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The concept of the genus Clinopodium L. has changed considerably since its first description. Most of the currently accepted species of the genus have traditionally been treated as separate genera in the group Satureja sensu lato: Clinopodium L., Calamintha sensu Miller or Moench, and Acinos sensu Miller or Moench. This study aimed to gain a better insight into the species diversity of Clinopodium L. from the Balkans by analyzing the taxa that have traditionally been placed in separate genera. The alkane profile and the micromorphological characteristics of the leaves are analyzed. The leaves are visualized using scanning electron microscopy, and alkanes are isolated using n-hexane as a solvent and analyzed using gas chromatography/mass spectrometry. The alkane profile showed the differentiation of the Acinos-group from the other taxa based on the dominant n-C31, while most of the other taxa contained n-C33 as the dominant alkane. The micromorphological features also showed clear differences between the previously recognized genera, especially in the capitate trichomes. The results showed that micromorphological patterns are highly variable in certain groups of the genus Clinopodium. [ABSTRACT FROM AUTHOR]

In the present work, the emission of volatile organic compounds (VOCs) from plastic packaging materials and their migration to the packaged product was investigated. Fresh-cut artichokes were chosen as a case study owing to their nutritional profile, including phenolic compounds, antioxidants, inulin and fiber, and the high market demand. Artichokes were cut into quarters, packaged in active modified atmosphere (5% O2 and 10% CO2) in three different micro-perforated (MP) packages (polypropylene (PP), polypropylene/polyamide (PP/PA) and polylactic acid (PLA)) and stored for 10 days at 5° C. For the detection of VOCs on the packaging materials and in the packaged product, three approaches were considered. First, VOCs emitted from a piece of package were extracted by solid phase micro extraction (SPME), at 30°C, and analyzed by gas-chromatography coupled to mass spectrometry (GC–MS). Second, VOCs from the headspace of the empty closed bag were extracted by SPME, at 5°C, to understand if any packaging volatile compound was transferred into the package atmosphere in this temperature condition. Finally, packaged artichokes were also analyzed by SPME/GC–MS to detect any presence of packaging volatiles compared to the fresh product. Emitted VOCs were different according to the material; in particular PP/PA emitted the greatest number of VOCs, most of them belonging to the class of branched alkanes and alkenes, such as 4-methyl-heptane, 2,4-dimethyl-heptane, 4-methyl-octane and 2,4 dimethyl heptene; PP emitted octane, aldehydes, and 1-metoxy-2-propanol; PLA emitted aldehydes and propanoic acid. Some VOCs were found into the atmosphere of the empty bags as well as on packaged artichokes, while they were not found in the fresh samples before packaging, suggesting that a study on the emission of VOCs from different plastic materials in contact with food and on the effect of different storage conditions is very critical for a better understanding of this issue.

The concept of the genus Clinopodium L. has changed considerably since its first description. Most of the currently accepted species of the genus have traditionally been treated as separate genera in the group Satureja sensu lato: Clinopodium L., Calamintha sensu Miller or Moench, and Acinos sensu Miller or Moench. This study aimed to gain a better insight into the species diversity of Clinopodium L. from the Balkans by analyzing the taxa that have traditionally been placed in separate genera. The alkane profile and the micromorphological characteristics of the leaves are analyzed. The leaves are visualized using scanning electron microscopy, and alkanes are isolated using n-hexane as a solvent and analyzed using gas chromatography/mass spectrometry. The alkane profile showed the differentiation of the Acinos-group from the other taxa based on the dominant n-C31, while most of the other taxa contained n-C33 as the dominant alkane. The micromorphological features also showed clear differences between the previously recognized genera, especially in the capitate trichomes. The results showed that micromorphological patterns are highly variable in certain groups of the genus Clinopodium.

