某些还原性生物分子对竹红菌甲素敏化产生^1O~2的抑制作用

存在还原性的生物分子如甲硫氨酸、尿酸和 还原性谷胱甘肽时,竹红菌甲素经受单电子还原形成甲素的半醌自由基、在去氧溶液中观察到了 甲素半醌负离子自由基的ESR信号.在充氧的溶液中检测到了超氧负离子自由基.还原剂的存在降低了单重态氧的生成并引起超氧负离子自由基的生成.     

某些还原性生物分子对竹红菌甲素敏化产生^1O~2的抑制作用

存在还原性的生物分手如甲硫氨酸、尿酸和还原性谷胱甘肽时,竹红菌甲素经受单电子还原形成甲素的半醌自由基、在去氧溶液中观察到了甲素半醌负离子自由基的ESR信号.在充氧的溶液中检测到了超氧负离子自由基.还原剂的存在降低了单重态氧的生成并引起了超氧负离子自由基的生成.     

ESR方法检测竹红菌素的半醌负离子自由基

从顺磁共振波谱检测到通过竹红菌素的光诱导还原和基态竹红菌素跟脂肪胺的电子转移两条途径所得到的自由基信号, 并由电化学还原得到同一自由基, 确认它为半醌负离子自由基。竹红菌素溶液中加入芳香胺观察不到ESR信号。它的3,10位上与醌基相邻近的羟基离解以后, 无论在基态还是在激发态都观察不到ESR信号。此外, 还从吸收光谱观察到半醌负离子自由基吸收以及竹红菌素跟脂肪胺之间的相互作用。     

ESR方法检测竹红菌素的半醌负离子自由基

从顺磁共振波谱检测到通过竹红菌素的光诱导还原和基态竹红菌素跟脂肪胺的电子转移两条途径所得到的自由基信号,并由电化学还原得到同一自由基,确认它为半醌负离子自由基。竹红菌素溶液中加入芳香胺观察不到ESR信号。它的3,10位上与醌基相邻近的羟基离解以后,无论在基态还是在激发态都观察不到ESR信号。此外,还从吸收光谱观察到半醌负离子自由基吸收以及竹红菌素跟脂肪胺之间的相互作用。     

醌类化合物在苯酚羟化反应中的电子传递作用

Fenton试剂是某些烃类化合物的有效氧化剂^[1],该体系对芳香化合物具有羟化作用。我们^[2]曾报道了含Cu类钙钛石型复合氧化物在苯酚烃化反应中的催化活性,并提出了相应的反应机理。高价态的过渡金属离子如C^3 [2]和Fe^3 [3]通常被认为是中间自由基的氧化剂。实际上,醌类化合物及其还原形式半醌、氢醌与生物体内许多电子转移过程密切相关^[4],如泛醌或辅酶Q在生物体呼吸链电子传递过程中起重要作用^[5]。在实验中我们观察到苯酚羟化反应中不仅有苯醌生成,而且生成的苯醌还能促进羟化反应。本文报道了醌类化合物在苯酚羟化循环中的传递电子作用。     

竹红菌甲素半醌自由基的变化特点

通过研究竹红菌甲素半醌负离子自由基衰减的动力学,建立了甲素半醌自由基在624nm的可见吸收强度和ESR信号强度的平行关系.在624nm的可见吸收属于甲素半醌自由基的吸收.这个研究结果对研究甲素的半醌自由基具有实用意义.讨论了还原型谷胱甘肽存在下光诱导所产生的甲素 半醒自由基的衰变特点.     

漆酶/O2体系获取半醌自由基的研究

本文综述了在静态条件下用漆酶／O2体系获取高稳定浓度半醌自由基阴离子的有效办法。依据漆酶的单电子转移特性,分别采用强吸电子基团使未偶电子离域以稳定半醌自由基、适当的有机溶剂延缓半醌自由基衰减和ESR自旋稳定化技术三种途径。     

