Dark Oxidation Research Articles

Effects on the Flavor and Oxidative Stability of Stripped Soybean and Sunflower Oils with Added Pure Tocopherols

Effects of tocopherols on the oxidative stability of stripped vegetable oils were studied by adding pure tocopherols--alpha, beta, gamma, and delta--in their naturally occurring proportions in soybean and sunflower oils to the triacylglycerols (TAG) of soybean and sunflower oils. Soybean and sunflower oils were purified by stripping all minor constituents, leaving the triacylglycerols. Pure tocopherols in the proportion typical of sunflower oil--high alpha, low gamma, and low delta--were added to purified sunflower oil and to purified soybean oil. Pure tocopherols in the proportion typical of soybean oil--low alpha, high gamma, and high delta--were added to the purified oils. Oils were subjected to accelerated autoxidation using oven storage at 60 degrees C in the dark and accelerated photooxidation at 7500 lx light intensity at 30 degrees C. Oxidation levels of aged oils were measured by the formation of both peroxides and volatile compounds and by flavor analysis. Results from substituting the tocopherol profile from one oil type to another varied on the basis of whether they were oxidized in the dark or in the light. For example, during autoxidation in the dark, soybean oil with the typical soybean tocopherol profile had the lowest levels of peroxides and total volatile compounds, whereas sunflower oil with the sunflower tocopherol profile had the highest levels. In flavor analyses of the same oils, sunflower oil with the soybean tocopherol profile was the most stable. Soybean oil with the profile of sunflower tocopherols was the least stable in dark oxidation. In contrast to the data from autoxidation in the dark, addition of tocopherols typical of sunflower oil significantly improved light stability of both oil types compared to the addition of soybean tocopherols to sunflower oil. The tocopherol profile typical of soybean oil was significantly more effective in inhibiting autoxidation in the dark; however, the tocopherol profile typical of sunflower oil inhibited light oxidation significantly more than the soybean tocopherol profile.

Synthesis and morphological investigation of pulsed current formed nano-structured lead dioxide

Synthesis and morphological investigation of pulsed current formed nano-structured lead dioxide

Fracture modes of HAYNES ® 230 ® alloy during fatigue-crack-growth at room and elevated temperatures

Fracture modes of HAYNES ® 230 ® alloy during fatigue-crack-growth at room and elevated temperatures

Dark Oxidation of Dissolved and Liquid Elemental Mercury in Aquatic Environments

Elemental mercury (Hg0) can be found in liquid or dissolved forms in aquatic systems. Whereas dissolved Hg0 is measured in virtually all aquatic systems, liquid Hg0 droplets are mainly observed at poorly lit sediment/water interfaces of ecosystems with local point sources such as hydro-thermal vents, gold extraction sites, and near industrial facilities. Here, we report that, in the dark, liquid and dissolved forms of Hg behave differently with respect to their oxidation. Liquid Hg0 is rapidly oxidized in oxygenated solution in the presence of chloride. Liquid Hg0 oxidation rates are positively correlated with chloride concentrations and droplet surface area. When liquid Hg is removed from solution, the oxidation stops even though the solution is still saturated with dissolved Hg0. Liquid Hg0 droplets in oxygenated marine or brackish environments should be oxidized and release Hg2+ to solution. In freshwaters or anoxic seawater, liquid Hg will dissolve releasing Hg(aq)0 which, itself, will slowly oxidize.

Sunlight and iron(III)-induced photochemical production of dissolved gaseous mercury in freshwater.

Mechanistic understanding of sunlight-induced natural processes for production of dissolved gaseous mercury (DGM) in freshwaters has remained limited, and few direct field tests of the mechanistic hypotheses are available. We exposed ferric iron salt-spiked fresh surface lake water (Whitefish Bay, Lake Superior, MI) in Teflon bottles and pond water (Oak Ridge, TN) in quartz bottles to sunlight in the field to infer if sunlight and Fe(III)-induced photochemical production of DGM could mechanistically contribute partly to natural photochemical production of DGM in freshwaters. We found that exposure of freshwater spiked with fresh Fe(III) (approximately 5 or 10 microM) to sunlight led to repeatable, significantly larger increases in DGM production (e.g., 380% in 1 h, 420% in 2 h, and 470% in 4 h for Whitefish Bay water) than exposure without the spike (e.g., 200% in 6 h). DGM increased with increasing exposure time and then often appeared to approach a steady state in the tests. Higher Fe(III) spike levels resulted in the same, or even less, DGM production. Storage of the water with or without Fe(III) spike in the dark after sunlight exposure led to significant, apparently first-order, decreases in DGM. These phenomena were hypothetically attributed to sunlight-induced photochemical production of highly reducing organic free radicals through photolysis of Fe(III)-organic acid coordination compounds and subsequent reduction of Hg(II) to Hg(0) by the organic free radicals; the reduction was also accompanied by dark oxidation of Hg(0) by photochemically originated oxidants (e.g., .OH). This study suggests that sunlight and Fe(III)-induced photochemical reduction of Hg(II) could be one of the mechanisms responsible for natural photochemical production of DGM in freshwaters and that Fe species may be influential in mediating Hg chemodynamics and its subsequent toxicity in aquatic ecosystems.

