Aliphatic Research Articles

Pore Morphology and Oxidation Behaviour of Deep-Loaded Granular Coal at High Initial Temperatures

ABSTRACT As coal mining proceeds deeper, fragmented coal is subjected to high geostress and elevated thermal environments, causing changes in its micro-physical properties and spontaneous combustion (SC) risks. Deep mining operations entail significant risks of coal fires. In order to investigate the effects of high stress and high thermal environments on the microstructural and physicochemical damage of fragmented coal, and to elucidate the mechanisms influencing oxidation behavior, we conducted experiments including low-temperature nitrogen adsorption, synchronous thermal analysis, and in-situ diffuse reflectance spectroscopy. These experiments aimed to explore the pore morphology and oxidation characteristics of high initial temperature unloading granular coal (HITU-GC) unloading conditions. The results indicate that with increasing initial temperature, characteristic point temperatures initially rise and then decrease, while both the mass loss and heat release during the low-temperature oxidation stage decrease. After pressure-unloading composite treatment, the oxidation process accelerates with more intense reactions, resulting in an overall increase in heat release. The pore shapes of HITU-GC show no significant difference compared to the original coal, mainly comprising non-rigid aggregates of micropores, platy or layered matrix particles, including numerous slit-shaped pores. The coal surface also exhibits ink bottle-shaped pores and cone-shaped pores. Higher pre-oxidation temperatures correlate with higher specific surface areas. Higher stress levels from pressurized unloading correlate with lower specific surface areas. The specific surface area of sample O60-P16 is reduced by 0.879 m2/g compared to sample O60-P0. Pressurized unloading treatment disrupts mesoporous pores. Following thermal environment and pressure-unloading, the coal’s aromatic hydrocarbon content decreases, while the contents of hydroxyl, aliphatic hydrocarbons, and oxygen-containing functional groups (FG) all increase. Sample O60-P4 shows the highest content of active FG. While thermal environments enhance coal oxidation activity, pressure-unloading treatment increases the extent of coal surface fragmentation. The synergistic effect of both significantly increases the SC risk of coal. This study provides a theoretical basis for controlling thermal hazards associated with high-initial-temperature unloading fragmented coal in deep goaf areas.

Phytochemical Profiling and Antioxidant Evaluation of Rhododendron arboreum Sm leaf and flower: Integrative Analysis using Advanced Analytical Techniques

ABSTRACT Objective This study investigates the biological activities of Rhododendron arboreum Sm from the eastern Himalayas, addressing a literature gap on its properties. It explores the plant's phytochemical, antioxidant, and medicinal characteristics. Significance: Evaluating methanolic extracts of R. arboreum offers valuable insights into its bioactive potential. Comprehensive GC-MS analysis identified a diverse array of compounds, highlighting the plant's chemical composition. Methods: Methanolic leaf and flower extracts underwent sequential extraction and phytochemical profiling using column chromatography, TLC, and GC-MS analysis. Spectral studies aided compound identification, and antioxidant activity was assessed via spectrophotometric assays. Results: Column chromatography separated methanol leaf and flower extracts into 17 and 24 distinct fractions, respectively. TLC analysis showed specific Rf values for leaf (0.58, 0.65, 0.75, 0.8, 0.86, 0.9) and flower samples (0.91, 0.38, 0.48, 0.51, 0.56, 0.6, 0.65, 0.75, 0.85, 0.96). GC-MS analysis revealed a variety of organic functional groups, including aliphatic hydrocarbons, aromatic compounds, heterocyclic molecules, phenolic compounds, steroids, terpenoids, alcohols, esters, and other bioactive compounds. FTIR spectra identified functional groups such as hydroxyls, primary amines, alkanes, and alkynes. NMR data indicated a complex molecular composition with diverse proton environments. Leaf extracts demonstrated superior antioxidant activity compared to flower extracts in DPPH, ABTS, hydrogen peroxide scavenging, lipid peroxidation inhibition, and FRAP assays. Conclusion: The study identifies diverse phytochemicals in R.arboreum extracts and highlights their potential applications in pharmaceuticals, nutraceuticals, and functional foods, owing to the superior antioxidant activity of leaf extracts compared to flowers.

