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光泽精与在肾上腺素自氧化体系中(pH=10.20)产生的超氧阴离子自由基反应,其氧化产物在 -1.16 V(vs.SEC)和-1.60V(vs. SEC)处有两个还原峰,其中-1.16 V处的还原峰是光泽精被氧化的中 间产物的双电子还原峰,-1.60V处的还原峰是最终产物 N-甲基吖啶酮(NMA)的双电子还原峰。形成 反应中间体和 NMA的反应是一级反应,其反应速度常数分别为 2.07× 10-4s-1和 2.23 × 10-5s-1。 相似文献
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示波极谱法测定金属铅及铅锌矿浸出渣中微量锑 总被引:5,自引:0,他引:5
在pH2.4的邻苯二酚紫-Se体系中,Sb产生一个灵敏的极谱波,其导数峰电位为-0.28V,线性范围0.008-0.4μg.ml^-1,许多离子不干扰,不用分离和富集,可直接测定金属铅及铅锌矿浸出渣中微量锑。方法具有灵敏,快速,准确的特点。 相似文献
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聚硫堇修饰微带金电极的性质及对NADH的催化氧化 总被引:12,自引:0,他引:12
报道了硫堇在微带金电极上的电化学聚合过程,用红外光谱对聚硫堇进行了表征;研究了聚硫堇的电化学性质,发现聚硫堇在+0.5~-0.7V(vs.SCE)电位范围内有两对氧化还原峰,峰电位分别为:E=-0.03V、E=0.05V,E=-0.24V、E=-0.17V(vs.SCE)。它们的式量电位E~(o')随pH而变化,在弱酸性溶液中,E~(o')/pH为-29mV/pH(25℃);而在弱碱性溶液中则为-56mV/pH。聚硫堇修饰微带金电极对NADH的氧化具有催化作用,文中对电催化过程进行了探讨。 相似文献
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氯代烃光解活泼自由基的ESR研究 总被引:1,自引:0,他引:1
本文用2,4-二硝基苯亚甲基特丁基氮氧化物(DNPBN)作自由基捕捉剂研究了氯代烃光解过程产生的自由基中间体。实验结果表明在汞灯照射下键能较低的多氯代烷烃分子中的碳-氯键极易发生均裂而产生碳中心自由基与活泼的氯原子, 并且后者可被DNPBN捕获, 形成颇为稳定的氮氧自由基加合物[Cl-DNPBN]~·。对多氯代苯,随着取代氯原子数目增多, 加合物[Cl-DNPBN]~·的ESR信号强度也明显增加。此外, DNPBN对氯原子的大量捕捉实验还证明它对氯原子是一种高效的特征捕捉剂。 相似文献
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Abstract The photoallergens bithionol (BT) and fentichlor (FT) generated free radical photoproducts upon UV photolysis which were observable by direct electron spin resonance (ESR). Both the yield and the type of free radical photoproducts were affected by pH, and to some extent, concentration of oxygen and concentrations of the photosensitizers. At pH 8.5, bithionol (0.9 mM) generated a semiquinone type free radical (BI) via a mechanism which probably involves substitution of the 4-chlorine by hydroxyl to form the corresponding hydroquinone followed by oxidation. The photolysis of 4-chlorophenol, 4-chlorocatechol and 2,2'-methylene-bis(4-chlorophenol) also generated the corresponding semiquinone radicals, suggesting that this mechanism is shared by other 4-chlorophenols. At pH 8.5, only photoproduct BI was observed during the irradiation of BT; FT related photoproducts were not observed at this pH. However, at higher pH values (pH 10.7 or pH 12), FT photoproducts were also observed in addition to BI upon prolonged irradiation. Moreover, the yield of BI increased drastically at higher pH. Oxygen did not play any role at pH 10.7, although it enhanced the yield of BI at pH 8.5. At pH 8.5, irradiated fentichlor generated, in roughly equal amounts, a semiquinone radical (Fla) and an unidentified species which contained two inequivalent protons (FII). At higher pH values (pH 10.7 and pH 12), at least four species were observed. All of the species are believed to be semiquinone radicals and two have been unambiguously identified. The yield of FI increased by a factor of 50 as the pH was increased from 8.5 to 12. Oxygen played only a minor role at pH 10.7 and above. However, at pH 8.5, it also enhanced the yield of FI. 相似文献
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Colin F. Chignell B. Kalyanaraman Robert H. Sik Ronald P. Mason 《Photochemistry and photobiology》1981,34(2):147-156
