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In this study, a series of structurally rigid cyclooctyl-fused iminopyridine iron complexes, [L2FeCl][FeCl4] and [2L3Fe][Cl][3FeCl4], was synthesized via a one-pot method and investigated as precatalysts in conjunction with methylaluminoxane for isoprene (Ip) polymerization. Combined characterization through FTIR analysis, elemental analysis and single crystal XRD analysis fully verified the structure of these complexes. The most active iron complex, FeH, exhibited a trisligated nature, with its cation adopting an octahedral geometry around the metal center. In contrast, all the other iron complexes (Fe2Me, Fe2Et, Fe2iPr, Fe3Me, Fe2Et,Me) displayed bisligated configurations, with distorted trigonal bipyramidal geometry of cations. During isoprene polymerization, the extent of steric hindrance of the ligand framework exerted a significant impact on catalytic performance. The FeH precatalyst with less steric hindrance demonstrated excellent performance, producing high molecular weight polyisoprenes with conversions exceeding 99% for 4000 equiv. of monomer. Even at very low catalyst loadings, as low as 0.0025 mol% (Fe/Ip), the polymerization of isoprene could proceed smoothly with an exceptionally high activity of 4.0 × 106 gPI (molFe, h)−1. Moreover, this precatalyst exhibited good thermal stability, maintaining high activity levels (typically 105 gPI (molFe, h)−1) across a broad temperature range from −20 °C to 100 °C. Additionally, by adjusting steric substituents and the reaction temperature, the 1,4/3,4 regioselectivity could be modulated from 9/91 to 69/31 while maintaining a high stereoselectivity of cis-1,4 structures (cis/trans: >99/1). [ABSTRACT FROM AUTHOR]

Climate change profoundly affects the timing of seasonal activities of organisms, known as phenology. The impact of climate change is not unidirectional; it is also influenced by plant phenology as plants modify atmospheric composition and climatic processes. One important aspect of this interaction is the emission of biogenic volatile organic compounds (BVOCs), which link the Earth's surface, atmosphere, and climate. BVOC emissions exhibit significant diurnal and seasonal variations and are therefore considered essential phenological traits. To understand the dynamic equilibrium arising from the interplay between plant phenology and climate, this review presents recent advances in comprehending the molecular mechanisms underpinning plant phenology and its interaction with climate. We provide an overview of studies investigating molecular phenology, genome-wide gene expression analyses conducted in natural environments, and how these studies revolutionize the concept of phenology, shifting it from observable traits to dynamic molecular responses driven by gene–environment interactions. We explain how this knowledge can be scaled up to encompass plant populations, regions, and even the globe by establishing connections between molecular phenology, changes in plant distribution, species composition, and climate. [ABSTRACT FROM AUTHOR]

A combination of electrospray ionization, matrix-assisted laser desorption/ionization and gas chromatography–mass-spectrometry (GC–MS) with electron ionization is used for the analysis of products and intermediates of the isoprene telomerization reaction catalyzed by N-heterocyclic carbene Pd(II) complexes in presence of methanol. It is shown that soft ionization mass spectrometry techniques allow the detection of the main catalytically active cationic intermediate of palladium in real time whereas GC–MS is efficient in the structure determination of hydrogenated telomerization products. The data obtained are confirmed by NMR spectrometry. [ABSTRACT FROM AUTHOR]

Several cobalt(II) complexes Co1–Co3 bearing pyridine–oxime ligands (L1 = pyridine-2-aldoxime for Co1; L2 = 6-methylpyridine-2-aldoxime for Co2; L3 = phenyl-2-pyridylketoxime for Co3) and picolinaldehyde O-methyl oxime (L4)-supported Co4 were synthesized and well characterized by FT-IR, mass spectrum and elemental analysis. The single-crystal X-ray diffraction of complex Co2 reveals that the cobalt center of CoCl2 is coordinated with two 6-methylpyridine-2-aldoxime ligands binding with Npyridine and Noxime atoms, which feature a distorted octahedral structure. These Co complexes Co1–Co4 displayed extremely high activity toward isoprene polymerization upon activation with small amount of AlClEt2 in toluene, giving polyisoprene with high activity up to 16.3 × 105 (mol of Co)−1(h)−1. And, the generated polyisoprene displayed high molecular weights and narrow molecular distribution with a cis-1,4-enriched selectivity. The type of cobalt complexes, cocatalyst and reaction temperature all have effects on the polymerization activity but not on the microstructure of polymer. [ABSTRACT FROM AUTHOR]

Isoprene is a crucial non-methane biogenic volatile organic compound (BVOC) that exhibits the largest emissions globally. It is chemically reactive in the atmosphere and serves as the primary source of generating secondary organic aerosols (SOA) in terrestrial and remote marine regions. However, a comprehensive estimation of marine isoprene emissions is currently lacking. Here we built a module to present a 20-year (2001–2020) global hourly dataset for marine isoprene emissions, including phytoplankton-generated biological emissions (BIO emissions) and photochemistry-generated emissions in the sea surface microlayer (SML emissions) based on the latest advancements in biological, physical, and chemical processes, with high spatial resolutions. Our dataset suggests the annual global marine isoprene emissions amount to 1.097±0.009 Tg yr -1. Among these, the BIO emissions are 0.481±0.008 Tg yr -1 while SML emissions contribute 0.616±0.003 Tg yr -1. The ability of this module to estimate marine isoprene emissions was evaluated through comparison with a series of observations of marine isoprene concentrations and emission fluxes. The annual total isoprene emissions across the tropical ocean show a declining trend from 2001 to 2020. Most ocean regions exhibit a 1-year emission period, whereas a significant intraseasonal period is found in the tropical ocean. This dataset can be employed as input for the simulation of marine SOA formation in earth system models. This work provides the foundation for further studies into the impact of the air–sea system on marine SOA formation and its climate effect. The DOI link for the dataset is 10.11888/Atmos.tpdc.300521 (Cui and Zhu, 2023). [ABSTRACT FROM AUTHOR]

Co‐oxidation of a range of alkenes, dienes, and aromatic compounds by whole cells of the isoprene‐degrading bacterium Rhodococcus sp. AD45 expressing isoprene monooxygenase was investigated, revealing a relatively broad substrate specificity for this soluble diiron centre monooxygenase. A range of 1‐alkynes (C2–C8) were tested as potential inhibitors. Acetylene, a potent inhibitor of the related enzyme soluble methane monooxygenase, had little inhibitory effect, whereas 1‐octyne was a potent inhibitor of isoprene monooxygenase, indicating that 1‐octyne could potentially be used as a specific inhibitor to differentiate between isoprene consumption by bona fide isoprene degraders and co‐oxidation of isoprene by other oxygenase‐containing bacteria, such as methanotrophs, in environmental samples. The isoprene oxidation kinetics of a variety of monooxygenase‐expressing bacteria were also investigated, revealing that alkene monooxygenase from Xanthobacter and soluble methane monooxygenases from Methylococcus and Methylocella, but not particulate methane monooxygenases from Methylococcus or Methylomicrobium, could co‐oxidise isoprene at appreciable rates. Interestingly the ammonia monooxygenase from the nitrifier Nitrosomonas europaea could also co‐oxidise isoprene at relatively high rates, suggesting that co‐oxidation of isoprene by additional groups of bacteria, under the right conditions, might occur in the environment. [ABSTRACT FROM AUTHOR]

