Evaluation of the antioxidant properties of spices by cyclic voltammetry

The individual antioxidants of spices (gallic and rosmarinic acids, capsaicin, thymol, and eugenol) are irreversibly oxidized at 0.88–1.25 V at a glassy carbon electrode in 0.1 M LiClO₄ solution in ethanol. Corresponding electrode reactions are proposed. A linear dependence of the oxidation step area on the concentration is observed for all the analytes. The detection limits and the lower limits of quantification vary from 0.57–12 and 1.8–40 μM, respectively. Distinct steps and peaks of oxidation are observed on cyclic voltammograms of the methanolic extracts of spices; the potentials and areas of these peaks depend on the type of spice. The contribution of individual antioxidants to integral responses of spice extracts is evaluated. A method is developed for the voltammetric evaluation of the antioxidant capacity (AOC) of spices based on the oxidation of their antioxidants. The total area of the oxidation steps was selected as a parameter characterizing the antioxidant properties. The AOC of spices was expressed as a weight of gallic acid in milligrams per 1 g of a dry spice. Seventeen different spices were tested. The AOC decreases in the series of clove > juniper berries > nutmeg > cinnamon > rosemary > anise ≥ oregano > black pepper ≥ ginger ≥ basil > turmeric > red pepper ≈ bay leaf ≥ coriander ≈ red sweet pepper > cumin > caraway. A correlation between the AOC obtained by voltammetry and the total AOC, ferric reducing power, antiradical activity, and total content of phenolic compounds and these parameters with each other is found; the correlation coefficients vary in the range 0.8886–0.9615.     

Kinetic spectrophotometric determination of rutin by its inhibitory effect on the oxidation of amaranth by potassium periodate

A novel kinetic spectrophotometric method is described for the determination of rutin. The method is based on the inhibitory effect of rutin on the oxidation reaction of amaranth by potassium periodate in acidic media at 100 degrees C. The linear range for the determination of rutin is 0.02 - 0.50 microg/ml, and the detection limit is 0.014 microg/ml. The method has been successfully applied to the determination of rutin in medicine of rutin tablet and traditional Chinese medicine.     

Electrocatalytic oxidation of NADH by rutin in biomembrane-like films on glassy carbon electrode

Stable lipid film was made by casting dipalmitoylphosphatidylcholine (DPPC) and rutin onto the surface of a glassy carbon (GC) electrode. The electrochemical behavior of rutin in the DPPC film was studied. The modified electrode coated with rutin gave quasi-reversible reduction-oxidation peak on cyclic voltammogram in the phosphate buffer (pH 7.4). The peak current did not decrease apparently after stored at 4°C for 8 hours in refrigerator. This model of biological membrane was used to investigate the oxidation of dihydronicotinamide adenine dinucleotide (NADH) by rutin. Rutin in the film acts as a mediator. The modified electrode shows a great enhancement and the anodic peak potential was reduced by about 220 mV in the oxidation of 5×10⁻³ mol L⁻¹ NADH compared with that obtained at a bare glassy carbon electrode.     

Studies on the antioxidant effect of rutin in the microenvironment of cationic micelles

UV-vis spectra, fluorescence emission spectra, cyclic voltammetric and electron spin resonance are employed to study the location of rutin in cetyltrimethylammonium bromide (CTAB) micelles with different microstructures and microenvironments, and to gain information about the antioxidant capacity (hydroxyl radical scavenge activity) of rutin in CTAB micelles. Rutin molecules can be partly solubilized in CTAB spherical micelles through electrostatic attraction and hydrophobic force, which leads to the bathochromic shift of absorption spectra, decrease of the microenvironment polarity of pyrene and the hydroxyl radical scavenge activity. However, CTAB rod-like micelles congregate rutin molecules on their surfaces, which results in the hypochromic shift of absorption spectra compared to the spectrum in CTAB spherical micelles and also heightens the antioxidant capacity of rutin. Correspondence: Rong Guo, School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, P.R. China     

