Major Primary Products Research Articles

Atmospheric chemistry of (Z)‐CF2HCF=CHCl: Kinetics and products of reaction with Cl atoms and OH radicals

AbstractLong path length FTIR‐smog chamber techniques were used to study the title reactions in 650 Torr of N2, oxygen, or air diluent at 296 ± 3 K. Values of k(Cl + (Z)‐CF2HCF = CHCl)═(6.6 ± 0.7) × 10−11 and k(OH + (Z)‐CF2HCF═CHCl)═(4.1 ± 0.7) × 10−12 cm3 molecule−1 s−1 were measured. The IR spectrum of (Z)‐CF2HCF═CHCl is reported. The atmospheric lifetime of (Z)‐CF2HCF═CHCl is determined by the reaction with OH and is approximately 2.8 days. Reaction of (Z)‐CF2HCF═CHCl with Cl atoms gives HC(O)Cl and CF2HC(O)F as major primary products. Under environmental conditions, the OH radical initiated oxidation gives CF2HC(O)F and HC(O)Cl in yields of (98 ± 8)% and (100 ± 4)%, respectively. Accounting for non‐uniform horizontal and vertical mixing leads to a 100‐year time‐horizon global warming potential value for (Z)‐CF2HCF═CHCl of essentially zero.

Plasmalogen oxidation induces the generation of excited molecules and electrophilic lipid species.

Plasmalogens are glycerophospholipids with a vinyl ether linkage at the sn-1 position of the glycerol backbone. Despite being suggested as antioxidants due to the high reactivity of their vinyl ether groups with reactive oxygen species, our study reveals the generation of subsequent reactive oxygen and electrophilic lipid species from oxidized plasmalogen intermediates. By conducting a comprehensive analysis of the oxidation products by liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS), we demonstrate that singlet molecular oxygen [O2 (1Δg)] reacts with the vinyl ether bond, producing hydroperoxyacetal as a major primary product (97%) together with minor quantities of dioxetane (3%). Furthermore, we show that these primary oxidized intermediates are capable of further generating reactive species including excited triplet carbonyls and O2 (1Δg) as well as electrophilic phospholipid and fatty aldehyde species as secondary reaction products. The generation of excited triplet carbonyls from dioxetane thermal decomposition was confirmed by light emission measurements in the visible region using dibromoanthracene as a triplet enhancer. Moreover, O2 (1Δg) generation from dioxetane and hydroperoxyacetal was evidenced by detection of near-infrared light emission at 1,270 nm and chemical trapping experiments. Additionally, we have thoroughly characterized alpha-beta unsaturated phospholipid and fatty aldehydes by LC-HRMS analysis using two probes that specifically react with aldehydes and alpha-beta unsaturated carbonyls. Overall, our findings demonstrate the generation of excited molecules and electrophilic lipid species from oxidized plasmalogen species unveiling the potential prooxidant nature of plasmalogen-oxidized products.

Metabolic niches in the rhizosphere microbiome: dependence on soil horizons, root traits and climate variables in forest ecosystems.

Understanding belowground plant-microbial interactions is important for biodiversity maintenance, community assembly and ecosystem functioning of forest ecosystems. Consequently, a large number of studies were conducted on root and microbial interactions, especially in the context of precipitation and temperature gradients under global climate change scenarios. Forests ecosystems have high biodiversity of plants and associated microbes, and contribute to major primary productivity of terrestrial ecosystems. However, the impact of root metabolites/exudates and root traits on soil microbial functional groups along these climate gradients is poorly described in these forest ecosystems. The plant root system exhibits differentiated exudation profiles and considerable trait plasticity in terms of root morphological/phenotypic traits, which can cause shifts in microbial abundance and diversity. The root metabolites composed of primary and secondary metabolites and volatile organic compounds that have diverse roles in appealing to and preventing distinct microbial strains, thus benefit plant fitness and growth, and tolerance to abiotic stresses such as drought. Climatic factors significantly alter the quantity and quality of metabolites that forest trees secrete into the soil. Thus, the heterogeneities in the rhizosphere due to different climate drivers generate ecological niches for various microbial assemblages to foster beneficial rhizospheric interactions in the forest ecosystems. However, the root exudations and microbial diversity in forest trees vary across different soil layers due to alterations in root system architecture, soil moisture, temperature, and nutrient stoichiometry. Changes in root system architecture or traits, e.g. root tissue density (RTD), specific root length (SRL), and specific root area (SRA), impact the root exudation profile and amount released into the soil and thus influence the abundance and diversity of different functional guilds of microbes. Here, we review the current knowledge about root morphological and functional (root exudation) trait changes that affect microbial interactions along drought and temperature gradients. This review aims to clarify how forest trees adapt to challenging environments by leveraging their root traits to interact beneficially with microbes. Understanding these strategies is vital for comprehending plant adaptation under global climate change, with significant implications for future research in plant biodiversity conservation, particularly within forest ecosystems.

