Carbon Molecules Research Articles

Computational prediction of complex cationic rearrangement outcomes.

Recent years have seen revived interest in computer-assisted organic synthesis1,2. The use of reaction- and neural-network algorithms that can plan multistep synthetic pathways have revolutionized this field1,3-7, including examples leading to advanced natural products6,7. Such methods typically operate on full, literature-derived 'substrate(s)-to-product' reaction rules and cannot be easily extended to the analysis of reaction mechanisms. Here we show that computers equipped with a comprehensive knowledge-base of mechanistic steps augmented by physical-organic chemistry rules, as well as quantum mechanical and kinetic calculations, can use a reaction-network approach to analyse the mechanisms of some of the most complex organic transformations: namely, cationic rearrangements. Such rearrangements are a cornerstone of organic chemistry textbooks and entail notable changes in the molecule's carbon skeleton8-12. The algorithm we describe and deploy at https://HopCat.allchemy.net/ generates, within minutes, networks of possible mechanistic steps, traces plausible step sequences and calculates expected product distributions. We validate this algorithm by three sets of experiments whose analysis would probably prove challenging even to highly trained chemists: (1) predicting the outcomes of tail-to-head terpene (THT) cyclizations in which substantially different outcomes are encoded in modular precursors differing in minute structural details; (2) comparing the outcome of THT cyclizations in solution or in a supramolecular capsule; and (3) analysing complex reaction mixtures. Our results support a vision in which computers no longer just manipulate known reaction types1-7 but will help rationalize and discover new, mechanistically complex transformations.

Carbon dots and their biomedical and biotechnological applications

Carbon dots, a recently discovered nanoparticle, have attracted significant attention due to their impressive fluorescent, chemical, mechanical, photostability, and biocompatibility properties. Carbon quantum dots (CQDs) are a novel form of nano-carbon whose use has recently surpassed semiconductor quantum dots (QDs) in terms of their many desirable properties. This is because CQDs are made up of carbon atoms rather than carbon molecules. This study clarifies the process of synthesis and optical characteristics of CQDs, as well as current breakthroughs in CQDs’ biological applications in bioimaging. This paper discusses the recent developments and achievements reached with CQDs, with a particular emphasis on their synthetic pathways, chemical and optical characteristics, and biological applications, as well as fresh perspectives on this fascinating and potentially fruitful topic of research.

Research Progress of Biochar and Pollution Control

In recent years, due to the impact of climate change caused by the emission of greenhouse gases such as carbon dioxide, nitrous oxide and methane, scientists have begun to pay attention to the use of biochar, because it helps to capture and remove greenhouse gases in the atmosphere by means of biochar storage, converting it into a very stable form and storing it in the soil for thousands of years. This paper focuses on the hazards of organic pollutants, the treatment of pollutants by biochar and the benefits of environmental remediation. Biochar is the product of biomass energy raw material after pyrolysis, and its main component is carbon molecule. In terms of pollution treatment, biochar has a strong adsorption capacity for organic pollutants such as phenol, and can also improve soil heavy metal pollution by increasing soil cation exchange capacity (CEC) and PH. In addition, biochar is also used in low-temperature NH3-SCR denitrification catalysts to deal with nitrogen oxides in atmospheric pollutants and other aspects. Biochar is easy to ignite, non-polluting, smokeless and tasteless, less residue after combustion, light weight and high calorific value, the use of performance is better than most similar materials, known as the main force of human new energy and future fuel. The purpose of this paper is to provide the basis and reference for the development of biochar basic science and application technology.

Colossal C130 Fullertubes: Soluble [5,5] C130-D5h(1) Pristine Molecules with 70 Nanotube Carbons and Two 30-Atom Hemifullerene End-caps.

