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United States Environmental Protection Agency guidance on the use of photochemical models for assessing the efficacy of an emissions control strategy for ozone requires that modeling be used in a relative sense. Consequently, testing a modeling system's ability to predict changes in ozone resulting from emission changes is critical. We evaluate model simulations for precursor species (NOx, CO, and volatile organic compounds [VOCs]), radicals (OH and HO2), a secondary pollutant (O3), and the model response of these compounds to weekend/weekday emission changes during California Nexus study in 2010. The modeling system correctly simulated the broad spatial and temporal variation of NOx and O3 in California South Coast. Although the model generally underpredicted the daytime mixing ratios of NO2 at the surface and overpredicted the NO2 column, the simulated weekend to weekday ratios are consistent with each other and match the observed ratios well. The modeling system exhibited reasonable performance in simulating the VOC compounds with fossil fuel origins but has larger bias in simulating certain species associated with noncombustion sources. The modeling system successfully captured the weekend changes of the enhancement ratios for various VOC species to CO and the relative changes of HOx, which are indicators of faster chemical processing on weekends. This work demonstrates satisfactory model performances for O3 and most relevant chemical compounds with more robust performance in simulating weekend versus weekday changes. Improved planetary boundary layer height simulations, a better understanding of OH-HO2 cycling, continued improvement of emissions, especially urban biogenic emissions and emissions of oxygenated VOCs, are important for future model improvement.

A prototypical hydroperoxyalkyl radical (•QOOH) intermediate, transiently formed in the oxidation of volatile organic compounds, was directly observed through its infrared fingerprint and energy-dependent unimolecular decay to hydroxyl radical and cyclic ether products. Direct time-domain measurements of •QOOH unimolecular dissociation rates over a wide range of energies were found to be in accord with those predicted theoretically using state-of-the-art electronic structure characterizations of the transition state barrier region. Unimolecular decay was enhanced by substantial heavy-atom tunneling involving O-O elongation and C-C-O angle contraction along the reaction pathway. Master equation modeling yielded a fully a priori prediction of the pressure-dependent thermal unimolecular dissociation rates for the •QOOH intermediate—again increased by heavy-atom tunneling—which are required for global models of atmospheric and combustion chemistry. [ABSTRACT FROM AUTHOR]

Two new pregnane glycosides were isolated from the leaves of Gymnema sylvestre (Retz.) R.Br. ex Sm. Their chemical structures were determined as (20S)−12β-tigloyloxy-5α-hydroperoxy-3β,8β,14β,17β,20-pentahydroxypregn-6-ene 3-O-β-D-glucopyranosyl-(1→4)‐6-deoxy-3-O-methyl-β-D-allopyranosyl-(1→4)-β-D-oleandropyranosyl-(1→4)-β-D-cymaropyranosyl-(1→4)-β-D-cymaropyranoside (1) and (20S)−12β-benzoyloxy-5α-hydroperoxy-3β,8β,14β,17β,20-pentahydroxypregn-6-ene 3-O-β-D-glucopyranosyl-(1→4)‐6-deoxy-3-O-methyl-β-D-allopyranosyl-(1→4)-β-D-oleandropyranosyl-(1→4)-β-D-cymaropyranosyl-(1→4)-β-D-cymaropyranoside (2) on the basis of the extensive spectroscopic methods, including 1D, 2D NMR, HRESIMS, and in comparison with the reported data. At the concentration of 200 µM, compounds 1 and 2 showed moderate anti α-glucosidase and α-amylase activities with inhibitory percentage of 31.1 ± 1.2 and 42.3 ± 1.7% (for α-glucosidase), and 27.8 ± 1.3 and 34.5 ± 1.5% (for α-amylase), respectively. [ABSTRACT FROM AUTHOR]

The CH3 + HO2 reaction system was studied theoretically by a newly developed, HEAT345-(Q) method based CHEAT1 protocol and includes the combined singlet and triplet potential energy surfaces. The main simplification is based on the CCSDT(Q)/cc-pVDZ calculation which is computationally inexpensive. Despite the economic and black-box treatment of higher excitations, the results are within 0.6 kcal/mol of the highly accurate literature values. Furthermore, the CHEAT1 surpassed the popular standard composite methods such as CBS-4M, CBS-QB3, CBS-APNO, G2, G3, G3MP2B3, G4, W1U, and W1BD mainly due to their poor performance in characterizing transition states (TS). For TS structures, various standard DFT and MP2 method have also been tested against the resulting CCSD/cc-pVTZ geometry of our protocol. A fairly good agreement was only found in the cases of the B2PLYP and BHandHLYP functionals, which were able to reproduce the structures of all TS studied within a maximum absolute deviation of 7%. The complex reaction mechanism was extended by three new low lying reaction channels. These are indirect water elimination from CH3OOH resulted formaldehyde, H2 elimination yielded methylene peroxide, and methanol and reactive triplet oxygen were formed via H-shift in the third channel. CHEAT1 protocol based on HEAT345-(Q) method is a robust, general, and cheap alternative for high accurate kinetic calculations. [ABSTRACT FROM AUTHOR]

Two atmospherically relevant dihalogenated methylperoxy radicals CHX2OO. (X=F and Cl) have been generated through O2‐oxidation of the corresponding alkyl radicals CHX2. in the gas phase. The IR spectroscopic characterization of both radicals in cryogenic Ar‐ and N2‐matrices (15 K) is supported by 18O‐labeling and ab initio calculations at the UCCSD(T)/aug‐cc‐pVTZ level. Upon 266 nm laser irradiation, both radicals decompose mainly by releasing hydroxyl radicals (→HO.+X2CO) via the intermediacy of intriguing α‐hydroperoxyalkyl radicals (.CX2OOH), implying that the photooxidation of dihalogenated hydrocarbons might serve as important sources of HO. radicals in the atmosphere. [ABSTRACT FROM AUTHOR]

Two atmospherically relevant dihalogenated methylperoxy radicals CHX2OO. (X=F and Cl) have been generated through O2‐oxidation of the corresponding alkyl radicals CHX2. in the gas phase. The IR spectroscopic characterization of both radicals in cryogenic Ar‐ and N2‐matrices (15 K) is supported by 18O‐labeling and ab initio calculations at the UCCSD(T)/aug‐cc‐pVTZ level. Upon 266 nm laser irradiation, both radicals decompose mainly by releasing hydroxyl radicals (→HO.+X2CO) via the intermediacy of intriguing α‐hydroperoxyalkyl radicals (.CX2OOH), implying that the photooxidation of dihalogenated hydrocarbons might serve as important sources of HO. radicals in the atmosphere. [ABSTRACT FROM AUTHOR]

In this study, we discovered that a clear decrease in the electrochemiluminescence (ECL) intensities of luminol occurred upon increasing the electron donating capacity of amides. Therefore, herein, a novel ECL probe was used for the first time to screen the strength of the hydrogen bonds formed between HOOṖ radicals and amides. This proposed hydrogen bonding strength-sensitive ECL probe has a significant prospect in distinguishing the hydrogen bonding strength of different radicals. [ABSTRACT FROM AUTHOR]

