Cyclic Voltammetry and Polarography

In the polarography area, half-wave potentials have been ranployed as a tool for predicting the scope and limitation of the reaction of a,P-unsaturated ketones 

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Cyclic voltammetry and polarography have been used to study the mechanisms of fluorination and provide an indicator of their relative strengths [92JFC(59)157,92T1595], Two mechanisms have been proposed involving SN2 or electron transfer, although it is likely that which is followed depends on the N—F reagent used. 

Nevertheless, the mid-peak potentials determined by cyclic voltammetry and other characteristic potentials obtained by different electroanalytical techniques (such as pulse, alternating current, or square wave voltammetries) supply valuable information on the behavior of the redox systems. In fact, for the majority of redox reactions, especially for the novel systems, we have only these values. (The cyclic voltammetry almost entirely replaced the polarography which has been used for six decades from 1920. However, the abundant data, especially the half-wave potentials, 1/2, are still very useful sources for providing information on the redox properties of different systems.)... 

The quasi-reversihle electroreduction processes of Zn(II) in the absence and in the presence of Ai,Ai -dimethylthiourea (DMTU) were quantitatively compared by Sanecld [91], It has been shown that in the presence of DMTU enhanced response of cyclic voltammetry and normal pulse polarography was complex and could be resolved into its regular reduction part and a part caused by the catalytic influence of adsorption of organic substance. 

The cavity of diphenylglycoluril derivative 3 is well suited to partially encapsulate a [4Fe-4S] cluster. Compound 29 which contains four arms terminating with thiol groups was synthesized and treated with (n-Bu)4N 2 Fe4S4Cl4) in dimethylformamide to give cluster complex 30 [31]. The product was characterized by a number of techniques, including cyclic voltammetry and differential pulse polarography. The current response of 30 was very small, but improved upon addition of a modulator, e.g. Ba or Na" ions. This behavior is similar to that observed for certain redox active enzymes [32]. As in the natural systems, a maximum response is observed when the Ba concentration is... 

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... 

Misonidazole and its azo- and azoxy derivatives have been investigated in detail by polarography, cyclic voltammetry, and pulse radiolysis methods [947],... 

The electron affinity of 3-(iV-methylpiperazino)-5-nitroindazole, 3,5-dinitroindazole, and molecular complex of the last with water is discussed on the basis of their half-wave potentials and in connection with their eventual radiosensitizing properties [667], The mechanism of EC behavior of 2-substituted 5(6)-nitrobenzimidazoles in acetonitrile has been investigated by classical polarography, cyclic voltammetry, and platinum rotating disk electrode with a ring (RDER) [888,991], It is shown that... 

The electrochemical behavior, in non-aqueous solvents, of some mono- and bis-Cp oxo homo- and heteropoly-nuclear titanium derivatives containing oxo bridges between different metals has been investigated (Scheme 347). Cyclic voltammetry, square wave voltammetry, and polarography have been used to determine and compare the redox properties of these compounds.829... 

Part IV is devoted to electrochemical methods. After an introduction to electrochemistry in Chapter 18, Chapter 19 describes the many uses of electrode potentials. Oxidation/reduction titrations are the subject of Chapter 20, while Chapter 21 presents the use of potentiometric methods to obtain concentrations of molecular and ionic species. Chapter 22 considers the bulk electrolytic methods of electrogravimetry and coulometry, while Chapter 23 discusses voltammetric methods including linear sweep and cyclic voltammetry, anodic stripping voltammetry, and polarography. 

This important mechanism, which results in enhanced currents owing to resupplying of Yyj to the electrode is studied by polarography, linear-scan or cyclic voltammetry and a.c. polarography. ... 

Surface excesses of electroactive species are often examined by methods sensitive to the faradaic reactions of the adsorbed species. Cyclic voltammetry, chronocoulometry, polarography, and thin layer methods are all useful in this regard. Discussions of their application to this type of problem are provided in Section 14.3. In addition to these electrochemical methods for studying the solid electrode/electrolyte interface, there has been intense activity in the utilization of spectroscopic and microscopic methods (e.g., surface enhanced Raman spectroscopy, infrared spectroscopy, scanning tunneling microscopy) as probes of the electrode surface region these are discussed in Chapters 16 and 17. 

Cyclic voltammetry and differential pulse polarography have been used to investigate the redox properties of the di-Ni(II) species in acetonitrile. Effectively, a two-electron step was observed for the complex of 30, whereas that of 29 (n = 2) yielded two clear one-electron steps. This is in accord with the occurrence of an interaction between the nickel sites for the latter system containing the shorter link between the isocyclams. 

The electrode reduction mechanism of benzenodicarbonitrile isomers was examined by polarography, cyclic voltammetry and controlled potential electrolysis in DMF solutions at a Hg cathode. 1,2- and 1,4-dicyanobenzenes were reduced in two successive steps under polarographic conditions, where the first step corresponds to a quasi-reversible one-electron transfer. Cyclic voltammetric experiments provided more information on the electrode reduction mechanism and allowed one to suggest the mechanistic scheme for 1,2-and 1,4-dicyanobenzenes shown in Scheme 16. 

From 1953, much research has been done on the electrochemical behavior of CDs and their inclusion complexes. It is known that the effect of CDs on electrochemical properties of the guest molecules can be used in potentiometry, polarography and voltametry, cyclic voltammetry and amperometry. The ability of CDs to bond, orient and separate molecules and to form inclusion complexes in solution or on modified electrodes can be utilized for electrocatalysis, electrosynthesis and electroanalysis [78]. 

In a study of the cathodic reduction of cyclo-octatetraene in DMF and DMSO, Allendoerfer and Rieger used cyclic voltammetry and a.c. polarography to show that the reduction to the radical anion is quasi-reversible with a rate constant, ky, equal to 8.5 x 10" cm s at 25°C. The heat of activation was found to be 7.7 kcal mol" and the small values of a which were observed were interpreted in terms of the transition state at the equilibrium potential resembling the product radical anion more closely than it resembles the reactant molecule. The transition state is therefore presumably planar, as is the radical anion. This conclusion is supported by the similarity of the experimental value for the free energy of activation to the literature derived values for the free energy of activation in the bond isomerisation reaction of cyclo-octatetraene. 

Each electroanalytical technique has certain characteristic potentials, which can be derived from the measured curves. These are the half-wave potential in direct current polarography (DCP), the peak potentials in cyclic voltammetry (CV), the mid-peak potential in cyclic voltammetry, and the peak potential in differential pulse voltammetry (DPV) and square-wave voltammetry. In the case of electrochemical reversibility (see Chap. 1.3) all these characteristic potentials are interrelated and it is important to know their relationship to the standard and formal potential of the redox system. Here follows a brief summary of the most important characteristic potentials. 

Abbrevations DPV is differential pulse voltammetry CV, cyclic voltammetry and DPP, differential pulse polarography. Source Ref. 6... 

We have synthesized a number of ligands and the corresponding complexes in which both the cavity for transition metal cations as well as the cavity for the alkali or alkaline earth metal cations are systematically varied [ref 7]. TTie complexes were studied by X-ray crystallography, polarography, cyclic voltammetry, and EPR spectroscopy. The ultimate goal is to realize bimetallic (electro)catalysis with well-defined complexes. 

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