Linear Hydrocarbon Chains Research Articles

Evaluation of the ratio of the evaporation energy to the activation energy for estimating the thermodiffusion coefficient

AbstractThermodiffusion has an important role in displacements of hydrocarbon reservoir. The ratio of the evaporation energy to the activation energy of viscous flow in pure limits, τpure,k, is of a great importance in estimating the thermodiffusion coefficient for non‐associating fluid mixtures. Several methods may be used to estimate τpure,k which causes different values for thermodiffusion coefficients. A fixed value for τpure,k was considered to predict the thermodiffusion coefficient. In this paper, Abbasi et al.'s [J. Non‐Equilib. Thermodyn. 2010;35:1–14] model and Shukla and Firoozabadi's model have been applied to predict thermodiffusion coefficients for linear chain hydrocarbon binary mixtures. The results show a very good performance of the simple approach in respect to the previous models in estimating thermodiffusion coefficients. © 2011 Canadian Society for Chemical Engineering

Anomalous Behavior of Linear Hydrocarbon Chains in Water–DMSO Binary Mixture at Low DMSO Concentration

We find that at a mole fraction 0.05 of DMSO (x(DMSO) = 0.05) in aqueous solution, a linear hydrocarbon chain of intermediate length (n=30-40) adopts the most stable collapsed conformation. In pure water, the same chain exhibits an intermittent oscillation between the collapsed and the extended coiled conformations. Even when the mole fraction of DMSO in the bulk is 0.05, the concentration of the same in the first hydration layer around the hydrocarbon of chain length 30 (n=30) is as large as 17%. Formation of such hydrophobic environment around the hydrocarbon chain may be viewed as the reason for the collapsed conformation gaining additional stability. We find a second anomalous behavior to emerge near x(DMSO)=0.15, due to a chain-like aggregation of the methyl groups of DMSO in water that lowers the relative concentration of the DMSO molecules in the hydration layer. We further find that as the concentration of DMSO is gradually increased, it progressively attains the extended coiled structure as the stable conformation. Although Flory-Huggins theory (for binary mixture solvent) fails to predict the anomaly at x(DMSO)=0.05, it seems to capture the essence of the anomaly at 0.15.

Evaluation of the activation energy of viscous flow for a binary mixture in order to estimate the thermodiffusion coefficient

The evaluation of the activation energy in Eyring's viscosity theory is of great importance in estimating the thermodiffusion coefficient for associating and non-associating fluid mixtures. Several methods were used to estimate the activation energies of pure components and then extended to mixtures of linear hydrocarbon chains. Results show that the recent model of Abbasi et al. [J. Chem. Phys. 131: 014502, 2009.] gives a good outcome in determining the activation energy of the components of a binary mixture. The activation energy model for pure components is shown to be useful for obtaining the activation energy of the mixture. In this paper, the activation energy model using alternative forms of Eyring's viscosity theory is used to estimate the thermodiffusion coefficient values for hydrocarbon binary mixtures. Comparisons of predicted thermodiffusion coefficients using different theoretical models with the experimental data show good capability of the activation energy model.

Molecular basis of the selectivity of the immunoproteasome catalytic subunit LMP2-specific inhibitor revealed by molecular modeling and dynamics simulations.

Given that immunoproteasome inhibitors are currently being developed for a variety of potent therapeutic purposes, the unique specificity of an α',β'-epoxyketone peptide (UK101) toward the LMP2 subunit of the immunoproteasome (analogous to β5 subunit of the constitutive proteasome) has been investigated in this study for the first time by employing homology modeling, molecular docking, molecular dynamics simulation, and molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) binding free energy calculations. On the basis of the simulated binding structures, the calculated binding free energies are in qualitative agreement with the corresponding experimental data, and the selectivity of UK101 is explained reasonably. The observed selectivity of UK101 for the LMP2 subunit is rationalized by the requirement for both a linear hydrocarbon chain at the N terminus and a bulky group at the C terminus of the inhibitor, because the LMP2 subunit has a much more favorable hydrophobic pocket interacting with the linear hydrocarbon chain, and the bulky group at the C terminus has a steric clash with the Tyr 169 in β5 subunit. Finally, our results help to clarify why UK101 is specific to the LMP2 subunit of immunoproteasome, and this investigation should be valuable for rational design of more potent LMP2-specific inhibitors.

