Interactive enhancements of ascorbic Acid and iron in hydroxyl radical generation in quinone redox cycling

Quinones are toxicological substances in inhalable particulate matter (PM). The mechanisms by which quinones cause hazardous effects can be complex. Quinones are highly active redox molecules that can go through a redox cycle with their semiquinone radicals, leading to formation of reactive oxygen species. Electron spin resonance spectra have been reported for semiquinone radicals in PM, indicating the importance of ascorbic acid and iron in quinone redox cycling. However, these findings are insufficient for understanding the toxicity associated with quinone exposure. Herein, we investigated the interactions among anthraquinone (AQ), ascorbic acid, and iron in hydroxyl radical (·OH) generation through the AQ redox cycling process in a physiological buffer. We measured ·OH concentration and analyzed the free radical process. Our results showed that AQ, ascorbic acid, and iron have synergistic effects on ·OH generation in quinone redox cycling; i.e., ascorbyl radical oxidized AQ to semiquinone radical and started the redox cycling, iron accelerated this oxidation and enhanced ·OH generation through Fenton reactions, while ascorbic acid and AQ could help iron to release from quartz surface and enhance its bioavailability. Our findings provide direct evidence for the redox cycling hypothesis about airborne particle surface quinone in lung fluid.     

Geomicrobiological redox cycling of the transuranic element neptunium

Microbial processes can affect the environmental behavior of redox sensitive radionuclides, and understanding these reactions is essential for the safe management of radioactive wastes. Neptunium, an alpha-emitting transuranic element, is of particular importance because of its long half-life, high radiotoxicity, and relatively high solubility as Np(V)O(2)(+) under oxic conditions. Here, we describe experiments to explore the biogeochemistry of Np where Np(V) was added to oxic sediment microcosms with indigenous microorganisms and anaerobically incubated. Enhanced Np removal to sediments occurred during microbially mediated metal reduction, and X-ray absorption spectroscopy showed this was due to reduction to poorly soluble Np(IV) on solids. In subsequent reoxidation experiments, sediment-associated Np(IV) was somewhat resistant to oxidative remobilization. These results demonstrate the influence of microbial processes on Np solubility and highlight the critical importance of radionuclide biogeochemistry in nuclear legacy management.     

2-甲基-1,4-萘醌在乙醇中溶解度的测定及关联

测定了常压下2-甲基-1,4-萘醌在乙醇中的溶解度,并用经验方程、二参数方程和三参数方程对实验数据进行关联,平均相对误差分别为2.49%,1.28%和0.80%,其中三参数方程拟合效果最好.     

An EPR study of free radical generation during maceration of uncooked vegetables

Electron paramagnetic resonance (EPR) spectroscopy has been used to study free radicals formed in a range of plant tissues as a result of physical damage, with the objective of gaining some insight into the free radical chemistry that is initiated when uncooked vegetable products (eg salads) are eaten. Chemical spin traps were used to aid the detection of unstable free radicals; more stable radicals were detected directly. Commonly observed ‘stable’ species were the monodehydroascorbate radical, which has a characteristic doublet spectrum, and a single‐peak resonance, which is presumed to come from free radical centres stabilised in macromolecules. In mushrooms (Agaricus spp), spin‐trapping experiments using either α‐(4‐pyridyl‐1‐oxide)‐N‐t‐butyl‐nitrone (4‐POBN) or phenyl‐t‐butyl‐nitrone (PBN) showed the formation of large quantities of adducts of the radical from 4‐hydroxymethylbenzene diazonium salts. Pleurotus species, in contrast, gave signals consistent with the formation of unidentified C‐centred radicals. With other foodstuffs, reaction with 4‐POBN was complex and signals from 4 ? POBN· and adducts were observed along with the t‐butylhydronitroxide radical (an adduct breakdown product). Investigation of carrot hypocotyl rootstock in the presence of 5‐(diethoxyphosphoryl),5‐methyl‐1‐pyrroline‐N‐oxide (DEPMPO) revealed adducts of ·OH and unidentified C‐centred radicals. Free radical interactions between food components were demonstrated by the suppression of the signal from the 4‐POBN adducts of lettuce by onion, garlic, satsuma or vinaigrette, but not by olive oil. In addition, an appreciable decrease in spectral intensity of the 4‐POBN adduct from lettuce was observed in the presence of saliva, which suggests that saliva contains free radical scavengers which are able to compete successfully with the spin trap. © 2002 Society of Chemical Industry     

