Quercetin-dependent reduction of salivary nitrite to nitric oxide under acidic conditions and interaction between quercetin and ascorbic acid during the reduction

A salivary component, nitrate, is reduced to nitrite in the oral cavity. Polyphenols in foods are mixed with nitrite in the saliva to be swallowed into the stomach. An objective of the present study is to elucidate reactions between a polyphenol quercetin and a nitrite under acidic conditions. Nitric oxide, which is formed by the reactions between nitrous acid and quercetin or ascorbic acid (AA), can be measured using an oxygen electrode in the saliva as well as a buffer solution. The initial oxidation of quercetin was inhibited by AA, and quercetin enhanced the oxidation of AA, suggesting AA-dependent reduction of quercetin radicals, which might be formed during the oxidation of quercetin by nitrous acid. On the basis of the above results, the usefulness of an oxygen electrode for the measurement of nitrite-dependent nitric oxide formation under acidic conditions is proposed and the possible mechanism of reduction of nitrous acid by quercetin and the interaction between quercetin and AA, which is a normal component in the gastric juice, for the reduction of nitrous acid is discussed.     

Evaluation of the Reactivity of Organic Pollutants during O3/H2O2 Process

The reactivity of selected compounds in Lake Huron water was evaluated during ozone/hydrogen peroxide-based advanced oxidation process (AOP) and conventional treatment (coagulation?Csedimentation?Cfiltration). Elimination of these compounds via advanced oxidation and conventional treatment processes were strongly related to their molecular structures. Overall removal of target compounds was quite similar in effluents from both the AOP and the combined treatment process (AOP?+?conventional) with the exception of fluoxetine. Reaction rate constants for the decomposition of the target compounds were substantially higher during AOP compared to conventional treatment alone.     

Kinetic characterization of the oxidation of chlorogenic acid by polyphenol oxidase and peroxidase. Characteristics of the o-quinone

Chlorogenic acid is the major diphenol of many fruits, where it is oxidized enzymatically by polyphenol oxidase (PPO) or peroxidase (POD) to its o-quinone. In spectrophotometric studies of chlorogenic acid oxidation with a periodate ratio of [CGA]0/[IO4-]0 < 1 and [CGA]0/[IO4-]0 > 1, the o-quinone was characterized as follows: lambda(max) at 400 nm and epsilon = 2000 and 2200 M-1 cm-1 at pH 4.5 and 7.0, respectively. In studies of o-quinone generated by the oxidation of chlorogenic acid using a periodate at ratio of [CGA]0/[IO4-]0 > 1, a reaction with the remaining substrate was detected, showing rate constants of k = 2.73 +/- 0.17 M-1 s-1 and k' = 0.05 +/- 0.01 M-1 s-1 at the above pH values. A chronometric spectrophotometric method is proposed to kinetically characterize the action of the PPO or POD on the basis of measuring the time it takes for a given amount of ascorbic acid to be consumed in the reaction with the o-quinone. The kinetic constants of mushroom PPO and horseradish POD are determined.     

Effect of pH on absorbance of azo dye formed by reaction between nitrite and sulfanilamide/N-(1-naphthyl)ethylenediamine in residual nitrite methods for foods

Current methods used for determining residual nitrite concentration in foods involve forming an azo dye that is measured spectrophotometrically. Conventional procedures do not specify control of pH for the final colored solution. Because many indicator dyes are pH-dependent, absorbance of the azo dye may vary not only because of nitrite concentration differences, but also because of pH variation. Thus, erroneous results could arise from a standard curve developed at one pH and used for a test sample at a different pH. This would cause an inaccurate concentration conversion from the standard curve. In this study, absorbances at lambda max wavelengths were recorded at 28 pH values (range 1.0-4.5) for each of 5 nitrite concentrations. A mathematical equation was fitted to these data and its plot gives a 3-dimensional response surface showing the relationships between pH, nitrite concentration, and absorbance. A modification for the spectrophotometric measurement of nitrite is proposed.     