Above room temperature spin crossover in mononuclear iron(II) complexes featuring pyridyl-benzimidazole bidentate ligands adorned with aliphatic chains.

Two bidentate ligands (L1 = 1-pentyl-2-(pyridin-2-yl)-1H-benzimidazole and L2 = 1-heptyl-2-(pyridin-2-yl)-1H-benzimidazole) were employed for the synthesis of five mononuclear Fe(II) coordination compounds 1-5 containing perchlorate, tetrafluoroborate and triflate counterions. Single-crystal X-ray diffraction analysis confirmed the expected molecular structures of all the reported compounds, revealing a moderately distorted octahedral geometry of {FeN6} coordination chromophores. All five compounds exhibit thermal spin crossover with T1/2 temperatures allocated above 400 K. The theoretical calculations supported the experimental magnetic investigation and helped to explain the electronic structures of the reported complexes with respect to the occurrence of thermal spin state switching. In addition, compound 4 was employed for the preparation of Langmuir-Blodgett films and fabrication of molecular films using the method of spontaneous evaporation of the subphase. While the formation of Langmuir-Blodgett films was unsuccessful due to the instability of the compound at the water/air interface, the latter technique allowed the formation of molecular films of 4 with well-defined thickness and homogeneity.

Preparation and Characterization of Bio-Asphalt Based on Sludge-Derived Heavy Oil

To achieve the efficient resource utilization of municipal sludge and promote the sustainability of pavement materials, this study employed liquefaction technology to process municipal sludge. The resulting liquefied-sludge-derived heavy oil was blended with 50# asphalt to prepare a bio-asphalt that can replace petroleum asphalt. Firstly, orthogonal experiments were conducted to analyze the effects of the solid–liquid ratio (dried sludge:anhydrous ethanol), liquefaction temperature, and reaction time on the yield of the sludge-derived heavy oil. Then, the basic characteristics of the sludge-derived heavy oil were studied using an elemental analyzer, gel permeation chromatography, thermal analysis, gas chromatography–mass spectrometry, and Fourier transform infrared spectroscopy, and the differences between the sludge-derived heavy oil and petroleum asphalt were compared. Finally, to determine the appropriate content range of sludge-derived heavy oil in bio-asphalt, a comprehensive evaluation of the three major indicators, aging resistance, storage stability, low-temperature performance, and high-temperature performance was carried out for the prepared bio-asphalts. The results indicated that the optimal preparation process for liquefied sludge oil involves a liquefaction temperature of 275 °C, a solid–liquid ratio of 1:15, and a reaction time of 1 h, resulting in an oil production rate of 22.36%. The sludge-derived heavy oil demonstrated good thermal stability, with its primary components being aliphatic compounds (carboxylic acids, ketones, aldehydes, alcohols, alkanes, esters, etc.), with esters being the most abundant. Furthermore, the sludge-derived heavy oil was highly compatible with 50# asphalt, but no chemical reaction occurred between them. When the sludge-derived heavy oil content ranged from 5% to 20%, bio-asphalt showed favorable aging resistance and storage stability. As the content of the sludge-derived heavy oil increased, its low-temperature performance improved, but there was a slight decrease in high-temperature performance. Additionally, correlation analysis highlighted that the influence of sludge-derived heavy oil content on the high-temperature performance of bio-asphalt was notably greater than on other properties. Therefore, the recommended dosage of sludge-derived heavy oil should be between 5% and 10%.