Hydroxyl radical production via the photo-Fenton reaction in the presence of fulvic acid

The photo-Fenton reaction, the reaction of photoproduced Fe(II) with H2O2 to form the highly reactive hydroxyl radical (OH*), could be an important source of OH* in sunlit natural waters. To determine if the photo-Fenton reaction is significant in mildly acidic surface waters, we conducted experiments simulating conditions representative of natural freshwaters using solutions of standard fulvic acid and amorphous iron oxide at pH 6.0. A probe method measuring 14CO2 produced by the reaction of 14C-labeled formate with OH* was used to detect small OH* production rates without otherwise influencing the chemical reactions occurring in the experiments. Net H2O2 accumulation was simultaneously measured using an acridinium ester chemiluminescence method. Measured losses of H2O2 by reaction with Fe(II) in dark experiments produced approximately the expected quantities of OH*. The difference between H2O2 accumulation in the presence and absence of Fe(III) in fulvic acid solutions exposed to light was interpreted as the loss of H2O2 by reaction with photoproduced Fe(II), consistent with measured OH* production rates. The Fe ligand desferrioxamine mesylate eliminated both OH* production and H2O2 photoloss induced by Fe. Our results imply that when Fe is a major sink of H2O2, the photo-Fenton reaction is likely to be the most important source of OH*, leading to a significant sink of organic compounds in a wide variety of sunlit freshwaters.     

混合办公废纸漂白过程中DCS的生成机理

利用气-质联用技术研究了混合办公废纸漂白过程中溶解与胶体物质的生成机制.结果表明,过氧化氢漂白过程中释放出的糖基主要是葡萄糖,约占总糖基的50%;释放出的亲脂性物质主要是十六碳酸（又称软脂酸）、双（乙基己基）邻苯二甲酯,两者占总量的40%左右.FAS漂白过程中释放出的糖基主要是葡萄糖和木糖,但释放量较过氧化氢漂白低得多;释放出的亲脂性物质主要是十六碳酸、双（乙基己基）邻苯二甲酯、9-十八碳烯酸.     

Hydroxyl radical formation upon oxidation of reduced humic acids by oxygen in the dark

Humic acids (HAs) accept and donate electrons in many biogeochemical redox reactions at oxic/anoxic interfaces. The products of oxidation of reduced HAs by O(2) are unknown but are expected to yield reactive oxygen species, potentially including hydroxyl radical (·OH). To quantify the formation of ·OH upon oxidation of reduced HAs by O(2), three HAs were reduced electrochemically to well-defined redox states and were subsequently oxidized by O(2) in the presence of the ·OH probe terephthalate. The formation of ·OH upon oxidation increased with increasing extent of HA reduction. The yield of ·OH ranged from 42 to 160 mmol per mole of electrons donated by the reduced HA. The intermediacy of hydrogen peroxide (H(2)O(2)) in the formation of ·OH was supported by enhancement of ·OH formation upon addition of exogenous H(2)O(2) sources and by the suppression of ·OH formation upon addition of catalase as a quencher of endogenous H(2)O(2). The formation of ·OH in the dark during oxidation of reduced HA represents a previously unknown source of ·OH formation at oxic/anoxic interfaces and may affect the biogeochemical and pollutant redox dynamics at these interfaces.     

Antimicrobial activity of 5-hydroxy-1,4-naphthoquinone isolated from Caesalpinia sappan toward intestinal bacteria