Chinese cabbage extracts and sulforaphane can protect H2O2-induced inhibition of gap junctional intercellular communication through the inactivation of ERK1/2 and p38 MAP kinases

The cruciferous vegetables such as Chinese cabbages and broccoli are known to have anticancer phytochemicals, and the consumption of cruciferous vegetables has been proposed to protect against various cancers. The anticarcinogenic properties of some Chinese cabbage extracts and sulforaphane glucosinolate (SFN) were assessed by examining their ability to prevent the inhibition of gap junctional intercellular communication (GJIC) induced by hydrogen peroxide (H2O2) in WB-F344 normal rat liver epithelial cells. The cells were preincubated with Chinese cabbage extracts and SFN for 24 h followed by cotreatment with cells and H2O2 (750 microM) for 1 h. Chinese cabbage extracts and SFN prevented the inhibition of GJIC and phosphorylation of gap junction protein connexin43 (Cx43) by H2O2 treatment. Chinese cabbage extracts and SFN were able to prevent the inhibition of GJIC through the blocking of Cx43 phosphorylaton and inactivation of ERK 1/2 and p38 MAP kinase. The results suggest that cruciferous vegetables and their components, SFN, may exert the anticancer effect by targeting the GJIC as a functional dietary chemopreventive agent.     

The Oxidation of Di-(2-Ethylhexyl) Phthalate (DEHP) in Aqueous Solution by UV/H2O2 Photolysis

The oxidation of di-(2-ethylhexyl) phthalate (DEHP) in solution using UV/H₂O₂ and direct UV photolysis are analyzed in this study. It was found that DEHP was 100% removal in the solution by 180-min UV/H₂O₂ treatment and 73.5% removal by 180-min direct UV photolysis. The effect of different factors, such as DEHP concentration, H₂O₂ concentration, and UV light intensity, on photochemical degradation was investigated. The degradation mechanism of DEHP and the acute toxicity of intermediates were also studied. The photochemical degradation process was found to follow pseudo-first-order kinetics. The results of our study suggested that the concentration with 40 mg/L H₂O₂ and 5 μg/mL DEHP in the solution at pH 7 with 10.0?×?10^?6 Einstein l^?1?s^?1 UV was the optimal condition for the photochemical degradation of DEHP. The photochemical degradation with UV/H₂O₂ can be an efficient method to remove DEHP in wastewater.     

Free radical scavenging activity of grape seed extract and antioxidants by electron spin resonance spectrometry in an H(2)O(2)/NaOH/DMSO system.

The scavenging effects of grape seed extract (GSE) on free radicals formed in an H(2)O(2)/NaOH/DMSO system were examined using a spin-trapping electron spin resonance (ESR) method and compared with other natural antioxidants, ascorbic acid, dl-alpha-tocopherol, and beta-carotene. GSE reduced greatly the ESR signal intensity of superoxide radical-5,5-dimethyl-1-pyrroline-N-oxide (DMPO) adducts. GSE also exhibited weak scavenging activity on hydroxyl radical and a little scavenging activity on methyl radical. Ascorbic acid exhibited strong superoxide and hydroxyl radical scavenging activities, but it increased the amount of methyl radical at high concentration. dl-alpha-Tocopherol reduced the amount of superoxide anion, especially the amount of methyl radical. However, it slightly reduced the amount of hydroxyl radical. beta-Carotene reduced the amount of hydroxyl radical and methyl radical, but it also slightly reduced superoxide anion. In the case of combination use of beta-carotene and dl-alpha-tocopherol, all radical species were suppressed. Combination of GSE and dl-alpha-tocopherol also could reduce all radical species. beta-Carotene and dl-alpha-tocopherol could reduce the methyl radical formation induced by ascorbic acid.     

气管材质和长度对农田小气候CO2/H2O分析仪读数稳定时间的影响

CO₂和H₂O气体浓度是农田小气候的2个重要指标,一般采用CO₂/H₂O分析仪进行测定,为减少人为干扰,需使用气管将待测区域气体传输至分析器,而气管的材质及其长度会影响CO₂/H₂O测定时读数稳定所需的时间。本研究采用8种常用材质的气管及5种气管长度进行双因素随机区组试验,以筛选CO₂/H₂O测定所需的最佳气管材质及长度。结果表明：不同材质气管测定CO₂浓度的稳定时间为9.20～11.47s,测定H₂O气体浓度的稳定时间为9.67～18.93s。利用主效可加互作可乘（Additive main effects and multi-plicative interaction,AMMI）模型对CO₂/H₂O气体浓度达到稳定的时间进行方差分析和稳定性分析发现,在CO₂浓度观测过程中,气管长度的固定效应导致的变异最大,材质次之,材质与长度互作效应较小;各材质中,CO₂读数稳定时间最短的为蠕动泵管;在H₂O气体浓度观测过程中,存在显著的材质和长度间的互作效应,其中材质的固定效应导致的变异最大,长度次之,PVC管的读数稳定时间最短。不同材质与不同长度的交互作用不同,每种材质对不同长度都有其特殊的适应性。因此,应根据测定指标,选择稳定时间短的材质和长度,以提高农田CO₂和H₂O气体浓度的测定效率。     

Evaluation of free radical scavenging activities of antioxidants with an H(2)O(2)/NaOH/DMSO system by electron spin resonance.

