linoleic-acid and chlorobenzene

We re-examined the antioxidative mechanism of allicin as a radical scavenger on the basis of the reactivity toward 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and peroxyl radicals. Initially, it was found that allicin decomposed more rapidly in n-hexane and chlorobenzene than in acetonitrile, ethanol, and ethanol/water solutions and decomposed into ajoene and vinyldithiins in these solvents. Furthermore, the decomposition of allicin and the following formations of ajoene and vinyldithiins from allicin were accelerated by the reaction of allicin with DPPH and peroxyl radicals. These results show that 2-propenesulfenic acid, which arises by Cope elimination from allicin, is proposed to contribute to scavenge these radicals because ajoene and vinyldithiins were produced from allicin through the use of 2-propenesulfenic acid. Next, allicin was more effective at inhibiting the linoleic acid oxidation at 50 °C than at 30 °C and in cyclohexane than in acetonitrile. These results indicate that allicin decomposed rapidly at high temperatures in a hydrogen-bond-acceptor solution to 2-propenesulfenic acid. In addition, 2-propene-1-sulfinothionic acid S-methyl ester, which does not produce sulfenic acid through Cope elimination, has no activity against the radicals. On the other hand, methanesulfinothionic acid S-2-propenyl ester, which produces methanesulfenic acid through Cope elimination, has the same or increased activity as its allicin against the radicals. Based on these results, the Cope elimination product, sulfenic acid, from thiosulfinates with an α-sulfenyl proton was found to make a larger contribution to the radical scavenger than that of allicin itself.. We examined the antioxidant activity of allicin on the oxidation of cumene and linoleic acid in homogeneous solutions. It is obvious from these results that 2-propenesulfenic acid was found to make a larger contribution to the radical scavenger than that of allicin itself.

Topics: Acetonitriles; Antioxidants; Benzene Derivatives; Chlorobenzenes; Disulfides; Ethanol; Hexanes; Linoleic Acid; Oxidation-Reduction; Sulfenic Acids; Sulfinic Acids; Sulfoxides

6-(Ethylthio)-, 6-(ethylseleno)-, and 6-(ethyltelluro)-2,2,4-trimethyl-1,2-dihydroquinoline-three heavier chalcogen analogues of ethoxyquin-were prepared by dilithiation of the corresponding 6-bromodihydroquinoline followed either by treatment with the corresponding diethyl dichalcogenide (sulfur derivative) or by insertion of selenium/tellurium into the carbon-lithium bond, oxidation to a diaryl dichalcogenide, borohydride reduction, and finally alkylation of the resulting areneselenolate/arenetellurolate. Ethoxyquin, its heavier chalcogen analogues, and the corresponding 6-PhS, 6-PhSe, and 6-PhTe derivatives were assayed for both their chain-breaking antioxidative capacity and their ability to catalyze reduction of hydrogen peroxide in the presence of a stoichiometric amount of a thiol reducing agent (thiol peroxidase activity). Ethoxyquin itself turned out to be the best inhibitor of azo-initiated peroxidation of linoleic acid in a water/chlorobenzene two-phase system. In the absence of N-acetylcysteine as a coantioxidant in the aqueous phase, it inhibited peroxidation as efficiently as alpha-tocopherol but with a more than 2-fold longer inhibition time. In the presence of 0.25 mM coantioxidant in the aqueous phase, the inhibition time was further increased by almost a factor of 2. This is probably due to thiol-mediated regeneration of the active antioxidant across the lipid-aqueous interphase. The ethyltelluro analogue 1d of ethoxyquin was a similarly efficient quencher of peroxyl radicals compared to the parent in the two-phase system, but less regenerable. Ethoxyquin was found to inhibit azo-initiated oxidation of styrene in the homogeneous phase (chlorobenzene) almost as efficiently (kinh = (2.0 +/- 0.2) x 106 M-1 s-1) as alpha-tocopherol with a stoichiometric factor n = 2.2 +/- 0.1. At the end of the inhibition period, autoxidation was additionally retarded, probably by ethoxyquin nitroxide formed during the course of peroxidation. The N-H bond dissociation enthalpy of ethoxyquin (81.3 +/- 0.3 kcal/mol) was determined by a radical equilibration method using 2,6-dimethoxyphenol and 2,6-di-tert-butyl-4-methylphenol as equilibration partners. Among the investigated compounds, only the tellurium analogues 1d and, less efficiently, 1g had a capacity to catalyze reduction of hydrogen peroxide in the presence of thiophenol. Therefore, analogue 1d is the only antioxidant which is multifunctional (chain-breaking and preventive) in character and which can a

Topics: Antioxidants; Catalysis; Chemistry, Organic; Chlorobenzenes; Electron Spin Resonance Spectroscopy; Ethoxyquin; Kinetics; Linoleic Acid; Models, Chemical; Reducing Agents; Selenium; Sulfur; Tellurium; Time Factors; Water

The aerobic oxidation kinetics of methyl eicosapentaenoate (20:5n-3) and methyl linoleate (18:2n-6) were compared in homogeneous chlorobenzene solution and in Triton X-100 aqueous micelles at 37 degrees C. The rate of disappearance of 20:5n-3 was two times faster than that of 18:2n-6 in chlorobenzene, while the former was five times slower than the latter in aqueous micelles. It was also observed that delta O2 = delta 18:2n-6 and delta O2 = 2 delta 20:5n-3 in aqueous micelles. In the oxidation of a 1:1 mixture of 20:5n-3 and 18:2n-6 in micelles, the rate of disappearance of 20:5n-3 was 3.6 times faster than that of 18:2n-6, and the rate of total substrate disappearance was reduced by a factor of 5 as compared with 18:2n-6 oxidation. These data suggest that the peroxyl radical derived from 20:5n-3 is more polar than that from 18:2n-6, and the former is likely to diffuse from the core to the micelle surface. This lowers the oxidizability for 20:5n-3 in aqueous micelles by enhancing the termination reaction rate for peroxyl radicals and by reducing the rate of propagation since there may be more 20:5n-3 peroxyl radicals at the surface than in the micelle core.

Topics: Amidines; Azo Compounds; Chlorobenzenes; Eicosapentaenoic Acid; Esters; Fatty Acids, Unsaturated; Kinetics; Linoleic Acid; Linoleic Acids; Micelles; Models, Chemical; Nitriles; Octoxynol; Oxidation-Reduction; Peroxides