An assessment of the pathways of dark reduction and oxidation of the plastoquinone pool in thylakoid membranes of higher plants and green algae

Several possible `chlororespiratory? pathways have been proposed for both reduction and oxidation of the plastoquinone pool in the dark in cells of both higher plants and green algae. However, bioinformatic analysis of the recently published genome of Arabidopsis thaliana sets limits to the types of respiratory-related components that could be present in higher plant thylakoids: for example, homologues of cytochrome c oxidase, succinate dehydrogenase and alternative NDH-2 enzymes in thylakoids can be ruled out and there are also no thylakoid-targetted homologues of the NADH-reactive fragment of mitochondrial complex I (the 75kDa, 51 kDa and 30 kDa subunits) that might provide an NADH dehydrogenase fragment for the other complex I homologues that are encoded in the chloroplast genome. In parallel to these considerations, direct assay of pathways of dark reduction and oxidation of plastoquinone has been made in intact leaves and in cells of Chlamydomonas reinhardtii by monitoring P700+ reduction, the slow phase of the carotenoid bandshift and turnover kinetics of the cytochrome bf complex. Combination of these measurements with effects of a wide range of specific inhibitors of various quinone-reactive sites has allowed further definition of the types of pathways and their extents.

Redox Changes of Cytochrome b559 in the Presence of Plastoquinones

We have found that short chain plastoquinones effectively stimulated photoreduction of the low potential form of cytochrome b(559) and were also active in dark oxidation of this cytochrome under anaerobic conditions in Triton X-100-solubilized photosystem II (PSII) particles. It is also shown that molecular oxygen competes considerably with the prenylquinones in cytochrome b(559) oxidation under aerobic conditions, indicating that both molecular oxygen and plastoquinones could be electron acceptors from cytochrome b(559) in PSII preparations. alpha-Tocopherol quinone was not active in the stimulation of cytochrome photoreduction but efficiently oxidized it in the dark. Both the observed photoreduction and dark oxidation of the cytochrome were not sensitive to 3-(3,4-dichlorophenyl)-1, 1-dimethylurea. It was concluded that both quinone-binding sites responsible for the redox changes of cytochrome b(559) are different from either the Q(A) or Q(B) site in PSII and represent new quinone-binding sites in PSII.

Photoelectrochemical Oxidation of Aqueous Sulfite on Ni−TiO2 Composite Film Electrodes

The photoelectrochemical oxidation of aqueous sulfite on composite electrode films comprising titania particles as the dispersed component and nickel as the matrix (Ni−TiO2) is described. These composite films exhibit unusual photocurrent enhancement for sulfite oxidation relative to the corresponding neat TiO2 films containing no nickel. Both the morphology of the composite films and their surface chemical composition (Ni:Ti ratio) are shown to play a role in the photocurrent enhancement mechanism. Two potential domains for sulfite photooxidation separated by the onset of dark oxidation of sulfite by the nickel matrix itself are considered.

Characteristics of p-chlorophenol degradation by Photo Fenton oxidation

This study investigated the characteristics of Photo Fenton oxidation in comparison with Fenton oxidation in dark environments. The specific objective was to provide an in-depth understanding as to how the presence of UV would effect the reaction and its efficiency as compared to the Dark Fenton Oxidation. All reactions were carried out in batch mode at an initial pH of 3.5, with H2O2 in excess and iron in catalytic concentrations. The medium pressure mercury lamp (320-400 nm) was used as a UV source. The role of UV in Photo Fenton Oxidation of p-chlorophenol was found to be manyfold as compared to Dark Fenton Oxidation. It included the expedition of ferric ion reduction and the photolysis of H2O2, which exerted a direct impact on the p-chlorophenol degradation kinetics by enhancing the production of OH radical. Also included in the role was alteration of the quantity (and potentially quality) of intermediates, which would lead to a change in the decomposition kinetics in an indirect manner. Therefore, it was concluded that the performance of Photo Fenton Oxidation as compared to Dark Fenton Oxidation could vary in complicated ways depending upon the characteristics of target compounds and their intermediates.

Biochemistry of Indian summer: physiology of autumnal leaf coloration.