Chemical Fate of Oils on Indoor Surfaces: Ozonolysis and Peroxidation.

Unsaturated triglycerides found in food and skin oils are reactive in ambient air. However, the chemical fate of such compounds has not been well characterized in genuine indoor environments. Here, we monitored the aging of oil coatings on glass surfaces over a range of environmental conditions, using mass spectrometry, nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) techniques. Upon room air exposure (up to 17 ppb ozone), the characteristic ozonolysis products, secondary ozonides, were observed on surfaces near the cooking area of a commercial kitchen, along with condensed-phase aldehydes. In an office setting, ozonolysis is also the dominant degradation pathway for oil films exposed to air. However, for indoor enclosed spaces such as drawers, the depleted air flow makes lipid autoxidation more favorable after an induction period of a few days. Forming hydroperoxides as the major primary products, this radical-mediated peroxidation behavior is accelerated by indoor direct sunlight, but the initiation step in dark settings is still unclear. These results are in accord with radical measurements, indicating that indoor photooxidation facilitates radical formation on surfaces. Overall, many intermediate and end products observed are reactive oxygen species (ROS) that may induce oxidative stress in human bodies. Given that these species can be widely found on both food and household surfaces, their toxicological properties are worth further attention.

Effects of solvent on pyrolysis-assisted catalytic hydrogenolysis of softwood lignin for high-yield production of monomers and phenols, as studied using coniferyl alcohol as a major primary pyrolysis product

Solvents affect the monomer yield and product selectivity via altering pyrolytic and catalytic reactions during pyrolysis-assisted catalytic hydrogenolysis of lignin.

NMR Analysis of Lipid Oxidation in Flaxseed Oil-in-Water Emulsions.

The formation of linolenic (Ln) and linoleic (L) acyl oxidation products during storage of flaxseed oil (FO)-in-water emulsions was monitored using proton nuclear magnetic resonance (1H NMR) spectroscopy, as well as chemical analytical methods and gas chromatography. Emulsions containing 10% FO and 1% Tween 60 were prepared by homogenization and then stored at 37 °C in the dark for 21 days under accelerated oxidation conditions (500 μmol ferrous sulfate). The induction time of the emulsions, after which rapid lipid oxidation was first observed, was 5-7 days, as shown by increases in peroxide values and hydroperoxide concentrations determined by NMR spectroscopy. Analysis of the hexanal and propanal concentrations during storage by HS-SPME-GC indicated that the oxidation of Ln and L acyls in the emulsions occurred simultaneously. The oxidation products originating from the Ln and L acyls were monitored using 1H NMR spectroscopy throughout the oxidation process. These results also showed that the Ln and L acyls oxidized simultaneously, and isomers of hydroperoxy-cyclic hydroperoxides (HCPs), Z,E-conjugated dienic hydroperoxides (ZECDHPs), and E,E-conjugated dienic hydroperoxides (EECDHPs) were the major primary oxidation products. Aldehydes were observed after 7 days, which was taken to be the start of the propagation stage, with the formation of a significant amount of oxygenated α, β-unsaturated aldehydes (OαβUAs). Based on the concentrations of hydroperoxides originating from the Ln and L acyls, our results suggested that the loss rate of L acyls was parallel to that of Ln acyls. This result was consistent with Ln acyls adopting a tighter packing at the oil-water interface in the emulsions than L acyls. This hypothesis was supported by the NMR relaxation time data. A good correlation between the isomer concentrations of ZECDHPs and HCPs in Ln acyls and between ZECDHPs and EECDHPs in L acyls was shown, with the mole ratios between them being 1.2 and 1.1, respectively. Droplet size and microstructure analyses showed that droplet aggregation occurred from 11 days onwards, which was attributed to polar oxidation products located at the oil droplet surfaces promoting coalescence. Zeta-potential measurements indicated that the droplets became more negative during storage, which was attributed to the accumulation of anionic reaction products at the droplet surfaces.

