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1.
Humic acids (HAs) accept and donate electrons in many biogeochemical redox reactions at oxic/anoxic interfaces. The products of oxidation of reduced HAs by O(2) are unknown but are expected to yield reactive oxygen species, potentially including hydroxyl radical (·OH). To quantify the formation of ·OH upon oxidation of reduced HAs by O(2), three HAs were reduced electrochemically to well-defined redox states and were subsequently oxidized by O(2) in the presence of the ·OH probe terephthalate. The formation of ·OH upon oxidation increased with increasing extent of HA reduction. The yield of ·OH ranged from 42 to 160 mmol per mole of electrons donated by the reduced HA. The intermediacy of hydrogen peroxide (H(2)O(2)) in the formation of ·OH was supported by enhancement of ·OH formation upon addition of exogenous H(2)O(2) sources and by the suppression of ·OH formation upon addition of catalase as a quencher of endogenous H(2)O(2). The formation of ·OH in the dark during oxidation of reduced HA represents a previously unknown source of ·OH formation at oxic/anoxic interfaces and may affect the biogeochemical and pollutant redox dynamics at these interfaces.  相似文献   

2.
Quinones are toxicological substances in inhalable particulate matter (PM). The mechanisms by which quinones cause hazardous effects can be complex. Quinones are highly active redox molecules that can go through a redox cycle with their semiquinone radicals, leading to formation of reactive oxygen species. Electron spin resonance spectra have been reported for semiquinone radicals in PM, indicating the importance of ascorbic acid and iron in quinone redox cycling. However, these findings are insufficient for understanding the toxicity associated with quinone exposure. Herein, we investigated the interactions among anthraquinone (AQ), ascorbic acid, and iron in hydroxyl radical (·OH) generation through the AQ redox cycling process in a physiological buffer. We measured ·OH concentration and analyzed the free radical process. Our results showed that AQ, ascorbic acid, and iron have synergistic effects on ·OH generation in quinone redox cycling; i.e., ascorbyl radical oxidized AQ to semiquinone radical and started the redox cycling, iron accelerated this oxidation and enhanced ·OH generation through Fenton reactions, while ascorbic acid and AQ could help iron to release from quartz surface and enhance its bioavailability. Our findings provide direct evidence for the redox cycling hypothesis about airborne particle surface quinone in lung fluid.  相似文献   

3.
The electrochemical behavior of 2,3-dihydroxybenzoic acid (2,3-DHBA) and the electron-transfer characteristics between Cu(II) and 2,3-DHBA were studied in aqueous solutions using cyclic voltammetry (CV). The overall electrochemical oxidation process of 2,3-DHBA by Cu(II) may be classified as a chemical reaction involving one-electron oxidation of 2,3-DHBA to its semiquinone radical in solution, followed by an electron-transfer reaction involving the oxidation of the semiquinone radical to a quinone at the electrode surface. In the presence of H2O2, oxidation of 2,3-DHBA by Cu(II) is enhanced due to the regeneration of Cu(II) by H2O2 oxidizing Cu(I). The redox cycling between Cu(I)/Cu(II) and H2O2 also produces hydroxyl radicals (OH). Even though the presence of OH may not be detected at the surface of a glassy carbon electrode, production of electroactive dissolved oxygen (O2) suggests the presence of OH. The production of O2 is dependent on Cu(II):H2O2 concentration ratio. At the electrode surface and when the initial Cu(II):H2O2 is less than 1, O2 is produced, suggesting that H2O2 may act as a scavenger for OH; at initial Cu(II):H2O2 > 1, the production of O2 is not favored, and OH will be involved in the oxidation of Cu(I) and the organic ligand. The reaction mechanisms proposed in this study indicate that OH production by chelator-mediated Fenton reactions is favorable under conditions found in the wood cell wall.  相似文献   

4.
Pulse radiolysis with spectrophotometric and conductometric detection was utilized to study the formation and reactions of radicals from benzene and dienes in aqueous solutions. The benzene OH adduct, *C6H6OH, reacts with O2 (k = 3 x 10(8) L mol(-1) s(-1)) in a reversible reaction. The peroxyl radical, HOC6H6O2*, undergoes O2*- elimination, bimolecular decay, and reaction with benzene to initiate a chain reaction, depending on the dose rate, benzene concentration, and pH. The occurrence of the chain reaction is demonstrated in low-dose-rate gamma radiolysis experiments where the consumption of O2 was monitored. 1,4-Cyclohexadiene, 1,4-hexadiene, and 1,4-pentadiene form OH-adducts and undergo H-abstraction by O*- radicals. The OH-adducts react with O2 to form peroxyl radicals. These peroxyl radicals, however, do not undergo unimolecular O2*- elimination but rather decay by second-order processes, which lead to subsequent steps of O2*- elimination.  相似文献   