Effect of Immersion Temperature on Reburning Characteristics of Coal with Different Preoxidation Degrees

ABSTRACT In light of the phenomenon where water immersion and high ground temperatures impact coal oxidation, this study conducted temperature-programmed heating and FTIR experiments to investigate the effect of water immersion temperature on the reignition characteristics of coal with varying preoxidation levels. The results show that the overall oxygen consumption capacity of coal reburning is strong with the increase in water immersion temperature at 180°C and 230°C. When the water immersion temperature is 50°C, the -CH3/-CH2- value of coal is higher than that of water immersion at 30°C and 40°C, and the maximum difference in aliphatic hydrocarbon ratio before and after reburning is 1.64%. When the temperature of pre-oxidation and immersion is 180°C and 50°C, respectively, the hydroxyl content decreases by 17.73% before and after reburning. The carbonyl content in coal after reburning exhibits varying decreasing trends under different treatment conditions. When immersed in water at 40°C, the carbonyl content in coal decreases more rapidly before and after reburning.

Essential oils of Plumeria alba L. and Plumeria rubra L. growing in Egypt: GC/MS analysis, molecular dynamics and in-vitro anti-cholinesterase activity

AimEssential oils (EOs) from Plumeria species exhibit noteworthy chemical compositions and diverse biological activities, rendering them valuable constituents for use in medicine, cosmetics, and perfumery. Our aim is to investigate the chemical profiles of P. alba L. and P. rubra L. cultivated in Egypt as biologically active crops. MethodsThe EOs of the flowers of P. alba and P. rubra cultivated in Egypt were prepared by steam distillation and headspace and analyzed by GC/MS. Principal components analysis (PCA) was used to assess the correlation between the chemical composition of the EOs and those reported for EOs of Plumeria species in other countries. ResultsThe score plot revealed a notable difference in the components of EOs prepared by steam distillated and headspace. Geranyl benzoate (27.55 %) was the major compound identified in steam distillated sample of P. alba and linalool (32.52 %) was the major in that prepared by headspace. On the other hand, 1-heptacosanol (23.86 %) was the major compound in the steam distillated sample of P. rubra and 2-methyl-butyl aldoxime (36.38 %) was the major compound in that prepared by headspace. Both EOs demonstrated in-vitro inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. Docking study revealed that aromatic compounds have better fitting, while aliphatic compounds have better stability with lower docking interaction energy, and geranyl benzoate showed docking results and binding mode similar to that of the ligands of both enzymes; its stability after docking was confirmed by molecular dynamics. ConclusionEOs from Plumeria species are highly recommended for developing natural and effective aromatherapy products for Alzheimer’s disease.

Behavioral and electrophysiological responses of the male medfly, Ceratitis capitata, to thymol and carvacrol ethers.

The Mediterranean fruit fly, Ceratitis capitata, is one of the most economically important insect pests attacking fruits and vegetables in tropical and subtropical areas of the world. Semiochemical-based pest management programs are being used to provide environmentally friendly control methods for medflies. The goals of the current study were to discover potential new, attractive, kairomones by designing, synthesizing, and testing simplified ethers of thymol and carvacrol along with their ether derivatives in short-range attraction assays and electroantennogram (EAG) assays with male C. capitata. To the best of our knowledge, this study represents the first investigation of thymol and carvacrol, and their respective ethers for attractancy to C. capitata, a major agricultural pest worldwide. In short-range attraction bioassays, parent compounds, thymol and carvacrol, along with their propyl, butyl, benzyl, and octyl ethers captured the most male C. capitata. The attraction patterns changed over time and captures were only significant if they were greater than the positive controltea tree oil (TTO) at 90 min. In EAG assays, thymol benzyl, octyl ethers, and carvacrol benzyl ether evoked significantly greater antennal responses than their parent compounds. The EAG responses did not correlate with short-range male attraction. The aliphatic side chains of thymol and carvacrol had a small effect on the activity. Future studies will investigate the long-range attraction of the ethers that elicited large EAG responses. This report provides new information for discovering potential kairomones through synthesis and structure-activity studies for sterile male medflies. Thymol, carvacrol, and several of their ether derivatives displayed improved longevity of attraction compared with TTO (a strong medfly attractant), with significantly higher captures than TTO observed at 90 min in laboratory bioassays. Further chemical synthesis of thymol and carvacrol ethers within this series may lead to the development of ethers that are more attractive or persistent than their parent compounds, thymol and carvacrol. © 2024 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

A study on source identification of contaminated soil with total petroleum hydrocarbons (aromatic and aliphatic) in the Ahvaz oil field.

