N-heterocyclic Compounds Research Articles

Simultaneous assay of mousy off-flavor markers in wine

The compounds described as being responsible for mousy off-flavor in wine are 2-acetylpyrroline (APY), 2-acetyltetrahydropyridine (ATHP) and 2-ethyltetrahydropyridine (ETHP). However, assay of these compounds is difficult due to their physical-chemical characteristics. The aim of this study was to develop a simple and effective method for simultaneously determining the concentration of these three N-heterocyclic compounds in wine. This new method is a decisive tool for better defining this spoilage phenomenon in wine and guarding against it.

Copper-Catalyzed Asymmetric Allylation of N-Aryl Aldimines.

The copper-catalyzed enantioselective allylation reaction of N-aryl aldimines has been developed using a combination of Cu(OAc)2 and SPINOL-based phosphonamidite. This protocol significantly broadens the substrate scope, such that imines bearing various ortho-substituents on the N-aryl were converted smoothly into homoallylic amines in up to 99% yield and 98% ee. Taking advantage of the diversity of the N-aryl motif, three kinds of N-heterocyclic compounds were constructed, respectively, from the corresponding homoallylic amines in merely one step.

Coffee charcoal as a green catalyst for oxidative dehydrogenation

Nitrogen heterocyclic (N-heterocyclic) compounds are extensively present in natural products and active drug molecules. However, their synthesis typically requires the use of noble metal catalysts and harsh conditions. In this study, we report a novel approach using coffee charcoal as a green catalyst for the mildly mechanically driven oxidative dehydrogenation of N-heterocyclic compounds. A one-step strategy was employed to construct a microporous coffee charcoal catalyst with C defects, in-situ co-doping of multi-atoms (N, O), and abundant modification of functional groups (–OH and –COOH). Under room temperature and with H2O as solvent, the coffee charcoal catalyst demonstrates a high yield of approximately 94 % and allows for gram-scale reactions with H2O being the only by-product. Moreover, the catalyst exhibits excellent reusability, maintaining its activity for over 13 cycles. Results indicate that the defects and atom doping can enhance the adsorption of O2, which is then activated to singlet oxygen (1O2) through the conversion of –OH functional groups on the catalyst’s surface. The singlet oxygen (1O2) can strengthen the oxidative dehydrogenation of N-heterocyclic compounds. Furthermore, the mechanically driven technique both activates the reaction interface and supplies the necessary reactive energy, thus providing a comprehensive explanation for the mild reaction conditions observed. In conclusion, our research proposes a sustainable and environmentally friendly method for the oxidative dehydrogenation of N-heterocyclic compounds, which can drive crucial reactions with significant relevance to sustainability.

Review on Natural Colorants Used in Cosmetic

This review offers an examination of the properties and recent advancements in research concerning the utilization of plant-derived colorants across the domains of food, cosmetics, and textile materials. The comprehensive analysis encompasses various types of colorants, including polyphenols such as anthocyanins, flavonol-quercetin, and curcumin, as well as isoprenoids like iridoids, carotenoids, and quinones. Additionally, N-heterocyclic compounds such as betalains and indigoids, along with melanins and tetrapyrroles, are scrutinized for their potential industrial applications. The review also delves into future perspectives, exploring the evolving landscape of applying plant-derived colorants in the coloration of diverse materials.

CN and CCH azirine derivatives, possible precursors of prebiotic molecules: formation and spectroscopic parameters

ABSTRACT N-heterocycles are of special relevance in astrobiology but at present no nitrogen-containing heterocycles have been detected in the interstellar medium (ISM). Thus far, the simplest N-heterocyclic compound, 2H-Azirine (c-C2H3N), has not been conclusively identified, despite being searched for. Recently, several cyano and ethynyl derivatives of unsaturated hydrocarbons have been discovered in the cold prestellar core Taurus Molecular Cloud 1 (TMC-1). The purpose of this work is to assess the feasibility of the possible formation of cyano and ethynyl derivatives of azirine (c-C2H2N-CN, c-C2H2N-CCH) under interstellar conditions and provide high-level theoretical spectroscopic parameters of the most relevant cyano- and ethynyl-azirine isomers to facilitate their experimental identification. Six isomers are located for each, cyano- and ethynyl-azirine derivatives, and their interconversion processes are studied. The reactions of 2H-azirine with the CN or CCH radicals in the gas phase are explored as possible formation routes of cyano and ethynyl azirine. We found that the formation processes of the most stable isomers, namely 3-cyano-2H-azirine, 2-cyano-2H-azirine, 3-ethynyl-2H-azirine, and 2-ethynyl-2H-azirine, are exothermic and barrier free. Thus, these compounds stand out as potential targets to be searched for in space. Based on the newly determined rotational spectroscopic parameters, which also account for 14N hyperfine splittings, we compile a line catalogue for each system up to 50 GHz as a preliminary and required step to characterize these molecules experimentally, whether in the laboratory or directly in the ISM.

