Ferrocyanide/ferricyanide couple

Figure 8. U, values for the (lll)-face of n-GaP (dark) at various concentrations of the ferricyanide/ferrocyanide couple (equal concentrations) (9) 0M (O) 0.005M (A) 0.05M (A) 0.4M E(Ox/R) redox potential of the redox couple determined by the cyclic voltammetry (ij/) the Us for a p-GaP in the absence of...

Fig. 2 Cyclic voltammograms of the heterogeneous reduction of tetracyanoquinodimethane (TCNQ) by the ferricyanide/ferrocyanide couple across the water DCE interface at various scan rates (a). The composition of the electrochemical cell is as in Fig. 1 but with a ratio 0.01 /0.4 M Fe(CN)6 /Fe(CN)6 and 6 lO- M TCNQ in DCE. Absorption spectra obtained in total internal reflection from the DCE phase as the potential is swept from 0.190 to 0.260 V, with a difference 40 mV between each spectrum (b). The spectra show the main features of the radical TCNQ as the potential is swept toward the reduction potential. (Fig. 2a was reprinted from Ref [25] with permission from Royal Society of Chemistry. Fig. 2b was reprinted from Ref [26] with permission from Elsevier Science.)...

A way to reduce interferences by cooxi-dizable sample constituents is by keeping the applied electrode potential as low as possible. Therefore, a reaction partner is chosen to be electrochemically indicated that is converted at low potential. For this purpose, the natural electron acceptors of many oxidoreductases have been replaced by redox-active dyes or other reversible electron mediators. Among them are the ferricyanide/ferrocyanide couple, V-methylphenazinium sulfate, fer-rocenes, and benzoquinone. With these mediators an electrode potential around -1-200 mV can be applied, which decreases... 

A commonly used mediator is the ferricyanide/ferrocyanide couple, and Equations (10.9) and (10.10) show the reaction sequence involved ... 

The redox potential of DPN and TPN is —0.32 v. (62) as contrasted to the -f 0.43 V. (76) of the ferricyanide-ferrocyanide couple. This low potential makes the pyridine nucleotides unfavorable Hill... 

Noftle RE, Fletcher D (1990) An interpretation of the formal potential for the ferricyanide/ ferrocyanide couple as a function of solvent composition. J Electroanal Chem Interfacial Electrochem 293 273-277... 

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). 

The Surface Potential arising from the Interaction between the Surface "States" and the Redox Couples in the Solution. When the ferricyanide/ferrocyanide redox couple is present in a 0.1 N NaOH solution, the dark cathodic current of the n-GaP (111)-face sets out at —1.1 V (SCE), showing that an electron transfer occurs... 

The energy levels in the solution are kept constant, and the applied voltage shifts the bands in the oxide and the silicon. The Gaussian curves in Figure 4b represent the ferrocyanide/ferricyanide redox couple with an excess of ferrocyanide. E° is the standard redox potential of iron cyanide. With this, one can construct (a) to represent conditions with an accumulation layers, (b) with flatbands, where for illustration, we assume no charge in interface states, and (c) with an inversion or deep depletion layer (high anodic... 

It is, however, to be pointed out that this simplified picture constitutes at the utmost a rough approximation to the real situation. In fact, a close examination of reorganization energies, derived from different series of experimental data shows large differences between X values of various ions and even between those concerning the same ionic species. Thus, for instance, the values of X mentioned in the literature for the ferricyanide/ferrocyanide redox couple vary from 0.4 to about 1.2... 

A number of assumptions must be made in such calculations, and Hagan and Coury [34] studying the ferrocyanide/ferricyanide redox couple in aqueous KC1 at a 1 mm radius platinum disk arrived at a figure of 160,000 rpm. This corresponds to a very fast rotation that would be situated in the turbulent flow regime at a conventional rotating disk, and suggests that ultrasound can achieve limiting-current conditions beyond those attainable in practice by rotation. These workers... 

Cyclic voltammograms of pseudocapacitance for ferricyanide and ferrocyanide couple free in solution (solid line), compared to ferrocyanide bound to a collector with PVP (dashed Hne). (Source Conway, B. E., V. Birss, and J. Wojtowicz. 1997. Journal of Power Sources, 66, 1-14. With permission.)... 

Calcium Ion Sensor. Cyclic voltammograms (CV) of ferrocyanide/ferricyanide redox couple with the modified electrode were measured. The peak currents due to the reversible electrode reaction of a Fe(CN) /Fe(CN) system on a bare Pt electrode were almost completely suppressed by the coating witti the polyvinyl-polypeptide block copolymer. This indicates that the electrode was covered with the hydrophobic polymer and was insulated from redox active species. 

Cyclic voltammograms of ferrocyanide/ferricyanide redox couple with the bare and the modified electrodes are shown in Figure 8. The peak currents due to the reversible electrode reaction of a Fe(CN)5 /Fe(CN>5 system on the bare Au electrode were significantly suppressed by the treatment with the disulfide-modified DNA. In contrast, the treatment with unmodified DNA made no suppression, and that with 2-hydroxyethyl disulfide (HEDS) did only a slight as seen in Figure 8. These results indicate that the surface-anchored DNA blocks the electrochemical reaction of Fe(CN) with the underlying Au electrode, due to the electrostatic repulsion between the polyanionic DNA and the anionic redox couple ions. 

