Diffusion Coefficients of Superoxide Ion in Various Media

Ohsaka, Takeo; Tsushima, Manabu; Okajima, Takaharu; Tokuda, Koichi

doi:10.5796/electrochemistry.62.1300

Cited by 9 publications

(6 citation statements)

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“…The cyclic voltammogram for the redox reaction of the O 2 /O 2 - couple was obtained before each preparative electrolysis of O 2 - to know a sketchy outline of its redox behavior in each medium in comparison with the previous studies. − The cyclic voltammetric experiments were carried out with a computer-controlled electrochemical measuring system (Model CS1090, Cypress System, Inc.), where the working electrode was a GC disk with diameter of 1 mm and the reference and counter electrodes were the same as those used in the above-mentioned preparative electrolysis.…”

Section: Methodsmentioning

confidence: 99%

Water-Induced Disproportionation of Superoxide Ion in Aprotic Solvents

et al. 1996

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The water-induced disproportionation of the electrogenerated superoxide ion (O2 -) in acetonitrile, dimethylformamide, and dimethyl sulfoxide media containing various concentrations of water as a Brønsted acid has been examined by UV−vis spectroscopy. Analysis of the kinetics as a function of O2 - and water concentrations and of the measurement time demonstrated that the disproportionation of O2 - by water in these media obeys a common mechanism: O2 - + H2O ⇄ HO2 • + OH- (k 1, k -1) HO2 • + O2 - → HO2 - + O2 (k 2) (HO2 •, hydroperoxyl radical; HO2 -, hydrogen peroxide anion). The solvent dependence of the obtained kinetic parameters of (k 1/k -1)k 2, k 1 and k -1/k 2 is discussed in terms of the solvation of O2 - and H2O as well as the effective acidities of H2O in different aprotic solvents.

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Section: Methodsmentioning

confidence: 99%

Water-Induced Disproportionation of Superoxide Ion in Aprotic Solvents

et al. 1996

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“…28,29 The diffusion coefficients and saturated concentrations of O 2 in the AMIBF 4 RTILs are also estimated by hydrodynamic chronocoulometry ͑HCC͒. [30][31][32]…”

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confidence: 99%

Electroreduction of Dioxygen in 1-n-Alkyl-3-methylimidazolium Tetrafluoroborate Room-Temperature Ionic Liquids

Zhang

Okajima

Matsumoto

et al. 2004

J. Electrochem. Soc.

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117

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The electrode reaction of the molecular oxygen (O 2 )/superoxide ion (O 2 Ϫ) redox couple at glassy carbon ͑GC͒, gold ͑Au͒, and platinum ͑Pt͒ electrodes in three 1-n-alkyl-3-methylimidazolium tetrafluoroborate (AMIBF 4 ) room-temperature ionic liquids ͑RTILs͒, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-n-propyl-3-methylimidazolium tetrafluoroborate, and 1-n-butyl-3methylimidazolium tetrafluoroborate, has been analyzed quantitatively using cyclic voltammetry, normal pulse voltammetry, and hydrodynamic chronocoulometry ͑HCC͒. Cyclic voltammetric measurements showed that the redox reaction of the O 2 /O 2 Ϫ couple in these RTILs is a quasi-reversible process and that the resulting O 2 Ϫ is stable. The relevant thermodynamic and kinetic parameters ͓the formal potential (E 0 Ј), the standard rate constant (k 0 ), and the cathodic transfer coefficient (␣ c )] of the O 2 /O 2 Ϫ redox couple were evaluated using cyclic and normal pulse voltammetry: ͑i͒ the E 0 Ј values are almost the same irrespective of the media and electrode materials examined, i.e., ca. Ϫ1.0 V vs. an internal standard potential of the ferrocene ͑Fc͒/ferricinium ion (Fc ϩ ) redox couple, ͑ii͒ the k 0 value is dependent on the electrode material and increases in the order k 0 (Pt) Ͻ k 0 (Au) Ͻ k 0 (GC), and ͑iii͒ the values of ␣ c are in the range of 0.35-0.47. The diffusion coefficients (D O 2 ) and saturated concentrations (C O 2 ) of O 2 in three AMIBF 4 RTILs were also determined by HCC.

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“…b From Guiraud and Foote d From Oshaka et al e Parameters relating to the sensitized production of singlet oxygen by perylene: andare the fractions of quenching events producing singlet oxygen from the sensitizer singlet and triplet states, respectively. The parameteris the fraction of singlet quenching events yielding the sensitizer triplet state; f T is the fraction of triplet states quenched by ground-state oxygen,is the triplet yield in the absence of oxygen, andand τ S are the rate constant for the oxygen quenching of and the lifetime of the sensitizer singlet state, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…The respective diffusion coefficients are denoted by D. Note that the diffusion coefficient of superoxide, D SO , is smaller than that of ground-state oxygen, D O , because of stronger solvation by acetonitrile. 37 We have also assumed that the diffusion coefficient for singlet oxygen, D ∆ , is the same as that for groundstate oxygen, D O , despite the fact that the polarizabilities of the respective molecules are slightly different. 38 All relevant parameters are collected in Table 2.…”

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Spatial and Temporal Electrochemical Control of Singlet Oxygen Production and Decay in Photosensitized Experiments

et al. 2008

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Active spatial and temporal modulation of domains of singlet oxygen activity is demonstrated using electrochemical tools. Using singlet oxygen microscopy in photosensitized experiments, it is shown that singlet oxygen concentrations around an ultramicroelectrode can be controlled by applying a bias voltage to the electrode. Two phenomena that can be exploited separately or collectively are examined: (1) the singlet oxygen concentration can be altered by local oxidation or reduction of the photosensitizer, which is the precursor to singlet oxygen, and (2) the reduction of oxygen to produce the superoxide anion which, among other things, is an effective singlet oxygen quencher, results in a local decrease in the concentration of singlet oxygen around the electrode. Both of these phenomena depend significantly on the diffusion of molecules along concentration gradients established by the biased electrode. The results reported herein demonstrate that one can indeed exert local electrochemical control and readily manipulate the population of singlet oxygen produced in a photosensitized process.

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Diffusion Coefficients of Superoxide Ion in Various Media

Cited by 9 publications

References 0 publications

Water-Induced Disproportionation of Superoxide Ion in Aprotic Solvents

Water-Induced Disproportionation of Superoxide Ion in Aprotic Solvents

Electroreduction of Dioxygen in 1-n-Alkyl-3-methylimidazolium Tetrafluoroborate Room-Temperature Ionic Liquids

Spatial and Temporal Electrochemical Control of Singlet Oxygen Production and Decay in Photosensitized Experiments

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