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In atmospheric pressure chemical ionization mass spectrometry (APCI-MS), [M−3H+H2O]+ ions can deliver analyte-specific signals that enable direct analysis of volatile n-alkane mixtures. The underlying ionization mechanisms have been the subject of open debate, and in particular the role of water is insufficiently clarified to allow for reliable process analytics when the humidity level changes over time. This can be a problem, particularly in online monitoring, where analyte accumulation in the ion source can also occur. Here, we investigated the role of water during APCI-MS of volatile n-alkanes by changing the carrier gas for sample injection from a dry to a wetted state as well as by using 18O-labeled water. This allowed for a distinction between gaseous and surface-adsorbed water molecules. While adsorbed water seems to be responsible for the desired [M−3H+H2O]+ signals through surface reactions with the analyte molecules, gaseous water was found to promote the formation of CnH2n+1O+ of different (and analyte-independent) hydrocarbons, revealing a reaction with hydrocarbon species which accumulated in the ion source during continuous operation. At the same time, gaseous water competed with analyte molecules for ionization and thus suppressed the formation of alkyl (CnH2n+1+) and alkenyl (CnH2n−1+) ions. The results reveal a memory effect due to hydrocarbon adsorption, which may cause severe interpretation difficulties when the ionization chamber undergoes sudden humidity changes. The use of [M−3H+H2O]+ for n-alkane analysis in alkane/water mixtures can be facilitated by constantly maintaining high humidity and hence stabilizing the ionization conditions. [ABSTRACT FROM AUTHOR]

The topological indices are reported to be very useful in various QSPR studies as these indices can be utilized as a tool to predict the physicochemical properties of a diverse set of chemical compounds. The objective of this communication is twofold. First, to introduce some neighborhood degree sum‐based topological indices and perform a comparative QSPR analysis of the indices with their corresponding degree‐based topological indices to analyze the usefulness of the new indices. Second, to investigate isomer discrimination ability of the newly defined indices on the basis of degeneracy test. Neighborhood degree sum‐based topological indices not only consider the degree of each atom in the molecule but also the degrees of its neighboring atoms. Moreover, these indices are expected to provide information about how connected and dense the neighborhoods of atoms are within the molecule. In this study, we observe that the proposed neighborhood degree sum‐based topological indices exhibit better correlation with some physicochemical properties of Octane Isomers and 66 alkanes as compared to their corresponding degree‐based topological indices. Also, the supremacy in terms of sensitivity of the neighbourhood degree sum‐based topological indices as compared to the classical degree‐based ones is established. [ABSTRACT FROM AUTHOR]

Taurine (2-aminoethanesulfonic acid) is a free sulfur-containing β-amino acid widely distributed in many mammalians. Owing to the energizing effects, it is mostly used in soft drinks and supplements for athletes. Regular intake of soft drinks may lead to an overdose of caffeine, taurine, and guarana and loss of bone mass, overweight, hypertension, and in older age, osteoporosis and cardiovascular diseases. Therefore, it is essential to control the maximum amount of taurine consumed by humans in the food and beverages. Here, a fast, simple, accurate, and robust method based on ultrahigh-performance liquid chromatography hyphenated with mass spectrometry (UHPLC-MS) was successfully applied for the determination of taurine in selected soft drinks sold in Slovakia. The method was characterized by coefficient of determination higher than 0.99, and the predicted value of the limit of detection was 4.29 μmol/L. The analyzed levels of taurine in selected commercial drinks ranged from 2.8 to 3.78 mg/mL. The concentration in one brand of the investigated drinks was found to be extremely low (about 70%) compared to the declared content by the manufacturer. [ABSTRACT FROM AUTHOR]

The nature of volatile compounds in Agaricus bisporus was investigated by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry. The relative level of each constituent was determined by area normalization method and internal standard method. A total of 84 volatile compounds were identified in Agaricus bisporus, including 22 esters, 11 aldehydes, 11 acids, 11 alcohols, 9 ketones, 6 alkanes, 4 pyridines, 4 amidines, 2 ethers, 1 phenol, and 3 others. The main compounds were benzyl alcohol (28.84%, 3015.92 ng/g), benzaldehyde (25.88%, 2706.80 ng/g), benzoic acid (7.25%, 757.98 ng/g), 9,12-octadecadienoic acid (Z,Z)-, methyl ester (4.13%, 431.74 ng/g), benzeneacetaldehyde (3.72%, 389.34 ng/g), and butanoic acid (3.16%, 330.08 ng/g). [ABSTRACT FROM AUTHOR]

Rationale: Chlorinated aromatics and alkanes are widely used for their flame retardancy, but they need to be monitored when used in recycled pulp. This paper reports the use of palladium acetate/activated carbon (Pa/Ac) activated by nitric acid as an online catalyst to determine chlorinated aromatics and chlorinated alkanes in recycled paper products using gas chromatography–tandem mass spectrometry (GC–MS/MS), which significantly improves the sensitivity of the method and remarkably lowers the detection limits. Methods: The Pa/Ac catalyst was prepared using a self‐made catalytic device and used as key to the online catalytic conversion of target chlorinated aromatic hydrocarbons and chlorinated alkanes for GC–MS/MS analysis. The response surface model was used to optimize catalytic conditions. Then GC–MS/MS in the multireaction monitoring mode with online catalysis was applied for the analysis of polychlorinated biphenyls, polychlorinated terphenyls, polychlorinated naphthalene, and chlorinated paraffins (CP) in recycled paper products. Results: Compared with traditional methods, the Pa/Ac catalyst can transform chlorinated aromatic hydrocarbons into aromatic hydrocarbons through dechlorination hydrogenation, thus lowering the detection limit of the GC–MS/MS method significantly. It can transform paraffin chloride into the corresponding alkane to better distinguish short‐chain, medium‐chain, or long‐chain CPs. Online catalytic conversion significantly improved the sensitivity and reproducibility (88.7%–113.1%) of the method. Tissue samples with various concentration levels of chlorinated aromatics and chlorinated alkanes were tested. The linearity range of the reduced target compounds in the reduction product solution was 0.02–1.00 μg/ml (R2 > 0.995). The quantitative detection limit was 0.03–0.05 μg/kg, and relative standard deviation was less than 6.9%. Conclusion: This study was the first to introduce the Pa/Ac catalytic device as an online catalytic unit in the determination of chlorinated aromatics and chlorinated alkanes using the GC–MS/MS method. The target compounds were converted into alkanes and aromatic hydrocarbons with unchanged carbon structures, and the method could achieve a low detection limit with no need for high‐end methods such as GC‐chemical ionization ion source (CI)‐MS or high‐resolution mass spectrometry. These methods are suitable for the determination of chlorine pollutants in recycled paper and its raw materials. [ABSTRACT FROM AUTHOR]

An accurate dry matter intake (DMI) measurement method is of great importance for determining the performance of dairy cows. While n-alkane technique is commonly used to estimate the DMI of ruminants, the protocols used to measure alkanes are complex, time consuming and low throughput. Herein we present a simplified and miniaturised protocol that combines a smaller sample matrix (60 mg of faeces or herbage), a shorter (3 h) saponification step and a direct purification of the crude extract by filtration through silica powder or mixing with silica powder prior to GC-FID analysis. In addition to a much higher throughput compared with the existing methods, by skipping the commercial SPE columns and reducing the organic solvent volume, our miniaturised protocol should significantly reduce the sample processing cost and is thus suitable for alkane determination for large-scale experiments. [ABSTRACT FROM AUTHOR]