Multiscale modeling of thermal conductivity of polymer/carbon nanocomposites

Molecular dynamics simulation was used to estimate the interfacial thermal (Kapitza) resistance between nanoparticles and amorphous and crystalline polymer matrices. Bulk thermal conductivities of the nanocomposites were then estimated using an established effective medium approach. To study functionalization, oligomeric ethylene–vinyl alcohol copolymers were chemically bonded to a single wall carbon nanotube. The results, in a poly(ethylene–vinyl acetate) matrix, are similar to those obtained previously for grafted linear hydrocarbon chains. To study the effect of non-covalent functionalization, two types of polyethylene matrices. -- aligned (extended-chain crystalline) vs. amorphous (random coils) were modeled. Both matrices produced the same interfacial thermal resistance values. Finally, functionalization of edges and faces of plate-like graphite nanoparticles was found to be only modestly effective in reducing the interfacial thermal resistance and improving the composite thermal conductivity.

Structure and water permeability of fully hydrated diphytanoylPC

Diphytanoylphosphatidylcholine (DPhyPC) is a branched chain lipid often used for model membrane studies, including peptide/lipid interactions, ion channels and lipid rafts. This work reports results of volume measurements, water permeability measurements P f , X-ray scattering from oriented samples, and X-ray and neutron scattering from unilamellar vesicles at T = 30 °C. We measured the volume/lipid V L = 1426 ± 1 Å 3. The area/lipid was found to be 80.5 ± 1.5 Å 2 when both X-ray and neutron data were combined with the SDP model analysis (Kučerka, N., Nagle, J.F., Sachs, J.N., Feller, S.E., Pencer, J., Jackson, A., Katsaras, J., 2008. Lipid bilayer structure determined by the simultaneous analysis of neutron and X-ray scattering data. Biophys. J. 95, 2356–2367); this is substantially larger than the area of DOPC which has the largest area of the common linear chain lipids. P f was measured to be (7.0 ± 1.0) × 10 −3 cm/s; this is considerably smaller than predicted by the recently proposed 3-slab model (Nagle, J.F., Mathai, J.C., Zeidel, M.L., Tristram-Nagle, S., 2008. Theory of passive permeability through lipid bilayers. J. Gen. Physiol. 131, 77–85). This disagreement can be understood if there is a diminished diffusion coefficient in the hydrocarbon core of DPhyPC and that is supported by previous molecular dynamics simulations (Shinoda, W., Mikami, M., Baba, T., Hato, M., 2004. Molecular dynamics study on the effects of chain branching on the physical properties of lipid bilayers. 2. Permeability. J. Phys. Chem. B 108, 9346–9356). While the DPhyPC head–head thickness ( D HH = 36.4 Å), and Hamaker parameter ( H = 4.5 × 10 −21 J) were similar to the linear chain lipid DOPC, the bending modulus ( K C = 5.2 ± 0.5 × 10 −21 J) was 30% smaller. Our results suggest that, from the biophysical perspective, DPhyPC belongs to a different family of lipids than phosphatidylcholines that have linear chain hydrocarbon chains.