Atmospheric Chemistry of N-Methylmethanimine (CH3N═CH2): A Theoretical and Experimental Study.

The OH-initiated photo-oxidation of N-methylmethanimine, CH3N=CH2, was investigated in the 200 m3 EUPHORE atmospheric simulation chamber and in a 240 L stainless steel photochemical reactor employing time-resolved online FTIR and high-resolution PTR-ToF-MS instrumentation and in theoretical calculations based on quantum chemistry results and master equation modeling of the pivotal reaction steps. The quantum chemistry calculations forecast the OH reaction to primarily proceed via H-abstraction from the =CH2 group and π-system C-addition, whereas H-abstraction from the −CH3 group is a minor route and forecast that N-addition can be disregarded under atmospheric conditions. Theoretical studies of CH3N=CH2 photolysis and the CH3N=CH2 + O3 reaction show that these removal processes are too slow to be important in the troposphere. A detailed mechanism for OH-initiated atmospheric degradation of CH3N=CH2 was obtained as part of the theoretical study. The photo-oxidation experiments, obstructed in part by the CH3N=CH2 monomer–trimer equilibrium, surface reactions, and particle formation, find CH2=NCHO and CH3N=CHOH/CH2=NCH2OH as the major primary products in a ratio 18:82 ± 3 (3σ-limit). Alignment of the theoretical results to the experimental product distribution results in a rate coefficient, showing a minor pressure dependency under tropospheric conditions and that can be parametrized k(T) = 5.70 × 10–14 × (T/298 K)3.18 × exp(1245 K/T) cm3 molecule–1 s–1 with k298 = 3.7 × 10–12 cm3 molecule–1 s–1. The atmospheric fate of CH3N=CH2 is discussed, and it is concluded that, on a global scale, hydrolysis in the atmospheric aqueous phase to give CH3NH2 + CH2O will constitute a dominant loss process. N2O will not be formed in the atmospheric gas phase degradation, and there are no indications of nitrosamines and nitramines formed as primary products.

Monitoring the ripening attributes of Turkish white cheese using miniaturized vibrational spectrometers

Monitoring the ripening process by prevalent analytic methods is laborious, expensive, and time consuming. Our objective was to develop a rapid and simple method based on vibrational spectroscopic techniques to understand the biochemical changes occurring during the ripening process of Turkish white cheese and to generate predictive algorithms for the determination of the content of key cheese quality and ripening indicator compounds. Turkish white cheese samples were produced in a pilot plant scale and ripened for 100 d, and samples were analyzed at 20 d intervals during storage. The collected spectra (Fourier-transform infrared, Raman, and near-infrared) correlated with major composition characteristics (fat, protein, and moisture) and primary products of the ripening process and analyzed by pattern recognition to generate prediction (partial least squares regression) and classification (soft independent analysis of class analogy) models. The soft independent analysis of class analogy models classified cheese samples based on the unique biochemical changes taking place during the ripening process. partial least squares regression models showed good correlation (RPre = 0.87 to 0.98) between the predicted values by vibrational spectroscopy and the reference values, giving low standard errors of prediction (0.01 to 0.57). Portable and handheld vibrational spectroscopy units can be used as a rapid, simple, and in situ technique for monitoring the quality of cheese during aging and provide real-time tools for addressing deviations in manufacturing.

