Alkane Chain Length Research Articles

Use of N-alkanes to Estimate Intake and Digestibility by Beef Steers

The objective of the study was to evaluate the use of n-alkanes to estimate DM intake and digestibility by beef cattle. Six steers were blocked (3 blocks, 2 animals/block) according to the body weight (279±19 kg) and randomly allotted within blocks to two diets (3 steers/diet). A second trial was conducted with the same animals (321±18 kg) after 36 days (d), using a switch back design. The diets consisted of two types of chopped sun-cured hay, alfalfa (Medicago sativa L) hay, or fescue (Festuca arundinacea Schreb) and alfalfa mixture, which were fed in equal amounts to steers. Animals were dosed with C32 and C36 alkanes, employing an intra-ruminal controlled-release device at the beginning of each trial. Hay intake per animal was measured from d 6 to 12 and sub samples were taken for chemical analysis. Rectal samples of feces were taken from each animal once/daily from d 8 to 14, freeze dried, and ground prior to alkane analysis. Alkanes were extracted from ground hay and feces. Feed intake was calculated from the dose rate of C32 alkane and, the herbage and fecal concentrations of adjacent odd (C33 or C31) and even (C32) chain length alkanes. Crude Protein, NDF, ADF, ash concentrations and In vitro dry matter digestibility (IVDMD) were 17.7, 42.2, 28.4, 7.9 and 71.7 for alfalfa, and 12.4, 56.5, 30.4, 6.9 and 69.1% for fescue/alfalfa mixture, respectively. For both diets, intake estimated from C33:C32 ratio was not different from the measured intake, but intake estimated from C31:C32 ratio was lower (p<0.05), than the measured intake for both diets. The average estimated forage intake from C33:C32 ratio was 4.86 and 0.69% below than the measured intake for alfalfa and, fescue/alfalfa mixed diets, respectively. The respective estimates with C31:C32 ratio were 9.59 and 11.33% below than the measured intake. According to these results, alkane C33:C32 ratio is better than alkane C31:C32 ratio for the estimation of intake by beef steers. (Asian-Aust. J. Anim. Sci. 2005. Vol 18, No. 11 : 1564-1568)

Rheological behaviours of the hexagonal and lamellar phases of glucopone (APG) surfactant

The rheological behaviours of hexagonal and lamellar liquid crystalline phases of glucopone–water–hydrocarbon systems were investigated. Four different types of hydrocarbon namely heptane, octane, dodecane and tetradecane were considered. Small-angle X-ray scattering (SAXS) and optical polarizing microscopy were used for phase identification and structure characterization. The SAXS data was further analyzed in terms of lattice parameters and area per surfactant head group. The area head group of the hexagonal phases seemed not to depend on the alkane chain length. On the other hand, the area head group for the lamellar phases was found to increase as the alkane chain is lengthened. The frequency-dependent storage and loss modulus were found to exhibit characteristics of the hexagonal and lamellar phases in the linear viscoelastic regions. The elastic properties of hexagonal phases were also found to be unaffected when higher homologue of the alkane series was considered, while for lamellar phases the elastic properties were found to decrease. The effects of temperature on the rheological behaviours of hexagonal and lamellar phases were also investigated and their melting transition temperatures were found to be almost similar. Moreover, the melting transition temperatures determined by rheology differ only slight from that determined by microscopy. The rheological quantities were found to decrease when the temperature was increased. In general, the effects of different types of hydrocarbon in the rheological behaviours were found to be more profound in the lamellar than in the hexagonal phases.

Self-assembled monolayers and electrostatically self-assembled multilayers of polyalkylviologens on sulfonate-modified gold and indium–tin–oxide electrodes

Self-assembly (SA) of polyviologens with linear alkyl spacers PVn ( n = 3–10) on sulfonate-primed gold and ITO electrode surfaces has been investigated by CV, QCM, XPS and AFM. The polymers form stable and relatively dense monolayers even from 10 −4 M PVn concentration. The viologen surface density is decreased as n is increased but for n = 10 and on alkylsulfonate-primed surfaces a strong adsorption takes place, with decreased redox potential and very narrow cyclic voltammogram of the absorbed layer due to organized structures on the surface. Stable and regular electrostatically self-assembled (ESA) multilayers are built on sulfonate-primed surfaces with PV3 and polysulfonates. From XPS analysis, the composition of the PVn/polysulfonate multilayers corresponds to a 1:1 ratio of polyanion and polycation charges, i.e., no extra non-polymeric ion is present, independently from the alkane chain length. The rate of electron transfer within the multilayers (diffusion coefficient = ca. 10 −9 cm 2 s −1) is higher than for analogous bulk materials.

