scholarly journals Aromatic-radical oxidation chemistry

1993 ◽  
Author(s):  
I. Glassman ◽  
K. Brezinsky
Keyword(s):  
Radical Oxidation ◽  
Aromatic Radical ◽  
Oxidation Chemistry

scholarly journals Nighttime and daytime dark oxidation chemistry in wildfire plumes: an observation and model analysis of FIREX-AQ aircraft data

2021 ◽  
Vol 21 (21) ◽  
pp. 16293-16317
Author(s):  
Zachary C. J. Decker ◽  
Michael A. Robinson ◽  
Kelley C. Barsanti ◽  
Ilann Bourgeois ◽  
Matthew M. Coggon ◽  
...  
Keyword(s):  
Air Quality ◽  
Atmospheric Chemistry ◽  
The United States ◽  
Urban Environments ◽  
Nitrate Radical ◽  
Mobile Platforms ◽  
Radical Oxidation ◽  
Research Aircraft ◽  
Oxidation Chemistry ◽  
The Impact

Abstract. Wildfires are increasing in size across the western US, leading to increases in human smoke exposure and associated negative health impacts. The impact of biomass burning (BB) smoke, including wildfires, on regional air quality depends on emissions, transport, and chemistry, including oxidation of emitted BB volatile organic compounds (BBVOCs) by the hydroxyl radical (OH), nitrate radical (NO3), and ozone (O3). During the daytime, when light penetrates the plumes, BBVOCs are oxidized mainly by O3 and OH. In contrast, at night or in optically dense plumes, BBVOCs are oxidized mainly by O3 and NO3. This work focuses on the transition between daytime and nighttime oxidation, which has significant implications for the formation of secondary pollutants and loss of nitrogen oxides (NOx=NO+NO2) and has been understudied. We present wildfire plume observations made during FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality), a field campaign involving multiple aircraft, ground, satellite, and mobile platforms that took place in the United States in the summer of 2019 to study both wildfire and agricultural burning emissions and atmospheric chemistry. We use observations from two research aircraft, the NASA DC-8 and the NOAA Twin Otter, with a detailed chemical box model, including updated phenolic mechanisms, to analyze smoke sampled during midday, sunset, and nighttime. Aircraft observations suggest a range of NO3 production rates (0.1–1.5 ppbv h−1) in plumes transported during both midday and after dark. Modeled initial instantaneous reactivity toward BBVOCs for NO3, OH, and O3 is 80.1 %, 87.7 %, and 99.6 %, respectively. Initial NO3 reactivity is 10–104 times greater than typical values in forested or urban environments, and reactions with BBVOCs account for >97 % of NO3 loss in sunlit plumes (jNO2 up to 4×10-3s-1), while conventional photochemical NO3 loss through reaction with NO and photolysis are minor pathways. Alkenes and furans are mostly oxidized by OH and O3 (11 %–43 %, 54 %–88 % for alkenes; 18 %–55 %, 39 %–76 %, for furans, respectively), but phenolic oxidation is split between NO3, O3, and OH (26 %–52 %, 22 %–43 %, 16 %–33 %, respectively). Nitrate radical oxidation accounts for 26 %–52 % of phenolic chemical loss in sunset plumes and in an optically thick plume. Nitrocatechol yields varied between 33 % and 45 %, and NO3 chemistry in BB plumes emitted late in the day is responsible for 72 %–92 % (84 % in an optically thick midday plume) of nitrocatechol formation and controls nitrophenolic formation overall. As a result, overnight nitrophenolic formation pathways account for 56 %±2 % of NOx loss by sunrise the following day. In all but one overnight plume we modeled, there was remaining NOx (13 %–57 %) and BBVOCs (8 %–72 %) at sunrise.

scholarly journals Evaluation of the Chemical Composition of Gas and Particle Phase Products of Aromatic Oxidation

