Longer Alkanes Research Articles

Binding and Assembly of a Benzotriazole Cavitand in Water.

A water-soluble cavitand bearing a benzotriazole upper rim was prepared and characterized. It exists as a dimeric velcraplex in D2 O, but forms host-guest complexes with hydrophobic and amphiphilic guests. Alkanes (C5 to C10), cyclic ketones (C6-C10), cyclic alcohols (C6-C8) and various amphiphilic guests form 1 : 1 cavitand complexes. A cyclic array of hydrogen bonds, bridged by solvent/water (D2 O) molecules, stabilizes the vase conformation of the complexes. With longer alkanes (C12-C15), symmetrical dialkyl amine, urea and phosphate, 2 : 1 host:guest capsules are formed. Computations indicate that additional waters on the upper rim create a self-complementary hydrogen-bonding pattern for capsule formation.

Binding and Assembly of a Benzotriazole Cavitand in Water

AbstractA water‐soluble cavitand bearing a benzotriazole upper rim was prepared and characterized. It exists as a dimeric velcraplex in D2O, but forms host–guest complexes with hydrophobic and amphiphilic guests. Alkanes (C5 to C10), cyclic ketones (C6–C10), cyclic alcohols (C6–C8) and various amphiphilic guests form 1 : 1 cavitand complexes. A cyclic array of hydrogen bonds, bridged by solvent/water (D2O) molecules, stabilizes the vase conformation of the complexes. With longer alkanes (C12–C15), symmetrical dialkyl amine, urea and phosphate, 2 : 1 host:guest capsules are formed. Computations indicate that additional waters on the upper rim create a self‐complementary hydrogen‐bonding pattern for capsule formation.

A DFT study on recombination of alkyl radicals to C2-C17 normal alkanes & branched C8 alkanes and corresponding C-C bond pyrolysis reaction

Alkane C–C dissociation is one of the key elementary reactions in combustion and pyrolysis. Corresponding rate constants are important in kinetic models. However, reliable rate constants for long and branched alkanes are still limited, and accurate rate constant calculation for large alkanes is time-consuming. In this work we have systematically investigated the high-pressure-limit rate constants of alkyl recombination to normal CnH2n+2 (n=2–17) and some branched alkanes with UM06-2X/cc-pvdz//VRC-TST method.Corresponding dissociation rate constants have been converted using calculated free energies at G4MP2 level. This combined method is found to reproduce dissociation rate constants well (error < 101) for small alkanes at 700–2000 K. Our results suggested that it’s a good approximation to use short alkane (C3 for example) dissociation rate constants for longer alkanes above 800 K. Dissociation reactions leading to CH3 radical are much harder than those leading to other alkyls.It's a good approximation to use rate constant of dissociation leading to C2H5 radical for other alkyl dissociations other than CH3. Both modified and a four-parameter Arrhenius equations give good fitting to calculated rate constants. Our results give further insight into C–C bond dissociation of long and branched alkanes, and provide alternative kinetic data for relevant combustion/pyrolysis kinetic models.

Crystal Structure of a Putative Cytochrome P450 Alkane Hydroxylase (CYP153D17) from Sphingomonas sp. PAMC 26605 and Its Conformational Substrate Binding.

Enzymatic alkane hydroxylation reactions are useful for producing pharmaceutical and agricultural chemical intermediates from hydrocarbons. Several cytochrome P450 enzymes catalyze the regio- and stereo-specific hydroxylation of alkanes. We evaluated the substrate binding of a putative CYP alkane hydroxylase (CYP153D17) from the bacterium Sphingomonas sp. PAMC 26605. Substrate affinities to C10–C12 n-alkanes and C10–C14 fatty acids with Kd values varied from 0.42 to 0.59 μM. A longer alkane (C12) bound more strongly than a shorter alkane (C10), while shorter fatty acids (C10, capric acid; C12, lauric acid) bound more strongly than a longer fatty acid (C14, myristic acid). These data displayed a broad substrate specificity of CYP153D17, hence it was named as a putative CYP alkane hydroxylase. Moreover, the crystal structure of CYP153D17 was determined at 3.1 Å resolution. This is the first study to provide structural information for the CYP153D family. Structural analysis showed that a co-purified alkane-like compound bound near the active-site heme group. The alkane-like substrate is in the hydrophobic pocket containing Thr74, Met90, Ala175, Ile240, Leu241, Val244, Leu292, Met295, and Phe393. Comparison with other CYP structures suggested that conformational changes in the β1–β2, α3–α4, and α6–α7 connecting loop are important for incorporating the long hydrophobic alkane-like substrate. These results improve the understanding of the catalytic mechanism of CYP153D17 and provide valuable information for future protein engineering studies.