In recent years, anthropogenic activities and climate change have significantly increased exposure of plants to environmental stresses (single or multiple) and pollutants, which negatively affect plant growth, survival, and productivity. Plants may activate an armament of defenses against such environmental stresses. Isoprene, the most abundant biogenic volatile organic compound emitted by plants, is supposed to induce stress tolerance directly, by quenching reactive oxygen species, or indirectly by strengthening photosynthetic membranes and reprogramming expression of genes that are involved in antioxidant defense mechanisms. On the other hand, isoprene is also involved in tropospheric chemistry that contributes to the production of air pollutants when mixing with anthropogenic gases. In this review, we summarized current knowledge about the impact of air and soil pollutants on isoprene emission from plants, focusing on possible feedback and feedforward mechanisms that may affect whole ecosystem functioning and evolution of plant species. Despite limited available information, especially about long-term effects of soil pollutants, it may be speculated that isoprene generally improves fitness of plants challenged by air and soil pollutants, and their interaction with other organisms. [ABSTRACT FROM AUTHOR]

This study aimed to explore the influence of temperature on the growth and isoprene metabolism pathways of Eucommia ulmoides seedlings. Growth indices and levels of rubber and total triterpenoids in leaves were assessed under three temperature treatments: low (15 °C/10 °C), control (25 °C/20 °C), and high (35 °C/30 °C). High-throughput sequencing identified 2309 differentially expressed genes, of which 1608 were upregulated and 701 were downregulated. After 40 days, leaf length, leaf width, and plant height were significantly lower in low- and high-temperature treatments compared with the control. Specific leaf weight was higher in LT-treated leaves. Chlorophyll a and b contents were 1.372 mg.g−1 and 0.594 mg.g−1, respectively, in control leaves, followed by low- and high-temperature treatments. Carotenoid content was the highest in LT treatment. The rubber content of LT and HT groups significantly decreased by 16.5% and 38%, respectively, compared with that of the control group. Total triterpene content was the lowest in control leaves at 1.02%, which was 30% and 20% less than that in low- and high-temperature treatments, respectively. This study provides insights into the efficient cultivation of E. ulmoides and the regulatory network of secondary metabolic pathways. [ABSTRACT FROM AUTHOR]

Isoprene is an important volatile organic compound causing photochemical smog in the atmosphere; thus, accurate analysis of isoprene is essential. In this study, the effect of sampling conditions, including adsorbent types, sampling temperatures, and flow rates on the recovery of isoprene, was investigated. Common adsorption traps of isoprene, including Tenax TA/Carbosieve SIII, Tenax TA/Carbotrap, were used as adsorbents. Sampling temperatures varied from 25 °C to 40 °C. Sampling flow rates were 50, 100, and 200 mL min−1. It was found that the Tenax/Carbotrap trap revealed the highest isoprene recovery rate; however, the Tenax/Carbosieve SIII trap depicted more significant loss of isoprene than the other one. As for sampling variables, the lower the temperatures and flow rates concerned were, the higher the isoprene recovery was. It was concluded that sampling temperatures and flow rates should be ≤35 °C and ≤50 mL min−1 during a sampling process, respectively. In addition, Carbosieve SIII should not be used for isoprene sampling due to its poor recovery rate. [ABSTRACT FROM AUTHOR]

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Marine isoprene plays a crucial role in the formation of secondary organic aerosol within the remote marine boundary layer. Due to scarce field measurements of oceanic isoprene and limited laboratory‐based studies of isoprene production, assessing the importance of marine isoprene on atmospheric chemistry and climate is challenging. Calculating in‐field isoprene production rates is a crucial step to predict marine isoprene concentrations and the subsequent emissions to the atmosphere. The distribution, sources, and dominant environmental factors of isoprene were determined in the Northwest Pacific Ocean in 2019. The nutrient enrichment in the Kuroshio Oyashio Extension (KOE) surface seawater, driven by the upwelling and atmospheric deposition, promoted the growth of phytoplankton and elevated the isoprene concentration. This was confirmed by observed responses of isoprene to nutrients and aerosol dust additions in a ship‐based incubation experiment, where the isoprene concentrations increased by 70% (t = 4.417, p < 0.001) and 35% (t = 2.387, p < 0.05), respectively. Biogenic isoprene production rates in the deck incubation experiments were positively related to chlorophyll a, temperature, and solar radiation, with an average production of 7.33 ± 4.27 pmol L−1 day−1. Photochemical degradation of dissolved organic matter was likely an abiotic source of isoprene, contributing to approximately 14% of the total production. Driven by high isoprene production and extreme physical disturbance, the KOE showed very high emissions of isoprene of 46.0 ± 13.0 nmol m−2 day−1, which led to a significant influence on the oxidative capacity of the local atmosphere. Key Points: Nutrient enrichment in the surface seawater driven by upwelling and atmospheric deposition promoted the biological production of isoprenePhotochemical production was confirmed as an abiotic source of marine isopreneApproximately 10%∼63% of net isoprene produced in the mixed layer was transferred to the atmosphere [ABSTRACT FROM AUTHOR]

Abstract In this study, the oxidation characteristics of isoprene were investigated using a custom-designed mini closed pressure vessel test (MCPVT). The results show that isoprene is unstable and polymerization occurs under a nitrogen atmosphere. Under an oxygen atmosphere, the oxidation process of isoprene was divided into three stages: (1) isoprene reacts with oxygen to produce peroxide; (2) Peroxides produce free radicals through thermal decomposition; (3) Free radicals cause complex oxidation and thermal runaway reactions. The oxidation of isoprene conforms to the second-order reaction kinetics, and the activation energy was 86.88 kJ·mol−1. The thermal decomposition characteristics of the total oxidation product and purified peroxide mixture were determined by differential scanning calorimetry (DSC). The initial exothermic temperatures T on were 371.17 K and 365.84 K, respectively. And the decomposition heat Q DSC were 816.66 J·g−1 and 991.08 J·g−1, respectively. It indicates that high concentration of isoprene peroxide has a high risk of thermal runaway. The results of thermal runaway experiment showed that the temperature and pressure of isoprene oxidation were prone to rise rapidly, which indicates that the oxidation reaction was dangerous. The reaction products of isoprene were analyzed by gas chromatography-mass spectrometry (GC–MS). The main oxidation products were methyl vinyl ketone, methacrolein, 3-methylfuran, etc. The main thermal runaway products were dimethoxymethane, 2,3-pentanedione, naphthalene, etc. Based on the reaction products, the possible reaction pathway of isoprene was proposed.