The viscosity of bitumen is extremely high at ambient temperature and in order to produce and transport the bitumen, it is necessary to reduce its viscosity. In this regard various n-alkane with different surface tension dilutes bitumen. This study features the application of artificial neural network for prediction of surface tension of branched alkanes. Modeling results showed that the both models are accurate and effective in prediction of surface tension of branched alkanes. However, the results were compared with experimental data and it was found that the estimated surface tension by ANN-MLP is more accurate than radial basis function network. [ABSTRACT FROM AUTHOR]

Shear viscosity is one of the key subjects of molecular modeling studies since this quality is used in the development of lubricants. In this paper, we use molecular dynamics methods to predict viscosity dependence on pressure up to 1000 MPa for 2,2,4-trimethylhexane. The COMPASS class II force field is used to determine atomic interactions in the model. The shear viscosity is calculated using Green-Kubo and Müller-Plathe methods. To achieve the convergence of the Green-Kubo integral, the time decomposition method is used. The approach is validated by 2,2,4-trimethylpentane for which experimental data are available. The calculated 2,2,4-trimethylhexane viscosity coefficient dependence is fit by Tait-like equation and does not show super-Arrhenius behavior. The Tait fit matches the experiment produced by Scott Bair for the pressures up to 500 MPa within the accuracy of the methods. [ABSTRACT FROM AUTHOR]

Abstract In this research, the oxidation behavior of six linear and branched alkanes was investigated using high-pressure differential scanning calorimeter (HP-DSC) and thermogravimetry coupled with Fourier-transform infrared spectroscopy (TG-FTIR) to compare the similarities and differences between branched and linear alkanes. The results indicated that both branched and linear alkanes showed only low-temperature oxidation (LTO), which implies that alkanes barely contribute in coke formation and thus no obvious high-temperature oxidation (HTO) was observed as no enough fuel was deposited. The LTO of linear alkanes seems to be independent of their carbon number, which, however, does not apply to branched alkanes. The oxidation behavior of branched alkanes was different from their linear chain counterparts due to the effect of their different molecule structure. Branched alkanes reacted earlier and faster at initial stage relative to their linear chain counterparts, but their reaction rates became slower at later stage with the increase of temperature. Branched alkanes can produce some oxidized compounds with C O group, while linear alkanes can form more carbonyl groups and some oxidized compounds (like carboxylic acids) that can help to produce more CO 2 by decomposition. Graphical abstract Unlabelled Image Highlights • Both branched and linear alkanes only showed low-temperature oxidation (LTO). • The LTO of linear alkanes was independent of their carbon number. • LTO behavior of branched alkanes is different from their linear chain counterparts. • Branched alkanes reacted earlier and faster at initial stage than linear alkanes. • Reaction rate of branched alkanes became slower at later stage than linear alkanes. [ABSTRACT FROM AUTHOR]

The current study highlights the application of a model based on least square support vector machine (LSSVM) for prediction of surface tension of branched alkanes. An optimization algorithm, namely, coupled simulated annealing (CSA) was applied to the model. Surface tensions of alkanes show a specific interaction between adjacent molecules of the branched alkanes which affects the anisotropic dispersion force component of the surface energy. In this paper, surface tension of branched alkanes was studied in temperature range of 283.15 and 448.15 K. To evaluate the performance and accuracy of this model, statistical and graphical error analyses have been used simultaneously. By applying CSA-LSSVM on 600 data points and finding optimum parameters, the estimated values of surface tension of branched alkanes were compared with experimental data which showed a reasonable agreement with the experimental results. Results demonstrate that the model is precise and viable for prediction of solubility data. The model shows an overall R2 and AARD% estimations of 0.9921 and 0.89%, respectively. [ABSTRACT FROM AUTHOR]

This study features the application of artificial neural network for prediction of surface tension of branched alkanes. Surface and interfacial tensions of alkanes show a specific interaction between adjacent molecules of the higher n-alkanes which results in an anisotropic dispersion force component of the surface energy. The surface tension of branched alkanes was studied for temperatures between 283.15 and 448.15 K. Two intelligent models named multilayer perceptron model (MLP) and radial basis function (RBF) model were developed and the accuracy of two models was examined by different graphical and statistical methods. Results showed that the both models are accurate and effective in prediction of surface tension of branched alkanes. However, the results were compared with experimental data and it was found that the estimated surface tension by multi-layer perceptron neural network is more accurate than radial basis function network. [ABSTRACT FROM AUTHOR]

