Electrochemical Approach to Concerted Proton and Electron Transfers. Reduction of the Water−Superoxide Ion Complex

Costentin, Cyrille; Evans, Dennis H.; Robert, Marc; Savéant, Jean‐Michel; Singh, Pradyumna S.

doi:10.1021/ja053911n

Cited by 134 publications

(143 citation statements)

References 11 publications

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“…One exception concerns the reduction of superoxide ions (25)(26)(27). Another exception, concerning phenol oxidation, is a series of cleverly designed experiments, nicely mimicking the oxidation of tyrosine in photosystem II, in which the variation of the log of the rate constant with pH was found to exhibit a 1∕2 slope in a substantial portion of the pH range (28)(29)(30).…”

mentioning

confidence: 99%

Intrinsic reactivity and driving force dependence in concerted proton–electron transfers to water illustrated by phenol oxidation

Bonin

Costentin

Louault

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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109

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Three experimental techniques, laser flash photolysis, redox catalysis, and stopped-flow, were used to investigate the variation of the oxidation rate constant of phenol in neat water with the driving force offered by a series of electron acceptors. Taking into account a result previously obtained with a low-driving force electron acceptor thus allowed scanning more than half an electronvolt driving force range. Variation of the rate constant with pH showed the transition between a direct phenol oxidation reaction at low pH, where the rate constant does not vary with pH, and a stepwise reaction involving the prior deprotonation of phenol by OH − , characterized by a unity-slope variation. Analyses of the direct oxidation kinetics, based on its variation with the driving force and on the determination of H/D isotope effects, ruled out a stepwise mechanism in which electron transfer is followed by the deprotonation of the initial cation radical at the benefit of a pathway in which proton and electron are transferred concertedly. Derivation of the characteristics of counterdiffusion in termolecular reactions allowed showing that the concerted process is under activation control. It is characterized by a remarkably small reorganization energy, in line with the electrochemical counterpart of the reaction, underpinning the very peculiar behavior of water as proton acceptor when it is used as the solvent.photochemistry | proton-coupled electron transfer | water as proton acceptor

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mentioning

confidence: 99%

Intrinsic reactivity and driving force dependence in concerted proton–electron transfers to water illustrated by phenol oxidation

Bonin

Costentin

Louault

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

109

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“…18.9a), instead of the irreversible disproportionation reaction (Eq. 18.19) which is usually observed even in the presence of small quantities of water [26]. It is important to highlight that Eq.…”

Section: Mechanism In Quaternary Phosphonium-based Ionic Liquidsmentioning

confidence: 84%

Oxygen Reduction Reaction in Ionic Liquids: An Overview

Pozo‐Gonzalo

2015

Electrochemistry in Ionic Liquids

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“…The reaction in which both H ? and e -are transferred in a single kinetic step to different molecular centers (Scheme 1) is termed as a [5,6] separated-concerted proton-coupled electron transfer (s-CPET). In aqueous solution, in the absence of base, water acts as a proton acceptor for the s-CPET process.…”

Section: Introductionmentioning

confidence: 99%

Proton-coupled electron transfer reactions: kinetic studies on the oxidation of dihydroxybenzenes by heteropoly 10-tungstodivanadophosphate in aqueous acidic medium

Shanmugaprabha¹,

Selvakumar²,

Vairalakshmi³

et al. 2015

Transition Met Chem

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Kinetic studies on the oxidation of hydroquinone and catechol by the heteropoly 10-tungstodivanadophosphate anion, [PV V V V W 10 O 40 ] 5-, have been carried out in aqueous acidic medium at 25°C by UV-visible spectrophotometry. The oxidation of hydroquinone shows simple second-order kinetics overall, with first-order dependence of the rate on both [oxidant] and [hydroquinone] at constant [H ? ]. For catechol oxidation, the order of the reaction with respect to [oxidant] is unity, while the order with respect to [catechol] is variable; this reaction shows Michaelis-Menten-type kinetics at constant [H ? ]. The rate of the reaction is insensitive to [H ?] in the pH range 1.2-1.7. Rate retardation for deuterated hydroquinone and catechol (C 6 H 4 (OD) 2 ) in D 2 O indicates breaking of the -OH bond in the rate-limiting step. Based on the observed kinetic isotope effect and calculated ground-state free energy change (DG 0 ) values, a hydrogen atom transfer mechanism is suggested for the reaction; i.e., in the ratelimiting step, one electron and one proton are transferred from the reductant to the oxidant in a concerted manner. Rates of oxidation of hydroquinone by this oxidant in neat acetonitrile at 25°C have also been measured. By applying the Marcus equation, the self-exchange rate constant of the oxidant (V V V IV OH/H Á ) in acetonitrile has been evaluated.

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Electrochemical Approach to Concerted Proton and Electron Transfers. Reduction of the Water−Superoxide Ion Complex

Cited by 134 publications

References 11 publications

Intrinsic reactivity and driving force dependence in concerted proton–electron transfers to water illustrated by phenol oxidation

Intrinsic reactivity and driving force dependence in concerted proton–electron transfers to water illustrated by phenol oxidation

Oxygen Reduction Reaction in Ionic Liquids: An Overview

Proton-coupled electron transfer reactions: kinetic studies on the oxidation of dihydroxybenzenes by heteropoly 10-tungstodivanadophosphate in aqueous acidic medium

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