Alkane Chain Length Research Articles

Determination of Volatile Organic Compounds in Selected Strains of Cyanobacteria

Microalgal biomass can be used in creating various functional food and feed products, but certain species of microalgae and cyanobacteria are known to produce various compounds causing off-flavour. In this work, we investigated selected cyanobacterial strains ofSpirulina,Anabaena, andNostocgenera originating from Serbia, with the aim of determining the chemical profile of volatile organic compounds produced by these organisms. Additionally, the influence of nitrogen level during growth on the production of volatile compounds was investigated forNostocandAnabaenastrains. In addition, multivariate techniques, namely, principal component analysis (PCA) and hierarchical cluster analysis (HCA), were used for making distinction among different microalgal strains. The results show that the main volatile compounds in these species are medium chain length alkanes, but other odorous compounds such as 2-methylisoborneol (0.51–4.48%), 2-pentylfuran (0.72–8.98%),β-cyclocitral (0.00–1.17%), andβ-ionone (1.15–2.72%) were also detected in the samples. Addition of nitrogen to growth medium was shown to negatively affect the production of 2-methylisoborneol, while geosmin was not detected in any of the analyzed samples, which indicates that the manipulation of growth conditions may be useful in reducing levels of some unwanted odor-causing components.

Structure and transport properties of liquid alkanes in the vicinity of α-quartz surfaces

Abstract Structure and mass transport properties of several liquid n-alkanes, methane, decane and tetracosane, in the vicinity of α-quartz surfaces of three crystal planes have been investigated by using molecular dynamics simulations. Solid α-quartz surfaces were terminated with –H and –OH groups to create hydrophobic and hydrophilic surfaces, respectively. It was observed that adsorption of the liquid alkane molecules is more noticeable near the (0 0 1) crystal plane when compared with other two planes (0 1 1) and (1 0 0). For a given alkane, the number of molecules adsorbed near a α-quartz wall marginally depends upon the crystal plane and type of surface termination. Ordering parameter and radius of gyration for liquid molecules were examined in the interface region to gain the knowledge about molecular alignment and chain configuration in the interface region. Liquid molecules in the first adsorption layer near the hydrophilic and hydrophobic surfaces are more parallel to the interface in the following order (0 0 1), (0 1 1) and (1 0 0). Portions of decane and tetracosane liquid molecules tend to enter into the H-terminated side with an orientation in the parallel direction to the interface and into the OH-terminated side with an orientation in the perpendicular direction for (1 0 0) crystal plane. Molecules are flattened in the direction perpendicular to the interface and are elongated in the other direction in the interface region for decane and tetracosane. It is observed that the in-plane self-diffusion coefficient of liquids, the self-diffusion coefficient according to the migration of molecules in the directions parallel to the interface, is smaller in the vicinity of the solid surface and approaches to the bulk liquid value away from the interface. For methane, decane and tetracosane, the in-plane diffusion in the first adsorption layer near the smoother silica surface (0 0 1), which has molecularly smoother surface than the other two surfaces (0 1 1) and (1 0 0), for both of the terminations is higher as compared with the other two surfaces (0 1 1) and (1 0 0). It was found that the diffusion coefficients in the two directions of the 2-D in-plane diffusion are different significantly and this anisotropic nature is resulted by the topology of the solid surface. At the same reduced temperature, a tendency was observed that the in-plane diffusion near the H-terminated and OH-terminated surfaces for three crystal planes increases with an increase in the chain length of the liquid alkanes.

Length-dependent thermal transport along molecular chains.

We present heat-transport measurements conducted with a vacuum-operated scanning thermal microscope to study the thermal conductance of monolayers of nine different alkane thiols self-assembled on Au(111) surfaces as a function of their length (2 to 18 methylene units). The molecular thermal conductance is probed in a confined area with a diameter below 10 nm in the contact between a silicon tip and the self-assembled monolayer. This yields a pWK(-1) sensitivity per molecule at a tip temperature of 200-300 °C versus the gold at room temperature. We found a conductance variance of up to a factor of 3 as a function of alkane chain length, with maximum conductance for a chain length of four carbon atoms.