[Display omitted] • VWSE instrument successfully automates chromatographic sample preparation. • The VWSE automation prototype significantly reduces labor requirements. • The development instrument automation was valid for low-concentration analytes. • VWSE is the ability to isolate low-polarity analytes from an aqueous matrix. Automation has transformed the field of analytical chemistry by enhancing efficiency and precision in laboratory processes. A crucial step in analytical workflows, sample preparation, has traditionally relied on manual techniques, leading to variability and inefficiency. Vial wall sorptive extraction (VWSE) is a promising alternative for automating and enhancing sample preparation in analytical processes. This study aims to evaluate the performance of automated VWSE in the analysis of alkanes (C10-C18) in aqueous phases and to explore its potential use in routine laboratory settings for analyzing contaminants in environmental analysis, quality control, and forensics. VWSE devices were developed and characterized, a chromatographic method was established, and the sample preparation process was automated using an automated liquid handling system. The devices manufactured exhibit the best overall response and low standard deviation. Statistical tests confirm the equivalence of the vials prepared. The developed method achieved good results in analytical validation, a wide linear range with a high coefficient of determination (R2 > 0.90), low limits of detection (0.01–1.02 ng mL−1), and low limits of quantification (0.05–1.05 ng mL−1) were achieved. The parameters repeatability (<26.91 %), recovery (91 to 116 %), and intermediate precision (<22.29 %) also achieved a good analytical performance. The developed automated VWSE method proves effective in quantifying alkanes and meets analytical method validation criteria. This research highlights the potential of automated VWSE for sample preparation in various analytical applications. [ABSTRACT FROM AUTHOR]

Ex situ bioremediation of crude oil in bioreactors by oleophilic bacteria permits to regulate temperature, nutrients and oxygen and the results in petroleum removal are much more effective than in situ bioremediation. This article quantify the biodegradation of alkanes which conform crude oil in bioreactors by three oleophilic strains. Samples were collected from the bioreactors and extracted in dichloromethane (10:1 aqueous/organic v/v) for amplification in GC-FID analysis of individual alkanes. 94% of crude oil (initial concentration 8.6 g l−1) is removed in 24 days by Bacillus licheniformis and in 38 days by Pseudomonas putida and Paenibacillus glucanolyticus. Higher biodegradation rates (9.0–26.5 mg l−1d−1) are reached for the lightest fraction of crude oil by Bacillus licheniformis (C10–C16), and much lower for C22–C25 alkanes (4.4–8.9 mg l−1d−1). Pseudomonas putida and Paenibacillus glucanolyticus degrade a wide range of alkanes at 1.6–9.6 mg l−1d−1, with preference over C8–C16 hydrocarbons. Heptane and octane (alkanes cited to be toxic) are difficult for biodegradation in two strains (B. licheniformis and P. putida) and a recalcitrant "window" C18–C21 is observed for the three oleophilic strains in the alkane range studied. [Display omitted] • Biodegradation of crude oil in bioreactors improves highly bioremediation of petroleum spills. • Oleophilic bacteria degrade alkanes depending on the enzymatic system present in the host cell. • Bacteria can modulate alkanes to be degraded depending on strain, enzymes and crude oil. • High alkane biodegradation rates can be obtained in bioreactors (9.0–26.5 mg l−1d−1). [ABSTRACT FROM AUTHOR]

The treatment of Salmonella infections is threatened by multidrug resistance necessitating the search for alternative treatments, such as from medicinal plants. There are several reports on the antibacterial activity of Annona muricata. This study assessed the activity against multidrug-resistant (MDR) Salmonella and also the toxicity of the leaves of this plant. The hexane and methanol extracts of the leaves were screened against characterized MDR isolates by disc diffusion and microdilution methods. A cytotoxicity test was performed on monkey kidney epithelial cells; an acute toxicity test was conducted in BALB/c mice and the liver and kidney functions were assessed at the end of the test. Both extracts recorded weak activity in the disc test. Conversely, the extracts showed a wide range of activity against specific Salmonella isolates in the microdilution assay, and the lowest minimum inhibitory concentration value recorded was 0.0625 mg/mL. The hexane extract (ANOHEX) was not cytotoxic (CC50 = 57.7 µg/mL) and was also not toxic to the mice at 2000 mg/Kg bodyweight, while the methanol extract (ANOMET) was cytotoxic (CC50 = 18.44 µg/mL), and mortality was recorded at 2000 mg/Kg but not at 300 mg/Kg. There were no significant changes in biomarkers of the liver (alanine aminotransferase and aspartate aminotransferase) and kidney (creatinine and urea) functions P > 0.05 , except for ANOHEX which significantly decreased creatinine P = 0.01 , in the test mice which was not considered a toxic effect. In conclusion, this study has demonstrated high bacteriostatic activity against MDR Salmonella and a low risk of toxicity of A. muricata leaves. Hence, the leaves are a potential alternative treatment for resistant Salmonella infection. The natural products should be further investigated in vitro and in vivo. [ABSTRACT FROM AUTHOR]

• Sediment direct introduction and analysis of paraffinic alkanes by thermodesorption-GC–MS. • Chemometric optimisations of microwave-assisted and thermal desorptions. • Sediment dilution with sand reduces matrix effects from TD for accurate quantification. • Solventless, automated TD-GC–MS is suitable for alkanes direct analysis from sediments. Direct sample introduction thermal desorption (TD) coupled to GC–MS was investigated for the analysis of paraffinic hydrocarbons (HCs) from polluted sediments. TD-GC–MS is sometimes used for analysing paraffinic HCs from atmospheric particles but rarely for their direct desorption from sediments. So, the new TD methodology, applied to sediments, required development, optimization and validation. A definitive screening experimental design was performed to discriminate the critical factors on TD efficiency, from model sediments containing various organic matter (OM) amounts. Low molecular weight HCs had extraction behaviours markedly different from high molecular ones (HMW-HCs), but a compromise was found using very few sediment amount (5 mg), high temperature rate (55 °C min−1) and final temperature (350 °C). Linear HCs (n -C10 to n -C40) could be quantified using the matrix-matched calibration method, with very low detection limits (3.8–13.4 ng). The amount of the overall paraffinic alkanes was also determined as a sum of unresolved components between predefined equivalent carbon ranges. The developed solventless methodology was compared to an optimized solvent microwave assisted extraction (MAE). Matrix effects could be higher for TD compared to MAE but it depended on sediment matrix. When matrix effect was strong, particularly on HMW-HCs signal depletion, a dilution with pure non-porous sand was favourable for accurate quantification. The sum of resolved and unresolved HCs gave comparable results between MAE and TD extractions, with an exception of alkanes greater than C30 which were less quantitatively extracted via TD. However, TD-GC–MS was more sensitive than MAE-GC–MS. So TD-GC–MS is useful for analyzing sediments containing a great range of paraffinic HCs (C9-C34) and it has the advantages of being fully automated, with few sample preparation and operator intervention, using very low amounts of solvent, and generating few wastes. [ABSTRACT FROM AUTHOR]

Many approaches, which have been developed to express the potential energy of large systems, exploit the locality of the atomic interactions. A prominent example is the fragmentation methods in which the quantum chemical calculations are carried out for overlapping small fragments of a given molecule that are then combined in a second step to yield the system's total energy. Here we compare the accuracy of the systematic molecular fragmentation approach with the performance of high-dimensional neural network (HDNN) potentials introduced by Behler and Parrinello. HDNN potentials are similar in spirit to the fragmentation approach in that the total energy is constructed as a sum of environment-dependent atomic energies, which are derived indirectly from electronic structure calculations. As a benchmark set, we use all-trans alkanes containing up to eleven carbon atoms at the coupled cluster level of theory. These molecules have been chosen because they allow to extrapolate reliable reference energies for very long chains, enabling an assessment of the energies obtained by both methods for alkanes including up to 10 000 carbon atoms. We find that both methods predict high-quality energies with the HDNN potentials yielding smaller errors with respect to the coupled cluster reference. [ABSTRACT FROM AUTHOR]