The oil industry in Khuzestan province (Southwest Iran) is one of the main reasons contributing to the pollution of the environment in this area. TPH, including both aromatic and aliphatic compounds, are important parameters in creating pollution. The present study aimed to investigate the source of soil contamination by TPH in the Ahvaz oil field in 2022. The soil samples were collected from four oil centers (an oil exploitation unit, an oil desalination unit, an oil rig, and a pump oil center). An area outside the oil field was determined as a control area. Ten samples with three replicates were taken from each area according to the standard methods. Aromatic and aliphatic compounds were measured by HPLC and GC methods. The positive matrix factorization (PMF) model and isomeric ratios were used to determine the source apportionment of aromatic compounds in soil samples. The effects range low and effects range median indices were also used to assess the level of ecological risk of petroleum compounds in the soil samples. The results showed that Benzo.b.fluoranthene had the highest concentration with an average of 5667.7 ug/kg in soil samples in the Ahvaz oil field. The highest average was found in samples from the pump oil center area at 7329.48 ug/kg, while the lowest was found in control samples at 1919.4 ug/kg-1. The highest level of aliphatic components was also found in the pump oil center, with a total of 3649 (mg. Kg-1). The results of source apportionment of petroleum compounds in soil samples showed that oil activities accounted for 51.5% of the measured PAHs in soil. 38.3% of other measured compounds had anthropogenic origins, and only 10.1% of these compounds were of biotic origin. The results of the isomeric ratios also indicated the local petroleum and pyrogenic origin of PAH compounds, which is consistent with the PMF results. The analysis of ecological risk indices resulting from the release of PAHs in the environment showed that, except for fluoranthene, other PAHs in the oil exploitation unit area were above the effects range median level (ERM) and at high risk. The results of the study showed that soil pollution by total petroleum hydrocarbons (TPH), both aromatic and aliphatic, is at a high level, and is mainly caused by human activities, particularly oil activities.

Coomassie Brilliant Blue G for Smart Colorimetric Determination of the Ionic Surfactants in Triton X-100 Solutions.

The conditions for the smart colorimetric determination of cetylpyridinium chloride and sodium dodecyl sulfate by reaction with Coomassie brilliant blue G (CBBG) have been proposed. The nature of the absorption and fluorescence spectra of aqueous solutions of CBBG as a function of acidity has been investigated. A variety of reagent forms and associations with ionic surfactants have been demonstrated. The composition of the associates formed in the CBBG-cationic surfactant system has been established. The increase in the analytical signal of the cationic surfactant and the stabilization of the colloid-chemical state of the system during reactions in the organized medium of the nonionic surfactant Triton X-100 has been demonstrated. These effects are realized through association in premicellar solutions and as a result of the solubilization of components in Triton X-100 micellar solutions. The addition of long-chain cationic surfactants to the reagent occurs with the replacement of the heteroatom proton. The absorption of CBBG-cationic surfactant associates solutions increases with the length of the cationic surfactant hydrocarbon chain. Ethanol additives decrease the aggregation of CBBG. The technique of cationic surfactant determination has been tested in the analysis of the pharmaceutical. The results show that the simplicity of analytical signal registration with satisfactory correctness and acceptably high sensitivity of determination is an advantage of the developed technique.