United States Environmental Protection Agency guidance on the use of photochemical models for assessing the efficacy of an emissions control strategy for ozone requires that modeling be used in a relative sense. Consequently, testing a modeling system's ability to predict changes in ozone resulting from emission changes is critical. We evaluate model simulations for precursor species (NOx, CO, and volatile organic compounds [VOCs]), radicals (OH and HO2), a secondary pollutant (O3), and the model response of these compounds to weekend/weekday emission changes during California Nexus study in 2010. The modeling system correctly simulated the broad spatial and temporal variation of NOx and O3 in California South Coast. Although the model generally underpredicted the daytime mixing ratios of NO2 at the surface and overpredicted the NO2 column, the simulated weekend to weekday ratios are consistent with each other and match the observed ratios well. The modeling system exhibited reasonable performance in simulating the VOC compounds with fossil fuel origins but has larger bias in simulating certain species associated with noncombustion sources. The modeling system successfully captured the weekend changes of the enhancement ratios for various VOC species to CO and the relative changes of HOx, which are indicators of faster chemical processing on weekends. This work demonstrates satisfactory model performances for O3 and most relevant chemical compounds with more robust performance in simulating weekend versus weekday changes. Improved planetary boundary layer height simulations, a better understanding of OH‐HO2 cycling, continued improvement of emissions, especially urban biogenic emissions and emissions of oxygenated VOCs, are important for future model improvement. Key Points: We evaluate model simulations for O3, NOx, VOCs, and HOx as well as their response to weekend emission changes during CalNex 2010The model results show a robust ability to simulate the weekend effect, for a majority of the relevant chemical speciesFurther understanding is needed for urban biogenic emissions and emissions of oxygenated VOCs such as ethanol, methanol, and acetone [ABSTRACT FROM AUTHOR]

Abstract The fungal linoleate diol synthase (LDS) family contains over twenty characterized 8-, 9-, and 10-dioxygenases (DOX), usually fused to catalytically competent cytochromes P450. Crystal structures are not available, but indirect evidence suggests that linoleic acid enters the active site of 8 R -DOX-LDS headfirst and enters 9 S -DOX-allene oxide synthase (AOS) with the ω-end (tail) first. Fatty acids derivatized with amino acids can conceivably be used to study oxidation in tail first position by enzymes, which bind natural fatty acids headfirst. The results might reveal catalytic similarities of homologous enzymes. 8 R -DOX-5,8-LDS oxidize 18:2 n -6-Ile and 18:2 n -6-Gly in tail first position to 9 S -hydroperoxy metabolites, albeit with less position and stereo specificity than 9 S -DOX-AOS. The oxygenation mechanism of 9 S -DOX-AOS with antarafacial hydrogen abstraction at C-11 and oxygen insertion at C-9 was also retained. Two homologues, 8 R -DOX-7,8-LDS and 8 R -DOX-AOS, oxidized 18:2 n -6-Ile and 18:2 n -6-Gly at C-9, suggesting a conserved feature of 8 R -DOX domains. 9 R -DOX-AOS, with 54% sequence identity to 9S-DOX-AOS, did not oxidize the derivatized C 18 fatty acids. 9 Z ,12 Z -16:2, two carbon shorter than 18: n -6 from the ω-end, was rapidly metabolized to an α-ketol, but 7Z ,10 Z -16:2 was not a substrate. An unsaturated carbon chain from C-1 to C-8 was apparently more important than the configuration at the ω-end. 8 R -DOX-LDS and 9 R -DOX-AOS may thus bind 18:2 n -6 in the same orientation. The oxidation of 18:2 n -6 in straight or reverse head-to-tail positions illustrates evolutionary traits between 8- and 9 -DOX domains. Fatty acids derivatized with amino acids provide a complementary tool for the analysis of evolution of enzymes. Highlights • Linoleic acid enters fungal 8 R - and 9 S -dioxygenases in opposite orientation. • Linoleic acid derivatized with Ile only enters 8 R -dioxygenases with the omega end. • Both 8 R -and 9 S -dioxygenases oxidize linoleic acid derivatized with Ile at carbon 9. • The linoleic acid derivative reveals catalytic similarities of 8- and 9-dioxygenases. [ABSTRACT FROM AUTHOR]

The first wintertime in situ measurements of hydroxyl (OH), hydroperoxy (HO2) and organic peroxy (RO2) radicals (ROxD OHCHO2 CRO2/ in combination with observations of total reactivity of OH radicals, kOH in Beijing are presented. The field campaign "Beijing winter finE particle STudy - Oxidation, Nucleation and light Extinctions" (BEST-ONE) was conducted at the suburban site Huairou near Beijing from January to March 2016. It aimed to understand oxidative capacity during wintertime and to elucidate the secondary pollutants' formation mechanism in the North China Plain (NCP). OH radical concentrations at noontime ranged from 2:4×106 cm-3 in severely polluted air (kOH ~ 27s-1/ to 3:6×106 cm-3 in relatively clean air (kOH ~ 5s-1/. These values are nearly 2-fold larger than OH concentrations observed in previous winter campaigns in Birmingham, Tokyo, and New York City. During this campaign, the total primary production rate of ROx radicals was dominated by the photolysis of nitrous acid accounting for 46% of the identified primary production pathways for ROx radicals. Other important radical sources were alkene ozonolysis (28%) and photolysis of oxygenated organic compounds (24%). A box model was used to simulate the OH, HO2 and RO2 concentrations based on the observations of their longlived precursors. The model was capable of reproducing the observed diurnal variation of the OH and peroxy radicals during clean days with a factor of 1.5. However, it largely underestimated HO2 and RO2 concentrations by factors up to 5 during pollution episodes. The HO2 and RO2 observed-tomodeled ratios increased with increasing NO concentrations, indicating a deficit in our understanding of the gas-phase chemistry in the high NOx regime. The OH concentrations observed in the presence of large OH reactivities indicate that atmospheric trace gas oxidation by photochemical processes can be highly effective even during wintertime, thereby facilitating the vigorous formation of secondary pollutants. [ABSTRACT FROM AUTHOR]

Oxidation flow reactors (OFRs) are an emerging technique for studying the formation and oxidative aging of organic aerosols and other applications. In these flow reactors, hydroxyl radicals (OH), hydroperoxyl radicals (HO2), and nitric oxide (NO) are typically produced in the following ways: photolysis of ozone (O3) at λ = 254 nm, photolysis of H2O at λ = 185 nm, and via reactions of O(¹D) with H2O and nitrous oxide (N2O); O(¹D) is formed via photolysis of O3 at λ = 254 nm and/or N2O at λ = 185 nm. Here, we adapt a complementary method that uses alkyl nitrite photolysis as a source of OH via its production of HO2 and NO followed by the reaction NO + HO2 → NO2 + OH. We present experimental and model characterization of the OH exposure and NOx levels generated via photolysis of C3 alkyl nitrites (isopropyl nitrite, perdeuterated isopropyl nitrite, 1,3-propyl dinitrite) in the Potential Aerosol Mass (PAM) OFR as a function of photolysis wavelength (λ = 254 to 369 nm) and organic nitrite concentration (0.5 to 20 ppm). We also apply this technique in conjunction with chemical ionization mass spectrometer measurements of multifunctional oxidation products generated following the exposure of α-pinene to HOx and NOx obtained using both isopropyl nitrite and O3 + H2O + N2O as the radical precursors. [ABSTRACT FROM AUTHOR]