In this work, the heterosegmented GC-PC-SAFT model is parameterized for branched alkanes. Branched alkanes can be regarded as the skeleton of more complex molecules. Analyzing experimental data of branched alkanes in comparison to the linear analogous gives rationale to decisions about what substances require a more refined or individualized parameterization. A neighborhood-correction of the segment-number parameter is then proposed for branched alkanes as function of the distance between the functional groups. This correction leads to better agreement with experimental data in the prediction of vapor pressure (27% AAD compared to 39%) and allows distinguishing isomers. [ABSTRACT FROM AUTHOR]

Petroleum is the main source of energy used in the world. The oil industry faces challenges in trying to understand the chemical composition of crude oils, quantitatively and qualitatively. The application of specific and sophisticated techniques allows a detailed characterization and provides important information that impacts from the exploration to production, transportation, and crude oil refining. A set of twelve crude oil samples with different API gravity were analyzed via comprehensive two-dimensional (2D) gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-TOFMS) aimed at the detection, identification and semi-quantification of hydrocarbon classes using extracted ion chromatogram (EIC) and total ion chromatogram (TIC). The use of the polar/non-polar column configuration provided better separation between the hydrocarbon classes which allowed the identification and semi-quantification of the same. Therefore, series of n - and iso -alkanes, alkyl-cyclohexanes, alkyl-cyclopentanes, alkyl-decalines, alkyl-naphthalenes, alkyl-phenanthrenes and alkyl-9H-fluorenes were characterized. In the present study, a semi-quantification approach to data assessment using TIC is proposed. Comprehensive evaluation provided the chromatographic fingerprint of each sample in a single analysis followed by the semi-quantification of the hydrocarbon classes. The oil samples presented completely different hydrocarbon class data, even when presenting similar API gravity values. Branched alkanes and n -alkanes were the major semi-quantified compounds, and branched alkane concentrations were higher than n -alkanes in the majority of samples. These results afford valuable information for the petrochemical industry. GC × GC-TOFMS was applied for speciation and group-type semi-quantification using a single oil drop without a fractionation or clean up step. [ABSTRACT FROM AUTHOR]

A new approach for the production of low-freezing-point, high-quality fuels from lignocellulose-derived molecules was developed with Michael addition as the key step. Among the investigated catalysts, CoCl2·6H2O was found most active for the Michael addition of 2,4-pentanedione with FA (single aldol adduct of furfural and acetone, 4-(2-furanyl)-3-butene-2-one). Over CoCl2·6H2O, a high carbon yield of C13 oxygenates (about 75%) can be achieved under mild conditions (353 K, 20 h). After hydrodeoxygenation, low-freezing-point (<223 K) branched alkanes with 13 carbons within jet fuel ranges were obtained over a Pd/NbOPO4 catalyst. Furthermore, C18,23 fuel precursors could be easily synthesized through Michael addition of 2,4-pentanedione with DFA (double-condensation product of furfural and acetone) under mild conditions and the molar ratio of C18/C23 is dependent on the reaction conditions of Michael addition. After hydrodeoxygenation, high density (0.8415 gmL-1) and low-freezing-point (<223 K) branched alkanes with 18, 23 carbons within lubricant range were also obtained over a Pd/NbOPO4 catalyst. These highly branched alkanes can be directly used as transportation fuels or additives. This work opens a new strategy for the synthesis of highly branched alkanes with low freezing point from renewable biomass. [ABSTRACT FROM AUTHOR]

The solvent effect on the solute conformations of straight and branched-chain alkanes infinitely diluted in methanol and carbon tetrachloride is studied. An additive scheme is used that takes into account the strong relation between limiting partial molar volumes and the average numbers of gauche conformations adopted by the solute molecules in each solvent. These numbers were determined using the Pitzer’s steric partition function with different values of anti→gauche transition enthalpy variations, ranging from (+2931 to −1465) kJ·mol −1 . The partial molar volumes at infinite dilution for three mono branched-chain alkanes (2-methylpentane, 3-methylpentane and 2-methylheptane) were experimentally determined in methanol to complement other series consisting mainly of straight, bi and tri branched-chain alkanes obtained in previous works. The conformational analysis performed using statistical methods is quite convincing about the strong effect of the solvent on the solute conformation equilibrium. Conclusions about close-packing and structure effects related to anti-gauche transitions in these two solvents are also drawn. [ABSTRACT FROM AUTHOR]