An H(2)O(2)/NaOH/DMSO system has been developed for the formation of three free radicals, and the application of the system was examined with the antioxidants ascorbic acid and tocopherol. Superoxide anion, hydroxyl radical,and methyl radical are simultaneously generated in this system. The scavenging activity of ascorbic acid and tocopherol for these radicals was estimated by 5, 5'-dimethyl-1-pyrroline-N-oxide spin trapping electron spin resonance. Both water-soluble and oil-soluble antioxidants could be evaluated by using this system. Ascorbic acid specifically inhibited the superoxide anion and hydroxyl radical, whereas tocopherol suppressed the methyl radical.     

Effects of combined and sequential addition of dual oxidants (H2O2/S2O8(2-)) on the aqueous carbofuran photodegradation

Carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate) (CBF) is a widely used insecticide. Traditional methods like hydrolysis and direct photolysis cannot remove CBF effectively. In this study, the photodecay of 0.1 mM CBF in UV/H2O2, UV/S2O8(2-), and UV/H2O2/S2O8(2-) and sequential addition of a second oxidant were studied under UV light at 254 nm. The degradations of CBF follow pseudo-first-order decay kinetics. Direct photolysis was slow, but the corresponding degradation rate was increased with the addition of hydrogen peroxide (H2O2) or potassium peroxydisulfate (K2S2O8). In the UV/H2O2 reaction, the optimum reaction rate was 0.9841 min-1 at 10 mM H2O2 (pH 7); however, retardation is observed if H2O2 is overdosed. Such retardation is not observed in the UV/S2O8(2-) system, but a nonlinear increment of removal efficiency is identified. The UV/H2O2/S2O8(2-) process on the other hand shows the best performance in CBF degradation, but it has a less effective mineralization than that of the sole UV/S2O8(2-) reaction.     

Pseudoperoxidase activity of myoglobin: kinetics and mechanism of the peroxidase cycle of myoglobin with H2O2 and 2,2-azino-bis(3-ethylbenzthiazoline-6-sulfonate) as substrates

Using 2,2-azino-bis(3-ethylbenzthiazoline-6-sulfonate) (ABTS) as substrate, it has been shown that the increased peroxidase activity for decreasing pH of myoglobin activated by hydrogen peroxide is due to a protonization of ferrylmyoglobin, MbFe(IV)=O, facilitating electron transfer from the substrate and corresponding to pK(a) approximately 5.2 at 25.0 degrees C and ionic strength 0.16, rather than due to specific acid catalysis. On the basis of stopped flow absorption spectroscopy with detection of the radical cation ABTS(.+), the second-order rate constant and activation parameters for the reaction between MbFe(IV)=O and ABTS were found to have the values k = 698 +/- 32 M(-1) s(-1), DeltaH# = 66 +/- 4 kJ mol(-1), and DeltaS# = 30 +/- 15 J mol(-1) K(-1) at 25.0 degrees C and physiological pH (7.4) and ionic strength (= 0.16 M NaCl). At a lower pH (5.8) corresponding to the conditions in meat, values were found as follows: k = 3.5 +/- 0.3 x 10(4) M(-1) s(-1), DeltaH# = 31 +/- 6 kJ mol(-1), and DeltaS# = -53 +/- 19 J mol(-1) K(-1), indicative of a shift from outersphere electron transfer to an innersphere mechanism. For steady state assay conditions, this shift is paralleled by a shift from saturation kinetics at pH 7.4 to first-order kinetics for H2O2 as substrate at pH 5.8. In contrast, the activation reaction between myoglobin and hydrogen peroxide was found at 25.0 degrees C to be slow and independent of pH with values of 171 +/- 7 and 196 +/- 19 M(-1) s(-1) found at physiological and meat pH, respectively, as determined by sequential stopped flow spectroscopy, from which a lower limit of k = 6 x 10(5) M(-1) s(-1) for the reaction between perferrylmyoglobin, .MbFe(IV)=O, and ABTS could be estimated. As compared to the traditional peroxidase assay, a better characterization of pseudoperoxidase activity of heme pigments and their denatured or proteolyzed forms is thus becoming possible, and specific kinetic effects on activation, substrate oxidation, or shift in rate determining steps may be detected.     