Hydroxyl and hydroperoxy radicals are key species for the understanding of atmospheric oxidation processes. Their measurement is challenging due to their high reactivity, therefore very sensitive detection methods are needed. Within this study, the measurement of hydroperoxy radicals (HO2) using chemical ionization combined with an high resolution time of flight mass spectrometer (Aerodyne Research Inc.) employing bromide as primary ion is presented. The 1σ limit of detection of 4.5×107moleculescm-3 for a 60s measurement is below typical HO2 concentrations found in the atmosphere. The detection sensitivity of the instrument is affected by the presence of water vapor. Therefore, a water vapor dependent calibration factor that decreases approximately by a factor of 2 if the water vapor mixing ratio increases from 0.1 to 1.0% needs to be applied. An instrumental background most likely generated by the ion source that is equivalent to a HO2 concentration of 1.5±0.2×108moleculescm-3 is subtracted to derive atmospheric HO2 concentrations. This background can be determined by overflowing the inlet with zero air. Several experiments were performed in the atmospheric simulation chamber SAPHIR at the Forschungszentrum Jülich to test the instrument performance by comparison to the well-established laser-induced fluorescence (LIF) technique for measurements of HO2. A high linear correlation coefficient of R²=0.87 is achieved. The slope of the linear regression of 1.07 demonstrates the good absolute agreement of both measurements. Chemical conditions during 15 experiments allowed testing the instrument's behavior in the presence of atmospheric concentrations of H2O, NOx and O3. No significant interferences from these species were observed. All these facts are demonstrating a reliable measurement of HO2 by the chemical ionization mass spectrometer presented. [ABSTRACT FROM AUTHOR]

The Rieske dioxygenases are a major subclass of mononuclear nonheme iron enzymes that play an important role in bioremediation. Recently, a high-spin FeIII-(hydro)-peroxy intermediate (BZDOp) has been trapped in the peroxide shunt reaction of benzoate 1,2-dioxygenase. Defining the structure of this intermediate is essential to understanding the reactivity of these enzymes. Nuclear resonance vibrational spectroscopy (NRVS) is a recently developed synchrotron technique that is ideal for obtaining vibrational, and thus structural, information on Fe sites, as it gives complete information on all vibrational normal modes containing Fe displacement. In this study, we present NRVS data on BZDOp and assign its structure using these data coupled to experimentally calibrated density functional theory calculations. From this NRVS structure, we define the mechanism for the peroxide shunt reaction. The relevance of the peroxide shunt to the native FeII/O2 reaction is evaluated. For the native FeII/O2 reaction, an FeIII-superoxo intermediate is found to react directly with substrate. This process, while uphill thermodynamically, is found to be driven by the highly favorable thermodynamics of proton-coupled electron transfer with an electron provided by the Rieske [2Fe-2S] center at a later step in the reaction. These results offer important insight into the relative reactivities of FeIII-superoxo and FeIII-hydroperoxo species in nonheme Fe biochemistry. [ABSTRACT FROM AUTHOR]

Abstract: Sowohl durch natürliche als auch durch vom Menschen beeinflusste Vorgänge werden Kohlenwasserstoffe in sehr großer Menge in die Erdatmosphäre emittiert. Ihre atmosphärischen Oxidationsvorgänge bilden fast ausschließlich reaktive RO2‐Radikale als Zwischenprodukte, deren atmosphärisches Schicksal noch nicht vollständig erforscht ist. Hier wird gezeigt, dass Gasphasenreaktionen von zwei RO2‐Radikalen Aufbauprodukte bilden, die aus dem Kohlenstoffgerüst beider Reaktionspartner bestehen. RO2‐Radikale, die funktionelle Gruppen tragen, zeigen hohe Bildungsgeschwindigkeiten der Aufbauprodukte, die mit denen der entsprechenden Reaktionen mit NO und HO2 konkurrieren. Dieses Reaktionsverhalten, das bei der Modellierung von atmosphärischen Prozessen noch nicht berücksichtigt wurde, kann für das Schicksal von RO2‐Radikalen in allen Bereichen der Atmosphäre wichtig oder sogar vorherrschend sein. Darüber hinaus können die gebildeten Aufbauprodukte einen besonders niedrigen Dampfdruck aufweisen, der sie als wirksame Quelle für das sekundäre organische Aerosol kennzeichnet. [ABSTRACT FROM AUTHOR]

One technique used to measure concentrations of the hydroperoxy radical (HO2) in the atmosphere involves chemically converting it to OH by addition of NO and subsequent detection of OH. However, some organic peroxy radicals (RO2) can also be rapidly converted to HO2 (and subsequently OH) in the presence of NO, interfering with measurements of ambient HO2 radical concentrations. This interference must be characterized for each instrument to determine to what extent various RO2 radicals interfere with measurements of HO2 and to assess the impact of this interference on past measurements. The efficiency of RO2-to-HO2 conversion for the Indiana University laser-induced fluorescence–fluorescence assay by gas expansion (IU-FAGE) instrument was measured for a variety of RO2 radicals. Known quantities of OH and HO2 radicals were produced from the photolysis of water vapor at 184.9 nm, and RO2 radicals were produced by the reaction of several volatile organic compounds (VOCs) with OH. The conversion efficiency of RO2 radicals to HO2 was measured when NO was added to the sampling cell for conditions employed during several previous field campaigns. For these conditions, approximately 80 % of alkene-derived RO2 radicals and 20 % of alkane-derived RO2 radicals were converted to HO2. Based on these measurements, interferences from various RO2 radicals contributed to approximately 35 % of the measured HO2 signal during the Mexico City Metropolitan Area (MCMA) 2006 campaign (MCMA-2006), where the measured VOCs consisted of a mixture of saturated and unsaturated species. However, this interference can contribute more significantly to the measured HO2 signal in forested environments dominated by unsaturated biogenic emissions such as isoprene. [ABSTRACT FROM AUTHOR]