The recently developed TLVMie (Transferable Liquid Viscosity Mie) force field for accurate estimation of liquid viscosity and density from standardized molecular simulation is extended to include compounds containing alkyl branching. The prediction capability is evaluated with 49 branched alkanes and 6 branched alkylbenzenes. Performance is compared to: experimental data for compounds outside the training set used to parameterize the model, molecular simulation using the MiPPE and TraPPE force fields, and existing group contribution and corresponding states methods. Experimental saturated liquid densities are predicted to within 0.42% average absolute error and saturated liquid viscosities are reproduced with an average absolute error of 5.7%. Viscosity prediction accuracy is shown to be superior to existing techniques while also being more transferable to compounds or conditions with little experimental data. [ABSTRACT FROM AUTHOR]

Synthesis of branched long-chain alkanes from renewable biomass has attracted intensive interest in recent years, but the feedstock for this synthesis is restricted to platform chemicals. Here, we develop an effective and energy-efficient process to convert raw lignocellulosic biomass (e.g., corncob) into branched diesel-range alkanes through three tandem steps for the first time. Furfural and isopropyl levulinate (LA ester) were prepared from hemicellulose and cellulose fractions of corncob in toluene/water biphasic system with added isopropanol, which was followed by double aldol condensation of furfural with LA ester into C15 oxygenates and the final hydrodeoxygenation of C15 oxygenates into branched long-chain alkanes. The core point of this tandem process is the addition of isopropanol in the first step, which enables the spontaneous transfer of levulinic acid (LA) into the toluene phase in the form of LA ester through esterification, resulting in LA ester co-existing with furfural in the same phase, which is the basis for double aldol condensation in the toluene phase. Moreover, the acidic aqueous phase and toluene can be reused and the residues, including lignin and humins in aqueous phase, can be separated and carbonized to porous carbon materials. [ABSTRACT FROM AUTHOR]

The impact of continuous inputs of hydrocarbons from domestic waste oil recycling industries and further remediation practices, like inertization (liming and addition of ashes), have been studied in peri-urban soils in Spain in order to monitor the fate and spatial distribution patterns of potentially hazardous organic compounds. Physical and chemical properties of undisturbed soils or contaminated with waste-oil were determined. Lipid fractions were extracted using a dichloromethane:methanol mixture and analyzed by gas chromatography–mass spectrometry (GC/MS) in search for environmental proxies. A pollution gradient (distance to the waste oil spill) was accompanied by the following chromatographic features: (i) the increasing extent of the unresolved ‘hump’ caused by branched/cyclic alkanes with non-biogenic signature, (ii) the depletion of fatty acids and alkanol series, and (iii) the accumulation of phenols and polycyclic hydrocarbons. An increase in the C-preference index (odd-C/even-C numbered homologues) of fatty acids was also detected with an opposed trend in alkane chains. Concerning alkanes and fatty acids chain length, there was a generalized decrease whereas a progressive increase of alien long-chain (>C 20 ) homologues was observed. Signature compounds found in waste oil (mainly squalene, steroids and waxes) were almost absent from neighbor soils, either undisturbed or inertized, suggesting the occurrence of rapid biodegradation or condensation processes in the soil matrix probably aided by the remediation practices or by abiotic humification processes. [ABSTRACT FROM AUTHOR]

