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Sample records for alkane monolayers studied

  1. Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. II. Dynamics

    DEFF Research Database (Denmark)

    Enevoldsen, Ann Dorrit; Hansen, Flemming Yssing; Diama, A.;

    2007-01-01

    The dynamics of monolayer films of the n-alkane tetracosane (n-C24H52) and the branched alkane squalane (C30H62) adsorbed on graphite have been studied by quasielastic and inelastic neutron scattering and molecular dynamics (MD) simulations. Both molecules have 24 carbon atoms along their carbon...... backbone, and squalane has an additional six methyl side groups symmetrically placed along its length. The authors' principal objective has been to determine the influence of the side groups on the dynamics of the squalane monolayer and thereby assess its potential as a nanoscale lubricant. To investigate...... analysis of the quasielastic scattering. They conclude that there are no major differences in the monolayer dynamics caused by intramolecular branching. It remains to be seen whether this similarity in monolayer dynamics also holds for the lubricating properties of these molecules in confined geometries...

  2. Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. I. Structure

    DEFF Research Database (Denmark)

    Enevoldsen, Ann Dorrit; Hansen, Flemming Yssing; Diama, A.;

    2007-01-01

    ) tetracosane film is roughly the same as the bulk melting point, the surface strongly stabilizes the 2D squalane film such that its melting point is 91 K above its value in bulk. Therefore, squalane, like tetracosane, will be a poor lubricant in those nanoscale devices that require a fluid lubricant at room......The structure of a monolayer film of the branched alkane squalane (C30H62) adsorbed on graphite has been studied by neutron diffraction and molecular dynamics (MD) simulations and compared with a similar study of the n-alkane tetracosane (n-C24H52). Both molecules have 24 carbon atoms along their...... backbone and squalane has, in addition, six methyl side groups. Upon adsorption, there are significant differences as well as similarities in the behavior of these molecular films. Both molecules form ordered structures at low temperatures; however, while the melting point of the two-dimensional (2D...

  3. Ordered Self-assembled Alkane Monolayer on Graphite and Graphene Surface

    Science.gov (United States)

    Su, Yudan; Han, Huiling; Wang, Feng; Cai, Qun; Tian, Chuanshan; Shen, Y. R.

    2015-03-01

    The 2D self-assembly of long chain alkane molecule on graphite and graphene had been studied with phase-sensitive sum-frequency vibrational spectroscopy (PS-SFVS) and scanning tunneling microscopy (STM). The spectrum of Imχs(2) (ωIR) which directly characterizes the surface resonances, shows 10-cm-1 red-shift of the symmetric-stretch frequency of the CH2 groups pointing towards graphite (or graphene) surface indicating Van der Waals interaction in between. The Gibbs adsorption energy of polyethylene (PE, n ~ 140) on graphite from chloroform solution was determined to be -42kJ/mol per molecule or -0.6 kJ/mol per CH2 unit. This large adsorption energy drives the long alkane chain to form an ordered self-assembled monolayer on graphite (or graphene). The sum frequency spectra suggest the orientation of carbon skeleton plane of alkane is predominately perpendicular to the graphite/graphene surface. Our STM result also provides clear evidence for the proposed molecular adsorption model. These results explain the large amount residual of long chain alkane on polystyrene (PS) or poly(methyl methacrylate) (PMMA) transferred graphene, and facilitate a better way to fabricate cleaner large-size graphene.

  4. Comparative study of the effects of several n-alkanes on phospholipid hexagonal phases.

    OpenAIRE

    Chen, Z; Rand, R P

    1998-01-01

    The effects of a series of normal alkanes (decane, dodecane, tetradecane, hexadecane, and octadecane) on the hexagonal H(II) structures containing dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC) were studied using x-ray diffraction and osmotic stress. The alkanes affect structural dimensions and the monolayer intrinsic curvature and bending modulus. The alkane effects are chain-length dependent and are attributed to their different distribution within the H(II) ...

