Formation Pathways Research Articles

Formation of the emerging disinfection byproducts halocyclopentadienes from phenolic compounds after chlorination

Halocyclopentadienes (HCPDs) are an emerging class of alicyclic disinfection by-products (DBPs) with high toxicity in disinfected drinking water. However, their potential precursors remain unclear, which hinders the understanding of their formation and further development of control strategies. In this study, two HCPDs, 1,2,3,4-tetrachloro-1,3-cyclopentadiene (TCC) and 1,2,3,4,5,5-hexachloro-1,3-cyclopentadiene (HCC), were identified in chlorinated lignin and tannic acid samples for the first time. The chlorination of four lignin-like and two tannic-like phenolic model compounds confirmed that guaiacol and digallic acid can produce HCPDs. According to their structures, ortho-substituents of phenolic compounds were speculated to be crucial for HCPDs formation. The simulated disinfection of catechol, 2-ethoxyphenol (2-EOP), 2-propoxyphenol (2-POP) and 3,4-dihydroxy-5-methoxybenzoic acid (DH-5-MBA) with different ortho-substituents demonstrated that three of these compounds can generate HCPDs, except catechol, which further indicates that ortho-substituents, such as the methoxy, ethoxy and propoxy groups, contribute to HCPDs generation. Guaiacol was the simplest compound for generating HCPDs, and possible formation pathways during chlorination were proposed. Seven hydroxy-chlorocyclopentadienes were tentatively identified and are likely important intermediates of HCPDs formation. Additionally, TCC and HCC were confirmed in tap water and chlorinated SRNOM samples with total concentrations up to 11.07 ng/L and 65.66 ng/L, respectively, further demonstrating the wide existence of HCPDs and their precursors. This study reports the clear precursors of HCPDs and provides a theoretical foundation for controlling HCPDs formation in disinfected drinking water.

Biomimetic Capsid-Like Nanoshells Self-Assembled from Homopolypeptides.

The preparation of capsid-like nanoshells and the elucidation of their formation pathways are crucial for the application potential of capsid-like nanomaterials. In this study, we have prepared biomimetic capsid-like nanoshells (CLNs) through the solution self-assembly of poly (β-phenethyl-L-aspartate) homopolypeptide (PPLA). The formation of CLNs is governed by an aggregation-fusion mechanism. Initially, PPLA molecules self-assemble into small spherical assemblies as subunits and the initial nuclei are formed through fusing some subunits. Subsequently, additional subunits rapidly fuse onto these nuclei, leading to the growth of full or partial CLNs during the growth phase. Moreover, the suitable condition benefiting CLNs formation is clarified by a morphological phase diagram based on the initial PPLA concentration against water content. Molecular-level measurements suggest that the molecular flexibility of PPLA is a key factor in the arrangement and fusion of subunits for the formation of CLNs. These findings offer new perspectives for a deeper understanding of the formation pathways of capsid-like nanoshells derived from synthetic polymers.

Photocatalytic Synthesis of Glycine from Methanol and Nitrate.

Photocatalytic utilization of methanol and nitrate as carbon and nitrogen sources for the direct synthesis of amino acids could provide a sustainable way for the valorization of green "liquid sunlight" and nitrate waste. In this study, we developed an efficient photochemical method to synthesize glycine directly from methanol and nitrate, which cascades the C-C coupling to form glycol, nitrate reduction to NH3, and finally C-N coupling to generate glycine. Interestingly, the involved photocatalytic tandem reactions show a synergistic effect, in which the presence of nitrate is the dominant factor to enable the overall reaction and reach high synthetic efficiency. Ba2+-TiO2 nanoparticles are confirmed as a feasible and efficient catalyst system for the photosynthesis of glycine with a remarkable glycine photosynthesis rate of 870 μmol gcat-1 h-1 under optimal conditions. This work establishes a novel catalytic system for amino acid synthesis from methanol and nitrate under mild conditions. These results also allow us to further suppose the formation pathways of amino acids on the primitive earth, as an extension to proposals based on the Miller-Urey experiments.

