Ferricyanide/ferrocyanide couple redox

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...

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 For this purpose, the natural electron acceptors of many oxidoreductases have been replaced by redox-active dyes or other reversible electron mediators.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... 

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... 

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... 

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... 

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... 

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... 

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... 

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.

The standard potential for the Ru(II/III) redox transformation is 712 mV in aqueous perchlorate media, whereas the standard potential for the ferrocyanide/ferricyanide couple is 375 mV. Hence the driving force for the mediation is some 337 mV, which corresponds to an equilibrium constant of 5 X 10 at 298 K. Thus we see that equilibrium lies very much on the rhs. Typical RDE voltammograms for the oxidation of Fe(CN)e in 0.1 M HCIO4 at uncoated glass carbon and metallopolymer-coated glassy carbon electrodes are shown in Fig. 2.24. Note that the reduction of Fe(CN) is quite sluggish. This is to be expected due to the unfavorable thermodynamics. Two anodic oxidation waves are observed at the metallopolymer-coated electrode. The first occurs at a potential where Fe(CN)6 is oxidized at the bare electrode, so it corresponds to the direct unmediated oxidation of substrate at the inner electrode/polymer interface. The second wave is due to the mediated oxidation via the Ru(II) redox sites, as just discussed. This mediated wave exhibits linear Koutecky-Levich behavior. It is clear that we are dealing with Case C here, since the direct unmediated oxidation of substrate occurs at a less positive potential than the mediated oxidation via the Ru(III) sites in the film. 

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. 

In regards to ferro/ferricyanide, the oxidation of ferrocyanide is known to be surface sensitive and with the above points in mind it is unsurprising that low rates of electron transfer are observed for the redox couple. 

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. 

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