The auto-ignition quality of diesel fuels, quantified by their cetane number or derived cetane number ( DCN ), is a critical design property to consider when producing and upgrading synthetic paraffinic fuels. It is well known that auto-ignition characteristics of paraffinic fuels depend on their degree of methyl substitution. However, there remains a need to study the governing chemical functionalities contributing to such ignition characteristics, especially in the case of methyl substitutions, which have not been studied in detail. In this work, the auto-ignition of 2,6,10-trimethyltridecane has been compared with the reference hydrocarbons used for cetane number determination, i.e. n -hexadecane and heptamethylnonane, all of them being C16 isomers. Results from a constant-volume combustion chamber under different pressure and temperature initial conditions showed that the ignition delay time for both cool flame and main combustion events increased less from n -hexadecane to trimethyltridecane than from trimethyltridecane to heptamethylnonane. Additional experimental results from blends of these hydrocarbons, together with kinetic modelling, showed that auto-ignition times and combustion rates were correlated to the concentration of the functional groups indicative of methyl substitution, although not in a linear manner. When the concentration of these functional groups decreased, the first stage OH radical concentration increased and ignition delay times decreased, whereas when their concentration increased, H 2 O 2 production was slower and ignition was retarded. Contrary to the ignition delay times, DCN was correlated linearly with functional groups, thus homogenizing the range of values and clarifying the differences between fuels. [ABSTRACT FROM AUTHOR]

Highlights: [•] We measured the ignition delay times for three branched alkanes: 2,4-dimethylpentane, 2,5-dimethylhexane, and iso-octane. [•] The measured ignition delay times for branched alkanes are higher than their normal alkane isomers. [•] The measured ignition delay times increase with the carbon branching ratio. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hydride Transfer between isobutane isotopomers on USY zeolite was monitored by in situ MAS NMR. [•] The intermolecular H/D exchange is described by a set of two coupled kinetics reactions. [•] The activation energy of the hydride transfer occurring between the isoalkanes was determined. [•] The chemical process follows a carbenium intermediate mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Social insect colonies contain attractive resources for many organisms. Cleptoparasites sneak into their nests and steal food resources. Social parasites sneak into their social organisations and exploit them for reproduction. Both cleptoparasites and social parasites overcome the ability of social insects to detect intruders, which is mainly based on chemoreception. Here we compared the chemical strategies of social parasites and cleptoparasites that target the same host and analyse the implication of the results for the understanding of nestmate recognition mechanisms. The social parasitic wasp Polistes atrimandibularis (Hymenoptera: Vespidae), and the cleptoparasitic velvet ant Mutilla europaea (Hymenoptera: Mutillidae), both target the colonies of the paper wasp Polistes biglumis (Hymenoptera: Vespidae). There is no chemical mimicry with hosts in the cuticular chemical profiles of velvet ants and pre-invasion social parasites, but both have lower concentrations of recognition cues (chemical insignificance) and lower proportions of branched alkanes than their hosts. Additionally, they both have larger proportions of alkenes than their hosts. In contrast, post-invasion obligate social parasites have proportions of branched hydrocarbons as large as those of their hosts and their overall cuticular profiles resemble those of their hosts. These results suggest that the chemical strategies for evading host detection vary according to the lifestyles of the parasites. Cleptoparasites and pre-invasion social parasites that sneak into host colonies limit host overaggression by having few recognition cues, whereas post-invasion social parasites that sneak into their host social structure facilitate social integration by chemical mimicry with colony members. [Copyright &y& Elsevier]

Abstract: A microbial consortium capable of degrading turbine oil (TuO) consisting mainly of recalcitrant branched and polycyclic alkanes, has been established using a sludge sample collected from an oil-water separation tank of a hydraulic plant, by repeated enrichment cultivation. When this consortium, named the tank-2 consortium, was cultivated in a minimal salts medium containing 0.5% TuO, it degraded approximately 90% of TuO at 30 °C under shaking at 160 rpm in five days. During cultivation, the consortium formed cell aggregates. Fourteen bacterial species were isolated from the consortium. Although the mixtures of all of the isolated strains (IM) and predominant strains selected from the IM (PM) degraded approximately 60% of the TuO maximally in seven days after repeated enrichment, the degradation rate was not maintained. The decreased rate of TuO degradation in the PM was recovered by inoculation with a mixture (AM) consisting of isolates involved in the cell aggregate formation in the tank-2 consortium, suggesting that the formation of bacterial aggregates is an important factor for the degradation of TuO by the bacterial consortia. Interestingly, the formation of bacterial aggregates was only observed when cyclic alkanes were added to the consortium as a source of carbon. The cell surface hydrophobicity of the bacterial aggregates was significantly high (77.6%). These results suggest that the growth of bacteria with high cell hydrophobicity can be induced by the cyclic alkanes fraction of TuO, and that the formation of aggregates facilitates cells to form contact with the recalcitrant components of TuO and uptakes these components. [Copyright &y& Elsevier]

