Cathodic peaks

The relative importance of the disproportionation process (SET between two anion radicals) depends principally on the thermodynamic constant (K). It can be easily determined more or less accurately from the potential difference existing between the first cathodic peak and the second one. (An exact calculation would be possible from the thermodynamic potentials of the two reversible transfers in the absence of proton sources and at reasonable sweep rates so as to inhibit any undesirable chemical reaction.)... 

Voltammograms of a polythiophene film showing reasonably reversible electrochemistry of both types are shown in Fig. 2.M The formal potentials (average of the anodic and cathodic peak potentials) for p- and n-doping can provide useful estimates of the energies of the polymer s valence and conduction bands and its band gap35... 

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. 

Figure 14.6 Charge in the cathodic peak between 0.11 and 0.06 V as a function of Pt surface content diamonds, PC submonolayers on Ru(OOOl) circles, PcRui-j,/Ru(0001) surface alloys the lines are predicted trends for linear or polynomial correlations between charge and Pt surface...

Figure 9 summarizes the electrode responses toward a variety of DNA-binding substrates [14c]. For intercalators (quinacrine, acridine orange, and safranin) and groove binders (spermine and spermidine), a steep rise followed by a saturation of the concentration response curve is commonly observed. If one compares the specific concentration which gives a 50% response in the increment of the cathodic peak current (A/p ) for each substrate, a selectivity order of quinacrine acridine orange > spermine > spermidine > safranin can be estimated. The binding constants measured in aqueous media for the affinity reaction with ds DNA are as follows quinacrine, 1.5 x 10 (38 mM NaCl)... 

FIG. 9 The substrate-dependent changes in cathodic peak current (/p ) of CVs taken similarly to those in Figs. 5 and 7. 

FIG. 10 The metal-ion-dependent changes in the cathodic peak current (I ) on DNA-modified An electrode. Experimental conditions are the same as those in Fig. 5. and O, Mg (two different electrodes) A, Ca + , Ba +. For filled symbols, the same electrode was used. 

The diffusion problem can be solved to predict that one wave in NPV or one pair of anodic and cathodic peak currents in CV are to be observed the half-wave potential is expressed by... 

Dinitrophenol (DNP) gives a single wave in NPV and a pair of anodic and cathodic peak currents in CV at the NB/W interface in pH range studied. Figure 7 shows a cyclic voltammogram of 0.6 mM DNP (NB) at O.IM TPenATPB (NB)-O.IM LiCl, 50 mM phosphate buffer, pH 6.3 (W), that can be assigned to one-proton transfer assisted by A present in NB. The E]j2 vs. pH plot is shown in Fig. 8, in which the results obtained with... 

On the basis of theoretical calculations Chance et al. [203] have interpreted electrochemical measurements using a scheme similar to that of MacDiarmid et al. [181] and Wnek [169] in which the first oxidation peak seen in cyclic voltammetry (at approx. + 0.2 V vs. SCE) represents the oxidation of the leucoemeraldine (1 A)x form of the polymer to produce an increasing number of quinoid repeat units, with the eventual formation of the (1 A-2S")x/2 polyemeraldine form by the end of the first cyclic voltammetric peak. The second peak (attributed by Kobayashi to degradation of the material) is attributed to the conversion of the (1 A-2S")x/2 form to the pernigraniline form (2A)X and the cathodic peaks to the reverse processes. The first process involves only electron transfer, whereas the second also involves the loss of protons and thus might be expected to show pH dependence (whereas the first should not), and this is apparently the case. Thus the second peak would represent the production of the diprotonated (2S )X form at low pH and the (2A)X form at higher pH with these two forms effectively in equilibrium mediated by the H+ concentration. This model is in conflict with the results of Kobayashi et al. [196] who found pH dependence of the position of the first peak. 

The nature of the species that gives rise to the more negative cathodic peak observed on cyclic voltammetry of uric acid (Fig. 2) is not clear. It must be due to some relatively transient species since the peak is not pronounced at the com-pletation of the electrolysis nor is a large amount of parabanic acid formed,... 

Eq. 3). Species II might be the species responsible for the major contribution to the more negative cathodic peak observed cyclic voltammetrically. 

New anodic and cathodic peaks appear which indicates some degree of reversibility of the anion intercalation. Figure 5 and Figure 6 show the... 

Of particular interest is the relationship between the peak current and the concentration of the reacting species for the anodic and cathodic peak current, p.a Slid fp,c... 

Useful experimental parameters in cyclic voltammetry are (i) the value of the separation of the potentials at which the anodic and cathodic peak currents occur, A = Pia — PiC, and (ii) the half wave potential, 1/2, the potential mid-way between the peak potentials. A value of AE of c. 0.057 V at 25°C is diagnostic of a Nernstian response, such as that shown in Figure 2.87. More generally, if n electrons are transferred from R, then the separation will be 0.057/n V. It should be noted that the expected value for AE of 0.57/nV has no relationship to the usual Nernstian slope of RT/nF = 0.059/n V at 25UC. 

This would lower the free energy of the system, and hence would give rise to the observed shift to lower potentials of the cathodic peak, Oc. 

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