Oxidation by ferricyanide

A few data exist on the oxidation by ferricyanide. This is simple second-order (in oxidant and neutral hydrazine), and leads to quantitative production of nitrogen in accordance with scheme (71)-(74) with A 4 k and A i. No scrambling occurs during oxidation of N-labelled N2H4 indicating that all N2 is formed via di-imine" Di-imine so prepared is capable of hydrogenating added unsaturated compounds, for example, phenylpropiolic acid gives m-cinnamic acid" " . 

The quaternary [l,2,3]triazolo[4,5-c]pyridinium salt 147 is oxidized by ferricyanide to the triazolopyridin-5-one.169... 

NADH-methemoglobin reductase 826 NADH ubiquinone oxidoreductase 788 oxidation by ferricyanide 780 NADP+ (NADP) 507, 765 - 771, 767s, 779 in catalase 853 isolation of 767... 

The redox activity of Cyt c bound to the galleries of a-ZrP was found to be similar to that of the native protein. Dithionite or ascorbate can reduce Fe(IIII)Cyt c to the ferrous form, which can be oxidized by ferricyanide to the Fe(III) form. Retention of this redox property of Cyt c-a-ZrP is indicated by the absorption spectrum of Cyt c-a-ZrP. Although ascorbate and a-ZrP surface are both negatively charged, the addition of ascorbate to Cyt c-a-ZrP rapidly yields the reduced form of Cyt c (Fig. 49A). The absorption at 550 nm, due to Fe(II) form, grows with time and reaches a maximum value after 20 min. The addition of ferricyanide to Fe(II)Cyt c oxidizes it back to the Fe(III) form and restores the original absorption spectrum. These observations highlight the accessibility of bound protein to external small molecules and these immobilized proteins... 

The ring closure can be achieved stereospecifically, thus allowing the individual isomers of asymmetrically substituted furoxans to be prepared. For example, the two amphi forms (100) and (101) of p-methoxybenzil dioxime are specifically oxidized by ferricyanide to (102) and (103), whereas the syn and anti isomers (104) and (105) give mixtures of the two furoxans. With some oxidants the process is non-stereospecific, either due to a change of mechanism, or as a result of isomerization of the dioxime prior to cyclization. 

Catechol, with its more readily ionized protons (and other o-diphenols), in aqueous alkaline solution forms soluble, colourless anionic species. Stability constants for the 1 1 and 2 1 species have been measured (log X, = 7.5, log K2 = 5.7) and the 3 1 species forms at pH > 11. In 0.3 M NaOH, the latter is readily oxidized by ferricyanide to Mn,u. Some crystalline species have been described, but need further characterization and most seem to be very air sensitive.212,282 Again the interest in these compounds has been directed mainly towards their oxidation to Mn111 and MnIV species. 

The rather small As value at 320 nm for the (Yz -Yz) change is further supported by the double-flash experiment shown in the inset of Fig, 8. As mentioned above, the initial rise portion upon flash excitation consists of absorbance changes due to Yz oxidation andQA reduction. Yz is re-reduced by ferrocyanide in 165 ms and Qa is re-oxidized by ferricyanide in 4 s. At 805 ms after the first flash, a second excitation flash is applied. At this moment, all the Yz would have been completely re-reduced by ferrocyanide but only about half of the Qa re-oxidized by ferricyanide. The second flash should be able to reduce all the Qa that had been re-oxidized by ferricyanide in the dark and re-oxidize a corresponding amount of the reduced Yz. The inset trace shows that the second flash brought about an absorbance increase to approximately the same level as after the first flash. One can therefore conclude that the contribution by Yz to the initial absorbance increase at 320 nm is quite small. The dashed tail indicates the decay path of the absorbance increase is due to that induced by the first flash alone. 

A typical example is the recently purified cssa from the green algae, Kirchneriella obesa (308). It has one heme per 12,000 molecular weight, absorption bands at 553, 522, and 417 nm, an acid isoelectric point, and a rather high standard reduction potential at pH 7 of - -400 mV. Oxidized C663 from K. obesa is easily reduced by ascorbate or dithionite, and the reduced form does not bind CO and is not autoxidized, but can be oxidized by ferricyanide, all being traits familiar from respiratory c. The c-type heme is held to the polypeptide chain by two thioether links. 

The hydroquinone thus formed is immediately oxidized by ferricyanide incorporated in the reaction mixture. 

The flavoprotein can be reduced by NADPH to the fully reduced state (FMNHj, FADH2 ) and is oxidized by ferricyanide to the fully oxidized state (FMN, FAD) . ... 

Thiamin (vitamin Bi) Thiamin in the body is chiefly found in the phosphorylated form thiamin pyrophosphate (TPP) which is a coenzyme. The majority (80%) of thiamin in the blood is found in the erythrocytes and assay of blood thiamin is a more reliable indicator of deficiency than assay of erythrocyte transketolase. The phosphorylated vitamers are enzymically converted to thiamin in samples using diastase following deproteinization. To reach the low picomolar concentrations the thiamin compounds are oxidized by ferricyanide to form thiochromes, which are highly fluorescent. The thiochromes are then separated by reversed-phase HPLC and detected by their emission at 425-450 nm. 

CPE followed by spectrofluorimetry was applied to analyse the concentration of vitamin Bi in samples of urine (Tabrizi 2006). In this method, Triton-XI14 surfactant was used for CPE. The procedure was accomplished by adding an aqueous solution of thiamin, ferricyanide and Triton-X114 in an alkaline medium. The surfactant-rich turbid phase and diluted aqueous phase were attained after centrifugation of the mixture. The surfactant-rich phase was collected and diluted in an ethanol water mixture prior to measurement of the fluorescence excitation and emission intensity. Thiamin was oxidized by ferricyanide under alkaline conditions to form thiochrome, which is a fluorescent species. During the extraction procedure, thiochrome was entrapped in surfactant micelles. Thus, thiamin was separated from the biological matrix after derivatization. The fluorescence intensity responded linearly with the concentration of thiamin under optimized conditions. 

Figure 20 shows the change of the potential shift in the full system upon illumination as a function of the incident light intensity. The maximum potential shift is + 0.2 V. As evidenced by the measurements, the potential shift arising in the system when DNP is added is equal to — 0.2 V and results from the existence at the interface of the anionic form of a weak acid, RO". Therefore, the potential shift in the positive direction by + 0.2 V indicates the disappearance of this shift due to the formation of the protonated form, ROH. Presumably, in the course of the reaction a proton was generated by the reducing agent NADH as it was oxidized by ferricyanide ... 

Some protein groups other than SH are oxidized by ferricyanide (73). This was indicated by the increased quantity of ferricyanide reduced as the concentration of ferricyanide was increased. Since tyrosine and tryptophan, but not histidine, reduce ferricyanide it has been suggested that it is these two amino acids in proteins that are oxidized. This was ven some support by the fact that gelatin which is devoid of tyrosine and tryptophan failed to reduce ferricyanide, while zein which contains tyrosine, but not trsrptophan, reacted rapidly. However, native egg... 

The hydrazine analogues of pyridine imines (see above), oxidized by ferricyanide in the presence of phenols, give the coupling products438 shown... 

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