We report the seminal experimental isolation and DFT characterization of pristine [5,5] C130-D5h(1) fullertubes. This achievement represents the largest soluble carbon molecule obtained in its pristine form. The [5,5] C130 species is the highest aspect ratio fullertube purified to date and now surpasses the recent gigantic [5,5] C120-D5d(1). In contrast to C90, C100, and C120 fullertubes, the longer C130-D5h has more nanotubular carbons (70) than end-cap fullerenyl atoms (60). Starting from 39,393 possible C130 isolated pentagon rule (IPR) structures and after analyzing polarizability, retention time, and UV-vis spectra, these three layers of data remarkably predict a single candidate isomer and fullertube, [5,5] C130-D5h(1). This structural assignment is augmented by atomic resolution STEM data showing distinctive and tubular "pill-like" structures with diameters and aspect ratios consistent with [5,5] C130-D5h(1) fullertubes. The high selectivity of the aminopropanol reaction with spheroidal fullerenes permits facile separation and removal of fullertubes from soot extracts. Experimental analyses (HPLC retention time, UV-vis, and STEM) were synergistically used (with polarizability and DFT property calculations) to down select and confirm the C130 fullertube structure. Achieving the isolation of a new [5,5] C130-D5h fullertube opens the door to application development and fundamental studies of electron confinement, fluorescence, and metallic character for a fullertube series of molecules with systematic tubular elongation. This [5,5] fullertube family also invites comparative studies with single-walled carbon nanotubes (SWCNTs), nanohorns (SWCNHs), and fullerenes.

Accurate Quantum Chemical Reaction Energies for Lithium-Mediated Electrolyte Decomposition and Evaluation of Density Functional Approximations.

An important concern related to the performance of Li-ion batteries is the formation of a solid electrolyte interphase on the surface of the anode. This film is formed from the decomposition of electrolytes and can have important effects on the stability and performance. Here, we evaluate the decomposition pathway of ethylene carbonate and related organic electrolyte molecules using a series of density functional approximations and correlated wave function (WF) methods, including the coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)] and auxiliary-field quantum Monte Carlo (AFQMC). We find that the transition state barrier associated with ring opening varies widely across different functionals, ranging from 3.01 to 17.15 kcal/mol, which can be compared to the value of 12.84 kcal/mol predicted by CCSD(T). This large variation underscores the importance of benchmarking against accurate WF methods. A performance comparison of all of the density functionals used in this study reveals that the M06-2X-D3 (a meta-hybrid GGA), CAM-B3LYP-D3 (a range-separated hybrid), and B2GP-PLYP-D3 (a double hybrid) perform the best, with average errors of about 1.50-1.60 kcal/mol compared to CCSD(T). We also compared the performance of the WF methods that are more scalable than CCSD(T), finding that DLPNO-CCSD(T) and phaseless AFQMC with a DFT trial wave function exhibit average errors of 1.38 and 1.74 kcal/mol, respectively.

Rapid, simple and sustainable preparation of N-rich activated carbons with high performance for gas adsorption, via microwave heating

Rising the activity of activated carbons by surface modification has attracted considerable research attention in the fields of gas adsorption and energy storage. However, conventional functionalization of activated carbons typically requires high cost and long-term heating process. In this work, we report a simple and feasible strategy to prepare N-rich activated carbons with well-developed porosities through microwave heating. Through microwave heating, N-rich (up to 9.35 at.%) activated carbons with high porosities can be prepared within 20 min, reducing preparation time and energy consumption by 77.0% and 99.4%. Under microwave irradiation, the interaction between melamine and carbon precursors is promoted to generate an amount of defects, resulting in the introduction of N species and reducing the consumption of nitrogenous reagents (50%). Moreover, due to the enhanced van der Waals interactions between the nitrogenous carbon surface and molecules, the prepared N-rich activated carbons present excellent increase in breakthrough adsorption capacity of toluene (up to 26.0 %) and CO2 uptake (9.8 %) with similar pore structure. In summary, this study provides a facile, efficient, and universal strategy for surface modification of activated carbons toward a range of applications.