Recent studies have found concentrations of reactive chlorine species to be higher than expected, suggesting that atmospheric chlorine chemistry is more extensive than previously thought. Chlorine radicals can interact with hydroperoxy (HOx) radicals and nitrogen oxides (NOx / to alter the oxidative capacity of the atmosphere. They are known to rapidly oxidize a wide range of volatile organic compounds (VOCs) found in the atmosphere, yet little is known about secondary organic aerosol (SOA) formation from chlorineinitiated photooxidation and its atmospheric implications. Environmental chamber experiments were carried out under low-NOx conditions with isoprene and chlorine as primary VOC and oxidant sources. Upon complete isoprene consumption, observed SOA yields ranged from 7 to 36%, decreasing with extended photooxidation and SOA aging. Formation of particulate organochloride was observed. A highresolution time-of-flight chemical ionization mass spectrometer was used to determine the molecular composition of gasphase species using iodide-water and hydronium-water cluster ionization. Multi-generational chemistry was observed, including ions consistent with hydroperoxides, chloroalkyl hydroperoxides, isoprene-derived epoxydiol (IEPOX), and hypochlorous acid (HOCl), evident of secondary OH production and resulting chemistry from Cl-initiated reactions. This is the first reported study of SOA formation from chlorineinitiated oxidation of isoprene. Results suggest that tropospheric chlorine chemistry could contribute significantly to organic aerosol loading. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) is ubiquitous in the natural environment, and it is now widely used for pollutant control in water and wastewater treatment processes. However, current analytical methods for H2O2 inevitably require reactions between H2O2 and other reactants to yield signals and are thus likely subjective to the interferences of coexisting colored, oxidative, and reductive compounds. In order to overcome these barriers, we herein for the first time propose to analyze H2O2 by ion chromatography (IC) using an ultraviolet (UV) detector. The proposal is based on two principles: first, that H2O2 can deprotonate to hydroperoxyl ion (HO2-) when eluent pH is higher than the acid-dissociation coefficient of H2O2 (pKa = 11.6); and second, that after separation from other compounds via IC column, H2O2 can be quantified by a UV detector. Under favorable operating conditions, this method has successfully achieved acceptable recoveries (>91%) of H2O2 dosed to ultrapure and natural waters, a calibration curve with R² > 0.99 for a wide range of H2O2 concentrations from 0.1 to 50 mg/L and a method detection limit of 0.027 mg/L. In addition, this approach was shown to be capable of distinguishing H2O2 from anions (e.g., fluoride and chloride) and organics (e.g., glycolate) and monochloramine, suggesting that it is insensitive to many neighboring compounds as long as they do not react quickly with H2O2. Hence, this study proves the combination of IC and UV detector a facile and reliable method for H2O2 measurement. [ABSTRACT FROM AUTHOR]

We report measurements of hydroxyl (OH) and hydroperoxy (HO2) radicals made by laser-induced fluorescence spectroscopy in a computer classroom (i) in the absence of indoor activities (ii) during desk cleaning with a limonene-containing cleaner (iii) during operation of a commercially available 'air cleaning' device. In the unmanipulated environment, the one-minute averaged OH concentration remained close to or below the limit of detection (6.5×105 molecule cm−3), whilst that of HO2 was 1.3×107 molecule cm−3. These concentrations increased to ~4×106 and 4×108 molecule cm−3, respectively during desk cleaning. During operation of the air cleaning device, OH and HO2 concentrations reached ~2×107 and ~6×108 molecule cm−3 respectively. The potential of these OH concentrations to initiate chemical processing is explored using a detailed chemical model for indoor air (the INDCM). The model can reproduce the measured OH and HO2 concentrations to within 50% and often within a few % and demonstrates that the resulting secondary chemistry varies with the cleaning activity. Whilst terpene reaction products dominate the product composition following surface cleaning, those from aromatics and other VOCs are much more important during the use of the air cleaning device. [ABSTRACT FROM AUTHOR]

An efficient and practical method has been developed for the facile synthesis of 1,2,4-trioxanes by the condensation of β-hydroperoxy alcohols and carbonyl compounds in the presence of a catalytic amount of silica-supported ferric chloride (FeCl3/SiO2) at room temperature. The method has the benefits of operational simplicity, high yields and potential large-scale application. Moreover, the catalyst can be readily recovered by simple filtration and reused up to five times while almost maintaining its catalytic activity. [ABSTRACT FROM AUTHOR]

One technique used to measure concentrations of the hydroperoxy radical (HO2) in the atmosphere involves chemically converting it to OH by addition of NO and subsequent detection of OH. However, some organic peroxy radicals (RO2) can also be rapidly converted to HO2 (and subsequently OH) in the presence of NO, interfering with measurements of ambient HO2 radical concentrations. This interference must be characterized for each instrument to determine to what extent various RO2 radicals interfere with measurements of HO2 and to assess the impact of this interference on past measurements. The efficiency of RO2 to HO2 conversion for the Indiana University Laser-Induced Fluorescence - Fluorescence Assay by Gas Expansion (IU-FAGE) instrument was measured for a variety of RO2 radicals. Known quantities of OH and HO2 radicals were produced from the photolysis of water vapor at 184.9 nm, and RO2 radicals were produced by the reaction of several volatile organic compounds with OH. The conversion efficiency of RO2 radicals to HO2 was measured when NO was added to the sampling cell for conditions employed during several previous field campaigns. For these conditions, approximately 80 % of alkene derived RO2 radicals and 20 % of alkane derived RO2 radicals were converted to HO2. Based on these measurements, interferences from various RO2 radicals contributed to approximately 35 % of the measured HO2 signal during the Mexico City Metropolitan Area (MCMA) 2006 campaign, where the measured VOCs consisted of a mixture of saturated and unsaturated species. However, this interference can contribute more significantly to the measured HO2 signal in forested environments dominated by unsaturated biogenic emissions such as isoprene. [ABSTRACT FROM AUTHOR]

The albedo and microphysical properties of clouds are controlled in part by the hygroscopicity of particles serving as cloud condensation nuclei (CCN). Hygroscopicity of complex organic mixtures in the atmosphere varies widely and remains challenging to predict. Here we present new measurements characterizing the CCN activity of pure compounds in which carbon chain length and the numbers of hydroperoxy, carboxyl, and carbonyl functional groups were systematically varied to establish the contributions of these groups to organic aerosol apparent hygroscopicity. Apparent hygroscopicity decreased with carbon chain length and increased with polar functional groups in the order carboxyl > hydroperoxy > carbonyl. Activation diameters at different supersaturations deviated from the -3/2 slope in log-log space predicted by Köhler theory, suggesting that water solubility limits CCN activity of particles composed of weakly functionalized organic compounds. Results are compared to a functional group contribution model that predicts CCN activity of organic compounds. The model performed well for most compounds but underpredicted the CCN activity of hydroperoxy groups. New best-fit hydroperoxy group/water interaction parameters were derived from the available CCN data. These results may help improve estimates of the CCN activity of ambient organic aerosols from composition data. [ABSTRACT FROM AUTHOR]

Hydroperoxyl radical (HO2) is a key species to atmospheric chemistry. At warm temperatures, the HO2 and NO2 come to a rapid steady state with pernitric acid (HO2NO2). This paper presents the derivation of HO2 from observations of HO2NO2 and NO2 in metropolitan Atlanta, US, in winter 2014 and summer 2015. HO2 was observed to have a diurnal cycle with morning concentrations suppressed by high NO from the traffic. At night, derived HO2 levels were nonzero and exhibited correlations with O3 and NO3, consistent with previous studies that ozonolysis and oxidation by NO3 are sources of nighttime HO2. Measured and model calculated HO2 were in reasonable agreement: Without the constraint of measured HO2NO2, the model reproduced HO2 with a model-to-observed ratio (M/O) of 1.27 (r = 0.54) for winter, 2014, and 0.70 (r = 0.80) for summer, 2015. Adding measured HO2NO2 as a constraint, the model predicted HO2 with M/O = 1.13 (r = 0.77) for winter 2014 and 0.90 (r = 0.97) for summer 2015. These results demonstrate the feasibility of deriving HO2 from HO2NO2 measurements in warm regions where HO2NO2 has a short lifetime. [ABSTRACT FROM AUTHOR]

