Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 3.550
Filtrar
1.
Nature ; 585(7824): 225-233, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32908268

RESUMO

Isoprene is the dominant non-methane organic compound emitted to the atmosphere1-3. It drives ozone and aerosol production, modulates atmospheric oxidation and interacts with the global nitrogen cycle4-8. Isoprene emissions are highly uncertain1,9, as is the nonlinear chemistry coupling isoprene and the hydroxyl radical, OH-its primary sink10-13. Here we present global isoprene measurements taken from space using the Cross-track Infrared Sounder. Together with observations of formaldehyde, an isoprene oxidation product, these measurements provide constraints on isoprene emissions and atmospheric oxidation. We find that the isoprene-formaldehyde relationships measured from space are broadly consistent with the current understanding of isoprene-OH chemistry, with no indication of missing OH recycling at low nitrogen oxide concentrations. We analyse these datasets over four global isoprene hotspots in relation to model predictions, and present a quantification of isoprene emissions based directly on satellite measurements of isoprene itself. A major discrepancy emerges over Amazonia, where current underestimates of natural nitrogen oxide emissions bias modelled OH and hence isoprene. Over southern Africa, we find that a prominent isoprene hotspot is missing from bottom-up predictions. A multi-year analysis sheds light on interannual isoprene variability, and suggests the influence of the El Niño/Southern Oscillation.


Assuntos
Atmosfera/química , Butadienos/análise , Butadienos/química , Mapeamento Geográfico , Hemiterpenos/análise , Hemiterpenos/química , Imagens de Satélites , África , Austrália , Brasil , Conjuntos de Dados como Assunto , El Niño Oscilação Sul , Formaldeído/química , Radical Hidroxila/análise , Radical Hidroxila/química , Ciclo do Nitrogênio , Óxidos de Nitrogênio/análise , Óxidos de Nitrogênio/química , Oxirredução , Estações do Ano , Sudeste dos Estados Unidos
2.
Free Radic Res ; 54(7): 517-524, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32781874

RESUMO

The present study reports radiation-chemical yields of 2.5-diaminoimidazolone (Iz) derivatives in X-irradiated phosphate-buffered solutions of guanosine and double-stranded DNA. Various gassing conditions (air, N20/O2 (4:1), N2O, vacuum) were employed to elucidate the contribution of several alternative pathways leading to Iz in reactions initiated by hydroxyl radical attack on guanine. In all systems, Iz was identified as the second by abundance guanine degradation product after 8-oxoguanine, formed in 1:5 (guanosine) and 1:3.3 (DNA) ratio to the latter in air-saturated solutions. Experimental data strongly suggest that the addition of molecular oxygen to the neutral guanine radical G(-H)• plays a major in Iz production in oxygenated solutions of double-stranded DNA while in other systems it may compete with recombination of G(-H)• with superoxide and/or alkyl peroxyl radicals. The production of Iz through hydroxyl radical attack on 8-oxoguanine was also shown to take place although the chemical yield of Iz (ca 6%) in this process is too low to compete with the other pathways. The linearity of Iz accumulation with dose also indicates a negligible contribution of this channel to its yield in all systems.


Assuntos
Dano ao DNA , DNA/química , Radicais Livres/química , Radical Hidroxila/química , Imidazóis/química , 8-Hidroxi-2'-Desoxiguanosina/química , Animais , DNA/efeitos da radiação , Diaminas/química , Guanosina/química , Masculino , Salmão
3.
Food Chem ; 332: 127396, 2020 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-32615386

RESUMO

The effects of oxidation degree on the isoelectric point (pI), aggregation, and structural characteristics for pork myofibrillar protein (MP) were studied by employing extracted MP, which was incubated by using a hydroxyl radical oxidation system. The concentrations of hydrogen peroxide (H2O2) were 0, 0.5, 1, 3, 5, 10, and 20 mM. With the increased oxidation degree, the contents of α-helix, ionic bonds, and hydrogen bonds decreased significantly (P < 0.05). Moreover, the pI value and total amino acids showed a declining trend, and the ß-sheet as well as solubility rised firstly and then declined. On the contrary, random curl, ß-turn, and turbidity increased significantly (P < 0.05). Therefore, amino acid side chain groups were modified, and the opposite effect, caused by oxidation that leads to protein cross-linking and aggregation, was greater than the promotion effect, such as net negative charge, these are the main factors that leads to the instability of protein solution systems.