大黄酚光敏化产生自由基和单重态氧

应用电子自旋共振技术研究由中草药大黄中分离纯化的大黄酚光敏化活性. 在氮气饱和的二甲基亚砜中, 用波长大于430 nm 可见光照射大黄酚产生半醌负离子自由基, 且随着还原型辅酶的加入而增强, 表明自由基来源于光敏剂的基态和激发态之间发生了电子转移. 在空气饱和的二甲基亚砜中, 产生可以被DMPO捕获的超氧负离子自由基, 实验证明该自由基不是由单重氧产生, 并与DMPO、大黄酚、氧气和照射时间有关. 光照大黄酚也能产生单重态氧、羟基自由基. 从而说明大黄酚的光敏机制包含电子转移的Ⅰ型机制(Type I)和能量转移的Ⅱ型机制 (TypeⅡ). 作为光敏化活性评价, 测量得到大黄酚、大黄素、大黄的蒽醌混合物产生超氧负离子自由基的相对产率分别为1.8, 1.1, 1.0, 单重态氧的相对产率分别是0.36, 0.53, 0.14. 因此, 这种短波长吸收的光敏剂有可能在光动力医疗微血管类疾病有潜在的应用前景; 同时大黄中初提的蒽醌衍生物的混合物有可能作为一种廉价的光活化农药.     

醌型木素模型物的光学特性

为探索醌型木素化学结构与颜色的关系,以五种醌型木素模型物2-甲氧基-1,4-苯醌(I)、1,2-苯醌(II)、4-亚烯丙基-2-甲氧基-2,5-环己二烯酮(亚甲基醌)(III)、5-甲氧基-1,4-苯醌-2-氧负离子(IV)和5-甲基-1,4-苯醌-2-氧负离子(V)作为纸浆中醌型木素发色体的代表,在B3LYP/6-311++G(2d,p)水平上获得了它们在乙醇中的稳定基态构型,采用含时密度泛函理论(TD-DFT)在同等水平上计算了其在乙醇溶液中的电子光谱,并分析了它们在可见光范围内的吸收.结果发现:五种模型物在可见光范围内的吸收均源于电子的π→π*跃迁,它们的最大吸收波长顺序依次为IIIIIIIVV,吸光系数顺序依次为IVIVIIIII;漂白过程中生成的醌氧负离子以及邻醌类模型物具有中等大小的吸光系数(ε=1978-3197),吸收波长较长(445.47-552.36 nm),是漂白后纸浆具有颜色的重要原因.对醌类模型物吸收波长较小(414.91 nm),吸光系数大小为中等(ε=2094),亚甲基醌类模型物虽然吸光系数大(ε=31935),但吸收波长较小(407.90 nm),二者对漂白后纸浆的颜色影响较小.     

一些丹参醌类二萜醌在电子轰击下的裂解反应—关于一种不常见的(M-O)碎片离子的观察

本文对从丹参、大紫丹参及小红参等三种植物中分得的八个二萜邻醌类化合物及它们的四个衍生物进行了质谱研究,阐明了它们在电子轰击下的裂解途径;并在一些羟基取代的丹参醌类化合物的质谱中,观察到一种不常见的(M—O)碎片离子。亚稳测量与高分辨质谱结果表明,氧的消除是通过醌基与邻近羟基间的功能团相互作用而引起的。     

Applications of a simultaneous assay of ascorbic acid, dehydroascorbic acid and ascorbic sulphate in biological materials

A modified spectrophotometric assay for ascorbic acid and its derivatives based on their reaction with 2,4-dinitrophenylhydrazine (DNPH) is described. Using standard ascorbic acid or ascorbic sulphate solutions, together with animal tissue or compound diet extracts, the conditions for ascorbic acid degradation were determined. For the differential measurement of reduced ascorbic acid (AA), dehydroascorbic acid (dAA) and ascorbic sulphate (AS), five series of simultaneous determinations were performed. These included the use of (1) KBrO3 for the hydrolysis of AS, (2) 2,6-dichlorophenolindophenol as an oxidant, (3) DNPH to form a hydrazone derivative with dAA and (4 and 5) two blanks (where ascorbate was degraded) to correct for interfering substances. A variety of vertebrate and invertebrate tissues were examined for their ascorbate content, and the advantages of the modified procedure over currently available assays are discussed. The results suggest that the Artemia cyst is a unique material in which ascorbic sulphate is present in large amounts whereas fish tissues do not contain this form of vitamin C.     