The design of innovative combustion processes relies on a comprehensive understanding of biodiesel oxidation kinetics. The present study aims at unraveling the reaction mechanism involved in the epoxidation of a realistic biodiesel surrogate, methyl trans-3-hexenoate, by hydroperoxy radicals using a bottom-up theoretical kinetics methodology. The obtained rate constants are in good agreement with experimental data for alkene epoxidation by HO2. The impact of temperature and pressure on epoxidation pathways involving H-bonded and non-H-bonded conformers was assessed. The obtained rate constant was finally implemented into a state-of-the-art detailed combustion mechanism, resulting in fairly good agreement with engine experiments. [ABSTRACT FROM AUTHOR]

This paper describes the production of ligninolytic enzymes by the white-rot fungus Pleurotus sajor caju under solid-state fermentation conditions using a cost-effective medium consisting of agro-industrial wastes. From the different agro-industrial wastes tested (i.e. orange, banana, mango and cantaloupe peels), banana peels led to the highest manganese-dependent peroxidase (MnP) activity (6.3 U/mL on the 10 day). MnP from banana peel cultures was purified and applied to the discoloration of the azo dye Congo Red (CR). The optimum temperature, pH and enzyme concentration for maximum discoloration (i.e. 95% in 1 h) were found to be 35°C, 4.0, and 1.4 U/mL, respectively. In addition, the phytotoxicity (with respect to Sorghum vulgare and Phaseolus radiatus seeds) of CR was considerably reduced after the treatment of plant material with MnP produced by P. sajor caju. The products obtained after discoloration of CR were characterized using GC/MS as 8-amino naphthol 3-sulfonic acid, 3-hydroperoxy 8-nitrosonaphthol, p-p'-dihydroxybiphenyl. Therefore, this approach holds promise for the production and application of MnP from P. sajor caju on a larger scale. [ABSTRACT FROM AUTHOR]

We have used quantum mechanical chemical calculations (CCSD(T)-F12a/cc-pVDZ-F12//M06-2X/aug-cc-pVTZ) to investigate the hydrogen shift (H-shift) reactions in acyl peroxy and hydroperoxy acyl peroxy radicals. We have focused on the H-shift reactions from a hydroperoxy group (OOH) (1,X-OOH H-shift with X = 6, 7, 8, or 9) in the hydroperoxy acyl peroxy radicals, this H-shift is a reversible reaction and it scrambles between two peroxides, hydroperoxy acyl peroxy and peroxy peroxoic acid radicals. The forward reaction rate constants of the 1,X-OOH H-shift reactions are estimated to be above 103 s-1 with transition state theory corrected with Eckart quantum tunnelling correction. The ratio between the forward and reverse reaction rate constant of the 1,X-OOH H-shift reactions is around ~105. Therefore, the equilibrium is pushed toward the production of peroxy peroxoic acid radicals. These very fast 1,X-OOH H-shift reactions are much faster than the reactions with NO and HO2 under most atmospheric conditions and must be included in the atmospheric models when hydroperoxy acyl peroxy radicals are oxidized. Finally, we have observed that H-shift reactions in a pentane acyl peroxy radical (C5-AOO) is fast (>1 s-1); this can have a significant influence on the possible formation of large acyl peroxy nitrate molecules. [ABSTRACT FROM AUTHOR]

High-level ab initio and Born-Oppenheimer molecular dynamic calculations have been carried out on a series of hydroperoxyalkyl (α-QOOH) radicals with the aim of investigating the stability and unimolecular decomposition mechanism into QO+OH of these species. Dissociation was shown to take place through rotation of the C−O(OH) bond rather than through elongation of the CO−OH bond. Through the C−O(OH) rotation, the unpaired electron of the radical overlaps with the electron density on the O−OH bond, and from this overlap the C=O π bond forms and the O−OH bond breaks spontaneously. The CH2OOH, CH(CH3)OOH, CH(OH)OOH, and α-hydroperoxycycloheptadienyl radical were found to decompose spontaneously, but the CH(CHO)OOH has a decomposition energy barrier of 5.95 kcal mol−1 owing to its steric and electronic features. The systems studied in this work provide the first insights into how structural and electronic effects govern the stabilizing influence on elusive α-QOOH radicals. [ABSTRACT FROM AUTHOR]

Ten peroxide compounds based upon the 3,6-di(hydroperoxy)-1,2-dioxane, 2-hydroxy-6-hydroperoxy-1,2-dioxane, 3,5-di(hydroperoxy)-1,2-dioxolane, and 3-hydroxy-5-hydroperoxy-1,2-dioxolane skeletons have been synthesized, structurally characterized, and fully evaluated for their energetic materials properties. The solid-state structures of these compounds are dominated by hydrogen bonding interactions involving the hydroperoxy and hydroxy groups. Energetic materials testing shows that most of the compounds are highly sensitive toward impact and friction, with similar properties to highly sensitive peroxides such as triacetone triperoxide. 3,5-Diethyl-5-hydroperoxy-1,2-dioxolan-3-ol ( 3b) and 3,5-dimethyl-5-hydroperoxy-1,2-dioxolan-3-ol ( 5b) have lower impact and friction sensitivities than the other compounds, with values that are appropriate for use as primary explosives. [ABSTRACT FROM AUTHOR]

Aerosol formation is directly influenced by meteorological properties such as temperature and relative humidity. This study examines the influence of temperature on the physical properties and chemical composition of the aerosol produced from radical oxidation of aliphatic amines. Aerosol formation for temperatures ranging from 10 to 40°C was investigated in dual 90 m3indoor atmospheric chambers. Further, chemical and physical responses of aerosol formed at one temperature and then raised/cooled to another were investigated in detail. Around two to three times more aerosol formation occurred at 10°C than at 40°C. This has important implications for locations influenced by amine emissions during the winter months. Significant aerosol formation occurred with the oxidation of amines with nitrate radical (100–600 μg/m3) and consisted largely of amine nitrate salts. These reactions are important contributors to aerosol formation during the nighttime hours, when nitrate radical is the dominant oxidant and temperatures tend to be cooler. Solid/gas partitioning of amine nitrate salt aerosol was consistent with literature results. A novel, temperature dependent, mechanism describing peroxy and hydroperoxy radical reactions was observed in the trimethylamine with hydroxyl radical oxidation experiments. Copyright © 2016 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

The mammalian glutathione peroxidase (GPx) family is a key component of the cellular antioxidative defence system. Within this family, GPx4 has unique features as it accepts a large class of hydroperoxy lipid substrates and has a plethora of biological functions, including sperm maturation, regulation of apoptosis and cerebral embryogenesis. In this paper, the structure of the cytoplasmic isoform of mouse phospholipid hydroperoxide glutathione peroxidase (O70325-2 GPx4) with selenocysteine 46 mutated to cysteine is reported solved at 1.8 Å resolution using X-ray crystallography. Furthermore, solution data of an isotope-labelled GPx protein are presented. [ABSTRACT FROM AUTHOR]