Volatile and non-volatile metabolite profiling of under-explored crop Piper colubrinum link. With chromatography mass spectrometry approach and its biochemical diversity from medicinally valued Piper species

Piper colubrinum Link. is an underexplored crop regarding its metabolites and therapeutic attributes. Current study aimed to identify the possible volatile and non-volatile metabolites of P. colubrinum fruit and studied its metabolite diversity with medicinally valued Piper species viz. P. nigrum L., P. longum L. and P. chaba Hunter. The volatile constituents of P. colubrinum essential oil by GC–MS revealed the presence of sesquiterpenes as the major contribution. The sesquiterpenes α-muurolol (12.5 %) and β-caryophyllene (11.3 %) were the predominant volatile components. Few aliphatic compounds like n-heptadecane and trace amounts of monoterpenes (α- and β-pinene and α-terpineol) were also identified from this crop. The fatty acid profiling by GC–MS revealed mainly oleic acid (41.3 %) followed by palmitic and linoleic acids. HPLC analysis demonstrated that the major pungent alkaloid piperine was found to be trace (0.04 %) in P. colubrinum. The LC-QTOF-MS/MS profiling of the chloroform extract of the P. colubrinum revealed the presence of non-volatile constituents including phenolic and alkaloid compounds. Ferulic acid, rosmarinic acid, salicylic acid, kaempferol-5-glucoside, 5-methoxysalicylic acid, apigenin-7-galactoside, kaempferide-3-glucoside, luteolin, kaempferol, apigenin and scutellarein-4′-methyl ether were the phenolic compounds whereas piperlonguminine was the alkaloid compound identified. Finally, the biochemical parameters of this crop were compared with that of P. nigrum, P. longum and P. chaba and average linkage cluster dendrogram revealed that P. colubrinum was biochemically distinct from other three Piper species.

High electrical conductivity induced by charge transfer interactions in naphthalenediimide derivatives

Various studies have shown the influence of aliphatic, aromatic and bulky side chains on the optical, electrical conductivity and charge transport properties of naphthalenediimide (NDI) derivatives. The morphology, structural arrangement and the aggregation behaviour of these derivatives play an important role in influencing the charge transfer interactions between the donor and acceptor. These properties influence the electrical conductivity of the derivatives due to presence of charge transfer interactions. The present work focuses on the structure property relationship of the four NDI derivatives (SB-NDI) synthesized by imidization of dianhydride precursor with primary amine terminated Schiff bases (SB). The SB-NDI derivatives bear terminal phenyl ring attached to NDI through unsaturated or double unsaturated linkers bearing different electron withdrawing and donating groups. Among these, SB-NDI-2 derivative bearing –NO2 group in trans position at the terminal phenyl ring shows lowest –ΔGoET(CS) which allows favorable intramolecular charge separation. The Scanning electron microscopy shows ribbon like morphology for SB-NDI-2. The micron sized ribbons provide better charge transport and a conductivity of ∼1 Sm−1 at the room temperature without any additives. The special structure of SB-NDI provides charge transport properties allowing wide applications in the field of optoelectronics.

Temperature effects on chemical reactions and product yields in the Co-pyrolysis of wood sawdust and waste tires: An experimental investigation

This study investigates the effects of varying temperatures on the co-pyrolysis of wood sawdust (WS) and waste tires (WT) within a stainless steel fixed-bed reactor under a nitrogen atmosphere. The experiments were conducted at three different temperatures: 400 °C, 500 °C, and 600 °C, focusing on the thermal behavior and resultant product yields. At 600 °C, WS produced the highest oil yield (63.6 wt%), suggesting a tendency to generate more aqueous and volatile components. Conversely, WT alone showed an optimal oil yield of 46.4 wt% at 500 °C, while the WS-WT blend achieved 55.6 wt%. Gas chromatography-mass spectrometry (GC-MS) analyses of the pyrolytic oils indicated that WS-heavy mixtures were rich in aliphatic compounds, whereas WT-dominant samples had increased aromatic and phenolic contents, demonstrating the potential for creating valuable chemicals from waste. Additionally, gas analysis highlighted significant variations in syngas composition, with increased methane and decreased CO2 levels at higher temperatures, emphasizing the role of the water-gas shift reaction. These findings underscore the critical importance of temperature control in optimizing the efficiency and quality of products from co-pyrolysis, presenting a viable method for enhancing the value derived from waste materials.