Comparative exploration of biological treatment of hydrothermal liquefaction wastewater from sewage sludge: Effects of culture, fermentation conditions, and ammonia stripping

Hydrothermal liquefaction wastewater from sewage sludge (sludge HTLWW) is an emerging waste stream that requires treatment before being discharged into the environment. Biological treatment of sludge HTLWW is an attractive option due to the low cost and operational flexibility. In this study, we investigated and compared the performance of three bacterial strains and four fungal strains for biodegradation of sludge HTLWW. Our screening experiments established pH and mineral supplementation (iron, magnesium, calcium, and phosphorus) conditions that greatly improved COD removal and chemical compound degradation by the microbes. An ammonia stripping pretreatment improved COD removal efficiency of Rhodococci jostii RHA1 by 44%. All tested bacterial strains can tolerate 10× dilution of HTLWW and remove 35–44% of COD in 2–15 days, while all tested fungal strains were able to tolerate 20× dilution and were better at degrading phenolic compounds than bacteria. HTLWW treatment with biomass pellets of fungus Aspergillus niger NRRL 2001 achieved the best COD removal efficiency of 47% in 12 days without the need of nutrient supplementation. Comparisons on chemical compound degradation by the tested microbes suggested that organic acids in HTLWW were highly degradable, followed by phenolic compounds. N-heterocyclic compounds were resistant to biodegradation and were removed by 38%. This study demonstrated pure culture biological treatment of sludge HTLWW with diverse types of microorganisms, which would guide the culture development and bioprocess parameter optimization for treating HTLWW of different compositions.

N-heterocycles: Recent Advances in Biological Applications

Abstract: Nitrogen based heterocycles display an impressive repertoire of biological activities, including antioxidant, antimicrobial, anti-tuberculosis, analgesic, anti-inflammatory, anti-viral, anti-HIV, anti-cancer, anti-helminthic, and other pharmacological activities. Numerous novel nitrogen-based heterocycles have been synthesized, which showed various physiological properties, and their application in medicinal chemistry is ever-growing. The present review will provide an in-depth view of N-heterocyclic compounds that showed biological activities in the last 5 years (2017-2021). This review article will be helpful for the structural design of effective and sustainable N-heterocyclic drugs against diseases with minimal side effects.

Hydrothermally synthesized mesoporous titanium-containing Y zeolites with different titanium contents and their high activity for hydrodenitrogenation of quinoline and indole

Herein, the effect of in-situ Ti modification on the physicochemical properties of the TixY zeolites and the corresponding NiW supported TixY-A catalysts, as well as on the catalytic performances for aromatic N-heterocyclic compounds hydrodenitrogenation (HDN) was investigated. The existing forms of Ti atoms in the Y zeolites and the active metal states of the corresponding catalysts were investigated by XRD, ICP-OES, SEM, FTIR, UV–Vis DRS, CP-MAS NMR, N2 physical adsorption–desorption, Py-FTIR, H2-TPR, HRTEM, XPS and DFT calculation. The results show that the Ti atoms can be effectively introduced into the Y zeolite framework by the in-situ hydrothermal crystallization method. With the increase of TiO2/Al2O3 molar ratio in the Y zeolite, the amount of Brønsted acid sites of the zeolite tended to decrease constantly, but the reducibility of the catalyst and the stacking layer number as well as the sulfidation degree of the NiWS active phase continued to be enhanced. The highest quinoline and indole conversions of 86.5 % and 46.9 % at 320 °C, 4.0 MPa, 300 H2/oil (v/v), and 10 h−1 LHSV, as well as the highest TOFs of 2.24 h−1 and 1.04 h−1, the highest kHDN values of 12.4 × 10−4 mol·g−1·h−1 and 3.6 × 10−4 mol·g−1·h−1, and the highest denitrogenated product selectivities of 46.1 % and 66.2 % under quinoline and indole conversions of about 15 % and 50 % respectively have been achieved in catalyst NiW/Ti0.1Y-A due to the perfect matching of its hydrogenation and hydrogenolysis performance, which was mainly derived from the remarkable synergistic effect between the Brønsted acid sites of the Y zeolite and the NiWS active phase of the catalyst.