We discuss the optimisation as well as the convergence of a recently developed molecular simulation method using a Wang-Landau sampling scheme, combined with multiple time-step hybrid Monte Carlo (MC) simulations in the isothermal-isobaric ensemble, to determine vapour-liquid equilibria. This method has the advantage of being simple to use, as only a single simulation run at a given temperature directly gives the coexistence properties, and of being transferable to any kind of fluid, since the method is readily applicable to any molecular architecture. We apply this method to two branched alkanes, isopentane and isobutane, and discuss how we optimise the various simulation parameters. The vapour-liquid coexistence curve as well as the critical point obtained in this work are in excellent agreement with those found experimentally and in previous work using a combination of the Gibbs ensemble MC method with the configurational bias technique. [ABSTRACT FROM AUTHOR]

Abstract: Mo/HZSM-5 has been found active in Fischer–Tropsch synthesis (FTS). The catalysts were evaluated under various reaction conditions with low H2/CO (molar ratio ∼1.0) syngas typical of a synthesis gas derived from biomass gasification. Liquid hydrocarbons formed on the Mo/HZSM-5 were composed mainly of alkyl-substituted aromatics and lower branched and cyclized alkanes. Aliphatic hydrocarbons were detected only in trace amounts. Lower hydrocarbons produced included mainly methane, ethane, propane and iso-butane. Higher alcohols and carboxylic acids (C1–C6) were detected in the water phase liquids from FTS. It is supposed that the formation of hydrocarbons on Mo/zeolite is through bifunctional-zeolite acidity and molybdenum metal catalysis via mixed alcohols as the intermediates. Investigation on the effects of zeolite structure indicated that zeolite Y is also an excellent support for Mo in the FTS. [Copyright &y& Elsevier]

In the present work, we have optimised the dynamical behaviour of the anisotropic united atom (AUA) intermolecular potential for branched alkanes developed by Bourasseau et al. [E. Bourasseau, P. Ungerer, A. Boutin, and A.H. Fuchs, Monte Carlo simulation of branched alkanes and long chain n-alkanes with anisotropic united atoms intermolecular potential, Mol. Sim. 28 (2002), pp. 317-336], by a modification of the energetic barrier of the torsion potential. The new potential (AUA(4m)) preserves all the intermolecular parameters and only explores an increment in the trans-gauche and gauche+-gauche - transition barrier of the torsion potential. This modification better reproduces transport properties like the shear viscosity, keeping the accuracy achieved in the original work for equilibrium properties. An extensive investigation of the shear viscosity of 12 different types of branched alkanes in a wide range of pressures and temperatures, shows that the AUA(4m) improves the accuracy of the original AUA4, reducing the absolute average deviation from 24 to 15%. In addition, molecular simulation results of the shear viscosity of olefins reveal that the original AUA potential is accurate enough to reproduce the experimental data with less than 12% of deviation. Finally, we present a consistent lumping methodology to perform molecular simulations on complex multi-component systems such as fuel gasoline by representing the real system by a simplified mixture with only tenths of species. [ABSTRACT FROM AUTHOR]