Preparation of oil-soluble carbon-dot based room temperature phosphorescent materials by surface modification

The strategy of preparing carbon dots-based room temperature phosphorescent materials by using inorganic substrate to promote the triplet excited transition of carbon dots (CDs) has been extensively studied. The stable existence of room temperature phosphorescent materials prepared by inorganic substrate materials in the organic phase is still a great challenge. In this study, a new strategy for obtaining oil-soluble CDs@SiO2 room temperature phosphorescent materials by surface modification were proposed. The hydrophobic long hydrocarbon chain was introduced on the surface of CDs@SiO2 composites by esterification reaction to obtain oil-soluble CDs@SiO2 room temperature phosphorescent materials (SSA composites). The decay lifetime of SSA composites is 1.263 s, SSA composites phosphors have a quantum yield (QY) of 48 %. Finally, the application of SSA composites in electrostatic spinning successfully improves the hydrophobicity of nano spun films and expands the new function of electrostatic spinning in anti-counterfeiting.

Deactivation mechanism of NiWS/SAPO-11 catalyst in hydroisomerization of n-hexadecane: Insights into coke deposition behavior and active phase migration

The application of non-noble metal supported catalysts in the hydroisomerization of long-chain n-alkanes is a novel field, and there is currently not any research available on the deactivation process of these catalysts. We investigated into the deactivation mechanism of NiWS/SAPO-11 catalyst in the hydroisomerization of n-hexadecane in this work for the first time. Specifically, coke deposition behavior and active phase migration were investigated. The reduction of catalytic efficiency of the catalyst was partially aided by the decrease in specific surface area, pore volume, and acid density. From the perspective of the active phase, the clusters of NiWS active phase migrated as the reaction time increased, mostly resulting in an increase in both the stacking number and the length of active phase slabs. The migration of active phase increased the distance between active phase clusters and metal sites, and decreased the utilization ratio of active metal atoms. From the perspective of coke deposition, the coke formed on the catalyst includes soft coke and hard coke. The formation and evolution of coke on the catalyst were investigated. The soft coke (aliphatic compounds) progressively transformed into hard coke (polycyclic aromatic hydrocarbons and graphite-like), and the coke gradually migrated from the external surface of the catalyst to the pore channels as the reaction time increased. It is expected to provide theoretical basis and reference value for the deactivation research and design of non-noble metal supported hydroisomerization catalyst.

Fe3O4/AM-PAA/Ni nanomagnetic spheres: A breakthrough in in-situ catalytic reduction of heavy oil viscosity

In-situ catalytic technology for heavy oil reservoirs is widely regarded as one of the most promising methods for heavy oil extraction. However, its large-scale application faces significant challenges due to the lack of efficient stable catalysts, and issues related to the dispersion of catalysts during the injection process. This study introduces a modified nanomagnetic sphere, Fe3O4/AM-PAA/Ni, with catalytic and surface-active properties. With a 1 % mass fraction of Fe3O4/AM-PAA/Ni and 1 % tetrahydronaphthalene (hydrogen donor) at 180°C, heavy oil viscosity dropped by 94.21 %, and asphaltenes and resin reduced by approximately 20 %. Core flooding and alternating magnetic field experiments demonstrated superior dispersion and heating effects for Fe3O4/AM-PAA/Ni nanoparticles compared to traditional Fe3O4. Mechanism analysis revealed that the unpaired electrons and d-orbitals on Fe3O4/AM-PAA/Ni’s transition metals facilitated hydrocarbon chain breakdown and interaction with heteroatoms, while nanoscale nickel enhanced catalytic activity for C-S bond cleavage, further reducing oil viscosity. The amphiphilic polymers on the surface of magnetic nanospheres significantly enhanced the dispersion of the catalyst in heavy oil, increasing the reaction contact area and thereby improving the catalytic performance. This research not only offers vital theoretical insights and practical strategies for efficient heavy oil extraction but also paves the way for advancements in reservoir in-situ modification technologies, showcasing significant application potential and academic value.

