双氧水对自呼吸式燃料电池性能的影响

将双氧水加入到阳极燃料甲醇溶液中来研究其对DMFC性能的影响。双氧水作为阳极助氧化剂将甲醇催化氧化产生的中间体CO氧化成气体CO2排出,从而减少中间体在催化层表面的吸附,增强催化剂的催化性能,从而提高电池的输出性能。通过探讨不同双氧水浓度和不同温度情况下,甲醇催化氧化的氧化峰电流密度及自呼吸式燃料电池的极限功率密度,阻抗等性能来分析双氧水在其中的作用。结果表明低浓度的双氧水确实能提高DMFC的输出性能,并且在双氧水的浓度为0.05 mol/L,温度为55℃时DMFC性能最佳。     

Analysis of tryptophan oxidation by fluorescence spectroscopy: Effect of metal-catalyzed oxidation and selected phenolic compounds

The suitability of using fluorescence spectroscopy to assess tryptophan (TRYP) depletion by quantifying the loss of natural TRYP fluorescence during metal-catalyzed oxidation (MCO) was assessed. To analyze the effect of the oxidation conditions, N-acetyl-l-tryptophanamide (NATA) solutions were oxidized in the presence of Cu²⁺ and Fe²⁺ (40 and 80 μM), with and without 0.8 mM H₂O₂. Also, the effect of selected phenolic compounds (PhC), namely, catechin, genistein, quercetin, rutin, gallic acid and chlorogenic acid (0.08, 0.8 and 8.0 μM), on TRYP MCO was studied. Oxidation systems catalyzed by Fe²⁺ had a major oxidative potential as a result of a higher amount of free radicals formed through the Fenton reaction. PhC could exert both antioxidant and pro-oxidant effects depending on their concentration, chemical structure of the PhC and the oxidation system. In general, all PhC acted as pro-oxidant agents at the highest dose. The major pro-oxidant effect was displayed by gallic and chlorogenic acid in the presence of Fe²⁺, Cu²⁺ or Cu²⁺/H₂O₂. Quercetin, rutin and gallic acid showed antioxidant effect against TRYP oxidation at low concentrations in Fe²⁺/H₂O₂ systems. Plausible mechanisms for the antioxidant and pro-oxidant effects of PhC on TRYP oxidation are discussed in the present article. The antioxidant efficiency of PhC or PhC-rich extracts must be studied before being used as functional food ingredients.     

“Fifty Shades” of Black and Red or How Carboxyl Groups Fine Tune Eumelanin and Pheomelanin Properties

Recent advances in the chemistry of melanins have begun to disclose a number of important structure-property-function relationships of crucial relevance to the biological role of human pigments, including skin (photo) protection and UV-susceptibility. Even slight variations in the monomer composition of black eumelanins and red pheomelanins have been shown to determine significant differences in light absorption, antioxidant, paramagnetic and redox behavior, particle morphology, surface properties, metal chelation and resistance to photo-oxidative wear-and-tear. These variations are primarily governed by the extent of decarboxylation at critical branching points of the eumelanin and pheomelanin pathways, namely the rearrangement of dopachrome to 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA), and the rearrangement of 5-S-cysteinyldopa o-quinoneimine to 1,4-benzothiazine (BTZ) and its 3-carboxylic acid (BTZCA). In eumelanins, the DHICA-to-DHI ratio markedly affects the overall antioxidant and paramagnetic properties of the resulting pigments. In particular, a higher content in DHICA decreases visible light absorption and paramagnetic response relative to DHI-based melanins, but markedly enhances antioxidant properties. In pheomelanins, likewise, BTZCA-related units, prevalently formed in the presence of zinc ions, appear to confer pronounced visible and ultraviolet A (UVA) absorption features, accounting for light-dependent reactive oxygen species (ROS) production, whereas non-carboxylated benzothiazine intermediates seem to be more effective in inducing ROS production by redox cycling mechanisms in the dark. The possible biological and functional significance of carboxyl retention in the eumelanin and pheomelanin pathways is discussed.     

Lipid Oxidation in Poultry Döner Kebab: Pro-oxidative and Anti-oxidative Factors

ABSTRACT: The effect of mechanically separated turkey (MST), ascorbate, and vacuum packaging on rates of lipid oxidation in chicken döner kebab during storage at 4 °C or -20 °C was investigated. MST and MST/ascor-bate accelerated lipid oxidation compared to control kebab. Ascorbate application and vacuum packaging inhibited lipid oxidation. The antioxidative effect of ascorbate in the absence of MST was converted to a pro-oxidative effect in the presence of MST. This suggests that the excess lipid hydroperoxides and iron complexes in MST were activated as lipid oxidation catalysts by ascorbate to overwhelm the ability of ascorbate to inhibit lipid oxidation at lower concentrations of hemoglobin, iron, and peroxides.     