Abstract— The photodecomposition of sulfanilamide, 4-aminobenzoic acid and related analogs in aqueous solution has been studied with the aid of spin traps 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and CH3 NO2 as well as by direct electron spin resonance techniques. The NH2 radical was trapped by DMPO during the photolysis of aqueous solutions of sulfanilamide with a Xe arc lamp. Studies with [15 N1 ]-sulfanilamide indicated that the NH2 radical was generated by homolytic fission of the sulfur-nitrogen bond. Under the same conditions DMPO trapped the H and SO− 3 radicals during photolysis of sulfanic acid. Direct photolysis of sulfanilamide, sulfanilic acid and Na2 SO3 in the absence of any spin trap yielded the SO− 3 radical. Photolysis of 4-aminobenzoic acid at pH 7 gave the H radical which was trapped by DMPO. At low pH values OH and C6 H4 COOH radicals were generated during the photolysis of 4-aminobenzoic acid. No e− aq were trapped by CH3 NO2 when acid (pH 4) and neutral aqueous solutions of sulfanilamide or 4-aminobenzoic acid were photoirradiated. The mechanism of formation of known photoproducts from the free radicals generated by sulfanilamide and 4-aminobenzoic acid during irradiation are discussed. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects. 相似文献
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Fe协同热活化过一硫酸氢钾盐诱导自由基脱除NO的研究 《燃料化学学报》2018,46(12):1520-1527
在气液撞击流反应器中,研究了Fe~(2+)协同热活化过一硫酸氢钾盐诱导自由基脱除模拟烟气中的NO。考察了主要工艺参数(溶液温度、Fe~(2+)浓度、过一硫酸氢钾盐浓度、溶液pH值、NO入口浓度)对NO脱除效率的影响。分析检测了反应产物和自由基。基于不同系统的对比研究、反应产物检测和活性自由基的捕获,揭示了NO脱除过程的机制和反应路径。结果表明,提高溶液温度、Fe~(2+)浓度和过一硫酸氢钾盐浓度均提高了NO的脱除效率,而提高溶液pH值和NO入口浓度均降低了NO的脱除效率。Fe~(2+)和热对活化过一硫酸氢钾盐产生自由基有显著的协同效应。自由基氧化是NO脱除的主要路径,而过一硫酸氢钾盐直接氧化是次要的脱除路径。Fe~(2+)和热的协同活化体系具有比其他体系高得多的NO脱除率。 相似文献
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High-field 285 GHz electron paramagnetic resonance study of indigenous radicals of humic acids 总被引:1,自引:0,他引:1
Christoforidis KC Un S Deligiannakis Y 《The journal of physical chemistry. A》2007,111(46):11860-11866
Humic substances, the largest source of carbon on Earth, contain indigenous stable free radicals that are involved in important biogeochemical environmental processes occurring in soil and water systems. Here, we present the first high-magnetic-field 285GHz electron paramagnetic resonance spectra for humic acids from various geographical origins. All humic acids irrespective of their origin contain two limiting types of indigenous stable radicals, types I and II, with distinct electronic structure. Type I, which prevails at acidic pH 5, is characterized by a g tensor with principal values gIx = 2.0032, gIy = 2.0032, and gIz = 2.0023. Type II, which prevails at alkaline pH 12, is characterized by gIIx = 2.0057, gIIy = 2.0055, and gIIz = 2.0023. The two limiting types are correlated in a unified reversible manner with pH, irrespective of the geographic origin of the HA. Both types of radical centers are consistent with pi-type radicals. They persist not only in liquid solutions but also in humic acid powders. 相似文献
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Bueno C Mikelsons L Maretti L Scaiano JC Aspée A 《Photochemistry and photobiology》2008,84(6):1535-1542