Formation of reaction intermediates and primary volatiles during acid-catalysed fast pyrolysis of cellulose in a wire-mesh reactor

This study aims to understand the fundamental reaction mechanisms during fast pyrolysis of the acid-impregnated cellulose in a wire-mesh reactor at 40–450 °C and 20 °C/s, via quantifying key compounds in the reaction intermediates and primary volatiles. Acid impregnation reduces the onset reaction temperature of cellulose pyrolysis. During acid-catalysed cellulose pyrolysis, 1,6-anhydro-β-d-glucofuranose (AGF), levoglucosenone (LGO) and 5-hydroxymethylfurfural (5-HMF) are identified as major products in the primary volatiles, and the formation of levoglucosan is greatly suppressed. At temperatures < 100 °C, acid catalyses hydrolysis reactions to produce glucose, which is further dehydrated to AGF at 120 °C. At temperatures > 160 °C, acid enhances the dehydration of glucose, levoglucosan and AGF to produce 5-HMF and LGO as major primary products. Once produced, those products can be easily released into the vapour phase, as either aerosols via thermal ejection or vapours via evaporation. As the pyrolysis temperature increases to 240 °C, aromatic compounds can be identified in the primary volatiles, indicating condensation reactions also play important roles during acid-catalysed cellulose pyrolysis under the conditions. As a result, char formation becomes the favoured pathway during acid-catalysed cellulose pyrolysis at temperatures > 300 °C.

Representative model compounds for understanding the pyrolytic behavior of pre-oxidized β-ether-type lignin

To achieve a better understanding of the pyrolysis behavior of pre-oxidized β-ether-type lignin, three Cα=O type dimers with different substituent groups on the aromatic ring were synthesized and analyzed by a simultaneous thermal analysis instrument (STA), in-situ Fourier transform infrared spectroscopy (in-situ FTIR), and pyrolysis-gas chromatography/ mass spectrometry (Py-GC/MS). The results showed that major primary pyrolysis reactions of Cα=O type models normally occurred at 200 to 400 °C, and connecting bridge structures of models were completely destroyed, causing the emission of abundant volatiles. Substituent groups of aromatic rings played direct roles in thermal stability of models, volatiles emission, product characteristics, and secondary reaction pathways of major primary products. Particularly, the aryl–OCH3 group clearly enhanced the reactivity of intramolecular linkages and was an important active functional group for secondary reactions. As major primary products and intermediates, guaiacol and 2-methoxy-benzaldehyde were formed via the cleavage of Cα–O and Cα–Cβ bonds and could also be converted into phenol, benzaldehyde, and 2-methylphenol via rearrangement of aryl–OCH3 into an aryl–CH3 group or –OCH3 group removal. Oxidization of benzylic alcohol to benzylic ketone not only simplified depolymerization pathways, but also resulted in better selectivity of phenolic monomers and a predictable product distribution.

Lipid Hydroperoxidation Effect on the Dynamical Evolution of the Conductance Process in Bilayer Lipid Membranes: A Condition Toward Criticality.

Cell membranes are one of the main targets of oxidative processes mediated by reactive oxygen species (ROS). These chemical species interact with unsaturated fatty acids of membrane lipids, triggering an autocatalytic chain reaction, producing lipid hydroperoxides (LOOHs) as the first relatively stable product of the ROS-mediated lipid peroxidation (LPO) process. Numerous biophysical and computational studies have been carried out to elucidate the LPO impact on the structure and organization of lipid membranes. However, although LOOHs are the major primary product of LPO of polyunsaturated fatty acids (PUFAs), to the best of our knowledge, there is no experimental evidence on the effects of the accumulation of these LPO byproducts on the electrical properties and the underlying dynamics of lipid membranes. In this work, bilayer lipid membranes (BLMs) containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocoline (POPC) with increasing hydroperoxidized POPC (POPC-OOH) molar proportions (BLMPC/PC-OOH) are used as model membranes to investigate the effect of LOOH-mediated LPO propagation on the electrical behavior of lipid bilayers. Voltage-induced ion current signals are analyzed by applying the fractal method of power spectrum density (PSD) analysis. We experimentally prove that, when certain LOOH concentration and energy threshold are overcome, oxidized membranes evolve toward a critical state characterized by the emergence of non-linear electrical behavior dynamics and the pore-type metastable structures formation. PSD analysis shows that temporal dynamics exhibiting "white" noise (non-time correlations) reflects a linear relationship between the input and output signals, while long-term correlations (β > 0.5) begin to be observed closely to the transition (critical point) from linear (Ohmic) to nonlinear (non-Ohmic) behavior. The generation of lipid pores appears to arise as an optimized energy dissipation mechanism based on the system's ability to self-organize and generate ordered structures capable of dissipating energy gradients more efficiently under stressful oxidative conditions.