  5. Adsorption Behaviors of Mixed Monolayers of n-Alkanes at the Liquid-Solid Interface.

    Science.gov (United States)

    Hibino, Masahiro

    2016-05-17

    To understand the self-assembly of monolayers at the liquid-solid interface, a thermodynamic model, which describes the contributions of the molecular interactions, is essential. We present an adapted Zimm-Bragg model of the cooperativity transitions for determining the Gibbs free energy for self-assembly at the liquid-solid interface. Scanning tunneling microscopy was used to observe the monolayers formed on graphite from phenyloctane solutions of binary mixtures of n-hexacosane (C26H54) and n-tetratriacontane (C34H70). This revealed that the sharp transition in the monolayers from the full surface coverage of the long-chain alkane, which is adsorbed preferentially, to the full coverage of the short-chain alkane is a function of the mixture composition. The model allows for the estimation of the free-energy changes associated with the difference in the alkyl chain length and the interface between the two different alkane regions in the monolayers. It is also suitable for understanding more complex systems that exhibit intermolecular interactions. PMID:27124544

  6. Highly organized crystalline monolayer of a semi-fluorinated alkane on a solid substrate obtained by spin-coating

    International Nuclear Information System (INIS)

    We have obtained a 40 nm parameter crystalline monolayer of a semifluorinated alkane on a silicon wafer using the spin-coating technique. Its structure, analyzed by atomic force microscopy (AFM), is identical to that recently observed at the air-water interface, showing the existence of hexagonal nanodomains, organized on a long range order hexagonal lattice of a few tens of nanometers lateral parameter. Considering AFM images published on films transferred by the usual Langmuir-Blodgett method, one can note that the monolayers form locally ordered rounded domains. With our procedure, the original highly organized large crystalline structure is recovered.

  7. Fractal analysis methods for solid alkane monolayer domains at SiO2/air interfaces.

    Science.gov (United States)

    Knüfing, Lydia; Schollmeyer, Hauke; Riegler, Hans; Mecke, Klaus

    2005-02-01

    A systematic evaluation of various fractal analysis methods is essential for studying morphologies of finite and noisy experimental patterns such as domains of long chain alkanes at SiO(2)/air interfaces. The derivation of trustworthy fractal dimensions crucially relies on the definition of confidence intervals for the assumed scaling range. We demonstrate that the determination of the intervals can be improved largely by comparing the scaling behavior of different morphological measures (area, boundary, curvature). We show that the combination of area and boundary data from coarse-grained structures obtained with the box-counting method reveals clear confidence limits and thus credible morphological data. This also holds for the Minkowski density method. It also reveals the confidence range. Its main drawback, the larger swing-in period at the lower cutoff compared to the box-counting method, is compensated by more details on the scaling behavior of area, boundary, and curvature. The sandbox method is less recommendable. It essentially delivers the same data as box-counting, but it is more susceptible to finite size effects at the lower cutoff. It is found that the domain morphology depends on the surface coverage of alkanes. The individual domains at low surface coverage have a fractal dimension of approximately 1.7, whereas at coverages well above 50% the scaling dimension is 2 with a large margin of uncertainty at approximately 50% coverage. This change in morphology is attributed to a crossover from a growth regime dominated by diffusion-limited aggregation of individual domains to a regime where the growth is increasingly affected by annealing and the interaction of solid growth fronts which approach each other and thus compete for the alkane supply. PMID:15667180

  8. The organization of n-alkanes in lipid bilayers.

    Science.gov (United States)

    McIntosh, T J; Simon, S A; MacDonald, R C

    1980-04-24

    The interaction of n-alkanes (C6--C16) with phosphatidylcholine has been studied by the combined use of differential scanning calorimetry, X-ray diffraction and monolayer techniques. It has been found that the thermal properties and ultrastructure of lipid-alkane vesicles are strongly dependent on the length of the n-alkanes. Long alkanes, such as tetradecane and hexadecane, increase the transition temperature of dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine, while the X-ray data indicate that these long alkanes align parallel to the lipid acyl chains. In contrast, shorter alkanes, such as hexane and octane, decrease and broaden the thermal transition and electron density profiles show that these alkanes increase bilayer width by partitioning between the apposing monolayers of the bilayer. For lipids in the gel and liquid crystalline states, the short alkanes form an alkane region in the geometric center of the bilayer. PMID:6892885