Assuntos
Proteínas Musculares/química , Agregados Proteicos , Animais , Peróxido de Hidrogênio/química , Radical Hidroxila/química , Ponto Isoelétrico , Oxirredução , Solubilidade , Suínos
4.
Chemosphere ; 259: 127396, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32645596

RESUMO

The performance of the UV/H2O2 advanced oxidation process (AOP) is dependent on water quality parameters, including the UV absorbance coefficient at 254 nm and hydroxyl radical (•OH) water background demand (scavenging factor, s-1). The •OH scavenging factor represents the •OH scavenging rate of the background substances in the water matrix, and it is known to be one of the key parameters to predict the performance of the UV/H2O2 process. The •OH scavenging factor has been determined experimentally by using a probe compound such as pCBA and rhodamine B. The experimental method has been validated to accurately predict the micropollutants removal in the UV/H2O2 process, but there is a need for an easier and simple method of determining the OH scavenging factor. We evaluated the alternative method to analyze the •OH scavenging factor using fluorescence excitation-emission matrix and parallel factor analysis (F-EEM/PARAFAC). The correlation between •OH scavenging factor and the spectroscopic characteristics and structure of different organic matter types was evaluated. Organic matter was characterized using a fluorescence excitation-emission matrix, parallel factor analysis, and liquid chromatography-organic carbon detection. Second-order reaction rates of humic acid sodium salt, sodium alginate, Suwannee River humic acid and bovine serum albumin were calculated as 1.30 × 108 M-1 s-1, 1.39 × 108 M-1 s-1, 1.03 × 108 M-1 s-1, and 3.17 × 107 M-1 s-1, respectively. Results of PARAFAC analysis, the ratio of humic and fulvic fluorescence component 2 to terrestrial humic-like fluorescence component 1 (C2/C1), and •OH scavenging factor showed high linearity. A predictive model, which combines with the F-EEM/PARAFAC method, predicted the optimal UV and H2O2 dose to achieve target compound removal.


Assuntos
Poluentes Químicos da Água/química , Purificação da Água/métodos , Análise Fatorial , Fluorescência , Substâncias Húmicas/análise , Peróxido de Hidrogênio/análise , Radical Hidroxila/química , Oxirredução , Rios/química , Espectrometria de Fluorescência/métodos , Água/análise , Poluentes Químicos da Água/análise , Qualidade da Água
5.
Chemosphere ; 259: 127331, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32650175

RESUMO

The atmospheric degradation of polycyclic aromatic hydrocarbons (PAHs) can generate organic pollutants that contribute to the formation of secondary organic aerosols (SOAs) and exacerbate their carcinogenicity. Indene is an example of styrene-like bicyclic hydrocarbons that are not fully aromatic. The OH-initiated atmospheric oxidation of indene in the presence of O2 and NO was investigated using quantum chemical methods at M06-2X/6-311++G(3df,2p)//M06-2X/6-311+G(d,p) level. The oxidation products are oxygenated polycyclic aromatic hydrocarbons (OPAHs) containing hydroxyindene, indenone, dialdehydes and 2-(formylmethyl)benzaldehyde. Calculation results showed that 7-indene radical, which is the precursor of various PAHs, has a high production ratio that is 35.29% in the initial reaction, indicating that the OH-initiated oxidation increase the environmental risks of indene in the atmosphere. The rate constants for the crucial elementary reactions were calculated based on Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The overall rate constant of the initial reaction is calculated to be 1.04 × 10-10 cm3 molecule-1 s-1 and the atmospheric lifetime of indene is determined as 2.74 h. This work provides a comprehensive understanding on the oxidation mechanisms of indene and the findings could help to clarify the fate of indene in the atmosphere.