Co(II) acetateassisted direct synthesis of acyl hydrazones from acyl hydrazides under mild condition.

Acyl hydrazones are a class of synthetically important organic compounds that are recurrently in high demand for synthesis and use in various fields of chemistry and biology. We report the first Co(II) catalyzed one-component one-pot sustainable synthesis of acyl hydrazones only from acyl hydrazides under mild reaction conditions. Traditional and contemporary methodologies use two components (usually acyl hydrazides and aldehydes/ketones/alcohols/styrene) as the coupling partners. Our protocol, on the other hand, involves the in situ generation of aldehyde intermediate (detected by gas chromatography) from the acyl hydrazide, which then undergoes condensation with another molecule of the same acyl hydrazide in the same pot to yield acyl hydrazones in presence of mild base K2CO3 and low-cost Co(OAc)2·4H2O as catalyst. This method shows good functional group tolerance with good to excellent yield of products. Furthermore, some of the resulting acyl hydrazones have been used as synthetic precursors and explored in various post-synthetic modifications to afford N-heterocyclic compounds. Furthermore, photoswitchable properties of few synthesized acyl hydrazones are also explored using their E/Z isomerization around the C=N bond, as realized by high-pressure liquid chromatography (HPLC) and UV-vis spectroscopic studies.

N-N self-inhibition effect of aromatic N-heterocyclic compounds on NiWS supported γ-Al2O3 hydrotreating catalyst

The reason for high-difficulty nitrogen removal of aromatic N-heterocyclic compounds in petroleum fractions was investigated from the main thought of “NiWS property - Reaction behavior - DFT calculation”. The properties of the used catalyst were characterized by a series of techniques with the aim of providing the basis for model construction in the DFT calculations. The kinetic experiments in fixed-bed reactor revealed that although 1,2,3,4-tetrahydroquinoline (THQ1) and decahydroquinoline (DHQ), o-ethylaniline (OEA) exhibited relatively high yields in the HDN reaction of quinoline and indole respectively, they were all able to show high conversions and HDN rates when reacted as feedstocks alone. The study of product normalizations in the reaction system of the mixed feedstocks demonstrated that the difficulty of conversion of THQ1 and DHQ in quinoline HDN was mainly due to the inhibition effect of quinoline feedstock. While in the HDN of indole, the presence of the intermediate product OEA was the main factor for the low conversion of indole. This phenomenon of inhibition originating from within the molecular reaction network was proposed as N-N self-inhibition effect for the first time. The DFT calculations suggested that the inhibition of quinoline on THQ1 could be attributed to the adsorption advantage of quinoline, while the inhibition on DHQ was mainly due to the steric hindrance effect of DHQ itself. And the inhibition effect of OEA on indole can be mainly attributed to its greater nucleophilicity and stronger adsorption ability on the active sites compared with IND.

Effects of Lipids and Type of Amino Acid in Protein in Microalgae on Nitrogen Reaction Pathways during Hydrothermal Liquefaction.

It is meaningful to understand the conversion pathways of nitrogen during the hydrothermal liquefaction process of microalgae to reveal the related reaction mechanisms and develop effective methods to prevent N from ending in biocrude, which eventually increases the quality of biocrude. Extending from our previous works that mainly focused on two high-protein (>50 wt%) microalgae (Chlorella sp. and Spirulina sp.), Nannochloropsis sp., which has a high lipid content (>70 wt%), was used as the feedstock for this project using the same methodology. The high lipid content in Na. induced less nitrogen during the oil phase and as a result, reduced the heteroatom content while also improving the quality of biocrude. It is worth noting that another investigation was conducted on the model compounds with different types of amino acids to specify the effects of the types of amino acids in the proteins in microalgae on the N pathway and their distribution in the products (aqueous phase, oil, solid, and gas). It was found that the basic amino acid in microalgae caused the formation of more N-heterocyclic compounds in the biocrude. The mass flow based on the mass balance was demonstrated to further refine the map showing the predicted reaction pathway of nitrogen from the previous version.

N-Heterocyclic Compounds, In silico Molecular Docking Studies, and In vitro Enzyme Inhibition Effect against Acetylcholinesterase Inhibitors.