活性炭催化氧化脱除单质汞的研究

模拟煤气的气氛,在硫化氢（H₂S）和氧气（O₂）存在条件下,对活性炭催化氧化吸附单质汞（Hg⁰）的性能进行了研究。结果表明,H₂S和O₂存在条件下,活性炭对Hg⁰的吸附能力明显提高。在180min内,H₂S和O₂共存气氛下,脱汞效率约为78%;只有H₂S存在下,脱汞效率约为69%;没有H₂S和O₂气氛下活性炭脱汞效率快速下降为28%。随着吸附温度的升高,入口汞浓度的提高和吸附剂粒径的增大,活性炭的脱汞效率会随着下降。通过XRD表征表明,Hg⁰的吸附反应机理是Hg⁰在活性炭催化氧化下与H₂S形成硫化汞（HgS）,从而实现了Hg⁰的稳定化脱除。     

Study on electrochemical oxidation behaviors and the diffusion mechanism of hydroquinone at pre-anodized carbon paste electrode by cyclic voltammetry

A functional pre-anodized carbon paste electrode (PACPE) was constructed by using successive cyclic voltammetry. The electrochemical oxidation behaviors of hydroquinone (HQ) were carefully investigated by various electrochemical techniques. The diffusion mechanism of HQ has been put forward for the first time. The driving force for the HQ transport towards anode not only related to the concentration diffusion but also depended on the transport of H(+) in the feed phase along a concentration gradient towards the cathode. The results indicated that the PACPE exhibited excellent electrocatalytic activity towards the oxidation of HQ. Compared with the bare carbon paste electrode, the oxidation and reduction peak separation (ΔE(p)) of HQ at the PACPE has been decreased from 578 to 83 mV. Under the optimum conditions, the oxidation peak current was linear with HQ concentration in the range of 4 × 10(-7) to 1.0 × 10(-4) M with the linear correlation coefficient of 0.9986. The detection limit was 1.05 × 10(-7) M. This method can be successfully applied to the determination of HQ in wastewater.     

芦丁与胰α-淀粉酶的作用研究

1 引言 芦丁（rutin）又名芸香苷、紫桷皮苷,是桷皮素的3-O-芸香糖苷,属黄酮类化合物。主要存在于豆科植物、芸香科植物籽苗中。芦丁具有维生素P样作用,能降低毛细血管通透性和脆性,促进细胞增生和防止血细胞凝聚以及抗炎、抗过敏、利尿、解痉、镇咳、降血脂等方面的作用。临床上芦丁主要用于高血压病的辅助治疗和防治因芦丁缺乏所致的其它出血症,同时还用于预防和治疗糖尿病及合并高血脂症。胰-淀粉酶（PPA）是存在于人和动物肠道的淀粉消化酶,芦丁通常作为口服制剂进入肠道后不可避免地与PPA结合,芦丁对PPA的特性影响如何？国内外迄今未见报道。     

Mechanism of antioxidant interaction on polymer oxidation by thermal and radiation ageing

The mechanism of polymer oxidation by radiation and thermal ageing was investigated for the life evaluation of cables installed in radiation environments. The antioxidant as a stabilizer was very effective for thermal oxidation with a small content in polymers, but was not effective for radiation oxidation. The ionizing radiation induced the oxidation to result in chain scission even at low temperature, because the free radicals were produced and the antioxidant could not stop the oxidation of radicals with the chain scission. A new mechanism of antioxidant effect for polymer oxidation was proposed. The effect of antioxidant was not the termination of free radicals in polymer chains such as peroxy radicals, but was the depression of initial radical formation in polymer chains by thermal activation. The antioxidant molecule was assumed to delocalize the activated energy in polymer chains by the Boltzmann statics (distribution) to result in decrease in the probability of radical formation at a given temperature. The interaction distance (delocalization volume) by one antioxidant molecule was estimated to be 5–10 nm by the radius of sphere in polymer matrix, though the value would depend on the chemical structure of antioxidant.     

The changes of adsorption properties of active carbon by wet oxidation

Summary The surface changes of active carbon by wet oxidation and the resulting changes in adsorptivity were studied. The oxidation of active carbon with hydrogen peroxide or nitric acid solutions caused the changes of the specific surface area from 1101 m2/g to 574 m²/g, immersional heat into water from 9.1 cal/g to 22.9 cal/g and immersional heat into ethanol from 28.4 cal/g to 18.8 cal/g. The average electrostatic field strength increased from 0 to 1.90 x 104 e. s. u./cm² as well. Pore structure with the diameter around 14 A was partly damaged. The adsorption of water vapor and alizarin yellow and aniline dissolved in ethanol by the carbon was promoted by these oxidations whereas the adsorption of phenol, aniline and alizarin yellow from aqueous solutions were depressed.