2020 ◽  
Author(s):  
Archit Mehra ◽  
Yuwei Wang ◽  
Jordan E. Krechmer ◽  
Andrew Lambe ◽  
Francesca Majluf ◽  
...  
Keyword(s):  
Urban Areas ◽  
Minor Component ◽  
Chemical Mechanism ◽  
Particle Phase ◽  
Radical Oxidation ◽  
Anthropogenic Pollutants ◽  
Trimethyl Benzene ◽  
Propyl Benzene ◽  
Oxidation Chemistry ◽  
A Minor

Abstract. Aromatic volatile organic compounds (VOC) are key anthropogenic pollutants emitted to the atmosphere and are important for both ozone and secondary organic aerosol (SOA) formation in urban areas. Recent studies have indicated that aromatic hydrocarbons may follow previously unknown oxidation chemistry pathways, including autoxidation that can lead to the formation of highly oxidised products. In this study we evaluate the gas and particle phase ions formed during the hydroxyl radical oxidation of substituted C9-aromatic isomers (1,3,5-trimethyl benzene, 1,2,4-trimethyl benzene, propyl benzene and isopropyl benzene) and a substituted polyaromatic hydrocarbon (1-methyl naphthalene) under low and medium NOx conditions. The majority of product signal in both gas and particle phases comes from ions which are common to all precursors, though signal distributions are distinct for different VOCs. Gas and particle phase composition are distinct from one another, and comparison with the near explicit gas phase Master Chemical Mechanism (MCMv3.3.1) highlights a range of missing highly oxidised products in the pathways. In the particle phase, the bulk of product signal from all precursors comes from ring scission ions, many of which have undergone further oxidation to form HOMs. Under perturbation of OH oxidation with increased NOx, the contribution of HOM ion signals to the particle phase signal remains elevated for more substituted aromatic precursors. Up to 25 % of product signal comes from ring-retaining ions including highly oxygenated organic molecules (HOMs); this is most important for the more substituted aromatics. Unique products are a minor component in these systems, and many of the dominant ions have ion formulae concurrent with other systems, highlighting the challenges in utilising marker ions for SOA.

scholarly journals Nighttime and Daytime Dark Oxidation Chemistry in Wildfire Plumes: An Observation and Model Analysis of FIREX-AQ Aircraft Data

2021 ◽  
Author(s):  
Zachary C. J. Decker ◽  
Michael A. Robinson ◽  
Kelley C. Barsanti ◽  
Ilann Bourgeois ◽  
Matthew M. Coggon ◽  
...  
Keyword(s):  
Air Quality ◽  
Atmospheric Chemistry ◽  
The United States ◽  
Urban Environments ◽  
Nitrate Radical ◽  
Mobile Platforms ◽  
Radical Oxidation ◽  
Research Aircraft ◽  
Oxidation Chemistry ◽  
The Impact