Thermal property prediction and measurement of organic phase change materials in the liquid phase near the melting point

Organic phase change materials (PCMs) are a popular choice for many thermal energy storage applications including solar energy, building envelope thermal barriers, and passive cooling of portable electronics. Since the extent of phase change during a heating or cooling process is dependent upon rapid thermal penetration into the PCM, accurate knowledge of the thermal diffusivity of the PCM in both solid and liquid phases is crucial. This study addresses the existing gaps in information for liquid-phase PCM properties by examining an approach that determines the best path to prediction (BPP) for the thermal diffusivity of both alkanes and unsaturated acids. Knowledge of the BPP will enable researchers to explore the influence of PCM molecular structure on bulk thermophysical properties, thereby allowing the fabrication of optimized PCMs.The BPP method determines which of the tens of thousands of combinations of 22 different available theoretical techniques provides best agreement with thermal diffusivity values based on reported or measured density, heat capacity, and thermal conductivity for each of five PCMs (heneicosane, tricosane, tetracosane, oleic acid, and linoleic acid) in the liquid phase near the melting point. Separate BPPs were calibrated for alkanes based on heneicosane and tetracosane, and for the unsaturated acids. The alkane and unsaturated acid BPPs were then tested on a variety of similar materials, showing agreement with reported/measured thermal diffusivity within ∼15% for all materials. The alkane BPP was then applied to find that increasing the length of alkane chains decreases the PCM thermal diffusivity, showing how the determination of the BPP can be used to aid in the prediction of how the molecular structure of organic PCMs influences PCM performance in energy storage applications.

Surface-Enhanced Raman Spectroscopy of Self-Assembled Monolayer Conformation and Spatial Uniformity on Silver Surfaces

We apply well-characterized silver nanowire grating (Ag-NWG) plasmonic surfaces as a Raman surface spectroscopy tool, which is based on surface-enhanced Raman scattering (SERS), to study the surface conformation characteristics of amine terminated alkanethiol self-assembled monolayers (SAMs). The surface conformation has implications for amine group availability, which is important when SAMs are used as linking layers for the binding of secondary molecules. Two different alkanethiols with different alkane chain lengths, namely 2-aminoethanethiol (cysteamine, CEA) and 11-aminoundecanethiol (AUT), are investigated. It is shown that both alkanethiols bind to Ag surfaces forming corresponding Ag-thiolates, however surface conformations, which are related to the ordering of the SAM, are different for these two SAM systems. The degree of SAM ordering is assessed by quantifying the integrated intensity ratio of the trans to gauche nu(C-S) vibrational bands from single spectra measurements and from spatially averaged spectra. These vibrational modes occur at different vibrational frequencies depending on the conformation (trans versus gauche) of the neighboring carbon atom. We demonstrate that the CEA SAMs are less ordered than AUT SAMs; thus, the amine terminal group availability differs between both systems.

Enhanced H2 Uptake of n-Alkanes Confined in Mesoporous Materials

The hydrogen uptake in hybrid sorbents consisting of n-alkane solvents confined in mesoporous silica aerogel is measured at different temperatures from 273 to 313 K and pressures up to 40 bar. An apparent “oversolubility” effect is observed as the H2 uptake in the hybrid sorbents is much larger than that in bulk solvents. The H2 uptake in the hybrid sorbents is found to increase with increasing temperature, which suggests that the flexibility and conformation of n-alkane molecules confined in the aerogel play a crucial role; high-entropy (disordered) alkane configurations lead to the creation of numerous cavities which make it possible to solubilize a larger number of H2 molecules. This departs from adsorption-driven solubility effects for which the number of solubilized molecules decreases with increasing temperature. For a given temperature and pressure, it is found that the number of solubilized H2 molecules per unit volume increases with decreasing alkane chain length. Such an effect, which is observe...