Monte Carlo Simulations of Thin Hydrocarbon Films: Composition Heterogeneity and Structure at the Solid–Liquid and Liquid–Vapor Interfaces

The structural properties of 10 nm thick lubricant films consisting of binary and ternary n-alkane mixtures (8 ≤ n ≤ 12) adsorbed on a structureless metal substrate were studied for several temperatures and compositions using Monte Carlo simulations. Configurational-bias Monte Carlo identity switch moves are essential to sample the spatial distribution in these mixtures. Longer alkanes are found to preferentially adsorb onto the substrate while shorter alkanes are enriched at the liquid-vapor interface. This preferential adsorption is evident even when the two chains differ by only one methylene unit and the longer chain is the minor component. Enhanced composition heterogeneity and orientational ordering and fewer gauche defects are characteristic features of the first layer near the substrate.

Computational Investigation of the n-Alkane/Water Interface with Many-Body Potentials: The Effect of Chain Length and Ion Distributions

Molecular dynamics simulations with polarizable potentials were carried out to investigate the n-alkane/water interface, including sodium-halide ion distributions. A new polarizable force field was developed for n-alkanes, which gave good agreement with experiment for liquid densities and heats of vaporization for different n-alkanes at different temperatures. Also, good agreement with experiment was found for alkane/water interfacial tensions for a variety of alkanes. Alkane/water interfaces with linear alkanes of different chain lengths had fairly similar properties, except that with longer alkanes, the interfacial width decreased. Water induced dipoles were reduced at the alkane/water interface in comparison with the bulk, but their induced dipoles were greater at the alkane/water interface than at the air/water interface. Furthermore, the water structure expanded at the alkane/water interface in comparison with the bulk, but this expansion was not as significant as at the air/water interface. Sodium-h...

Review of Crystalline Structures of Some Selected Homologous Series of Rod-Like Molecules Capable of Forming Liquid Crystalline Phases

The crystal structures of four homologous series of rod-like molecules are reviewed, two of which form hydrogen bonds and two with a symmetric chemical constitution. Many of the compounds investigated turn into liquid crystalline phases upon temperature increase. It is of valuable interest to know possible conformations and possible packing arrangements as prerequisites to model liquid crystalline structures. The hydrogen bonds of homologous series of pure 4-(ω-hydroxyalkyloxy)-4′-hydroxybiphenyl (HnHBP, n the alkyloxy tail length) are realized through head to tail arrangements of the hydroxyl groups and crystallize except one compound in chiral space groups without the molecules containing any asymmetric carbon. The hydrogen bonds of the homologous series of 4-substituted benzoic acids with various lengths of the tail provide dimers through strong polar bonding of adjacent carboxyl groups and thus provide the stiff part of a mesogenic unit prerequisite for liquid crystalline phases. The homologous series of dialkanoyloxybiphenyls (BP-n, n = 1, 19), of which nine compounds could be crystallized, show liquid crystalline behavior for longer alkane chain lengths, despite the high mobility of the alkane chain ends already detectable in the crystal phase. A single molecule, half a molecule or two half molecules form the asymmetric unit in a centrosymmetric space group. The homologous series of 1,4-terephthalidene-bis-N-(4′-n-alkylaniline) (TBAA-n) exhibit a large variety of packing arrangements in the crystalline state, with or without relying on the symmetry center within the molecules.

Ethylene Films Adsorbed onto Purified HiPco Single Walled Carbon Nanotubes: A Comparison with Ethane and Longer Alkanes

The results of adsorption isotherm measurements for ethylene on purified HiPco SWNTs conducted at 11 different temperatures (between 110 K and 220 K) are reported, together with a comparison with the results we have obtained for ethane on the same substrate. Two groups of distinct binding sites were observed for ethylene on bundles of carbon nanotubes; this is in agreement with previously reported observations for ethane on this same sorbent. In addition, a consistent value of the specific surface area of the substrate was obtained from the ethylene and ethane data measured at approximately the same temperature. We have also determined the coverage dependence of the isosteric heat of adsorption for ethylene on the HiPco nanotube bundles. The reported experimental isosteric heat results are compared with simulation results for ethane and ethylene.