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.

Experimental solubility data of various n-alkane waxes: effects of alkane chain length, alkane odd versus even carbon number structures, and solvent chemistry on solubility

Solubility data were measured for eight different n-alkanes ranging from tetracosane to tetratetracontane (C 24H 50–C 44H 90). Included are: (1) solubility data in toluene for all the n-alkanes studied and (2) solubility data of n-hexatriacontane (C 36H 74) in several solvent and solvent mixture systems. Illustrated in the data are the effects on solubility of alkane chain length, alkane odd versus even carbon number structures, and solvent chemistry. The measurements were made to provide fundamental equilibrium data.

Thermal Desorption in Pure Hexane and Hexane/Butane Mixtures on Graphite

The results of an extensive study of desorption in hexane (monolayer and submonolayer) and hexane/butane mixtures initially adsorbed onto the graphite basal plane is presented. Molecular dynamics (MD) simulations are utilized to carry out atomistic simulations at temperatures 300≤T≤700 for all three cases studied. Results from submonolayer and monolayer hexane indicate that the desorption energy needed for the system to proceed with the desorption process is independent of the system’s coverage, which is in good agreement with experimental results. It is also found that simulations of desorption of hexane/butane mixtures yield a high ratio of butane molecules being desorbed from the surface at lower temperatures (300 K), suggesting a strong dependence of the desorption barrier upon alkane chain length. The results are discussed and compared to previous experimental and theoretical results.

Observation of two diffusive relaxation modes in microemulsions by dynamic light scattering.

Water-in-oil microemulsions stabilized by AOT and dispersed in n-alkane oils with a constant molar water-to-surfactant ratio were studied by dynamic light scattering. A dilution series (in the range of volume fraction of water plus surfactant, phi approximately 0.02-0.52) was used, which allowed us to extract information about droplet sizes, diffusion coefficients, interactions, and polydispersity from experimental data. We report the observation of two diffusive relaxation modes in a concentrated microemulsion (0.20 < phi < 0.5) due to density (collective diffusion) and concentration or polydispersity (self-diffusion) fluctuations. Below this concentration it was difficult to resolve two exponentials unambiguously, and in this case one apparent relaxation mode was observed. It was found that for a given composition self-diffusion is more pronounced in apparent relaxation mode for a shorter chain length alkane. The concentration dependence of these diffusion coefficients reflects the effect of hard sphere and the supplementary attractive interactions. It was observed that the attractive part becomes more pronounced in the case of a large alkane chain oil at a given temperature. This explains the shift of the region of microemulsion stability to lower temperatures for higher chain length alkanes. Increase in hydrodynamic radius, Rh, obtained from the diffusion coefficient extrapolated to infinite dilution was observed with increase of alkane chain length. The polydispersity in microemulsion systems is dynamic in origin. Results indicate that the time scale for local polydispersity fluctuations is at least 3 orders of magnitude longer than the estimated time between droplet collisions.

Self-diffusion ofn-alkanes in MFI type Zeolite using Molecular Dynamics Simulations with an Anisotropic United Atom (AUA) Forcefield

We have investigated the effect of different guest–host forcefields, an united atoms and an anisotropic united atoms forcefields, on the self-diffusion of n-alkanes in MFI zeolite. The trend of the self-diffusion factor at infinite dilution is slightly affected by the choice of the forcefield: a small increase of the self-diffusion factor versus alkane chain length is observed with the UA forcefield between n-hexane and n-octane, whereas a decrease is observed with the AUA forcefield. We also investigated the effect of extraframework cations on diffusivities by introducing atomic defects that act as “obstacles” to molecular diffusion. A better quantitative agreement with self-diffusion data from QENS experiments is then observed, although the steep decrease of the diffusivity experimentally observed between n-hexane and n-octane is not reproduced.

Electrical Conductivity and Vapor-Sensing Properties of ω-(3-Thienyl)alkanethiol-Protected Gold Nanoparticle Films

Gold nanoparticles protected with thiophene-terminated alkanethiols having different alkane chain lengths have been synthesized, and vapor-sensing properties of their spin-coated films have been investigated. Transmission electron microscopy and measurement of the sulfur and gold peak areas of the films by X-ray photoelectron spectroscopy indicate gold core diameters in the 3−5-nm range. Exposure of the films to chloroform, toluene, hexane, and ethanol vapors results in significant and selective increases in electrical resistance, with the response to the vapors having the following order: toluene > chloroform > hexane ≫ ethanol. The magnitude of the maximum resistance change correlates well with solubility properties of the protected gold nanoparticles, as determined by optical absorbance spectroscopy and the energy of the gold plasmon. The detection sensitivity of the films increases with increasing alkanethiol chain length. These data are consistent with a sensing mechanism in which organic vapors cau...