Quantitative analysis of molecular structure characterization of different liptinite-rich coals using FTIR spectroscopy

As one of the important components in low-rank coals, liptinite plays an indispensable role in the formation and utilization of coal, thus, understanding the occurrence and structures of liptinite-rich coals provides a theoretical basis for the origin and clean utilization of coals. In this study, the occurrence of liptinite and the functional groups and molecular structure of different liptinite-rich coals were quantitatively characterized by using optical microscope and Fourier transform infrared spectroscopy (FTIR), respectively. The results showed that the sample JS-7 from Yunnan Province mainly enriched sporinite and bituminite, the sample JS-15 from Yunnan Province is rich in dispersed resin and the amber-rich coal from Liaoning Province mainly contains bulk resin. The FTIR results indicated that the amber-rich coal, the sample JS-7 and pure amber (Liaoning Province) consist mainly of trisubstituted benzene. The sample JS-7 has the highest content of trisubstituted benzene (63.4%) due to the high content of sporinite and bituminite. The sample JS-15 is mainly composed of tetrasubstituted and pentasubstituted benzene, which may be relevant to the cyclization of aliphatic chains and the decarboxylation reaction of benzene rings. The CC group has not been detected in the sample JS-7 and pure amber. The FTIR structural parameters indicate that the pure amber has the lowest maturity, the lowest degree of aromatization, but the highest hydrocarbon generation potential. The highest CH2/CH3 group value (14.69) and the lowest A factor value (0.36) of the sample JS-15 indicate a well-developed aliphatic chain structure and lowest hydrocarbon generation potential, respectively, which probably caused by the low content of CO group.

Molecular structure refinement based on residual dipolar couplings using magnetic-field rotational sampling.

A method for structure refinement of molecules based on residual dipolar coupling (RDC) data is proposed. It calculates RDC values using magnetic-field rotational sampling of the rotational degrees of freedom of a molecule in conjunction with molecule-internal configurational sampling. By applying rotational sampling, as is occurring in the experiment, leading to observable RDCs, the method stays close to the experiment. It avoids the use of an alignment tensor and, therefore, the assumptions that the overall rotation of the molecule is decoupled from its internal motions and that the molecule is rigid. Two simple molecules, a relatively rigid and a very flexible cyclo-octane molecule with eight aliphatic side chains containing 24 united atoms, serve as so-called "toy model" test systems. The method demonstrates the influence of molecular flexibility, force-field dominance, and the number of RDC restraints available on the outcome of structure refinement based on RDCs. Magnetic-field rotational sampling is basically equivalent but more efficient than explicitly sampling the rotational degrees of freedom of the molecule. In addition, the performance of the method is less dependent on the number NRDC of measured RDC-values available. The restraining forces bias the overall orientation distribution of the molecule correctly. This study suggests that the information content of RDCs with respect to molecular structure is limited.