Nitrogen migration and transformation during the pyrolysis of corn straw with iron-based catalyst

The pyrolysis of renewable biomass into biofuels and high-value chemicals showcases remarkable application value and extensive market potential. However, the pyrolysis of biomass with high nitrogen content results in the production of NOX precursors that contribute to environmental pollution. Therefore, it is proposed to introduce iron-based catalysts to change the formation pathway of NOX precursors and control their production.The study elucidates the influence of iron-based catalysts on the conversion of nitrogen-containing products between gas, liquid and solid phases during corn straw pyrolysis. First, the effects of iron-based catalyst types on pyrolysis kinetics of corn straw were estimated using Thermogravimetry-mass spectrometry (TG-MS). Based on this, the effects of catalyst type and dispersion on the migration path of three-phase nitrogen-containing products were investigated, and the chemical morphology of the catalyst during pyrolysis was monitored by in-situ XRD to clarify the main catalytic active phase for N2 formation. Results showed that the addition of Fe, FeCl3 and Fe2O3 changed the distribution ratio of three-phase nitrogen-containing products, and the gas phase yield was significantly improved. Notably, the chemical form of Fe2O3 will change and transform into FeOOH, Fe3O4 and α-Fe during pyrolysis. It was confirmed that α-Fe was the main active phase for catalyzing the conversion of nitrogen-containing substances. Higher N2 conversion can be achieved by preparing high purity α-Fe. The mechanism is that α-Fe catalyzes the secondary decomposition of tar nitrogen into NH3 and HCN. Simultaneously, α-Fe reacts with char nitrogen, NH3, and HCN to form FeXN, which decomposes to produce environmentally friendly N2. The research findings offer theoretical guidance for the control of nitrogen pollutant emissions and the targeted acquisition of pyrolysis products (For example, NH3 can be used as a carbon-free hydrogen-rich fue).

The screening of iron oxides for long-term transformation into vivianite to recover phosphorus from sewage

The reducibility of iron oxides, depending on their properties, influences the kinetics of dissimilatory iron reduction (DIR) during vivianite recovery in sewage. This study elucidated the correlation between properties of iron oxides and kinetics of DIR during the long-term transformation into vivianite, mediated by Geobacter sulfurreducens PCA and sewage. The positive correlation between surface reactivity of iron oxides and reduction rate constant (k) influenced the terminal vivianite recovery efficiency. Akaganeite with the highest adhesion work and surface energy required the lowest reduction energy (Ea), obtained the highest k of 1.36 × 10–2 day-1 and vivianite recovery efficiency of 43 %. The vivianite yield with akaganeite as iron source was 76–164 % higher than goethite, hematite, feroxyhyte, and ferrihydrite in sewage. The distribution of P with akaganeite during DIR in sewage further suggested a more efficient pathway of direct vivianite formation via bio-reduced Fe(II) rather than indirect reduction of ferric phosphate precipitates. Thus, akaganeite was screened out as superior iron source among various iron oxides for vivianite recovery, which provided insights into the fate of iron sources and the cycle of P in sewage.

Reactant Discovery with an Ab Initio Nanoreactor: Exploration of Astrophysical N-Heterocycle Precursors and Formation Pathways.

The incorporation of nitrogen atoms into cyclic compounds is essential for terrestrial life; nitrogen-containing (N-)heterocycles make up DNA and RNA nucleobases, several amino acids, B vitamins, porphyrins, and other components of biomolecules. The discovery of these molecules on meteorites with non-terrestrial isotopic abundances supports the hypothesis of exogenous delivery of prebiotic material to early Earth; however, there has been no detection of these species in interstellar environments, indicating that there is a need for greater knowledge of their astrochemical formation and destruction pathways. Here, we present results of simulations of gas-phase pyrrole and pyridine formation from an ab initio nanoreactor, a first-principles molecular dynamics simulation method that accelerates reaction discovery by applying non-equilibrium forces that are agnostic to individual reaction coordinates. Using the nanoreactor in a retrosynthetic mode, starting with the N-heterocycle of interest and a radical leaving group, then considering the discovered reaction pathways in reverse, a rich landscape of N-heterocycle-forming reactivity can be found. Several of these reaction pathways, when mapped to their corresponding minimum energy paths, correspond to novel barrierless formation pathways for pyridine and pyrrole, starting from both detected and hypothesized astrochemical precursors. This study demonstrates how first-principles reaction discovery can build mechanistic knowledge in astrochemical environments as well as in early Earth models such as Titan's atmosphere where N-heterocycles have been tentatively detected.

