Selective Determination of Quercetin Using Carbon Nanotube‐Modified Electrodes

Electrochemical detection of quercetin has been carried out on glassy carbon electrodes modified with carbon nanotubes and Nafion (GC/Nafion‐CNT). GC/Nafion‐CNT electrodes did not show passivation effect that occurs on the unmodified electrodes and displayed better stability and reproducibility. Quercetin oxidation was most favorable in acidic conditions and current gradually decreased as the solution pH increased. No oxidation was observed when two ? OH groups in a catechol moiety were fully deprotonated. These electrodes enabled selective determination of quercetin in the presence of interfering species such as ascorbic acid, uric acid, glucose, and catechol in large excess. Quantification of quercetin in a yellow onion has been made and favorably compared with reported values. Good selectivity and high sensitivity obtained by Osteryoung sSquare‐wave voltammetry can open new possibilities of direct quercetin determination in vegetables with a minimal sample treatment.     

聚酰胺修饰碳糊电极测定槲皮素的研究

用聚酰胺修饰碳糊电极在ｐＨ３６０的Ｂｒｉｔｏｎ－Ｒｏｂｉｎｓｏｎ缓冲溶液中，将槲皮素开路富集一定时间后，从０４５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）向阴极化扫描至－０５５Ｖ获得Ｉ－Ｅ曲线。槲皮素的峰电位为０１８Ｖ。峰电流与槲皮素浓度在１０～４００μｍｏｌ／Ｌ范围内呈良好的线性关系。所拟定方法用于芦丁水解产物测定，结果满意。     

Electrochemical Oxidation of Quercetin

The mechanism of electrochemical oxidation of quercetin on a glassy carbon electrode has been studied using cyclic, differential pulse and square‐wave voltammetry at different pH. It proceeds in a cascade mechanism, related with the two catechol hydroxyl groups and the other three hydroxyl groups which all present electroactivity, and the oxidation is pH dependent. Quercetin also adsorbs strongly on the electrode surface; and the final oxidation product is not electroactive and blocks the electrode surface. The oxidation of the catechol 3′,4′‐dihydroxyl electron‐donating groups, occurs first, at very low positive potentials, and is a two electron two proton reversible reaction. The hydroxyl group oxidized next was shown to undergo an irreversible oxidation reaction, and this hydroxyl group can form a intermolecular hydrogen bond with the neighboring oxygen. The other two hydroxyl groups also have an electron donating effect and their oxidation is reversible.     

Quercetin attenuates cisplatin-induced ovarian toxicity in rats: Emphasis on anti-oxidant,anti-inflammatory and anti-apoptotic activities

Ovarian toxicity is a devastating adverse effect of cisplatin therapy. The objective of the current study was to address whether or not quercetin could protect against cisplatin-induced ovarian toxicity in rats as well as the possible underlying mechanisms. Rats were allocated into five groups. Group 1 represented the control, group 2 was administered quercetin (10 mg/kg), group 3 received cisplatin (6 mg/kg single i.p. dose) on days 7 and 14, the forth group was given cisplatin + quercetin (5 mg/kg) and the fifth group was administered cisplatin + quercetin (10 mg/kg). Quercetin ameliorated cisplatin-induced histopathological changes in ovarian tissues and significantly prevented the decline in the percentage of healthy follicles and serum anti-Mullerian hormone (AMH). Quercetin exhibited significant anti-oxidant effects evidenced by preventing MDA accumulation, glutathione depletion and superoxide and glutathione peroxidase exhaustion in the ovary. Also, quercetin displayed activities against cisplatin-induced inflammatory responses in the ovary. Quercetin significantly inhibited expression of NFκb, Cox-2 and IL-6 and elevated ovarian content of TNF-α. Further, quercetin showed anti-apoptotic activity as demonstrated by decreased caspase-3 content and modulation of Bax and Bcl2 expression in the ovary. Conclusively, quercetin protects against cisplatin-induced ovarian toxicity in rats. This is mediated, at least partly, by its anti-oxidant, anti-inflammatory and anti-apoptotic activities.     