Conductivity and Dissociation Constants of Quaternary Ammonium Perchlorates and Picrates in 4-Methyl-pentan-2-one

The dissociation of 14 ionophores, namely, seven symmetrical (C1 to C7) and five asymmetrical quaternary ammonium perchlorates and two tetraalkylammonium picrates (all with linear hydrocarbon chains), in 4-methyl-pentan-2-one was studied at 25 °C (er = 12.92) using the conductance method. The values of the association constants of the quaternary ammonium cation, Ct+, with ClO4− vary from (7.4 ± 0.3)·103 L·mol−1 for tetramethylammonium to (2.4 ± 0.1)·103 L·mol−1 for tetrahexyl- and tetraheptylammonium; a distinct dependence on the size of the Ct+, especially for symmetrical cations, is evident. The values of the limiting molar conductivities Λ0/S·mol−1·cm2 vary from 122.8 to 90.0 (± 0.7). The plot of Λ0 versus the reciprocal cube root of the total van der Waals volume of the cations, VCt−1/3, is close to linear up to tetrapentylammonium and hexadecyltrimethylammonium, while for larger cations (with 21 to 28 carbon atoms) the Λ0 values stay practically constant. At the same time, symmetrical and asymmetrica...

Theoretical and experimental comparison of the Soret effect for binary mixtures of toluene and n-hexane, and benzene and n-heptane

Thermodiffusion along with molecular diffusion occurs in many engineering systems and in nature. Thermodiffusion has a great effect on concentration distribution in binary mixtures. A new approach to predicting the Soret coefficient in binary mixtures of linear chain and aromatic hydrocarbons using the thermodynamics of irreversible processes is presented. In particular, this approach is based on free volume theory, which explains the diffusivity in diffusion-limited systems. Free volume states that the transfer kinetics of molecules depends greatly on molecular size and shape. The proposed model, combined with Shukla and Firoozabadi’s model, was applied to predict the Soret coefficient. The perturbed chain statistical associating fluid theory equation of state (PCSAFT-EoS) was used to calculate the related thermodynamic properties. Comparisons of the theoretical results with experimental data show good agreement.

Removing Bisphenol A from Aqueous Solution by Phosphorylated Cotton in the Presence of Cetyl Trimethyl Ammonium Bromide

Removal of bisphenol A (BPA) was investigated by hydrophobic sorption of hemimicelles with phosphorylated cotton (PC) as a sorbent and cetyl trimethyl ammonium bromide (CTAB) as a cationic surfactant. CTAB was sorbed on oppositely charged PC through coulombic attraction and formed hemimicelles at a certain concentration level called critical hemimicellar concentration (CHC). BPA was subsequently sorbed on the sorbent through hydrophobic interaction between the linear hydrocarbon chain of CTAB on hemimicelles and the aromatic alkyl group of BPA. BPA removal was found to be dependent on initial pH and CTAB dosage. Isothermal data of BPA sorption conformed well to the Langmuir model, and the maximum sorption capacity (Qm) of PC for BPA was 48.78 mg/g. The BPA removal process could be described by a pseudosecond-order kinetic model. The thermodynamic study indicated that the BPA removal process was spontaneous and exothermic.

A new proposed approach to estimate the thermodiffusion coefficients for linear chain hydrocarbon binary mixtures

Thermodiffusion behaviors in nonassociating mixtures have an important role in separation processes of the oil industry. The variations of composition and temperature may either lessen or enhance the separation in mixtures. A new model regarding the prediction of thermodiffusion coefficients for linear chain hydrocarbon binary mixtures using the thermodynamics of irreversible process is proposed. The model predicts the net amount of heat transported based on available volume for each molecule. This newly proposed model combined with the perturbed chain statistical associating fluid theory equation of state has been applied to predict thermodiffusion coefficients for binary hydrocarbon mixtures of C(10)-nC(i) (i=5,6,7,15,16,17,18), C(12)-nC(i) (i=5,6,7,8,9), and C(18)-nC(i) (i=5,6,7,8,9,12). Comparisons of the calculated theoretical results with the experimental data show good performance of the proposed model. In particular, this model which is based on the kinetic approaches has been found to be the most reliable and represents a significant improvement over the earlier models.

