Absolute determination of electron consumption in transient or steady state electrochemical techniques

Amatore, Christian; Azzabi, Mohamed; Calas, P.; Jutand, Anny; Lefrou, Christine; Rollin, Y.

doi:10.1016/0022-0728(90)80024-z

Cited by 173 publications

(132 citation statements)

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“…The aim of the present article is to characterize the effect of halogenation processes and the perturbation of protonation reactions to determine the n app values characterizing the stoichiometry of the voltammetric methods. For determining the electron-consumption in voltammetric time-scale, the method offered by Amatore et al was used in this study [7]. Because of the proton production of the electrodimerization, the protonation constants of the appropriate halogeno-anilines were determined in the used acetonitrile media.…”

Section: Introductionmentioning

confidence: 99%

The Electrooxidation of Halogeno‐Anilines at Microelectrodes in Acetonitrile Solution

2003

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The electrochemical oxidation of 4-chloro-, 2,4-dichloro-, 2,4,6-trichloro-anilines and 4-bromo-, 2,4-dibromo-, 2,4,6-tribromo-anilines and 4-iodo-aniline were investigated in unbuffered acetonitrile solution. The main reaction at the electrooxidation of these compounds is the dimerization which is accompanied by release of the p-substituent halide and formation of protons. To complete the so far achieved results by the apparent electron exchange number (n app ) determination in the voltammetric time scale have been attempted. These measurements were carried out with the aim, to have a clearer picture on the n app influencing role of the following complicating factors: The rejected halogenides in MeCN solvent at lower potential values as the substrates can be oxidized to the corresponding halogens, and these halogens except the iodine substitute the substrate which takes place even in the voltammetric time scale by increasing the n app value characteristic for the dimerization only. The measurable n app values are influenced by the protons produced at the oxidation as well, in the opposite direction. The explanation for the latter is, that the solvent is aprotic, therefore the differently basic primary amino groups of the diffusing substrate molecules binding partly the protons and in this way voltammetrically inactive substrate species are formed. This reaction is a typical equilibrium type and this inactivation effect decrease the measurable n app value. This effect depends on the quality and number of halogene substituent at a given substrate because these affect the protonation constant of the substrate. Therefore the protonation constants of the substrates had to be determined. In the knowledge of these quantitative data the explanation of the trends in the n app values measured in the voltammetric time scale is attempted. The mechanistic study of the dimerization reaction of these substrates is in progress in our laboratory.

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Section: Introductionmentioning

confidence: 99%

The Electrooxidation of Halogeno‐Anilines at Microelectrodes in Acetonitrile Solution

2003

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“…6 Bipyranylidene and pyrane are produced by the reversible reduction of the dimer. 7 We have found that upon encapsulation in the internal voids of zeolites, owing to the impossibility to form dimers, pyrylium ions display an apparently more simple electrochemistry consisting on the quasi-reversible reduction to TP. Compartmentalization of TP + inside the zeolite Y impedes its diffusion and eventually that of the corresponding TP pyranyl radicals, and therefore radical coupling is inhibited.…”

mentioning

confidence: 99%

Electrocatalysis of neurotransmitter catecholamines by 2,4,6-triphenylpyrylium ion immobilized inside zeolite Y supercages

Doménech¹,

Doménech‐Carbó²,

Garcı́a³

et al. 1999

Chem. Commun.

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2,4,6-Triphenylpyrylium ions entrapped inside the supercages of Y zeolite exert a remarkable catalytic effect toward the electrochemical oxidation of dopamine and norepinephrine (neurotrasmitter catecholamines) in neutral aqueous media.Encapsulation of organic species inside the rigid matrix of microporous zeolites has proved to be a general methodology to control the molecular properties of the incorporated guest. 1 Zeolites are a large family of crystalline aluminosilicates whose structure defines strictly uniform channels and cavities of molecular dimensions (micropores). It is in these internal voids where a guest can be accommodated provided that its molecular size is smaller than the void dimensions. In particular, the structure of zeolite Y is formed by an array of spherical cavities (1.4 nm diameter) that are tetrahedrally interconnected through four smaller apertures (0.74 nm diameter).We have already reported that the bulky 2,4,6-triphenylpyrylium ion (TP + , ≈ 1.3 nm) can be prepared inside the zeolite Y supercages through a 'ship-in-a-bottle' synthesis that relies on the diffusion of much smaller synthetic precursors. 2 After the encapsulation, TP + remains mechanically immobilized inside the zeolite Y supercages, but it still can interact with smaller molecules through the cavity windows.Recently one of us has shown that while the BF 4 2 salt of TP + in water undergoes a rapid hydrolytic ring opening, when TP + is encapsulated within the restricted space provided by the supercages of zeolite, the host framework protects it from the nucleophilic attack of water. 3 As a result, TP + within Y zeolite (TPY) is completely persistent in water. This opens the opportunity for new applications of TP + in aqueous media, as reported herein on the catalytic effect of TPY on the electrochemical oxidation of catecholamines in aqueous solution.The electrochemistry of pyrylium ions in solution is well understood. TP + undergoes one-electron reduction in protic solvents. 4 Controlled potential electrolysis produces the corresponding dipyran which in turn can be reoxidized back to TP + . In aprotic solvents, reduction of pyrylium ions leads to the corresponding bipyranylidene together with pyrane. 5 In this case, the transient reduction wave is controlled kinetically by the irreversible dimerization of the radicals formed after the initial electron transfer. 6 Bipyranylidene and pyrane are produced by the reversible reduction of the dimer. 7 We have found that upon encapsulation in the internal voids of zeolites, owing to the impossibility to form dimers, pyrylium ions display an apparently more simple electrochemistry consisting on the quasi-reversible reduction to TP. Compartmentalization of TP + inside the zeolite Y impedes its diffusion and eventually that of the corresponding TP pyranyl radicals, and therefore radical coupling is inhibited.Preliminary experiments on the electrochemistry of TP + incorporated within zeolite Y confirmed the inhibition of dimerization processes. Paraloid B72 † and Elvacite 2044, ‡ w...