Transition temperatures and contact angles in the sequential-wetting scenario of n-alkanes on (salt) water

Alkanes of medium chain length show an unusual wetting behavior on (salt) water, exhibiting a sequence of two changes in the wetting state. When deposited on the water surface at low temperatures, the liquid alkane forms discrete droplets that are interconnected only by a molecularly thin film. On increase of the temperature, there occurs a sudden jump of the film thickness and, at this first-order transition, a mesoscopically thick layer of liquid alkane is formed. Heating the system further leads to a divergence of the film thickness in a continuous manner. While the long-range forces between substrate and adsorbate are responsible for the critical transition, which occurs at the temperature at which the Hamaker constant changes sign, it is primarily the short-range components of the forces that bring about the first-order transition. We calculate the Hamaker constant of the system and show how, within a modified Cahn theory, accurate predictions of the first-order transition temperatures can be obtained for n-alkanes (pentane and hexane) on water and even on brine. Furthermore, we study the variation of the contact angle as a function of temperature.

Self-assembly of ordered, robust, three-dimensional gold nanocrystal/silica arrays.

We report the synthesis of a new nanocrystal (NC) mesophase through self-assembly of water-soluble NC micelles with soluble silica. The mesophase comprises gold nanocrystals arranged within a silica matrix in a face-centered cubic lattice with cell dimensions that are adjustable through control of the nanocrystal diameter and/or the alkane chain lengths of the primary alkanethiol stabilizing ligands or the surrounding secondary surfactants. Under kinetically controlled silica polymerization conditions, evaporation drives self-assembly of NC micelles into ordered NC/silica thin-film mesophases during spin coating. The intermediate NC micelles are water soluble and of interest for biolabeling. Initial experiments on a metal-insulator-metal capacitor fabricated with an ordered three-dimensional gold nanocrystal/silica array as the "insulator" demonstrated collective Coulomb blockade behavior below 100 kelvin and established the current-voltage scaling relationship for a well-defined three-dimensional array of Coulomb islands.

Support-Mediated Alkane Activation over Pt–SO4/Al2O3Catalysts

Sulphate-promoted alkane combustion has been investigated over a series of Pt/Al2O3 catalysts using pre-sulphated alumina supports. Catalyst sulphation greatly enhanced ethane combustion over Pt/Al2O3, and also improved methane and propane light-off performance. Catalyst activity increased with Pt loading, however the magnitude of sulphate promotion was independent of Pt loading under oxidising conditions, but scaled with alkane chain length. Propane combustion activity was directly proportional to the surface coverage of aluminium sulphate sites; support-mediated alkane activation is the dominant process in sulphate promotion.

Squeezing Molecularly Thin Alkane Lubrication Films: Layering Transitions and Wear

The properties of alkane lubricants confined between two approaching solids are investigated by a model that accounts for the curvature and the elastic properties of the solid surfaces. We consider linear alkane molecules of different chain lengths, C3H8, C4H10, C8H18, C9H20, C10H22, C12H26, and C14H30 confined between smooth gold surfaces. We observe well-defined molecular layers develop in the lubricant film when the width of the film is of the order of a few atomic diameters. An external squeezing-pressure induces discontinuous changes in the number n of lubricant layers. We find that with increasing alkane chain length, the transition from n to n - 1 layers occurs at higher pressure, as expected based on the increasing wettability with increasing chain length. We obtain good correlation between our theoretical results and wear experiments.