1,2-Dihydroxy isoprene (1,2-DHI), a product of isoprene oxidation from multiple chemical pathways, is produced in the atmosphere in large quantities; however, its chemical fate has not been comprehensively studied. Here, we perform chamber experiments to investigate its gas-phase reactions. We find that the reactions of 1,2-DHI with OH radicals and ozone are rapid (kOH = 8.0 (±1.3) × 10-11 cm3 molecule-1 s-1; kO3 = 7.2 (±1.1) × 10-18 cm3 molecule-1 s-1). Reaction with OH, which dominates 1,2-DHI loss, leads primarily to fragmentation and radical recycling; major products under both high- and low-NO conditions include hydroxyacetone, glycolaldehyde, and 2,3-dihydroxy-2-methyl-propanal (DHMP). Radical-terminating hydroperoxide formation from the peroxy radical (RO2) reaction with HO2 and organonitrate formation from RO2 + NO are not observed in the gas phase, possibly due to low volatility; constraints for their branching ratios are instead derived by mass balance. We also measure secondary organic aerosol mass yields from 1,2-DHI (0-23%) and show that oxidation in the presence of aqueous particles leads to formic and acetic acid production. Finally, we incorporate results into GEOS-Chem, a global chemical transport model, to compute the global production (25.3 Tg a-1) and gas-phase loss (20.2 Tg a-1) of 1,2-DHI and show that its oxidation provides non-negligible contributions to the atmospheric budgets of hydroxyacetone, glycolaldehyde, hydroxymethyl hydroperoxide, formic acid, and DHMP.

Abstract Biogenic volatile organic compounds (BVOCs) with high photochemical activity and short atmospheric lifetimes are major contributors to tropospheric ozone and other photochemical air pollution. Although several studies have been conducted on BVOC emissions in Japan, no comprehensive observations have been made to determine the actual state of BVOCs in the atmosphere. Therefore, we conducted time-resolved measurements of atmospheric BVOCs in urban and forested areas throughout the year. The concentrations of BVOCs were higher in summer than in the other seasons. Isoprene concentrations were higher during hours with higher temperatures and solar radiation. However, there were also months and times of the year when monoterpenes showed high concentrations, which indicates that the behavior of the BVOC components differed depending on the time of the year. The results of the propylene equivalent concentration indicated that BVOCs considerably contributed to tropospheric ozone production. The year-long observations of BVOCs in this study contribute to our understanding of the actual status of atmospheric BVOC concentrations and components and the uncertainty in the calculation results of chemical transport models.

Abstract Warming climate in the Arctic is leading to an increase in isoprene emission from ecosystems. We assessed the influence of temperature on isoprene emission from Arctic willows with laboratory and field measurements. Our findings indicate that the hourly temperature response curve of Salix spp., the dominant isoprene emitting shrub in the Arctic, aligns with that of temperate plants. In contrast, the isoprene capacity of willows exhibited a more substantial than expected response to the mean ambient temperature of the previous day, which is much stronger than the daily temperature response predicted by the current version of the Model of Emissions of Gases and Aerosols from Nature (MEGAN). With a modified algorithm from this study, MEGAN predicts 66% higher isoprene emissions for Arctic willows during an Arctic heatwave. However, despite these findings, we are still unable to fully explain the high temperature sensitivity of isoprene emissions from high latitude ecosystems.

Rust infection results in stress volatile emissions, but due to the complexity of host-pathogen interaction and variations in innate defense and capacity to induce defense, biochemical responses can vary among host species. Fungal-dependent modifications in volatile emissions have been well documented in numerous host species, but how emission responses vary among host species is poorly understood. Our recent experiments demonstrated that the obligate biotrophic crown rust fungus (P. coronata) differently activated primary and secondary metabolic pathways in its primary host Avena sativa and alternate host Rhamnus frangula. In A. sativa, emissions of methyl jasmonate, short-chained lipoxygenase products, long-chained saturated fatty acid derivatives, mono- and sesquiterpenes, carotenoid breakdown products, and benzenoids were initially elicited in an infection severity-dependent manner, but the emissions decreased under severe infection and photosynthesis was almost completely inhibited. In R. frangula, infection resulted in low-level induction of stress volatile emissions, but surprisingly, in enhanced constitutive isoprene emissions, and even severely-infected leaves maintained a certain photosynthesis rate. Thus, the same pathogen elicited a much stronger response in the primary than in the alternate host. We argue that future work should focus on resolving mechanisms of different fungal tolerance and resilience among primary and secondary hosts.

This study revealed the importance of two isoprene-derived pathways in the formation of sulfate aerosol (SO42−(p)), which are related to the gas-phase reactions of Criegee intermediates (CIs) and liquid-phase reactions of isoprene hydroxy hydroperoxide (ISOPOOH), in the atmosphere in the Asian region, using the community multiscale air quality (CMAQ) modeling system. The results showed that the incorporation of both isoprene-derived CIs and ISOPOOH chemistry increased the SO42−(p) concentration in specific domains of Asia, particularly isoprene hotspots, with up to 1% of the total SO42−(p) concentration compared to that obtained by the basic chemical transport model. The impact of ISOPOOH to SO42−(p) formation exhibited a more localized pattern compared to that of CIs, attributed to the tendency of ISOPOOH to condense in low-NO regions. SO42−(p) formation from CIs affected the compositions of nitrate (NO3−), ammonium (NH4+), and secondary organic aerosols (SOA) in the particle phase, and in most of the analyzed sites, those compositions increased from 0.5% to 2.5%. In contrast, SO42−(p) formation from ISOPOOH exhibits a negative impact on SOA, resulting in a potential reduction of up to 5% due to the loss of SOA precursor by incorporating the ISOPOOH uptake reaction. The sensitivity analysis results showed that most of the SO42−(p) was generated by the gas-phase reaction of SO2 with OH; however, the CIs and ISOPOOH also affected the SO42−(p) formation more than the liquid-phase SO42−(p) formations by H2O2, O3, O2, etc.

As a large number of organic compounds possessing two isoprene units, monoterpenes and monoterpenoids play important roles in pharmaceutical, cosmetic, agricultural, and food industries. In nature, monoterpenes are constructed from geranyl pyrophosphate (C10) via various transformations. Herein, the bulk C5 chemical—isoprene, is used for the creation of various monoterpenoids via a nucleophilic aromatization of monoterpenes under cascade catalysis of nickel and iodine. Drugs and oil mixtures from conifer and lemon can be convergently transformed to the desired monoterpenoid. Preliminary mechanistic studies are conducted to get insights about reaction pathway. Two types of cyclic monoterpenes can be respectively introduced onto two similar heterocycles via orthogonal C–H functionalization. And various hybrid terpenyl indoles are programmatically assembled from abundant C5 or C10 blocks. This work not only contributes a high chemo-, regio-, and redox-selective transformation of isoprene, but also provides a complementary approach for the creation of unnatural monoterpenoids. Organic compounds possessing two isoprene units play important roles in chemical industry. Herein, the authors use bulk C5 chemical—isoprene to synthesise various monoterpenoids via a nucleophilic aromatization of monoterpenes under cascade catalysis of nickel and iodine [ABSTRACT FROM AUTHOR]

Epoxidation of the carbon-carbon double bonds on unsaturated rubber macromolecules can produce novel modified rubber species with special properties, and construct eco-friendly crosslinking pathway via the reaction of epoxide groups to solve the problems brought by conventional sulfur vulcanization system. In this contribution, a novel modified product of isobutylene isoprene rubber (IIR), epoxy-functionalized IIR (EIIR) was successfully prepared by in situ epoxidation technique for the first time, and the crosslinking of EIIR was achieved by the reaction of oxirane groups with maleic anhydride (MAH) without additional additives. The reaction conditions for preparing EIIR were optimized through systematic research on the epoxidation process. Under optimal condition, the degree of epoxidation of the rubber reached around 99% without side reactions. The obtained EIIR/carbon black composites cured by MAH had excellent mechanical properties comparable to those of IIR composites. More importantly, compared with IIR composites, the air-tightness of the EIIR composites was improved by about 50%, and the flexural fatigue life of first-level cracks and sixth-level cracks was increased by several times. The significant improvement of these properties is of great significance for the application safety and energy saving of IIR materials. [ABSTRACT FROM AUTHOR]