Complementary feeding of 6‐ to 24‐month‐old infants and young children with adequate, safe and developmentally appropriate food is essential to child health. Inappropriate complementary foods and feeding practices are linked to the high incidences of undernutrition among infant and young children in most developing countries, including Tanzania. Mycotoxin risk is an additional concern, given the documented presence of aflatoxin and fumonisin in food systems of Africa, especially maize and groundnut. In preparation for a trial of mycotoxin mitigation, we conducted focus group discussions and recipe trials to explore complementary foods and feeding practices in Kongwa, a rural district of central Tanzania. Sixty mothers of infants from 6 to 18 months of age in five villages across the district were purposefully sampled. During focus group discussions, mothers reported to mostly feed their children with cereal and groundnut‐based foods as thin or thick porridges. The most common porridge preparations contained cereal (mostly, maize) ranging from 66.7% to 80.0% by weight and groundnuts from 7.7% to 33.3%. The ratio of cereal to groundnut ranged from 3:1 to 4:1. For the recipe trial sessions, mothers chose similar ingredients reported during discussions to prepare complementary foods. The reliance on maize and groundnuts in complementary foods predisposes the children to undernutrition and exposure to aflatoxins and fumonisins. These formative research results suggest multiple intervention points to improve complementary feeding and reduce mycotoxin exposure in this population, including education messages package on feeding practices, mycotoxin control practices and complementary food formulation. [ABSTRACT FROM AUTHOR]

Using a combination of molecular dynamics simulations and first‐principles calculations, the interaction of n‐alkanes with {101¯4} calcite/dolomite is investigated. It is observed that the n‐alkane molecules align preferentially parallel to the interface, despite interaction by weak physisorption, and give rise to distinct adsorption layers. The ordering turns out to be more pronounced on calcite than dolomite due to a smaller average velocity of the n‐alkane molecules. The observations are explained in terms of adsorption energies and charge transfers. The results show that functionalization is no prerequisite of structural ordering and a distinct mass density profile perpendicular to the interface. [ABSTRACT FROM AUTHOR]

We present relaxations in the metastable rotator phase of the n-alkane eicosane (C20H42). The relaxation times found by calorimetry increase with increasing temperature on approaching the melting temperature of the rotator phase. This is the opposite behavior than the one found for classical activated processes. The relaxation behavior found by calorimetry is confirmed by investigations of the lattice structure with X-ray diffraction. It is shown that one lattice parameter of the orthorhombic phase relaxes on the same time scales found in calorimetry, whereas another lattice parameter reacts almost instantly on temperature perturbations. Increasing cooperativity for the creation of conformational defects in the alkane chains is proposed to be responsible for the observed behaviour. [ABSTRACT FROM AUTHOR]

Before applying gas chromatography-gas isotope mass spectrometry (GC-C-IRMS) to analyze the carbon isotopes of normal alkanes, it is necessary to pre-separate and enrich normal alkanes and isoparaffins in saturated hydrocarbon samples. In the pre-separation and enrichment process Whether the carbon isotope fractionation of n-alkane monomer occurs is the key to the high-precision analysis of the carbon isotope ratio (δ 13 C) of n-alkane monomer . In this paper, a mixed solution of n-alkane is used as the object, column chromatography, 5 molecular sieve complexation, cyclohexane-n-pentane mixed solvent is used for two elutions, and the carbon isotope of n-alkane monomer is analyzed by GC-C-IRMS. Whether the carbon isotopes of normal alkanes are fractionated during the process. The results show that the carbon isotope ratio of most n-alkane monomers before and after the separation by column chromatography differs from -0.2% to 0.2%; when the 5 molecular sieve is not completely complexed, the carbon isotope ratio of the uncomplexed n-alkane monomers is about heavier. 0.7%, weak carbon isotope fractionation may have occurred, but it did not affect the eluted n-alkane monomer carbon isotope ratio; before and after elution with cyclohexane-n-pentane mixed solvent, the difference in carbon isotope ratio was -0.2%~0.5%, eluted in the same way for the second time, the obtained n-alkane monomer carbon isotope ratio is different from the simulated sample by -0.3%~0.2%. Analyzing the monomer carbon isotope ratios of normal alkanes with different recovery rates (>20%), the difference before and after treatment is basically within 0.3%. It can be seen that when the recovery rate of normal alkanes is as low as about 20%, the monomer carbon isotope ratios are still No significant fractionation occurred. Column chromatography separation -5 molecular sieve complexation-mixed solvent elution method is suitable for the carbon isotope analysis of normal alkanes monomers with a recovery rate greater than 20%. [ABSTRACT FROM AUTHOR]

In this work, an extension is proposed to the standard iterative Boltzmann inversion (IBI) method used to derive coarse-grained potentials. It is shown that the inclusion of target data from multiple states yields a less state-dependent potential, and is thus better suited to simulate systems over a range of thermodynamic states than the standard IBI method. The inclusion of target data from multiple states forces the algorithm to sample regions of potential phase space that match the radial distribution function at multiple state points, thus producing a derived potential that is more representative of the underlying interactions. It is shown that the algorithm is able to converge to the true potential for a system where the underlying potential is known. It is also shown that potentials derived via the proposed method better predict the behavior of n-alkane chains than those derived via the standard IBI method. Additionally, through the examination of alkane monolayers, it is shown that the relative weight given to each state in the fitting procedure can impact bulk system properties, allowing the potentials to be further tuned in order to match the properties of reference atomistic and/or experimental systems. [ABSTRACT FROM AUTHOR]

The most common volatile substances used in suicide are liquefied petroleum gas mixtures, which consist of propane and butane gases mixed in different proportions. These substances are odourless and colourless. Some substances, such as ethanethiol, are added to liquefied petroleum gas mixtures to provide a garlic scent. The main causes of death in acute liquefied petroleum gas inhalation are cardiac arrest and asphyxia, but determining the manner of death is difficult. We present a case of a 30-year-old man found dead at home. On his head was a black plastic bag with a hole through which he had run a gas hose connected to a domestic liquefied petroleum gas cylinder tank. Toxicological analysis revealed butane and ethanethiol in his body. This study aims at understanding the lethal role of ethanethiol through the analysis of its chemical action and its influence on decomposition. [ABSTRACT FROM AUTHOR]

This study reports the examination of the chronically fuel oil-polluted soil Streptomyces flora and their analysis for harboring the alkane hydroxylase gene (alkB) by PCR. Twenty Streptomyces isolates were recovered and the PCR analysis for the occurrence of alkB gene in the isolates 1d, 1e, 1f, 6a, 9a, and 9k showed three groups with different band size products; group 1 (G1) (215-227 bp), group 2 (G2) (334 bp), and group 3 (G3) (460-550 pb). Variation of the PCR size product of G1 from previous reports probably represents another form of alkB gene in these isolates. [ABSTRACT FROM AUTHOR]