Assuntos
Poluentes Atmosféricos/química , Atmosfera/química , Radical Hidroxila/química , Indenos/química , Aerossóis , Cinética , Óxidos de Nitrogênio/química , Oxirredução , Oxigênio/química , Hidrocarbonetos Policíclicos Aromáticos
6.
Arch Biochem Biophys ; 690: 108432, 2020 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-32663474

RESUMO

Oxidative stress is proposed to be one of the major causes of neurodegenerative diseases. Cellular prion protein (PrP) oxidation has been widely studied using chemical reagents such as hydrogen peroxide. However, the experimental conditions used do not faithfully reflect the physiological environment of the cell. With the goal to explore the conformational landscape of PrP under oxidative stress, we conducted a set of experiments combining the careful control of the nature and the amount of ROS produced by a60Co γ-irradiation source. Characterization of the resulting protein species was achieved using a set of analytical techniques. Under our experimental condition hydroxyl radical are the main reactive species produced. The most important findings are i) the formation of molecular assemblies under oxidative stress, ii) the detection of a majority of unmodified monomer mixed with oxidized monomers in these molecular assemblies at low hydroxyl radical concentration, iii) the absence of significant oxidation on the monomer fraction after irradiation. Molecular assemblies are produced in small amounts and were shown to be an octamer. These results suggest either i) an active recruitment of intact monomers by molecular assemblies' oxidized monomers then inducing a structural change of their intact counterparts or ii) an intrinsic capability of intact monomer conformers to spontaneously associate to form stable molecular assemblies when oxidized monomers are present. Finally, abundances of the intact monomer conformers after irradiation were modified. This suggests that monomers of the molecular assemblies exchange structural information with intact irradiated monomer. All these results shed a new light on structural exchange information between PrP monomers under oxidative stress.


Assuntos
Proteínas Priônicas/química , Sequência de Aminoácidos , Escherichia coli/genética , Humanos , Peróxido de Hidrogênio/química , Radical Hidroxila/química , Espectrometria de Massas , Concentração Osmolar , Oxirredução , Estresse Oxidativo , Proteínas Priônicas/genética , Conformação Proteica , Multimerização Proteica , Espécies Reativas de Oxigênio/química
7.
Proc Natl Acad Sci U S A ; 117(31): 18216-18223, 2020 08 04.
Artigo em Inglês | MEDLINE | ID: mdl-32680962

RESUMO

Cysteine disulfides, which constitute an important component in biological redox buffer systems, are highly reactive toward the hydroxyl radical (•OH). The mechanistic details of this reaction, however, remain unclear, largely due to the difficulty in characterizing unstable reaction products. Herein, we have developed a combined approach involving mass spectrometry (MS) and theoretical calculations to investigate reactions of •OH with cysteine disulfides (Cys-S-S-R) in the gas phase. Four types of first-generation products were identified: protonated ions of the cysteine thiyl radical (+Cys-S•), cysteine (+Cys-SH), cysteine sulfinyl radical (+Cys-SO•), and cysteine sulfenic acid (+Cys-SOH). The relative reaction rates and product branching ratios responded sensitively to the electronic property of the R group, providing key evidence to deriving a two-step reaction mechanism. The first step involved •OH conducting a back-side attack on one of the sulfur atoms, forming sulfenic acid (-SOH) and thiyl radical (-S•) product pairs. A subsequent H transfer step within the product complex was favored for protonated systems, generating sulfinyl radical (-SO•) and thiol (-SH) products. Because sulfenic acid is a potent scavenger of peroxyl radicals, our results implied that cysteine disulfide can form two lines of defense against reactive oxygen species, one using the cysteine disulfide itself and the other using the sulfenic acid product of the conversion of cysteine disulfide. This aspect suggested that, in a nonpolar environment, cysteine disulfides might play a more active role in the antioxidant network than previously appreciated.