Gas-Phase Reaction of trans-2-Methyl-2-butenal with Cl: Kinetics, Gaseous Products, and SOA Formation

The gas-phase reaction between trans-2-methyl-2-butenal and chlorine (Cl) atoms has been studied in a simulation chamber at 298 ± 2 K and 760 ± 5 Torr of air under free-NOx conditions. The rate coefficient of this reaction was determined as k = (2.45 ± 0.32) × 10-10 cm3 molecule−1 s−1 by using a relative method and Fourier transform infrared spectroscopy. In addition to this technique, gas chromatography coupled to mass spectrometry and proton transfer time-of-flight mass spectrometry were used to detect and monitor the time evolution of the gas-phase reaction products. The major primary reaction product from the addition of Cl to the C-3 of trans-2-methyl-2-butenal was 3-chloro-2-butanone, with a molar yield (YProd) of (52.5 ± 7.3)%. Acetaldehyde (Y = (40.8 ± 0.6)%) and HCl were also identified, indicating that the H-abstraction by Cl from the aldehyde group is a reaction pathway as well. Secondary organic aerosol (SOA) formation was investigated by using a fast mobility particle sizer spectrometer. The SOA yield in the Cl + trans-2-methyl-2-butenal reaction is reported to be lower than 2.4%, thus its impact can be considered negligible. The atmospheric importance of the titled reaction is similar to the corresponding OH reaction in areas with high Cl concentration.

Creation and Evolution of Impact-generated Reduced Atmospheres of Early Earth

Abstract The origin of life on Earth seems to demand a highly reduced early atmosphere, rich in CH4, H2, and NH3, but geological evidence suggests that Earth's mantle has always been relatively oxidized and its emissions dominated by CO2, H2O, and N2. The paradox can be resolved by exploiting the reducing power inherent in the “late veneer,” i.e., material accreted by Earth after the Moon-forming impact. Isotopic evidence indicates that the late veneer consisted of extremely dry, highly reduced inner solar system materials, suggesting that Earth's oceans were already present when the late veneer came. The major primary product of reaction between the late veneer's iron and Earth's water was H2. Ocean-vaporizing impacts generate high pressures and long cooling times that favor CH4 and NH3. Impacts too small to vaporize the oceans are much less productive of CH4 and NH3, unless (i) catalysts were available to speed their formation, or (ii) additional reducing power was extracted from pre-existing crustal or mantle materials. The transient H2–CH4 atmospheres evolve photochemically to generate nitrogenated hydrocarbons at rates determined by solar radiation and hydrogen escape, on timescales ranging up to tens of millions of years and with cumulative organic production ranging up to half a kilometer. Roughly one ocean of hydrogen escapes. After the methane is gone, the atmosphere is typically H2- and CO-rich, with eventual oxidation to CO2 rate-limited by water photolysis and hydrogen escape.

Mechanistic insights into the primary reactions during acid-catalysed pyrolysis of levoglucosan at 80–140 °C

This paper reports an experimental investigation into the pyrolysis of acid-impregnated levoglucosan at 80–140 °C to understand the fundamental reaction mechanism of acid-catalysed levoglucosan pyrolysis. Glucose, anhydro-disaccharides and disaccharides of various linkages have been successfully identified as major primary products during acid-catalysed levoglucosan pyrolysis at such low temperatures. Among all identified primary products, glucose has the highest initial selectivity of ~20%, indicating hydrolysis reaction plays an important role during acid-catalysed levoglucosan pyrolysis. The formation of anhydro-disaccharides of various α and β linkages (including 1,4-, 1,3-, and 1,2-glycosidic bond) clearly demonstrates the importance of polymerisation reactions during acid-catalysed levoglucosan pyrolysis. In addition, disaccharides of various α and β linkages (including 1,6-, 1,4-, 1,3-, 1,2-, 1,1-glycosidic bond) are also minor primary products from acid-catalysed levoglucosan pyrolysis. Once those primary products are formed, they are easily polymerised into high-DP anhydro-sugar and sugar oligosaccharides, with a highest DP of up to ~10 at 120 °C. At 140 °C, the oligosaccharides are also easily condensed to form char, as evidenced by post-hydrolysis results. Increasing acid loading level enhances the formation of glucose and disaccharides, but has negligible effect on the formation of anhydro-disaccharides. These results provide new insights into the fundamental mechanism of acid-catalysed levoglucosan pyrolysis for producing biofuels and biochemicals.