维生素C在新陈代谢中的生理功能

维生素C不仅通过直接清除活性氧簇还通过间接维持其他抗氧化剂的还原态在生物体内起着非常重要的抗氧化作用,而且在更多其他方面也起着非常重要的作用。本文从维生素C的抗氧化作用、作为双加氧酶的共基质所起的作用、维生素C基因表达上所起的的作用以及维生素C在脂类氧化和DNA损伤中的作用做了综述,希望人们以更加全面的观点来看待维生素C。     

Synthetic Pathways and the Therapeutic Potential of Quercetin and Curcumin

Polyphenols are considered popular ingredients in the pharmaceutical and medical fields due to their preventive and therapeutic properties. However, the potential effects and mechanisms of action of individual polyphenols remain largely unknown. Herein, we analyzed recent data on the synthetic pathways, features, and similarity of the properties of quercetin, as the most famous flavonoid, and curcumin, a representative of curcuminoids that despite their anti-oxidant activity, also have a pro-oxidant effect, depending on the concentration and the cellular environment. This review focuses on an analysis of their anti-cancer efficacy against various cancer cell lines via cell cycle arrest (regulation of p53/p21 and CDK/cyclins) and by triggering the mitochondrial intrinsic (Bcl-2/Bax/caspase 9) apoptotic pathway, as well as through the modulation of the signaling pathways (PI3K/Akt, Wnt/β-catenin, JAK/STAT, MAPK, p53, and NF-ĸB) and their influence on the non-coding RNAs involved in angiogenesis, invasion, migration, and metastasis. The therapeutic potential of quercetin and curcumin is discussed not only on the basis of their anti-cancer effects, but also with regard to their anti-diabetic, anti-obesity, anti-inflammatory, and anti-bacterial actions.     

Redox (pro-oxidant/antioxidant) balance in the spray drying of orange peel extracts

ABSTRACT

Phenolic compounds have been reported to show both antioxidant and pro-oxidant properties. The effects of spray drying conditions on the balance between antioxidant and pro-oxidant properties of orange peel extract have been evaluated in this work. The inlet drying temperatures (ranging between 100 and 175°C) gave no significant effect on the redox recoveries. On the other hand, the main air flow rate (between 28 and 38?m³/h) and feed pump rate (between 4 and 7?mL/min) significantly affected the pro-/antioxidant recovery ratio. The ratios of pro-/antioxidant recovery were found to be between 1.00 and 1.13, and the pro-oxidant and antioxidant recoveries in this study were found to be between 87–96 and 83–93%, respectively.     

Relationships among Headspace Oxygen, Peroxide Value, and Conjugated Diene Content of Soybean Oil Oxidation

ABSTRACT: Relationships among headspace oxygen uptake, peroxide value, and conjugated dienes content in the oxidation of soybean oils in a gas-tight bottle were studied for 24 h under light and 96 h in the dark at 55°C. The theoretical peroxide value determined by oxygen uptake continuously increased as storage time increased. The headspace oxygen method is simple and reproducible and may be the best analytical method to evaluate the oxidative stability of oils.     

黄绿色碳量子点的热合成荧光探针及其在白皮杉醇促氧化作用中的研究

为使用经济、省时地探讨白皮杉醇（Pic）的促氧化作用,本研究以邻苯二胺为原料,采用水热法合成了黄绿色荧光的碳量子点（CDs）,通过紫外可见分光光度计、荧光分光光度计、透射电镜、傅里叶红外光谱仪对CDs进行表征,同时研究了其在不同温度、pH、离子强度和紫外照射时间下的稳定性,最后研究了Pic在Cu2+催化下对CDs荧光的淬灭作用及其促氧化作用的量效关系。结果表明：该CDs在水溶液中最佳发射波长为570 nm,最佳激发波长为385 nm,尺寸约为7.4 nm,表面具有酰胺键等官能团;并且其有良好的抗光漂白性,对温度和离子强度不敏感,在pH 5~10内,有良好的发光性;在100 μmol/L Cu2+条件下,Pic在浓度为1.5~12.5 μmol/L时,荧光探针的淬灭程度与Pic浓度成线性关系,而当Pic浓度高于12.5 μmol/L时,体系的荧光下降趋于平缓,促氧化效果不再明显。本研究可为Pic作为功能性食品的应用提供理论依据。     

Antioxidant activity of some edible plants of the Turkmen Sahra region in northern Iran

The antioxidant properties of 10 edible plants of the Turkmen Sahra region in Golestan province in northern Iran, including Allium paradoxum, Allium rubellum, Foeniculum vulgare, Mentha longifolia, Origanum vulgare, Prunus divaricata, Rubus sanctus, Rumex tuberosus, Satureja mutica and Spinacia turkestanica were evaluated by four different methods; free radical scavenging using 2,2-diphenyl-1-picrylhydrazyl (DPPH), evaluation of xanthine-oxidase activity, inhibition of lipid peroxidation by the ferric thiocyanate method, and the deoxyribose degradation assay. All species tested except A. paradoxum and P. divaricata showed antioxidant activity at least in one assay.