Assuntos
Antioxidantes/química , Cisteína/química , Radical Hidroxila/química , Espectrometria de Massas , Modelos Moleculares , Estrutura Molecular , Compostos de Sulfidrila/química
8.
Chemosphere ; 260: 127460, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32673866

RESUMO

Advanced oxidation processes (AOPs), such as photolysis, photocatalysis, ozonation, Fenton process, anodic oxidation, sonolysis, and wet air oxidation, have been investigated extensively for the removal of a wide range of trace organic contaminants (TrOCs). A standalone AOP may not achieve complete removal of a broad group of TrOCs. When combined, AOPs produce more hydroxyl radicals, thus performing better degradation of the TrOCs. A number of studies have reported significant improvement in TrOC degradation efficiency by using a combination of AOPs. This review briefly discusses the individual AOPs and their limitations towards the degradation of TrOCs containing different functional groups. It also classifies integrated AOPs and comprehensively explains their effectiveness for the degradation of a wide range of TrOCs. Integrated AOPs are categorized as UV irradiation based AOPs, ozonation/Fenton process-based AOPs, and electrochemical AOPs. Under appropriate conditions, combined AOPs not only initiate degradation but may also lead to complete mineralization. Various factors can affect the efficiency of integrated processes including water chemistry, the molecular structure of TrCOs, and ions co-occurring in water. For example, the presence of organic ions (e.g., humic acid and fulvic acid) and inorganic ions (e.g., halide, carbonate, and nitrate ions) in water can have a significant impact. In general, these ions either convert to high redox potential radicals upon collision with other reactive species and increase the reaction rates, or may act as radical scavengers and decrease the process efficiency.


Assuntos
Poluentes Químicos da Água/análise , Purificação da Água , Benzopiranos , Carbonatos/química , Substâncias Húmicas , Peróxido de Hidrogênio/química , Radical Hidroxila/química , Oxirredução , Fotólise , Raios Ultravioleta
9.
Chemosphere ; 257: 127256, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32531489

RESUMO

Five kinds of Al2O3 were characterized by SEM, TEM, FT-IR and BET surface area, and then used as carriers to investigate the photochemical removal of hexachlorobenzene (HCB) in aqueous system. The results showed that HCB coated on the surfaces of all Al2O3 could be photodegraded rapidly, and Neutral-Al2O3 presented the best performance. Meanwhile, the efficient removal of HCB in real water matrices, including tap water, river water and secondary clarifier effluent showed the potential practical application of Al2O3. EPR and theoretical calculation revealed the generation of hydroxyl radicals on Al2O3 surface under 500 W Xe lamp irradiation. Nine intermediates and a small amount of Cl- were identified by GC/MS, LC/MS and IC analysis, which was further verified by transition state calculations. These results can provide a new technique for HCB removal in water and wastewaters, and give more insights into the environmental ecological risk assessment of this pollutant.


Assuntos
Óxido de Alumínio/química , Hexaclorobenzeno/química , Poluentes Químicos da Água/química , Cromatografia Gasosa-Espectrometria de Massas , Radical Hidroxila/química , Cinética , Espectroscopia de Infravermelho com Transformada de Fourier , Água
10.
Chemosphere ; 258: 127268, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32569955

RESUMO

In this work, UVA radiation that is part of solar light is taken as the irradiation source and radicals (HO, SO4- and HO2/O2-) are generated through activation of hydrogen peroxide (H2O2), sodium persulfate (Na2S2O8) and Bismuth catalyst (BiOCl), respectively. The distinguished performance in removing acetaminophen (ACTP), a model pharmaceutical pollutant, by these three radicals was compared for the first time. Effect of pH, halide ions concentration and interfacial mechanism have been investigated in detail. Interestingly, results show that heterogeneous UVA/BiOCl process has higher degradation efficiency than homogeneous UVA/H2O2 and UVA/Na2S2O8 systems whatever the solution's pH. To explain these results, second order reaction rate constant (kradical, ACTP) have been determined with laser flash photolysis (LFP) or radical scavenging experiments. The strongly interfacial-depended HO2/O2- radicals have the lowest second order rate constant with ACTP but highest steady state concentration. BiOCl is much easier activated by UVA, and outstanding ACTP mineralization can be achieved. Combination of BiOCl and Na2S2O8 exhibits synergistic effects rather than antagonism effects with H2O2. This study highlights the relative effective utilization of solar light through interfacial directed BiOCl photocatalysis and its synergistic effects with traditional oxidants.