Bent Alkanes in a New Thiourea-Containing Capsule

The synthesis of a cavitand featuring thiourea hydrogen bonding sites and its dimerization in the presence of suitable guests are reported. Dimerization creates a capsule host wider than the corresponding urea or imide structures, and longer alkanes can be accommodated. Specifically, n-C(15)H(32) is encapsulated, but this guest appears folded inside as deduced from NMR studies. Apparently, the plasticity of hydrogen bonds between thiourea groups allows a stable encapsulation complex to persist in solution even though the guest is contorted.

Structural characterization of the δ-clathrate forms of syndiotactic polystyrene with n-alkanes

The δ-clathrate forms of syndiotactic polystyrene (s-PS) containing a homologous series of guests characterized by an increasing molecular volume ( n-alkanes ranging from n-pentane to n-dodecane) have been investigated. The present analysis allows concluding that the volume of the guest plays a crucial role in the choice of the type of δ-clathrate that can be obtained. As a matter of fact, longer n-alkanes, such as n-octane, n-nonane or n-decane, turned out to give rise triclinic δ-clathrates presenting a guest/monomeric-unit ratio of 1/8, while δ-clathrates containing shorter alkanes, like n-hexane or n-heptane, instead, present a monoclinic or a triclinic structure with a guest/monomeric-unit ratio of 1/4. These results confirm the validity of a simple criterion to predict the type of s-PS δ-clathrate with a certain guest on the basis of the experimental d 010, as described in Macromolecules 2010, 43, 8549–8558. Moreover, our analysis confirms previous solid state 13C NMR and Raman spectroscopy data, indicating that shorter n-alkanes molecules, like n-hexane, are hosted in the cavities with an all- trans conformation while longer alkanes, like n-nonane, present bent conformations. The effect of n-alkanes molecules on the crystallization of s-PS amorphous samples has been investigated too.

Material Transfer in Cubosome−Emulsion Mixtures: Effect of Alkane Chain Length

We present here results on the transfer kinetics of monoglyceride and n-alkanes in water. Transfer kinetics between cubosomes and emulsion droplets were followed using time-resolved small-angle X-ray scattering measurements, while dynamic light scattering was used to study the changes in the particle radii. The effect of the initial size of cubosomes and emulsion droplets on the final droplet size of the mixed components was investigated. Decane was transferred into the cubosomes with the disappearance of all emulsion droplets, with no detectable transfer of monoglyceride. Cubosomes were even found to absorb bulk decane into the solution from a surface layer, which raises the possibility of using cubosomes to bind hydrophobic molecules from the bulk phase. In mixtures with longer alkanes, transfer of both monoglyceride and oil was observed; while with octadecane the transfer of monoglyceride into emulsion droplets dominated. Calculating the point at which the transfer of monoglyceride becomes dominant over that of oil as the alkane chain length is increased shows that, in compositional ripening, monoglyceride behaves as an alkane with 15.3 carbons. These results further our understanding of the interactions of internally self-assembled particles in various media and suggest possible ways of controlling the size of the particles.

Molecular simulations for adsorption and separation of natural gas in IRMOF-1 and Cu-BTC metal-organic frameworks

We use Monte Carlo simulations to study the adsorption and separation of the natural gas components in IRMOF-1 and Cu-BTC metal-organic frameworks. We computed the adsorption isotherms of pure components, binary, and five-component mixtures analyzing the siting of the molecules in the structure for the different loadings. The bulk compositions studied for the mixtures were 50 : 50 and 90 : 10 for CH4-CO2, 90 : 10 for N2-CO2, and 95 : 2.0 : 1.5 : 1.0 : 0.5 for the CH4-C2H6-N2-CO2-C3H8 mixture. We choose this composition because it is similar to an average sample of natural gas. Our simulations show that CO2 is preferentially adsorbed over propane, ethane, methane and N2 in the complete pressure range under study. Longer alkanes are favored over shorter alkanes and the lowest adsorption corresponds to N2. Though IRMOF-1 has a significantly higher adsorption capacity than Cu-BTC, the adsorption selectivity of CO2 over CH4 and N2 is found to be higher in the latter, proving that the separation efficiency is largely affected by the shape, the atomic composition and the type of linkers of the structure.