Self-Organization of n-Alkane Chains in Water: Length Dependent Crossover from Helix and Toroid to Molten Globule

We demonstrate a chain length dependent crossover in the structural properties of linear hydrocarbon (n-alkane) chains using detailed atomistic simulations in explicit water. We identify a number of exotic structures of the polymer chain through energy minimization of representative snapshots collected from molecular dynamics trajectory. While the collapsed state is ring-like (circular) for small chains (CnH2n+2; n<or=20) and spherical for very long ones (n=100), we find the emergence of ordered helical structures at intermediate lengths (n approximately 40). We find different types of disordered helices and toroid-like structures at n=60. We also report a sharp transition in the stability of the collapsed state as a function of the chain length through relevant free energy calculations. While the collapsed state is only marginally metastable for C20H42, a clear bistable free energy surface emerges only when the chain is about 30 monomers long. For n=30, the polymer exhibits an intermittent oscillation between the collapsed and the coil structures, characteristic of two stable states separated by a small barrier.

Modeling vibrational resonance in linear hydrocarbon chain with a mixed quantum-classical method

The quantum dynamics of a vibrational excitation in a linear hydrocarbon model system is studied with a new mixed quantum-classical method. The method is suited to treat many-body systems consisting of a low dimensional quantum primary part coupled to a classical bath. The dynamics of the primary part is governed by the quantum corrected propagator, with the corrections defined in terms of matrix elements of zeroth order propagators. The corrections are taken to the classical limit by introducing the frozen Gaussian approximation for the bath degrees of freedom. The ability of the method to describe dynamics of multidimensional systems has been tested. The results obtained by the method have been compared to previous quantum simulations performed with the quasiadiabatic path integral method.

Hydrocarbons characterization in coastal sediments of the Argentine Patagonia using the nuclear magnetic resonance (NMR) spectroscopy

Hydrocarbons in Patagonian sediments were analyzed to evaluate their biogenic or petrogenic origins. Structural determination by 1H-NMR spectrometry and principal component analysis (PCA) show that the first two principal components accounted for more than 75.7% of the variance. The results indicate that biogenic hydrocarbons have mainly linear hydrocarbon chains and polar groups (high H2, H4, H5, and HCOOH), while petrogenic hydrocarbons show more branched chains and mainly mono-aromatic components, e.g., crude oil (high H1, H1A, and H3) or mainly poly-aromatic components (high H4, and H2A) in weathering oil.

Intrinsic parameters for structural variation of reverse micelles in nonionic surfactant (glycerol α-monolaurate)/oil systems: a SAXS study

Using Small-Angle X-ray scattering (SAXS), we have studied self-assembled structures of glycerol alpha-monolaurate (C(12)G(1)) in different nonpolar solvents, such as cyclohexane, n-octane, n-decane, n-tetradecane, and n-hexadecane, as a function of composition, temperature, and added polar additives. The dilute mixtures of C(12)G(1) with the aforementioned oils are essentially a solid dispersion at lower temperatures without forming any liquid crystalline phases, which are transformed into isotropic reverse micellar solutions upon heating. The generalized indirect Fourier transformation (GIFT) analysis of the SAXS data has drawn a clear picture of the structural variations of the reverse micellar aggregates in the isotropic solution phase. A notable effect on the micellar growth emerges when cyclohexane is replaced with the linear-chain hydrocarbon oils; a gradual increase of the carbon number of the hydrocarbon skeleton from octane to hexadecane, ellipsoidal prolate-like micelles are eventually transformed to long rod-like ones. Far more pronounced structural enhancement could be achieved by increasing the hydrophilicity of the surfactant, as short-rod micelles observed in the C(12)G(1)/decane system are replaced with long cylindrical ones when a more hydrophilic diglycerol monolaurate (C(12)G(2)) is used. This fact also supports a scenario that regulates the ability to form elongated to reverse structures. Lowering the temperature and increasing the surfactant concentration similarly lead to micellar growth while the cross-sectional structure remains essentially unchanged. In contrast, polar additive-induced growth is accompanied by the rapid swelling of the micellar core. Our data demonstrate that optimization of the oil properties and/or other outer conditions provide possible routes to flexibly controlling the size, shape, and internal structure of the reverse micelles despite lower universality for a shorter hydrophilic chain surfactant.

