Energetics of the Sequential Electroreduction and Electrooxidation Steps of Benzenoid Hydrocarbons

Kubota, Tanekazu; Kano, Kenji; Uno, Bunji; Konse, Tomonori

doi:10.1246/bcsj.60.3865

Cited by 64 publications

(72 citation statements)

References 45 publications

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“…23 Tetrapropylammonium perchlorate (TPAP) was prepared as described previously, 23 and used as a supporting electrolyte for CH3CN. TPAP was dried well under a high vacuum just before use.…”

Section: Chemicalsmentioning

confidence: 99%

“…The energetics of the electron-transfer steps has been discussed on the basis of molecular orbital theory in previous papers. 23,24 It is well recognized that hydroxylic and carboxylic additives involving hydrogen-bonding or protonating ability cause significant effects in the electrochemistry of AQ in neutral aprotic solvents. Three clearly different types of electrochemical behavior were observed, in association with the acidity of the proton donors, for the voltammograms of AQ with increasing concentrations of hydrogen donors.…”

Section: Cyclic Voltammograms Of Aq In the Presence Of Hydrogen Donorsmentioning

confidence: 99%

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Mechanistic Study on the Electrochemical Reduction of 9,10-Anthraquinone in the Presence of Hydrogen-bond and Proton Donating Additives

et al. 2012

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The electrochemical reduction of 9,10-anthraquinone (AQ) was investigated in CH3CN in both the absence and presence of the hydrogen-bond and proton donating additives, CH3OH, CH(CF3)2OH, phenol, 4-methoxyphenol, 4-cyanophenol, 2,4,6-trichlorophenol, and benzoic acid (BA). Three clearly different types of electrochemical behavior were observed with increasing concentrations of the additives, and were simulated to analyze the reaction mechanisms. Type I was observed for weakly interacting additives, such as CH3OH, characterized by positive shifts of the two well-separated reduction waves, corresponding to the formation of AQ • -and AQ 2-, with no loss of reversibility. The second wave shifted more strongly, and finally merged with the first. These behaviors are explained by the association of AQ 2-with the additives via strong hydrogen-bonding. Type II is attributed to a reduction mechanism involving quantitative formation of strong hydrogen-bonded complexes of AQ 2-with additives, such as CH(CF3)2OH, phenol and 4-methoxyphenol, showing a reversible or quasireversible two-electron reduction wave with increasing concentrations of the additives. The behavior of Type III, observed in the presence of strongly interacting additives, such as 2,4,6-trichlorophenol and BA, is characterized by a voltammogram composed of the 2-electorn cathodic and the broad anodic waves without keeping reversibility, facilitated by proton transfer in the hydrogen-bonded complexes, AQ • --BA and AQ 2--BA. The effects of hydrogen-bonding and protonation on the electrochemistry of AQ have been systematically demonstrated in terms of the potentials and reaction pathways of the various species, which appear in quinone-hydroquinone systems.

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“…23 Tetrapropylammonium perchlorate (TPAP) was prepared as described previously, 23 and used as a supporting electrolyte for CH3CN. TPAP was dried well under a high vacuum just before use.…”

Section: Chemicalsmentioning

confidence: 99%

Section: Cyclic Voltammograms Of Aq In the Presence Of Hydrogen Donorsmentioning

confidence: 99%

Mechanistic Study on the Electrochemical Reduction of 9,10-Anthraquinone in the Presence of Hydrogen-bond and Proton Donating Additives

et al. 2012

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“…The peak separation has turned out to be small with a decrease in v. The average of the peak potentials (-1.66 V vs. SCE) agrees with that obtained by the usual electrochemical cell. 10 These results indicate that the electrode potential is precisely controlled at slow v, especially at a fixed potential. Simultaneous ESR and voltammetric measurements in a linear potential sweep mode (v=10 mV s-') gave results in which the ESR signal intensity of the anion radical increases in parallel to the integrated reduction current.…”