Alkane/Alcohol Mixed Monolayers at the Solid/Liquid Interface

In this work, we present the behavior of solid monolayers of binary mixtures of alkanes and alcohols adsorbed on the surface of graphite from their liquid mixtures. We demonstrate that solid monolayers form for all the combinations investigated here. Differential scanning calorimetry (DSC) is used to identify the surface phase behavior of these mixtures, and elastic neutron incoherent scattering has been used to determine the composition of the mixed monolayers inferred by the calorimetry. The mixing behavior of the alcohol/alkane monolayer mixtures is compared quantitatively with alkane/alkane and alcohol/alcohol mixtures using a regular solution approach to model the incomplete mixing in the solid monolayer with preferential adsorption determining the surface composition. This analysis indicates the preferential adsorption of alcohols over alkanes of comparable alkyl chain length and even preferential adsorption of shorter alcohols over longer alkanes, which contrasts strongly with mixtures of alkane/alkane and alcohol/alcohol of different alkyl chain lengths where the longer homologue is always found to preferentially adsorb over the shorter. The alcohol/alkane mixtures are all found to phase separate to a significant extent in the adsorbed layer mixtures even when molecules are of a similar size. Again, this contrasts strongly with alkane/alkane and alcohol/alcohol mixtures where, although phase separation is found for molecules of significantly different size, good mixing is found for similar size species.

Orbital phase control of the preferential branching of chain molecules.

The orbital phase theory was applied to the stabilities of the branched isomers (1) of E(4)H(10) (E = C, Si, Ge, Sn) relative to the normal ones (2). The orbital phase prediction was confirmed by ab initio molecular orbital (MO) and density functional theory (DFT) calculations as well as by some experimental results. Further applications to the relative stabilities of other alkane and alkene isomers lead to the preference of the branched to the normal isomers, the neopentane-type to isobutane-type branching, the terminal to inner methyl branching, and the methyl to ethyl inner substitution in the longer alkanes, as well as the preference of isobutene to 2-butene moieties. The preferential stabilization of the branched isomers was shown to be general and controlled by the orbital phase.

Experimentally determined temperature-concentration phase diagrams of monodisperse alkanes with chains containing between 100 and 200 carbons

The temperature–concentration phase (T–c) diagrams of the uniform n-alkanes C102H206, C122H246, C162H326, and C198H398 in toluene have been determined for solution concentrations in the range 0.1 to 6% (w/w). The shorter alkanes display a “classical” behavior with the expected, strong dependence of dissolution temperature on solution concentration. The longest alkane displays a very different, “polymeric” type behavior with a concentration independent dissolution temperature (for both extended and folded chain crystals). It is argued that no current theory of polymer dissolution is able to explain this behavior. It is suggested that a locally higher concentration occurs when molecules are partially attached to a crystal either during crystallization or dissolution, and that this increased local concentration accounts for the independence of dissolution temperature on the global concentration. There are some small variations in the dissolution temperature of crystals of the same thickness grown at the same concentration, but at different temperatures. These are ascribed to differences in the stacking of the separate layers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3188–3200, 1999

Properties of surfactant monolayers in relation to microemulsion phase behaviour

The relationship between the properties of surfactant monolayers at oil-water interfaces and the phase behaviour in bulk of mixtures of oil + water + surfactant is discussed. Such monolayer properties include the spontaneous curvature, c o the interfacial tension, I γ, the elasticity K (or rigidity) associated with the mean curvature, and the elasticity K associated with the Gaussian curvature. The model system chosen for investigation is the anionic surfactant AOT + aqueous NaCl + n-alkane at 20°C. In such systems, inversion of microemulsion type from oil-in-water (o/w) to water-in-oil (w/o) is possible with increasing electrolyte concentration. The tension, γ, passes through an ultralow minimum value at conditions corresponding to the formation of three phases. Using small angle neutron scattering, we have determined the structure of surfactant-rich third phases (c o ~ 0) formed with the different alkanes. Lamellar phases consisting of surfactant monolayers separated alternately by oil and water appear with short alkanes, whereas L 3 and bicontinuous phases form in systems containing longer alkanes. The bending elasticity K has been measured for planar monolayers at the oil-water interface by ellipsometry. K is independent of salt concentration but depends markedly on alkane chain length N, falling from ~ 1 k BT for N < 11 to ~0.1 k BT for N = 14. This is discussed in terms of the differing extents of oil penetration into the surfactant chains. Higher rigidities favouring lamellar phases and lower rigidities favouring bicontinuous microemulsions are in line with the theoretical predictions of de Gennes and Taupin. Estimates of the constant K have been obtained in droplet microemulsions (w/o) from a knowledge of their size, K and γ. The sign of the constant is in agreement with the geometry of the phases formed in three phase systems. Finally, the ideas and concepts developed in the oil-water systems described above are used to explain the wetting behaviour by alkanes of AOT monolayers at the air-water surface.

Computation of total molecular surface area from gas phase ion mobility data and its correlation with aqueous solubilities of hydrocarbons

AbstractGas phase ion mobility data of molecular ions were utilized to estimate the total molecular surface area (TSA) of neutral molecules. Assumptions are made in the first approximation that ions/molecules can be represented as equivalent hard spheres and that the radii of the neutral molecule and its gas phase molecular ion are equal. TSA values derived from experimental ion mobilities measured by plasma chromatography compared reasonably (±5%) with TSA data derived from computer‐simulated molecular models for the polynuclear aromatic hydrocarbons, butylbenzene isomers and linear alkanes. The known relationship between logarithms of aqueous solubility and TSA for the solute was examined utilizing TSA values derived from ion mobility data. Correlation coefficients exceeded 0.95 for aromatic hydrocarbons and for linear alkanes of fewer than 12 carbons but not for longer alkane chains.

A simple thermodynamic analysis of solid-solution formation in binary systems of homologous extended-chain alkanes

Binary mixtures of n-alkane chains of comparable length are treated within the Bragg-Williams approximation. A simple model is developed to explain which pairs will form a continuous series of solid solutions (close to their respective melting points). Results are fit very well by the empirical rule that c t ⩽ 1.22 c s ensures such a continuous, mutual solubility. Here, c t is the number of carbon atoms in the longer alkane and c s the smaller number. Close analogies are found to the well known Hume-Rothery and Vegard's Law generalizations for metallic systems. The issue of crystal similarity as a requirement for solid solubility is successfully treated as a minor, possibly spurious complication.

Effects of the anti-lipogenic antibiotic cerulenin on growth and fatty acid composition of n-alkane-utilizingCandida lipolytica

The effects of cerulenin, an anti-lipogenic antibiotic, on the growth and cellular fatty acid composition ofCandida lipolytica were investigated by changing the chain length of n-alkane, the growth substrate. The antibiotic inhibited almost completely the growth of the yeast on glucose, n-undecane and n-dodecane, but partly that on n-tridecane. The yeast growth on longer alkanes, e.g., from n-tetradecane to n-octadecane, was not affected by this antibiotic, indicating that a chain elongation system and/or intact incorporation system predominantly operate in the formation of cellular fatty acids from such longer chain n-alkanes. Comparison of the fatty acid profiles between the cells grown on n-alkanes of different chain lengths, especially on n-pentadecane, in the presence and absence of cerulenin, supported the supposition that only the de novo synthesis system of the yeast would be affected by the antibiotic, whereas the chain elongation system would not.

Inhibition of glucose assimilation and transport by n-decane and other n-alkanes in Candida 107.

SUMMARY: Candida 107 constitutively oxidizes n-nonane and longer alkanes. Decane and longer alkanes have little effect on endogenous respiration (measured as 14CO2 expiration from yeast grown on [U-14C]glucose). Alkane-grown yeast assimilated [1-14C]decane more rapidly than glucose-grown yeast though without a lag in both cases. Glucose did not inhibit these incorporations. [U-14C]Glucose was assimilated without a lag into glucose-grown yeast and, at a quarter of this rate, into alkane-grown yeast: if the latter yeast was pre-incubated with glucose for 60 min, it took up [U-14C]glucose at the higher rate. n-Decane (0.5 to 1.0 mg/mg yeast dry wt) severely and rapidly inhibited glucose assimilation. Longer chain alkanes were progressively less effective. All alkanes were more inhibitory with alkane-grown yeast. The rate of glucose assimilation was inversely proportional to the concentration of decane and directly proportional to the yeast concentration. Transport of glucose, as distinct from its assimilation, was also inhibited by decane. Uptake of fucose, a non-metabolizable deoxyhexose, was similarly affected. Passive transport of glucose did not occur. Alkanes did not prevent glucose access to the yeast surface as pristane, a non-metabolizable paraffin, had no effect on glucose assimilation in Candida 107 and dodecane was not inhibitory against carbohydrate transport in Saccharomyces carlsbergensis. Alkanes probably inhibit by causing accumulation of fatty acids or acyl CoA esters which may, either through feedback inhibitions or by further metabolism, cause build-up of ATP, acetyl CoA, and glucose 6-phosphate, thus leading to cessation of glucose transport and metabolism.