Ab initio quantum mechanical methods were employed to study the reaction of methylperoxy and hydroperoxy radicals. Three intermediates and seven transition states involved in the reaction mechanism were located. The two reaction pathways determined in the room temperature lead to the formation of CH 3 OOH + O 2 and CH 2 O + H 2 O + O 2 . The first reaction channel appears to be more feasible, whereas the formation of CH 2 O increases in lower energies in accordance with the experimental results. [ABSTRACT FROM AUTHOR]

The reaction of methanimine (CH2NH) with the hydroperoxy (HO2) radical has been investigated by using a combination of ab initio and density functional theory (CCSD(T)/CBSB7//B3LYP+Dispersion/CBSB7) and master equation calculations based on transition state theory (TST). Variational TST was used to compute both canonical (CVTST) and microcanonical (μVTST) rate constants for barrierless reactions. The title reaction starts with the reversible formation of a cyclic prereactive complex (PRC) that is bound by ∼11 kcal/mol and contains hydrogen bonds to both nitrogen and oxygen. The reaction path for the entrance channel was investigated by a series of constrained optimizations, which showed that the reaction is barrierless (i.e., no intrinsic energy barrier along the path). However, the variations in the potential energy, vibrational frequencies, and rotational constants reveal that the two hydrogen bonds are formed sequentially, producing two reaction flux bottlenecks (i.e., two transition states) along the reaction path, which were modeled using W. H. Miller's unified TST approach. The rate constant computed for the formation of the PRC is pressure-dependent and increases at lower temperatures. Under atmospheric conditions, the PRC dissociates rapidly and its lifetime is too short for it to undergo significant bimolecular reaction with other species. A small fraction isomerizes via a cyclic transition state and subsequent reactions lead to products normally expected from hydrogen abstraction reactions. The kinetics of the HO2 + CH2NH reaction system differs substantially from the analogous isoelectronic reaction systems involving C2H4 and CH2O, which have been the subjects of previous experimental and theoretical studies. [ABSTRACT FROM AUTHOR]

The main biological cause of oxysterols is the oxidation of cholesterol. They differ from cholesterol by the presence of additional polar groups that are typically hydroxyl, keto, hydroperoxy, epoxy, or carboxyl moieties. Under typical conditions, oxysterol concentration is maintained at a very low and precisely regulated level, with an excess of cholesterol. Like cholesterol, many oxysterols are hydrophobic and hence confined to cell membranes. However, small chemical differences between the sterols can significantly affect how they interact with other membrane components, and this in turn can have a substantial effect on membrane properties. In this spirit, this review describes the biological importance and the roles of oxysterols in the human body. We focus primarily on the effect of oxysterols on lipid membranes, but we also consider other issues such as enzymatic and nonenzymatic synthesis processes of oxysterols as well as pathological conditions induced by oxysterols. [ABSTRACT FROM AUTHOR]

Hydroperoxy radicals (HO2/ play an important part in tropospheric photochemistry, yet photochemical models do not capture ambient HO2 mixing ratios consistently. This is likely due to a combination of uncharacterized chemical pathways and measurement limitations. The indirect nature of current HO2 measurements introduces challenges in accurately measuring HO2; therefore a direct technique would help constrain HOx chemistry in the atmosphere. In this work we evaluate the feasibility of using chemical ionization mass spectrometry (CIMS) and propose a direct HO2 detection scheme using bromide as a reagent ion. Ambient observations were made with a high-resolution timeof- flight chemical ionization mass spectrometer (HR-ToFCIMS) in Atlanta over the month of June 2015 to demonstrate the capability of this direct measurement technique. Observations displayed expected diurnal profiles, reaching daytime median values of ~5 ppt between 2 and 3 p.m. local time. The HO2 diurnal profile was found to be influenced by morning-time vehicular NOx emissions and shows a slow decrease into the evening, likely from non-photolytic production, among other factors. Measurement sensitivities of approximately 5.1±1.0 cps ppt-1 for a bromide ion (79Br-/ count rate of 106 cps were observed. The relatively low instrument background allowed for a 3σ lower detection limit of 0.7 ppt for a 1 min integration time. Mass spectra of ambient measurements showed the 79BrHO-2 peak was the major component of the signal at nominal mass-to-charge 112, suggesting high selectivity for HO2 at this mass-to-charge. More importantly, this demonstrates that these measurements can be achieved using instruments with only unit mass resolution capability. [ABSTRACT FROM AUTHOR]

The catalyst-free oxidation of various pyridine derivatives and tertiary amines to their corresponding N-oxides with 1,1,2,2-tetrahydroperoxy-1,2-diphenylethane as an efficient oxidant has been developed. The methodology proved to tolerate a number of functional groups. The reactions proceeded smoothly under solvent-free and mild conditions at room temperature. All the products were easily extracted from the reaction mixtures in excellent yields. Graphical abstract: The catalyst-free oxidation of various pyridine derivatives and tertiary amines to their corresponding N-oxides with 1,1,2,2-tetrahydroperoxy-1,2-diphenylethane as an efficient oxidant has been developed. The methodology proved to tolerate a number of functional groups. The reactions proceeded smoothly under solvent-free and mild conditions at room temperature. All the products were easily extracted from the reaction mixtures in excellent yields. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Comprehensive low-temperature oxidation mechanisms are needed to accurately predict fuel auto-ignition properties. This paper studies the effects of a previously unconsidered third O 2 addition reaction scheme on the simulated auto-ignition of n -alkanes. We demonstrate that this extended low-temperature oxidation scheme has a minor effect on the simulation of n -pentane ignition; however, its addition significantly improves the prediction of n -hexane auto-ignition under low-temperature rapid compression machine conditions. Additional simulations of n -hexane in a homogeneous charge compression ignition engine show that engine-operating parameters (e.g., intake temperature and combustion phasing) are significantly altered when the third O 2 addition kinetic mechanism is considered. The advanced combustion phasing is initiated by the formation and destruction of additional radical chain-branching intermediates produced in the third O 2 addition process, e.g. keto-dihydroperoxides and/or keto-hydroperoxy cyclic ethers. Our results indicate that third O 2 addition reactions accelerate low-temperature radical chain branching at conditions of relevance to advance engine technologies, and therefore these chemical pathways should also be considered for n -alkanes with 6 or more carbon atoms. [ABSTRACT FROM AUTHOR]

An efficient and facile procedure usingtrans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane has been developed for oxidative desulfurization of thioureas and thiobarbituric acids. The reactions proceeded smoothly very fast under mild conditions in basic media at room temperature to afford the respective ureas in excellent yields. Simple procedure and work up, mild conditions, high yields, short reaction times, use of highly potent and non-toxic oxidant are the main merits of the present method. [ABSTRACT FROM PUBLISHER]