Carpobrotus edulis (L.) is a plant commonly found in the Eastern Cape Province of South Africa and is used for the general treatment of infections relating to the human immunodeficiency virus (HIV). HIV-1 protease plays an important role during HIV replication and maturation to its infectious form, and therefore inhibition of the enzyme is one of the main focus areas in drug development. The inhibitory effect of a water extract of C. edulis leaves against HIV-1 protease activity was determined using the SensoLyte® 520 HIV-1 protease assay fluorimetric kit and employing a HiLyte Fluor™488/QXL™520 fluorescence resonance energy transfer (FRET) peptide. Cytotoxicity of the extract towards HeLa Chang cell lines was determined using an in vitro MTT assay, and the phytochemical profile of the extract was determined with FT-IR and LC-MS. HIV-1 protease activity was inhibited 83.06% (IC50 1.6 mg/ml) (p < 0.0001) by the pepstatin A inhibitor control. Treatment with all C. edulis extract concentrations (16, 1.6, 0.16, and 0.016 mg/ml) inhibited HIV-1 protease activity significantly (p < 0.0001) in a typical dose response manner. With regards to cytotoxicity, the negative controls containing untreated HeLa Chang cells exhibited high formazan formation rates in contrast with the positive controls, containing curcumin, which reduced formazan formation significantly (p < 0.001), exhibiting cytotoxicity towards the cells. There was no significant (p > 0.05) difference in the formazan formation rates between the negative controls and 1, 0.5, 0.125, 0.065, 0.031, and 0.015 mg/ml plant extract, confirming no toxicity of C. edulis extracts towards HeLa Chang cells. Major functional phytochemical compounds identified included alcohols, phenols, alkanes, amines, carboxylic acids, and esters. LC-ESI-TOF/MS analysis revealed the putative identities of main compounds present in the aqueous leaves extract, including some that contribute to its anti-HIV-1 protease action. [ABSTRACT FROM AUTHOR]

Background: M. aboensis has wide ethnopharmacological applications but very little has been done on the pharmacological basis for these indications. This study evaluated the antioxidant potentials of the leaf extracts of M. aboensis. Methods: Total phenolic content of the extract and fractions was carried out using folin-ciocalteu method while in vivo site specific effect determined using carbon tetrachloride (CCl4)-induced liver oxidative damage. Chromatographic separations of the most active fraction led to the isolation of compounds 1 and 2 with their structures elucidated by a combination of 1D and 2D NMR and mass spectrometry. Inhibition of liver microsome lipid peroxidation was used to evaluate the antioxidant activities of these compounds while DPPH test was used to study their interaction. Results: Ethyl acetate fraction had the highest phenolic content of 305.2 mgGAE/g with n-hexane fraction having the least (26.1 mgGAE/g). Structural elucidation revealed compound 1 as epicathechin-(2β→O→7, 4β→8)-cathechin and compound 2 as epicathechin-(2β→O→7, 4β→8)-epicathechin. Compounds 1 & 2 inhibited liver microsome lipid peroxidation with EC50 of 46 and 55 µg/mL respectively. Combination of the compounds produced synergic inhibition of DPPH radical with EC50 of 7 µg/mL against 9 µg/mL produced by ascorbic acid. Conclusion: M. aboensis expressed strong antioxidant property which may explain its diverse ethnopharmacological uses. [ABSTRACT FROM AUTHOR]

Many glove manufacturers of chemical protective clothing produce chemical resistance guides to aid in selection of an appropriate product. Some manufacturers provide permeation data, but others provide a general rating system without reporting testing their own products. A critical issue is that considerable variation in chemical resistance, both with breakthrough times and steady-state permeation rates, have been observed with disposable nitrile gloves. The main purpose of this study was to determine whether significant variation in chemical resistance was present between products from a single brand that provided a generalized chemical resistant guide. The objective was to determine if the ratings noted on the chemical resistance guide were sufficient for protection against chemical permeation. The chemical permeation of ten disposable nitrile gloves against three organic solvents of varying polarity (cyclohexane, tert-butanol, and cyclohexanol) was performed in triplicate. Despite the similar chemical resistant ratings for the products, significant variation in both breakthrough times and steady-state permeation rates were observed among the ten nitrile gloves. The largest variation in breakthrough time was about 8-fold. The largest variation in steady-state permeation rate was about 177-fold. A proposed chemical resistance rating system was used to further evaluate the variation in performance, as it would relate to similar rating systems used by glove manufacturers or brands. Polarity played a role in the observed performance, with the nitrile gloves providing increased protection with an increase in solvent polarity, more notably with the dielectric constant. Using a proposed rating system, the percentages of products rating as excellent to good were 20% (cyclohexane), 60% (tert-butanol), and 90% (cyclohexanol). Ultimately, the ratings noted on the general chemical resistance guide were not sufficient for worker protection against chemical permeation. It is not valid to assume that little variation should exist among the different glove products under a same brand or based on the use of generic chemical resistant data. When critical, occupational health and safety professionals should base glove selection on product-specific chemical permeation data. [ABSTRACT FROM AUTHOR]

Accidental fuel oil spills and improper disposal of toxic waste oil into waterways have caused serious pollution problems worldwide. This study is focused on the use of microorganisms and enzymes they produce to address problems of waste oil pollution. Complete genes for enzymes alkane 1-monooxygenase (AlkM) and catechol 1,2-dioxygenase (CatA) implicated in bunker oil degradation were amplified and sequenced from two new strains of Acinetobacter baumannii (S341 and S354) isolated from the polluted Pasig River in the Philippines. Genes for both AlkM and CatA enzymes and predicted proteins exhibited almost identical sequences with the type strain A. baumannii (ATCC 19606). Sequence identity (80%) of alkM genes is lower than the sequence identity (90%) of predicted enzymes between A. baumannii environmental strains and most of the other species under the same genus. Genes for AlkM (or for enzymes with equivalent functions as AlkM like AlkB) and CatA from species that do not belong to the genus Acinetobacter exhibited very low gene and protein sequence identities (49.8-54.6%) with corresponding genes and proteins in strains S341 and S354. Stretches of conserved amino acids in the predicted protein sequences (eight histidine motifs in AlkM/AlkB) and a ferric ion ligated by four amino acids (Tyr164, Tyr200, His224, and His226) in the CatA protein were observed, consistent with previous reports. These conserved regions may be crucial in protein function. The study also reports the successful cloning, in the correct orientation, of complete alkM and catA genes from A. baumannii strains S341 and S354 in pBAD Thio-TOPO plasmid for future expression of the recombinant proteins in non-pathogenic host cells. [ABSTRACT FROM AUTHOR]

Background: Commelina benghalensis Linn. (Family: Commelinaceae) is a common weed available in Bangladesh with several uses in traditional medicine. However, the chemical profile of this medicinal plant is scarce in relation to its medicinal uses. The aerial parts of this plant have been investigated for the isolation of secondary metabolites and evaluation of the biological activities. Methods: Major phytochemical groups were analyzed using chromogenic reagents, whereas n-hexane soluble fractionates of the methanol extract were subjected to 1H nuclear magnetic resonance (NMR) spectroscopic analysis. The antioxidant property of the obtained compounds was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH). Results: Dammara-12-en-3-one (CB-1), stigmasterol (CB-2) and 3 (2,3,4,5,6-pentahydroxy)-cinnamoyl dammara-12-ene (CB-3) were isolated from the n-hexane fractionate of methanol extract of C. benghalensis. In the study of DPPH radical scavenging activity, IC50 values were predicted to be 790.18, 4186.94 and 2001.16 µg/mL for CB-1, CB-2 and CB-3, respectively, whereas standard ascorbic acid showed IC50 at 1.26 µg/mL. Conclusions: Two new dammarane-type triterpene (CB-1 and CB-3) and one phytosterol (CB-2) were identified in C. benghalensis with mild antioxidant property. [ABSTRACT FROM AUTHOR]

Development of micro gas chromatography (μGC) is aimed at rapid and in situ analysis of volatile organic compounds (VOCs) for environmental protection, industrial monitoring, and toxicology. However, due to the lack of appropriate microcolumns and associated stationary phases, current μGC is unable to separate highly volatile chemicals such as methane, methanol, and formaldehyde, which are of great interest for their high toxicity and carcinogenicity. This inability has significantly limited μGC field applicability. To address this deficiency, this paper reports the development and characterization of a microfabricated porous layer open tubular (μPLOT) column with a divinylbenzene-based stationary phase. The separation capabilities of the μPLOT column are demonstrated by three distinct analyses of light alkanes, formaldehyde solution, and organic solvents, exhibiting its general utility for a wide range of highly volatile compounds. Further characterization shows the robust performance of the μPLOT column in the presence of high moisture and at high temperatures (up to 300 °C). The small footprint and the ability to separate highly volatile chemicals make the μPLOT column highly suitable for integration into μGC systems, thus significantly broadening μGC's applicability to rapid, field analysis of VOCs. [ABSTRACT FROM AUTHOR]

