Investigation of the anthracene-nitroxide hybrid molecule as a probe for hydroxyl radicals.

A new method for the determination of hydroxyl radicals is proposed. The method is based on the use of a hybrid molecule consisting of a fluorescent chromophore, anthracene, and a nitroxide radical. In the hybrid molecule, the nitroxide quenches the fluorescence of anthracene strongly. The reaction of hydroxyl radicals with dimethyl sulfoxide generates quantitatively methyl radicals, which then combine with the nitroxide moiety of the hybrid molecules to result in an increase in the fluorescence intensity. The fluorescence increase is proportional to the concentration of hydroxyl radicals. The proposed method is capable of detecting hydroxyl radicals generated in the Fenton system. It is a simple and sensitive technique for the determination of hydroxyl radicals.     

Evidence for hydroxyl radical generation during lipid (linoleate) peroxidation

The autoxidation of methyl linoleate in benzene at 37 degrees C by peroxyl radicals was found to generate hydroxyl radicals (.OH) from a secondary oxidation mechanism. The yield of hydroxyl radicals (approximately 2%) was determined by trapping these reactive radicals with benzene to give phenol. We propose that alphaC-H hydrogen abstraction from lipid hydroperoxides, the main autoxidation products, is the source of hydroxyl radicals.     

The roles of hydroxyl radicals, photo-generated holes and oxygen in the photocatalytic degradation of humic acid

This article is aimed at studying on the roles of the hydroxyl radicals, photo-generated holes, and oxygen in the photocatalytic degradation of humic acid (HA) in acid and alkaline conditions. The results indicate that hydroxyl radicals?? scavenger alone can inhibit the photocatalytic degradation process completely in alkaline condition, which implies that photo-generated holes cannot directly degrade the organic matter in alkaline condition. Moreover, the reaction sites between hydroxyl radicals and HA is on the TiO₂ surface in acid condition. But in alkaline condition, hydroxyl radicals diffuse and react with HA in the solution. The generation of hydroxyl radicals almost stops and the photocatalytic degradation is inhibited seriously without oxygen, which illustrates that oxygen plays an important role in the photocatalytic degradation of HA.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS–XII. SPIN TRAPPING STUDY OF THE FREE RADICALS GENERATED DURING THE PHOTOLYSIS OF PHOTO ALLERGENS BITHIONOL and FENTICHLOR

Free radicals were trapped and observed by ESR when photoallergens bithionol and fentichlor were irradiated in the presence of spin traps N- t -butyl-α-phenylnitrone (PBN) and 5,5-dimethyl-pyrroline-N-oxide (DMPO). In the absence of air, both PBN and DMPO trapped a carbon-centered radical. The carbon-centered radical, which was capable of abstracting a hydrogen atom from cysteine, glutathione, ethanol and formate, was identified as an aryl radical derived from the homolytic cleavage of the carbon-chlorine bond. In the presence of air, both carbon-centered radicals and hydroxyl radicals were trapped by DMPO. Under similar conditions, the yield of the hydroxyl radicals was greater from bithionol than from fentichlor. The presence of the hydroxyl radical was confirmed by kinetic experiments employing hydroxyl radical scavengers (ethanol, formate). Superoxide and H₂O₂ were not involved. Experiments with oxygen-¹⁷O indicated that the hydroxyl radicals came exclusively from dissolved oxygen. The precursor of the hydroxyl radical is postulated to be a peroxy intermediate (ArOO*) derived from the reaction of an aryl radical (Ar*) with molecular oxygen. Both bithionol and fentichlor photoionized only when excited in the UVC (<270 nm) region. Free radicals have long been postulated in the photodechlorination of bithionol and fentichlor and the present study provides supporting evidence for such a mechanism. Aryl and hydroxyl radicals are reactive chemical species which may trigger a series of events that culminate in photoallergy.     

THE GENERATION OF HYDROXYL RADICALS IN BIOLOGIC SYSTEMS: TOXICOLOGICAL ASPECTS

Abstract— The formation of hydroxyl radicals in vitro was studied through their reaction with 2-keto-4-thiomethylbutyric acid to form ethylene gas. The autoxidation reaction of 6-aminodopamine served as a model source of hydroxyl radicals. Ethylene production was suppressed by catalase and by superoxide dismutase, indicating that both hydrogen peroxide and superoxide were involved in the reaction. Hydroxyl radical scavengers (thiourea > benzoate > ethanol) suppressed ethylene production in good agreement with their respective rate constants for reaction with hydroxyl radicals. Urea served as a negative control. Several substituted thiourea derivatives also suppressed ethylene production to a similar degree as thiourea itself. Biologic studies centered on several cytotoxic agents whose mechanisms of action are thought to involve hydroxyl radicals. These agents included alloxan, which destroys the beta cells of the pancreas, and 6-hydroxy- and 6-aminodopamine, which destroy sympathetic nerves. Damage to tissues in vivo was blocked to varying degrees by pretreatment of animals with hydroxyl radical scavengers such as ethanol or the thiourea derivatives. In addition, hydroxyl radical scavengers blocked the action of 5,7-dihydroxytryptamine, a neurotoxin whose effects on noradrenaline neurons were previously shown to be blocked by inhibitors of monoamine oxidase. The data indicate that these cell toxins produce their damaging actions on specific target cells through the intracellular generation of hydroxyl radicals.     

