- Kinetic study of the quenching reaction of singlet oxygen by carotenoids and food extracts in solution. development of a singlet oxygen absorption capacity (SOAC) assay method
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A kinetic study of the quenching reaction of singlet oxygen ( 1O2) with eight kinds of carotenoids and α-tocopherol was performed in ethanol/chloroform/D2O (50:50:1, v/v/v) solution at 35 °C. The overall rate constants, kQ (= kq + kr, physical quenching + chemical reaction), for the reaction of carotenoids with 1O2 were measured, using the competition reaction method, where endoperoxide was used as a singlet oxygen generator, 2,5-diphenyl-3,4-benzofuran (DPBF) as an UV-vis absorption prove, and α-tocopherol as a standard compound. The rate constants, kQ (S) and kQ (t1/2), were determined by analyzing the first-order rate constant (S) and the half-life (t1/2) of the decay curve of DPBF with carotenoids, respectively, showing good accordance with each other. Similar measurements were performed for tomato and carrot extracts. From the results, a new assay method that can quantify the singlet oxygen absorption capacity (SOAC) of antioxidants, including carotenoids, α-tocopherol, and vegetable extracts, has been proposed.
- Ouchi, Aya,Aizawa, Koichi,Iwasaki, Yuko,Inakuma, Takahiro,Terao, Junji,Nagaoka, Shin-Ichi,Mukai, Kazuo
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- Kinetic study of the quenching reaction of singlet oxygen by flavonoids in ethanol solution
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The quenching rate of singlet oxygen (1O2) by seven kinds of flavonoids (flavone, flavonol, chrysin, apigenin, rutin, quercetin, and myricetin) with 2,3-double bonds has been measured spectrophotometrically in ethanol at 35°C. The overall rate constants kQ (=kq + kt, physical quenching + chemical reaction) increased as the number of OH groups substituted to the flavone skeleton (that is, the total electron-donating capacity of flavonoids) increases. The existence of catechol or pyrogallol structure in the B-ring is essential for the 1O 2 quenching of flavonoids. Log kQ was found to correlate with their peak oxidation potentials, EP; the flavonoids that have smaller EP values show higher reactivities. Similarly, log k Q values of flavonoids correlate with the energy level of the highest occupied molecular orbital (EHOMO), calculated by the PM3 MO method, and the longest wavelength ππ* excitation energy (Eex). The contribution of the chemical reaction (kr) was found to be negligible in these flavonoids. The kQ values of rutin, quercetin, and myricetin [(1.21-5.12) × 108 M-1 s-1] were found to be larger than those of lipids [(0.9-6.4) × 104 M-1 s-1], amino acids (7 M-1 s-1), and DNA (5.1 × 105 M -1s-1). The result suggests that these flavonoids may contribute to the protection of oxidative damage in foods and plants, by quenching 1O2.
- Nagai, Souichi,Ohara, Keishi,Mukai, Kazuo
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- Naphthalenes as water-soluble singlet oxygen carriers and detectors: Hydrophobic and kinetic properties
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The syntheses of endoperoxides of naphthalene derivatives with propionic acid and ethanesulfonic acid side chains are described. The partition coefficients and half-lives for the thermal decomposition in phosphate buffer of all compounds have been determined. Because of their high stability in phosphate buffer at 37°C, 3,3'-(4-Methyl-1,3-naphthylene)dipropionic acid and its corresponding methyl ester may be used as chemical traps for the detection of 1O2 in biological systems.
- Muller,Ziereis
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p. 219 - 223
(2007/10/02)
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- Formation of Superoxide Ion via One-Electron Transfer from Electron Donors to Singlet Oxygen
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The formation of superoxide ion (O2-.) via one-electron transfer from substituted N,N-dimethylanilines to singlet oxygen (1O2) was examined in phosphate buffer by employing a water-soluble oxygen source and a combination of p-nitrotetrazolium blue (NBT) and superoxide dismutase (SOD) as a detecting reagent for O2-..When a solution of an electron-donor-substituted N,N-dimethylaniline, NBT, and 3-(1,4-epidioxy-4-methyl-1,4-dihydro-1-naphthyl)propionic acid in phosphate buffer at pH 7.5 was incubated at 35 deg C, NBT was reduced to formazan.The inhibition of the reduction of NBT to formazan by SOD indicated the formation of O2-..Control experiments demonstrated that O2-. is produced by a direct reaction between 1O2 and the amine.Both the yield of O2-. and the quenching rate constants of 1O2 are well correlated with the oxidation potentials of these amines.Tetramethyl-p-phenylenediamine having a quenching rate constant close to a diffusion-controlled limit is the most effective for the generation of O2-. A plot of the log of the quenching rate constant of 1O2 by the amines against the calculated free-energy change (ΔG) for full electron transfer showed a linear relationship with a slope of -0.19 +/- 0.05 mol/kcal.The correlation of the log of the relative yield of O2-. against ΔG strongly supports the electron-transfer mechanism for the formation of O2-..It was demonstrated that an electron-transfer reaction giving rise to O2-. is only possible for aromatic amines with oxidation potentials less than ca. 0.5 V vs.SCE in aqueous media.
- Saito, Isao,Matsuura, Teruo,Inoue, Kenzo
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p. 3200 - 3206
(2007/10/02)
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