Glassy carbon electrodes redox behavior

Figure 1. The redox behavior of I,4-dlhydrobenzene at a deactivated versus various activated glassy carbon electrodes.

Electrochemical behavior of indole-3-propionamide derivatives (Fig. 27) was investigated in order to establish experimental conditions for the electrochemical oxidation and determination of these derivatives using a glassy carbon electrode [158]. Cyclic voltammetry has been used in studying the redox mechanism that is related to antioxidant activity of the derivatives. The results showed that the compounds might have profound effects on the understanding of their in vivo redox processes and pharmaceutical activity. Indole-... 

Further studies have also appeared in the mass transfer properties of the modifying layers. The mass transfer behavior of the polymer [Os(bipy)2(PVP)ioCl]Cl in para-toluene sulphonic acid has been studied in de-tail. In this study the effect of the non-rigidity of the layer on the mass transport data is discussed in some detail. A detailed study of the pH dependence of the mass transfer of a glassy carbon electrode modified with the [Ru(bipy)2(PVP)io(H20)] is reported. This study shows that the EQCM can be used very effectively for the study of redox reactions which show complicated (in this case pH dependent) features. (See also Section 8.2). 

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. 

In Section 2 we showed that the properties of amorphous carbon vary over a wide range. Graphite-like thin films are similar to thoroughly studied carbonaceous materials (glassy carbon and alike) in their electrode behavior. Redox reactions proceed in a quasi-reversible mode on these films [75], On the contrary, no oxidation or reduction current peaks were observed on diamondlike carbon electrodes in Ce3+/ 41, Fe(CN)63 4. and quinone/hydroquinone redox systems the measured current did not exceed the background current (see below, Section 6.5). We conventionally took the rather wide-gap DLC as a model material of the intercrystallite boundaries in the polycrystalline diamond. Note that the intercrystallite boundaries cannot consist of the conducting graphite-like carbon because undoped polycrystalline diamond films possess excellent dielectric characteristics. 

Various molecules are capable to bind to the DNA duplex or to single-stranded DNA. The application of DNA binding molecules for the detection of base-pair mismatches is discussed below. For instance, Millan et al. demonstrated sequence-selective electrochemical DNA sensing using hybridization indicators [9]. In this detection scheme, DNA capture strands were covalently immobilized on a glassy carbon 14 electrode and [Co(bpy)3] + and [Co(phen)3] + served as hybridization indicators that display reversible redox behavior. Presumably, electrostatic interactions with the negatively charged... 

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