PHOTOINDUCED GENERATION OF HYDROGEN PEROXIDE AND HYDROXYL RADICALS IN MELANINS

The hydrogen peroxide produced during photolysis of melanin pigments has been measured using an oxidase electrode. The photooxidation has been shown to occur via the superoxide intermediate. In the presence of superoxide dismutase the rate of photo-induced production of hydrogen peroxide is increased, reflecting the ability of melanin to scavenge superoxide radicals. Evidence for metal-ion dependent formation of hydroxyl radicals during photooxidation of melanin pigments was obtained using electron spin resonance-spin trapping procedures. Superoxide dismutase increased the rate of formation of hydroxyl radicals in the system. Mechanisms of metal ion-induced production of hydroxyl radicals during photolysis of melanin pigments are discussed.     

水杨基荧光酮荧光法测定钴(Ⅱ)-过氧化氢体系产生 的羟自由基

本实验发现Co     

萃取-催化氧化光度法测定H2O2的羟基自由基 (Ⅱ)

利用混合稀土与微量过氧化氢催化氧化二苯基碳酰肼，建立了萃取－催化氧化光度法测定过氧化氢的羟基自由基的新方法，该法具有仪器简单，体系稳定，操作方便等优点，非常适合于筛选羟基消除剂。     

一种表征羟基自由基的新型荧光探针

表征羟基自由基 (· OH)的方法主要有电子自旋共振法[1] 和芳环羟基化法[2 ,3] 两大类 .电子自旋共振法灵敏度不高 ,且仪器设备昂贵 ,不适于常规分析 .芳环羟基化法操作较简单 ,灵敏度高 ,但芳环羟基化的产物往往不止一种 ,使得定量测定变得复杂 .其它方法如高效液相色谱法[4 ] ,化学发光法[5] 等也有报道 .顺磁性氮氧化合物能有效地清除自由基 [6 ,7] ,同时也是一种芳烃单重激发态的有效猝灭剂 [8,9] .当顺磁性氮氧化合物与荧光分子共价结合 ,所形成的荧光分子 -氮氧自由基复合物 (即自旋标记荧光分子 )仍保留对自由基反应的活性 ,但由于…     

Mechanism of hydroxyl radical induced antimalarial action of hybrid analogues of 10-dihydroartemisinin

Kinetic schemes of intramolecular oxidation were constructed for ten hybrid analogues of 10-dihydroartemisinin with heteroatom-containing substituents (N, F, Cl). All steps of the kinetic scheme were characterized by the enthalpy of the reaction. The activation energies and rate constants were calculated using the intersecting parabolas model. During intramolecular oxidation of the model compounds, free radicals are generated, and the key role belongs to hydroxyl radicals. The kinetic method was developed, which provides the possibility to differentiate the therapeutic effect of hybrid compounds induced by the hydroxyl radicals alone from that induced in addition by the presence of substituents. Some compounds showed therapeutic effect which exceeds the effect caused by generation of the hydroxyl radicals alone. Several compounds bear substituents, which decrease the action induced by generation of the hydroxyl radicals. Substituents were identified, which made additional contribution to the therapeutic effect of the substance, thus providing the complex action.     

硒化合物对羟基自由基作用的研究

本文选用硒代蛋氨酸(Se-Met)和无机硒化合物,采用自旋捕集技术,在温和条件下进行硒化合物与羟基自由基作用的ESR研究。实验结果表明,硒化合物对羟基自由基具有清除作用。     

羟基自由基的流动注射荧光法测定

本文研究Fenton反应产生的·OH与Ce3+作用后Ce3+被氧化生成无荧光的Ce4+,通过测定Ce3+的荧光强度的下降可间接测定所产生的羟自由基,并结合流动注射技术,确定了体系最佳实验条件。同时测定抗氧化剂清除羟自由基的实验证明,该体系可作为在线筛选抗氧化剂以及在线测定羟自由基的方法。     

Hydrogen radical and hydroxyl radical hydrogen abstraction reaction from formyl fluoride studied with hybrid density functional theory methods

With the goal of reducing flame velocity in combustion reactions, this study focused on the conversion of hydrogen and hydroxyl radicals into relatively unreactive hydrogen and water molecules through the inter-conversion of formyl fluoride to fluoroformyl radicals. Hybrid DFT computational methods were employed to confirm these results. Based on this, the fluoroformyl radical-assisted transformation of the hydrogen and hydroxyl radicals into hydrogen and water molecules was discussed.     

利用电子自旋共振(ESR)技术研究啤酒原辅料自由基及其对麦汁自由基的影响

利用电子自旋共振(ESR)技术研究了啤酒生产原辅料固有自由基含量,发现麦芽自由基量最多,大麦其次,大米中未测到;且自由基存在于皮壳中.全麦麦汁和30%大米辅料麦液都含有羟基自由基和FR1.随糖化进行,羟基自由基上升,FR1下降;但全麦麦汁羟基出现较早,且糖化终了含量较高.     