The tensile and shear failure behavior dependence on chain length and temperature in amorphous polymers

The tensile and shear failure behavior dependence on chain length and temperature in amorphous polymers are scrutinized using molecular dynamics simulations. A wide range chain length of alkane is tested under tension and shear with various temperatures. We find that the broken rate (the broken bond number to all polymer chain number ratios) under tension and shear increases with increasing chain length and temperature. For a given chain length and temperature, the broken rates under shear are always higher than those under tension at a same large strain. For a given chain length, the tensile and shear stresses decrease with increasing temperature. We propose three typical fracture mechanisms to effectively elucidate the ductile fracture response based on the predominance of chain scission process.

Phase Behavior of Nitrate Based Ionic Liquids with Thiophene and Alkanes

In this study, the extraction of thiophene from alkane compounds (hexane, heptane, and octane) was investigated by using 1-butyl 3- methylimidazolium nitrate ([Bmim][NO3]) and 1-methyl 3-octylimidazolium nitrate ([Omim][NO3]). Liquid–liquid equilibrium (LLE) data for ternary systems of ionic liquid + thiophene + alkane were reported at atmospheric pressure and 298.15 K. The calculated selectivity and solute distribution coefficient values from the experimental data demonstrate that the selectivities increase with increasing alkane chain length while the solute distribution coefficients decrease. Moreover, the selectivity values for the systems containing [Bmim][NO3] are higher than those containing [Omim][NO3]. This implies that [Bmim][NO3] is a more suitable solvent than [Omim][NO3] for desulfurization of alkane. The nonrandom two-liquid (NRTL) and universal quasi-chemical (UNIQUAC) models were used to correlate the experimental data. The results show both models can correlate the experimental data with ...

Low latitude hydro-climatic changes during the Plio-Pleistocene: evidence from high resolution alkane records in the southern South China Sea

High resolution records of long chain n-alkane biomarkers from the southern South China Sea reveal tightly response of n-alkane distribution to hydro-climate changes over the past 5 Ma, with increasing longer chain n-C31 alkanes indicating a correlation with drier conditions and increasing shorter chain n-C27 alkanes with wetter conditions. The variations of the C31/C27 ratio, or the alkane chain length index, imply humid conditions before 2.9 Ma, progressively reduced moisture since then and to bigger fluctuations between wet and dry conditions since 1.2 Ma. This long term hydro-climate trend is superimposed by glacial dry and interglacial wet patterns over the Plio-Pleistocene glacial cycles. Combined with other proxy records, our results indicate that precipitation over the tropical Asia-Pacific strengthened before the onset of the northern hemisphere glaciation and the mid-Pleistocene climate transition at about 1.2 Ma. These dramatic humidity changes over major climate transitions imply a crucial role of tropical hydrology dynamics on global climate change in the late Cenozoic.

Thermodynamic Properties of Liquid Mixtures Deduced from Ultrasonic Speed and Viscosity

Excess molar isentropic compressibilities KS, m E and the deviation u of the speeds of sound u from those in the ideal mixtures u, from speeds of sound values are reported. Measurements have been carried out in order to assess the effects of increasing the alkyl chain length of alkane. Further, we have calculated the ideal and excess internal pressures for the binary mixtures 2-butanol + alknae and some other parameters like heat of vaporization, cohesive energy density, solubility parameter, free volume which have been calculated from the internal pressure are also reported. Various physicochemical parameters like intermolecular free length, acoustic impedance, molecular association, relative association, available volume for the pure components as well as for the binary mixtures have also been calculated along with some of their excess counterparts. Results have been discussed in terms of intermolecular interactions.