Cigarette mainstream smoke (MSS) is a complex aerosol consisting of a vapour and a particulate phase. Cigarette design has been largely evolved over the last decades with the incorporation of new tobacco processes, papers, filters, and several ingredients (flavorings, casing materials, humectants), which either alone or in combination have the potential to modify the quantity and/or the quality of the smoke yielded. In the present study, polycyclic aromatic hydrocarbons (PAHs), n-alkanes and branched alkanes were determined in the particulate and gas phase of the MSS yielded from 59 manufactured cigarette brands (brands of unknown tobacco and blend type commercially available in the Greek market) with variable tar yields and physical/technological characteristics (existence/absence of filtered tip, tar yield, cigarette length, cigarette diameter, ventilation rate, pressure drop). The potential associations of particulate- and gas-phase organic components with cigarette technology and other MSS components (e.g. TPM, tar yield, nicotine and CO) were investigated. The data set offers a unique perspective into the assessment of smokers' exposure to hazardous constituents of cigarette smoke. [ABSTRACT FROM AUTHOR]

Abstract: Cyclohexane and C5–C20 n-alkanes undergo oxidation, giving rise to ketones and alcohols in the V(V)/H2O2/AcOH system. The products of oxidation of branched alkanes are indicative of the C–C bond cleavage in these substrates. A number of short-chain ketones, alcohols (and their acetates) were found among the products of isooctane oxidation. A concept is developed, according to which the active oxidant is a vanadium(V) complex containing the coordinated ligand. The transfer of O atom from the complex to a substrate gives rise to the hydroxylation products. The transfer of O+• radical cation from the coordinated ligand is assumed to be responsible for the ketonization or/and C–C bond cleavage. To cite this article: A.E. Gekhman et al., C. R. Chimie 7 (2004). [Copyright &y& Elsevier]

Chemical trees are the graph representations of alkanes. Recently the extremely branched chemical trees have been determined [Z. Naturforsch. 57a (2002) 49], namely the species that among all chemical trees with a given number n of vertices have the smallest connectivity and Wiener indices, and the greatest first ordinary and first Laplacian eigenvalues. Because of steric reasons, for larger values of n these extremal molecular graphs do not correspond to chemically sound molecules. By means of the PM3 semiempirical MO method we now determine the value of n until which the ‘extremely branched alkanes’ are stable molecules: (n around 16), as well as the value of n beyond which these cannot exist (n around 20). [Copyright &y& Elsevier]

Indigenous microorganisms, enriched and isolated from refinery waste sludge, were observed to possess a broad range of metabolic activities for mixtures of several classes of substrates of petroleum hydrocarbons, such as monoaromatic and polycyclic aromatic hydrocarbons (PAHs) and n- and branched alkanes. Three of the best-growing bacterial isolates selectively enriched with these compounds were identified by 16S rDNA sequencing as belonging to the genera Enterobacter and Ochrobactrum. Two of them, Enterobacter sp. strain EK3.1 and Ochrobactrum sp. strain EK6 utilise a hydrocarbon mixture of the branched alkane 2,6,10,14-tetramethylpentadecane and the PAHs acenaphthylene and acenaphthene. Enterobacter sp. strain EK4 can grow with a mixture of 2,6,10,14-tetramethylpentadecane, toluene, acenaphthylene and acenaphthene as carbon sources. Nucleic acid fingerprint analysis, by terminal restriction fragment length polymorphism (T-RFLP) of the PCR-amplified 16S rRNA genes, of the autochthonous bacterial community in contaminated soil samples showed complex and different community structures under different treatments of refinery waste sludge in landfarm areas. The characteristic peaks of the T-RFLP profiles of the individual, isolated degrading bacteria Enterobacter spp. and Ochrobactrum sp. were detected in the T-RFLP fingerprint of the bacterial community of the four months old treated landfarm soil, suggesting the enrichment of bacteria belonging to the same operational taxonomic units, as well as their importance in degrading activity. [ABSTRACT FROM AUTHOR]

Vapor pressure, density, and internal energy data from the literature are correlated in terms of the intermolecular interactions as represented by stepwise potential energies. Discontinuous molecular dynamics simulations are performed for united atom hard chain models of ethane, n-butane, n-hexane, n-octane, and benzene. Assuming square-well attractions ending at r/σ=1.2, 1.5, 1.8, and 2.0, the depths of each well are regressed by computing the physical properties from thermodynamic perturbation theory at each set of trial depths and minimizing the deviations from experimental observation. The result is an equation-of-state for each fluid derived directly from the intermolecular potential model. Because molecular dynamics form the basis for the reference fluid simulations, transport properties may also be derived. Vapor pressure, density, and internal energy are correlated to roughly 1% average absolute deviation. The trends in the resulting potential models suggest that the change in disperse attractions with distance may vary from one functional group to another. For example, the optimized potential model for benzene diminishes to zero more slowly than the model for ethane. [ABSTRACT FROM AUTHOR]