Assuntos
Acetaminofen/análise , Peróxido de Hidrogênio/química , Oxidantes/química , Compostos de Sódio/química , Sulfatos/química , Raios Ultravioleta , Poluentes Químicos da Água/análise , Bismuto/química , Catálise , Radical Hidroxila/química , Modelos Teóricos , Oxirredução
11.
Chemosphere ; 258: 127216, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32535436

RESUMO

The degradation of fluopyram (FLP) was investigated under ozone-microbubble treatment (OMBT). Kinetic models were established to study the influence of three treatments: ozonated water, microbubbles (MCB), and OMBT. FLP degraded completely in OMBT, and a clearance rate of 89.8-100% was achievable. Three direct transformation products [product 1 (F1), product 2 (F2), and product 3(F3)] were isolated and identified using a hybrid ion trap-orbitrap mass spectrometer. Moreover, a transformation theory of FLP degradation was developed according to targeted fragmentation, accurate mass measurements, and degradation profiles. These analyses showed that the products originated from a series of chemical reactions involving dechlorination, hydroxyl substitution, cleavage and oxidation, and were further confirmed based on molecular electrostatic potential and molecular orbital theory. In addition, the stability and toxicity of FLP and its transformation products were tested using the Toxicity Estimation Software Tool (T.E.S.T.) and the Ecological Structure Activity Relationships (ECOSAR) program. Products F1, F2 and F3 were found to be toxic substances, but their toxicity to aquatic organisms was lower than that of FLP. However, they were more toxic to rats than FLP, and their physicochemical properties were more stable. Overall, OMBT is a highly effective method for FLP removal during wastewater treatment.


Assuntos
Benzamidas/análise , Microbolhas , Ozônio/química , Piridinas/análise , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Animais , Organismos Aquáticos/efeitos dos fármacos , Benzamidas/toxicidade , Radical Hidroxila/química , Cinética , Dose Letal Mediana , Oxirredução , Piridinas/toxicidade , Ratos , Testes de Toxicidade Aguda , Águas Residuárias/química , Poluentes Químicos da Água/toxicidade
12.
Chemosphere ; 258: 127208, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32544810

RESUMO

Pyridine and organics containing pyridine rings are widely used but persist in the environment and cause toxic pollution. Due to the attraction of the nitrogen atoms to the electrons in the pi bond, the pyridine ring is difficult to oxidize by oxidant. Here, we propose that ultraviolet (UV) irradiation activates the electrons in the pi bond and enables combination with the hydroxyl radical (OH) originating from hydrogen peroxide (H2O2) to eliminate pyridine quickly and mineralize the byproducts. The removal rates of pyridine and total organic carbon (TOC) were compared in different treatments: UV irradiation, UV/H2O2 treatment and Fenton oxidation with different initial pyridine concentrations, pH values and H2O2 concentrations. The UV/H2O2 treatment yielded a higher pyridine removal rate and greater mineralization than the other treatments. The removal rate of pyridine was highest in neutral aqueous solution and H2O2 concentration of 10 mM. At an initial H2O2 concentration of 10 mM, more than 90% of the pyridine was degraded in 10 min, and approximately 70% of the TOC was removed in 60 min. The absorption of UV light at 254 nm by the pi bond of pyridine can accelerate the damage to the stable pyridine structure, especially in the presence of OH. This study provides a promising alternative for the removal and mineralization of pyridine ring-containing materials.


Assuntos
Peróxido de Hidrogênio/química , Fotólise , Piridinas/análise , Raios Ultravioleta , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Estudos de Viabilidade , Concentração de Íons de Hidrogênio , Radical Hidroxila/química , Oxirredução , Piridinas/efeitos da radiação , Poluentes Químicos da Água/efeitos da radiação
13.
Chemosphere ; 258: 127378, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32554023