The Addition of a High Concentration of Phosphorus Reduces the Diversity of Arbuscular Mycorrhizal Fungi in Temperate Agroecosystems

Phosphorus (P) is an essential macronutrient crucial for both plant growth and crop production, playing a pivotal role in agriculture since the early 20th century. The symbiotic relationship between AMF and plants serves as a classic illustration. These fungi play a regulatory role in the growth and development of plants, especially in facilitating the absorption of P and carbon molecules by plants. While there has been a growing body of research on the community assembly of arbuscular mycorrhizal fungi (AMF) in recent decades, our knowledge of the processes governing the coexistence of these AMF communities influenced by P in agroecosystems remains limited. To investigate the impact of various P fertilizers on AMF communities in temperate agroecosystems, this study was conducted using soils sourced from wheat–maize rotation farmland at Henan Agricultural University Yuanyang Base. With the Illumina MiSeq high-throughput sequencing technique, we systematically examined the taxonomic composition of soil AMF at the Yuanyang Base of Henan Agricultural University in a wheat–maize rotation agricultural field. Our primary objective was to unravel the mechanisms behind AMF community assembly and stability under varying P gradient fertilization conditions. Nonmetric Multidimensional Scaling (NMDS) analysis revealed significant differences among AMF communities in field soil subjected to various treatments (p < 0.05). A torus translations test demonstrated positive associations with the three treatments in 36 out of the 51 examined AMF operational taxonomic units (OTUs), making up 70.59% (p < 0.05) of the results. Furthermore, 37.84% (14/37) of the OTUs displayed preferences for the low P concentration treatment, while 34.29% (12/35) and 32.26% (10/31) favored medium and high P concentrations, respectively. An analysis of the Normalized Stochasticity Ratio (NST) and Checkerboard Score (C-score) indicated that in temperate agroecosystems, deterministic processes predominantly governed AMF in all treatment groups, with high P conditions exerting a stronger influence than low or medium P conditions. This study underscores the profound impact of long-term P fertilizer application on AMF community structures within temperate agricultural systems employing wheat–maize rotation. Additionally, it highlights the dominant role played by deterministic processes in shaping the assembly of AMF communities in these temperate agricultural systems that use P fertilizers. These findings emphasize the need for balanced nutrient management, particularly concerning P, to ensure the stability of AMF communities.

Controlling the Surface Morphology of Two-Dimensional Nano-Materials upon Molecule-Mediated Crystal Growth.

The surface morphology of Mg-Al-layered double hydroxide (LDH) was successfully controlled by reconstruction during systematic phase transformation from calcined LDH, which is referred to as layered double oxide (LDO). The LDH reconstructed its original phase by the hydration of LDO with expanded basal spacing when reacted with water, including carbonate or methyl orange molecules. During the reaction, the degree of crystal growth along the ab-plane and stacking along the c-axis was significantly influenced by the molecular size and the reaction conditions. The lower concentration of carbonate gave smaller particles on the surface of larger LDO (2000 nm), while the higher concentration induced a sand-rose structure. The reconstruction of smaller-sized LDH (350 nm) did not depend on the concentration of carbonate due to effective adsorption, and it gave a sand-rose structure and exfoliated the LDH layers. The higher the concentration of methyl orange and the longer the reaction time applied, the rougher the surface was obtained with a certain threshold point of the methyl orange concentration. The surface roughness generally increased with the loading mount of methyl orange. However, the degree of the surface roughness even increased after the methyl orange loading reached equilibrium. The result suggested that the surface roughening was mediated by not only the incorporation of guest molecules into the LDH but also a crystal arrangement after a sufficient amount of methyl orange was accommodated.

Differential Aluminum tolerance in Arabidopsis thaliana ecotypes is seemingly related to metabolite changes

Plants are negatively affected by aluminum (Al) in acidic soils (pH ≤ 5.0), which impairs root growth and ultimately plant yield. Organic acids are closely related to Al neutralization improving the metal tolerance with an expansive metabolic cost. Here, we investigated phenotypic, metabolic, and genetic responses of three Arabidopsis thaliana ecotypes, Columbia (Col-0), Wassilewskija (Ws) and Landsberg erecta (Ler) in response to Al. By comparing the respective control plants with Al-exposed plants, the ecotypes Col-0 and Ws displayed stronger reductions in root growth and reproductive yield than Ler. All ecotypes presented high expression of ALMT1, an Al-resistance associated gene. Further analyses revealed a large accumulation of diverse amino acids, carbohydrates and organic acids following Al stress in both shoot and root tissues of Col-0 and Ws plants, but not in Ler. Altogether, our results suggest that a higher capacity for using and translocating reduced carbon molecules seems crucial to overcoming Al stress in the Ler ecotype. In addition, lower expenses in carbon molecules might be linked to a higher capacity to deal with Al stress, supporting a tight relationship between primary metabolism and Al stress responses. Finally, novel insights on the influence of Al over plant growth and primary metabolism in both shoots and roots are described.