The photophysical properties of the nitroxide prefluorescent probes 4-(3-hydroxy-2-methyl-4-quinolinoyloxy)-2,2,6,6-tetramethyl-piperidin-4-yl) ester free radical (QT) and 2,3,4,6,7,8-hexahydro-quinolizino [1,10,9-gh] coumarin-3-carboxylic acid (1-oxyl-2,2,6,6-tetramethyl-piperidin-4-yl) ester free radical (C343T) were evaluated as a function of pH and solvent properties. The absorbance of QT showed high pH sensitivity. The pKa values for the different ionization forms involved in the acid-base equilibrium of the quinoline chromophore were determined in the ground and excited states. The fluorescence lifetimes of QT, and N-hydroxylamine (QTH) and quinoline methyl ester (QMe) derivatives, showed that the intramolecular quenching efficiency by the nitroxide moiety is independent of the quinoline ionization form. The fluorescence and absorbance of C343T were highly sensitive to solvent polarity in agreement with a charged transfer excited state of the chromophore. However, we noted a decrease in the intramolecular fluorescence quenching efficiency by the nitroxide moiety when changing the polarity of the solvent from hexane to water. This behavior has been attributed to a suppression of an energy transfer mechanism in the nitroxide quenching process in very polar solvents. The results obtained in micelles allow us to propose QT and C343T as sensors for pH and micropolarity, respectively, in addition to their role as monitors for free radicals or hydrogen transfer from phenols. 相似文献
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Reactions of eaq-, H-atom and OH radicals with 3-pyridine methanol (3-PM) and 3-pyridine carboxaldehyde (3-PCA) have been studied at various pHs using pulse radiolysis technique. eaq- was found to be highly reactive with both 3-PM and 3-PCA (k approx. 1010 dm3 mol1 s-1). Semi-reduced species formed in both cases were strongly reducing in nature. In the case of 3-PM, electron addition leads to the formation of pyridinyl radicals whereas in the case of 3-PCA, PyCHOH type radicals are formed. At pH 6.8, H-atom reaction with 3-PCA also gives semi-reduced species (PyCHOH), whereas at pH 1, H-atoms add to the ring. (CH3)2˙COH radicals were found to transfer electron to 3-PCA at all the pH values tested and by making use of changes in the absorption spectra, pKa values of the semi-reduced species were determined to be 4.5 and 10.6. OH radicals were found to undergo addition reaction with 3-PCA, whereas in the case of 3-PM they reacted by H-abstraction as well as addition reaction. By following the yield of methylviologen radical cation formed by electron transfer reaction, it was estimated that approx. 50% of OH radicals react with 3-PM by H-atom abstraction at pH 6.8, giving reducing radicals, whereas at pH 3.2, where 3-PM is in the protonated form, the same is only about 10%. At pH 13, O-˙ radical anions were found to react exclusively by H-atom abstraction. Reaction of SO4-˙ radicals with 3-PCA was found to give a species identical to the one formed by one electron reduction of nicotinic acid at acidic pH values. 相似文献
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Reactions of eaq -, H-atom and OH radicals with 3-pyridine methanol (3-PM) and 3-pyridine carboxaldehyde (3-PCA) have been studied at various pHs using pulse radiolysis technique. eaq - was found to be highly reactive with both 3-PM and 3-PCA (k approx. 