三种野菜提取物对羟基自由基清除率的实验研究

在酸性介质中,以Fe~(2+)-H_2O_2体系产生的羟基自由基迅速氧化罗丹明B溶液使其褪色,利用紫外-可见分光光度法在553 nm处测定其吸光度的变化,可间接测定羟基自由基的生成量,野菜菜叶提取物可以消除溶液中的羟基自由基,从而使溶液的吸光度下降程度减弱,据此建立了一种测定野菜菜叶对羟基自由基的清除率的新方法。实验测定3种常见野菜菜叶水提取物和无水乙醇提取物对自由基的清除率,结果表明野菜菜叶对羟基自由基都有一定的清除,其中水提取中以白蒿菜叶的清除率较强,而以乙醇提取中以苜蓿叶的自由基清除率较强。     

三种野菜提取物对羟基自由基清除率的实验研究

在酸性介质中,以Fe⁽²⁺⁾-H_2O_2体系产生的羟基自由基迅速氧化罗丹明B溶液使其褪色,利用紫外-可见分光光度法在553 nm处测定其吸光度的变化,可间接测定羟基自由基的生成量,野菜菜叶提取物可以消除溶液中的羟基自由基,从而使溶液的吸光度下降程度减弱,据此建立了一种测定野菜菜叶对羟基自由基的清除率的新方法。实验测定3种常见野菜菜叶水提取物和无水乙醇提取物对自由基的清除率,结果表明野菜菜叶对羟基自由基都有一定的清除,其中水提取中以白蒿菜叶的清除率较强,而以乙醇提取中以苜蓿叶的自由基清除率较强。     

分光光度法测定羟基自由基捕获剂的研究进展

主要介绍了分光光度法测·OH用二甲基亚砜(DMSO)、茜素紫、邻二氮菲、水杨酸、亚甲基蓝、细胞色素C和溴邻苯三酚红等捕获剂的适用环境,并评价了其优缺点。     

几种光催化反应体系中羟基自由基表观生成率的实验研究

采用邻二氮啡-Fe(II)(橙红色)分光光度法间接测定了Fenton、UV/Fenton、UV/草酸铁/H2O2、UV/TiO24种体系中在不同条件下.OH的表观生成率,初步探讨了体系中各影响因子的作用机制.结果分析表明:对于Fenton体系、UV/Fenton、UV/草酸铁/H2O2而言,其最佳反应条件为pH=4.0、m(H2O2)/m(Fe)=1/25、铁离子的质量浓度以25 mg/L左右为宜;TiO2光催化体系催化产生的.OH尽管受环境pH的影响相对较小,但在同等条件下.OH的表观生成率最低;4种体系中以UV/草酸铁/H2O2体系中.OH表观生成率最高,而且以线性的规律递增.     

25种中草药对羟基自由基的消除能力评价

羟基自由基是一种活性很高的氧化剂,它会不定性的攻击生物体的重要组织,导致细胞损伤或死亡。本研究用Fenton法作为羟基自由基发生体系,水杨酸作为捕捉剂,利用分光光度法,对三种不同医学活性的中草药的羟基自由基消除能进行了评价。结果表明抗衰老类中药对羟基自由基有很强的消除能力。     

紫外-可见分光光度法测定薇菜中总黄酮含量

目的:采用紫外-可见分光光度法对梵净山地区野生的薇菜中总黄酮进行测定.采用超声振荡以95%的乙醇对其进行提取,通过紫外可见扫描确定最大吸收波长,以芦丁为对照品制定标准曲线,并进行方法回收率实验.结果:最大吸收波长为420nm,测得生薇菜中总黄酮含量为0.500mg /g,RSD为1.07%,生薇菜回收率为96.59%, RSD为0.59%;干薇菜中总黄酮含量为0.300mg /g,RSD为1.40%,干薇菜回收率为99.23%,RSD为1.05%.结论:该方法具有操作方便,测定快捷等优点.     

紫外分光光度法测定2-氨基4,6-二羟基嘧啶的含量

采用紫外分光光度法在 2 6 1纳米波长下 ,测定 2 -氨基 - 4,6 -二羟基嘧啶的含量。该法简单、快速、准确 ,其标准偏差为 0 44 ,变异系数为 0 47% ,回收率为 97 47%～ 10 1 6 %     

分光光度法测定微量硒的研究

研究了利用罗丹明B对硫氰酸盐和硒 (Ⅳ )的结合反应来定量测定微量硒的分光光度法。实验表明 :pH为2 .95时 ,在Se -SCN -BRB三元体系中 ,硒量在 0～ 10 μg/ 2 5mL的范围内符合朗伯比尔定律ε=9.97× 10 4 L/mol·cm ,该法用于饮水、污水、生物样品、微化剂中硒的分析 ,结果满意。     

紫外-可见分光光度法测定噻唑磷含量

建立紫外-可见分光光度法测定噻唑磷含量的方法.溶剂为正己烷,测定波长为213.9 nm,样品质量浓度为36.375 mg/L.采用对照比较法计算含量.噻唑磷在23.92～95.68 mg/L质量浓度范围内呈线性关系线性相关系数为0.9996.精密度实验RSD不超过0.74%,准确性分析表明噻唑磷的回收率在100.21%～101.16%之间.     