Section: Resultsmentioning

confidence: 79%

“…A cyclic voltammetry at higher v as well as the other electrochemical measurements was performed as described in a previous paper. 10 ESR measurement by means of an electrochemical method Samples were dissolved in suitable solvents containing a supporting electrolyte. For experiments using solvents such as DMF and CH3CN the supporting electrolyte was 0.15 mol dm-3 of TPAP.…”

Section: Instrumentsmentioning

confidence: 99%

In-Situ Electron Spin Resonance and Voltammetric Studies Using an Internal-Flow-Type Electrolysis Cell

et al. 1989

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“…However, the results highly depend on the stabilization energy from organic solvents and electrolytes, especially redox potentials are very sensitive to electrolyte concentrations. 1,2) This mutual dependence sometimes causes problems in understanding the meaning of the potentials.…”

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confidence: 99%

Electrochemical Analysis in a Liposome Suspension Using Lapachol as a Hydrophobic Electro Active Species

Okumura

Wakamatsu

Uno

2014

CHEMICAL & PHARMACEUTICAL BULLETIN

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This study demonstrated that the electro-chemical analysis of hydrophobic quinones can be performed in liposome suspension systems. We prepared and analyzed liposome suspensions containing lapachol, which is a quinone-based anti-tumor activity compound. In this suspension system, a simple one redox couple of lapachol is observed. These results are quite different from those obtained in organic solvents. In addition, the pH dependence of redox behaviors of lapachol could be observed in multilamellar vesicle (MLV) suspension system. This MLV suspension system method may approximate the electrochemical behavior of hydrophobic compounds in aqueous conditions. A benefit of this liposome suspension system for electrochemical analysis is that it enables to observe water-insoluble compounds without using organic solvents.Key words cyclic voltammogram; lapachol; liposome; multilamellar vesicle (MLV) Electrochemical analyses of organic compounds with cyclic voltammetry or pulse voltammetry provide us general information about the redox property of those compounds. Commonly, organic solvents are used for the analysis of organic compounds with an excessive amount of supporting electrolytes such as tetraalkyl ammonium salts. The combination of an organic solvent with an electrolyte enables it to analyze electrochemical behaviors of organic compounds. However, the results highly depend on the stabilization energy from organic solvents and electrolytes, especially redox potentials are very sensitive to electrolyte concentrations.1,2) This mutual dependence sometimes causes problems in understanding the meaning of the potentials.On the other hand, quinones play an important role in biological systems and serve as active sites for quinoenzymes in biological functions. It is presumed that the redox properties of quinones are controlled by hydrogen bonding with surrounding proteins or solvents. As a result, hydrogen-bonding interactions have been the primary focused of most studies. [3][4][5] Most studies are performed using quinone compounds and proton donors in coexistence with organic solvents, so as to increase the solubility. However, it is unclear whether the results of an electrochemical measurement using organic solvents reflect real in vivo behavior.We propose that liposome suspensions might serve as a substitute for organic solvents. Liposomes have been studied as an artificial biomembranes and also play important roles as drug delivery systems. The possibility of liposomal use diverges into many scientific branches. Recently, an interesting study reported that electrochemical measurements were performed using a liposome-modified electrode.6,7) On the basis of these studies, we attempted to perform electrochemical measurements using a liposome suspension in place of organic solvents. Results and DiscussionPreparation of a Liposome Suspension Using a Hydrophobic Electro-Active Compound First, we tried to prepare electro-active liposome suspensions. A chloroform solution containing soy lecithin (200 mg) is taken in a round...

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Energetics of the Sequential Electroreduction and Electrooxidation Steps of Benzenoid Hydrocarbons

Cited by 64 publications

References 45 publications

Mechanistic Study on the Electrochemical Reduction of 9,10-Anthraquinone in the Presence of Hydrogen-bond and Proton Donating Additives

Mechanistic Study on the Electrochemical Reduction of 9,10-Anthraquinone in the Presence of Hydrogen-bond and Proton Donating Additives

In-Situ Electron Spin Resonance and Voltammetric Studies Using an Internal-Flow-Type Electrolysis Cell

Electrochemical Analysis in a Liposome Suspension Using Lapachol as a Hydrophobic Electro Active Species

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