RESUMO

Light driven degradation is very promising for pollutants remediation. In the present work, photochemical reaction of tetrabromobisphenol A (TBBPA) under LED white light (λ > 400 nm) irradiation system was investigated to figure out the TBBPA photochemical degradation pathways and isotope fractionation patterns associated with transformation mechanisms. Results indicated that photochemical degradation of TBBPA would happen only with addition to humic acid in air bubbling but not in N2 bubbling. For photochemical reaction of TBBPA, singlet oxygen (1O2) was found to be important reactive oxygen species for the photochemical degradation of TBBPA. 2,6-Dibromo-4-(propan-2-ylidene)cyclohexa-2,5-dienone and two isopropyl phenol derivatives were identified as the photochemical degradation intermediates by 1O2. 2,6-Dibromo-4-(1-methoxy-ethyl)-phenol was determined as an intermediate via oxidative skeletal rearrangement, reduction and O-methylation. Hydrolysis product hydroxyl-tribromobisphenol A was also observed in the reductive debromination process. In addition, to deeply explore the mechanism, carbon and bromine isotope analysis were performed using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) and gas chromatography-multicollector inductively coupled plasma mass spectrometry (GC/MC/ICPMS) during the photochemical degradation of TBBPA. The results showed that photochemical degradation could not result in statistically significant isotope fractionation, indicated that the bond cleavage of C-C and C-Br were not the rate controlling process. Stable isotope of carbon being not fractionated will be useful for distinguishing the pathways of TBBPA and tracing TBBPA fate in water systems. This work sheds light on photochemical degradation mechanisms of brominated organic contaminants.


Assuntos
Recuperação e Remediação Ambiental/métodos , Fotólise , Bifenil Polibromatos/análise , Poluentes Químicos da Água/análise , Substâncias Húmicas/análise , Radical Hidroxila/química , Isótopos , Modelos Teóricos , Oxirredução , Bifenil Polibromatos/efeitos da radiação , Oxigênio Singlete/química , Poluentes Químicos da Água/efeitos da radiação
14.
Food Chem ; 331: 127350, 2020 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-32590267

RESUMO

Fish by-products are excellent sources of collagen. Acid-soluble collagen (ASC) derived from a mixed by-product of different fish species was hydrolyzed to obtain peptide fractions and evaluate their biological and functional activities. All fractions obtained (F1: ≥30, F2: 10-30, F3: 5-10, F4: 1-5, and F5: ≤1kDa) exhibited antioxidant activity at concentrations of 5, 10, and 15 mg/mL. However, F5 registered the highest reducing power (absorbance 0.366) and hydroxyl-radical-scavenging activity (91%) at 15 mg/mL; whereas the highest DPPH scavenging activity (81%) was also detected in F5 at 5 mg/mL. The solubility of F1, F2, and F3 was ≥ 95% at pH 7. The highest foaming capacity (78%), foaming stability (60%), and emulsion stability index (42 min) were registered for F1. However, the highest emulsifying activity index (130 m2/g) was for F3. These results place collagen obtained from a mixed by-product of different fish species as a potential biotechnological alternative for the industry.


Assuntos
Antioxidantes/farmacologia , Colágeno/química , Produtos Pesqueiros , Proteínas de Peixes/química , Peptídeos/química , Peptídeos/farmacologia , Aminoácidos/análise , Animais , Antibacterianos/química , Antibacterianos/farmacologia , Antioxidantes/química , Emulsificantes/química , Proteínas de Peixes/farmacologia , Depuradores de Radicais Livres/química , Concentração de Íons de Hidrogênio , Hidrólise , Radical Hidroxila/química , Hidrolisados de Proteína/química , Solubilidade
15.
Chemosphere ; 256: 126994, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32445996

RESUMO

Dichloroacetonitrile (DCAN) is one of the most toxic and common nitrogenous disinfection by-products in water treatment. It is necessary to understand how this compound can be removed. In this study, the effectiveness of vacuum ultraviolet (VUV) at 185 nm was evaluated to destroy DCAN. When water is exposed to VUV, hydroxyl radicals (HO•), hydrogen atoms (H•), and hydrated electrons (eaq-) are generated. The individual contributions of these reactive species to DCAN degradation were distinguished using multiple scavengers. The results showed that eaq- was the most important species for DCAN degradation. The second-order rate constant for eaq- reacting with DCAN was calculated to be 3.16 × 1010 M-1s-1 using a quantitative structure-activity relationship (QSAR) method adopted from previous study, and determined to be 3.76 (±0.02) × 1010 M-1s-1 by competition kinetics. Although dissolved oxygen (DO) at 8 mg/L consumed 86% eaq-, the rest of eaq- still led to 93% removal of DCAN within 20 min. Chloride was the major inorganic product of DCAN degradation, while nitrate and nitrite were minor products. Quantum chemical calculation and mass balance calculation under an oxygen free condition further suggested that cleavage of C-Cl bonds was the major pathway by eaq- attack. This study demonstrated the significant role of eaq- in micropollutant destruction during VUV treatment.