  9. Molecular dynamics study of the water/n-alkane interface

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Molecular dynamics simulations on the interface between liquid water and liquid n-alkane (including octane, nonane, decane, undecane and dodecane) have been performed with the purpose to study the interfacial properties: (Ⅰ) density profile; (Ⅱ) molecular orientation; (Ⅲ) interfacial tension and the temperature effect on the interfacial tension. Simulation results show that at the interface the structures of both water and n-alkane are different from those in the bulk. Water has an orientational preference due to the number of hydrogen bonds per molecule maximized. N-alkane has a more lateral orientation with respect to the interface in order to be in close contact with water. The calculated individual phase bulk density and interfacial tension of water/n-alkane systems are in good agreement with the corresponding experimental ones.

  10. Intramolecular and Lattice Melting in n-Alkane Monolayers: An Analog of Melting in Lipid Bilayers

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Herwig, K.W.; Matthies, B.;

    1999-01-01

    to 350 K above which a large thermal expansion and decrease in coherence length occurs. The MD simulations provide evidence that this behavior is due to a phase transition in the monolayer in which intramolecular and translational order are lost simultaneously. This melting transition is qualitatively...

  11. Formation of Underbrushes on thiolated Poly (ethylene glycol) PEG monolayers by Oligoethylene glycol (OEG) terminated Alkane Thiols on Gold

    DEFF Research Database (Denmark)

    Lokanathan, Arcot R.

    2011-01-01

    Adding underbrushes of oligoethylene glycol (OEG) to monolayers of long chain PEG molecules on a surface is one of the strategies [1] in designing a suitable platform for antifouling purpose, where it is possible to have high graft density and molecular conformational freedom[4] simultaneously......, there by maximal retention of activity of covalently immobilised antifouling enzyme [2] on PEG surfaces along with resistance to protein adsorption[3]. Here we present some our studies on the addition of OEG thiol molecules over a self assembled monolayer of PEG thiol on gold. The kinetics of addition...... of OEG thiol to monolayers of PEG thiol was followed using X- ray photoelectron spectroscopy (XPS), which indicated the time point of maximum graft density and beyond this time point there was predominant desorption of OEG thiol as indicated by the C/O ratio. The initial increase in graft density was...

  12. Theoretical study of n-alkane adsorption on metal surfaces

    DEFF Research Database (Denmark)

    Morikawa, Yoshitada; Ishii, Hisao; Seki, Kazuhiko

    2004-01-01

    The interaction between n-alkane and metal surfaces has been studied by means of density-functional theoretical calculations within a generalized gradient approximation (GGA). We demonstrate that although the GGA cannot reproduce the physisorption energy well, our calculations can reproduce the...

  13. Spectrin-phospholipid interaction. A monolayer study

    NARCIS (Netherlands)

    Mombers, C.; Gier, J. de; Demel, R.A.; Deenen, L.L.M. van

    1980-01-01

    1.(1) The interaction of synthetic and natural phospholipids with spectrin, purified from human erythrocyte membranes, was studied using the monolayer technique at constant surface pressure. Spectrin penetration into the lipid monolayer was recorded as the rate of surface area increase on a two-comp

  14. Two-Step Freezing in Alkane Monolayers on Colloidal Silica Nanoparticles: From a Stretched-Liquid to an Interface-Frozen State.