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Zusammenfassung Es wurden Oberflächenveränderungen von Aktivkohlen durch nasse Oxidation und die daraus resultierenden Adsorptionseigenschaften untersucht. Die Oxidation der Aktivkohle mit Wasserstoffperoxid oder Salpetersäure verminderte die spezifische Oberfläche von 1101 m²/g auf 574 m²/g, erhöhte die Benetzungswärme in Wasser von 9,1 cal/g auf 22,9 cal/g und verminderte die Benetzungswärme in Ethanol von 28,4 cal/g auf 18,8 cal/g. Die mittlere elektrostatische Feldstärke stieg gleichzeitig von 0 auf 1,90. 104 e.s.u./cm². Die Porenstruktur mit einem Durchmesser von etwa 14 Å wurde zerstört. Durch die Oxidation wurde das Adsorptionsvermögen von Wasserdampf, Alizaringelb und Anilin in Åthanollösung verbessert, die Adsorption von Phenol, Anilin und Alizaringelb in wäßriger Lösung dagegen herabgesetzt.

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With 8 figures and 2 tables     

毛细管电泳法测定复方芦丁片中的芦丁和维生素C

用毛细管电泳紫外检测法同时测定了复方芦丁片中芦丁和抗坏血酸的含量 ,研究了各种条件的影响 ,得到了优化的实验条件 ,在 30 mmol/L Na2 B4 O7-H3BO3( p H7.5 0 )缓冲溶液中 ,芦丁和维生素 C在 1 3min内得到了良好的分离 ,芦丁和维生素 C分别在 0 .5～ 0 .0 0 5 mg和 5 .0～ 0 .0 5 mg浓度范围内与电泳峰高呈现良好线性关系 ,检测下限分别为 0 .0 0 2 mg和 0 .0 1 mg,应用于实际样品的测定     

Azodioxy-carbonyl compounds by oxidation of cyclic imines with m-CPBA

This article reports a simple and efficient synthesis of C-nitroso compounds (azodioxy esters or ketones and oximes) through a double oxidation of cyclic imines (4,5-dihydrooxazoles and 3,4-dihydro-2H-pyrroles) with m-CPBA. C-Nitroso derivatives seem to be potential donors of nitric oxide, one of the most powerful biological messenger.     

Study of electrochemical oxidation of nickel catecholate complexes with bis(diphenylphosphino)ethane by cyclic voltammetry and ESR

One-and two-electron electrochemical oxidation of the (dppe)Ni(Cat) complexes (dppe is bis(diphenylphosphino)ethane, Cat is the sterically hindered catechol dianion) was studied. The transfer of the first electron proceeds reversibly to give paramagnetic species; parameters of their EPR spectra attest to a square planar geometry of one-electron oxidation products. The transfer of the second electron is irreversible because of co-proportionation of radical cations involving the initial complexes and the generated dications. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 99–102, January, 2007.     

Kinetic study of the oxidation of some catecholamines by digital simulation of cyclic voltammograms

Electrochemical oxidation of some catecholamines such as dopamine ( 1 ), L ‐dopa ( 2 ), and methyldopa ( 3 ) has been studied in various pH values, using cyclic voltammetry. The results indicate participation of catecholamines ( 1–3 ) in intramolecular cyclization reaction to form the corresponding o‐quinone derivatives ( 1d–3d ). In various pHs, based on ECE mechanism, the observed homogeneous rate constants (k_obs) of cyclization reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital‐simulated results. Also, the cyclization rate constants (k_cyc) were calculated using microscopic acidic dissociation constant of ammonium groups. The significant differences in electrochemical behavior, k_obs and k_cyc, of L ‐dopa ( 2 ) and methyldopa ( 3 ) with dopamine ( 1 ) are due to the effects of the side chain carboxyl group. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 17–24, 2005     

DFT study on hydrogen-bonding adsorption mechanism of rutin onto macroporous adsorption resins functionalized with amino, hydroxyl, and carboxyl groups