Gas chromatography–mass spectrometry on serially coupled capillary columns with different polarity of stationary phases showed that the soil cyanobacterium Microcoleus vaginatusfrom the Negev desert produces an unusual mixture of 4 normal and more than 60 branched alkanes, as well as a number of fatty acids, cyclic and unsaturated hydrocarbons, aldehydes, alcohols, and ketones. The dominant compounds were heptadecane (12%), 7-methylheptadecane (7.8%), hexadecanoic acid (6.5%), ( Z)-9-hexadecenoic acid (5.6%), 4-ethyl-2,2,6,6-tetramethylheptane (2.8%), ( Z)-9-octadecenoic acid (2.8%), and 4-methyl-5-propylnonane (2.7%). [ABSTRACT FROM AUTHOR]

Delocalization in alkanes? The case is made for the role of electron delocalization as a cause for the greater stability of branched alkanes relative to their linear isomers. Electron delocalization plays a similar role in linear alkanes as manifest in “protobranching stabilization.” A sizeable component of the stabilization is found to be attributable to geminal σ→σ* delocalization. [ABSTRACT FROM AUTHOR]

What are the factors that make branched alkanes more stable? A recent article suggested that greater electron delocalization is the key, but here it is argued that delocalization is just one of many factors, and that interactions of a more global nature, such as geminal interactions, make a better basis set for analyzing these systems. [ABSTRACT FROM AUTHOR]

Measurements of excess molar enthalpies at the temperature 298.15 K in a flow microcalorimeter are reported for the five binary mixtures formed by mixing 1-hexene with the branched alkanes: 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, and 2,2,4-trimethylpentane. Smooth Redlich–Kister representations of the results are described. It was found that the Liebermann–Fried model also provided good representations of the results. [Copyright &y& Elsevier]

The cuticular hydrocarbons of diapausing pupae of the tobacco hornworm, Manduca sexta (L.), are composed of two types of hydrocarbons: n-alkanes (3%) and unsaturated hydrocarbons (97%). The integument, fat body, muscle, and hemolymph are composed of three types of hydrocarbons: n-alkanes (9, 6, 9, and 2%, respectively), branched alkanes (75, 85, 80, and 56%, respectively), and unsaturated hydrocarbons (16, 9, 11, and 42%, respectively). The absence of branched alkanes on the cuticular surface indicated that hydrocarbons are selectively synthesized or deposited according to the presence or absence of methyl branches in the molecule. The hydrocarbons consisted of homologous series of n-alkanes from 21 to 41 carbon atoms, monomethylalkanes from 23 to 39 carbon atoms, dimethylalkanes from 25 to 43 carbon atoms, and trimethylalkanes from 33 to 37 carbon atoms. All branched components had methyl groups near the center of the molecule, and the di- and trimethyl branched components had three methylene units between the branch points. Straight chain alkenes, alkadienes, and alkatrienes from 23 to 44 carbon atoms were partially characterized. The percentage composition of each homologous series varied from tissue to tissue.

Using a combination of gas–liquid chromatography and mass spectrometry, the presence of 39 aliphatic hydrocarbons was firmly established in the unsaponifiable fraction of anhydrous milk fat. The hydrocarbons were the C14 to C27 and the C29 to C31 straight-chain paraffins, their monoolefin analogs, and the C25 to C29 branched alkanes. Phytene (3,7,11,15-tetramethyl-n-hexadec-2-ene), identified for the first time in milk fat, was isolated and identified by high-resolution mass spectrometry and infrared analysis. The total hydrocarbon content amounted to 30 ppm of the milk fat. Polychlorinated biphenyls also were detected in trace amounts in the area of the chromatogram between the C18 and the C23 hydrocarbons.