Biochemistry of Indian summer: physiology of autumnal leaf coloration.

Microbiological Explorations in the Northern Part of the Barents Sea in Early Winter

The total number of microorganisms and rates of microbial processes of the carbon cycle were determined in snow, sea ice, water, and seafloor sediments of the northern part of the Barents Sea from September to October, 1998. The explorations were carried out in two areas: along the transection from Franz Josef Land to Victoria Island and along the continental slope region covered with solid ice at latitude 81°–82° N and longitude 37°–39° E. At the time of study, the ice cover was represented by thick one-year old ice (up to 1.2 m), perennial ice (up to 1.85 m), and pack ice. The number of bacteria in the snow cover, sea ice, and seawater was 12 to 14, 50 to 110, and 10 to 240 × 103 cells/ml, respectively. Rates of dark CO2 assimilation, glucose utilization, and methane oxidation by bacteria were determined. The highest rate of microbial processes was found in samples of the lowermost newly formed sea ice. The lowest level of activity for all processes was observed in melted snow water. A direct relation was shown between the concentration of Corg, the bacterial biomass, and the values of δ13Corg in mixtures of melted snow and ice. The number of microorganisms and rates of microbial processes in seafloor sediments measured at the stations on the continental slope are comparable to those in the central part of the Barents Sea and the northern part of the Kara Sea.

Mechanism of reduced flavin transfer from Vibrio harveyi NADPH-FMN oxidoreductase to luciferase.

The mechanisms of reduced flavin transfer in biological systems are poorly understood at the present. The Vibrio harveyi NADPH-FMN oxidoreductase (FRP) and the luciferase pair were chosen as a model for the delineation of the reduced flavin transfer mechanism. FRP, which uses FMN as a cofactor to mediate the reduction of the flavin substrate by NADPH, exhibited a ping-pong kinetic pattern with a Km, FMN of 8 microM and a Km,NADPH of 20 microM in a single-enzyme spectrophotometric assay monitoring the NADPH oxidation. However, the kinetic mechanism of FRP was changed to a sequential pattern with a Km,FMN of 0.3 microM and a Km,NADPH of 0.02 microM in a luciferase-coupled assay measuring light emission. In contrast, the Photobacterium fischeri NAD(P)H-FMN oxidoreductase FRG showed the same ping-pong mechanism in both the single-enzyme spectrophotometric and the luciferase-coupled assays. Moreover, for the FRP, FMN at concentrations over 2 microM significantly inhibited the coupled reaction in both light intensity and quantum yield, and showed apparent noncompetitive and competitive inhibition patterns against NADPH and luciferase, respectively. No inhibition of the NADPH oxidation was detected under identical conditions. These results are consistent with a scheme that the reduced flavin cofactor of FRP is preferentially utilized by luciferase for light emission, the reduced flavin product generated by the reductase is primarily channeled into a dark oxidation, and luciferase competes against flavin substrate in reacting with the FRP reduced flavin cofactor. An FRP derivative containing 2-thioFMN as the cofactor was also used to further examine the mechanism of flavin transfer. Results again indicate a preferential utilization of the reductase reduced flavin cofactor by luciferase for the bioluminescence reaction.

Photochemistry of Tetracene Adsorbed on Dry Silica: Products and Mechanism

Abstract The photochemistry of tetracene (1) has been studied on dry silica at very low surface coverages (less than 3% of a monolayer). Irradiation of degassed samples of 1 adsorbed on silica surface proceeds very slowly to produce both syn (2) and anti (3) dimers. Under aerated conditions photolysis of 1 at surface coverages <1% of a monolayer gives mainly tetracene‐5, 12‐endoperoxide (4) and very little dimer. The endoperoxide slowly decomposes to form 5, 12‐tetracenequinone (5), 5, 12‐dihydroxytetracene (6) and 5, 12‐dihydro‐5, 12‐dihydroxytetracene (7), respectively. As the surface coverage is increased above 1% of a monolayer, dimerization becomes more pronounced as a result of pairing and/or aggregation. The photooxidation process is mediated by the addition of singlet molecular oxygen to 1. Tetracene also undergoes a dark oxidation reaction on the silica surface to give 5 (major), 6 and 7 (minors) as products. The first‐order rate constant for this Lewis acid‐catalyzed oxidation was determined to be 1 × 105 S−1.