The methanol extract of Caesalpinia sappan heartwoods was tested for the growth effects toward five intestinal microorganisms. The biologically active constituent of the C. sappan extract was characterized as 5-hydroxy-1,4-naphthoquinone (C₁₀H₆O₃). The growth responses varied depending on the bacterial species and dose tested. In the test with Clostridium perfringens, 5-hydroxy-1,4-naphthoquinone produced the strong (+++) inhibition at 5 and 2 mg/disk and moderate (++) inhibition at 1, 0.5, and 0.25 mg/disk. Furthermore, this isolate revealed a weak (+) growth inhibition against Lactobacillus casei at 5 and 2 mg/disk. In comparison of naphthoquinone derivatives, 5-hydroxy-2-methyl-1,4-naphthoquinone had moderate growth inhibition against C. perfringens at 5 and 2 mg/disk, whereas 1,4-naphthoquinone at 5 mg/disk significantly inhibited the growth of all bacteria tested. 1,2-Naphthoquinone had growth inhibition against all bacteria tested at 1 mg/disk. The structure-activity relationship revealed that 5-hydroxy-1,4-naphthoquinone had selective growth inhibition against C. perfringens. These results indicate that hydroxyl functional group of naphthoquinone seems to be required for selective growth-inhibiting activity against C. perfringens. Accordingly, as naturally occurring antimicrobial agents, C. sappan heartwood-derived material could be useful as a preventive agent against diseases caused by C. perfringens.     

Hydroxyl radical oxidation destabilizes subfragment-1 but not the rod of myosin in chicken myofibrils

The thermal denaturation process of myosin in oxidized chicken myofibrils was investigated. Exposures of myofibrils to hydroxyl radical-generation systems (HRGS) resulted in an enhanced susceptibility of myosin to thermal inactivation of Ca-ATPase and a loss of salt solubility. The chymotryptic production of subfragment-1 (S-1) from myosin in oxidized myofibrils decreased more rapidly than that in un-oxidized myofibrils upon heating, which paralleled the Ca-ATPase decay. However, the heat-induced decrease in chymotryptic production of rod from myosin was not affected by the HRGS treatment. The results suggested that free radical oxidation promoted thermal destabilization of myosin in the S-1 portion instead of the rod portion. The altered myosin denaturation pattern due to hydroxyl radical oxidation was likely a cause for functionality changes in oxidatively stressed myofibrillar proteins in meat processing.     

微波处理对糙米制粉多样产物的自由基水平及贮藏稳定性的影响

以糙米制粉的多样产物为研究对象,采用电子顺磁共振(electron paramagnetic resonance,EPR)技术,对米粉自由基进行研究,考察不同微波处理条件对米粉加热后自由基生成及贮藏稳定性的影响。结果发现:在米粉的EPR谱图中均检测到Fe~(3+)(g=4.30)和碳自由基(g=2.00)的特征峰,并且在米糠和糙米中还出现了Mn~(2+)的典型六重峰(g=2.00)。相同微波条件下,精米较糙米和米糠所产生自由基信号强度小;米粉样品的自由基信号强度均随微波时间和功率的提高而增大,尤其在精米中上升的幅度最大;对微波处理后米粉自由基的贮藏稳定性研究发现精米和糙米的自由基信号强度在微波处理后出现迅速下降并缓慢上升至稳定,而米糠的自由基信号强度在迅速下降后持续上升。     

咸蛋加工过程的腌制成熟机理初探

分析探讨了成蛋加工成熟过程内部物理性状和主要化学成分含量的变化规律、影响成蛋腌制过程的成熟期的因素,归纳出禽蛋腌制过程的成熟机制主要是NaCI的作用引起可调控的蛋内粘度变化机制.     

酪蛋白酶解产物·OH清除和ACE抑制活性的稳定性

研究温度、pH值、金属离子和不同浓度的糖、盐对酪蛋白酶解产物羟自由基清除活性和ACE抑制活性的影响。结果表明:酪蛋白酶解产物的羟自由基清除活性对热不稳定,而ACE抑制活性对热稳定;在酸性条件下羟自由基清除活性和ACE抑制活性略有下降,在碱性条件下,活性丧失较多;金属离子能降低羟自由基清除活性,其影响大小顺序为Mg2+>Cu2+>Zn2+>K+>Ca2+,而对ACE抑制活性影响不大;在加热条件下,葡萄糖能增强羟自由基清除活性,而蔗糖和NaCl对其影响不大,葡萄糖和蔗糖对ACE抑制活性的影响均不显著,而质量分数为2%以上的NaCl可使ACE抑制活性明显降低。     