An evaluation of alkylthiols and dialkyl disulfides on deactivation of Cu/Zn catalyst in hydrogenation of dodecyl methyl ester to dodecanol

Deactivation of co-precipitated Cu/Zn catalyst caused by exposure to either alkylthiols or dialkyl disulfides in catalytic hydrogenation of dodecyl methyl ester to dodecanol is explored in a stirred batch reactor. Catalytic activity decrement is highly dependent on levels of poisons, types of thiols/disulfides, chain length of alkanes. XRD, EDS and XPS are employed to characterize the fresh and spent Cu/Zn catalysts. It is evident that sulfuric species prefer to attack zinc oxide, forming chemically adsorbed Zn-SR at low sulfur levels, and ZnS is formed in the highly reductive atmosphere before sulfuric species attacking copper (forming Cu7S4 or Cu31S16).

Study on the separation of propylbenzene from alkanes using two methylsulfate-based ionic liquids at (313 and 333) K

The separation of propylbenzene from dodecane or tetradecane using different ionic liquids (ILs) based on the methylsulfate anion (CH3SO4−) was studied at two temperatures (313 and 333)K and atmospheric pressure. The ionic liquids, 1, 3-dimethylimidazolium methylsulfate [(mmim)(CH3SO4)] and 1-ethyl-3-methylimidazolium methylsulfate [(emim)(CH3SO4)], were evaluated as solvents for the extraction process. Four ternary systems were formed by {dodecane or tetradecane+propylbenzene+[(mmim)(CH3SO4)] or [(emim)(CH3SO4)]}. The degree of quality of the experimental data was ascertained using the Othmer–Tobias correlation. A comparison of the phase behaviour of the systems studied has allowed us to investigate the effect of ILs cation, alkane chain length, temperature and solvent-to-feed ratio upon solubility, percent aromatic removal, distribution ratio, and selectivity. Finally, the experimental LLE data was correlated using the UNIQUAC and the NRTL models.

The Ionic Hydrogen/Deuterium Bonds between Diammoniumalkane Dications and Halide Anions.

Halide-anion binding to 1,12-dodecanediammonium, tetramethyl-1,12-dodecanediammmonium, and tetramethyl-1,7-heptanediammonium has been investigated with infrared multiple-photon dissociation (IRMPD) spectroscopy in the 1000-2250 cm-1 spectral region and with theory. Both charged ammonium groups in these diammonium compounds interact with the halide anion resulting in an ionic hydrogen bond (IHB) stretching frequency outside of the spectral frequency range that can be measured with the free-electron laser (FEL). This frequency is shifted into the spectral range upon exchanging all of the labile hydrogen atoms with deuterium atoms, thus making measurement of the ionic deuterium bond (IDB) stretching frequency possible. The IDB stretching frequency shifts to higher values with increasing halide-anion size, methylation of the ammonium groups, and alkane chain length, consistent with the halide-anion-deuterium bond strength decreasing with decreasing gas-phase basicity of the halide anion and the increasing gas-phase basicity of the ammonium groups. The IDB stretching frequency also depends on the alkane chain length owing to constraints on the angle of the bonds between the halide anion and the two ammonium groups. There are additional bands in the IDB stretching feature in the IRMPD spectra, which are attributed to Fermi resonances and arise from coupling with overtone or combination bands that can be identified from theory and depend on the halide-anion identity and alkane chain length.

Calculation of complex phase equilibria of DMF/alkane systems using the PCP-SAFT equation of state

The Perturbed Chain Polar Statistical Association Fluid Theory (PCP-SAFT) equation of state is applied to calculate phase equilibria data for several DMF/alkane systems. DMF/alkane systems exhibit a peculiar phase behavior, due to overlapping liquid–liquid and vapor–liquid coexistence regions. Hetero- and homoazeotropes appear and disappear depending on temperature/pressure conditions and the chain length of the alkane. The vapor–liquid, liquid–liquid and vapor–liquid–liquid equilibria of DMF/alkanes systems including alkanes from C5 to C10 were studied in detail over wide temperature and pressure ranges. A single, linear expression for the binary interaction parameter kij as function of temperature and alkane chain length was used to model the experimental data. This expression was determined only by using experimental liquid–liquid equilibria (LLE) data of DMF/alkane systems. Using that, the PCP-SAFT equation of state provides very satisfying results for the description of the phase behavior in all considered systems.