Currently, there is relatively limited research on the organic components of condensable particulate matter (CPM o). This work quantitatively investigated two typical CPM o : high-toxic polycyclic aromatic hydrocarbons (PAHs) and high-content normal alkanes (n-alkanes). The effects of oxygen content (OC) and exhaust temperature (ET) on their emission concentrations were explored. The results showed that the percentage of CPM o in this work were relatively large, averaging 81.22% in different operating conditions. CPM o were greatly affected by the OC. Under different OC and ET conditions, PAHs in CPM o were mainly concentrated in 4- and 5-ring, with a relatively small proportion in others. The minimum amount of PAHs was generated under the high OC and the low ET condition. After analyzing the toxic equivalent quantity (TEQ), it was found that 5-ring PAHs were the largest contributors to TEQ, followed by 4- and 6-ring PAHs. PAHs with higher concentrations do not necessarily have higher toxicity. In addition, the emission concentration of n-alkanes showed a unimodal distribution under different conditions, with the highest concentration of n-alkanes between C22 and C32. The concentration of n-alkanes gradually increased as the ET decreased and the OC increased. [Display omitted] • Quantitative studies were performed on polycyclic aromatic hydrocarbons (PAHs) in CPM. • Quantitative analysis of normal alkanes (n-alkanes) in CPM was investigated. • 4- and 5-ring PAHs and C22–C32 n-alkanes are the dominant organic components in CPM. • The risk of PAHs in CPM is suggested to be assessed by the toxic equivalent quantity. • Combustion adjustment is helpful for the reduction of PAHs and n-alkanes. [ABSTRACT FROM AUTHOR]

Background: Gastric Ulcer (GU) is the most prevalent gastrointestinal disorder induced by various factors and Non-Steroid Anti-Inflammatory Drugs (NSAIDs) as one of the most common reasons. Due to the absence of appropriate molecular markers for GU, the aim of this study was to utilize a metabolomics approach in order to find potential metabolite markers for the disease. Methods: Stomach tissue samples from indomethacin-treated rats and normal controls were used to perform a 1H-NMR metabolomics study. The altered metabolites were identified using random forest multivariate analysis. Results: ROC curves showed that the random forest model had a good predictive performance with AUC of 1 for the test and 0.708 for the training sets. Seventeen differentially expressed metabolites were found between GU and normal tissue sample. These metabolites included trimethylamine, betaine, carnitine, methionine, acetylcho line, choline, N,N-Dimethylglycine, cis-aconitate, tryptophan, spermidine, acetylcarnitine, creatinine, pantothenate, taurine, isoleucine, glucose and kynurenine. Conclusion: The results of the study demonstrated that metabolomics approach could serve as a viable method to find potential markers for GU. Surely, further studies are needed for the validation of the results. [ABSTRACT FROM AUTHOR]

Abstract Ethnopharmacological relevance In Mexico, plants are an important element of traditional medicine, and many are considered part of Mexican cultural heritage from prehispanic and colonial times. Nevertheless, relatively few systematic scientific studies have been conducted to fully characterize the chemical composition and pharmacological activities of Mexican medicinal plants. Acacia farnesiana is used in Mexican traditional medicine to treat dysentery and tuberculosis and therefore could have bioactive compounds that may explain its traditional use. Aims of the study i) To isolate and characterize the compounds from the hexanic, chloroformic and methanolic extracts; ii) to identify the volatile compounds from methylated hexanic and chloroformic extracts using GC-FID and GC-MS methods; iii) to identify the compounds from methanolic and aqueous extracts using HPLC-Q-TOF-MS; iv) to test the activity of extracts and isolated compounds against Mycobacterium tuberculosis and dysentery bacteria. Material and methods A. farnesiana fruits were collected in Acatlán de Osorio, Puebla, Mexico. Hexanic, chloroformic, methanolic and aqueous extracts were prepared and analyzed by different chromatographic techniques including column chromatography, flash chromatography, GC-FID, GC-MS and HPLC-Q-TOF-MS. Structural elucidation was carried out by NMR spectroscopic analysis. The activity of extracts, phytochemicals and semi-synthetic derivatives against Mycobacterium tuberculosis H37Rv and G122 as well as dysentery bacteria (Campylobacter jejuni , Shigella flexneri , Salmonella enteritidis , Yersinia enterocolitica and enterohemorrhagic Escherichia coli) was determined by the broth microdilution method and reported as minimal inhibitory concentration (MIC µg/mL). Results From both hexane and chloroform extracts, tetracosanoic acid (2 S)-2,3-dihydroxypropyl ester (1) and (3β,22 E)-estigmasta-5,22-dien-3-yl β-D-glucopyranoside (2) were isolated and characterized. From the methanolic extract, methyl gallate (3), gallic acid (4), (3β,22 E)-estigmasta-5,22-dien-3-yl β-D-glucopyranoside (2), (2 S) naringenin 7- O -β-glucopyranoside (prunin, 5), pinitol (6) and sucrose (7) were isolated and characterized. Furthermore, hexanic and chloroformic extracts were analyzed by GC-FID and GC-MS and 18 methylated fatty acids were identified for each extract in addition to three sterols. The methanolic and aqueous extracts were analyzed separately by HPLC-Q-TOF-MS, and 15 compounds were identified in each extract. The compounds 1 , 2 , and 7 , in addition to 13 fatty acids and eight phenolic compounds, were identified for the first time in A. farnesiana. The extracts showed antitubercular (MIC 100–200 µg/mL) and antidysentery activity (MIC 100–200 µg/mL). Methyl gallate and its acetylated derivative showed activity against the sensible strain M. tuberculosis H37Rv with MIC values of 50–25 µg/mL, respectively. The flavanone prunin showed activity against multidrug resistant M. tuberculosis G122 (MIC 50 μg/mL). Methyl gallate, gallic acid and prunin showed activity against C. jejuni (MIC 50 μg/mL). Conclusions The activity of tested extracts and isolated compounds against M. tuberculosis and dysentery bacteria justifies the ethnomedical use of A. farnesiana fruits for the treatment of tuberculosis and dysentery. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Graphical abstract Water-mediated self-assembly of an n -alkane with two single-sided capped carbon nanotubes resulting into a nano-capsule that triggers length-dependent conformational alterations in captured alkanes. Abstract Molecular conformations significantly influence the properties of materials. Both internal interactions as well as external impacts can trigger conformational revamping of molecules. By employing molecular dynamics simulations, here we have investigated shift in conformational motifs of n -alkanes confined within a minuscule hydrophobic cavity of self-sustaining capsular assembly of two capped carbon nanotubes. Depending upon relative host-guest dimensions, encapsulated n -alkanes depict either coiling or uncoiling with further adoption of gauche -rich helical structure or trans -dominated extended configuration. Mutual alkane-CNT and CNT-CNT vdw interactions along with the favorable dehydration of their hydrophobic surfaces drive the formation and sustenance of self-assembly. Further segregation of atomistic-level energetic interactions between host-guest molecules revealed that twisting in longer n -alkanes induces a dihedral strain giving an entropic penalty to the strength of formation of self-assembly, which however gets compensated by enhanced vdw interactions between n -alkanes and aromatic surfaces of capped nanotubes. [ABSTRACT FROM AUTHOR]