Using quantum mechanical calculations, we have investigated hydrogen shift (H-shift) reactions in peroxy radicals derived from the atmospheric oxidation of 1-pentene (CH2-CHCH2CH2CH3) and its monosubstituted derivatives. We investigate the peroxy radicals, HOCH2CH(OO)CR1HCH2CH3, HOCH2CH(OO)CH2CR1HCH3, and HOCH2CH(OO)CH2CH2CR1H2, where the substituent R1 is an alcoholic (OH), a hydroperoxy (OOH), or a methoxy (OCH3) group. For peroxy radicals with an OOH substituent, the H-shift reaction from the hydrogen atom on the OOH group to the OO group is extremely fast. We find that the rate constants of this type of H-shift reactions are greater than 10³ s-1 for both the forward and the reverse reactions. It leads to the formation of two different radical isomers that react through different reaction mechanisms and yield different products. These very fast H-shift reactions are much faster than the reactions with NO and HO2 under most atmospheric conditions and must be included in the atmospheric modeling of volatile organic compounds where hydroperoxy peroxy radicals are formed. [ABSTRACT FROM AUTHOR]

The effects of α- and δ-tocopherol on inhibition of hydroperoxides, keto and hydroxy compounds under Rancimat conditions, i.e. 100 °C and air bubbling, were studied in samples of fatty acid methyl esters (FAME) obtained from high linoleic (HL) and high oleic (HO) sunflower oils. Primary hydroperoxides from methyl linoleate and methyl oleate and secondary keto and hydroxy compounds derived from methyl linoleate hydroperoxides were analyzed by HPLC-UV-ELS. Different tocopherol concentrations, namely, 10, 50, 100, 500 and 1000 mg/kg, were tested. Irrespective of the lipid substrate and the initial concentration of tocopherol, results showed that the content of hydroperoxides accumulated during the induction period was remarkably higher in the samples containing δ-tocopherol. The relative concentrations of oleate hydroperoxides in the HO samples were also higher in the presence of δ-tocopherol. α-Tocopherol was more effective in inhibiting hydroperoxides at low levels, with 100 mg/kg as optimal concentration, while δ-tocopherol displayed optimal protection at 1000 mg/kg. Under the oxidation conditions applied, neither α- nor δ-tocopherol showed a protective effect on hydroperoxide decomposition at any level assayed. Formation of keto- and hydroxy-dienes was more related to the concentration of their hydroperoxide precursors. Furthermore, both tocopherols gave rise to increased concentrations of ketodienes at 500 and 1000 mg/kg compared to the controls. Such an effect was more pronounced for α-tocopherol and in the HL samples. [ABSTRACT FROM AUTHOR]

The gas-phase decomposition of the α-hydroxy methylperoxy radical has been theoretically examined, and the results provide insight into a new source of the hydroperoxy radical (HO2) in the troposphere. Bimolecular peroxy decomposition is promoted by the red-light or near-IR radiation excitation. The calculations suggest for the first time, an important chemical role for the H2OHO2 radical complex that exist in significant abundance in the troposphere. In particular, the reaction of organic peroxy radicals with the HO2 radical and the H2OHO2 radical complex represent an autocatalytic source of atmospheric HO2. This reaction is a new example of red-light-initiated atmospheric chemistry that may help in understanding the discrepancy between the observed and measured levels of the HOx at sunrise. [ABSTRACT FROM AUTHOR]

Formation of hydroperoxy-, keto- and hydroxy-dienes was studied at 40 °C in fatty acid methyl esters (FAME) microencapsulated in a dairy-like matrix formed by lactose and sodium caseinate. The FAME were obtained from conventional sunflower oil and the microcapsules were prepared by freeze-drying of an oil-in-water emulsion. For comparative purposes a neat sample of FAME was also tested. Results showed that for a given content of hydroperoxydienes much more elevated amounts of secondary products were detected in the microencapsulated sample compared to the neat sample of FAME. The contents of keto- and hydroxy-dienes found in the microencapsulated FAME ranged as a whole between 6 and 31 wt% of the analyzed compounds, while the neat sample showed values lower than 1.5 %. Along with the fact that relatively higher contents of polymers were also found in the encapsulated sample, these results can be attributed to lipid droplets with very different oxidation states. On the one hand, the extract would be formed from droplets in early stages of oxidation containing hydroperoxides and very low contents of secondary products and, on the other, from droplets in advanced stages with decreased hydroperoxides and substantial contents of secondary products. Unlike the neat sample, hydroxy-dienes formed with significantly higher amounts than keto-dienes in the microencapsulated FAME, suggesting a possible chemical role of the encapsulation matrix. [ABSTRACT FROM AUTHOR]

Wedescribe the products of the reaction of the hydroperoxy radical(HO2) with the alkylperoxy radical formed following additionof the nitrate radical (NO3) and O2to isoprene.NO3adds preferentially to the C1position ofisoprene (>6 times more favorably than addition to C4),followed by the addition of O2to produce a suite of nitrooxyalkylperoxy radicals (RO2). At an RO2lifetimeof ∼30 s, δ-nitrooxy and β-nitrooxy alkylperoxyradicals are present in similar amounts. Gas-phase product yieldsfrom the RO2+ HO2pathway are identified as0.75–0.78 isoprene nitrooxy hydroperoxide (INP), 0.22 methylvinyl ketone (MVK) + formaldehyde (CH2O) + hydroxyl radical(OH) + nitrogen dioxide (NO2), and 0–0.03 methacrolein(MACR) + CH2O + OH + NO2. We further examinedthe photochemistry of INP and identified propanone nitrate (PROPNN)and isoprene nitrooxy hydroxyepoxide (INHE) as the main products.INHE undergoes similar heterogeneous chemistry as isoprene dihydroxyepoxide (IEPOX), likely contributing to atmospheric secondary organicaerosol formation. [ABSTRACT FROM AUTHOR]

Self-reaction is an important sink for the hydroperoxy radical (HO2) in the atmosphere. It has been suggested (Denis, P. A.; Ornellas, F. R. J. Phys. Chem. A, 2009, 113 (2), 499-506) that the minor product hydrogen tetroxide (HO4H) may act as a reservoir of HO2. Here, we compute the thermochemistry of HO2 self-reactions to determine if either HO4H or the cyclic hydrogen-bound dimer (HO2)2 can act as reservoirs. We computed electronic energies using coupled-cluster calculations in the complete basis set limit, CCSD(T)/CBS[45]//CCSD(T)/cc-pVTZ. Our model chemistry includes corrections for vibrational anharmonicity in the zero-point energy and vibrational partition functions, core-valence correlation, scalar relativistic effects, diagonal Born-Oppenheimer, spin-orbit splitting, and higher-order corrections. We compute the Gibbs energy of dimerization to be (−20.1 ± 1.6) kJ/mol at 298.15 K (2σ uncertainty), and (−32.3 ± 1.5) kJ/mol at 220 K. For atmospherically relevant [HO2] = 108 molecules per cm³, our thermochemistry indicates that dimerization will be negligible, and thus H2O4 species are atmospherically unimportant. Under conditions used in laboratory experiments ([HO2] > 1012 molecules per cm³, 220 K), H2O4 formation may be significant. We compute two absorption spectra that could be used for laboratory detection of HO4H: the OH stretch overtone (near-IR) and electronic (UV) spectra. [ABSTRACT FROM AUTHOR]