Assuntos
Acetonitrilos/metabolismo , Poluentes Químicos da Água/metabolismo , Cloro , Desinfecção , Elétrons , Radical Hidroxila/química , Cinética , Nitratos , Nitrogênio , Fotólise , Raios Ultravioleta , Vácuo , Poluentes Químicos da Água/análise , Purificação da Água/métodos
16.
Chemosphere ; 256: 126997, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32473466

RESUMO

Syringic acid (Syr) is an abundant component in aerosol particles. Multiphase photo-oxidation in aerosol phase provides an important oxidation pathway for Syr in the atmosphere. In this work, we studied the multiphase degradation of Syr by measuring rate coefficients of its reactions with potential radical oxidants (OH and SO4-) in aqueous solutions and by theoretical calculations, and degradation mechanisms by identifying the (intermediate) products. Rate coefficients, in 109 M-1 s-1, were obtained as 32 ± 2 (pH 3) and 25 ± 2 (pH 6) for reactions with OH radical, and 1.7 ± 0.1 (pH 3) and 0.9 ± 0.02 (pH 6) for reactions with SO4-. Reactions of Syr with OH and SO4- were all in diffusion-control limit. Rate coefficients' difference under pH 6 and pH 3 in SO4- reaction was caused by Coulomb's force between negatively charged species. Theoretical calculations showed that the reaction of Syr with OH starts mainly by hydrogen atom transfer (HAT) from phenolic groups and secondly by OH addition to the aromatic ring. No product was identified in the reaction of Syr and OH radical at pH 3 due probably to the rapid mineralization of phenoxy radical formed from HAT, while products after OH additions were identified for a reaction at pH 6. On the other hand, reaction of Syr with SO4- starts by single-electron transfer (SET), forming Syr+, which can undergo hydrolysis, sulfation, and dimerization with Syr and other aromatic intermediates, etc. Dimerization products from the phenoxy-type radical were not found here.


Assuntos
Ácido Gálico/análogos & derivados , Poluentes Químicos da Água/química , Atmosfera , Transporte de Elétrons , Ácido Gálico/química , Hidrogênio , Concentração de Íons de Hidrogênio , Radical Hidroxila/química , Cinética , Oxirredução , Sulfatos/química , Água
17.
Chemosphere ; 255: 127031, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32417518

RESUMO

Oxidations of aniline (AN) initiated by OH-radicals are simulated in the temperature range 200-400 K using DFT/M06-2X/6-311++G(2df,2p) and ab initio ROCBS-QB3 levels. Chemical kinetics of such reactions were investigated based on several approaches including classical transition state theory (TST), conical variational transition state theory (CVT), and Rice-Ramsperger-Kassel-Marcus master equation (RRKM-ME) theories. Under atmospheric conditions, the reaction of OH radical with AN and the subsequent reactions with O2 molecules are investigated. The results indicate that the majority of O2 addition goes to the anti-directions with a branching ratio of 97.7% and produces the bicyclic peroxy radicals (BPRs) that can react with NO radical to form bicyclic alkoxy radicals (BARs). The latter compounds can be stabilized either by cyclization or via ring cleavage.