Formula omitted] process for photo-oxidation of waterborne hazardous substances — C 1C 6 chlorinated hydrocarbons

formula omitted] process for photo-oxidation of waterborne hazardous substances — C 1C 6 chlorinated hydrocarbons

Sunlight Induced Decoloration/Degradation of Non-Biodegradable Orange II Dye by Advanced Oxidation Technologies in Homogeneous and Heterogeneous Media

Abstract Light and dark oxidation processes of organic compounds involving H

Metal chelates of porphyrin derivatives as sensitizers in photooxidation processes of sulfur compounds and in photodynamic therapy of cancer

A number of porphyrin derivatives based on hematoporphyrin, 5,10,15,20-tetrasubstituted porphyrins, phthalocyanines, and naphthalocyanines were prepared either as low-molecular compounds or bonded with methoxypoly(ethylene glycol) or attached to silica of low surface area. The low-molecular weight and the polymer-bonded porphyrins exhibit comparable triplet lifetimes and activities in the photosensitized formation of singlet oxygen. For photoninduced processes, the monomeric state of sensitizers is fundamentally important. The porphyrins have been investigated as sensitizers for photooxidation of thiolates and sulfides, which occursvia singlet oxygen, and, therefore, is much more efficient than the corresponding catalytic dark oxidation. Polymer-bonded porphyrins and long-wavelength absorbing naphthalocyanines incorporated in liposomes exhibitin vivo high accumulation in tumor tissues. Under irradiation, singlet oxygen is produced, and efficient phototherapeutic effects are observed, which may be used for photodynamic cancer therapy.

A study of copper electrode behavior in alkaline solutions containing benzotriazole-type inhibitors by the photocurrent response method and intensity modulated photocurrent spectroscopy

A study of copper electrode behavior in alkaline solutions containing benzotriazole-type inhibitors by the photocurrent response method and intensity modulated photocurrent spectroscopy

Characterization of GaAs-(001) Surface Photo-Oxide Formed by Visible-Light Irradiation

The effects of visible-light irradiation (70-280 mW/cm2) on oxidation of a GaAs (001) surface under an oxygen atmosphere (3.6×101 and 8.6×104 Pa) were investigated by temperature programmed desorption and X-ray photoelectron spectroscopy (XPS). XPS showed that irradiation at an intensity of 140 mW/cm2 increased the amount of surface oxygen by about 15% over dark oxidation of the corresponding oxygen exposure. Under 540°C isothermal conditions, the oxide desorption rate was initially low, but reached its maximum level with a time delay, showing the existence of expanding voids in the oxide layer during desorption. Light irradiation, as well as higher oxygen exposure, decreased the initial desorption rate, and increased the time delay by up to 6.4 min. This is interpreted as indicating that irradiation reduces the density of the weak parts in the oxide layer through an increase in the oxide thickness.

Interactions of Halogenated Benzoquinones with the Non-Heme Iron (Q400) in Photosystem II

Abstract Interactions of halogenated benzoquinones with the acceptor side of Photosystem (PS) II were studied by measuring fluorescence induction curves and flash-induced absorbance changes in PS II particles isolated from Synechococcus vulcanus. Following results were obtained: 1) Addition of some halogenated benzoquinones prior to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) in the dark increased the area above the fluorescence induction curve (work integral) by a factor of two. 2) Based on the ability to increase the fluorescence work integral, halogenated benzoquinones could be divided into two groups. 3) 2,6-Dichlorobenzo-quinone (2,6-DCBQ), trichlorobenzoquinone (TCBQ) and tetrahalogenated benzoquinones except tetrafluorobenzoquinone (fluoranil) (group A) increased the work integral, but 2,5-DCBQ and fluoranil (group B) did not. 4) Rapid reoxidation of QA - was observed in the presence of quinones which belong to group A. These results were interpreted in terms of dark oxidation of by quinones belonging to group A. Possible mechanisms of oxidation of Q400 by these quinones in the dark are discussed.

Inhibition of chlororespiration by myxothiazol and antimycin A in Chlamydomonas reinhardtii

Myxothiazol and antimycin A are shown to suppress the oxygen transient previously attributed to the flash-induced inhibition of chlororespiration in Chlamydomonas reinhardtii (Peltier et al. 1987, Biochim Biophys Acta 893: 83-90). However, these two compounds do not affect the photosynthetic electron transport chain as inferred by the insensitivity of the CO2-dependent photosynthetic O2 evolution and of the flash-induced electrochromic effect. Chlorophyll fluorescence induction measurements carried out in dark-adapted cells of a mutant of Chlamydomonas lacking photosystem 1, show that myxothiazol and antimycin A significantly increase the redox state of the photosystem 2 acceptors. We conclude from these results that chlororespiration is inhibited by myxothiazol and antimycin A and that the site of inhibition is located on the dark oxidation pathway of the plastoquinone pool. This inhibition is interpreted through the involvement of a myxothiazol and antimycin A sensitive cytochrome in the chlororespiratory chain.