Arabinoxylan in Water through SANS: Single-Chain Conformation, Chain Overlap, and Clustering.

Using small-angle neutron scattering (SANS), we examine the structure and conformational behavior of wheat arabinoxylan (AX) prepared at various concentrations in a sodium phosphate aqueous buffer. As for another major hemicellulose, xyloglucan, we observe a small number of large clusters surrounded by AX chains that behave exactly as a polymer in good solvent with a Flory exponent ν = 0.588. The fit of the data at high q-values to a standard worm-like chain model gives the persistence length lp = 45 Å and cross section of the chains 2Rc = 11-12 Å. In addition, using a dedicated modeling approach, we extract from the SANS data at the intermediate q-range the correlation length ξ of the solutions in the semidilute regime. The decay of ξ with concentration follows a scaling law that further confirms the self-avoiding statistical behavior of the AX chains. This first comprehensive study about the properties of water-soluble AX at different length scales may help in the development of products and processes involving AX as a substitute for fossil carbon molecules.

Review of Carbon Nanotube Toxicity and Evaluation of Possible Implications to Occupational and Environmental Health

Carbon nanotubes (CNTs) are nanostructures made from rolled graphene planes and have several intriguing chemical and physical characteristics. Allotropes of carbon having a nanostructure that can have a length-to-diameter ratio greater than 1,000,000 are known as carbon nanotubes (CNTs). These cylindrical carbon molecules have unique features that could make them valuable in a variety of nanotechnology applications. Their distinct surface area, stiffness, strength, and durability have generated a significant amount of interest in the health industry to achieve bio-functionalities, CNTs can be connected with a variety of biological substances, such as hormones, proteins, and nucleic acids. There are two types of CNTs: single-walled (SWNTs) and multi-walled (MWNTs). Their high aspect ratio, ultralightweight, strength, strong thermal conductivity, and electrical properties ranging from metallic to semiconducting are just a few of their intriguing characteristics. Drug delivery, blood cancer, breast cancer, brain cancer, liver cancer, cervical cancer, immunological treatment, biomedical imaging, biosensors, and tissue engineering are all areas where CNTs are beneficial, and the toxicology of carbon nanotubes is also discussed here.

Facilitating structural elucidation of small environmental solutes in RPLC-HRMS by retention index prediction

Implementing effective environmental management strategies requires a comprehensive understanding of the chemical composition of environmental pollutants, particularly in complex mixtures. Utilizing innovative analytical techniques, such as high-resolution mass spectrometry and predictive retention index models, can provide valuable insights into the molecular structures of environmental contaminants. Liquid Chromatography-High-Resolution Mass Spectrometry is a powerful tool for the identification of isomeric structures in complex samples. However, there are some limitations that can prevent accurate isomeric structure identification, particularly in cases where the isomers have similar mass and fragmentation patterns. Liquid chromatographic retention, determined by the size, shape, and polarity of the analyte and its interactions with the stationary phase, contains valuable 3D structural information that is vastly underutilized. Therefore, a predictive retention index model is developed which is transferrable to LC-HRMS systems and can assist in the structural elucidation of unknowns. The approach is currently restricted to carbon, hydrogen, and oxygen-based molecules <500 g mol−1. The methodology facilitates the acceptance of accurate structural formulas and the exclusion of erroneous hypothetical structural representations by leveraging retention time estimations, thereby providing a permissible tolerance range for a given elemental composition and experimental retention time. This approach serves as a proof of concept for the development of a Quantitative Structure-Retention Relationship model using a generic gradient LC approach. The use of a widely used reversed-phase (U)HPLC column and a relatively large set of training (101) and test compounds (14) demonstrates the feasibility and potential applicability of this approach for predicting the retention behaviour of compounds in complex mixtures. By providing a standard operating procedure, this approach can be easily replicated and applied to various analytical challenges, further supporting its potential for broader implementation.

