Voltammetry, oxidation potential determination

Oxidation potentials determined by cyclic voltammetry in MeCN are considerable higher for monosulfides than those for the disulfides (XII) with w = = 3, w = 3, = 4,... 

Fig. 18. pH dependence of the oxidized Rieske fragment from bovine heart mitochondria (ISF). (a) Redox potential determined by cyclic voltammetry. The line was fitted to the data points, giving = 7.6 and pi a, x2 = 9-2. (b) CD intensity of the oxidized... 

In this section, we will present and discuss cyclic voltammetry and potential-step DBMS data on the electro-oxidation ( stripping ) of pre-adsorbed residues formed upon adsorption of formic acid, formaldehyde, and methanol, and compare these data with the oxidative stripping of a CO adlayer formed upon exposure of a Pt/ Vulcan catalyst to a CO-containing (either CO- or CO/Ar-saturated) electrolyte as reference. We will identify adsorbed species from the ratio of the mass spectrometric and faradaic stripping charge, determine the adsorbate coverage relative to a saturated CO adlayer, and discuss mass spectrometric and faradaic current transients after adsorption at 0.16 V and a subsequent potential step to 0.6 V. 

Chemical reactivity of unfunctionalized organosilicon compounds, the tetraalkylsilanes, are generally very low. There has been virtually no method for the selective transformation of unfunctionalized tetraalkylsilanes into other compounds under mild conditions. The electrochemical reactivity of tetraalkylsilanes is also very low. Kochi et al. have reported the oxidation potentials of tetraalkyl group-14-metal compounds determined by cyclic voltammetry [2]. The oxidation potential (Ep) increases in the order of Pb < Sn < Ge < Si as shown in Table 1. The order of the oxidation potential is the same as that of the ionization potentials and the steric effect of the alkyl group is very small. Therefore, the electron transfer is suggested as proceeding by an outer-sphere process. However, it seems to be difficult to oxidize tetraalkylsilanes electro-chemically in a practical sense because the oxidation potentials are outside the electrochemical windows of the usual supporting electrolyte/solvent systems (>2.5 V). 

The first ( ) and second (E ) oxidation potentials (versus saturated calomel electrode (SCE)) have been determined by voltammetry. The electrochemistry of the 4-(tel-luropyranyl)-4//-telluropyran has been examinated and compared to the O, S and Se analogues. 

Cyclic voltammetry can (i) determine the electrochemical reversibility of the primary oxidation (or reduction) step (ii) allow the formal potential, E°, of the reversible process to be estimated (iii) provide information on the number of electrons, n, involved in the primary process and (iv) allow the rate constant for the decomposition of the M"+ species to be measured. Additional information can often be obtained if intermediates or products derived from M"+ are themselves electroactive, since peaks associated with their formation may be apparent in the cyclic voltam-mogram. The idealized behaviour illustrated by Scheme 1 is a relatively simple process more complicated processes such as those which involve further electron transfer following the chemical step, pre-equilibria, adsorption of reactants or products on the electrode surface, or the attack of an electrogenerated product on the starting material, are also amenable to analysis. 

The oxidation potential decreases in the order Si—Si Si—Ge>Ge—Ge>Si—Sn> Ge—Sn >Sn—Sn in accord with the ionization potential (7P) of the corresponding dimetal. Anodic generation of silicenium ions from disilanes was also reported. The reduction potentials of silicenium ions were determined by cyclic voltammetry of neutral precursor disilanes49. The reduction potential shifted to the negative direction as the center element changed from C to Ge as shown in equation 44. 

Electrochemical studies confirmed the presence of redox-active nanoparticles. Differential pulse and cyclic voltammetry studies were conducted. Cyclic voltammetry showed that the complex displays an electrochemically reversible ferrocene/ ferrocenium couple (Figure 9.6). The oxidation potential for the hybrid CPMV-Fc conjugate and free ferrocenecarboxylic acid in solution was determined E1/2 of CPMV-Fc was 0.23 V, and Elj2 of free ferrocenecarboxylic acid was 0.32 V versus the Ag/AgCl electrode, respectively. This shift is expected for the conversion of the carboxyl group of ferrocenecarboxylic acid to an amide on coupling to the virus capsid, since the amide is less electron-withdrawing. 

The dimers D, 4 readily undergo electrochemical, irreversible, oxidation under anaerobic conditions on the pyrolytic graphite electrode, with oxidation peak potentials, determined by linear sweep voltammetry on 1 mM solutions, as shown in Table V). Note the much lower values of E for dimers Dj 3, relative to D4, testifying to the greater susceptibility of the former to oxidation. 

Thermodynamically relevant oxidation potentials of enolates were recently obtained from cyclic voltammetry studies on 60-63. Since the a-carbonyl radicals proved to be sufficiently stable, also their oxidation potentials were determined. They are much higher than the ones from the corresponding enolates and agree qualitatively with the reduction potentials of three related a-carbonyl cations as determined by Okamoto [157,158], Thus, depending on the oxidation power of the used oxidant either a-carbonyl radical or a-carbonyl cation chemistry can be triggered from enolates as demonstrated above. 

Since in good hydrogen bond accepting solvents such as DMSO, the equilibrium content of ends of 2-arylpropionaldehydes is relatively high (up to 50%) [187], their oxidation potentials were readily determined by cyclic voltammetry in at tonitrile/DMSO mixtures [171], A closer analysis, however, indicated that actually enol DMSO complexes were measured exhibiting some enolate character, since the oxidation potentials found proved to be significantly lower than the ones calculated by the above procedure. 

The one-electron reduction potentials of the radical cations of thioanisole, benzyl methyl sulphide, and 2-hydroxyethyl benzyl sulfide in water and several organic solvents were investigated by cyclic voltammetry. For comparison, the one-electron oxidations in water were also measured using pulse radiolysis. ° The two methods are complementary and the reversible potentials determined by pulse radiolysis are fairly close to the peak potentials determined by cyclic voltammetry (Table 8) indicating that the peak potentials do correspond to the formation of sulfur radical cations for all three sulfides. 

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