Electrochemical and ESR study on the transformation processes of α-hydroxy-quinones

Frontana, Carlos; Frontana‐Uribe, Bernardo A.; González, Ignacio

doi:10.1016/j.jelechem.2004.07.017

Cited by 33 publications

(42 citation statements)

References 29 publications

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“…This fact does not mean that a stable semiquinone cannot be formed. Since one of the products of the self-protonation pathway (equation 7) is the deprotonated original quinone (Q-O -) , the second reduction signal IIc´ for compound 2HNQ corresponds to the monoelectronic reduction of this intermediate, forming a detectable semiquinone-type radical species, 17 at more negative potentials (equation 8).…”

Section: Acidity Level Of the Oh Functionality And The Electrochemicamentioning

confidence: 99%

The role of intramolecular hydrogen bonding in the electrochemical behavior of hydroxy-quinones and in semiquinone stability

Frontana¹,

González²

2005

J. Braz. Chem. Soc.

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O estudo de um grupo selecionado de e -hidroxiquinonas ([ ] 2-hidroxi-1,4-naftoquinona 2HNQ, [ ] 5-hidroxi-1,4-naftoquinona 5HNQ and [ , ]5,8-dihidroxi-1,4-naftoquinona DHNQ) mostrou que ambos os tipos de funcionalidades diferem consideravelmente em termos de reatividade eletroquímica e química, e que essas diferenças também se manifestam na comparação de compostos do mesmo grupo. Os resultados provaram que a energia necessária para reduzir eletroquimicamente as hidroxoquinonas estudadas está relacionada com a estabilidade intramolecular das ligações de hidrogênio (IHBs) e com as reações de acoplamento que ocorrem durante a redução eletroquímica, tal como a seqüência de auto-protonação em 2HNQ. A análise da cinética de transferência de elétron associada com a redução monoeletronica que ocorre para 5HNQ e DHNQ mostraram que os efeitos IHB não afetam a cinética do primeiro processo de redução, mas induzem a grandes mudanças na cinética de segunda transferência eletrônica. Isso sugere que as semiquinonas são quimicamente diferentes dos compostos estudados, o que foi comprovado pela análise da estrutura eletrônica das semiquinonas por espectroscopia ESR. Essa análise parece relacionada com a perda de simetria no radical gerado eletronicamente e induz a valores ks de menor velocidade para a segunda redução de transferência de 5HNQ, comparada com DHNQ.The study of a selected group of and -hydroxyquinones ([ ] 2-hydroxy-1,4-naphthoquinone 2HNQ, [ ] 5-hydroxy-1,4-naphthoquinone 5HNQ and [ , ]5,8-dihydroxy-1,4-naphthoquinone DHNQ) showed that both type of functionalities differ considerably in terms of electrochemical and chemical reactivity, and these differences are also manifest even upon comparison between compounds of the same group. The results proved that the energy needed to electrochemically reduce the studied hydroxyquinones is related both to the stability of intramolecular hydrogen bonds (IHBs) and coupled chemical reactions occurring during their electrochemical reduction such as self-protonation sequences in 2HNQ. The analysis of the electron transfer kinetics associated with the monoelectronic reductions occurring for 5HNQ and DHNQ showed that IHB effects do not affect the kinetics of the first reduction process, but induce great changes in the second electron transfer kinetics. This suggests that semiquinone species are chemically different for the studied compounds, as was corroborated by the analysis of the electronic structure of semiquinone species by ESR spectroscopy. This analysis seems to be related to the loss of symmetry in the electrogenerated radical and induces a lower rate ks value for the second reduction transfer of 5HNQ, compared with DHNQ.