Spin-resolved transport of multifunctional C18 molecule-based nanodevices: a first-principles study

As is well known, Kasier et al first synthesized a cyclic molecule C18, as characterized by high-resolution atomic force microscopy, is a polyalkylene structure in which the 18 carbon atoms are linked by alternating single and triple bonds Kaiser et al (2019 Science 365 1299–301). Early studies have found that the C18 molecule has semiconducting properties, suggesting that a similar straight-chain carbon structure could become a molecular device. Inspired by this, an analysis of spin-resolved electronic transport of nanodevices made by C18 sandwiched between zigzag graphyne nanoribbon leads or zigzag graphene nanoribbon leads presents here. The computational results demonstrate that a good spin-filtering effect, spin rectifying effect and an obvious negative differential resistance behavior in designed model devices can be obtained. Moreover, a stable dual-spin filtering effect or diode effect can be occurred in considered model devices with leads in an antiparallel state. The intrinsic mechanisms of molecular nanodevices are explained in detail by analyzing the transmission spectrum under different bias voltage, local density of states, molecular projection Hamiltonian, Current–Voltage (I–V) characteristics, transmission pathways, et al. These results are particularly significant for the development of multifunctional spintronic nanodevices.

Study of isobaric vapor–liquid equilibria of diethyl carbonate + ethylene carbonate for lithium-ion battery electrolyte solvent recycling

The limited life-cycle of lithium-ion batteries (LIBs) remains a significant issue for the industry. Recycling electrolytes from the batteries is one crucial aspect of LIBs recycling, which can conserve resources and reduce environmental pollution. The vapor–liquid equilibrium (VLE) data and models for the currently widely used carbonates, such as ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), can play an important role in designing the recycling process. In this work, the VLE data of DEC and EC is measured for the first time. A sophisticated equation of state, the Perturbed-Chain Polar Statistical Associating Fluid Theory, is used to establish the VLE model, not only for the newly measured DEC and EC system but also for other carbonates and their mixtures. Through the discussion of how the molecular characteristics of carbonates influence the VLE behavior, the dipolar character of linear carbonate molecules has been revealed. This demonstrates the power and importance of sophisticated modelling approaches in investigating molecular behavior of electrolyte solvents in the context of LIB recycling. Hence, this work provides valuable experimental and model data for designing recycling processes of electrolyte solvents and offers molecular insight into carbonates.

Bridging multiscale interfaces for developing ionically conductive high-voltage iron sulfate-containing sodium-based battery positive electrodes

Non-aqueous sodium-ion batteries (SiBs) are a viable electrochemical energy storage system for grid storage. However, the practical development of SiBs is hindered mainly by the sluggish kinetics and interfacial instability of positive-electrode active materials, such as polyanion-type iron-based sulfates, at high voltage. Here, to circumvent these issues, we proposed the multiscale interface engineering of Na2.26Fe1.87(SO4)3, where bulk heterostructure and exposed crystal plane were tuned to improve the Na-ion storage performance. Physicochemical characterizations and theoretical calculations suggested that the heterostructure of Na6Fe(SO4)4 phase facilitated ionic kinetics by densifying Na-ion migration channels and lowering energy barriers. The (11-2) plane of Na2.26Fe1.87(SO4)3 promoted the adsorption of the electrolyte solution ClO4− anions and fluoroethylene carbonate molecules, which formed an inorganic-rich Na-ion conductive interphase at the positive electrode. When tested in combination with a presodiated FeS/carbon-based negative electrode in laboratory- scale single-layer pouch cell configuration, the Na2.26Fe1.87(SO4)3-based positive electrode enables an initial discharge capacity of about 83.9 mAh g−1, an average cell discharge voltage of 2.35 V and a specific capacity retention of around 97% after 40 cycles at 24 mA g−1 and 25 °C.