Hydroxyl radicals electrochemically generated in situ on a boron-doped diamond electrode

The hydroxyl radicals electrochemically generated in situ on a boron-doped diamond (BDD) electrode have been investigated for the first time in different electrolyte media, over the whole pH range between 1 and 11. A more extensive characterisation of BDD electrochemical properties is very important to understand the reactivity of organic compounds towards electrochemical oxidation on the BDD electrode, which is related to their interaction with adsorbed hydroxyl radicals due to water oxidation on the electrode surface. An oxidation peak corresponding to the transfer of one electron and one proton was observed in pH <9 electrolytes, associated with the water discharge process and electrochemical generation of hydroxyl radicals, which can interact and enhance the electro-oxidation of organic compounds. In pH >9 electrolytes the electrochemical generation of hydroxyl radicals was not observed; ammonia buffer electrolyte gave a pH-independent peak corresponding to the ammonia oxidation reaction. Additionally, for most pH values studied, a few small peaks associated with the electrochemical interaction between non-diamond carbon species on the doped diamond electrode surface and the electrolyte were also seen, which suggests that the doped diamond is relatively unreactive, but not completely inert, and the electrogenerated hydroxyl radicals play a role as mediator in the oxidation of organics.     

3-氨基-7,8-二甲氧基香豆素及其衍生物的合成及抗氧化活性

合成了3-氨基-7,8-二甲氧基香豆素及其衍生物共11个化合物,其中3个化合物(2b、2d、2e)为新型香豆素芳酰胺类化合物。 通过猝灭1,1-二苯基-2-三硝基苯肼(DPPH)、2,2'-联氮二(3-乙基苯并噻唑-6-磺酸)二铵盐阳离子自由基(ABTS^+·)和羟自由基实验考察了所合成化合物的抗氧化活性,结果表明化合物2b对DPPH自由基、羟自由基的清除能力超出或接近对照品维生素C,而衍生物2a、2b和2c的抗氧化活性优于母体。 故酰化可提高3-氨基-7,8-二甲氧基香豆素的抗氧化性能,尤其是普遍提高了羟基自由基的清除能力。     

HEMOLYSIS OF HUMAN ERYTHROCYTES BY ACTIVATED OXYGEN SPECIES

Abstract— The hemolysis of human erythrocytes by irradiation at 254 nm has been studied. Neither superoxide radicals nor singlet oxygen play a significant rôle and it is likely that the major species involved are hydroxyl radicals and, indirectly, carbonate anion or formate radicals. Similarly, when erythrocytes are treated with a system commonly used as source of superoxide radicals (photoreduction of riboflavin) it has been demonstrated that O^-₂ does not participate in lysis, but that singlet oxygen (possibly with hydroxyl radicals) is a major oxygen species involved in destruction of the cell membrane.     

明日叶黄酮类化合物清除羟基自由基活性研究

为了研究明日叶黄酮类化合物对羟基自由基的清除作用,以明日叶（主要取叶片）为原料,用体积分数为65％乙醇提取明日叶总黄酮,测定其总黄酮含量.通过Fenton反应体系产生羟基自由基,利用明日叶提取液中的功能成分黄酮类化合物对羟基自由基的清除作用进行研究.结果表明：明日叶提取物总黄酮质量分数为10.18％,且黄酮类化合物对羟基自由基有较强清除效力,当提取物总黄酮浓度在0.1～1.0 mg/mL范围内,其与清除率呈正相关.明日叶中黄酮类化合物对羟基自由基有较强清除效力,作为天然抗氧化产品开发具有一定价值.     

Mechanisms of photocatalytic remote oxidation

The mechanisms of photocatalytic remote oxidation have been elucidated. Hydrogen peroxide, generated on a photocatalyst (TiO2, Pt-TiO2, or Ag-TiO2), is transported in air and then photocleaved into hydroxyl radicals by UV light in the vicinity of a substrate, and the hydroxyl radicals attack the substrate.     

PHOTOSENSITIZED DEGRADATION OF DNA BY DAUNOMYCIN

Abstract Visible irradiation of DNA-daunomycin solutions resulted in a decrease of viscosity of the DNA and an increase of the rate of denaturation of DNA in formaldehyde. These changes are consistent with the induction of single-strand breaks in the DNA, some of which pair to cause fragmentation of the DNA. The DNA damage increases with drug: nucleotide ratio up to 0.2 and is diminished beyond that range. The damage also increases with ionic strength up to 0.6 M and is diminished above that value. These results suggest that the non-intercalated form of the drug is involved in the photosensitization process. Radicals that are produced accompanying the degradation have been trapped by 5,5-dimeth-yl-l-pyrroline-1-oxide and identified as hydroxyl radicals from their ESR spectrum. The DNA photosensitized damage is completely inhibited when hydroxyl radicals are removed by the spin-trap, suggesting a direct role for the hydroxyl radicals in the DNA photosensitized degradation process. The implications of the photosensitized DNA damage and the production of hydroxyl radicals in this process are discussed with respect to the medical uses and chemotherapeutic role of daunomycin.