    Science.gov (United States)

    Gao, Xia; Huber, Patrick; Su, Yunlan; Zhao, Weiwei; Wang, Dujin

    2016-08-01

    The crystallization behavior of an archetypical soft/hard hybrid nanocomposite, that is, an n-octadecane C18/SiO2-nanoparticle composite, was investigated by a combination of differential scanning calorimetry (DSC) and variable-temperature solid-state (13)C nuclear magnetic resonance (VT solid-state (13)C NMR) as a function of silica nanoparticles loading. Two latent heat peaks prior to bulk freezing, observed for composites with high silica loading, indicate that a sizable fraction of C18 molecules involve two phase transitions unknown from the bulk C18. Combined with the NMR measurements as well as experiments on alkanes and alkanols at planar amorphous silica surfaces reported in the literature, this phase behavior can be attributed to a transition toward a 2D liquid-like monolayer and subsequently a disorder-to-order transition upon cooling. The second transition results in the formation of a interface-frozen monolayer of alkane molecules with their molecular long axis parallel to the nanoparticles' surface normal. Upon heating, the inverse phase sequence was observed, however, with a sizable thermal hysteresis in accord with the characteristics of the first-order phase transition. A thermodynamic model considering a balance of interfacial bonding, chain stretching elasticity, and entropic effects quantitatively accounts for the observed behavior. Complementary synchrotron-based wide-angle X-ray diffraction (WAXD) experiments allow us to document the strong influence of this peculiar interfacial freezing behavior on the surrounding alkane melts and in particular the nucleation of a rotator phase absent in the bulk C18. PMID:27386888

  15. Spontaneous Imbibition Dynamics of an n-Alkane in Nanopores: Evidence of Meniscus Freezing and Monolayer Sticking

    CERN Document Server

    Gruener, Simon; 10.1103/PhysRevLett.103.174501

    2009-01-01

    Capillary filling dynamics of liquid n-tetracosane (n-C24H50) in a network of cylindrical pores with 7 and 10 nm mean diameter in monolithic silica glass (Vycor) exhibit an abrupt temperature-slope change at Ts=54 deg C, ~4 deg C above bulk and ~16 deg C, 8 deg C, respectively, above pore freezing. It can be traced to a sudden inversion of the surface tension's T slope, and thus to a decrease in surface entropy at the advancing pore menisci, characteristic of the formation of a single solid monolayer of rectified molecules, known as surface freezing from macroscopic, quiescent tetracosane melts. The imbibition speeds, that are the squared prefactors of the observed square-root-of-time Lucas-Washburn invasion kinetics, indicate a conserved bulk fluidity and capillarity of the nanopore-confined liquid, if we assume a flat lying, sticky hydrocarbon backbone monolayer at the silica walls.

  16. Magnetoluminescence study of WS2 monolayers

    Science.gov (United States)

    Scrace, T.; Tsai, Y.; Barman, B.; Schweidenback, L.; Petrou, A.; Kioseoglou, G.; Hawrylak, P.

    2014-03-01

    We have studied the photoluminescence (PL) spectra[2] from WS2 monolayers in the 5-150 K temperature range in magnetic fields up to 7 tesla applied along the normal to the sample plane. The luminescence was excited by a 488nm linearly polarized laser beam. The PL spectra have two features identified as the neutral (X) and negatively charged (X-) exciton. At zero magnetic field the X- feature has a large (as high as 30%), laser power-dependent circular polarization, in contrast to the small polarization of Xthat does not depend on laser power. The application of an external magnetic field has a profound effect on the circular polarization of the charged exciton. Its polarization increases by 10% at 7 tesla for any laser-power while its energy exhibits a small magnetic splitting (2meV at 7 tesla). On the other hand, the emitted circular polarization of the free exciton is not affected by the external magnetic field. This work has been supported by ONR.

  17. Surface tension of cavities and Tolman’s length in n-alkanes. A positron study

    International Nuclear Information System (INIS)

    Highlights: ► Surface tension in cavities produced by Ps in alkanes is larger than in flat surface. ► Absolute value of Tolman’s length rises with temperature. ► Ortho-Ps lifetime near the melting point is identical for all liquid alkanes. ► No change of ortho-Ps lifetime at the transition liquid–rotator phase for n > 24. - Abstract: Positron annihilation lifetime spectra were measured in n-alkanes. From the lifetime of ortho-positronium (o-Ps) one can determine the surface tension and Tolman’s length for the cavity produced by positronium in the liquid. This tension is found increased by factor of 1.4 ÷ 1.7 comparing to that of flat surface. The Tolman’s length is temperature dependent; in n-nonadecane it rises from about 0.06 nm at melting point to 0.08 nm at the temperature 100 K higher. Near the melting point the value of surface tension of Ps cavities is practically identical for all alkanes under study, i.e. from heptane C7H16 to pentacontane C50H102

  18. A QSPR STUDY OF NORMAL BOILING POINT OF ORGANIC COMPOUNDS (ALIPHATIC ALKANES) USING MOLECULAR DESCRIPTORS

    OpenAIRE

    B. Souyei; M. Korichi

    2013-01-01

    A quantitative structure–property relationship (QSPR) study is carried out to develop correlations that relate the molecular structures of organic compounds (Aliphatic Alkanes) to their normal boiling point (NBP) and two correlations were proposed for constitutionals and connectivity indices Models. The correlations are simple in application with good accuracy, which provide an easy, direct and relatively accurate way to calculate NBP. Such calculation gives us a model that gives results in r...

  19. A comparative study of n-alkane biomarker and pollen records: an example from southern China

    Institute of Scientific and Technical Information of China (English)

    ZHENG YanHong; ZHOU WeiJian; XIE ShuCheng; YU XueFeng

    2009-01-01

    We report the results of a comparative study of n-alkane biomarkers and pollens in lacustrine and peat deposits at Dingnan, Jiangxi Province in southern China, and discuss the likely causes for the discrepancy in the interpretations of the n-alkane biomarker and pollen records in terms of climate and vegetation change. The results show that past changes in climate and vegetation revealed by the n-alkane record are not always consistent with the pollen assemblage record in the whole section.Biomarkers do not permit direct identification of the plant family and/or genus and mainly record compositions of local plant remains, while pollens mainly reflect the regional vegetation change. Biomarkers and pollen records complement each other, providing a better picture of local and regional environments. Furthermore, biomarkers are more sensitive than pollen to climatic and vegetational change. Several climatic events are clearly identified by the n-alkane biomarker proxies, such as C31/(C27+C29+C31) ratio and can be correlated to the North Atlantic Heinrich event, B/A, YD and two dry-cool events during the early Holocene such as the periods of 9850 to 9585 cal a B.P. and 8590 to 7920 cal a B.P. These events are consistent with those found in the surrounding regions, suggesting that the regional climate was coupled with global-scale abrupt climatic events. Our results suggest that biomarker and pollen data can record the more detailed climate and vegetation information, thus improving the resolution and precision of vegetation and climate reconstruction.

  20. Molecular Dynamic Studies on Langmuir Monolayers of Stearic Acid

    Institute of Scientific and Technical Information of China (English)

    KONG Chui-peng; ZHANG Hong-xing; ZHAO Zeng-xia; ZHENG Qing-chuan

    2013-01-01

    Compression isotherm for stearic acid was obtained by means of molecular dynamic simulation and compared to experimentally measured values for the Langmuir monolayers.Compared to the previous simulation,the present simulation has provided a method to reproduce the compression of the monolayer.The result is consistent with other experimental results.By analyzing the alkyl tails,the configuration of stearic acid molecules during the compression process was studied and a uniform monolayer was obtained after compression.Stearic acid molecules were observed to form fine organized monolayer from completely random structure.Hexatic order of the arrangement has been identified for the distribution of stearic acid molecules in the monolayer.At the end of the compression,the stearic acid molecules were tightly packed in the gap of two other molecules.At last,the hydrogen bonds in the system were analyzed.The main hydrogen bonds were from stearic acid-water interaction and their intensities constantly decreased with the decreased of surface area per molecule.The weak hydrogen bond interaction between stearic acid molecules may be the reason of easy collapse.