HPLC法同时测定养心草中没食子酸、槲皮素和山萘酚的含量

建立了高效液相色谱法同时测定养心草中没食子酸、槲皮素和山萘酚的含量。采用Hypersil C18色谱柱（4.6mm×200mm,5μm）,流动相为甲醇（A）-0.2%磷酸水溶液（B）,梯度洗脱,流速1.0mL/min;柱温25℃;检测波长260nm。在选定色谱条件下没食子酸、槲皮素和山萘酚线性关系良好;没食子酸、槲皮素和山萘酚加标回收率分别为98.37%、99.61%、97.81%,RSD分别为2.32%、2.15%、2.20%。方法简便快速,结果准确可靠,可用于控制中药养心草的质量。     

反相高效液相色谱法测定罗布麻叶中槲皮素和山萘酚

采用反相高效液相色谱法(RP-HQLC)测定了罗布麻叶中槲皮素和山萘酚。色谱柱为Nova-pak C18(15cm×4.6mm i.d.),流动相为A.甲醇、B.1%乙酸,流速为0.6mL/min,检测波长为360nm。槲皮素在0.0137~0.136μg、山萘酚在0.0053~0.0265μg范围内与峰面积呈良好的线性关系,相关系数分别为0.9998和0.9980。槲皮素的回收率为99.6%,RSD为0.97%;山萘酚的回收率为98.2%,RSD为2.0%。方法可用于罗布麻叶中槲皮素和山萘酚的测定。     

Simultaneous characterization and quantification of flavonoids in Euonymus alatus (Thunb.) Siebold from different origins by HPLC-PAD–MS

A high-performance liquid chromatography coupled with photodiode array detection and electrospray ionization tandem mass spectrometry (HPLC-PAD–ESI-MS) method has been developed for the simultaneous identification and quantification of active compounds (rutin and quercetin) contained in Traditional Chinese Medicine (TCM) Euonymus alatus (Thunb.) Siebold (EAS). The herb samples from ten main origins and five medicinal portions (leaf, fruit, stem, pterygium and root) were investigated. The separation was performed on a Shim C₁₈ column at 30 °C with an isocratic elution. Methanol (A) and water (0.5% methanoic acid, v/v) (B) were used as mobile phases. The recoveries of the two compounds were 100.184% and 100.417%, respectively, and all of them showed good linearity (r² ? 0.9993) in relatively wide concentration ranges. The developed method was applied to identify and quantify the two major active compounds in the collected herb samples, and the results indicated that contents of the two compounds in EAS varied significantly from habitat to habitat. It was demonstrated that the proposed method was helpful for the quality evaluation of EAS.     

Fe3O4@SiO2‐PANI‐Au Nanocomposite Prepared for Electrochemical Determination of Quercetin in Food Samples and Biological Fluids

A new electrochemical sensor based on Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was fabricated for modification of glassy carbon electrode (Fe₃O₄@SiO₂‐PANI‐Au GCE). The Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was characterized by TEM, FESEM‐EDS‐Mapping, XRD, and TGA methods. The Fe₃O₄@SiO₂‐PANI‐Au GC electrode exhibited an acceptable sensitivity, fast electrochemical response, and good selectivity for determination of quercetin. Under optimal conditions, the linear range for quercetin concentrations using this sensor was 1.0×10^?8 to 1.5×10^?5 mol L^?1, and the limit of detection was 3.8×10^?9 mol L^?1. The results illustrated that the offered sensor could be a possible alternative for the measurement of quercetin in food samples and biological fluids.     

低含量点化合物测定的三种数据处理方法比较研究

对于多数定量分析需要绘制标准工作曲线,如果待测化合物的含量过低,靠近工作曲线的最低端则定量分析结果的偏差将较大。本文采用三种数据处理方法进行工作曲线的建立,包括一般线性回归(OLR)、加权线性回归(WLR)和稳健回归(RR)。通过高效液相色谱法对芹菜素含量进行检测,比较了这三种回归方法的准确性。结果表明:对于低含量点化合物而言,WLR较其它两种方法更准确,且处理过程并不复杂,是一种可行、更准确的定量数据处理方法。     

槲皮素酯类衍生物研究进展

健康生活方式特别强调食物质量,多酚在这方面发挥了关键作用。槲皮素是一种天然多酚,是多种植物性食品中发现最丰富的类黄酮类化合物之一。槲皮素是天然的抗氧化剂,可以保护细胞免受自由基造成的损害。槲皮素是一种亲脂性化合物,能够穿过细胞膜,可调节众多与疾病进展、化学预防有关的细胞内和细胞外信号通路。槲皮素具有广泛的药理活性,抗炎、抗菌、抗癌和预防心脑血管疾病,但是它低溶解度和生物利用度限制了在临床上的应用。对槲皮素的结构进行优化修饰获得了溶解性能好、生物利用度高、活性明显改善、抗癌活性增强的槲皮素衍生物。综述了近年来槲皮素酯衍生物的研究进展,为槲皮素衍生物的进一步开发提供参考。