Abstract. Wildfires are increasing in size across the western U.S., leading to increases in human smoke exposure and associated negative health impacts. The impact of biomass burning (BB) smoke, including wildfires, on regional air quality depends on emissions, transport, and chemistry, including oxidation of emitted BB volatile organic compounds (BBVOCs) by the hydroxyl radical (OH), nitrate radical (NO3), and ozone (O3). During the daytime, when light penetrates the plumes, BBVOCs are oxidized mainly by O3 and OH. In contrast, at night, or in optically dense plumes, BBVOCs are oxidized mainly by O3 and NO3. This work focuses on the transition between daytime and nighttime oxidation, which has significant implications for the formation of secondary pollutants and loss of nitrogen oxides (NOx = NO + NO2), and has been understudied. We present wildfire plume observations made during FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality), a field campaign involving multiple aircraft, ground, satellite, and mobile platforms that took place in the United States in the summer of 2019 to study both wildfire and agricultural burning emissions and atmospheric chemistry. We use observations from two research aircraft, the NASA DC-8 and the NOAA Twin Otter, with a detailed chemical box model, including updated phenolic mechanisms, to analyze smoke sampled during mid-day, sunset, and nighttime. Aircraft observations suggest a range of NO3 production rates (0.1–1.5 ppbv h−1) in plumes transported both mid-day and after dark. Modeled initial instantaneous reactivity toward BBVOCs for NO3, OH, and O3 is 80.1 %, 87.7 %, 99.6 %, respectively. Initial NO3 reactivity is 10–104 times greater than typical values in forested or urban environments and reactions with BBVOCs account for ≥ 98 % of NO3 loss in sunlit plumes (jNO2 up to 4 x 10–3 s–1), while conventional photochemical NO3 loss through reaction with NO and photolysis are minor pathways. Alkenes and furans are mostly oxidized by OH and O3 (11–43 %, 54–88 % for alkenes; 18–55 %, 39–76 %, for furans, respectively), but phenolic oxidation is split between NO3, O3, and OH (26–52 %, 22–43 %, 16–33 %, respectively). Nitrate radical oxidation accounts for 26–52 % of phenolic chemical loss in sunset plumes and in an optically thick plume. Nitrocatechol yields varied between 33 % and 45 %, and NO3 chemistry in BB plumes emitted late in the day is responsible for 72–92 % (84 % in an optically thick mid-day plume) of nitrocatechol formation and controls nitrophenolic formation overall. As a result, overnight nitrophenolic formation pathways account for 56 ± 2 % of NOx loss by sunrise the following day. In all but one overnight plume we model, there is remaining NOx (13 %–57 %) and BBVOCs (8 %–72 %) at sunrise.

Oxidase Catalysis via an Aerobically Generated Dess-Martin Periodinane Analogue

2018 ◽  
Author(s):  
Asim Maity ◽  
Sung-Min Hyun ◽  
Alan Wortman ◽  
David Powers
Keyword(s):  
Chemical Synthesis ◽  
Aerobic Oxidation ◽  
Substrate Oxidation ◽  
Oxidation Catalysis ◽  
Hypervalent Iodine ◽  
Oxidation Reactions ◽  
Broad Array ◽  
Oxidation Chemistry ◽  
Reactive Oxidants

<p>Hypervalent iodine(V) reagents, such as Dess-Martin periodinane (DMP) and 2-iodoxybenzoic acid (IBX), are broadly useful oxidants in chemical synthesis. Development of strategies to access these reagents from O2 would immediately enable use of O2 as a terminal oxidant in a broad array of substrate oxidation reactions. Recently we disclosed the aerobic synthesis of I(III) reagents by intercepting reactive oxidants generated during aldehyde autoxidation. Here, we couple aerobic oxidation of iodobenzenes with disproportionation of the initially generated I(III) compounds to generate I(V) reagents. The aerobically generated I(V) reagents exhibit substrate oxidation chemistry analogous to that of DMP. Further, the developed aerobic generation of I(V) has enabled the first application of I(V) intermediates in aerobic oxidation catalysis.</p>

State of the enzyme link of antioxidant protection in boys with hypoandrogenism

2020 ◽  
Vol 40 (4) ◽  
pp. 32-36
Author(s):  
L. K. Parkhomenko ◽  
◽  
L. A. Strashok ◽  
S. I. Turchina ◽  
G. V. Kosovtsova ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Superoxide Dismutase ◽  
Free Radical ◽  
Glutathione Peroxidase ◽  
Free Radical Oxidation ◽  
Conjugated Dienes ◽  
Delayed Puberty ◽  
Control Group ◽  
Antioxidant Protection ◽  
Radical Oxidation