Adaptation of the Hydrocarbonoclastic Bacterium Alcanivorax borkumensis SK2 to Alkanes and Toxic Organic Compounds: a Physiological and Transcriptomic Approach

The marine hydrocarbonoclastic bacterium Alcanivorax borkumensis is able to degrade mixtures of n-alkanes as they occur in marine oil spills. However, investigations of growth behavior and physiology of these bacteria when cultivated with n-alkanes of different chain lengths (C6 to C30) as the substrates are still lacking. Growth rates increased with increasing alkane chain length up to a maximum between C12 and C19, with no evident difference between even- and odd-numbered chain lengths, before decreasing with chain lengths greater than C19. Surface hydrophobicity of alkane-grown cells, assessed by determination of the water contact angles, showed a similar pattern, with maximum values associated with growth rates on alkanes with chain lengths between C11 and C19 and significantly lower values for cells grown on pyruvate. A. borkumensis was found to incorporate and modify the fatty acid intermediates generated by the corresponding n-alkane degradation pathway. Cells grown on distinct n-alkanes proved that A. borkumensis is able to not only incorporate but also modify fatty acid intermediates derived from the alkane degradation pathway. Comparing cells grown on pyruvate with those cultivated on hexadecane in terms of their tolerance toward two groups of toxic organic compounds, chlorophenols and alkanols, representing intensely studied organic compounds, revealed similar tolerances toward chlorophenols, whereas the toxicities of different n-alkanols were significantly reduced when hexadecane was used as a carbon source. As one adaptive mechanism of A. borkumensis to these toxic organic solvents, the activity of cis-trans isomerization of unsaturated fatty acids was proven. These findings could be verified by a detailed transcriptomic comparison between cultures grown on hexadecane and pyruvate and including solvent stress caused by the addition of 1-octanol as the most toxic intermediate of n-alkane degradation.

Forensic differentiation of diesel fuels using hydrocarbon isotope fingerprints

Compound-specific isotope analysis (CSIA) is fast becoming an important tool to provide chemical evidence in a forensic investigation. Attempts to trace environmental oil spills were successful where isotopic values were particularly distinct. However, difficulties arise when a large dataset is analyzed and the isotopic differences between samples are subtle. Thus, this study intends to demonstrate any linkages between diesel fuels in a large number of datasets where subtlety in the isotopic values is accentuated by the near single-point source of origin. Diesel fuels were obtained from various locations in the South Island of New Zealand. Aliquots of these samples were diluted with n-pentane and subsequently analyzed with gas chromatography-isotope ratio mass spectrometry (GC-IRMS) for carbon and hydrogen isotope values. The data obtained were subjected to principal component analysis (PCA) and hierarchical clustering. A wide range of δ13C and δ2H values were determined for the ubiquitous alkane compounds (the greatest values being −4.5‰ and −40‰, respectively). Based on the isotopic character of the alkanes it is suggested that diesel fuels from different locations were distinguishable and that the key components in the differentiation are the δ2H values of the shorter chain-length alkanes. However, while the stable isotope measurements may provide information to classify a sample at a broad scale, much more detailed information is required on the temporal and spatial variability of diesel compositions. The subtle differences of the stable isotope values within the alkanes of different diesel fuels highlighted the power of CSIA as a means of differentiating petroleum products of different origins, even more so when two or more stable isotopes data are combined. This paper shows that CSIA when used in tandem with multivariate statistical methods can provide suitable tools for source apportionment of hydrocarbons by demonstrating a straightforward approach, thus eliminating lengthy analytical processes.