Photodegradation of hexythiazox in different solvent systems under the influence of ultraviolet light and sunlight in the presence of TiO2, H2O2, and KNO3 and identification of the photometabolites

The photodegradation of the carboxamide acaricide hexythiazox in three different solvent systems (aqueous methanolic, aqueous isopropanolic, and aqueous acetonitrilic solutions) in the presence of H(2)O(2), KNO(3), and TiO(2) under ultraviolet (UV) light (λ(max) ≥ 250 nm) and sunlight (λ(max) ≥290 nm) has been assessed in this work. The kinetics of photodecomposition of hexythiazox and the identification of photoproducts were carried out using liquid chromatography-mass spectrometry. The rate of photodecomposition of hexythiazox in different solvents followed first-order kinetics in both UV radiation and natural sunlight, and the degradation rates were faster under UV light than under sunlight. Hexythiazox was found to be more efficiently photodegraded in the presence of TiO(2) than in the presence of H(2)O(2) and KNO(3). Two major photoproducts were separated in pure form using column chromatography and identified according to IR, (1)H NMR, and mass spectral information as cyclohexylamine and 5-(4-chlorophenyl)-4-methylthiazolidin-2-one. Another nine photoproducts were identified according to LC-MS/MS spectral information. The plausible photodegradation pathways of hexythiazox were proposed according to the structures of the photoproducts.     

Dual isotope and isotopomer measurements for the understanding of N2O production and consumption during denitrification in an arable soil

The aim of our research was to obtain information on the isotopic fingerprint of nitrous oxide (N₂O) associated with its production and consumption during denitrification. An arable soil was preincubated at high moisture content and subsequently amended with glucose (400 kg C ha^?1) and KNO₃ (80 kg N ha^?1) and kept at 85% water‐filled pore space. Twelve replicate samples of the soil were incubated for 13 days under a helium‐oxygen atmosphere, simultaneously measuring gas fluxes (N₂O, N₂ and CO₂) and isotope signatures (δ¹⁸O‐N₂O, δ¹⁵N^bulk‐N₂O, δ¹⁵N^α, δ¹⁵N^β and ¹⁵N site preference) of emitted N₂O. The maximum N₂O flux (6.9 ± 1.8 kg N ha^?1 day^?1) occurred 3 days after amendment application, followed by the maximum N₂ flux on day 4 (6.6 ± 3.0 kg N ha^?1 day^?1). The δ¹⁵N^bulk was initially ?34.4‰ and increased to +4.5‰ during the periods of maximum N₂ flux, demonstrating fractionation during N₂O reduction, and then decreased. The δ¹⁸O‐N₂O also increased, peaking with the maximum N₂ flux and remaining stable afterwards. The site preference (SP) decreased from the initial +7.5 to ?2.1‰ when the N₂O flux peaked, and then simultaneously increased with the appearance of the N₂ peak to +8.6‰ and remained stable thereafter, even when the O₂ supply was removed. We suggest that this results from a non‐homogenous distribution of NO in the soil, possibly linked to the KNO₃ amendments to the soil, causing the creation of several NO pools, which affected differently the isotopic signature of N₂O and the N₂O and N₂ fluxes during the various stages of the process. The N₂O isotopologue values reflected the temporal patterns observed in N₂O and N₂ fluxes. A concurrent increase in ¹⁵N site preference and δ¹⁸O of N₂O was found to be indicative of N₂O reduction to N₂.     

Tumor-promoting effect of GGN-MRP extract from the Maillard reaction products of glucose and glycine in the presence of sodium nitrite in C3H10T1/2 cells.