Fig. 6.12 Temperature-pulse voltammograms for reversible couples where the temperature coefficients of potential differ in sign at a platinum wire electrode 25 pm heated with 0.6 W. From left ferricyanide/ferrocyanide 5 mM each in KCl 0.1 M centre-, ferricyanide 2 mM in KCl 0.1 M right-, ferrocene 2 mM in acetonitrile/NBu4PF6 0.1 M. Reference electrodes left and centre bare cold platinum wire right. Ag/AgCl pseudo-reference electrode. The coefficient AEyJdT for ferricyanide/ferrocyanide is -1.6 mV/K, for ferrocene -1-0.8 mV/K...

Pharr, C. M. and Griffiths, P. R. 1997. Infrared spectroelectrochemical analysis of adsorbed hexacya-noferrate species formed during potential cychng in the ferrocyanide/ferricyanide redox couple. Anal. Chem. 69 4673 679. 

Similar to the study on R. sphaeroides, SECM is well suited to measure transport and investigate transport pathways in E. coli. To do so, a combination of hydrophilic and hydrophobic redox species may be used to shuttle the electrons between the SECM tip electrode noninvasively held in solution and the redox centers outside and inside E. coli (Figure 12.6). At present, the studies have often focused on the use of the ferricyanide and ferrocyanide couple. ... 

The redox potentials were determined by a chemical titration of the reaction center in tris-LDAO buffer at pH 7.8 with a potassium ferricyanide/ferrocyanide redox couple. The state of oxidation of the special pair was monitored by optical absorption spectroscopy. At most 70% reversibility to the original reduced state of the special pair was achieved with potassium ferrocyanide. At that point the solutions were so dilute that the concentration of the special pair could not be measured with sufficient accuracy. 

A typical outer-sphere charge-transfer reaction is the ferricyanide-ferrocyanide redox couple... 

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). 

Owing to the high charge of the anions, the effect of ionic strength is also large (E° = 0.46 V for 0.1 M solutions of both potassium ferrocyanide and ferricyanide), and the potential shift is in a direction opposite that observed for the aquo Fe(III)-Fe(II) couple because the more highly charged species is the reductant rather than the oxidant. 

In electroanalysis, electrodes of millimeter dimensions are termed millielec-trodes, while the more recently developed very small area electrodes of micron dimensions are termed microelectrodes there are differences in properties beyond simply the change of dimension. Thus in millielectrode-scale experiments the enhancement of the diffusion-limited current plateau has been observed by a number of other workers—for example, in the reduction of methylviologen in aqueous acetonitrile [32], in the oxidation of bis(cyclopentadienyl) molybdenum dichloride in acetonitrile [33], as well as in several other studies on the aqueous ferrocyanide/ferricyanide couple using wire or disc millielectrodes to study diffu-sional phenomena [34—36], Typical values of the diffusion layer thickness of approximately 5 pm are found under ultrasound [35] in contrast to the normal value of approximately 500 pm in silent conditions. 

Gerken, Dekker, Schlodder and Witt S utilized the same protocols that were used for isolating the AA(Qa -Qa) difference spectrum to indirectly obtain the difference spectrum just for the oxidation of the secondary donor Y, i.e., AA[Yz -YzJ. To isolate the difference spectrum, AA(Qa -Qa)5 electron transfer in the PS-II complex was blocked between Yz and P680 by Tris treatment and after Qa by DCMU. A ferri-/ferro-cyanide couple was added to the reaction mixture to intervene with oxidized Yz and reduced Qa following photo-excitation. Then, after a certain time after the flash, say, at 800 ms, the oxidized Yz would have been completely re-reduced by ferrocyanide rather than by the Mn-cluster, but Qa re-oxida-tion by ferricyanide would have occurred to a slight extent due to slower kinetics. When the absorbance... 

Fig. 9 shows the titration results for the following samples chloroplast lamellae and TSF-1 particles, both measured at 820 nm, and the CPI complex measured at 820 as well as 703 nm. Each sample was titrated oxidatively (starting with 100 pM ferrocyanide and adding ferricyanide to a maximum concentra tion of 10 mM) and reductively (starting with 1-5 mM ferricyanide and adding ferrocyanide to a maximum concentration of 10 mM). The titration is a plot of the light-induced AA V5. the actual redox-potential of the medium or the ferri-/ferrocyanide ratio as shown in Fig. 9. The plot of the data points clearly show that the titration was completely reversible and that P700 was in redox equilibrium with the ferri-/ferro-cya-nide couple. The solid line is the theoretical Nernst curve for a one-electron transition and the data points agree well with the theoretical course. The titration curve for both the chloroplast lamellae and the TSF-1, as well as D144 (data not shown here), yielded an value of+492 mV.

Chen and Liu (1977) utilized the spontaneous oxidation of NADH by potassium ferricyanide for the construction of a potentiometric LDH electrode. The coupled reduction of ferricyanide ions to ferrocyanide ions results in a measurable electrochemical zero-current potential. The potential was found to be Nemstian in nature and directly proportional to the logarithm values of lactate concentration over the range 0.02 to 50 mmol/1. The response time was as high as 10 min. 

The strength of the technique in this application is demonstrated by Fig. 51, which depicts the current-potential behaviour (calculated from the experimental data in Fig. 50) with reference to that of a reversible process. It is clear that the kinetic parameters of the ferrocyanide/ferricyanide couple, a typical reversible electrode reaction [163], can be measured. Vielstich and co-workers have suggested [99] that, with the condition I/IKV < 0.95 (over a reasonable potential range), the technique can be used to measure ks values up to 5 cm s"1 with an accuracy of around 10%. This... 

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