Influence of Molecular and Supramolecular Structure on the Gas−Liquid Interfacial Reactivity of Hydrocarbon Liquids with O(3P) Atoms

We have investigated the interfacial reactivity of gas-phase O(3P) atoms with a representative range of long-chain liquid hydrocarbons. These consisted of two branched molecules, squalane (C30H62, 2,6,10,15,19,23-hexamethyltetracosane) and pristane (C19H40, 2,6,10,14-tetramethylpentadecane), and three linear ones, n-docosane (C22H46), n-tetracosane (C24H50) and n-octacosane (C28H58). This represents the first systematic investigation of reactions of this type for molecules other than squalane. The O(3P) atoms were generated by 355-nm laser photolysis of a low pressure of NO2 above the liquid surface. The nascent gas-phase OH radical products were detected by laser-induced fluorescence (LIF). Measurements for the linear hydrocarbons were constrained by their vapor pressures to single temperatures slightly (∼1 K) above their respective melting points. Pristane was studied at the lowest temperature practically achievable. Squalane was compared as a reference at the full set of temperatures. Appearance profiles for all of the liquids showed similar characteristic differences between OH v‘=0 and 1. LIF excitation spectra were obtained for each of the vibrational levels at both the rising edge and peak of the appearance profiles. We conclude that the observed variations in rotational temperatures are consistent with dual contributions to the reaction mechanism for all the liquids, involving both direct escape and trapping-desorption components of the observed OH, as has previously been proposed for squalane. The relative yields of OH showed some surprising dependences on the liquid, including an unexpectedly strong variation with linear hydrocarbon chain length. These cannot all be explained by the relative reactivity of primary, secondary, and tertiary H−C units. We discuss the possibility that the known “surface freezing” phenomenon for linear hydrocarbons may play a role.

Initiated chemical vapor deposition of biopassivation coatings

Organosilicon polymers show great utility as both biocompatible and electrically insulating materials. In this work, thin films of a novel organosilicon polymer are synthesized by initiated CVD utilizing trivinyl–trimethyl cyclotrisiloxane as a monomer and terbutyl peroxide as a free radical generating initiator. Use of an initiator allows for formation of polymer films at filament temperatures as low as 250 °C which allows for retention of all siloxane ring moieties within the resulting polymer. The all-dry deposition process generates a highly crosslinked matrix material in which over 95% of the vinyl moieties present on the monomer units have been reacted out to form linear polymerized hydrocarbon chains. The material possesses an electrical resistivity of 4 × 10 15 Ω cm. In addition, biased soak testing of material samples in a simulated biological environment demonstrates retention of electrical material properties for greater than 2 years.

Ab Initio Analysis of the Structural Properties of Alkyl-Substituted Polyhedral Oligomeric Silsesquioxanes

Ab initio quantum mechanical calculations have been performed to establish the potentials for alkyl-substituted polyhedral oligomeric silsesquioxane (POSS) monomers RxH8-x(SiO1.5)8. More specifically, we have examined the unsubstituted POSS (SiO1.5H)8 cage as well as linear and cyclic alkyl-substituted cages where one of the terminating hydrogen atoms is replaced by a hydrocarbon group, that is, R1H7(SiO1.5)8. The results for the minimum-energy configurations indicate that the presence of the linear hydrocarbon chains and cyclic intermediates have very little effect on the structure of the POSS cage. Although the POSS monomeric cage does influence the partial charges of the first few carbon atoms covalently bound to the POSS monomer, its effect on the structural properties of the alkyl chain is small. Differences arise, however, for cyclic alkyl substitutents bound to the POSS cage due to the repulsive interactions between the POSS cage and bulkier cyclic intermediates that result upon rotation of the Si-C-C-C dihedral angles. The interatomic potentials for these rotational, or torsional, terms need to be modified slightly in order to appropriately simulate sterically hindered substitutents on the cage. Our results suggest that combining an atomistic force field independently developed to describe silsesquioxanes with an independent atomistic model developed to describe hydrocarbon chains can be used in classical molecular simulation studies of most alkyl-silsesquioxanes. This avoids the need to develop specific force fields for each substituted POSS cage studied and opens up the possibility of using molecular simulation to probe the thermodynamic and structural properties of these unique nanoscale building blocks.

Shape, Size, and Structural Control of Reverse Micelles in Diglycerol Monomyristate Nonionic Surfactant System

We have investigated the self-organization structures of diglycerol monomyristate (DGM) in different types of organic solvents. Study of phase behavior shows the presence of solid at lower temperature, and upon increasing temperature, the solid phase transforms to lamellar liquid crystal (L(alpha)) phase in the surfactant axis in all the DGM/oil systems. In the dilute regions, however, the dispersion of the solid or L(alpha) phase is observed, depending on the solvent and temperature. At higher temperatures, the L(alpha) phase melts to the isotropic reverse micellar solution phase. GIFT analysis of small-angle X-ray scattering data supported by a complementary modeling method have unambiguously shown that the structure of the DGM reverse aggregates can flexibly be controlled by optimizing the fundamental properties of solvent oils. In aromatic oils, the observed moderate micellar elongation is almost solely governed by the polarity of the aromatic ring, the length of the hydrocarbon side chain group showing no drastic effect. In contrast, when the solvent is replaced with linear-chain hydrocarbon oils, the drastic effects depending on the chain length emerge; by gradually increasing the length from decane to hexadecane, the long cylindrical particles in decane are finally transformed into planar aggregates, whose mechanism may be explained in terms of the transfer free energy of the diglycerol moiety from the hydrophilic environment to the hydrocarbon oils with a different chain length. We have also systematically examined the effects of temperature, the surfactant concentration, and added water.

Hydrocarbon Surfactants for CO2: An Impossible Dream?

It used to be thought that hydrocarbon ionic surfactants were incompatible with dense liquid or supercritical CO2, and fluorination of the chains was necessary to achieve any appreciable solubility. Here it is shown that branching of pendant hydrocarbon chains, especially methylation of the tips, can lead to substantial solubility enhancements in CO2 over normal linear chain hydrocarbon surfactants. In addition, increasing the number of these t-butyl-tipped groups from single-chained, through twin-tailed, to triple-chain surfactants has a profound effect on CO2 compatibility. High-pressure interfacial tension, small-angle neutron scattering, and near infrared spectroscopy have been applied to reveal the effects of surfactant structure on surface activity, aggregation, and solubility in CO2.

Cumulative π‐π interaction triggers unusually high stabilization of linear hydrocarbons inside the single‐walled carbon nanotube

AbstractThe interactions of linear hydrocarbons C2nH4 and C2nH2 (n = 1–4) with a finite‐length armchair (5,5) single‐walled carbon nanotube have been investigated using HF and MP2 methods in conjunction with 6‐31G(d) basis set, and molecular mechanics (MM) with MM2 force field. In all cases, the results obtained at MP2/6‐31G(d) level show stabilization of these supramolecular systems, contrary to the repulsive interactions obtained with the HF method. The interaction energies computed using MM with MM2 force field are in close agreement with the results obtained using the MP2/6‐31G(d) level. They increase gradually as the length of linear hydrocarbon chain increases. The present study indicates that cumulative π‐π interaction is the origin for the exceptionally high stabilization of the long nanotube‐hydrocarbon complexes. Mulliken population analysis reveals a very small charge transfer between the nanotube and the guest. Essentially there is no change in HOMO‐LUMO energy gap by the insertion of linear hydrocarbons. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007