Nd-based polydiene elastomers, including NdIR and NdBR, are regarded as indispensable key raw materials in preparing green tires with excellent performance capabilities, but their wide application is still limited by the relative higher cost of Nd precatalysts. Nd-mediated coordinative chain transfer polymerization (CCTP) of diene provides an effective strategy to reduce the precatalyst cost, because this method involves very high atom economy, i.e., each Nd molecule can generate multiple polymer chains. Nevertheless, all possible factors that could influence such CCTP behaviors are still mostly unexplored to date. In this report, the basic chemistry on the influence of external donors on the overall CCTP behaviors of isoprene was established for the first time. It was found that increasing the amount of external donors had a negative influence on the chain transfer efficiencies, resulting in gradually decreasing atom economies. Catalyst addition order studies revealed that the coordination of donors with cationic Nd active species, rather than alkylaluminium CTAs, contributed mostly to such decreased efficiencies. Moreover, it was found that when the ratio of donors and Nd compounds was higher than 1.0, the CCTP behaviors were corrupted, resulting in polymers with broad distributions, as well as resulting in low atom economies; nevertheless, when the ratio was lower than 0.5, the system still displayed CCTP characteristics, implying that the critical ratio for maintaining the CCTP was 0.5. Additionally, when such a ratio was 0.01, the high atom economy was almost the same as donor-free CCTP systems. Detailed kinetic studies at such a ratio demonstrated that the donor-contained system proceeded in a well-controlled manner, as concluded from the good linear relationship between the Mn of the PIps against the polymer yields, as well as the good linearity between the Mn against the (IP)/(Nd) ratios. Such maintained CCTP properties also allowed for seeding two-step polymerizations to prepare diblock copolymers with precisely controlled molecular weights. Expanding the types of donors to more phosphine, oxygen, and nitrogen containing compounds showed that they also affected the CCTP behaviors depending on their steric and electronic properties. [ABSTRACT FROM AUTHOR]

Cobalt complexes carrying 2‐acetyl‐6‐iminopyridine ligand are synthesized and characterized. Single‐crystal X‐ray diffraction reveals the cobalt ion is chelated with two nitrogen atoms and an acetyl oxygen atom additionally. A significant prolonged Co–O distance (2.3960(57) Å) is found, indicative of a labile character. Activated by diethylchloroaluminum, all complexes show high conversion rates for isoprene and myrcene polymerizations, affording cis‐1,4/3,4 regulated 1,3‐diene polymers. The polymerization of butadiene, interestingly, gives predominant cis‐1,4 selectivity (>99.2%) with moderate activity. The substituent at ortho‐position of arylimine plays a minor role in controlling activity and selectivity as well as the molecular weight of the resultant polymers. The properties of resultant poly(1,3‐diene)s are stable even in a wide range of operational conditions, such as [Al]/[Co] varied from 20 to 600, temperature spanning from 0°C to 60°C, and monomer–catalyst ratio from 1000 to 4000. These additional benefits of minimum fluctuation in catalytic performances may be suitable for industrial polymerization process. [ABSTRACT FROM AUTHOR]

The exchange reaction of equimolar amounts of the potassium radical anion salt of diazabutadiene [DADMe•−K(THF)n] (1) (DADMe = DippNC(Me)C(Me)NDipp; Dipp = = 2,6-Pri2C6H3) with anhydrous ScCl3 and NdCl3 afforded the dichloride complexes [DippN=C(Me)C(=CH2)NDipp]LnCl2(THF)2 (Ln = Sc (3), Nd (4)) in 75% and 71% yields, respectively. In these complexes, the DADMe ligand exists in the monoanionic amido-imino form. The reaction of [DADMe∸K(THF)n] with ScCl3 is accompanied by the formation of the minor unstable complex [DippNC(Me)=C(Me)NDipp]∸ScCl2(THF)2(2, ∼3% yield) containing the diazabutadiene radical anion ligand. All attempts to alkylate dichloride complexes 3 and 4 with two equivalents of LiCH2SiMe3 (or LiCH2C6H4-o-NMe2) resulted in the transfer of the amido-imino ligand to the Li+ cation giving the complex [{DippN=C(Me)C(=CH2)NDipp}Li]2 (5) in 36–38% yield. Complex 5 forms a dimeric structure through coordination of lithium ions by two nitrogen atoms (amide and imine N atoms) of one DAD ligand and the µ2-imine nitrogen atom of another ligand. Chloride complexes 3 and 4 involved in the two- and three-component catalytic systems (3 or 4)−[Ph3C][B(C6F5)4] (1: 1) and (3 or 4)−AlBui3−[Ph3C][B(C6F5)4] (1: 10: 1) initiate the oligomerization of isoprene (IP) at room temperature and provide the 25–100% conversion of monomer to oligomer ([IP]/[Ln] = 1000). The synthesized oligomer samples have predominantly a trans-1,4 structure (up to 75.6%) and a low number-average molecular weight (Mn = 0.45−1.24•103; Mw/Mn = 1.13–8.99). [ABSTRACT FROM AUTHOR]

The capacity to emit isoprene, among other stresses, protects plants from drought, but the molecular mechanisms underlying this trait are only partly understood. The Arecaceae (palms) constitute a very interesting model system to test the involvement of isoprene in enhancing drought tolerance, as their high isoprene emissions may have contributed to make them hyperdominant in neotropical dry forests, characterized by recurrent and extended periods of drought stress. In this study we isolated and functionally characterized a novel isoprene synthase, the gene responsible for isoprene biosynthesis, from Copernicia prunifera, a palm from seasonally dry tropical forests. When overexpressed in the non-emitter Arabidopsis thaliana, CprISPS conferred significant levels of isoprene emission, together with enhanced tolerance to water limitation throughout plant growth and development, from germination to maturity. CprISPS overexpressors displayed higher germination, cotyledon/leaf greening, water usage efficiency, and survival than WT Arabidopsis under various types of water limitation. This increased drought tolerance was accompanied by a marked transcriptional up-regulation of both ABA-dependent and ABA-independent key drought response genes. Taken together, these results demonstrate the capacity of CprISPS to enhance drought tolerance in Arabidopsis and suggest that isoprene emission could have evolved in Arecaceae as an adaptive mechanism against drought. [ABSTRACT FROM AUTHOR]