Structure of cubic phases in ternary systems Glucopone/water/hydrocarbon

Phase diagrams for the ternary systems of Glucopone, water and several hydrocarbons are reported. Four different types of hydrocarbon are used namely; heptane, octane, dodecane and tetradecane. Small angle X-ray scattering (SAXS) and polarizing microscope are used for phase identification and structure characterization. The ternary systems are shown to form different liquid crystalline phases with the increase of concentration in the following order—cubic, hexagonal, and lamellar. The liquid crystalline phases present in the ternary phase diagrams have been characterized by SAXS and further analyzed in terms of lattice parameters and area per surfactant head-group. An optical isotropic gel phase with strong elastic properties is found in these systems and identified as cubic phase. The cubic phase is optically isotropic, transparent and highly viscous phase with three-dimensional structure. The cubic samples showed several diffraction peaks and can be assigned to the Ia3 d space group. The rheological study on the cubic phase is performed. All cubic samples behave as solid-like material with storage modulus G′∼0.7×10 6 Pa typical of cubic lyotropic materials. The effect of the oil concentration and oil types on the storage and loss moduli for the cubic liquid crystalline phases is examined. For all systems, the elastic modulus and the complex viscosity are found to increase with oil concentration while decrease with increasing the length of hydrocarbon chain. Tetradecane ternary system shows completely opposite behaviors. The elastic modulus decreased when the oil content is increased. The effect of temperature on the dynamic moduli of the systems is also studied. The systems show very sharp melting transition. Both, storage and loss modulus are found to decrease as the temperature increased. It was possible to deduce the influence of the alkane chain lengths in the phase and rheological behaviors of the Glucopone surfactant. Generally, the ternary systems show similar rheological behaviors except for tetradecane system, which found to show completely opposite behaviors. The cubic phase region is found to shift to higher oil content with the increase in the alkane chain length of hydrocarbon. Finally, it is worth to mention that no cubic phases are found with toluene and cyclohexane as oil phase.

Accuracy of estimates of herbage intake of lactating cows using alkanes: comparison of two types of capsules

A feeding study with fresh forage was completed to evaluate the reliability of the alkane technique for estimating voluntary herbage intake in tropical conditions and compare the accuracy of herbage dry matter intake (DMI) estimates from two types of capsules used to deliver the even chain length alkanes to the rumen. Twelve lactating Holstein cows were housed in individual stalls and separately fed chopped fresh Panicum maximum (cv. Tobiatá) grass twice daily. From days 1 to 15 of the experimental period, six cows were dosed twice daily with a gelatin capsule containing synthetic C 32 alkane. The remaining cows were dosed with a controlled release capsule (CRC) on day 1. Individual intakes were measured daily and herbage intakes were estimated for 5 days using the alkane technique. Herbage intake differed between treatment groups, 6.3 and 8.3 kg DM per day for the gelatin and the CRC group, respectively. A 7-day equilibrium period was sufficient for the marker to reach a steady concentration in the feces for both delivery methods. Regardless of the delivery system used to administer the synthetic marker, estimated herbage intake using the C 33:C 32 alkane pair did not differ from the mean measured intake (mean bias=0.55 kg DM per day for each treatment). No obvious trend for increased recovery with alkane chain length was observed. Concentrations of alkanes in fecal samples collected throughout the day, and the resulting intake predictions, varied diurnally with the highest variation observed with the C 31:C 32 alkane pair. When the C 33:C 32 ratio was used, the least accurate herbage DMI estimate was obtained from the 4.30 h samples, for both delivery methods. The alkane technique has the potential to predict herbage intake of cows in the tropics. Although there were some differences in DMI estimates, the two types of capsules used for the alkane administration performed similarly.

Environmental swap energy and role of configurational entropy in transfer of small molecules from water into alkanes.

We studied the effect of segmented solvent molecules on the free energy of transfer of small molecules from water into alkanes (hexane, heptane, octane, decane, dodecane, tetradecane, and hexadecane). For these alkanes we measured partition coefficients of benzene, 3-methylindole (3MI), 2,3,4,6-tetrachlorophenol (TeCP), and 2,4,6-tribromophenol (TriBP) at 3, 11, 20, 33 [corrected], and 47 degrees C. For 3MI, TeCP, and TriBP the dependence of free energy of transfer on length of alkane chains was found to be very different from that for benzene. In contrast to benzene, the energy of transfer for 3MI, TeCP, and TriBP was independent of the number of carbons in alkanes. To interpret data, we used the classic Flory-Huggins (FH) theory of concentrated polymer solutions for the alkane phase. For benzene, the measured dependence of energy of transfer on the number of carbons in alkanes agreed well with predictions based on FH model in which the size of alkane segments was obtained from the ratio of molar volumes of alkanes and the solute. We show that for benzene, the energy of transfer can be divided into two components, one called environmental swap energy (ESE), and one representing the contribution of configurational entropy of alkane chains. For 3MI, TeCP, and TriBP the contribution of configurational entropy was not measurable even though the magnitude of the effect predicted from the FH model for short chain alkanes was as much as 20 times greater than experimental uncertainties. From the temperature dependence of ESE we obtained enthalpy and entropy of transfer for benzene, 3MI, TeCP, and TriBP. Experimental results are discussed in terms of a thermodynamic cycle considering creation of cavity, insertion of solute, and activation of solute-medium attractive interactions. Our results suggest that correcting experimental free energy of transfer by Flory-Huggins configurational entropy term is not generally appropriate and cannot be applied indiscriminately.

Density functional calculation of a potential energy surface for alkane thiols on Au(1 1 1) as function of alkane chain length

Density functional theory calculations of alkane thiols on Au(1 1 1) have been carried out as a function of the alkane chain length from 1 to 12 carbons using a slab geometry with periodic boundary conditions. Geometry optimized structures were obtained and the potential energy was calculated as a function of the binding site and distance from the surface. While the binding site of minimum energy is only subtly different for different chain lengths there is a pronounced difference in the Au–S bonding and side chain interactions of the methyl group of methane thiol compared to ethane thiol or any longer alkane thiol self-assembled monolayer. For example, the barrier to lateral motion along the surface is lowest for motion through fcc sites for methane thiol while the twofold bridge sites present the lowest barrier to ethane thiol and all longer alkane thiols. The hexagonal close-packed (hcp) and face-centered cubic (fcc) threefold sites were found to differ in energy by less than 1 kJ/mol and therefore only fcc sites were considered in the study. According to the calculated potential energy surfaces the top sites have weaker binding than either the bridge or threefold sites in all cases. The calculations show that ethane thiol is a reasonable model for longer alkane chains.

Computer Simulation of Incommensurate Diffusion in Zeolites: Understanding Window Effects

Dedicated molecular simulation techniques afford the study of the abnormal adsorption and diffusion of linear alkanes in ERI-, CHA-, and LTA-type zeolites. The exceptionally slow diffusion rates required the development of a combination of rare-event transition-state theory techniques and the configurational-bias Monte Carlo algorithm. The diffusion coefficients computed by this novel method agree well with the nondisputed rates determined experimentally for LTA-type sieves. The computed rates corroborate the nonmonotonic variation of the diffusion rate with alkane chain length published by Gorring, that is, the rate increases by orders of magnitude when the molecular and cage shape are no longer commensurate, so a molecule ends up stretched across a cage tethered at opposite windows. The simulations corroborate this “window effect” for both ERIand CHA-type sieves and suggest that it is characteristic for all sieves with windows approximately 0.4 nm across. They predict that it also occurs for LTA-type sieves provided that the n-alkane is long enough to exceed the diameter of the LTA-type supercage.

The Effect of Alkane Chain Length on the Liquid?Liquid Critical Temperatures of Oligostyrene/Linear-Alkane Mixtures

Upper critical solution temperatures (UCSTs) for liquid–liquid demixing in a set of mixtures of linear alkanes (pentane (N1=5) to pentacontane (N1=50)) with an oligostyrene (1241 amu, N2=12) are reported. We find strong correlation between the Hildebrand solubility parameters of the alkanes and the UCST. Correlations are developed which enable predictions concerning the miscibility of mixtures of compounds with longer chains.

Adsorption Competition Effects in Hydroconversion of Alkane Mixtures on Zeolites

In the present work, molecular competition effects in the hydroconversion of alkane mixtures in vapor and liquid phase were studied. The influence of the pore size was investigated by performing catalytic experiments with equimolar heptane/nonane mixtures on a series of bifunctional zeolite catalysts (Pt/H-Y, Pt/H-USY, Pt/H-Beta, Pt/H-MCM-22). Vapor phase catalytic experiments were performed at a total pressure of 4.5 bar, while a total pressure of 100 bar was applied in the liquid phase experiments. The experimental results were analyzed using a lumped adsorption-reaction model. In vapor phase, the longest chain is preferentially converted on all studied catalysts. In liquid phase, the differences in conversion rate were less pronounced. On Pt/H-MCM-22, with active pockets on the surface, and Pt/H-USY having large mesopores, the competition between short and long alkanes in liquid phase reflect the intrinsic reactivities of the reacting molecules. In zeolites with smaller pores (Pt/H-Y, Pt/H-Beta), an inversion of the reactivity order of alkanes of different chain length was observed when increasing the pressure from 4.5 bar and vapor phase to 100 bar and liquid phase. The inversion of apparent reactivity orders is due to changes in physisorption at high pressure, favoring uptake of the smallest molecules.