This work contains the synthesis of seven new N-heterocyclic compounds bearing imidazole, benzimidazole, pyridine, and morpholine moieties. We aimed to synthesize N-heterocyclic compounds for a more effective drug candidate to increase the amount of acetylcholine in synapses in Alzheimer's disease. All compounds were characterized by 1H NMR, 13C NMR, FTIR and elemental analysis. Enzyme inhibition activity of all compounds against acetylcholinesterase was investigated, which is an indirect treatment for Alzheimer's. Molecular docking was applied to estimate the binding energy of these compounds to the acetylcholinesterase. All compounds were synthesized from reactions of 2 equivalents of N-heterocyclic starting material and 1 equivalent of 4,4'-bis(chloromethyl)-1,1'-biphenyl. The inhibition parameters of IC50 and Ki were calculated by the spectrophotometric method. AutoDock4 was used to define the binding pose of the compounds. Ki values were found in the range of 80.03 ± 19.64 to 5014.98 ± 1139.60 nM for AChE as an enzyme inhibition strategy, which is an important parameter for the treatment of neurodegenerative such as Alzheimer's disease. In this study, molecular docking is exerted to predict the binding energy of heterocyclic compounds (especially 2, 3, and 5) against acetylcholinesterase enzyme. Their docking binding energies are in good agreement with experimental findings. These new syntheses are drugs that can be used as AChE inhibitors in Alzheimer's disease.

A combined theoretical and experimental study of the pyrolysis of pyrrolidine

Pyrrolidine is a suitable model substance featuring a five-membered N-heterocycle representing the typical structure of the N-containing compounds in biomass. Previous studies have provided ambiguous arguments on the reaction mechanism of pyrrolidine thermal decomposition. Knowledge on the fate of the most dominant decomposition product, the unstable diradical ·CH2NHCH2·, is lacking. In this work, a high-level potential energy surface of the unimolecular reactions of ·CH2NHCH2·, including isomerization and decomposition channels, was explored. Then, the rate coefficients of various channels were obtained by the RRKM/master equation method over 500–2000 K and 0.001–100 atm. The results show that the thermal stabilization of cyc-C2H5N is highly favored over other isomerization and decomposition channels. The channels isomerizing to CH3NCH2, cis-HNCHCH3 and trans-HNCHCH3 compete with each other, and the rate constants are at least two orders of magnitude lower than the formation of cyc-C2H5N. Being thermodynamically unstable, cyc-C2H5N will mainly isomerize back into the diradical at temperatures ≤ 1200 K at 1 atm or isomerize to cis-HNCHCH3 when the temperature is higher. To validate the postulated reaction pathways, a pyrolysis experiment of pyrrolidine was conducted in a SiC reactor with a short residence time (40–60 μs) at 1050 K and 0.263 atm. The experimental result confirms the collisional stabilization of H2NCHCH2 and cyc-C2H5N + CH3NCH2. The diradical ·CH2NHCH2· was not readily detectable due to its low concentration, which falls below the detection limit of current analytical techniques, while the stabilization of cis-HNCHCH3 and trans-HNCHCH3 was not sure because of their extremely low photoionization cross section under the studied energy range. The rate constants of the isomerization and decomposition reactions of diradical ·CH2NHCH2· and cyc-C2H5N are provided, which are valuable for developing the mechanism for pyrrolidine and deepening our understanding of the mechanism of N-heterocyclic compounds pyrolysis/combustion.

Genomic potential for inorganic carbon sequestration and xenobiotic degradation in marine bacterium Youngimonas vesicularis CC-AMW-ET affiliated to family Paracoccaceae.

Ecological studies on marine microbial communities largely focus on fundamental biogeochemical processes or the most abundant constituents, while minor biological fractions are frequently neglected. Youngimonas vesicularis CC-AMW-ET, isolated from coastal surface seawater in Taiwan, is an under-represented marine Paracoccaceae (earlier Rhodobacteraceae) member. The CC-AMW-ET genome was sequenced to gain deeper insights into its role in marine carbon and sulfur cycles. The draft genome (3.7Mb) contained 63.6% GC, 3773 coding sequences and 51 RNAs, and displayed maximum relatedness (79.06%) to Thalassobius litoralis KU5D5T, a Roseobacteraceae member. While phototrophic genes were absent, genes encoding two distinct subunits of carbon monoxide dehydrogenases (CoxL, BMS/Form II and a novel form III; CoxM and CoxS), and proteins involved in HCO3- uptake and interconversion, and anaplerotic HCO3- fixation were found. In addition, a gene coding for ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO, form II), which fixes atmospheric CO2 was found in CC-AMW-ET. Genes for complete assimilatory sulfate reduction, sulfide oxidation (sulfide:quinone oxidoreductase, SqrA type) and dimethylsulfoniopropionate (DMSP) cleavage (DMSP lyase, DddL) were also identified. Furthermore, genes that degrade aromatic hydrocarbons such as quinate, salicylate, salicylate ester, p-hydroxybenzoate, catechol, gentisate, homogentisate, protocatechuate, 4-hydroxyphenylacetic acid, N-heterocyclic aromatic compounds and aromatic amines were present. Thus, Youngimonas vesicularis CC-AMW-ET is a potential chemolithoautotroph equipped with genetic machinery for the metabolism of aromatics, and predicted to play crucial roles in the biogeochemical cycling of marine carbon and sulfur.