Plants emit biogenic volatile organic compounds (BVOCs) in response to changes in environmental conditions (e.g. temperature, radiation, soil moisture). In the large family of BVOCs, isoprene is by far the strongest emitted compound and plays an important role in ozone chemistry, thus affecting both air quality and climate. In turn, climate change may alter isoprene emissions by increasing temperature as well as the occurrence and intensity of severe water stresses that alter plant functioning. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) provides different parameterizations to account for the impact of water stress on isoprene emissions, which essentially reduces emissions in response to the effect of soil moisture deficit on plant productivity. By applying the regional climate–chemistry model RegCM4chem coupled to the Community Land Model CLM4.5 and MEGAN2.1, we thus performed sensitivity simulations to assess the effects of water stress on isoprene emissions and near-surface ozone levels over the Euro-Mediterranean region and across the drier and wetter summers over the 1992–2016 period using two different parameterizations of the impact of water stress implemented in the MEGAN model. Over the Euro-Mediterranean region and across the simulated summers, water stress reduces isoprene emissions on average by nearly 6 %. However, during the warmest and driest selected summers (e.g. 2003, 2010, 2015) and over large isoprene-source areas (e.g. the Balkans), decreases in isoprene emissions range from -20 % to -60 % and co-occur with negative anomalies in precipitation, soil moisture and plant productivity. Sustained decreases in isoprene emissions also occur after prolonged or repeated dry anomalies, as observed for the summers of 2010 and 2012. Although the decrease in isoprene emissions due to water stress may be important, it only reduces near-surface ozone levels by a few percent due to a dominant VOC-limited regime over southern Europe and the Mediterranean Basin. Overall, over the selected analysis region, compared to the old MEGAN parameterization, the new one leads to localized and 25 %–50 % smaller decreases in isoprene emissions and 3 %–8 % smaller reductions in near-surface ozone levels. [ABSTRACT FROM AUTHOR]

Isoprene, a key biogenic volatile organic compound, plays a pivotal role in atmospheric chemistry. Due to its high reactivity, this compound contributes significantly to the production of tropospheric ozone in polluted areas, and to the formation of secondary organic aerosols. The assessment of biogenic emissions is of great importance for regional and global air quality evaluation. In this study, we have implemented the biogenic emissions model MEGANv2.1 (Model of Emission of Gases and Aerosols from Nature, ver- sion 2.1) in the surface model SURFEXv8.1 (SURface EXternalisée in french, version 8.1). This coupling aims to improve the estimation of biogenic emissions using the detailed vegetation type-dependent treatment included in the SURFEX vegetation ISBA scheme. This scheme provides to MEGAN vegetation-dependent parameters allowing a more precise estimation of biogenic fluxes (e.g., leaf area index, soil moisture, wilting point data). The present study focuses on the assessment of the SURFEX-MEGAN model isoprene emissions. The evaluation of the cou- pled SURFEX-MEGAN model results was carried out by conducting a global isoprene emissions simulation in 2019 and comparing the simulation results with other MEGAN-based isoprene inventories. The coupled model estimates a total global isoprene emission of 442Tg in 2019. The estimated isoprene is within the range of results obtained with other MEGAN-based isoprene inventories, ranging from 311Tg to 637Tg. The spatial distribution of SURFEX-MEGAN isoprene is consistent with other studies, with some differences located in low isoprene emission regions. Several sensitivity tests were conducted to quantify the impact of different model inputs and configurations on isoprene emissions. Using different meteorological forcings resulted in a +/-5% change in isoprene emission using MERRA and IFS, respectively, compared with ERA5. The impact of using different emission factors data was also investigated. The use of PFT spatial coverage and PFT-dependent emission potential data resulted in a 14% reduction compared to using the isoprene emission potential gridded map. A significant reduction of around 38% in global isoprene emissions, was observed in the third sensitivity analysis, which applied a parameterization of soil moisture deficit, particularly in certain regions of Australia, Africa and South America. The significance of coupling the SURFEX and MEGAN models lies particularly in the ability of the coupled model to be able to be forced with meteorological data from any time period. This means, for instance, that this system can be used to predict biogenic emissions in the future. This aspect of this work is significant given the changes that biogenic organic compounds are expected to undergo as a result of changes in their climatic factors. [ABSTRACT FROM AUTHOR]

Isoprene is emitted by some plants and is the most abundant biogenic hydrocarbon entering the atmosphere. Multiple studies have elucidated protective roles of isoprene against several environmental stresses, including high temperature, excessive ozone, and herbivory attack. However, isoprene emission adversely affects atmospheric chemistry by contributing to ozone production and aerosol formation. Thus, understanding the regulation of isoprene emission in response to varying environmental conditions, for example, elevated CO2, is critical to comprehend how plants will respond to climate change. Isoprene emission decreases with increasing CO2 concentration; however, the underlying mechanism of this response is currently unknown. We demonstrated that high-CO2-mediated suppression of isoprene emission is independent of photosynthesis and light intensity, but it is reduced with increasing temperature. Furthermore, we measured methylerythritol 4-phosphate (MEP) pathway metabolites in poplar leaves harvested at ambient and high CO2 to identify why isoprene emission is reduced under high CO2. We found that hydroxymethylbutenyl diphosphate (HMBDP) was increased and dimethylallyl diphosphate (DMADP) decreased at high CO2. This implies that high CO2 impeded the conversion of HMBDP to DMADP, possibly through the inhibition of HMBDP reductase activity, resulting in reduced isoprene emission. We further demonstrated that although this phenomenon appears similar to abscisic acid (ABA)-dependent stomatal regulation, it is unrelated as ABA treatment did not alter the effect of elevated CO2 on the suppression of isoprene emission. Thus, this study provides a comprehensive understanding of the regulation of the MEP pathway and isoprene emission in the face of increasing CO2. [ABSTRACT FROM AUTHOR]

In Ficus septica, the short‐term control of isoprene production and, therefore, isoprene emission has been linked to the hormone balance between auxin (IAA) and jasmonic acid (JA). However, the relationship between long‐term changes in isoprene emission and that of plant hormones remains unknown.This study tracked isoprene emissions from F. septica leaves, plant hormone concentrations and signalling gene expression, MEP pathway metabolite concentrations, and related enzyme gene expression for 1 year in the field to better understand the role of plant hormones and their long‐term control.Seasonality of isoprenes was mainly driven by temperature‐ and light‐dependent variations in substrate availability through the MEP route, as well as transcriptional and post‐transcriptional control of isoprene synthase (IspS). Isoprene emissions are seasonally correlated with plant hormone levels. This was especially evident in the cytokinin profiles, which decreased in summer and increased in winter. Only 4‐hydroxy‐3‐methylbut‐2‐butenyl‐4‐diphosphate (HMBDP) exhibited a positive connection with cytokinins among the MEP metabolites examined, suggesting that HMBDP and its biosynthetic enzyme, HMBDP synthase (HDS), play a role in channelling of MEP pathway metabolites to cytokinin production.Thus, it is probable that cytokinins have potential feed‐forward regulation of isoprene production. Under long‐term natural conditions, the hormonal balance of IAA/JA‐Ile was not associated with IspS transcripts or isoprene emissions. This study builds on prior work by revealing differences between short‐ and long‐term hormonal modulation of isoprene emissions in the tropical tree F. septica. [ABSTRACT FROM AUTHOR]