Abstract Short-chain chlorinated paraffins (SCCPs) are produced in high volume and have the high potential to pose a threat to human health. However, little information is available for SCCP contamination in human blood/plasma/serum, mainly due to the difficulty of sample preparation and quantitative analysis. A method using high resolution gas chromatography coupled with electron capture negative ionization low resolution mass spectrometry (HRGC–ECNI/LRMS) was developed and validated to measure SCCPs in human plasma. The pretreatment process included protein denaturation and lipid elimination, liquid–liquid extraction with a mixture of n -hexane/dichloromethane (1:1, V/V), and cleanup on a multi-layer silica column. The blank controls, including procedural blank, vacuum blood collection tube blank, and instrumental blank, were the most pivotal points for the reliable analysis of SCCPs. The average value of procedural blanks was 9.0 ng/g; and the method detection limit (MDL), calculated as the sum of the average procedural blank value and 3 times of the standard deviation of the procedural blanks, was 12.6 ng/g plasma. The validated method was applied to measure the concentrations of the total SCCPs (∑ SCCPs) in 50 plasma samples from a general population. The measured plasma concentrations of ∑ SCCPs ranged from < MDL to 203 ng/g wet weight (ww), with an average value of 32.0 ng/g ww. The relative abundance profiles of SCCPs in plasma samples were dominated by C 10 - and C 11 -CP congener groups centered on Cl 6–7. The developed method can be used for the comprehensive and large-scale investigation of SCCP levels in human plasma. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Four oil-bearing sandstone samples of Chang 8 sub-unit were collected from Ordos basin and geochemical characteristics of hydrocarbon in different states during oil-filling process were determined. The occurrence of hydrocarbon in sandstone can be divided into four types by using sequential extraction. The features of alkanes, the diagram of Pr/nC17 versus Ph/nC18 and the cross plot of MPI-1 versus Rc show that four type hydrocarbons derived from same source rock, the organic matter includes aquatic organisms and higher plants, moreover, the thermal maturity of the free hydrocarbon is the highest, followed by the sealed hydrocarbon and the cement hydrocarbon, and the inclusion hydrocarbon is the lowest. The variation of geochemical features of hydrocarbons in different states may result from continuous oil-charging in geological history. [ABSTRACT FROM AUTHOR]

Abstract This work measured data of binary mixtures {CO 2 + n- hexane}, {CO 2 + tetralin}, {CO 2 + n- hexadecane} at high pressure, {tetralin + n- hexadecane} system at low pressure, and the ternary systems {CO 2 + n- hexane + tetralin} and {CO 2 + tetralin + n- hexadecane} at high pressures. Two experimental methodologies were used: synthetic static method and analytical dynamic method. The data obtained at high pressure were used to determine the binary interaction parameters using the Peng-Robinson equation of state and classical mixing rules. Regarding the low pressure data, the binary interaction parameter for the {tetralin + n- hexadecane} system was predicted by literature correlations and adjusted to correlate our experimental data. The binary parameters were also used to predict the behavior of the ternary systems {CO 2 + n- hexane + tetralin} and {CO 2 + tetralin + n- hexadecane} at high pressures. The model did not predict so accurately the bubble and dew pressures for the ternary systems at high temperatures and elevated CO 2 compositions using the parameters obtained from binary systems but the results were reasonable compared to experimental results. [ABSTRACT FROM AUTHOR]

Abstract Permeation measurements indicate that a SSZ-13 membrane exhibited significantly different adsorption behavior from SSZ-13 crystals. Both C 3 H 8 and n-C 4 H 10 adsorb to high loadings in SSZ-13 crystals, but they only have a small effect on CO 2 permeation through a SSZ-13 membrane at 293 K, indicating they do not adsorb in the SSZ-13 pores. Whereas 15% C 2 H 6 in the membrane feed decreased CO 2 permeance by 45%, 15% C 3 H 8 only decreased CO 2 permeance by 10%, even though C 3 H 8 adsorbs more strongly than C 2 H 6 in SSZ-13 crystals. Moreover, this 10% decrease is attributed to C 3 H 8 adsorption on the external surface of the membrane crystals because i-C 4 H 10 , which is significantly larger than SSZ-13 pores and thus does not adsorb in the pores, only decreased CO 2 permeance by 15%. The difference between SSZ-13 crystals and the SSZ-13 membrane is attributed to the presence of a diffusion barrier on the external surface of the membrane crystals. Thus, care should be taken in using adsorption measurements on zeolite powders to predict permeation behavior in zeolite membranes. Highlights • C 3 H 8 and n-C 4 H 10 did not adsorb in the pores of an SSZ-13 membrane even though they adsorbed in SSZ-13 crystal powders. • As a result, C 3 H 8 and n-C 4 H 10 reduced the CO 2 permeation through a SSZ-13 membrane much less than CH 4 and C 2 H 6. • CO 2 /C 3 H 8 separation selectivities greater than 104 were measured for the SSZ-13 membrane, indicating few defects. • Molecules too large to enter zeolite crystals can affect permeation through membranes by adsorbing on the external surface. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) as methane adsorbents are highly promising materials for applications such as methane‐powered vehicles, flare gas capture, and field natural gas separation. Pre‐ and post‐synthetic modification of MOFs have been known to help improve both the overall methane uptake as well as the working capacity. Here, a post‐synthetic modification strategy to non‐covalently modify MOF adsorbents for the enhancement of the natural gas uptake for the MOF material is introduced. In this study, PCN‐250 adsorbents were doped with C10 alkane and C14 fatty acid and their impact on the methane uptake capabilities was investigated. It was found that even trace amounts of heavy hydrocarbons could considerably enhance the raw methane uptake of the MOF while still being regenerable. The doped hydrocarbons are presumably located at the mesoporous defects of PCN‐250, thus optimizing the framework–methane interactions. These findings reveal a general approach that can be used to modify the MOF absorbents, improving their ability to be sustainable and renewable natural gas adsorption platforms. A non‐covalently modified mesoporous metal–organic framework (MOF) with long‐chain hydrocarbons could significantly increase the already high methane uptake. The long‐chain fatty acid was assumed to be coordinated to the open metal site and located at the mesoporous defects of the MOF. Through optimized partitioning of the mesoporous space of MOF by the doped hydrocarbons, more methane was packed into the pores of the MOF through hydrophobic interactions. [ABSTRACT FROM AUTHOR]

Abstract Lake Bolătău-Feredeu is a small (surface: 0.3 ha; catchment area: 31 ha) landslide-dammed lake in Bukovina (Eastern Carpathians, Romania). Elemental concentration, stable isotope composition of carbon and nitrogen, and n-alkane composition of the saturated hydrocarbon fraction of the organic material were analyzed along the sediment profile from Lake Bolătău-Feredeu covering the past ∼700 years. The ranges of δ 13C values (−30.5 to −26.6‰) and C/N atomic ratios (10.5 and 15.4) placed the organic material of the recent Bolătău-Feredeu sediment between the C3 Land Plants and the lacustrine algae. The n-alkane proxies provide better distinction between organic matter inputs. Detected major shifts in the n-alkane composition and the C and N concentrations along with the stable isotope compositions pointed towards three distinct stages in the environmental history of the lake-catchment system. The proxy information indicate a substantial landscape change characterized by deforestation and an increase in open pastureland with herbaceous vegetation from ∼1820. The C/N, δ 15N, and δ 13C values showed the highest variability probably linked to a variable lacustrine environment and decreased productivity in the catchment between ∼1640 and 1760. It can be assumed that the extended periods of lake ice cover during the cold decades experienced at the turn of the 17th-18th centuries resulted in diminished biological productivity both in the lake and its catchment. Finally, afforestation and the decline in lake productivity have been reconstructed for the period of ∼1470–1560. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Investigation of leaf wax n -alkanes was conducted in the Chinese Loess Plateau. • Average chain length could be utilized to distinguish between gymnosperms and angiosperms. • A P v index provided a new tool for distinguishing between dicots and monocots. Abstract Terrestrial ecosystems generally contain various plant types (e.g. dicots, monocots, gymnosperms), and an evaluation of the dominant plant type in an ecosystem is the key to understanding geological records in paleoenvironmental research. In this study, we examined n -alkane chain length distributions in terrestrial higher plants in the central Chinese Loess Plateau, and found that average chain length (ACL) could be utilized as an indicator for differentiating gymnosperms from angiosperms. ACL 21–33 was less than 27 for gymnosperms, but more than 27 for angiosperms. Moreover, a derived P v index from a selected n -alkane ratio, (i.e. (C 31 + C 33)/ΣC n(n=27–33)), provided a relative criterion for distinguishing between dicots and monocots within the angiosperms. When P v < −0.1, the ecosystem was predominated by dicots, but those with P v > 0.1, were dominated by monocots. Discrimination of the dominant plant type in an ecosystem is important when leaf wax n -alkanes are used as a proxy for paleoenvironmental reconstructions. [ABSTRACT FROM AUTHOR]