A synthetic cell-free pathway for biocatalytic upgrading of one-carbon substrates.

Biotechnological processes hold tremendous potential for the efficient and sustainable conversion of one-carbon (C1) substrates into complex multi-carbon products. However, the development of robust and versatile biocatalytic systems for this purpose remains a significant challenge. In this study, we report a hybrid electrochemical-biochemical cell-free system for the conversion of C1 substrates into the universal biological building block acetyl-CoA. The synthetic reductive formate pathway (ReForm) consists of five core enzymes catalyzing non-natural reactions that were established through a cell-free enzyme engineering platform. We demonstrate that ReForm works in a plug-and-play manner to accept diverse C1 substrates including CO2 equivalents. We anticipate that ReForm will facilitate efforts to build and improve synthetic C1 utilization pathways for a formate-based bioeconomy.

Effects of cellulose addition on sodium lignosulfonate pyrolysis: Product distribution and formation pathway

Effects of cellulose addition on sodium lignosulfonate pyrolysis: Product distribution and formation pathway

Differences in Interfacial Reactivity of Graphite and Lithium Metal Battery Electrodes Investigated Via Operando Gas Analysis.

Gases evolved from lithium batteries can drastically affect their performance and safety; for example, cell swelling is a serious safety issue. Here, we combine operando pressure measurements and online electrochemical mass spectrometry measurements to identify the nature and quantity of gases formed in batteries with graphite and lithium metal electrodes. We demonstrate that ethylene, a main gas evolved in SEI formation reactions, is quickly consumed at lithium metal electrodes unless they have been pretreated in the electrolyte. Polyolefins such as polyethylene are suggested as the possible reaction product from ethylene consumption, evidencing another pathway of SEI formation that had been previously overlooked because it does not produce any gas product.

Effect of Methyl Butyrate blending on soot formation in Jet A laminar diffusion flame

To investigate the effect of methyl butyrate (MB) blending on soot formation in a Jet A laminar diffusion flame, laser-induced incandescence (LII) and laser-induced fluorescence (LIF) techniques were employed to assess the distributions of soot-LII signal and polycyclic aromatic hydrocarbons (PAH) signal in Jet A with varying MB blending ratios from 0% to 80%. The experimental results revealed that an increase in the MB blending ratio resulted in decreased flame height, reduced radially integrated natural luminosity peak signal, and lower the total spatially integrated natural luminosity, while the flame base height increased. The starting position of soot-LII signal moved downstream gradually, and the peak signal magnitude on the axis decreased. The addition of MB effectively reduced the soot-LII signal in Jet A. Compared to pure Jet A, the average soot-LII signal for MB20, MB40, MB60, and MB80 decreased by 18.9%, 79.6%, 85.3%, and 94.2%, respectively. The maximum soot-LII signal decreased by 18.2%, 68.3%, 76.0%, and 93.5%, respectively. Furthermore, the PAH-LIF signal gradually decreased as the MB blending ratio increased. Moreover, the MB-Jet A-PAH mechanism was constructed, and the formation pathways of the soot precursor based on a diffusion flame model were calculated. The kinetic results indicate that an increase in the MB blending ratio reduces the rates of different reactions involved in the generation of A1, leading to a reduction in A1. The dilution of PBZ in Jet A by MB is identified as the primary factor for the reduction in soot.