GGN-MRP is an extract from the Maillard reaction products of nitrite with glucose and glycine in the Maillard browning system. No genotoxicity of GGN-MRP in culture hepatocyte was found. A two-stage transformation protocol was used to transform chemically mouse embryo fibroblast C3H10T1/2 cells. To initiate transformation, the cells were treated with benzo[a]pyrene [B(a)P; 0.1 microg/mL], and GGN-MRP (0.01, 0.1, and 1.0 mg/mL) was employed to subsequently complete the transformation process. Malignant transformed foci were formed in B(a)P-initiated and GGN-MRP-promoted C3H10T1/2 cells after 8 weeks. Cells treated with GGN-MRP alone failed to induce transformation. However, cells initiated with B(a)P and promoted by GGN-MRP demonstrated oncogenic properties. Transformed colonies derived from GGN-MRP-treated cells exhibited enhanced growth rate, anchorage independence, and tumorgenicity in animals relative to parent cells. These results indicated that GGN-MRP contains a tumor promoter and may induce tumor promotion by two-stage oncogenesis.     

Stimulation of heterotrophic nitrification and N2O production,inhibition of autotrophic nitrification in soil by adding readily degradable carbon

Journal of Soils and Sediments - This study aimed to test the hypothesis that readily degradable Carbon (C) has contrasting effect on soil N autotrophic and heterotrophic nitrification, can...     

Fluxes of CO2, CH4, and N2O in an alpine meadow affected by yak excreta on the Qinghai-Tibetan plateau during summer grazing periods

To assess the impacts of yak excreta patches on greenhouse gas (GHG) fluxes in the alpine meadow of the Qinghai-Tibetan plateau, methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) fluxes were measured for the first time from experimental excreta patches placed on the meadow during the summer grazing seasons in 2005 and 2006. Dung patches were CH₄ sources (average 586 μg m⁻² h⁻¹ in 2005 and 199 μg m⁻² h⁻¹ in 2006) during the investigation period of two years, while urine patches (average −31 μg m⁻² h⁻¹ in 2005 and −33 μg m⁻² h⁻¹ in 2006) and control plots (average −28 μg m⁻² h⁻¹ in 2005 and −30 μg m⁻² h⁻¹ in 2006) consumed CH₄. The cumulative CO₂ emission for dung patches was about 36-50% higher than control plots during the experimental period in 2005 and 2006. The cumulative N₂O emissions for both urine and dung patches were 2.1-3.7 and 1.8-3.5 times greater than control plots in 2005 and 2006, respectively. Soil water-filled pore space (WFPS) explained 35% and 36% of CH₄ flux variation for urine patches and control plots, respectively. Soil temperature explained 40-75% of temporal variation of CO₂ emissions for all treatments. Temporal N₂O flux variation in urine patches (34%), dung patches (48%), and control (56%) plots was mainly driven by the simultaneous effect of soil temperature and WFPS. Although yak excreta patches significantly affected GHG fluxes, their contributions to the whole grazing alpine meadow in terms of CO₂ equivalents are limited under the moderate grazing intensity (1.45 yak ha⁻¹). However, the contributions of excreta patches to N₂O emissions are not negligible when estimating N₂O emissions in the grazing meadow. In this study, the N₂O emission factor of yak excreta patches varied with year (about 0.9-1.0%, and 0.1-0.2% in 2005 and 2006, respectively), which was lower than IPCC default value of 2%.     

Microbiological characterization of the structures built by earthworms and ants in an agricultural field

The genesis and architecture of the structures built by ants and earthworms differ markedly, suggesting that—in addition to having different physical and chemical properties—the resident microbial community should also have unique properties. We characterized the inorganic N, biomass C, C mineralization rate, and functional diversity of the microbial communities of earthworm casts, earthworm burrow soil, ant mounds, and bulk soil from an agricultural field. Mound soil was most enriched in inorganic N and had the lowest pH, moisture content, and C mineralization rate. Functional diversity was evaluated by determining the ability of microorganisms to grow on 31 substrates using Biolog^®EcoPlates in combination with a most probable number (MPN) approach. Casts had MPNs that were one to two orders of magnitude higher than burrow, mound and bulk soil for most substrates. Casts also had the highest MPNs for particular substrate guilds relative to bulk soil, followed by mound and burrow soil. Indices of substrate diversity and evenness were highest for casts, followed by burrow, mound, and bulk soil. Differences in the type of habitat provided by the structures built by ants and earthworms result in the differential distribution of nutrients, microbial activity, and metabolic diversity of soils within an agricultural field that affect soil fertility and quality.