Thekinetics of hydrogen abstraction by five radicals (H, O(3P), OH, CH3, and HO2) frommethyl acetate (MA) is investigated theoretically in orderto gain further understanding of certain aspects of the combustionchemistry of biodiesels, such as the effect of the ester moiety. Weemploy ab initio quantum chemistry methods, coupled cluster singlesand doubles with perturbative triples correction (CCSD(T)) and multireferenceaveraged coupled pair functional theory (MRACPF2), to predict chemicallyaccurate reaction energetics. Overall, MRACPF2 predicts slightly higherbarrier heights than CCSD(T) for MA + H/CH3/O/OH, but slightlylower barrier heights for hydrogen abstraction by HO2.Based on the obtained reaction energies, we also report high-pressure-limitrate constants using transition state theory (TST) in conjunctionwith the separable-hindered-rotor approximation, the variable reactioncoordinate TST, and the multi-structure all-structure approach. Thefitted modified Arrhenius expressions are provided over a temperaturerange of 250 to 2000 K. The predictions are in good agreement withavailable experimental results. Abstractions from both of the methylgroups in MA are expected to contribute to consumption of the fuelas they exhibit similar rate coefficients. The reactions involvingthe OH radical are predicted to have the highest rates among the fiveabstracting radicals, while those initiated by HO2areexpected to be the lowest. [ABSTRACT FROM AUTHOR]

A new lanostan-type triterpenoid with hydroperoxy group, toosendanin A (1), together with two known triterpenoids, meliastatin 3 (2) and ursolic acid (3), were isolated and identified from the stems of Melia toosendan. The structures of these compounds were elucidated by 1D- and 2D-NMR spectra and other spectroscopic studies. These compounds were assayed for the antibacterial activities against some hospital pathogenic bacteria. Toosendanin A (1) exhibited strong antibacterial activity against K. pneumoniae. [ABSTRACT FROM AUTHOR]

For the first time quantitative measurements of the hydroperoxyl radical (HO2) in a jet-stirred reactor were performed thanks to a new experimental setup involving fast sampling and near-infrared cavity ring-down spectroscopy at low pressure. The experiments were performed at atmospheric pressure and over a range of temperatures (550-900 K) with n-butane, the simplest hydrocarbon fuel exhibiting cool flame oxidation chemistry which represents a key process for the auto-ignition in internal combustion engines. The same technique was also used to measure H2O2, H2O, CH2O, and C2H4 under the same conditions. This new setup brings new scientific horizons for characterizing complex reactive systems at elevated temperatures. Measuring HO2 formation from hydrocarbon oxidation is extremely important in determining the propensity of a fuel to follow chain-termination pathways from R + O2compared to chain branching (leading to OH), helping to constrain and better validate detailed chemical kinetics models. [ABSTRACT FROM AUTHOR]

Compromised systemic acquired resistance in eds1 mutant Arabidopsis plants is associated with a reduced ability of the mutant to accumulate azelaic acid and its precursor 9-oxo nonanoic acid.Systemic acquired resistance (SAR) is a form of inducible disease resistance that depends on salicylic acid and its upstream regulator ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1). Although local Arabidopsis thaliana defence responses activated by the Pseudomonas syringae effector protein AvrRpm1 are intact in eds1 mutant plants, SAR signal generation is abolished. Here, the SAR-specific phenotype of the eds1 mutant is utilized to identify metabolites that contribute to SAR. To this end, SAR bioassay-assisted fractionation of extracts from the wild type compared with eds1 mutant plants that conditionally express AvrRpm1 was performed. Using high-performance liquid chromatography followed by mass spectrometry, systemic immunity was associated with the accumulation of 60 metabolites, including the putative SAR signal azelaic acid (AzA) and its precursors 9-hydroperoxy octadecadienoic acid (9-HPOD) and 9-oxo nonanoic acid (ONA). Exogenous ONA induced SAR in systemic untreated leaves when applied at a 4-fold lower concentration than AzA. The data suggest that in planta oxidation of ONA to AzA might be partially responsible for this response and provide further evidence that AzA mobilizes Arabidopsis immunity in a concentration-dependent manner. The AzA fragmentation product pimelic acid did not induce SAR. The results link the C9 lipid peroxidation products ONA and AzA with systemic rather than local resistance and suggest that EDS1 directly or indirectly promotes the accumulation of ONA, AzA, or one or more of their common precursors possibly by activating one or more pathways that either result in the release of these compounds from galactolipids or promote lipid peroxidation. [ABSTRACT FROM AUTHOR]

Thermal rate constants of the CH + O = CH + HO reaction were calculated from first principles using both the conventional transition state theory (TST) and canonical variational TST methods with correction from the explicit hindered rotation treatment. The CCSD(T)/aug-cc-pVTZ//BH&HLYP/aug-cc-pVDZ method was used to characterize the necessary potential energy surface along the minimum energy path. We found that the correction for hindered rotation treatment, as well as the re-crossing effects noticeably affect the rate constants of the title process. The calculated rate constants for both forward and reverse directions are expressed in the modified Arrhenius form as $$k_{\text{forward}}^{\text{CVT/HR}} = 2.157 \times 10^{ - 18} \times T^{2.412} \times \,\exp \,( - \frac{25812}{T})$$ and $$k_{\text{reverse}}^{\text{CVT/HR}} = 1.375 \times 10^{ - 19} \times T^{2.183} \times \,{\kern 1pt} \exp \,\,(\frac{2032}{T})$$ (cm molecule s) for the temperature range of 300-2,500 K. Being in good agreement with literature data, the results provide solid basis information for the investigation of the entire alkane + O = alkyl radical + HO reaction class. [ABSTRACT FROM AUTHOR]

ABSTRACT Rate and equilibrium constants for the reaction of HO2 with formaldehyde [ABSTRACT FROM AUTHOR]

In this article, we describe a new, fast and reliable method for determining 5-LOX activity using the fluorescent probe dihydrorhodamine 123 (DHR). In the new assay, the products of 5-LOX, 5S-hydroperoxy-6E,8Z,11Z,14Z-eicosatetraenoic acid, can directly oxidize non-fluorescent DHR to highly fluorescent rhodamine 123. The fluorescence intensity can be measured using fluorescence spectroscopy at Ex/Em = 500/536 nm. As 5-LOX requires some cofactors to achieve its optimum activity, the effects of its cofactors on the fluorescence assay are also investigated. Using this new assay, we evaluated the inhibitory activity of two well-known 5-LOX inhibitors (NDGA and AA861) in a 384-well format and the IC50 values of them are consistent with previously references. The fluorescence assay is amenable to both purified 5-LOX and 5-LOX in cell lysates and will be widely used for the discovery of novel 5-LOX inhibitors for clinical application. [ABSTRACT FROM AUTHOR]