Assuntos
Poluentes Atmosféricos/análise , Compostos de Anilina/análise , Atmosfera/química , Radical Hidroxila/química , Modelos Teóricos , Aminofenóis/análise , Cinética , Nitrobenzenos/análise , Oxirredução , Fotoperíodo , Temperatura
18.
Chemistry ; 26(34): 7583-7588, 2020 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-32428322

RESUMO

Co single-atom catalysts (SACs) with good aqueous solubility and abundant labelling functional groups were prepared in Co/Fe bimetallic metal-organic frameworks by a facile solvothermal method without high-temperature calcination. In contrast to traditional chemiluminescence (CL) catalysts, Co SACs accelerated decomposition of H2 O2 to produce a large amount of singlet oxygen (1 O2 ) rather than superoxide (O2 .- ) and hydroxyl radical (OH. ). They were found to dramatically enhance the CL emission of the luminol-H2 O2 reaction by 1349 times, and, therefore, were employed as very sensitive signal probes for conducting CL immunoassay of cardiac troponin I. The detection limit of the target analyte was as low as 3.3 pg mL-1 . It is the first time that employment of SACs for boosting CL reactions has been validated. The Co SACs can also be employed to trace other biorecognition events with high sensitivity.


Assuntos
Radical Hidroxila/química , Luminol/química , Oxigênio Singlete/química , Catálise , Limite de Detecção , Luminescência , Medições Luminescentes/métodos , Estruturas Metalorgânicas , Superóxidos
19.
J Vis Exp ; (158)2020 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-32310230

RESUMO

Fast oxidation of proteins (FPOP) is a hydroxyl radical protein footprinting (HRPF) method used to study protein structure, protein-ligand interactions, and protein-protein interactions. FPOP utilizes a KrF excimer laser at 248 nm for photolysis of hydrogen peroxide to generate hydroxyl radicals which in turn oxidatively modify solvent-accessible amino acid side chains. Recently, we expanded the use of FPOP of in vivo oxidative labeling in Caenorhabditis elegans (C. elegans), entitled IV-FPOP. The transparent nematodes have been used as model systems for many human diseases. Structural studies in C. elegans by IV-FPOP is feasible because of the animal's ability to uptake hydrogen peroxide, their transparency to laser irradiation at 248 nm, and the irreversible nature of the modification. The assembly of a microfluidic flow system for IV-FPOP labeling, IV-FPOP parameters, protein extraction, and LC-MS/MS optimized parameters are described herein.


Assuntos
Caenorhabditis elegans/metabolismo , Radical Hidroxila/química , Pegadas de Proteínas/métodos , Animais
20.
Chemosphere ; 253: 126662, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32268253

RESUMO

In this study, pyrite (FeS2) was used as a novel activator of calcium peroxide (CaO2) for the degradation of diethyl phthalate (DEP) in both aqueous solution and soil. DEP (10 mg/L) in aqueous solution was completely degraded within 5.0 min by the FeS2 (0.30 g/L)/CaO2 (1.0 mM) system at pH 3.5. X-ray diffraction (XRD), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), free radical quenching, and X-ray photoelectron spectroscopy (XPS) were used to elucidate the mechanism of the catalytic decomposition of CaO2, radical formation and DEP degradation in the presence of by pyrite. The results show that hydroxyl radicals (OH) are the dominant active species responsible for DEP degradation. Surface or lattice Fe(II) of FeS2 readily activates H2O2 generated by CaO2 decomposition to produce OH, while the reducing sulfur species of FeS2 promotes the regeneration of surface of Fe(II) that catalyzes the production of additional OH, leading to the efficiently oxidative degradation of DEP. Although high concentration of common anions, such as Cl-, NO3-, SO42-, and HCO3-, exert inhibitory effects on DEP degradation by pyrite/CaO2, the reaction system can still efficiently degrade DEP in realistic soil. It was observed that 78% of DEP (25 mg kg-1) was degraded by 2.5% CaO2 (w/w) and 0.5% FeS2 (w/w) within 24 h. These results provide new insight into the mechanistic processes of CaO2 activation and OH formation by the novel FeS2 catalyst, demonstrating a promising alternative to the traditional H2O2-base Fenton process for contaminated soil remediation.


Assuntos
Ferro/química , Peróxidos/química , Ácidos Ftálicos/química , Sulfetos/química , Catálise , Espectroscopia de Ressonância de Spin Eletrônica , Radicais Livres , Peróxido de Hidrogênio/química , Radical Hidroxila/química , Oxirredução , Espectroscopia Fotoeletrônica , Enxofre
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA