Linear N-alkanes Research Articles

Analytical and behavioral characterization of 1-hexanoyl-LSD (1H-LSD).

The development of lysergic acid diethylamide (LSD) derivatives and analogs continues to inform the design of novel receptor probes and potentially new medicines. On the other hand, a number of newly developed LSD derivatives have also emerged as recreational drugs, leading to reports of their detection in some countries. One position in the ergoline scaffold of LSD that is frequently targeted is the N1-position; numerous N1-alkylcarbonyl LSD derivatives have been reported where the acyl chain is attached to the indole nitrogen, for example, in the form of linear n-alkane substituents, which represent higher homologs of the prototypical 1-acetyl-N,N-diethyllysergamide (1A-LSD, ALD-52). In this study, 1-hexanoyl-LSD (1H-LSD, SYN-L-027), a novel N1-acyl LSD derivative, was characterized analytically using standard techniques, followed by evaluation of its in vivo behavioral effects using the mouse head-twitch response (HTR) assay in C57BL/6J mice. 1H-LSD induced the HTR, with a median effective dose (ED50) of 192.4 μg/kg (equivalent to 387 nmol/kg), making it roughly equipotent to ALD-52 when tested previously under similar conditions. Similar to other N1-acylated analogs, 1H-LSD is anticipated to by hydrolyzed to LSD in vivo and acts as a prodrug. It is currently unknown whether 1H-LSD has appeared as on the research chemical market or is being used recreationally.

Source identification and ecological risks of parent and substituted polycyclic aromatic hydrocarbons in river surface sediment-pore water systems: Effects of multiple factors

Substituted polycyclic aromatic hydrocarbons (SPAHs) have shown higher health and ecological risks than the corresponding parent PAHs (PPAHs) from laboratory studies, their variations in freshwater system, especially in surface sediment and pore water, remain inadequate understanding. In this study, we revealed the coexistence, ecological risk, and multiple factors affecting variations and sources of PPAHs and SPAHs (nitrated PAHs (NPAHs), oxygenated PAHs (OPAHs)) in the surface sediment-pore water system from a typical urban river in Northern China. The concentration ranges of Σ26PPAHs, Σ10NPAHs, and Σ4OPAHs in the surface sediments were 153.0–5367.4, not detected (N.D.)–105.4, and 42.2–1177.0 ng·g−1 dry weight, and fell within 0.6–38.8, N.D.–297.9, and N.D.–212.6 ng·mL−1 in the pore waters. The t-distributed stochastic neighbor embedding (SNE) coupled with the partitioning around medoids (PAM) elucidated spatiotemporal the variations in PAHs, emphasizing the impacts of industrial activities and sewage discharges. Besides the geochemical and hydrochemical conditions, SPAHs were affected by the potential secondary formation, especially during the wet season. The method comparisons indicated the advantages of principal component analysis-multivariate linear regression (PCA-MLR) and n-alkanes model on source identification. PAHs mainly originated from fossil fuel combustion and vehicular exhaust. The top risk quotient (RQ) values for PAHs occurred in the urban and industrial sections. A majority of the surface sediment samples emerged with low to moderate exposure risks, while all the pore water samples showed high exposure risks. The RQs of OPAHs were significantly higher (p < 0.01) than those of PPAHs. The results suggested the secondary formation of SPAHs as an important role in ecological risks of PAHs in the urban river system.

Cumene extraction separation from alkanes using DMSO: Influence of the alkane structure

In this study, the liquid-liquid equilibrium of dimethyl sulfoxide (DMSO)-cumene-alkanes (including n-alkanes and cycloalkanes) systems are measured at 30 °C under atmospheric pressure. Following NRTL/UNIQUAC activity coefficient model correlation and the Gibbs energy minimization test are conducted. Moreover, the influence of alkane structure on the extraction results is elaborated. Finally, a set of wave function analyses are enacted to visualize the intermolecular interactions and quantify the physical contribution of different intermolecular effects. These investigations show that: The distribution coefficient and overall selectivity of cumene escalate with the increase of molecular weight, for both linear and cyclic alkane homologues. Meanwhile, the entrainment of alkane in the extraction phase decreases. The aromatic selectivity coefficient β for cycloalkane systems is lower than linear n-alkane with similar carbon number, regardless of more extracted model oil, which owes to high entrainment. The aromatic distribution coefficient Kar for cycloalkanes rises faster and eventually surpasses that of n-heptane system in terms of absolute value, which is verified by UNIFAC simulation. The interactions between cumene and n-alkanes/cycloalkanes are van der Waals interaction, driven by dispersion (70.10∼71.50%) and electrostatic (23.58∼24.66%) effect. As the molecular weight of the alkane increases, the dispersion contribution decreases, while the electrostatic interaction increases.