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“…2 or 3 we use a factor n rather than n 2 because the two electrons are not transferred simultaneously but sequentially through a ECEC square-scheme mechanism 60 in a sequence of two independent single electron transfer steps, 19 each one being followed by an acid-base reaction. 61 Within this framework, only the small population of h A h adsorbed dopamine molecules may be electroactive at high scan rates, giving rise to the small slope of the linear variations of i p corr (v) vs. v (Figures 5b, 5c and Table I). Conversely, the larger slope observed at small scan rates (Figures 5b, 5c and Table I) indicates that a larger population containing l A l ≈ 2.5 × h A h adsorbed dopamine molecules was involved as can be inferred from the relative slopes at low and high scan rates in Figure 5b and Table I.…”

Section: Discussionmentioning

confidence: 95%

Surface Heterogeneities Matter in Fast Scan Cyclic Voltammetry Investigations of Catecholamines in Brain with Carbon Microelectrodes of High-Aspect Ratio: Dopamine Oxidation at Conical Carbon Microelectrodes

Oleinick

Álvarez‐Martos

Svir

et al. 2018

J. Electrochem. Soc.

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Fast Scan Cyclic Voltammetry (FSCV) at high aspect ratio carbon microelectrodes shows adequate high temporal and spatial resolution for in vivo analysis of catecholamines. Though the presence of their surface heterogeneities has been recognized since their earliest introduction for in vivo measurements in the brain, the kinetic consequences on the measurements have not been investigated and FSCV measurements are treated based on pre-and post-calibrations. We establish here that surface heterogeneities play a consequent dynamic role on the oxidation of dopamine taken as an example of catecholamines. Hence, the FSCV current peak intensities do not scale with the scan rate v or its square root. This is rationalized with a simple model involving a co-existence of at least two types of surface nanodomains with different electrochemical reactivities and different time responses. At low scan rates (<100 V s −1 ) dopamine molecules that initially adsorbed onto non-electroactive nanodomains have enough time to migrate toward highly electroactive ones so all molecules initially adsorbed on the whole electrode surface may be oxidized during one FSCV cycle. Current peak intensities then increase proportionally to the scan rate. However, above 100 V s −1 , dopamine migration between sites starts to be kinetically limited so that FSCV current peak intensities do not increase any more proportionally to the scan rate. Ultimately, i.e., above 1000 V s −1 , the dopamine exchange between sites is almost totally blocked so only dopamine molecules initially adsorbed on the electroactive surface nanodomains may be oxidized; the current peak intensities then increase again proportionally with the scan rate though with a smaller slope than that observed at small scan rates. Since carbon fibers with large aspect ratios are frequently used in brain investigations, this effect should be a concern when extracting quantitative results even when each carbon fiber response is properly pre-or post-calibrated using the exact CV waveform and scan rate used during the in vivo measurements. Release and modulation of neurotransmitters fluxes and concentrations are essential in complex organisms since they regulate many key functions by transferring information between cells such as neurons in the brain, neurons and muscle cells as well as through stimulating specific actions in endocrine-related systems. Albeit their unique and ubiquitous functions are well recognized today, the very existence and identification of neurotransmitters has long been a matter of debate up to the end of the second third of the past century, 1-3 and still needs to be better understood. This explains why characterizing fluxes and nature of neurotransmitters release is still stimulating a quest for analytical methods sufficiently accurate, specific and sensitive to investigate dynamic effluxes and flows of neurotransmitters in vivo (e.g., within a living brain) 4-6 or ex vivo (e.g., at the single endocrine cell level, 7-9 or intrasynaptically 10-12 ) with an adequate tempo...

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Absolute determination of electron consumption in transient or steady state electrochemical techniques

Cited by 173 publications

References 31 publications

The Electrooxidation of Halogeno‐Anilines at Microelectrodes in Acetonitrile Solution

The Electrooxidation of Halogeno‐Anilines at Microelectrodes in Acetonitrile Solution

Electrocatalysis of neurotransmitter catecholamines by 2,4,6-triphenylpyrylium ion immobilized inside zeolite Y supercages

Surface Heterogeneities Matter in Fast Scan Cyclic Voltammetry Investigations of Catecholamines in Brain with Carbon Microelectrodes of High-Aspect Ratio: Dopamine Oxidation at Conical Carbon Microelectrodes

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