Spectrophotometric determination of ascorbic acid in pharmaceuticals by background correction and flow injection

Background correction has been shown to be an effective and indispensable modification in the spectrophotometric determination of ascorbic acid. The decomposition of ascorbic acid in pharmaceutical samples was carried out by incubation with sodium hydroxide to give products that were insensitive to ultraviolet light. The rapid oxidation in air of ascorbic acid, especially in dilute solutions, was avoided by the use of the flow injection principle for spectrophotometric determination and by employing a carrier stream of an anti-oxidizing nature consisting of 6 micrograms ml(-1) of 2-mercaptoethanol in 0.25% sulphuric acid. The optimized method with a single channel manifold made use of a carrier stream flow rate of 1.1 ml min(-1), an injection volume of 50 microl, a delay coil of 50 cm (0.5 mm i.d.) and detection at 245 nm. The throughput was at least 180 injections h(-1). The proposed flow injection method yielded results for the analysis of 0-20 micrograms ml(-1) of ascorbic acid that were 99-102% (relative standard deviation 0.6% or better) in agreement with those produced by comparable methods involving titration with iodine, chloranil or 2,6-dichlorophenolindophenol [4-(2,6-dichloro-4-hydroxyphenylimino)cyclohexa-2,5-dieno ne], and high-performance liquid chromatography. When the agreement was not good (as low as 14% with respect to the method being compared), this was traced to the presence of substances which are known to interfere in one or other of the methods of comparison.     

用修饰电极导数伏安法同时测定多巴胺和肾上腺素

研究了２,６－吡啶二甲酸在玻碳电极上电化学聚合的实验条件及修饰电极的电化学特性,发现该聚合物膜修饰电极对多巴胺和肾上腺素的电化学氧化有显著的催化作用,而对抗坏血酸等阴离子没有响应。利用在修饰电极上循环伏安阴极过程多巴胺和肾上腺素的峰电位不同,采用阴极化导数伏安法可同时测定多巴胺和肾上腺素。     

Milligram amount determination of thiol groups with ferricyanide. Use of 2,6-dichlorophenolindophenol as titrant

Summary Thiols are reacted at pH 7 with an excess of ferricyanide. The excess of reagent is determined by adding a measured excess of ascorbic acid followed by back titration of ascorbic acid with 2,6-dichlorophenolindophenol. A correction can be made for ascorbic acid, if present with thiols. Tested with dilute solutions of cysteine, glutathione, mercaptoacetic acid and some other water-soluble thiols gave results which are accurate to 0.1%. Glycine, cystine, methionine, etc. do not interfere.

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Zusammenfassung Thiole reagieren bei pH 7 mit überschüssigem Cyanoferrat (III). Der Überschuß läßt sich durch Zusatz einer gemessenen Menge Ascorbinsäure und deren Rücktitration mit 2,6-Dichlorphenolindophenol bestimmen. Ist neben Thiol bereits Ascorbinsäure zugegen, so ist eine entsprechende Korrektur anzubringen. Die Anwendung auf Lösungen von Cystein, Glutathion, Mercaptoessigsäure und einigen anderen wasserlöslichen Thiolen erbrachte auf 0,1% genaue Ergebnisse. Glycin, Cystin, Methionin usw. stören nicht.

     

Analytical applications of the determination of hexacyanoferrate(III) with ascorbic acid: Part IV. Determination of hydroxylamine

Hydroxylamine can be determined by reaction with an excess of standard potassium hexacyanoferrate(III) solution at pH 8–10. After 30 min the excess is titrated with ascorbic acid solution in the presence of 2,6-dichlorophenolindophenol indicator.     

Test determination of reducing agents using noncovalently immobilized quinonimine indicators

The noncovalent immobilization of indophenols (2,6-dichloroindophenol and 2,6-dibromoin-doguaiacol) and indamines (Variamine Blue and Bindshendler’s Green) on reversed-phase silica gels and ion exchangers was studied. It was shown that the properties of indicator powders can be improved by the double modification of reversed-phase silica gels with cetyltrimethylammonium chloride and 2,6-dichloroindophenol or with dodecyl sodium sulfate and Bindshlender’s Green. Ionization constants and formal redox potentials of the noncovalently immobilized quinonimine compounds were determined by solid-phase spectrophotometry. Indicator tubes and indicator powders were proposed for the test determination of 0.3–1000 mg/L ascorbic acid and 0.02–3.0 mg/L iron(II)     