The adsorption mechanism of a series of macroporous adsorption resins (p-(CH₃NH)PhL (L = NH₂, OH, COOH)) with rutin have been investigated using density functional theory calculations at B3LYP/6-31G(d,p) level of theory. Solvent effects on these species were explored using calculations that included a polarizable continuum model for the aqueous solvent. In this article, the geometry structure, interaction energies and the infrared spectra for the stable reactants and the adsorption complexes were obtained and analyzed. The results show that the hydrogen-bonding have been formed in the adsorption complexes. The higher interaction energy is calculated for the carboxyl group, while the resin with amino group has the highest adsorption capacity for rutin. The adsorption complexes become more and more stable as increasing the number of adsorbents. Our theoretical study is in good explanation for the experimental results.     

1,4-丁二醇在Pt及其修饰电极上吸附氧化过程研究

运用电化学循环伏安和石英晶体微天平研究了1，4-丁二醇(1，4-BDL)在Pt电极及以Sb和S吸附原子修饰的Pt(Pt／Sbad和Pt／Sad)电极上的吸附和氧化过程．结果表明，1，4-丁二醇的氧化与电极表面氧物种有着极其密切的关系，表面质量变化提供了吸附原子电催化作用的新数据．Pt电极表面Sb吸附原子能在较低的电位下吸附氧，可显提高1，4-丁二醇电催化氧化活性．与Pt电极相比，1，4-丁二醇在饱和吸附Sb原子的Pt电极上氧化的峰电位负移了0．20V，峰电流增加了1．5倍．相反，Pt电极表面S吸附原子的氧化会消耗表面氧物种，饱和吸附的S原子抑制了1，4-丁二醇的氧化．     

电化学方法研究芦丁与鲱鱼精DNA之间的相互作用

采用循环伏安法和交流阻抗法研究了固定在羟基磷灰石薄膜上的DNA与芦丁之间的相互作用.在pH 5.6～7.0范围内,芦丁在DNA修饰电极上的峰电位随pH的增加向负方向移动;在50～800 mV/s扫描速度范围内电极过程同时受扩散和吸附控制,且扩散控制占主导作用;随溶液离子强度增大,芦丁在DNA修饰电极上的表观式量电位不断正移,表明芦丁与DNA之间存在一定的嵌入作用,二者结合形成了超分子化合物.     

Autocatalysis by the nitroxyl radical in the cyclic mechanism of chain termination in polymer oxidation

The activation energy and rate constant of the reaction between the nitroxyl radical and N-alkoxyamine as a concerted abstraction–fragmentation reaction have been calculated using the intersecting parabolas model. This reaction proceeds fairly rapidly and leads to nitroxyl radical autoregeneration as a result of the following consecutive reactions:AmO^? + AmOR → AmOH + >C=O + Am^?, RO ₂ ^? + AmOH → ROOH + AmO^?, Am^?+ O₂ → Am ₂ ^? , and 2AmO ₂ ^? → 2AmO^? + O₂. Thus, the nitroxyl radical is an effective radical catalyst for its own regeneration from N-alkoxyamine. The rates of regeneration of the nitroxyl radical from its N-alkoxyamine under the action of alkyl, alkoxyl, peroxyl, nitroxyl, and hydroperoxyl radicals under conditions of polypropylene oxidation inhibited by the nitroxyl radical are compared. It is demonstrated that only peroxyl, hydroperoxyl, and nitroxyl radicals are involved in AmO^? regeneration from AmOR.     

Hazard evaluation for oxidation of cyclic ethers

Ethers are widely used as a solvent for synthesis reactions, however, they are known as hazardous chemicals as they have low flash points and form peroxides under oxidative conditions. In this study, the oxidative reactivity of cyclic ethers was evaluated by thermal analysis. The accelerated test was performed in a pressure vessel under a high oxygen pressure (2 MPa), and DSC was used to detect the products of the reaction. Tetrahydrofuran (THF) and 1,3-dioxolane were used as a sample. The result of the DSC measurement of THF without any antioxidant showed that the DSC curve depended on the exposure time. It was found that this method can be used for the oxidation evaluation. The DSC measurement was also used for the detection of ether peroxides, and this method was faster and simpler than the potassium iodine titration.