Discovery of Molecular Intermediates and Nonclassical Nanoparticle Formation Mechanisms by Liquid Phase Electron Microscopy and Reaction Throughput Analysis

Formation kinetics of metal nanoparticles are generally described via mass transport and thermodynamics‐based models, such as diffusion‐limited growth and classical nucleation theory (CNT). However, metal monomers are commonly assumed as precursors, leaving the identity of molecular intermediates and their contribution to nanoparticle formation unclear. Herein, liquid phase transmission electron microscopy (LPTEM) and reaction kinetic modeling are utilized to establish the nucleation and growth mechanisms and discover molecular intermediates during silver nanoparticle formation. Quantitative LPTEM measurements show that their nucleation rate decreases while growth rate is nearly invariant with electron dose rate. Reaction kinetic simulations show that Ag4 and Ag− follow a statistically similar dose rate dependence as the experimentally determined growth rate. We show that experimental growth rates are consistent with diffusion‐limited growth via the attachment of these species to nanoparticles. The dose rate dependence of nucleation rate is inconsistent with CNT. A reaction‐limited nucleation mechanism is proposed and it is demonstrated that experimental nucleation kinetics are consistent with Ag42+ aggregation rates at millisecond time scales. Reaction throughput analysis of the kinetic simulations uncovered formation and decay pathways mediating intermediate concentrations. We demonstrate the power of quantitative LPTEM combined with kinetic modeling for establishing nanoparticle formation mechanisms and principal intermediates.

Soil organic matter persistence in hyperhumic colluvial soils caused by palaeofires, root inputs and mineral binding

Understanding the formation of long-term persistent soil organic matter (SOM) is key to optimizing soil management and predicting the response of the terrestrial organic carbon (OC) pool to climate change, yet our knowledge of the soil-type dependent weight of different stabilization pathways (e.g., recalcitrance and mineral binding) is fragmentary. Owing to their stratigraphy, the exceptionally SOM-rich (up to 2 m of mineral soil with >5% OC) colluvial slope deposits of Atlantic Europe (Haplic Umbrisol [colluvic/hyperhumic]) are archives of palaeo-environmental conditions including SOM formation pathways. The objective of this study was to determine how the different drivers of persistent SOM formation influenced the formation of these organic-rich soils. For this purpose, we use Holocene (∼9000 yrs) molecular composition records obtained from pyrolysis-GC–MS (Py-GC–MS) and thermally assisted hydrolysis and methylation (THM-GC–MS). The results emphasize three pathways to stability (i.e., persistence on millennial timescales): 1) palaeofires that generated recalcitrant pyrogenic SOM, 2) release of root-derived aliphatic macromolecules (suberin-like SOM), and 3) formation of microbial necromass. Pathways 1 and 2 are controlled by land use: Pathway 1 was relatively important under intense anthropogenic fire regimes and pyrophytic shrubland expansion; Pathway 2 was stimulated during early forest phases and under pasture conditions, when past societies focused vegetation management on grazing instead of fire; Pathway 3 was controlled by binding with aluminium-dominated mineral phases. However, we found indications that Pathway 2 (suberin input and preservation) relied partially on sorptive preservation as well. Aided by structured equation modeling (SEM), we show that the formation of persistent SOM pools was driven by balanced weights of i) microbial vs. plant-derived SOM and ii) intrinsic chemical properties of SOM (recalcitrance continuum) vs. mineral binding/occlusion, which varied in keeping with interactions between past land use, topography and vegetation. These findings are inconsistent with the prevalent paradigm of persistent SOM formation by sorptive/occlusive preservation of microbial necromass alone.

Acidic pathway in formation of SiO2–AlO2–PO2 geopolymeric ceramic: Investigation of structural evolution and electrical behaviour

The investigation into the acidic pathway in geopolymer formation has been overlooked compared to the alkaline pathway. This study seeks to fill the gap by exploring the development mechanism and electrical properties of this type of geopolymer. The microstructural properties of geopolymer ceramics were assessed through the deconvolution of attenuated total reflectance-Fourier-transform infrared spectra (ATR-FTIR), powder X-ray diffraction (PXRD), scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), simultaneous thermogravimetric analysis and differential thermal analysis (TGA/DTA). Furthermore, the electrical properties of the prepared ceramics were monitored using solid-state impedance spectroscopy (ss-IS). Maintaining an Al to P molar ratio of 1:1, various post-treatment temperatures (60 °C, 105 °C, 300 °C, 1200 °C) were employed to observe their effects on the (micro)structural properties of the samples under investigation. This ratio ensures the formation of an amorphous structure of SiO2·Al2O3·P2O5·nH2O. Additionally, the emergence of new crystalline aluminium and phosphate phases was observed.