1010 dm3 mol 1 s-1). Semi-reduced species formed in both cases were strongly reducing in nature. In the case of 3-PM, electron addition leads to the formation of pyridinyl radicals whereas in the case of 3-PCA, PyCHOH type radicals are formed. At pH 6.8, H-atom reaction with 3-PCA also gives semi-reduced species (PyCHOH), whereas at pH 1, H-atoms add to the ring. (CH3)2 ·COH radicals were found to transfer electron to 3-PCA at all the pH values tested and by making use of changes in the absorption spectra, pK a values of the semi-reduced species were determined to be 4.5 and 10.6. OH radicals were found to undergo addition reaction with 3-PCA, whereas in the case of 3-PM they reacted by H-abstraction as well as addition reaction. By following the yield of methylviologen radical cation formed by electron transfer reaction, it was estimated that approx. 50% of OH radicals react with 3-PM by H-atom abstraction at pH 6.8, giving reducing radicals, whereas at pH 3.2, where 3-PM is in the protonated form, the same is only about 10%. At pH 13, O-· radical anions were found to react exclusively by H-atom abstraction. Reaction of SO4 -· radicals with 3-PCA was found to give a species identical to the one formed by one electron reduction of nicotinic acid at acidic pH values. 相似文献
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机体内果糖的自氧化过程中会产生多种自由基, 并最终转化为羟自由基, 苯甲酸钠可捕获羟自由基生成具有强荧光信号的羟基苯甲酸钠. 本文采用荧光光度法考察了影响果糖自氧化体系的各种因素, 建立了果糖自氧化产生羟自由基体系. 实验结果表明, 在果糖浓度为8.00 mmol/L, CuSO4浓度为20.0 μmol/L, 苯甲酸钠浓度为24.0 mmol/L, pH=7.4, 温度为37℃及反应时间为24 h的条件下, 果糖自氧化体系最终可产生19.27 μmol/L的羟自由基. 抗氧化剂的存在可清除果糖自氧化过程中产生的自由基, 使最终生成的羟自由基的量减少, 从而导致生成的羟基苯甲酸钠减少, 荧光信号减弱, 由此建立了基于果糖自氧化体系的抗氧化剂筛选方法. 利用本评价体系考察了抗氧化剂盐酸小檗碱和阿魏酸的抗氧化能力, 实验结果表明, 中药标准品盐酸小檗碱和阿魏酸均能有效清除果糖自氧化体系产生的羟自由基, 其IC50值分别为0.023和0.036 mmol/L. 相似文献
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Accurate determination of pK(a) values is important for proper characterization of newly synthesized molecules. In this work we have used CZE for determination of pK(a) values of new compounds prepared from intermediates, 2, 3 and 4-(2-chloro-acetylamino)-phenoxyacetic acids, by substituting chloride for 2-oxo-pyrrolidine, 2-oxo-piperidine or 2-oxo-azepane. These substances are expected to have a cognition enhancing activity and free radicals scavenging effect. Measurements were performed in a polyacrylamide-coated fused-silica capillary of 0.075 mm ID using direct UV detection at 254 nm. Three electrolyte systems were used for measurements to eliminate effects of potential interactions between tested compounds and components of the BGE. In the pH range 2.7-5.4, chloride, formate, acetate and phosphate were used as BGE co-ions, and sodium, beta-alanine and epsilon-aminocaproate as counterions. Mobility standards were measured simultaneously with the tested compounds for calculations of correct electrophoretic mobilities. Several approaches for the calculation of the pK(a) values were used. The values of pK(a) were determined by standard point-to-point calculation using Henderson-Hasselbach equation. Mobility and pH data were also evaluated by using nonlinear regression. Three parameter sigmoidal function fitted the experimental data with correlation coefficients higher than 0.99. Results from CZE measurements were compared with spectrophotometric measurements performed in sodium formate buffer solutions and evaluated at wavelength where the highest absorbance difference for varying pH was recorded. The experimental pK(a) values were compared with corresponding values calculated by the SPARC online calculator. Results of all three used methods were in good correlation. 相似文献