食品中花青素在热加工中的降解及其机制研究

花青素是广泛存在于植物性食物中的水溶性天然色素,主要以2-苯基苯并呋喃阳离子为基础形成的多羟基或多甲氧基衍生物,属类黄酮化合物。现已知的植物花青素种类主要有6种,天竺葵色素、矢车菊色素、飞燕草色素、芍药色素、牵牛花色素和锦葵色素。目前报道的花青素降解机制多为标准物质的热降解过程,可能为两种途径,本文综述了花青素标准物质这两种降解途径的过程。花青素很不稳定性,易受温度、pH值、氧气和金属离子影响,特别是热加工最易引起降解褪色。常见的食品热加工包括蒸、煮、炸和微波等,这些热加工方式都伴随着不同程度花青素的降解。食品热加工过程中花青素的大量丧失与其降解反应密切相关,而花青素的降解过程又与不同的热加工方式密切相关。     

葡萄皮渣中可溶性抗氧化膳食纤维提取工艺及羟自由基清除作用

采用超声协同复合酶法提取葡萄皮渣中可溶性抗氧化膳食纤维(SADF),并以提取物SADF对·OH清除效果作为抗氧化指标进行单因素和响应面法优化实验。单因素试验结果表明,影响葡萄皮渣中SADF抗氧化值大小的因素主次顺序为:超声波作用时间>纤维素酶量>料液比>α-淀粉酶作用时间。之后,运用响应曲面法进一步确定了葡萄皮渣中SADF的最佳提取工艺条件,即:超声波作用时间28.40min、纤维素酶量0.42m L/g、料液比41.50m L/g、α~-淀粉酶作用时间30.18min,此时提得的SADF抗氧化值可达0.903mmol Trolox/100 g SADF。     

Organic complexation of Fe(II) and its impact on the redox cycling of iron in rain

More than 80% of the iron(II) present in a dilute (pH 4.5) H2SO4 solution was oxidized by hydrogen peroxide (3 microM) in 24 h, whereas in rainwater Fe(II) remained stable for days indicating that a complexed form of Fe(II) exists in rainwater that protects it against oxidation. When a rain sample was irradiated for 2 h with simulated sunlight, there was a 57 nM increase in Fe(II) resulting from photoreduction of organic Fe(III) complexes. Once irradiation ceased, the photoproduced Fe(II) rapidly oxidized back to its initial concentration of 32 nM prior to irradiation, but not to zero. These photochemical studies demonstrate that during the daytime when sunlight is present there are dynamic interconversions between complexed and uncomplexed Fe(II) and Fe(III) species in rainwater. During the night, after the photochemically produced Fe(II) is reoxidized to Fe(III), virtually all remaining Fe(II) is complexed by ligands which resist further oxidation. Rain samples oxidized under intense UV light lost their ability to stabilize Fe(II), suggesting the ligands stabilizing Fe(II) are organic compounds destroyed by UV-irradiation. Additional UV-irradiation studies demonstrated that on average 25% of the Fe-complexing ligands in rainwater are extremely strong and cannot be detected by spectrophotometric analysis using ferrozine. The stability of organically complexed Fe(II) has important implications for the bioavailability of rainwater-derived Fe in the surface ocean.     

The mechanism for the promotion of tenderness in meat during the post-mortem process: a review.

The post-mortem changes in the chemical composition and structure of striated muscle have been reviewed on the basis of various concepts that emerged from the studies of different investigators to explain the course of tenderization of meat during aging. These concepts include the changes in the sarcoplasmic proteins, myofibrillar proteins (such as complete dissociation of actomyosin, partial dissociation of actomyosin, cleavage of disulfide linkages, depolymerization of F-actin filaments, cleavage of myosin filaments, disorganization of Z-bands and the troponin-tropomyosin complex), sarcolemma, connective tissue elements (collagen fibrils, ground substance), and the protein-ion relationship of the muscle cells (more strictly, syncytia). The experimental evidence for and against each of the views is discussed critically in the light of certain fundamentals of biophysical chemistry and biochemistry. Finally, an alternative hypothesis has been presented based on the differential effect of the post-mortem formation of lactic acid (H+ ion concentration) on the intra- and extracellular components of muscle and the possible role of lysosomal cathepsins. Consequently, a series of biophysical, biochemical, and ultrastructural changes seem to account for the mechanism by which meat becomes tender during the aging process.