Influence of bulk-phase acidity, organic fraction, and dissolved oxygen on the photosensitized renoxification of nitrate in NaNO3/humic acid mixtures

Nitrate renoxification significantly influences atmospheric nitrogen cycling and global OH budgets. Although numerous nitrite acid (HONO) formation pathways from nitrate photolysis have been widely reported, the influence of various environmental factors and aerosol properties on reactive nitrogen production remains largely unclear. In this work, we employed NaNO3/humic acid (HA) as a model nitrate photosensitization system to investigate the crucial roles of aerosol acidity, organic fraction, and dissolved oxygen in the production of HONO, NO2, and NO2-. The presence of HA at 10 mg/L resulted in a remarkable increase in HONO production rates by approximately 2–3 times and NO2- concentration by 3–6 times across a pH range of 5.2 to 2.0. Meanwhile, the molar fraction of gaseous HONO in total N(III) production increased from 4 % to 69 % as bulk-phase pH decreased from 5.2 to 2.0. The higher organic fraction (i.e., 20 and 50 mg/L HA concentration) instead inhibited HONO and NO2 release. The presence of dissolved oxygen was found to be adverse for reactive nitrogen production. This suggests that the HA photosensitizer promoted the secondary conversion of NO2 to HONO mainly via reduced ketyl radical intermediates, while superoxide radical formation might exert a negative effect. Our findings provide comprehensive insights into reactive nitrogen production from photosensitized nitrate photolysis mediated by various external and internal factors, potentially accounting for discrepancies between field observations and model simulations.

A systematic IR and VUV spectroscopic investigation of ion, electron, and thermally processed ethanolamine ice

ABSTRACT The recent detection of ethanolamine (EtA, HOCH$_2$CH$_2$NH$_2$), a key component of phospholipids, i.e. the building blocks of cell membranes, in the interstellar medium is in line with an exogenous origin of life-relevant molecules. However, the stability and survivability of EtA molecules under inter/circumstellar and Solar System conditions have yet to be demonstrated. Starting from the assumption that EtA mainly forms on interstellar ice grains, we have systematically exposed EtA, pure and mixed with amorphous water (H$_2$O) ice, to electron, ion, and thermal processing, representing ‘energetic’ mechanisms that are known to induce physicochemical changes within the ice material under controlled laboratory conditions. Using infrared (IR) spectroscopy, we have found that heating of pure EtA ice causes a phase change from amorphous to crystalline at 180 K, and further temperature increase of the ice results in sublimation-induced losses until full desorption occurs at about 225 K. IR and vacuum ultraviolet (VUV) spectra of EtA-containing ices deposited and irradiated at 20 K with 1 keV electrons as well as IR spectra of H$_2$O:EtA mixed ice obtained after 1 MeV He$^+$ ion irradiation have been collected at different doses. The main radiolysis products, including H$_2$O, CO, CO$_2$, NH$_3$, and CH$_3$OH, have been identified and their formation pathways are discussed. The measured column density of EtA is demonstrated to undergo exponential decay upon electron and ion bombardment. The half-life doses for electron and He$^+$ ion irradiation of pure EtA and H$_2$O:EtA mixed ice are derived to range between $10.8\!-\!26.3$ eV/16u. Extrapolating these results to space conditions, we conclude that EtA mixed in H$_2$O ice is more stable than in pure form and it should survive throughout the star and planet formation process.