The work discusses the solution of the problem of static optimization of a four-column unit designed for isoprene separation from pyrolysis fraction C5. A two-stage decomposition method of static optimization according to the selected optimality criterion in the form of specific energy costs to obtain a target product of a given quality is used; the first stage involves the sequential calculation of static modes of the technological apparatuses by separate criteria, taking into account the overall optimality criterion for the whole system. It is established that the main economic benefit is obtained from the first stage of optimization, where the technological scheme is decomposed into individual elements. Subsequent optimization at the second stage, with simultaneous variation of all control variables, is shown to provide limited benefit. [ABSTRACT FROM AUTHOR]

Balanced photosynthesis is essential for improved plant survival and agricultural benefits in terms of biomass and yield. Photosynthesis is the hub of energy metabolism in plants; however, drought stress (DS) strongly perturbs photosynthetic efficiency due to biochemical and diffusive limitations that reduce key photosynthetic components and close stomata. This review describes photosynthetic responses, chloroplast retrograde signalling, and genetic imprints that curtail DS damage to photosynthetic machinery. While stomatal closure, disrupted photosynthetic systems, over‐reduced electron transport rates (ETR), partial hindrance of the Calvin cycle, and reduced pigment contents strongly affect the repertoire of photosynthetic processes under DS, chloroplast retrograde signalling also has a plausible role in preserving photosynthetic capacity. Progress in agronomic, genetic engineering approaches and isoprene regulation would help to rescue photosynthetic apparatus under DS. [ABSTRACT FROM AUTHOR]

The cationic polymerization of isoprene using alkyl halide/Et2AlCl initiating system (alkyl halide: tert-butyl chloride, tert-butyl bromide, 2-chloro-2-methylbutane and isopropyl chloride) at different temperatures has been studied. It was shown for the first time that using of tertiary alkyl halide in conjunction with Et2AlCl allowed to synthesize fully soluble solid thermoplastic polymers with reduced unsaturation (41–48 mol%) as well as relatively high glass transition temperature (52–60°С) and softening point (102–128°С). The substitution of tertiary alkyl halides on the secondary one (isopropyl chloride) results in the obtaining of cross-linked polymers due to the low activity of isopropyl chloride in chain transfer to alkyl halide. It was found that alkyl halide nature, the ratio of alkyl halide to Et2AlCl, duration and temperature of the polymerization of isoprene have dramatic effect on the unsaturation of synthesized polymers as well as their molecular weight, polydispersity, physical and chemical properties. [ABSTRACT FROM AUTHOR]

Enzyme stability is often a limiting factor in the microbial production of high-value-added chemicals and commercial enzymes. A previous study by our research group revealed that the unstable isoprene synthase from Ipomoea batatas (IspSib) critically limits isoprene production in engineered Escherichia coli. Directed evolution was, therefore, performed in the present study to improve the thermostability of IspSib. First, a tripartite protein folding system designated as lac'-IspSib-'lac, which could couple the stability of IspSib to antibiotic ampicillin resistance, was successfully constructed for the high-throughput screening of variants. Directed evolution of IspSib was then performed through two rounds of random mutation and site-saturation mutation, which produced three variants with higher stability: IspSibN397V A476V, IspSibN397V A476T, and IspSibN397V A476C. The subsequent in vitro thermostability test confirmed the increased protein stability. The melting temperatures of the screened variants IspSibN397V A476V, IspSibN397V A476T, and IspSibN397V A476C were 45.1 ± 0.9°C, 46.1 ± 0.7°C, and 47.2 ± 0.3°C, respectively, each of which was higher than the melting temperature of wild-type IspSib (41.5 ± 0.4°C). The production of isoprene at the shake-flask fermentation level was increased by 1.94-folds, to 1,335 mg/L, when using IspSibN397V A476T. These findings provide insights into the optimization of the thermostability of terpene synthases, which are key enzymes for isoprenoid production in engineered microorganisms. In addition, the present study would serve as a successful example of improving enzyme stability without requiring detailed structural information or catalytic reaction mechanisms. [ABSTRACT FROM AUTHOR]

Plants, animals and humans metabolically produce volatile isoprene (C5H8). Humans continuously exhale isoprene and exhaled concentrations differ under various physio-metabolic and pathophysiological conditions. Yet unknown metabolic origin hinders isoprene to reach clinical practice as a biomarker. Screening 2000 individuals from consecutive mass-spectrometric studies, we herein identify five healthy German adults without exhaled isoprene. Whole exome sequencing in these adults reveals only one shared homozygous (European prevalence: <1%) IDI2 stop-gain mutation, which causes losses of enzyme active site and Mg2+–cofactor binding sites. Consequently, the conversion of isopentenyl diphosphate to dimethylallyl diphosphate (DMAPP) as part of the cholesterol metabolism is prevented in these adults. Targeted sequencing depicts that the IDI2 rs1044261 variant (p.Trp144Stop) is heterozygous in isoprene deficient blood-relatives and absent in unrelated isoprene normal adults. Wild-type IDI1 and cholesterol metabolism related serological parameters are normal in all adults. IDI2 determines isoprene production as only DMAPP sources isoprene and unlike plants, humans lack isoprene synthase and its enzyme homologue. Human IDI2 is expressed only in skeletal-myocellular peroxisomes and instant spikes in isoprene exhalation during muscle activity underpins its origin from muscular lipolytic cholesterol metabolism. Our findings translate isoprene as a clinically interpretable breath biomarker towards potential applications in human medicine. Healthy adults not exhaling isoprene contain a stop mutation in the IDI2 gene, only expressed in muscle peroxisomes, suggesting that isoprene origins from muscular lipolytic cholesterol metabolism. [ABSTRACT FROM AUTHOR]

Many terpenoids with isoprene unit(s) demonstrating critical biological activities have been isolated and characterized. In this study, we have developed a robust chem‐stamp strategy for the construction of the key isoprene unit, which consists of two steps: one‐carbon extension of aldehydes to the alkenyl boronates by the boron‐Wittig reaction and the rhodium‐catalyzed reaction of alkenyl boronates with 2,3‐allenols to yield enals. This chem‐stamp could readily be applied repeatedly and separately, enabling the modular concise synthesis of many natural and pharmaceutically active terpenoids, including retinal, β‐carotene, vitamin A, tretinoin, fenretinide, acitretin, ALRT1550, nigerapyrone C, peretinoin, and lycopene. Owing to the diversified availability of the starting materials, aldehydes and 2,3‐allenols, creation of new non‐natural terpenoids has been realized from four dimensions: the number of isoprene units, the side chain, and the two terminal groups. [ABSTRACT FROM AUTHOR]

Analysis of volatile organic compounds (VOC) within exhaled breath is subject to numerous sources of methodological and physiological variability. Whilst breathing pattern is expected to influence the concentrations of selected exhaled VOCs, it remains challenging to investigate respiratory rate and depth accurately in awake subjects. Online breath sampling was performed in 20 mechanically ventilated patients using proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS). The effect of variation in respiratory rate (RR) and tidal volume (TV) on the VOC release profiles was examined. A panel of nineteen VOCs were selected, including isoprene, acetone, propofol, volatile aldehydes, acids and phenols. Variation in RR had the greatest influence on exhaled isoprene levels, with maximum and average concentrations being inversely correlated with RR. Variations in RR had a statistically significant impact on acetone, C3–C7 linear aldehydes and acetic acid. In comparison, phenols (including propofol), C8–C10 aldehydes and C3–C6 carboxylic acids were not influenced by RR. Isoprene was the only compound to be influenced by variation in TV. These findings, obtained under controlled conditions, provide useful guidelines for the optimisation of breath sampling protocols to be applied on awake patients. [ABSTRACT FROM AUTHOR]

