the use of a palladium/gold sputtered electrode which catalyzes the oxidation of hydrogen peroxide In addition, peroxidase has been used to catalyze the reaction between hydrogen peroxide and iodide ferrocyanide and organo-fluorine compounds Am-... 

The electrochemical rate constants for hydrogen peroxide reduction have been found to be dependent on the amount of Prussian blue deposited, confirming that H202 penetrates the films, and the inner layers of the polycrystal take part in the catalysis. For 4-6 nmol cm 2 of Prussian blue the electrochemical rate constant exceeds 0.01cm s-1 [12], which corresponds to the bi-molecular rate constant of kcat = 3 X 103 L mol 1s 1 [114], The rate constant of hydrogen peroxide reduction by ferrocyanide catalyzed by enzyme peroxidase was 2 X 104 L mol 1 s 1 [116]. Thus, the activity of the natural enzyme peroxidase is of a similar order of magnitude as the catalytic activity of our Prussian blue-based electrocatalyst. Due to the high catalytic activity and selectivity, which are comparable with biocatalysis, we were able to denote the specially deposited Prussian blue as an artificial peroxidase [114, 117]. 

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. 

FerrocenecarboxyUc acid, lipid hydroperoxide determination, 686-7 Ferrocenol, bis(trimethylsilyl) peroxide reactions, 798-800 Ferrocenol esters, preparation, 800 Ferrocyanide, performic acid determination, 699... 

Ferrocyanide-hydrogen peroxide Ammonium chloride (0.5 g) is added to a 0.1% potassium ferro-cyanide solution in 0.2% hydrochloric acid, and the resulting solution is sprayed on the plate, which is then dried (100°C). The chromatogram is further sprayed with 30% hydrogen peroxide, heated (150°C, 30 min), and sprayed with 10% potassium carbonate to yield yellow/red spots. 

Sodium aquo ferrocyanide,2 Na3Fe(CN)s.H20, results when sodium nitroprusside reacts with hydroxylamine, etc., or when the salt is oxidised by potassium hypobromite or hydrogen peroxide. 

Altschul et al. (1, 2) originally discovered that cytochrome c peroxidase reacts with a stoichiometric amount of hydroperoxide to form a red peroxide compound, which will be referred to hereafter as Compound ES. It has a distinct absorption spectrum, as shown in Fig. 2. The formation of Compound ES from the enzyme and hydroperoxides is very rapid (fci > 10 10 sec"M. No intermediate, which precedes Compound ES, has been thus far detected. In the absence of reductants, or S2, Compound ES is highly stable. The rate constant of its spontaneous decay is of the order of 10 sec 22). The primary peroxide compound (Compound I) of horseradish peroxidase decays much faster at a rate of 10 sec (6). This unusual stability of Compound ES allows one to determine various physical and chemical parameters quantitatively and reliably. Titrations of Compound ES with reductants such as ferrocjHio-chrome c Iff, 20) and ferrocyanide 18, 34) have established that Compound ES is two oxidizing equivalents above the original ferric nnzyme. The absorption spectrum of Compound ES is essentially identical to that of Compound II of horseradish peroxidase which contains one oxidizing equivalent per mole in the form of Fe(IV). In addition, EPR examinations have revealed that Compound ES contains a stable free radical, the spin concentration of which is approximately one equivalent per mole (Fig. 3). Therefore, it is reasonable to conclude that two oxidiz-... 

Potassimn ethyl xanthate , see Potassimn O-ethyl dithiocarbonate Potassium ethynediolate, see Potassimn acety lene-1,2-dioxide, 0990 Potassimn ferricyanide , see Potassium hexacyanoferrate(lll), 2063 Potassimn ferrocyanide , see Potassimn hexacyanoferrate(ll), 2064 Potassium fluoride hydrogen peroxidate, 4300... 

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. 

R6. Rotilio, G., Morpurgo, L., Calabrese, L., and Mondovi, B On the mechanism of superoxide dismutase reaction of the bovine enzyme with hydrogen peroxide and ferrocyanide. Biochim. Biophys. Acta 302, 229-235 (1973). 

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