The ESO SupJup Survey

Context. It has been proposed that the distinct formation and evolutionary pathways of exoplanets and brown dwarfs may affect the chemical and isotopic content of their atmospheres. Recent work has indeed shown differences in the 12C/13C isotope ratio, which have provisionally been attributed to the top-down formation of brown dwarfs and the core accretion pathway of super-Jupiters. Aims. The ESO SupJup Survey is aimed at disentangling the formation pathways of isolated brown dwarfs and planetary-mass companions using chemical and isotopic tracers. The survey utilises high-resolution spectroscopy with the recently upgraded CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES+) at the Very Large Telescope, covering a total of 49 targets. Here, we present the first results of this survey: an atmospheric characterisation of DENIS J0255-4700, an isolated brown dwarf near the L-T transition. Methods. We analysed its observed CRIRES+ K-band spectrum using an atmospheric retrieval framework in which the radiative transfer code petitRADTRANS was coupled with the PyMultiNest sampling algorithm. Gaussian processes were employed to model inter-pixel correlations. In addition, we adopted an updated parameterisation of the pressure-temperature profile. Results. Abundances of CO, H2O, CH4, and NH3 were retrieved for this fast-rotating L-dwarf. The ExoMol H2O line list provides a significantly better fit than that of HITEMP. A free-chemistry retrieval is strongly favoured over equilibrium chemistry, caused by an under-abundance of CH4. The free-chemistry retrieval constrains a super-solar C/O-ratio of ~0.68 and a solar metallicity. We find tentative evidence (~3σ) for the presence of 13CO, with a constraint on the isotopologue ratio of 12CO/13CO = 184−40+61 and a lower limit of ≳97, which suggests a depletion of 13C compared to the local interstellar medium (12C/13C ~ 68). Conclusions. High-resolution, high signal-to-noise K-band spectra provide an excellent means of constraining the chemistry and isotopic content of sub-stellar objects, which is the main objective of the ESO SupJup Survey.

Alkaline saline lakes: A chemical evolution experiment evaluating the stability of formaldehyde in an aqueous saline environment

Formaldehyde condensation in the presence of a mineral catalyst and under alkaline conditions is considered to be a "messy" chemical system due to its dependence on the complex chemical equilibrium between the reaction intermediates, which has a significant impact on the final products.This chemical system is extremely important in prebiotic chemistry and has been proposed as a potential pathway for carbohydrate formation in the early Earth. Saline and soda lakes are alkaline systems that could concentrate and accumulate a wide variety of ions (such as phosphate) and clay minerals, which can catalyze prebiotic chemical reactions. These geological environments have recently been suggested as ideal environments in which prebiotic chemical reactions could have occurred.This study uses Lake Alchichica in Mexico as a physicochemical analog of an early Archean saline lake to examine the stability of formaldehyde in these aqueous saline environments. Formaldehyde decomposes into sugar-like and CHO molecules in alkaline, high-salinity environments depending on the minerals phases present. As phosphate ion (HPO42−) is available in the aqueous medium, the results of our experiments also imply that phosphorylation processes may have occurred in these natural settings.

Huanglian Jiedu decoction alleviates ischemia-induced cerebral injury in rats by mitigating NET formation and activiting GABAergic synapses.