Gas-Phase Chlorine Radical Oxidation of Alkanes: Effects of Structural Branching, NOx, and Relative Humidity Observed during Environmental Chamber Experiments

Chlorine-initiated oxidation of alkanes has been shown to rapidly form secondary organic aerosol (SOA) at higher yields than OH-alkane reactions. However, the effects of alkane volatile organic compound precursor structure and the reasons for the differences in SOA yield from OH-alkane reactions remain unclear. In this work, we investigated the effects of alkane molecular structure on oxidation by chlorine radical (Cl) and resulting formation of SOA through a series of laboratory chamber experiments, utilizing data from an iodide chemical ionization mass spectrometer and an aerosol chemical speciation monitor. Experiments were conducted with linear, branched, and branched cyclic C10 alkane precursors under different NOx and RH conditions. Observed product fragmentation patterns during the oxidation of branched alkanes demonstrate the abstraction of primary hydrogens by Cl, confirming a key difference between OH- and Cl-initiated oxidation of alkanes and providing a possible explanation for higher SOA production from Cl-initiated oxidation. Low-NOx conditions led to higher SOA production. SOA formed from butylcyclohexane under low NOx conditions contained higher fractions of organic acids and lower volatility molecules that were less prone to oligomerization relative to decane SOA. Branched alkanes produced less SOA, and branched cycloalkanes produced more SOA than linear n-alkanes, consistent with past work on OH-initiated reactions. Overall, our work provides insights into the differences between Cl- and OH-initiated oxidation of alkanes of different structures and the potential significance of Cl as an atmospheric oxidant.

N-Nonane hydroisomerization over hierarchical SAPO-11-based catalysts with sodium dodecylbenzene sulfonate as a dispersant

To enhance the gasoline octane number, low-octane linear n-alkanes should be converted into their high-octane di-branched isomers via n-alkane hydroisomerization. Therefore, hierarchical SAPO-11-based catalysts are prepared by adding different contents of sodium dodecylbenzene sulfonate (SDBS), and they are applied in n-nonane hydroisomerization. When n(SDBS)/n(SiO2) is less than or equal to 0.125, the synthesized hierarchical molecular sieves are all pure SAPO-11, and as the SDBS content increases, the submicron particle size decreases, and the external surface area (ESA) increases. Additionally, these hierarchical SAPO-11 have smaller submicron particles and higher ESA values than conventional SAPO-11. When n(SDBS)/n(SiO2) is greater than 0.125, with increasing SDBS content (n(SDBS)/n(SiO2) = 0.25), the synthesized SAPO-11 contains amorphous materials, which leads to a decline in the ESA; with the further increase in SDBS content (n(SDBS)/n(SiO2) = 0.5), the products are all amorphous materials. These results indicate that in the case of n(SDBS)/n(SiO2) = 0.125, the synthesized SAPO-11 molecular sieve (S–S3) has the most external Brønsted acid centers and the highest ESA of these SAPO-11, and these advantages favor generation of the di-branched isomers in hydrocarbon hydroisomerization. Among these Pt/SAPO-11 catalysts, Pt/S–S3 displays the highest selectivity to entire isomers (83.4%), the highest selectivity to di-branched isomers (28.1%) and the minimum hydrocracking selectivity (15.7%) in n-nonane hydroisomerization.

Enabling High Spectral Resolution of Liquid Mixtures in Porous Media by Antidiagonal Projections of Two-Dimensional 1H NMR COSY Spectra.

The noninvasive, in situ chemical identification of liquid mixtures confined in porous materials is experimentally challenging. NMR is chemically resolved and applicable to optically opaque systems but suffers from a significant loss in spectral resolution in the presence of the magnetic field inhomogeneities typical of porous media. In this work, we introduce a method of analysis of conventional two-dimensional (2D) 1H NMR correlation spectroscopy (COSY) spectra based on the extraction of 1D antidiagonal projections, which are free from line-broadening effects and can therefore be used for chemical species identification. Here, we show the application of the technique to the measurement of linear n-alkanes where the cross-to-diagonal peak ratios are shown to follow a power-law curve as a function of the chain length. This calibration enables quantifying mixtures of linear hydrocarbons confined in any porous material independently of temperature or inter-molecular dynamics. Thus, this is a promising tool for quantitative chemical reaction monitoring studies in heterogeneous systems under operando experimental conditions.

Near edge X-ray absorption fine structure spectra of linear n-alkanes: Variation with chain length

The effect of chain length on the carbon 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of linear n-alkanes has been examined with Transition Potential Density Functional Theory (TP-DFT) calculations. Species from propane (C3H8) to n-icosane (n-C20H42) and selected longer chains were examined. This study focuses on the prominent ‘CH band’ (287–288 eV) in these NEXAFS spectra. TP-DFT calculations show that contributions from interior methylene groups (3 or more positions from the chain end) are similar, while contributions from the terminal methyl and the first methylene groups differ. The evolution of the angle dependent and Rydberg-valence mixing with chain length are also examined.

Geochemical imprints of occurrence, vertical distribution and sources of aliphatic hydrocarbons, aliphatic ketones, hopanes and steranes in sediment cores from ten Iranian Coral Islands, Persian Gulf

The levels, vertical distribution and sources of hydrocarbons and petroleum biomarkers were estimated for the first time in sediment cores (0–40 cm) from ten coral Islands of the Persian Gulf, Iran. Discrepant hydrocarbons, including linear n-alkanes (n-C11 to n-C40) and isoprenoids (AHs), aliphatic ketones (AKs), hopanes and steranes were measured in all core samples, showing mean concentrations ranging from 209 to 5388 μg g−1dw (∑30AH), 2–244 μg g−1-dw (∑13AK), 189–3713 ng g−1dw (∑31hopane) and 42–3864 ng g−1dw (∑15sterane), respectively. All sediment cores were found to be petroleum polluted, with ∑30AH > ∑31hopane > ∑15sterane > ∑13AK, with higher levels recorded at 10–20 cm, mainly at industrial sites. Various diagnostic indices revealed that hydrocarbons derived mainly from anthropogenic inputs, with significant contribution of biogenic origin at sites less polluted. Moreover, total organic carbon (0.24–23.45 mg g−1-dw), terrestrial and marine organic matter had an overwhelming effect on hydrocarbons deposition in sediment cores. Overall, findings provide relevant information for monitoring and preventing petroleum pollution in the sensitive ecosystems of the Persian Gulf.

Analysis of two common algorithms to compute self-diffusion coefficients in infinite dilution from molecular dynamics simulations and application to n-alkanes ([formula omitted] to [formula omitted]) in water

In this study the order-n algorithm and the linear regression algorithm used to obtain self-diffusion coefficients from molecular dynamics simulations are compared using theoretical analysis and Monte Carlo simulations. This analysis shows that the order-n algorithm allows decreasing the uncertainty in self-diffusion coefficients without increased computational effort. Both algorithms are used to calculate self-diffusion coefficients of linear n-alkanes in infinite dilution in water. Using the same trajectories the results obtained by the order-n algorithm had an average deviation from the experimental value of 2%, whereas using the linear regression algorithm the deviation was 12.5%. A guideline for selecting an optimal frequency, in which the center of mass trajectories from the molecular dynamics simulations should be written out, is given for the order-n algorithm.

Experimental study of interactions between uranium and n-alkanes in hydrothermal conditions (500 bar, 200 °C)

Organic matter is commonly involved in uranium deposits by reducing and alteration processes. An experimental study of the pyrolysis of linear n-alkanes at 200 °C, 500 bar for 2 months in presence of water and/or uranium were carried out. These experiments reveal that the initiation mechanism of the reaction pathway is the reduction of uranium and the oxidation of organic matter and that the oxidation of n-alkanes produces different compounds (aldehydes, alcohols, ketones, carboxylic acids, esters) in different configurations and proportions by auto-oxidation and by free-radical reactions. Another parameter observed during the experiments is the increase of the oxidation process the longer the aliphatic chain is. The pyrolysis of n-octane particularly revealed the role of water as an oxidizing agent instead of auto-oxidation mechanisms.