Thermal decomposition behaviors of adamantane and 1-methyladamantane in oxygen atmosphere: ReaxFF molecular dynamics simulation

High energy density fuels (HEDFs) have garnered considerable interest in the aerospace applications due to their high density and effective heat dissipation capabilities. However, there is still no clear understanding of the pyrolysis and oxidation mechanisms of HEDFs. In this work, a computational strategy based on ReaxFF molecular dynamics reveals dehydrogenation and ring-opening reaction events for adamantane and 1-methyladamantane. A comparative analysis of the initial decomposition behavior, intermediate reaction mechanism, and final product distribution demonstrates that the decay of the reactants is dependent on temperature and oxygen concentration. The main decomposition pathways of adamantane and 1-methyladamantane involve multi-step dehydrogenation and ring opening by the following reaction: i. C10H16 → C10H15 → C7H10 + C3H5, ii. C10H16 → C10H12, iii. C11H18 → C11H16, iv. C11H18 → C11H15 → C2H4 + C9H11. C7H10, C3H5, and C9H11 undergo further bond-breaking reactions to form linear hydrocarbon chains. At low temperatures, C10H16 and C11H18 exhibit a preference for reacting with OH and HO2, accounting for 15 %–35 % of the reactions. At high temperatures, the preferred reaction for C10H16 and C11H18 is with O2, accounting for 33 %–64 % of the reactions. The bridge carbon atom acts as the initial dehydrogenation site for both adamantane and 1-methyladamantane, as well as the active site for ring opening. The decomposition energy barrier for 1-methyladamantane (108.16–130.39 kJ/mol) is lower than that for adamantane (130.72–142.61 kJ/mol). Our findings shed light on the complicated interplay of oxidation of adamantane and 1-methyladamantane.

Distribution, migration, and segmented risk assessment of the total petroleum hydrocarbons in soil, groundwater, and soil gas at an oil refinery

In this study, the concentrations of six petroleum hydrocarbons (n-alkane hydrocarbons (total petroleum hydrocarbons [TPH] (C6-C9) and (C10-C40)), BTEX(benzene, toluene, ethylbenzene, m & p-xylene)) in 261 soil, 31 groundwater, and 4 soil gas samples were measured to determine their spatial distribution，migration patterns and human health risks. To assess the rationality of parameter selection, GS-MS (gas chromatography-mass spectrometry) method was used to analyze the chemical composition of TPH (C6-C9), shanghai local regulation was referenced to assess TPH (C10-C40) various segmentation health risks. The results revealed that the contaminants were mainly concentrated in the refining workshop and the storage tank. The pathway of steam invasion in soil gas and the CR (carcinogenic risk) and HQ (hazard quotient) assessment of benzene in soil gas were 0–4 and 1–3 orders of magnitude higher than those in soil. TPH (C6-C9) was more similar to the Total Petroleum Hydrocarbons (Aromatic Low) in RSL (Regional Screening Level). Aliphatic hydrocarbons [AHCs]. (C10-C12) had the highest non-carcinogenic risk among all TPH (C10-C40) parts. The present study provided a reference to accurately determine the toxicological parameters of TPH (C6-C9) and TPH (C10-C40) and to improve the BTEX risk assessment methods.

Chemical composition, antioxidant and antimicrobial activities of Rumex obtusifolius L. essential oil from the highlands of Ecuador

The chemical composition, antioxidant and antimicrobial activities of the essential oil from the aerial parts of Rumex obtusifolius L. were studied. To the best of the authors’ knowledge, this essential oil has never been fully characterized. The component analysis of the essential oil was done by gas chromatography with flame ionization detector (GC-FID) and mass selective detector (GC-MS). A total of 104 compounds, representing 97.8% of the essential oil, were identified. Aliphatic compounds, mainly methyl ketones (74.2%) and monoterpene hydrocarbons (13.7%) were found to be the most abundant compounds. The major compounds were undecan-2-one (47.6%) and nonan-2-one (13.4%). The antioxidant activity of the essential oil, evaluated by DPPH (IC50 9.11 mg/mL) and ABTS (IC50 36.72 mg/mL) assays, exhibited a weak ability in scavenging radicals. The essential oil also showed a low ferric reducing activity. The essential oil exhibited very good activity against E. coli and S. aureus, but low activities against S. enterica serovar, P. aeruginosa and C. albicans. MIC values of the essential oil varied from 0.38-27.04 μL/mL, with the lowest for E. coli.