Comparative kinetic study for rate constant determination of the reaction of ascorbic acid with 2,6-dichlorophenolindophenol

The rate constant k of the reaction of ascorbic acid with 2,6-dichlorophenolindophenol (DCPI) in oxalic acid solutions is determined, by stopped-flow techniques. Four different methods are used to evaluate the results. The values and errors are compared statistically. The average of the rate constant is 56.5 x 10(3) l. mole(-1), sec(-1) and the overall standard deviation is 0.6 x 10(3) l. mole(-1), sec(-1) or 1.0% relative. The pH-dependence of the rate constant suggests that DCPI reacts with undissociated ascorbic acid.     

Kinetic method for determination of ascorbic acid on flow injection system by using its catalytic effect on the complexation reaction of an ultra sensitive colorimetric reagent of porphyrin with Cu(II)

A kinetic method performed on a flow injection system is described for the determination of ascorbic acid by using its catalytic effect on the complexation reaction of Cu(II) with 5,10,15,20-tetrakis(4-N-trimethyl-aminophenyl)porphyrin. The characteristic spectrum of porphyrin (Soret band), which shows intense absorption around 400 nm (epsilon>2.0 x 10(5) cm(-1)M(-1)), was used first time for determining ascorbic acid. By incorporating the complexation reaction into a flow injection system, ascorbic acid could be determined either over a broad dynamic range of 0.1-1000 microg/ml or at a trace level below 5 ng/ml. Good repeatability was also achieved by testing a working standard of 0.1 microg/ml with 10 injections at a throughput of 35 h(-1), obtaining a relative standard deviation of 0.11%. Substances like amino acids, vitamins, sugars, organic acids and metal ions, showed no or little interference even present at high concentrations. The method was validated in the determination of ascorbic acid contents of some commercially available soft drinks by comparison with the official 2,6-dichloroindophenol method with reasonable agreement.     

Determination of ascorbic acid in soft drinks, preserved fruit juices and pharmaceuticals by flow injection spectrophotometry: Matrix absorbance correction by treatment with sodium hydroxide

Two flow injection systems for the spectrophotometric determination of ascorbic acid at 245 nm have been described. On treatment with sodium hydroxide a fraction of the ascorbic acid was decomposed into substances, which do not absorb in UV region, and the decrease in signal measured. This was directly related to the amount of ascorbic acid present. The calibration graph was linear over the range 1-25 and 1-50 microg/ml in the two methods with a correlation coefficient of 0.9981 and 0.9994, respectively. The detection limit (2sigma) was 0.5 and 0.2 microg/ml, respectively. The RSD for 1 microg/ml standard was 2.5 and 1.8% (n = 6) in the two methods, and the sampling throughput 30/hr. The methods permitted the use of 6 microg/ml of 2-mercaptoethanol as an anti-oxidant and stabilizer for ascorbic acid, which is difficult to handle at its microg/ml level. Upon matrix absorbance correction, spiked samples that are known to contain UV-absorbing substances produced an average recovery of 101% with a RSD of 1.2%. The methods were used for the rapid and simple determination of ascorbic acid in soft drinks, preserved fruit juices and pharmaceuticals and the results thus produced compared with those obtained by previously checked methods involving titration with iodine, chloranil 2,6-dichlorophenolindophenol, and HPLC. When there was a disagreement between the results, this was traced to the presence of substances which are known to interfere in comparison methods.     

Determination of ascorbic acid with o-iodosobenzoate: analysis of mixtures of ascorbic acid with methionine and cysteine or glutathione

Ascorbic acid has been determined in pure solutions, pharmaceutical preparations, food-stuffs and biological fluids by titration with o-iodosobenzoate, with visual or photometric detection of the end-point, with leuco-2,6-dichlorophenolindophenol plus potassium iodide as indicator. Cysteine and glutathione, which interfere quantitatively, are masked by cyanoethylation; the cyanoethylated product and methionine have been determined with o-iodosobenzoate in the presence of acidified potassium bromide, with Methyl Red as indicator. Procedures are given for the analysis of mixtures of ascorbic acid with sulphur-containing amino-acids.