A multiplatform metabolomics/reactomics approach as a powerful strategy to identify reaction compounds generated during hemicellulose hydrothermal extraction from agro-food biomasses.

Hydrothermal treatment is commonly used for hemicelluloses extraction from lignocellulosic materials. In this study, we thoroughly investigated with a novel approach the metabolomics of degradation compounds formed when hazelnut shells are subjected to this type of treatment. Three different complementary techniques were combined, namely GC-MS, 1H NMR, and UHPLC-IM-Q-TOF-MS. Organic acids, modified sugars and aromatic compounds, likely to be the most abundant chemical classes, were detected and quantified by NMR, whereas GC- and LC-MS-based techniques allowed to detect many molecules with low and higher Mw, respectively. Furans, polyols, N-heterocyclic compounds, aldehydes, ketones, and esters appeared, among others. Ion mobility-based LC-MS method was innovatively used for this purpose and could allow soon to create potentially useful datasets for building specific databases relating to the formation of these compounds in different process conditions and employing different matrices. This could be a very intelligent approach especially in a risk assessment perspective.

π-conjugated n-heterocyclic quinone compound containing F atoms for high performance aqueous Zn-organic batteries

2F-BPD was synthesized by introducing two -F groups to benzo[b]phenazine-6,11-dione (BPD) and used as a cathode for improving performances of aqueous Zn-organic batteries. 2F-BPD delivers high capacities of 329 mAh/g at 0.05 A/g and 161 mAh/g at 5 A/g, as well as excellent capacity retention of 82% after 10,000 cycles. The charge storage mechanism was revealed that 2F-BPD simultaneously store Zn2+ and H+ at the C = N and C = O sites. Given the synergistic effects of electron-withdrawing and induction of -F, 2F-BPD not only stabilizes its structure during the discharge/charge process, but also exhibits slightly lower solubility and faster kinetics due to an increased specific surface area, resulting in improved rate and cycling performances compared to BPD. This work suggests that introduction of -F groups can provide valuable insights for realizing enhanced performances of Zn-organic batteries.

Carbonized Melamine Cyanurate as a Palladium Catalyst Support for the Dehydrogenation of N-heterocyclic Compounds in LOHC Technology

In this work, the use of graphite-like carbon nitride (g-C3N4) with improved texture characteristics for the synthesis of supported palladium catalysts of dehydrogenation of nitrogen-containing heterocycles was studied. This process is key to the creation of liquid organic carrier technology (LOHC) using N-heterocycles as reversibly hydrogenated/dehydrogenated substrates. For the preparation of graphite-like carbon nitride supports with advanced textural characteristics, well-established technology of the melamine cyanurate complex carbonization and standard techniques of adsorption precipitation together with wet impregnation were used for the synthesis of Pd-containing systems. The activity of the synthesized catalysts was studied in decahydroquinoline dehydrogenation. The high weight content of extractable hydrogen (7.2 wt%) and the high extraction rate, respectively, make it possible to consider these substances as the most promising N-heterocyclic compounds for this technology. It was shown that an increase in the specific surface area of g-C3N4 allows for achieving a slightly lower but comparable fineness of palladium particles for the 1 wt% Pd/MCA-500 sample, compared to the standard 1 wt% Pd/C. In this case, the catalytic activity of 1 wt% Pd/MCA-500 in the dehydrogenation of both substrates exceeded the analogous parameter for catalysts supported by nitrogen-free supports. This regularity is presumably associated with the electron-donor effect of surface nitrogen, which favorably affects the dehydrogenation rate as well as the stability of catalytic systems.

