Anodic Peak

Nature of current of additional peak was determined. It s multiple depending on the rate of polarizing tension. The absence of anodic peaks on the voltamperograms of calces testifies that the reduction of the compound is an irreversible process. 

Thus, the peak separation can be used to determine the number of electrons transferred, and as a criterion for a Nemstian behavior. Accordingly, a fast one-electron process exhibits a AEp of about 59 mV Both the cathodic and anodic peak potentials are independent of die scan rate. It is possible to relate the half-peak potential (Ep/2. where the current is half of the peak current) to the polarographic half-wave potential, El/2 ... 

Example 2-1 The reversible oxidation of dopamine (DA) is a two-electron process. A cyclic voltammetric anodic peak current of 2.2 pA is observed for a... 

The unusual cyclic voltammograms and responses to large-amplitude potential steps of a variety of conducting polymer films have prompted a number of groups to develop nucleation models for their oxidation. The key features that they have sought to explain are the peaks observed in anodic chronoamperometry (see Fig. 14), and the dependence of the anodic peak position on scan rate207 and the time spent in the undoped state.20 ... 

The conspicuous separation between the cathodic and anodic peak potentials was initially interpreted in terms of the simple theory for redox polymers as a kinetic effect of slow heterogeneous charge transfer the thermodynamic redox potential of the whole systems was calculated from the mean value between Ep and Ep ... 

One-half the sum of the cathodic and anodic peaks, in volts, vs. saturated calomel electrode (KCl). 

Value of the cathodic peak anodic peak not defined. 

Phosphate buffer Anodic peak (mV) Cathodic peak... 

Figure 26 shows the redox potential of 40 monolayers of cytochrome P450scc on ITO glass plate in 0.1 KCl containing 10 mM phosphate buffer. It can be seen that when the cholesterol dissolved in X-triton 100 was added 50 pi at a time, the redox peaks were well distinguishable, and the cathodic peak at -90 mV was developed in addition to the anodic peak at 16 mV. When the potential was scanned from 400 to 400 mV, there could have been reaction of cholesterol. It is possible that the electrochemical process donated electrons to the cytochrome P450scc that reacted with the cholesterol. The kinetics of adsorption and the reduction process could have been the ion-diffusion-controlled process. 

CV measurements showed that the reversible eleetrode reaetion of the [Fe(CN)6]" redox eouple was suppressed to some extent by the treatment with the DNA. The addition of the anti-DNA antibody further suppressed the redox reaetion thus decreasing the magnitudes of the CV peak currents. This is most likely caused by a steric hindrance of the bulky protein, which binds to the DNA double strands on the electrode surface, to mainly reduce the effective area of the electrode. The electrostatic repulsive effect may also contribute to the electrode response, since the isoelectric point of mouse IgM is commonly in the range of 4.5 to 7.0. Figure 11 shows the relationship between the decrease in the anodic peak current (A/p ) and the antibody concentration. As seen in this figure, the electrode system responded to the anti-DNA antibody in the concentration range of 1 — 100 nM. For the case of the mouse IgM, which does not interact with double-stranded DNA, the present system gave almost no response. The sensor did not respond to other serum proteins as well (data not shown). 

In commenting on the observations of Tinnemans et a/.,84 Augustynski remarked86 that the importance of the marked affinity of the hydrated Ti02 for C02 was apparent from anodic peaks observed on the voltammograms obtained on the reverse sweep after scanning up to a sufficient negative potential at which C02... 

In this connection, cyclic voltammetric measurements on the electrochemical reduction of C02 at n-Ti02 and platinized Ti02 film electrodes were reported a little later by Augustynski and co-workers.87 The existence of two electrochemically detectable species resulting from C02 reduction was suggested by anodic peaks on the cyclic voltammograms (Fig. 4). Unfortunately, however, no... 

Typical results of these authors are shown in Figure 3.46. A small faradaic re-oxidation wave was observed at very high sweep rates, i.e. up to 4400 Vs"1. The standard potential of the C02/C0 2 couple was evaluated as the middle of the interval between the cathodic and anodic peak potentials at 4400 Vs giving —2.21 V vs. SCE. 

To determine if CP was indeed lost in the chemical step the potential was held at — 1.7 V for 30s, then a positive-going scan initiated up to 1.5 V. A number of anodic peaks were observed with the largest and most significant at 1.2 V. This was unequivocally attributed to the oxidation of CP to Cl2 on the basis of a second experiment in which tetrabutylammonium chloride was added to the base electrolyte and the potential regime repeated. Hence, the chemical step after the addition of the first electron involves the ejection of the chloride anion. The identity of the species formed subsequent to this process was determined thus O Toole et al. prepared and characterised the hydrido and acetonitrile complexes (as the bipyridine derivatives) and determined their E° values as —1.46 V and —1.25 V, respectively, far removed from the observed value — 1.62 V hence neither of these species were taken as being the product. 

From the figure it can be seen that there is a pronounced anodic peak near 0.15 V vs. SCE that has also been observed in aqueous electrolyte. The current at this peak scales linearly with the scan rate, as expected for a surface-bound redox material (see section on cyclic voltammetry of adsorbed species). 

The cyclic voltammograms in Figure 3.73 show an interesting characteristic in that, at potentials greater than the anodic peak potential, the current tends towards a constant value. The charge passed, Q, in charging a capacitor C to a potential V is (see section 2.1.1.) ... 

A plot of the polaron and bipolaron electronic band intensities as a function of charge injected (as electrons removed per monomer ring) is shown in Figures 3.85(a) and (b). The point at which the polaron intensity attains a plateau and the bipolaron intensity starts to dominate, at the anodic peak... 

Thus, it appears that the transition represented by the anodic peak in the cyclic voltammogram of polypyrrole is due to a changeover in the dominant carrier type and is accompanied by a dramatic contraction of the film. The authors strongly suspected that this contraction was due to electro-striction associated with bipolaron formation. As a further test they also carried out experiments intended to test if proton expulsion from the film occurred on oxidation. They found that it did indeed occur but monotonically at alt potentials > -0.6 F, in agreement with the extremely elegant work of Tsai et at. (1987), and so could not be responsible for the relatively sudden contraction at potentials > —0.2 V. 

Figure 6.7 illustrates the voltammetric response of the third-generation SOD-based 02 biosensors with Cu, Zn-SOD confined onto cystein-modified Au electrode as an example. The presence of 02" in solution essentially increases both the cathodic and anodic peak currents of the SOD compared with its absence [150], Such a redox response was not observed at the bare Au or cysteine-modified Au electrodes in the presence of 02". The observed increase in the anodic and cathodic current response of the Cu, Zn-SOD/cysteine-modified Au electrode in the presence of 02 can be considered to result from the oxidation and reduction of 02, respectively, which are effectively mediated by the SOD confined on the electrode as shown in Scheme 3. Such a bi-directional electromediation (electrocatalysis) by the SOD/cysteine-modified Au electrode is essentially based on the inherent specificity of SOD for the dismutation of 02", i.e. SOD catalyzes both the reduction of 02 to H202 and the oxidation to 02 via a redox cycle of its Cu (II/I) complex moiety as well as the direct electron transfer of SOD realized at the cysteine-modified Au electrode. Thus, this coupling between the electrode and enzyme reactions of SOD could facilitate the development of the third-generation biosensor for 02". ...

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