Peroxyl and hydroxyl radical scavenging activity of some natural phenolic antioxidants

The autoxidation of linoleic acid dispersed in an aqueous media and the antioxidant effect of hydroxytyrosol, oleuropein, caffeic acid and tyrosol were studied. Linoleic acid autoxidation rate was estimated by the increase of conjugated diene level and by the decrease of linoleic acid content in the samples. The phenolic compounds exhibited an antioxidant activity which increased in the order: tyrosol < caffeic acid < oleuropein < hydroxytyrosol. The analysis of the hydroperoxide isomers pointed out that hydroxytyrosol, oleuropein and caffeic acid at a concentration of 10⁻⁴M inhibited the formation oftrans- trans isomers in the increasing order: caffeic acid < oleuropein < hydroxytyrosol. This inhibition could be related to the ability of phenolic compounds to scavenge peroxyl radical. Tyrosol did not inhibit the formation oftranstrans isomers. Phenolic compounds were degraded as a consequence of their antioxidant activity and their degradation rate was positively correlated to their antioxidant efficacy. These phenolic compounds, at a concentration of 6 × 10⁻³M, also scavenged hydroxyl radical, with an efficiency which increased in the order: tyrosol < hydroxytyrosol < oleuropein < caffeic acid. Polar substituents at the para position, such as in caffeic acid and oleuropein, were correlated with higher hydroxyl radical quenching ability.     

Determination of hydroxyl radical rate constants in a continuous flow system using competition kinetics

It is important to determine reaction kinetics of the hydroxyl radical (OH) with various water pollutants for understanding advanced oxidation processes (AOPs). Hence, a simple competition kinetics in a continuous flow system was employed to determine the second-order rate constants of OH with 14 organic and inorganic solutes selected in this study. In this method, p-nitrosodimethylaniline (PNDA) was specifically employed as a well-known reference probe for OH, which gave a competitive relationship between the PNDA and each solute over OH radicals. PNDA decay with OH radicals obeyed reaction kinetics in a first-order as long as the initial concentrations of H₂O₂ and PNDA were less than 30 μM and 2 μM, respectively. The second-order rate constants of OH radical with 14 solutes obtained in this study were found to be consistent with literature values using pulse radiolysis method.     

A radical scavenging reaction of α-tocopherol with methyl radical

To study a radical scavenging reaction of α-tocopherol, it was reacted with methyl radical in dimethyl sulfoxide. Two main products, a geminal dimethyl cyclohexadienone and methyl ether of α-tocopherol, were obtained and these structures were determined by¹³C nuclear magnetic resonance spectroscopy. The radical methylation data of α-tocopherol suggested that a delocalized radical species would be an intermediate. TMIG-RI No. 3.     

Reaction of dipyridamole with the hydroxyl radical

Dipyridamole [2,6-bis-diethanolamino-4,8-dipiperidinopyrimido-(5,4-d) pyrimidine], a well known platelet aggregation inhibitor, shows powerful hydroxyl radical scavenging activity by inhibiting OH-dependent salicylate and deoxyribose degradation. Steady-state competition kinetics experiments with deoxyribose were carried out to evaluate the second-order rateconstant for the reaction between hydroxyl radical and dipyridamole. OH· radicals were generated either by a Fenton-type reaction or by X-ray irradiation of water solutions. A second-order rate constant k_{(Dipyridamole+OH·)} of 1.72±0.11×10¹⁰M⁻¹ s⁻¹ and of 1.54±0.15×10¹⁰ M⁻¹ s⁻¹ was measured by Fenton chemistry and by radiation chemistry, respectively. Mannitol was used as an internal standard for hydroxyl radicals in steady-state competition experiments with deoxyribose. A rate constant k_{(Mannitol+OH·)} of 1.58±0.13×10⁹ M⁻¹ s⁻¹ and 1.88±0.14×10⁹ M⁻¹ s⁻¹ was measured in the Fenton model and in the water radiolysis system, respectively. Both these rate constants are in good agreement with the published data obtained by the “deoxyribose assay” and by pulse radiolysis.     