The performance of metal-organic frameworks in gas chromatographic separation investigations has been widely study in recent years. However, to use chromatographic methods to determine materials properties of metal-organic frameworks instead of using them just for analyte separations is a field still largely unexplored. The presented study has been conducted to quantify the systematic changes in the interaction of a series of related unbranched aliphatic analytes (C2-C10) with HKUST-1 as the stationary phase not only to obtain information about the MOF analyte interaction strength but also to gain materials parameters characterizing the MOF system, like its response to non-specific interactions. Thermodynamic as well as by kinetic parameters governing the adsorption process were determined using various chromatographic evaluation techniques. The method of inverse chromatography was used to derive the generic susceptibility of HKUST-1 to aliphatic methylene groups and to determine interfacial energy contributions of the intrinsic surface of the porous material. [ABSTRACT FROM AUTHOR]

This work presents an approach to accurately modeling the mutual solubilities and multiphase behavior of aqueous systems. For this purpose, a new PC-SAFT parameters set for water was proposed and temperature-dependent binary interaction parameters, k ij (T) were determined by fitting to the mutual solubilities data of water/n-hexane and water/benzene mixtures. These k ij (T) have been used to predict the mutual solubility and multiphase equilibria of similar mixtures for an extended temperature range up to 473 K. Very good agreement between predicted results and available experimental data has been obtained, including the description of the minimum of hydrocarbon solubility in water as a function of temperature. The model's overall average relative deviations from experimental data were 19.9% and 18.1% for the solubility of water in organic phase and of hydrocarbons in aqueous phase, respectively. To test the model's capabilities, the parameters were used to predict multiphase behavior for water-alcohol-hydrocarbon ternary systems and gave good results compared with experimental data. [ABSTRACT FROM AUTHOR]

The viscosity of fluid is known as resistivity of fluid to flow and straightly affected by temperature and pressure. As it is obvious, the viscosity of reservoir fluid is known as one of the critical parameters which extensively effect on production. Therefore, in the present paper, multilayer perceptron artificial neural network (MLP-ANN) is used as a novel and accurate model to predict dynamic viscosity of normal alkanes in the operational conditions. To this end, 228 dynamic viscosity points as function of carbon number of n-alkane, temperature, and pressure were collected from a reliable paper. The comparison between MLP-ANN outputs and experimental dynamic viscosities is performed in graphical and statistical manners. The calculated coefficients of determination 0.99739 and 0.99051 for training and testing phases express the great ability of MLP-ANN algorithm in prediction of dynamic viscosity of n-alkane. According to the analysis, MLP-ANN has enough accuracy and potential to be used as software for which applicable in petroleum industry. [ABSTRACT FROM AUTHOR]

The performance of a thermodynamic wax precipitation model strongly depends upon the n-paraffin thermophysical properties used. In order to estimate them, several correlations have been proposed, and their values have a great impact on both calculated wax disappearance temperature (WDT) and amount of wax precipitated at each temperature (WPC). The main goal of this work is to evaluate the correlations available for the relevant thermophysical properties aiming at achieving a reliable wax precipitation modeling. The methodology used involves the direct comparison of the correlations with the values of pure n-paraffin properties, and indirect evaluation by their use in the estimation of wax disappearance temperatures, the amount of wax precipitated at each temperature, and DSC experimental curves. This study contemplates two thermodynamic approaches for paraffin precipitation: the solid solution (SS), which considers the formation of one solid solution; and the multisolid phase model (MS), that assumes that each solid phase consists of a pure component. [ABSTRACT FROM AUTHOR]

The addition of tin (Sn) is commonly used as a design strategy for catalyst optimization of platinum-based catalysts. The mechanistic understanding of this class of systems is, however, obscured by the structural complexity. Herein, a series of catalyst characterization techniques including X-ray absorption fine structure (XAFS) and in-situ CO diffuse reflectance infrared fourier transform spectroscopy (CO-DRIFTS) were utilized to study the catalyst structure. It was found that the structure and catalytic properties are closely related with the interaction between Pt and SnO 2 (specifically the Pt-SnO 2 strong metal-support interaction (SMSI)), which can be continuously tuned by thermal treating the Pt-Sn/SiO 2 precursor at different atmospheres and temperatures. The treatment in an oxidative atmosphere (O 2 ) also can generate Pt-SnO 2 SMSI, which became weak at higher temperatures and led to the growth of Pt nanoparticles (NPs). Pt-SnO 2 SMSI became stronger when the oxygen atmosphere was changed to an inert (N 2 ) atmosphere. Small metallic Pt NPs were formed and their dispersion was increased with increasing treatment temperature with inert gas. The catalyst presented a moderate activity in the dehydrogenation of lower alkanes. The treatment in a reductive atmosphere (H 2 ) produced the strongest Pt-SnO 2 SMSI and most active catalyst. Highly dispersed Sn surface-enriched Pt–Sn alloy NPs were formed on SiO 2 , in which Pt was most electron rich. The apparent activation energy in n -butane dehydrogenation is higher on Pt–Sn/SiO 2 _1073 K H 2 than the corresponding one on Pt–Sn/SiO 2 _1073 K N 2 . The kinetic studies revealed that the extreme isolation of Pt on Pt–Sn/SiO 2 _1073 K H 2 (geometrical effects) dominantly contributed to its superior catalytic performance. The present work highlights the effects of thermal treatment-induced Pt-SnO 2 SMSI, providing a new insight into the structure of Pt–Sn bimetallic catalysts and the promotional role of Sn in the dehydrogenation of lower alkanes to olefins on Pt surfaces. [ABSTRACT FROM AUTHOR]

One of the important thermophysical properties is viscosity which expresses the resistance of fluid to flow. The least squares support vector machine (LSSVM) algorithm is proposed as a novel method for prediction of dynamic viscosity of different normal alkanes in a wide range of pressure and temperature. As this study is purely computational, 228 experimental data points were gathered from literature for training and validation of the model. The outcomes of the LSSVM algorithm were compared with the actual data with acceptable average absolute relative deviation and the coefficient of determination (R2) of 1.014 and 0.9968, respectively. The comparisons showed that the predicting model has the potential of prediction of n-alkane dynamic viscosity in terms of pressure, temperature, and carbon number of n-alkane, so this strategy can be used as a simple tool for predicting the behavior of reservoir fluids. [ABSTRACT FROM AUTHOR]