Huanglian Jiedu decoction (HLJD) has been used to treat ischemic stroke in clinic. However, the detailed protective mechanisms of HLJD on ischemic stroke have yet to be elucidated. The aim of this study is to elucidate the underlying pharmacological mechanisms of HLJD based on the inhibition of neuroinflammation and the amelioration of nerve cell damage. A middle cerebral artery occlusion reperfusion (MCAO/R) model was established in rats and received HLJD treatment. Effects of HLJD on neurological function was assessed based on Bederson's score, postural reflex test and asymmetry score. 2, 3, 5-Triphenyltetrazolium chloride (TTC) staining, Hematein and eosin (HE) and Nissl staining were used to observe the pathological changes in brain. Then, transcriptomics was used to screen the differential genes in brain tissue in MCAO/R model rats following HLJD intervention. Subsequently, the effects of HLJD on neutrophil extracellular trap (NET) formation-related neuroinflammation, gamma-aminobutyric acid (GABA)ergic synapse activation, nerve cell damage and proliferation were validated using immunofluorescence, western blot and enzyme-linked immunosorbent assay (ELISA). Our results showed that HLJD intervention reduced the Bederson's score, postural reflex test score and asymmetry score in MCAO/R model rats. Pathological staining indicated that HLJD treatment decreased the cerebral infarction area, mitigated neuronal damage and increased the numbers of Nissl bodies. Transcriptomics suggested that HLJD affected 435 genes in MCAO/R rats. Among them, several genes involving in NET formation and GABAergic synapses pathways were dysregulated. Subsequent experimental validation showed that HLJD reduced the MPO+CitH3+ positive expression area, reduced the protein expression of PAD4, p-P38/P38, p-ERK/ERK and decreased the levels of IL-1β, IL-6 and TNF-α, reversed the increase of Iba1+TLR4+, Iba1+p65+ and Iba1+NLRP3+ positive expression area in brain. Moreover, HLJD increased GABA levels, elevated the protein expression of GABRG1 and GAT3, decreased the TUNEL positive expression area and increased the Ki67 positive expression area in brain. HLJD intervention exerts a multifaceted positive impact on ischemia-induced cerebral injury in MCAO/R rats. This intervention effectively inhibits neuroinflammation by mitigating NET formation, and concurrently improves nerve cell damage and fosters nerve cell proliferation through activating GABAergic synapses.

Comparative studies of the NOx impacts on the photooxidation mechanisms of isomeric monoterpenes of β-pinene and limonene

It is highly challenging to precisely compare the impacts of anthropogenic pollutants on the photooxidation of isomeric volatile organic compounds with respect to molecular compositions and particle number/mass concentrations of secondary organic aerosols (SOAs). In this study, we conducted a series of well-defined indoor chamber experiments to compare the effects of NOx (NO and NO2) on the photooxidation of isomeric monoterpenes of β-pinene and limonene. For the photooxidation of β-pinene with NOx, the increase of the initial concentrations of NO ([NO]0) shows a monotonous suppression of the particle mass concentration, whereas the increase of [NO2]0 shows a monotonous enhancement of the particle mass concentration. For the photooxidation of limonene with NOx, the increase of [NO]0 exhibits a monotonous suppression of the particle mass concentration, whereas the increase of [NO2]0 shows a parabolic trend of the particle mass concentration. Utilizing a newly developed vacuum ultraviolet free electron laser (VUV-FEL), the online threshold photoionization mass spectrometry reveals a series of novel compounds at molecular weight (MW) = 232 and 306 for the β-pinene + NOx system and MW = 187, 261, 280, and 306 for the limonene + NOx system. The molecular structures and formation pathways of these species were inferred, which led to the prediction of the diversity and difference of SOA products (i.e., ester and peroxide accretion products) formed from different monoterpene precursors. To improve the predictions of future air quality, it is recommended that climate models should incorporate the NOx-driven diurnal photooxidation of monoterpenes for SOA formation mechanisms.

A Possible Additional Formation Pathway for the Interstellar Diatomic SiS

The formation of silicon monosulfide (SiS) in space appears to be a difficult process, but the present work shows that a previously excluded pathway may contribute to its astronomical abundance. Reaction of the radicals SH + SiH produces SiS with a submerged transition state and generates a stabilizing H2 molecule as a product to dissipate the kinetic energy. Such is a textbook chemical reaction for favorable gas-phase chemistry. While previously proposed mechanisms reacting atomic sulfur and silicon with SiH, SH, and H2S will still be major contributors to the production of SiS, an abundance of SiS in certain regions could be a marker for the presence of SiH where it has previously been unobserved. These quantum chemically computed reaction profiles imply that the silicon-chalcogen chemistry of molecular clouds, shocked regions, or protoplanetary disks may be richer than previously thought. Quantum chemical spectral data for the intermediate cis- and trans-HSiSH are also provided to aid in their potential spectroscopic characterization.