Ambient atmospheric concentrations of isoprene and monoterpenes were measured at two forest sites, one deciduous and one coniferous, over the year 2022. Both sites in a regional area were sampled monthly between April and September. The samples were taken using sorbent tubes and analyzed with thermal desorption–gas chromatography–mass spectrometry. The highest concentrations were determined in August at both sites. While isoprene is the most abundant compound at the deciduous forest with an average concentration of 5.59 µg m−3 in August, α-pinene and β-pinene dominate throughout the year at the coniferous forest with the highest concentrations also in August (3.44 µg m−3 and 1.51 µg m−3). Because other monoterpenes (camphene, sabinene, 3-carene, p-cymene and limonene) are also emitted in significant amounts, the total concentration measured in the coniferous forest is higher (7.96 µg m−3 in August) in comparison to the deciduous forest (6.08 µg m−3). Regarding the detected monoterpenes in the deciduous forest, sabinene is the dominant monoterpene in addition to α-pinene and is sometimes present in higher (July) or equal (August) concentrations. The seasonal and diurnal concentrations of all monoterpenes correlate very well with each other at both sites. An exception is sabinene with a diurnal concentration profile similar to isoprene. [ABSTRACT FROM AUTHOR]

In this study, the oxidation characteristics of isoprene were investigated using a custom-designed mini closed pressure vessel test (MCPVT). The results show that isoprene is unstable and polymerization occurs under a nitrogen atmosphere. Under an oxygen atmosphere, the oxidation process of isoprene was divided into three stages: (1) isoprene reacts with oxygen to produce peroxide; (2) Peroxides produce free radicals through thermal decomposition; (3) Free radicals cause complex oxidation and thermal runaway reactions. The oxidation of isoprene conforms to the second-order reaction kinetics, and the activation energy was 86.88 kJ·mol−1. The thermal decomposition characteristics of the total oxidation product and purified peroxide mixture were determined by differential scanning calorimetry (DSC). The initial exothermic temperatures Ton were 371.17 K and 365.84 K, respectively. And the decomposition heat QDSC were 816.66 J·g−1 and 991.08 J·g−1, respectively. It indicates that high concentration of isoprene peroxide has a high risk of thermal runaway. The results of thermal runaway experiment showed that the temperature and pressure of isoprene oxidation were prone to rise rapidly, which indicates that the oxidation reaction was dangerous. The reaction products of isoprene were analyzed by gas chromatography-mass spectrometry (GC–MS). The main oxidation products were methyl vinyl ketone, methacrolein, 3-methylfuran, etc. The main thermal runaway products were dimethoxymethane, 2,3-pentanedione, naphthalene, etc. Based on the reaction products, the possible reaction pathway of isoprene was proposed. [ABSTRACT FROM AUTHOR]

Formaldehyde (HCHO) is a high-yield product of the oxidation of volatile organic compounds (VOCs) released by anthropogenic activities, fires, and vegetations. Hence, we examined the spatiotemporal variation trends in HCHO columns observed using the Ozone Monitoring Instrument (OMI) during 2005–2021 across the Fenwei Plain (FWP) and analysed the source and variability of HCHO using multi-source data, such as thermal anomalies. The spatial distribution of the annual mean HCHO in the FWP increased from northwest to southeast during 2005–2021, and the high-value aggregation areas contracted and gradually clustered, forming a belt-shaped distribution area from Xi'an to Baoji, north of the Qinling Mountains. The annual mean HCHO concentration generally showed a two-step increase over the 17 years. Fires showed a single-peak trend in March and a double-peak M-shaped trend in March and October, whereas urban thermal anomalies (UTAs) showed an inverted U-shaped trend over 17 years, with peaks occurring in May. The HCHO peaks are mainly caused by the alternating contributions of fires and UTAs. The fires and UTAs (predominantly industrial heat sources) played a role in controlling the background level of HCHO in the FWP. Precipitation and temperature were also important influencing variables for seasonal variations, and the influence of plant sources on HCHO concentrations had significant regional characteristics and contributions. In addition, the FWP has poor dispersion conditions and is an aggregated area for the long-range transport of air pollutants. [ABSTRACT FROM AUTHOR]

Elucidating the mutual effects between the different volatile organic compounds (VOCs) is crucial for comprehending the formation mechanism of atmospheric secondary organic aerosols (SOA). Here, the mixed VOCs experiments of isoprene and Δ3-carene/β-caryophyllene were carried out in the presence of O 3 using an indoor smog chamber. The suppression effect of isoprene was recognized by the scanning mobility particle sizer spectrometer, online vacuum ultraviolet free electron laser (VUV-FEL) photoionization aerosol mass spectrometry, and quantum chemical calculations. The results indicate that the suppression effect of isoprene on the ozonolysis of Δ3-carene and β-caryophyllene shows fluctuating and monotonous trends, respectively. The carbon content of the precursor could be the main factor for regulating the strength of the suppression effect. Plausible structures and formation mechanisms of several new products generated from the single VOC precursor and VOC-cross-reaction are proposed, which enrich the category of VOC oxidation products. Meanwhile, a new dimerization mechanism of the RO 2 + R'O 2 reaction is suggested, which offers an intriguing perspective on the gas phase formation process of particle phase accretion products. The present findings provide valuable insights into clarifying the pivotal roles played by isoprene in the interplay between different VOCs and understanding of SOA formation mechanisms of VOC mixtures, especially nearby the emission origins. [Display omitted] [ABSTRACT FROM AUTHOR]

The copolymerization techniques of ethylene and conjugated diene, such as butadiene and isoprene, were summarized. The structure and performance characteristics of polymers obtained from different catalytic systems were reviewed with 26 references. The guidance and suggestions for the subsequent development of efficient catalytic systems of ethylene/conjugated diene copolymerization were previewed.

Oceanic biogenic emissions exert a significant impact on the atmospheric environment within the marine boundary layer (MBL). This study employs the extreme gradient boosting (XGBoost) machine learning method and clustering method combined with satellite observations and model simulations to discuss the effects of marine biogenic emissions on MBL formaldehyde (HCHO). The study reveals that HCHO columnar concentrations peaked in summer with 8.25 × 1015 molec/cm2, but the sea–air exchange processes controlled under the wind and sea surface temperature (SST) made marine biogenic emissions represented by isoprene reach their highest levels in winter with 95.93 nmol/m2/day. Analysis was conducted separately for factors influencing marine biogenic emissions and affecting MBL HCHO. It was found that phytoplankton functional types (PFTs) and biological degradation had a significant impact on marine biogenic emissions, with ratio range of 0.07~15.87 and 1.02~5.42 respectively. Machine learning methods were employed to simulate the conversion process of marine biogenic emissions to HCHO in MBL. Based on the SHAP values of the learning model, the importance results indicate that the factors influencing MBL HCHO mainly included NO2, as well as temperature (T) and relative humidity (RH). Specifically, the influence of NO2 on atmospheric HCHO was 1.3 times that of T and 1.6 times that of RH. Wind speed affected HCHO by influencing both marine biogenic emission and the atmospheric physical conditions. Increased marine biogenic emissions in air masses heavily influenced by human activities can reduce HCHO levels to some extent. However, in areas less affected by human activities, marine biogenic emissions can lead to higher levels of HCHO pollution. This research explores the impact of marine biogenic emissions on the HCHO status of the MBL under different atmospheric chemical conditions, offering significant insights into understanding chemical processes in marine atmospheres.