5.
Iron redox cycling is supposed to be one of the major mechanisms that control the geochemical boundary conditions in the near field of a geologic repository for UO2 spent nuclear fuel. This work investigates the impact of reactions between hydrogen peroxide (H2O2) and iron (Fe2+/Fe3+) on UO2 dissolution. The reaction partners were contacted with UO2 in oxygen-free batch reactor tests. The interaction in absence of UO2 gives a stoichiometric redox reaction of Fe2+ and H2O2 when the reactants are present in equal concentration. Predomination of H202 results in its delayed catalytic decomposition. With UO2 present, its dissolution is controlled by either a slow mechanism (as typical for anoxic environments) or uranium peroxide precipitation, depending strongly on the reactant ratio. Uranium peroxide (UO4 x nH2O, m-studtite), detected on UO2 surfaces after exposure to H2O2, was not found on the surfaces exposed to solutions with stoichometric Fe(II)/ H2O2 ratios. This suggests that H2O2 was deactivated in redox reactions before a formation of UO4 took place. ESR measurements employing the spin trapping technique revealed only the DMPO-OH adduct within the first minutes after the reaction start (high initial concentrations of the OH radical); however, in the case of Fe(II) and H2O2 reacting at 10(-4) mol/L with UO2, dissolved oxygen and Fe2+ concentrations indicate the participation of further Fe intermediates and, therefore, Fenton redox activities.  相似文献   

6.
通过测定石榴籽多酚的还原力,·OH、H2O2、NO2、O2·自由基的清除及其抗氧化活性,为石榴籽多酚的开发利用提供依据。在实验浓度范围内,多酚提取物对·OH、H2O2、NO2。和O2·的清除率分别高达83.93%、29.73%和89.66%和88.17%,并且清除能力随多酚浓度的增加而增强,其清除率与多酚的浓度间有一定的量效关系,说明多酚物质对自由基有较强的清除作用;添加抗氧化剂的试验组POV值均明显低于空白对照组的POV值,说明石榴籽多酚具有对菜籽油的抗氧化作用。  相似文献   

7.
探讨猕猴桃根提取物的体外抗氧化作用.采用DPPH自由基、超氧阴离子、羟基自由基、过氧化氢和还原力的反应体系,测定猕猴桃根提取物的体外抗氧化作用,并用VC进行对照实验.实验条件下,ERHM对DPPH自由基、超氧阴离子(·O2-)、羟基自由基(·OH)、过氧化氢H2O2等均有较强的清除或抑制作用,且显示较好的量效关系,同时具有一定的还原力.其消除DPPH自由基的EC50为8.03 μg/mL,清除超氧阴离子(·O2-)的EC5o为1.28 mg/mL,抑制羟基自由基(·OH)能力可达69.4%,浓度为100 μg/mL时对过氧化氢(H2O2)的清除率为42%.猕猴桃根提取物具有较强的还原力,能有效清除DPPH和超氧阴离子自由基,并抑制羟基自由基的产生.所以,ERHM有效成分具有较为显著的抗氧化作用.  相似文献   

8.
以木糖和甘氨酸为底物,控制不同的物质的量(木糖与甘氨酸物质的量之比分别为1∶0.1、1∶0.2、1∶0.4)进行美拉德反应,制备了三种不同的美拉德反应产物,并通过还原能力、清除H2O2能力、清除羟基自由基(.OH)、清除超氧阴离子自由基(O2-.)、清除亚硝酸根(NO2-)等体系研究了美拉德反应产物的抗氧化性能。结果表明,三种反应产物均具有较强的抗氧化能力,随着反应产物浓度的增加,抗氧化能力增强;三种产物的还原能力和清除O2-.的能力相当;木糖与甘氨酸物质的量之比为1∶0.2的美拉德反应产物清除H2O2、.OH和NO2-的能力要强于物质的量之比为1∶0.1和1∶0.4的反应产物。  相似文献   

9.
用流动注射化学发光法测定苹果多酚的体外抗氧化作用。将苹果多酚提取液加入3种化学发光体系,测量其发光强度,根据系统化学发光被抑制的程度评价苹果多酚对活性氧自由基的清除能力,并以抗坏血酸(VC)为阳性对照。结果表明,苹果多酚对三种活性氧自由基(O2-·、·OH、H2O2)的清除能力远强于VC;对H2O2和·OH的清除能力相当,强于对O2-·的清除能力。结果显示苹果多酚具有很好的抗氧化能力。  相似文献   

10.
鱼鳞胶原蛋白提取及抗氧化活性初探   总被引:2,自引:0,他引:2  
朱伟  张歆  黄山凌子 《食品科技》2012,(10):204-206,210
比较鱼鳞胶原蛋白提取方法,观察其体内外抗氧化作用,为鱼鳞开发利用奠定基础。通过水提法、酸法及酸法与热水提取相结合的方法提取鱼鳞胶原蛋白,体外观察鱼鳞胶原蛋白对超氧阴离子(·O2-)、羟自由基(·OH)的清除作用。体内观察水提法胶原蛋白对小鼠血清、肝脏、大脑中SOD、CAT含量的影响。结果表明:水提法及酸法与热水相结合的方法得到的胶原蛋白提取率明显优于酸法的提取率,3种方法得到的胶原蛋白对·O2-、·OH均具有良好的清除作用,并呈一定的剂量依赖关系;水提法得到的胶原蛋白能明显提高小鼠血清、肝脏、大脑中的SOD、CAT含量。水提法可很好提取鱼鳞胶原蛋白,且得到的胶原蛋白具有显著的抗氧化生物活性。  相似文献   

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