Temperature-dependent thermal properties of solid/liquid phase change even-numbered n-alkanes: n-Hexadecane, n-octadecane and n-eicosane

The thermal conductivity (λ) and thermal diffusivity (aT) of the solid/liquid phase change linear n-alkanes were measured simultaneously by the transient multi-current hot wire technique at atmospheric pressure in the range 258–348K. The same set-up was used to measure λ and aT of the liquid and the solid states at different electrical currents. Three n-alkanes, n-hexadecane (C16H34), n-octadecane (C18H38) and n-eicosane (C20H42) were studied. Differential scanning calorimetry was applied at the temperature range 248–348K to determine the melting/crystallization temperature, the heat of melting/crystallization and the specific heat of both the solid and liquid phases. Some results were compared with available literature data. The density of the n-alkanes at liquid state was also measured at different temperatures and their thermal diffusivity was estimated and compared to that obtained by the hot wire technique. The cumulative energy stored was estimated over a definite range of temperature for the three n-alkanes and this was found to be higher for eicosane.

Isolation and characterization of two novel strains capable of using cyclohexane as carbon source.

Two strains capable of degrading cyclohexane were isolated from the soil and sludge of the wastewater treatment plant of the University of Stuttgart and a biotrickling filter system. The strains were classified as gram negative and identified as Acidovorax sp. CHX100 and Chelatococcus sp. CHX1100. Both strains have demonstrated the capability to degrade cycloalkanes (C5-C8), while only strain CHX1100 used as well short linear n-alkanes (C5-C8) as the sole source of carbon and energy. The growth of Acidovorax sp. CHX100 using cyclohexane was much faster compared to Chelatococcus sp. CHX1100. Degenerated primers were optimized from a set sequences of cyclohexanol dehydrogenase genes (chnA) as well as cyclohexanone monooxygenases (chnB) and used to amplify the gene cluster, which encodes the conversion of cyclohexanol to caprolactone. Phylogenetic analysis has indicated that the two gene clusters belong to different groups. The cyclohexane monooxygenase-induced activity which oxidizes also indole to 5-hydroxyindole has indicated the presence of a CYP-type system monooxygenase involved in the transformation of cyclohexane to cyclohexanol.

On negative retentions in organic solvent nanofiltration

Some recent literature reports negative retentions in organic solvent nanofiltration. However, this phenomenon is little understood and requires systematic evaluation. The aim of this work is to extend the systematic investigations of solute transport through a dense PDMS-based polymeric OSN membrane. Experiments with four different solute classes, namely polyethylene glycol (194–590Da), linear carboxylic acid (228–340Da) polystyrene (MW=741Da) and n-alkanes (142–339Da) were performed. These solutes are dissolved in n-hexane, toluene, isopropanol or methanol.Depending on the solvent and the solute, there exist considerable differences in retentive behavior. Above mentioned negative retentions could be observed for linear carboxylic acids or n-alkane as solutes dissolved in isopropanol or methanol. The generally observed positive retention was measured for polyethylene glycol and polystyrene as solute. This systematic investigation proofs that strong solute–solvent–membrane interactions can cause a solubility determined solute transport resulting in up-concentration of the larger solute into the permeate. The surprising observation of larger transport rates for the larger solute molecules correlates with the growing contribution of the increasing partial molar volume to the chemical potential.

Heat conduction in chain polymer liquids: Molecular dynamics study on the contributions of inter- and intramolecular energy transfer

In this paper, the molecular mechanisms which determine the thermal conductivity of long chain polymer liquids are discussed, based on the results observed in molecular dynamics simulations. Linear n-alkanes, which are typical polymer molecules, were chosen as the target of our studies. Non-equilibrium molecular dynamics simulations of bulk liquid n-alkanes under a constant temperature gradient were performed. Saturated liquids of n-alkanes with six different chain lengths were examined at the same reduced temperature (0.7T(c)), and the contributions of inter- and intramolecular energy transfer to heat conduction flux, which were identified as components of heat flux by the authors' previous study [J. Chem. Phys. 128, 044504 (2008)], were observed. The present study compared n-alkane liquids with various molecular lengths at the same reduced temperature and corresponding saturated densities, and found that the contribution of intramolecular energy transfer to the total heat flux, relative to that of intermolecular energy transfer, increased with the molecular length. The study revealed that in long chain polymer liquids, thermal energy is mainly transferred in the space along the stiff intramolecular bonds. This finding implies a connection between anisotropic thermal conductivity and the orientation of molecules in various organized structures with long polymer molecules aligned in a certain direction, which includes confined polymer liquids and self-organized structures such as membranes of amphiphilic molecules in water.

Terahertz vibrational modes induced by heterogeneous nucleation in n-alkanes

We describe the observation of a broad and strongly temperature-dependent peak in the terahertz absorption spectrum of several linear n-alkanes. On cooling from the liquid into the rotator phase, the absorption is enhanced within a very narrow temperature range at the temperature of the first-order phase transition. This peak is associated with an enhancement in the vibrational density of states, induced by the heterogeneous nucleation of the rotator phase from the liquid. This is similar to the well-known Boson peak in glassy solids, and provides a new experimental tool for the characterization of nucleation dynamics in non-polar molecular liquids.