The plastidic 2-C-methylerythritol 4-phosphate (MEP) pathway supplies the precursors of a large variety of essential plant isoprenoids, but its regulation is still not well understood. Using metabolic control analysis (MCA), we examined the first enzyme of this pathway, 1-deoxyxylulose 5-phosphate synthase (DXS), in multiple grey poplar (Populus × canescens) lines modified in their DXS activity. Single leaves were dynamically labeled with 13CO2 in an illuminated, climate-controlled gas exchange cuvette coupled to a proton transfer reaction mass spectrometer, and the carbon flux through the MEP pathway was calculated. Carbon was rapidly assimilated into MEP pathway intermediates and labeled both the isoprene released and the IDP+DMADP pool by up to 90%. DXS activity was increased by 25% in lines overexpressing the DXS gene and reduced by 50% in RNA interference lines, while the carbon flux in the MEP pathway was 25–35% greater in overexpressing lines and unchanged in RNA interference lines. Isoprene emission was also not altered in these different genetic backgrounds. By correlating absolute flux to DXS activity under different conditions of light and temperature, the flux control coefficient was found to be low. Among isoprenoid end products, isoprene itself was unchanged in DXS transgenic lines, but the levels of the chlorophylls and most carotenoids measured were 20–30% less in RNA interference lines than in overexpression lines. Our data thus demonstrate that DXS in the isoprene-emitting grey poplar plays only a minor part in controlling flux through the MEP pathway.

Volatile organic compounds (VOCs) emitted by plants may help in understanding the status of a plant’s physiology and its coping with mild to severe stress. Future climatic projections reveal that shifts in temperature and CO2 availability will occur, and plants may incur the uncoupling of carbon assimilation and synthesis of key molecules. This study explores the patterns of emissions of key VOCs (isoprene, methanol, acetaldehyde, and acetic acid) emitted by poplar leaves (more than 350) under a combined gradient of temperature (12–42 °C) and air CO2 concentration (400–1500 ppm), along with measurements of photosynthetic rates and stomatal conductance. Isoprene emission exhibited a rise with temperature and CO2 availability, peaking at 39 °C, the temperature at which methanol emission started to peak, illustrating the limit of stress tolerance to severe damage. Isoprene emission was uncoupled from the photosynthesis rate, indicating a shift from the carbon source for isoprene synthesis, while assimilation was decreased. Methanol and acetaldehyde emissions were correlated with stomatal conductance and peaked at 25 °C and 1200 ppm CO2. Acetic acid emissions lacked a clear correlation with stomatal conductance and the emission pattern of its precursor acetaldehyde. This study offers crucial insights into the limitations of photosynthetic carbon and stress tolerance.

Ground-level ozone (O3) pollution has been a severe environmental and health problem for decades. The importance of biogenic volatile organic compounds (BVOCs) in the formation of tropospheric photochemistry O3 has been highlighted, especially in areas of rapid urbanization. We conducted simultaneous measurements of trace gases, including NO, NOX, O3, and BVOCs (i.e., isoprene and α-pinene), in the urban and rural forest areas of Beijing to determine the relationships between them. The results highlight the differences between the urban and rural forest areas of Beijing in terms of ambient air concentrations of BVOCs and O3, and the interrelationships between BVOCs, NOX, and ozone were quantified. Moreover, the isoprene concentration was found to be higher in the atmosphere of the urban site than of the rural site, which had higher α-pinene concentrations and higher O3 concentrations. The NOX concentration was higher at the urban site than at the rural site, and there was a significant exponential relationship between NOX and O3 at the urban site, indicating that the impact of NOx on O3 at the urban site was greater than that at the rural site. The O3 concentration increased with rising isoprene and α-pinene in both sites. In the case of substantially increased BVOC concentrations, declining NOX concentrations strongly promote the formation of O3. Consideration should be given to planting tree species with low-BVOC emissions, as they are crucial for mitigating O3 pollution in urban areas. Additionally, the relationships between BVOCs, NOX, and O3 should be considered in policymaking related to O3 control.

One of the most concerning global environmental issues is the pollution of agricultural soils by heavy metals (HMs), especially cadmium, which not only affects human health through Cd-containing foods but also impacts the quality of rice. The soil’s nitrification and denitrification processes, coupled with the release of volatile organic compounds by plants, raise substantial concerns. In this review, we summarize the recent literature related to the deleterious effects of Cd on both soil processes related to the N cycle and rice quality, particularly aroma, in different water management practices. Under both continuous flooding (CF) and alternate wetting and drying (AWD) conditions, cadmium has been observed to reduce both the nitrification and denitrification processes. The adverse effects are more pronounced in alternate wetting and drying (AWD) as compared to continuous flooding (CF). Similarly, the alteration in rice aroma is more significant in AWD than in CF. The precise modulation of volatile organic compounds (VOCs) by Cd remains unclear based on the available literature. Nevertheless, HM accumulation is higher in AWD conditions compared to CF, leading to a detrimental impact on volatile organic compounds (VOCs). The literature concludes that AWD practices should be avoided in Cd-contaminated fields to decrease accumulation and maintain the quality of the rice. In the future, rhizospheric engineering and plant biotechnology can be used to decrease the transport of HMs from the soil to the plant’s edible parts.

The exchange of isoprenoids, which includes isoprene, monoterpenes, and sesquiterpenes, between ecosystem soils and the atmosphere plays a significant role in soil ecology and atmospheric chemistry. However, research on flux exchange rates in subtropical ecosystems has been limited, as previous studies have mainly focused on temperate and boreal environments. In this study, we aimed to quantify the exchange of isoprenoids between the soil (with or without surface litter) and the atmosphere in a subtropical Eucalyptus urophylla plantation forest during the daytime in the wet season of subtropical China. Additionally, we investigated the influence of soil and litter variables on the fluxes of isoprenoids. Our results unveiled the exchange of isoprene and 17 terpenoid compounds, comprising 11 monoterpenes and 6 sesquiterpenes, between the studied soils and the atmosphere. Interestingly, regardless of the presence of surface litter, the studied soils acted as net sinks for isoprenoids, with isoprene being the most absorbed compound (−71.84 ± 8.26 μg m−2 h−1). The removal of surface litter had a significant impact on the exchange rates of two monoterpenes (α-pinene and β-pinene), resulting in decreased fluxes. Furthermore, the exchange rates of isoprene were positively correlated with litter dry weight and negatively correlated with soil temperature. The higher exchange rates of monoterpenes and sesquiterpenes were associated with increased levels of soil respiration and the abundance of leaf litter. These findings suggest that, in the context of projected global warming scenarios, the capacity of subtropical soils to act as sinks for isoprenoids is expected to increase in subtropical China. These changes in sink capacity may have implications for regional-scale atmospheric chemistry and ecosystem functioning.