Cyclic voltammetry aqueous reduction

The second approach, followed by Vayenas et al39 is direct measurement of Ntpb and N n using cyclic voltammetry, as in aqueous electrochemistry,49 and measuring the height, Ip, or the area fldt of the cathodic oxygen reduction peak (Fig. 5.28a). Then Ntpb can be estimated from ... 

Alemu et al. [35] developed a very sensitive and selective procedure for the determination of niclosamide based on square-wave voltammetry at a glassy carbon electrode. Cyclic voltammetry was used to investigate the electrochemical reduction of niclosamide at a glassy carbon electrode. Niclosamide was first irreversibly reduced from N02 to NHOH at —0.659 V in aqueous buffer solution of pH 8.5. Following optimization of the voltammetric parameters, pH and reproducibility, a linear calibration curve over the range 5 x 10 x to 1 x 10-6 mol/dm3 was achieved, with a detection limit of 2.05 x 10-8 mol/dm3 niclosamide. The results of the analysis suggested that the proposed method has promise for the routine determination of niclosamide in the products examined [35]. 

The imidazole complexes are unstable in aqueous solution and decompose rapidly to TCO2. At lower pH the complexes undergo acid-catalyzed decomposition. None of the complexes exhibited oxidation or reduction processes by cyclic voltammetry. However, it was chemically possible to reduce the imidazole complex with Zn in IM HCl. A defined complex formed that did not contain the Tc=0 group probably reduction to Tc complexes occurred. " ... 

The heteropentalenes (94) are reduced electrochemically to anion radicals (94 ). The process is reversible as demonstrated by cyclic voltammetry using a carbon paste working electrode <85JCS(P2)1797>. The electrochemical half-peak reduction potential in aqueous methanol j,/2 shows that ring units X = S, SO, SO2 ( — j,/2 = 437 423 383 mV) increase the ability of (94) (R = = H)... 

The polarographic behavior of all the bipyridines with the exception of the 3,4 -isomer has been investigated in aqueous solution. The difficulty of reduction increases in the order 4,4 -, 2,4 -, 2,3 -, 2,2 -, and 3,3 -bipyr-idine. Most of the work has been concerned with 2,2 - and 4,4 -bipyridines. Both isomers are reduced in aqueous solution by a two-electron process, sometimes observed as two separate one-electron steps, which is pH dependent because of the formation of a dihydro derivative. Complications in interpretation of the waves due to prewaves, catalytic hydrogen waves, wave maxima, and adsorption phenomena have frequently been observed. ° Polarography and cyclic voltammetry investigations have been extended to the study of 2,2 - and 4,4 -bipyridines... 

The electrochemical behavior of Np ions in basic aqueous solutions has been studied by several different groups. In a recent study, cyclic voltammetry experiments were performed in alkali ([OH ] = 0.9 — 6.5 M) and mixed hydroxo-carbonate solutions to determine the redox potentials of Np(V, VI, VII) complexes [97]. As shown in Fig. 2, in 3.1 M LiOH at a Pt electrode Np(VI) displays electrode processes associated with the Np(VI)/Np(V) and Np(VII)/Np(VI) couples, in addition to a single cathodic peak corresponding to the reduction of Np(V) to Np(IV). This latter process at Ep —400 mV (versus Hg/HgO/1 M NaOH) is chemically irreversible in this medium. Analysis of the voltammetric data revealed an electrochemically reversibleNp(VI)/Np(V)... 

The observation (112-115) that neutral aqueous solutions of [Ni11H 3G4]2 consume molecular oxygen with the appearance of a strongly absorbing transient at 350 nm lead to detailed investigations and discovery of nickel(III)-peptide complexes (113). The oxidized nickel complexes have absorption maxima around 325 and 240 nm (e = 5240 and 11,000 M I cm-1, respectively for [NiM1H 3G4]-). Reduction potentials (116) (Table II), measured by cyclic voltammetry, show a small dependence on ligand structure which can be correlated... 

The electrochemical oxidation of NADH in aqueous solutions is seen as a single peak by cyclic voltammetry and takes place at 0.4, 0.7, and IV vs SCE at carbon, Pt, and Au electrodes, respectively (37,38). No re-reduction of NADH related intermediates is observed in cyclic voltammetry even at fast scan rates (30 V/s) (39), reflecting the high chemical irreversibility of the reaction. It was early recognized that the oxidation of NADH resulted in electrode fouling, necessitating... 

Plasma polymerized N-vinyl-2-pyrrolidone films were deposited onto a poly(etherurethaneurea). Active sites for the immobilization were obtained via reduction with sodium borohydride followed by activation with l-cyano-4-dimethyl-aminopyridinium tetrafluoroborate. A colorometric activity determination indicated that 2.4 cm2 of modified poly(etherurethaneurea) film had an activity approximately equal to that of 13.4 nM glucose oxidase in 50 mM sodium acetate with a specific activity of 32.0 U/mg at pH 5.1 and room temperature. Using cyclic voltammetry of gold in thin-layer electrochemical cells, the specific activity of 13.4 nM glucose oxidase in 0.2 M aqueous sodium phosphate, pH 5.2, was calculated to be 4.34 U/mg at room temperature. Under the same experimental conditions, qualitative detection of the activity of a modified film was demonstrated by placing it inside the thin-layer cell. 

The oxidation-reduction behavior, ascertained by direct current (conventional) polarography, and its dependence on pH in aqueous solution of the [P2Mo18062] 6, [As2Moi8062]-6, and [P2Wi8062]-6 anions may be found in Refs.1S9 161>. The polarographic behavior of the dimeric 9-molybdophosphate anion of (NH4)6 [P2Moi 8062] was examined by cyclic voltammetry and alternating current... 

The electrochemical reduction of 2-nitroimidazole in an aqueous mixed [916] and aprotic [917] medium has been carried out using cyclic voltammetry at a mercury electrode. The voltammetric behavior of 2-nitroimidazole in the aqueous mixed medium is substantially different from that in nonaqueous medium in fact, only in the aqueous medium is it possible to study in isolation the nitro radical anion. 

Polarographic studies show, in addition to oxidation waves for [Os(bipy)3]2+, several reduction waves 130,158 this is also the case for [Os(4,4 -Me2bipy)3]2+, [Os(5,5 -Me2bipy)3]2+121 and [Os-(phen)3]2+. Recent cyclic voltammetry and coulombetry studies on [Os(bipy)3]2+ and [Os(phen)3]2+ in liquid S02 show successive one-electron oxidations to [Os(LL)3]3+ and [Os(LL)3]4+.lls There is a small but real difference in the Os111/u redox potential for [Os(phen)3]2+ in aqueous and in non-aqueous sodium lauryl sulfate micellar solutions.138 Correlations have been made between the oxidation potentials and charge-transfer transition frequencies in complexes [M(LL)3]2+ (Me = Fe, Ru, Os LL = bipy, 4,4 -Me2bipy, 5,5 -Me2bipy).159... 

The electrochemical irreversible reduction of [Cu(sar)]2+ cation in aqueous solution was studied by cyclic voltammetry [293], This cation is kinetically and thermodynamically stable except toward reduction of encapsulated copper(II) ion to copper ion E = - 800 mV vs SCE). After reduction, the coordination number of this copper ion diminishes from six (copper(II)) to four (copper(I)). 

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