Recently, interest in the problem of free radical oxidation in biological membranes, which is directly related to both the normal functioning of cells and the occurrence, course and outcome of many pathological conditions, has increased again in clinical medicine. The aim was to determine the role and impact of antioxidant defense in boys with hypoandrogenism. The study involved 75 adolescents with hypoandrogenism aged 13–18 years, who underwent a complex of clinical and laboratory examinations. All patients were conducted complex of anthropometric research and determination of the degree of delayed puberty, laboratory and instrumental examination. Free radical oxidation was determined by the levels of malondialdehyde, conjugated dienes, carbonated proteins, superoxide dismutase and catalase in the serum, and restored glutathione and glutathione peroxidase in whole blood. Based on their determination, the coefficient of oxidative stress was calculated. Statistical processing of results was performed using parametric and nonparametric methods. The study of indicators of the free radical oxidation process found that adolescents with hypoandrogenism have multidirectional changes in the oxidation of proteins and lipids, namely: the level of conjugated dienes increases, the concentration of malondialdehyde remains at the level of the control group, and the level of carbonated proteins tends to decrease. As for the activity of antioxidant protection enzymes, a significant decrease in the level of glutathione peroxidase was detected, while the level of superoxide dismutase and catalase remained at the level of normative indicators. Oxidative stress accompanies and is one of the pathogenetic links in the formation or maintenance of the state of hypoandrogenism in boys. This requires the use of antioxidants, the complex of which must be selected individually.

Adaptogenic correction of free radical brain damage in subchronic exposure to sodium fl uoride

2020 ◽  
pp. 381-386
Author(s):  
A. G. Zhukova ◽  
L. G. Gorokhova ◽  
A. S. Kazitskaya ◽  
T. K. Yadykina ◽  
N. N. Mikhailova ◽  
...  
Keyword(s):  
Cerebral Cortex ◽  
Free Radical ◽  
Brain Tissue ◽  
Free Radical Oxidation ◽  
Radical Oxidation ◽  
Free Radical Processes ◽  
Subchronic Exposure ◽  
Antioxidant Defense Enzymes ◽  
Radical Processes ◽  
Complex Drug

Introduction. Fluorine compounds in small doses, but with prolonged exposure, cause various disorders in organs at the cellular and molecular levels. Activation of free-radical processes plays an important role in the damaging eff ect of fl uorides. Th erefore, one of the most eff ective ways to limit fl uorine-induced damage is to directly aff ect free-radical processes using herbal preparations with antioxidant properties.The aim of the study is to study the eff ect of a dihydroquercetin-based drug on the activity of free radical processes in brain tissue under subchronic exposure to sodium fl uoride (NaF).Materials and methods. Th e work was performed on white male laboratory rats weighing 200-250 g. Th e rats were divided into 3 groups: 1 — control; 2 — rats with chronic exposure to sodium fl uoride (NaF) for 9 weeks; 3 — rats receiving a NAF solution with simultaneous administration of a complex drug based on dihydroquercetin at a dose of 3 mg/kg in 1% starch gel for 3, 6 and 9 weeks. The activity of free radical oxidation and antioxidant defense enzymes — superoxide dismutase (SOD) and catalase-was determined in the cerebral cortex. Th e level of expression of hypoxia-induced transcription factor HIF — 1A and inducible forms of proteins HSP72 and HSP32 were determined in the cytosolic fraction of brain tissue.Results. In the early stages of subchronic fl uoride exposure (1-3 weeks), the expression of protective proteins HIF-1α, HSP72, HSP32 and catalase was shown in the rat cortex, as a result of which the activity of free-radical processes was maintained at the control level. An increase in the timing of fl uoride intake to 9 weeks led to a decrease in antioxidant protection and signifi cant activation of free radical oxidation in brain tissue. Daily administration of a complex drug with dihydroquercetin for 3, 6 and 9 weeks to rats with subchronic fl uoride exposure led to a decrease in the severity of pro- and antioxidant balance disorders in the cerebral cortex. At the same time, the greatest protective eff ect of dihydroquercetin with fl uoride exposure was manifested by the 9th week of its administration.Conclusions. When subchronic intake of fl uorides in the body, the drug based on dihydroquercetin has a neuroprotective eff ect, which is manifested by an increase in the activity of antioxidant enzymes of fr ee radical oxidation and catalase and the resistance of the cortex to induced fr ee radical oxidation.

Sign in / Sign up

Export Citation Format

Share Document