Decomposition decreases molecular diversity and ecosystem similarity of soil organic matter

Soil organic matter (SOM) is comprised of a diverse array of reactive carbon molecules, including hydrophilic and hydrophobic compounds, that impact rates of SOM formation and persistence. Despite clear importance to ecosystem science, little is known about broad-scale controls on SOM diversity and variability in soil. Here, we show that microbial decomposition drives significant variability in the molecular richness and diversity of SOM between soil horizons and across a continental-scale gradient in climate and ecosystem type (arid shrubs, coniferous, deciduous, and mixed forests, grasslands, and tundra sedges). The molecular dissimilarity of SOM was strongly influenced by ecosystem type (hydrophilic compounds: 17%, P < 0.001; hydrophobic compounds: 10% P < 0.001) and soil horizon (hydrophilic compounds: 17%, P < 0.001; hydrophobic compounds: 21%, P < 0.001), as assessed using metabolomic analysis of hydrophilic and hydrophobic metabolites. While the proportion of shared molecular features was significantly higher in the litter layer than subsoil C horizons across ecosystems (12 times and 4 times higher for hydrophilic and hydrophobic compounds, respectively), the proportion of site-specific molecular features nearly doubled from the litter layer to the subsoil horizon, suggesting greater differentiation of compounds after microbial decomposition within each ecosystem. Together, these results suggest that microbial decomposition of plant litter leads to a decrease in SOM α-molecular diversity, yet an increase in β-molecular diversity across ecosystems. The degree of microbial degradation, determined by the position in the soil profile, exerts a greater control on SOM molecular diversity than environmental factors, such as soil texture, moisture, and ecosystem type.

The molecular chemistry of Type Ibc supernovae and diagnostic potential with the James Webb Space Telescope

Context. A currently unsolved question in supernova (SN) research is the origin of stripped-envelope supernovae (SESNe). Such SNe lack spectral signatures of hydrogen (Type Ib), or hydrogen and helium (Type Ic), indicating that the outer stellar layers have been stripped during their evolution. The mechanism for this is not well understood, and to disentangle the different scenarios’ determination of nucleosynthesis yields from observed spectra can be attempted. However, the interpretation of observations depends on the adopted spectral models. A previously missing ingredient in these is the inclusion of molecular effects, which can be significant. Aims. We aim to investigate how the molecular chemistry in SESNe affect physical conditions and optical spectra, and produce ro-vibrational emission in the mid-infrared (MIR). We also aim to assess the diagnostic potential of observations of such MIR emission with JWST. Methods. We coupled a chemical kinetic network including carbon, oxygen, silicon, and sulfur-bearing molecules into the nonlocal thermal equilibrium (NLTE) spectral synthesis code SUMO. We let four species – CO, SiO, SiS, and SO – participate in NLTE cooling of the gas to achieve self-consistency between the molecule formation and the temperature. We applied the new framework to model the spectrum of a Type Ic SN in the 100–600 days time range. Results. Molecules are predicted to form in SESN ejecta in significant quantities (typical mass 10−3 M⊙) throughout the 100–600 days interval. The impact on the temperature and optical emission depends on the density of the oxygen zones and varies with epoch. For example, the [O I] 6300, 6364 feature can be quenched by molecules from 200 to 450 days depending on density. The MIR predictions show strong emission in the fundamental bands of CO, SiO, and SiS, and in the CO and SiO overtones. Conclusions. Type Ibc SN ejecta have a rich chemistry and considering the effect of molecules is important for modeling the temperature and atomic emission in the nebular phase. Observations of SESNe with JWST hold promise to provide the first detections of SiS and SO, and to give information on zone masses and densities of the ejecta. Combined optical, near-infrared, and MIR observations can break degeneracies and achieve a more complete picture of the nucleosynthesis, chemistry, and origin of Type Ibc SNe.