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Section: Acidity Level Of the Oh Functionality And The Electrochemicamentioning

confidence: 99%

The role of intramolecular hydrogen bonding in the electrochemical behavior of hydroxy-quinones and in semiquinone stability

Frontana¹,

González²

2005

J. Braz. Chem. Soc.

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“…For this purpose, it is important to recall the similarities in the electrochemical behavior that these compounds present between each other. In the previous Table 1 Data from the voltammetric analysis of the studied a-hydroxyquinones studies [7,17], the analysis of the oxidation signal Ia for 2-hydroxy-1,4-naphthoquinone 1 and Perezone 2, showed that this signal is related to the oxidation of the electrogenerated hydroquinone ((HQ-OH) À or H 2 Q-OH, the products from Eqs. (3) or (4), respectively).…”

Section: Electrochemical Study Of a Series Of A-hydroxyquinonesmentioning

confidence: 98%

“…3. These experiments were performed in a similar way as it was done for 1 and 2 [17], defining the direct pulse at a potential value where reduction process Ic is diffusion limited, and the inverse pulse is set at a potential value in the base of the Ic peak. The low value of the quotient I(2h)/I(h) shows that, at the employed pulse times, the semiquinone species presents a low stability in solution.…”

Section: Electrochemical Study Of a Series Of A-hydroxyquinonesmentioning

confidence: 99%

“…This type of intermediates can be characterized by employing coupled Electrochemical-Electron Spin Resonance (EC-ESR) experiments [17]. As these intermediates are the only stable radical species present during the reduction of a-hydroxyquinones, they are promising candidates for understanding the biological activity of this kind of compounds.…”

Section: Introductionmentioning

confidence: 99%

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Effects of the molecular structure on the electrochemical properties of naturally occurring α-hydroxyquinones. An electrochemical and ESR study

Frontana¹,

González²

2007

Journal of Electroanalytical Chemistry

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“…Nonetheless, non-conducting films are typically formed by a few units of impermeable dimers or oligomers, subsequently producing few electroactive sites [9,10], such as in the dimerization of aniline [11][12][13], phenol [14][15][16] and quinones [17][18][19]. In this letter, we report the successful electrochemical synthesis of a conductive dapsone polymer using cyclic voltammetry in a lower potential window and high scan rates.…”

Section: Introductionmentioning

confidence: 99%

Conductive organic polymers: An electrochemical route for the polymerization of dapsone

Moura

Júnior

Machado

et al. 2015

Journal of Electroanalytical Chemistry

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The electropolymerization of dapsone by anodic oxidation is reported for the first time. The conditions in which a non-conducting oligomeric film or a conductive polymeric film of dapsone is formed are also discussed, based on the scan rate and potential window applied. The cyclic voltammetry of dapsone-polymer presented redox activities that have not been shown before, to the authors' knowledge, demonstrating its high electronic conductivity. The electrochemical impedance response of the dapsone-polymer indicates that their admittance is similar to pure and sulfonated polyanilines, while for the dapsone-oligomers is characteristic of insulating materials. Infrared spectroscopy of both oligomers and polymer supports that the polymerization occurs via amino-amino coupling, since no modifications in the aromatic ring is observed.KEYWORDS. polydapsone, electropolymerization, conductive polymer, Fe +3 /Fe +2 redox couple, polyaniline. Graphical abstract -0.2 0.0 0.2 0.4 0.6 0.8 -50 -40 -30 -20 -10 0 10 20 30 40 GCE GCE/Dapsone-Polymer GCE/Dapsone-Oligomers E / V (vs. Ag/AgCl) Fe +3 /Fe +2 redox couple

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Electrochemical and ESR study on the transformation processes of α-hydroxy-quinones

Cited by 33 publications

References 29 publications

The role of intramolecular hydrogen bonding in the electrochemical behavior of hydroxy-quinones and in semiquinone stability

The role of intramolecular hydrogen bonding in the electrochemical behavior of hydroxy-quinones and in semiquinone stability

Effects of the molecular structure on the electrochemical properties of naturally occurring α-hydroxyquinones. An electrochemical and ESR study

Conductive organic polymers: An electrochemical route for the polymerization of dapsone

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