三白草提取物对自由基的清除作用研究

考察了三白草乙醇提取物经不同溶剂萃取所得的各部分对1,1-二苯基-2-三硝基苯肼(DPPH)自由基、羟基自由基和超氧自由基的清除能力。以2,6-二叔丁基-4-甲基苯酚(BHT)为参考。结果表明,三白草乙醇提取物经不同溶剂萃取所得的各部分对DPPH自由基、羟基自由基和超氧自由基都具有清除能力,且随着提取物浓度的增加,清除能力逐渐增高;其中乙酸乙酯部分对DPPH自由基、羟基自由基和超氧自由基的清除作用最强。     

双羟基吡喃酮化合物的合成及清除自由基性能

以麦芽酚或乙基麦芽酚为起始原料，经乙酰化、钯碳氢化、羰基α位乙酰氧化和脱乙酰基等4步反应，合成了两种双羟基吡喃酮化合物。利用核磁共振氢谱、碳谱和高分辨质谱对每一步反应产物进了结构表征，优化了合成反应工艺，并通过清除自由基反应对化合物的抗氧化活性进行了测试。结果表明，双羟基吡喃酮化合物对ABTS+?、DPPH?和galvinoxyl?三种自由基清除率分别达到88.9%、83.8%和68.4%，明显高于维生素E和2,6-二叔丁基对甲酚的自由基清除率，表现出优异的抗氧化活性。构效关系研究表明，在吡喃酮结构中引入羟基或增强侧链取代基的给电子能力均能提高化合物清除自由基的能力，为新型抗氧化剂的合成开发提供了参考。     

Kinetic study of a radical scavenging effect of hyaluronic acid

The rate of the scavenging reaction of hyaluronic acid with hydroxyl radicals was investigated by means of competitive reaction with 4-nitrosodimethylaniline. It was found that the reactivity of hyaluronic acid with hydroxyl radicals depends on both the molecular weight and the concentration of hyaluronic acid. These features were accounted for by the characteristic molecular properties of hyaluronic acid in solution.     

新型分子内复合抗氧剂清除自由基的性能

以DPPH?为研究对象,采用紫外-可见光分光光度计研究了新型分子内复合抗氧剂对自由基的清除能力,并与市售抗氧剂1076和BHT进行对比。结果表明,相同条件下,该新型分子内复合抗氧剂清除自由基的能力优于市售抗氧剂1076和BHT;且清除自由基的能力随抗氧剂浓度的增加而增大,随清除反应时间的延长先增大后趋于稳定。清除反应温度对清除能力影响不大,表明该清除反应的反应活化能较低,该清除反应可在室温下快速进行。熔体流变速率和氧化诱导期测得的结果也证实了新型分子内复合抗氧剂的抗氧化能力优于市售抗氧剂BHT和1076。     

Free radical scavenging activity of cellulase‐treated chitosan

Partially N‐acetylated chitosan was hydrolyzed by the cheap, commercially available, and efficient cellulase. The products, with different molecular weight, were comparatively investigated by GPC, FT‐IR, XRD, and NMR. The results show that the decrease of molecular weight led to transformation of crystal structure and increase of water‐solubility, but the chemical structures of residues were not modified. Superoxide anion radical and hydroxyl radical quenching assay were used for the evaluation of free radical scavenging activity of cellulase‐treated chitosan in vitro. Low molecular weight chitosan (LMWC3, M_w 1.7 × 10³) exhibited high scavenging activity against free radical. It scavenged 79.3% superoxide radical at 0.1 mg mL^?1. At 2.0 mg mL^?1, scavenging percentage of initial chitiosan, LMWC1 (M_w 27.3 × 10³), LMWC2 (M_w 5.9 × 10³), and LMWC3 (M_w 1.7 × 10³) against hydroxyl radical was 14.3%, 33.1%, 47.4%, and 65.9%, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

三种黄酮清除自由基活性的研究

为比较黄酮2、3位单双键不同及3'、4'邻位取代基不同对清除自由基活性的影响。采用UV-Vis光谱法测定了木犀草素、香叶木素及橙皮素对1,1-二苯基-2-三硝基苯肼自由基(DPPH·)、超氧阴离子自由基(O2-·)的清除作用。结果显示3种黄酮化合物对两种自由基都有一定的清除作用,清除效果随浓度的增大而增大。但对自由基清除能力表现为木犀草素远强于香叶木素、香叶木素与橙皮素无显著差别。说明具有B环3'、4'邻二羟基结构的黄酮清除自由基的能力明显强于具有B环3'羟基、4'甲氧基结构的黄酮;黄酮C环2、3位单双键不同对自由基清除能力影响不显著。