Integrated FT-ICR MS and metabolome reveals diatom-derived organic matter by bacterial transformation under warming and acidification

Bacterial transformation and processing of diatom-derived organic matter (OM) is extremely important for the cycling of production and energy in marine ecosystems; this process contributes to the production of microbial food webs. In this study, a cultivable bacterium (Roseobacter sp. SD-R1) from the marine diatom Skeletonema dohrnii were isolated and identified. A combined Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS)/untargeted metabolomics approach was used to synthesize the results of bacterial transformation with dissolved OM (DOM) and lysate OM (LOM) under warming and acidification through laboratory experiments. Roseobacter sp. SD-R1 had different preferences for the conversion of molecules in S.dohrnii-derived DOM and LOM treatments. The effects of warming and acidification contribute to the increased number and complexity of molecules of carbon, hydrogen, oxygen, nitrogen, and sulfur after the bacterial transformation of OM. The chemical complexity generated by bacterial metabolism provides new insights into the mechanisms that shape OM complexity.

Connecting oxidative potential with organic carbon molecule composition and source-specific apportionment in PM2.5 in Xi'an, China

Epidemiological studies have suggested that exposure to excessive amounts of particle-bound reactive oxygen species (ROS) pollution can lead to a range of health problems. To identify the chemical composition and sources of particulate matter of diameter <2.5 μm (PM2.5)-bound ROS, high-time-resolution PM2.5 samples were collected in Xi'an, China in the periods July 24 to August 5, 2017 (summer), and January 1 to 6, 2017 (winter). Dithiothreitol (DTT) assay was used to measure the oxidative potential of PM2.5-bound ROS. The associations of six types of molecular compositions with ROS were evaluated, and source-specific contributions to ROS were quantified. The results indicated greater activity and diurnal fluctuations in PM2.5-bound ROS in winter than in summer. The mass-normalised DTT consumption rate (DTTm) reached a peak at 8:00 a.m. in summer for polluted and nonpolluted days. In winter, levels of ROS were higher during the day than night, regardless of PM2.5 pollution level. In summer, CHNO and CHOS had the greatest effect on DTTm on polluted days and CHO and CHNOS had the greatest effect on DTTm on nonpolluted days. On polluted days in winter, all molecules (CHO, CHNO, CHOS, CHNOS, CHN and CHNS) investigated in this study had limited effects on DTTm. DTTm on nonpolluted days was mainly affected by CHNO and CHNS. CHNO and CHNOS molecules from secondary reactions favoured ROS production. Results from source apportionment based on positive matrix factorization showed that in summer, vehicle emission was the primary contributor to ROS generation (41.3%), followed by secondary formation (33.7%), fugitive dust (18.6%), and coal combustion (6.3%), whereas in winter, biomass burning and secondary formation were the primary contributors (>58%) to ROS. Our work helps clarify the mechanisms of ROS formation and contributes to theoretical research on PM2.5 toxicity.

Temperature-Dependent Molecular Evolution of Biochar-Derived Dissolved Black Carbon and Its Interaction Mechanism with Polyvinyl Chloride Microplastics.

Biochar-derived dissolved black carbon (DBC) molecules are dependent on the BC formation temperature and affect the fate of emerging contaminants in waters, such as polyvinyl chloride microplastic (MPPVC). However, the temperature-dependent evolution and MPPVC-interaction of DBC molecules remain unclear. Herein, we propose a novel DBC-MPPVC interaction mechanism by systematically interpreting heterogeneous correlations, sequential responses, and synergistic relationships of thousands of molecules and their linking functional groups. Two-dimensional correlation spectroscopy was proposed to combine Fourier transform-ion cyclotron resonance mass spectrometry and spectroscopic datasets. Increased temperature caused diverse DBC molecules and fluorophores, accompanied by molecular transformation from saturation/reduction to unsaturation/oxidation with high carbon oxidation states, especially for molecules with acidic functional groups. The temperature response of DBC molecules detected via negative-/positive-ion electrospray ionization sequentially occurred in unsaturated hydrocarbons → lignin-like → condensed aromatic → lipid-/aliphatic-/peptide-like → tannin-like → carbohydrate-like molecules. DBC molecular changes induced by temperature and MPPVC interaction were closely coordinated, with lignin-like molecules contributing the most to the interaction. Functional groups in DBC molecules with m/z < 500 showed a sequential MPPVC-interaction response of phenol/aromatic ether C-O, alkene C═C/amide C═O → polysaccharides C-O → alcohol/ether/carbohydrate C-O groups. These findings help to elucidate the critical role of DBCs in MP environmental behaviors.