Predictions of the Fluorine NMR Chemical Shifts of Perfluorinated Carboxylic Acids, CnF2n+1COOH (n = 6−8)

Perfluorinated carboxylic acids (PFCAs) are a class of persistent environmental pollutants. Commercially available PFCAs are mixtures of linear and branched isomers, possibly with impurities. Different isomers have different physical and chemical properties and toxicities. However, little is known about the properties and the finer details of the structures of the individual branched isomers. Full geometry optimizations for the linear n-alkane (C(6)-C(27)) PFCAs indicated that all have helical structures. The helical angle increases slightly with increasing chain length, from 16.3 degrees in C(6)F(13)COOH to 17.0 degrees in C(27)F(55)COOH. This study predicts (19)F NMR parameters for 69 linear and branched isomers of the perfluoro carboxylic acids C(6)F(13)COOH, C(7)F(15)COOH, and C(8)F(17)COOH. B3LYP-GIAO/6-31++G(d,p)//B3LYP/6-31G(d,p) was used for the NMR calculations with analysis of the chemical shifts by the natural bond orbital method. The predictions of the (19)F chemical shifts revealed the differences among the CF(3), CF(2), and CF groups. In general, the absolute values for the chemical shifts for the CF(3) group are smaller than 90 ppm, for the CF larger than 160 ppm, and for the CF(2) between 110 and 130 ppm. The chemical shifts of the branched isomers are smaller in magnitude than the linear ones. The decrease is correlated with the steric hindrance of the CF(3) groups, the more hindered the CF(3), the greater the decrease in the (19)F chemical shifts. The predicted (19)F chemical shifts are similar to those for analogous perfluoro compounds with other terminal functional groups such as -SO(3)H or -SO(3)NH(2)CH(2)CH(3).

Molecular simulation study of the glass transition for a flexible model of linear alkanes

We present a molecular dynamics study in the isothermal–isobaric ensemble of a flexible model of linear n-alkanes for close to the glass transition. Our model is a modification of a realistic force field in which we have turned off the bond bending and the torsional intramolecular potentials to get the chain flexible. The glass transition is characterised by the change of slope of specific volume, as well as the vanishing of the self-diffusion coefficient and the divergence of the shear viscosity. Additionally we characterise the chain rearrangement dynamics above and close to the glass transition. Our results are in qualitative agreement with those previously obtained with more realistic models, so we conclude that the flexibility of the alkane chain does not play a dominant role in the glass transition.

Temperature influence on solution properties of ethanol + n-alkane mixtures

This paper contains the results of a new experimental study of the effect of temperature on density, refractive index on mixing and ultrasonic velocity for a number of linear n-alkanes combined with ethanol. The experimentally derived functions were also compared with those predicted by different theoretical procedures. A qualitative analysis reveals that structure disruptions are predominant in ethanol + n-alkane mixtures. This effect is reinforced when the temperature or solute chain length rises. A perusal of deviations between the experimental and calculated derived magnitudes shows that the predictive procedures give a qualitative estimation for the studied mixtures due to their high nonideality. Disposable literature was compared and commented upon.

The carbon–carbon bond dissociation energy as a function of the chain length

All the C–C fragmentations of the linear n-alkanes, C n H 2 n+2 , for n = 2 to n = 10 and the final C–H bond breaking have been calculated with the composite methods G2, G2MP2, G3, G3MP2B3 and G3B3. The results have been compared with the available experimental data.

Catalytic Alkane Metathesis by Tandem Alkane Dehydrogenation-Olefin Metathesis

With petroleum supplies dwindling, there is increasing interest in selective methods for transforming other carbon feedstocks into hydrocarbons suitable for transportation fuel. We report the development of highly productive, well-defined, tandem catalytic systems for the metathesis of n-alkanes. Each system comprises one molecular catalyst (a "pincer"-ligated iridium complex) that effects alkane dehydrogenation and olefin hydrogenation, plus a second catalyst (molecular or solid-phase) for olefin metathesis. The systems all show complete selectivity for linear (n-alkane) product. We report one example that achieves selectivity with respect to the distribution of product molecular weights, in which n-decane is the predominant high-molecular-weight product of the metathesis of two moles of n-hexane.