The atmospheric oxidation of hydroxyacetone: Chemistry of activated and stabilized CH3C(O)CH(OH)OO• radicals between 252 and 298 K

AbstractThe products of the Cl‐atom‐initiated oxidation of hydroxyacetone (HYAC, CH3C(O)CH2OH) have been examined under conditions relevant to the earth's lower atmosphere. Over the range of temperatures studied (252‐298 K), in the absence of NOx, methylglyoxal (CH3C(=O)CH=O, MGLY) was formed with a primary yield &gt;84% (96 ± 9% at 298 K), while in the presence of elevated NOx, MGLY and formic acid were both formed as major primary products. In contrast to a previous study, acetic acid was not identified as a major primary product under the conditions studied. The results are quantitatively interpreted from a consideration of the formation of a stabilized CH3C(O)CH(OH)OO• radical, either in a ≈50% yield from the addition of O2 to CH3C(O)CH•(OH) or in 100% yield from the addition of HO2 to MGLY. At high temperature and low NOx, decomposition of the stabilized CH3C(O)CH(OH)OO• radical to MGLY is favored, while lower temperatures and conditions of high NOx favor bimolecular reactions of the stabilized radical, with subsequent production of formic acid. Analysis of the data allows for a semiquantitative determination of K3 = (2.9 ± 0.4) × 10−16 cm3 molecule−1, for the HO2 + MGLY ↔ CH3C(O)CH(OH)OO• equilibrium process at 298 K and a roughly order of magnitude increase in K3 at 252 K.

Ethylene Conversion into Propylene and Aromatics on HZSM-5: Insights on Reaction Routes and Water Influence

Ethanol is an alternative for producing petrochemicals, especially propylene and aromatics (benzene, toluene, and xylenes). To understand ethanol processing routes into olefins and aromatics, it is interesting to use ethylene that is the major primary product of ethanol reaction into hydrocarbons and the intermediate for the formation of olefins and aromatics. In this work, the influence of the operating conditions (ethylene partial pressure, reaction temperature and contact time) in the ethylene conversion into propylene and aromatics, and in the product yield was investigated using HZSM-5 zeolite as catalyst. Lower contact time and ethylene partial pressure, and higher reaction temperature favored propylene yield. Olefin production was based on the formation of carbene species from ethylene that reacts with ethylene to produce propylene and on ethylene dimerization to form butenes. On the other hand, intermediate reaction temperatures and contact times, and higher ethylene partial pressure promote the formation of aromatics, where the dehydrocyclization reaction is favored over hydrogen transfer. The presence of water vapor in long-term reactions deactivated the catalyst. For propylene production, the decrease of ethylene conversion was due to zeolite framework dealumination, while for aromatic formation the reaction mechanism was changed.

Investigation into Photoinduced Auto-Oxidation of Polycyclic Aromatic Hydrocarbons Resulting in Brown Carbon Production.

Brown carbon (BrC) is a collection of oxidized atmospheric aromatic compounds detected worldwide with broad functionality. This multifunctional nature allows BrC to be water-soluble and bioavailable and demonstrate light absorption at multiple wavelengths. Polycyclic aromatic hydrocarbons (PAH) are major primary products of combustion emissions and have long been known to oxidize in the environment as components of secondary organic aerosols. In this study, we have exposed aqueous PAH suspensions to simulated sunlight to investigate oxidized PAH as BrC precursors. Illuminated samples of naphthalene and anthracene demonstrated growth of several new products with absorptions and oxidation consistent with humic-like substances (HULIS). Reactions of aqueous naphthalene, anthracene, and their oxidized derivatives were found to produce chromatographic and spectroscopic evidence of HULIS formation when exposed to sunlight. The association of oxyradicals with HULIS has implications on human health via lung tissue damage; and its absorption character may add to radiative forcing processes in the atmosphere. The overall product characterizations from naphthalene and anthracene indicate reaction mechanism pathways that use oxidized alcohol and quinone as intermediate species.