Facile synthesis of quinolines and N-alkylation reactions catalyzed by ruthenium(II) pincer type complexes: Reaction mechanism and evidences for ruthenium hydride intermediate

Amines, N-heterocyclic compounds, and their derivatives are ubiquitous in all naturally occurring compounds, particularly alkaloids, and are widely used in pharmaceuticals, agrochemicals, lubricants, and surfactants. The design of pincer type ligands and corresponding metal complexes is a fundamental step with a unique reactivity. In this article, the NNN-pincer type of ruthenium complexes were synthesized and analyzed using a variety of spectroscopic techniques, including UV-Visible, infrared, and NMR. The molecular structures of the complexes were examined by X-ray crystallography. These complexes were also employed to activate carbon and nitrogen (C-N bond) bonds in C-N coupling processes. This paper describes the synthetic approach, product purification, and spectroscopic characterization, and nuclear magnetic resonance (NMR) spectroscopy was used to demonstrate the catalytically synthesized substrates. A total number of 16 quinolines and 22 N-alkylated substrates were synthesized and characterized by NMR spectroscopic technique.

Acid/base-co-catalyzed cyclization of ketones with o-amino-benzylamines: Direct synthesis of quinoline compounds

A novel acid/base-co-catalyzed tandem cyclization of various ketones with o-amino-benzylamines employing molecular oxygen as the clean oxidant has been described. The reaction provides an efficient and general strategy for the construction of fused N-heterocyclic compounds, such as dihydrobenzo[c]acridines, indeno[1,2-b]quinolines, dihydro-5H-benzo[6,7]cyclohepta[1,2-b]- quinolines and quinolones in a single step. The broad scope and the use of oxygen as the sole oxidant make this transformation an attractive approach for the synthesis of the above mentioned scaffolds.

Impact of fossil and non-fossil fuel sources on the molecular compositions of water-soluble humic-like substances in PM2.5 at a suburban site of Yangtze River Delta, China

Abstract. Atmospheric humic-like substances (HULIS) affect the global radiation balance due to their strong light absorption at the ultraviolet wavelength. The potential sources and molecular compositions of water-soluble HULIS at a suburban site in the Yangtze River Delta from 2017 to 2018 were discussed, based on the results of the radiocarbon (14C) analysis and combining the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) technique in this study. The 14C results showed that the averaged non-fossil-fuel source contributions to HULIS were 39 ± 8 % and 36 ± 6 % in summer and winter, respectively, indicating significant contributions from fossil fuel sources to HULIS. The Van Krevelen diagrams obtained from the FT-ICR-MS results showed that the proportions of tannin-like and carbohydrate-like groups were higher in summer, suggesting significant contribution of HULIS from biogenic secondary organic aerosols (SOAs). The higher proportions of condensed aromatic structures in winter suggested increasing anthropogenic emissions. Molecular composition analysis on the CHO, CHON, CHOS, and CHONS subgroups showed relatively higher intensities of high O-containing macromolecular oligomers in the CHO compounds in summer, further indicating stronger biogenic SOA formation in summer. High-intensity phenolic substances and flavonoids, which were related to biomass burning and polycyclic aromatic hydrocarbon (PAH) derivatives indicating fossil fuel combustion emissions, were found in winter CHO compounds. Besides, two high-intensity CHO compounds containing condensed aromatic ring structures (C9H6O7 and C10H5O8) identified in the summer and winter samples were similar to those from off-road engine samples, indicating that traffic emissions were one of the important fossil fuel sources of HULIS at the study site. The CHON compounds were mainly composed of nitro compounds or organonitrates with significantly higher intensities in winter, which were associated with biomass burning emissions, in addition to the enhanced formation of organonitrates due to high NOx in winter. However, the high-intensity CHON molecular formulas in summer were referring to N-heterocyclic aromatic compounds, which were produced from the atmospheric secondary processes involving reduced N species (e.g., ammonium). The S-containing compounds were mainly composed of organosulfates (OSs) derived from biogenic precursors, namely long-chain alkane and aromatic hydrocarbon, which illustrate the mixed sources of HULIS. Generally, different policies need to be considered for each season due to the different seasonal sources (i.e., biogenic emissions in summer and biomass burning in winter for non-fossil-fuel sources, traffic emissions and anthropogenic SOA formation in both seasons, and additional coal combustion in winter). Measures to control emissions from motor vehicles and industrial processes need to be considered in summer. Additional control measures on coal power plants and biomass burning should be applied in winter. These findings add to our understanding of the interaction between the sources and the molecular compositions of atmospheric HULIS.