Vernonia anthelmintica Willd. seeds have been used in folk medicine for the treatment of leukoderma in Xinjiang, China, for more than 300 years. The promoting activities of its volatile oil (AVO) in melanogenesis and its chemical composition were investigated in this paper. The bioactivities of AVO were examined by melanin synthesis and tyrosinase activity assay in B16 cells. Using GC-QTOF-MS technology, each compound of AVO contains a single separated peak in GC and the retention indices of every GC peak were calculated by the retention times of C7~C30 n-alkanes that were injected at the same chromatographic conditions. Then each individual peak was identified by comparing its mass spectrum with the MS library (NIST 14). As a result, AVO increased the melanin content and tyrosinase activity in a dose-dependent manner at concentrations of 10-30μg·mL−1. The 64 compounds were identified in AVO which occupied 95.15% of total peak area in GC. They mainly contained caryophyllene (23.73%), sabinene (18.15%), α-thujene (6.57%), thymol (5.29%), 4-epi-α-acoradiene (4.98%), limonene (4.92%), anethole (3.44%), etc. According to the results the AVO can promote melanogenesis and upregulate tyrosinase activity in B16 cells. [ABSTRACT FROM AUTHOR]

Abstract: Synthesis of a well‐defined CuII complex 1 featuring a phenanthroline‐based tridentate scaffold, 2‐pyrazol‐(1,10‐phenanthroline) (L) and studies of its catalytic activity in the cross dehydrogenative coupling of acids with common alkanes to form allylic esters are reported. The complex 1 showed excellent catalytic activity in the oxidative cross dehydrogenative coupling of a wide variety of alkanes with acids to form the corresponding allylic esters in moderate to high yields. Several control experiments along with spectroscopic studies were carried out to characterize catalyst 1 and to explore the plausible mechanistic pathways. [ABSTRACT FROM AUTHOR]

Challenging functionalization of C(sp 3 )-H has recently attracted much attention of organic chemists. In this paper, we developed a Ni(acac) 2 -catalyzed activation of unreactive alkanes with formanilides in the presence of carbon monoxide to furnish moderate to excellent yields of amides. This is the first example of aminocarbonylation of inert alkanes using nickel-based catalyst, and formanilides is disclosed to be an interesting amine source owing to the peculiar deformylation nature of imide intermediates. [ABSTRACT FROM AUTHOR]

Studies of occluded oxygen-bearing compounds inside kerogen are scarce, although such studies are important in understanding early-stage transformation of organic matter. A relatively low-maturity kerogen from the late Permian mudstone of the Lucaogou Formation of the Santanghu Basin, northwestern China, was successively extracted with n -hexane, acetone and dichloromethane to release the adsorbed components, and the extracted kerogen was treated with a mild oxidation reagent H 2 O 2 to release the occluded components. Gas chromatography–mass spectrometry analysis of the adsorbed and occluded components revealed a suite of oxygen-bearing compounds, including n -alkan-2-ones, n -aldehydes and fatty acid methyl esters. The n -alkan-2-ones were mainly detected in the adsorbed fraction and n -aldehydes in the occluded component. Comparison of the long-chain oxygen-bearing compound distributions and their individual stable carbon isotope characteristics both suggest that the oxygen-bearing compounds released by H 2 O 2 treatment were occluded in the kerogen. The shorter-chain (C 15 to C 19 ) occluded n -aldehydes reflected similar isotopic distribution trends to the adsorbed n -alkan-2-ones, and the δ 13 C values of the mid-length (C 21 to C 25 ) occluded n -aldehydes were much closer to the adsorbed n -alkanes. Bacterially mediated methylation and decarbonylation of the n -aldehydes during kerogen formation may be important source(s) of n -alkan-2-ones and n -alkanes, respectively. The mid-chain ketones mainly originated from hydrothermal alteration of n -alkanes after kerogen formation. Uplift of the Lucaogou Formation in the Yuejingou section allowed surface-enhanced aerobic reactions. [ABSTRACT FROM AUTHOR]

Leaf wax n -alkanes provide a valuable palaeoecological proxy, but their interpretation requires an understanding of the scale of temporal and spatial integration in soils. Leaf wax n -alkanes are continually deposited into soils directly from local plants as well as from more distant plants via wind or water transport. In addition, n -alkanes can persist in soils for thousands of years, and tend to decrease in age with shallower depth. To explore whether the uppermost soils reflect recent leaf fall inputs we compared surface soils and modern vegetation from 20 sites along a transect across Australia. At each site, the three most dominant plant species and a soil sample from the top 3 cm were analysed for n- alkane concentration, average chain length (ACL), proportional abundance of C 33 and C 29 (Norm33) and carbon preference index (CPI). Chain length distributions differ between trees and grasses, with a higher proportion of C 29 in trees and C 33 in grasses. Norm33 in soils correlates with proportional grass to tree cover across the transect. To model n -alkane inputs for each site, we calculated a predicted ACL, Norm33 and CPI using the dominant plants at that site, weighted by proportional species cover and n -alkane concentration. Predicted ACL, Norm33 and CPI inputs were generally higher than the soils, demonstrating that recent and local inputs do not dominate soil n- alkanes at our study sites. Thus, n -alkane distributions in surface soils do not correlate with local, current vegetation, but do correlate with proportional grass and tree cover, suggesting they provide a faithful record of large scale ecosystem structure. [ABSTRACT FROM AUTHOR]

Abstract: For the initial activation of short-chain alkanes over Zn/HZSM-5 catalyst, the impact of branching degree and carbon numbers of reactants on the competition between dehydrogenation and cracking was systematically studied by experiment and calculation. The experiments were carried out on fixed-bed flow micro-reactor over HZSM-5 and Zn/HZSM-5 catalysts, by using n-butane/i-butane and propane/n-hexane as reactants with different branching degree and carbon numbers. Compared with HZSM-5, Zn/HZSM-5 obviously accelerated the cracking of C-H bond of short-chain alkanes and increased the selectivity of BTX aromatics. The selectivity to hydrogen produced from n-butane and n-hexane was higher than i-butane and propane, respectively. On the contrary, the selectivity to methane was correspondingly lower, i-butane and propane with high percentage of terminal carbons effectively suppressed the dehydrogenation. The key point to decide the reaction process through dehydrogenation or cracking is the initially activated sites of reactant. To verify this conclusion, theoretical calculations were carried out. The results showed that the (Zn-O-Zn)2+ Lewis acid sites of Zn/HZSM-5 accelerated the cracking of C-H and C-C bond simultaneously. Namely, if the initial activation occurred on the terminal carbons of reactant, the subsequent reaction would be kinetically competitive between cracking and dehydrogenation. Cracking would inevitably occur (thermodynamically favorable), and then the by-products of methane and ethane were produced in large amount. If the initial activation occurred on the internal carbons, the dehydrogenation reaction is kinetically favorable, which is beneficial to reducing the dry gas production. Therefore, cracking is more favorable than dehydrogenation for smaller alkanes and branched alkanes with high percentage of terminal carbons.Graphical Abstract: The percentage of terminal carbons of short-chain alkanes determines the probability of dehydrogenation route over Zn/HZSM-5. The activation of the internal carbon via the dehydrogenation route is more favorable for the normal alkane with higher carbon number during the first stage of conversion suppressing the formation of the by-products of methane and ethane. [ABSTRACT FROM AUTHOR]

Accurate determination of the bond dissociation energies (BDEs) of large alkanes is desirable but practically impossible due to the expensive cost of high-level ab initio methods. We developed a two-layer ONIOM-CCSD(T)/CBS method which treats the high layer with CCSD(T) method and the low layer with DFT method, respectively. The accuracy of this method was validated by comparing the calculated BDEs of n-hexane with that obtained at the CCSD(T)-F12b/aug-cc-pVTZ level of theory. On this basis, the C-C BDEs of C 6 -C 20 n-alkanes were calculated systematically using the ONIOM [CCSD(T)/CBS(D-T):M06-2x/6-311++G(d,p)] method, showing a good agreement with the data available in the literature. [ABSTRACT FROM AUTHOR]