Insecticide treated packaging for the control of stored product insects

Improper or poor post-harvest handling and storage of stored grains contributes significantly to product loss, and bagged stored grain presents an option for safe storage and handling. Bagged grain is intended to maintain quality and safety, while protecting it from infestations. The objective of this research was to determine the effect of deltamethrin-treated packaging material on adults and larvae of common stored product pests. Adults or larvae of several species of stored product insects were exposed to deltamethrin-treated packaging for time intervals ranging from 1 h to 4 weeks. The percentage of affected Prostephanus truncatus, Callosobruchus maculatus and Rhyzopertha dominica adults was 96% larval death within 1-2 weeks.The major primary stored product insects were highly susceptible to the deltamethrin-treated storage bags, but there was variation in susceptibility between species and life stages tested. The deltamethrin-treated storage bags can offer protection of bagged grains and be used as a preventative measure to reduce infestations during storage.

A review of mechanistic and mathematical modeling of n-heptane and cyclohexane pyrolysis

An extensive literature review of the mechanistic modeling of n-heptane and cyclohexane pyrolysis was carried out. It was shown that Rice–Kossiakoff free radical theory does not adequately account for product distributions of n-heptane pyrolysis in the high conversion regime. Secondary reactions of alpha higher olefins and di-olefins accounted for the major products (ethene, propene and 1-butene) of n-heptane pyrolysis. Predicted product distributions (CH4, C2H4, C3H6, 1-C4H8 and 1,3-C4H6) of n-heptane pyrolysis showed very good agreement with experimental data. The product distributions of cyclohexane pyrolysis in the high conversion regime were rationalized and adequately accounted for using decomposition reactions of cyclohexyl bi-radicals followed by secondary reactions of major primary products such as C3H6 and 1,3-C4H6. The latter expanded mechanism can be used to model cyclohexane pyrolysis in the high conversion regime. Rate parameters (pre-exponential factors and activation energy) for each of the elementary reactions of n-heptane mechanistic model were either obtained from the literature or estimated using thermochemical parameters. The use of steady state approximation in mathematical modeling of n-heptane pyrolysis led to erroneous results.

Deamination reaction mechanisms of protonated amines under hydrothermal conditions

Many experimental studies report rates of decomposition for amino acids under hydrothermal conditions without describing the kinetics of competing reactions or definitively characterizing individual reaction mechanisms. As a step toward comprehensive models for amino acid reactivity, this study provides a detailed description of the organic reaction kinetics and mechanisms for deamination of amine functional groups at acidic hydrothermal conditions, which favors their protonated aminium forms. Time series experiments yield hydrothermal deamination rates for model aminum compounds benzylaminium (BAH+) and α-methylbenzylaminium (α-CH3-BAH+), buffered at pH 3.3 at 250 °C and 40 bar (Psat). Both compounds are primary amines, but the amine group in the former is bonded to a primary carbon while in the latter to a secondary carbon; this difference has implications for reactivity that are relevant for naturally occurring amines. Deamination of the aminiums under these conditions forms alcohols as the major primary products. The deamination mechanisms were investigated by determining the reaction kinetics of ring-substituted BAH+ and α-CH3-BAH+ derivatives, which provided information on the nature of charge buildup in the transition state. The results for the deamination of BAH+ to form benzyl alcohol support nearly equal contribution from two reaction mechanisms, specifically unimolecular nucleophilic substitution (SN1, kSN1 ≈ 2.4 × 10−6 s−1) and bimolecular nucleophilic substitution (SN2, kSN2 ≈ 2.7 × 10−6 s−1), while α-CH3-BAH+ deaminates almost exclusively via a much faster SN1 mechanism (kα ≈ 7.6 × 10−4 s−1). These observed rates reinforce the notion that previously reported amino acid deamination rates may have resulted from catalysis mechanisms associated with certain reaction vessel materials (e.g., Pyrex and stainless steel). The observation of two competing mechanisms for BAH+ deamination/hydration implies that extrapolation of deamination rates to other temperatures is currently unreliable, since this is likely to be accompanied by a change in the predominant mechanism. However, this work establishes that mechanistic contributions can be quantified, which will enhance the accuracy of extrapolating deamination rates across the temperature and pH ranges common to aqueous geochemical environments.