Creation and control of defined protein patterns on glass: alkyl chain length controls stability

Here we present a method for the production of defined protein patterns on glass using trimethoxysilane-terminated self-assembled monolayer (SAM) chemistry. The surfaces were characterized by infrared spectroscopy to determine the relationship between alkyl chain length and monolayer order and, in turn, the critical alkyl chain length required to produce a tightly packed SAM. Protein resistance studies, which incorporated a glycol region into the monomer, further highlighted the importance of alkane chain length within the monolayer, as increased chain length was necessary to generate protein resistant regions that persisted for more than a few days. The long-chain trimethoxysilane-terminated monomers that we have developed are stable, can be purified using standard silicon gel chromatography, and can be easily patterned using methods developed for other SAMs. As a result, these monomers and the resulting monolayers produced from them provide a method for the functionalization of a wide variety of oxide substrates, including ordinary glass, which has enormous advantages over previous glycol-terminated trichlorosilane monomers.

Chemically transferable coarse-grained potentials from conditional reversible work calculations

The representability and transferability of effective pair potentials used in multiscale simulations of soft matter systems is ill understood. In this paper, we study liquid state systems composed of n-alkanes, the coarse-grained (CG) potential of which may be assumed pairwise additive and has been obtained using the conditional reversible work (CRW) method. The CRW method is a free-energy-based coarse-graining procedure, which, by means of performing the coarse graining at pair level, rigorously provides a pair potential that describes the interaction free energy between two mapped atom groups (beads) embedded in their respective chemical environments. The pairwise nature of the interactions combined with their dependence on the chemically bonded environment makes CRW potentials ideally suited in studies of chemical transferability. We report CRW potentials for hexane using a mapping scheme that merges two heavy atoms in one CG bead. It is shown that the model is chemically and thermodynamically transferable to alkanes of different chain lengths in the liquid phase at temperatures between the melting and the boiling point under atmospheric (1 atm) pressure conditions. It is further shown that CRW-CG potentials may be readily obtained from a single simulation of the liquid state using the free energy perturbation method, thereby providing a fast and versatile molecular coarse graining method for aliphatic molecules.

Expanding the Product Profile of a Microbial Alkane Biosynthetic Pathway

Microbially produced alkanes are a new class of biofuels that closely match the chemical composition of petroleum-based fuels. Alkanes can be generated from the fatty acid biosynthetic pathway by the reduction of acyl-ACPs followed by decarbonylation of the resulting aldehydes. A current limitation of this pathway is the restricted product profile, which consists of n-alkanes of 13, 15, and 17 carbons in length. To expand the product profile, we incorporated a new part, FabH2 from Bacillus subtilis , an enzyme known to have a broader specificity profile for fatty acid initiation than the native FabH of Escherichia coli . When provided with the appropriate substrate, the addition of FabH2 resulted in an altered alkane product profile in which significant levels of n-alkanes of 14 and 16 carbons in length are produced. The production of even chain length alkanes represents initial steps toward the expansion of this recently discovered microbial alkane production pathway to synthesize complex fuels. This work was conceived and performed as part of the 2011 University of Washington international Genetically Engineered Machines (iGEM) project.

Methodology for advanced measurement accuracy of the overall volumetric oxygen transfer coefficient with application to hydrocarbon–aqueous dispersions

AbstractAccurate quantification of the overall volumetric oxygen transfer coefficient (KLa) is essential for the success of aerobic bioprocesses. In hydrocarbon‐based bioprocesses where KLa is depressed at higher viscosities, this is particularly critical. In this study an accessible methodology for KLa determination has been developed and validated for alkane‐based systems under a wide range of process conditions. Critical to measurement accuracy in around 90% of the KLa values was the incorporation of the response lag. Neglect of the response lag resulted in errors greater than 5% above KLa = 0.3Kp to KLa = 0.6Kp (where Kp is the inverse response lag or probe constant), at least 1.5‐fold to 3‐fold lower than the analogous KLa in water. Further, Kp varied significantly with both alkane concentration and chain length. A sensitivity analysis confirmed − 25% to 90% error in KLa with 30% over‐ and under‐estimation of Kp respectively. When incorporating Kp values specific to the process conditions, accurate KLa values were confirmed in 0 to 20% (v/v) C10–13 and C14–20 aqueous dispersions over 600 to 1200 rpm agitation. Copyright © 2012 Society of Chemical Industry