  1. Theoretical Kinetic Study of the Ring Opening of Cyclic Alkanes

    CERN Document Server

    Sirjean, Baptiste; Ruiz-Lopez, M F; Fournet, René

    2009-01-01

    This work reports a theoretical study of the gas phase unimolecular decomposition of cyclobutane, cyclopentane and cyclohexane by means of quantum chemical calculations. A biradical mechanism has been envisaged for each cycloalkane, and the main routes for the decomposition of the biradicals formed have been investigated at the CBS-QB3 level of theory. Thermochemical data (?H\\degree f, S\\degree, C\\degree p) for all the involved species have been obtained by means of isodesmic reactions. Rate constants have been derived for all elementary reactions using transition state theory at 1 atm and temperatures ranging from 600 to 2000 K. These values have been compared with the few data available in the literature and showed a rather good agreement.

  2. A sum-frequency generation spectroscopic study of the Gibbs analysis paradox: monolayer or sub-monolayer adsorption?

    Science.gov (United States)

    Shahir, Afshin Asadzadeh; Nguyen, Khoi Tan; Nguyen, Anh V

    2016-03-23

    The Gibbs adsorption isotherm (GAI) has been considered as the foundation of surfactant adsorption studies for over a century; however, its application in determining the limiting surface excess has recently been intensively discussed, with contradictory experimental evidence either supporting or refuting the theory. The available arguments are based on monolayer adsorption models. In this paper, we experimentally and intellectually propose and validate the contribution of sub-monolayer adsorption to the GAI paradox. We utilize a powerful intrinsically surface-sensitive technique, vibrational sum-frequency generation spectroscopy (SFG), complementing with conventional tensiometric measurements to address these controversies both quantitatively and qualitatively. Our SFG results revealed that the precipitous decrease in surface tension directly corresponds to surface occupancy by adsorbates. In addition, the Gibbs analysis was successfully applied to the soluble monolayer of a surface-active alcohol to full saturation. However, the full saturation of the topmost monolayer does not necessarily mean that the surface adsorption was completed because the adsorption was observed to continuously occur in the sub-monolayer region soon after the topmost monolayer became saturated. Nonetheless, the Gibbs isotherm failed to account for the excess of alcohol adsorbed in this sub-monolayer region. This new concept of surface excess must therefore be treated thermodynamically. PMID:26661072

  3. Synthesis, conformational and theoretical studies of 1,n-di(2-formyl-4-phenylazophenoxy)alkanes

    Science.gov (United States)

    Balachander, R.; Manimekalai, A.

    2016-01-01

    1,n-di(2-Formyl-4-phenylazophenoxy)alkanes 1 and 2 and 1,3-di(2-formyl-4-phenylazophenoxymethyl)benzene 3 were synthesis and characterized by FT-IR, UV-Vis, 1H, 13C NMR and mass spectral studies. The stable conformations of 1-3 were predicted theoretically and selected geometrical parameters were derived from optimized structures. The molecular parameters of HOMO-LUMO energies, polarizability, hyperpolarizability, natural bond orbital (NBO), atom in molecule (AIM) analysis and molecular electrostatic potential (MEP) surfaces were determined by the density functional theory (DFT) method and analysed.

  4. A QSPR STUDY OF NORMAL BOILING POINT OF ORGANIC COMPOUNDS (ALIPHATIC ALKANES USING MOLECULAR DESCRIPTORS

    Directory of Open Access Journals (Sweden)

    B. Souyei

    2013-12-01

    Full Text Available A quantitative structure–property relationship (QSPR study is carried out to develop correlations that relate the molecular structures of organic compounds (Aliphatic Alkanes to their normal boiling point (NBP and two correlations were proposed for constitutionals and connectivity indices Models. The correlations are simple in application with good accuracy, which provide an easy, direct and relatively accurate way to calculate NBP. Such calculation gives us a model that gives results in remarkable correlations with the descriptors of blokes constitutionals (CON, and connectivity indices (CI (R2 = 0.950, δ = 0.766 (R2 = 0.969, δ = 0.782 respectively.

  5. Study of Some Alkanes Thermodynamic Parameters Using New Liquid Crystals Containing Sulfur as Stationary Phases

    Directory of Open Access Journals (Sweden)

    Mebrouk Djedid

    2015-06-01

    Full Text Available Most of the synthesized compounds which have liquid crystalline character in their composition comprise aromatic molecules. Furthermore there are few jobs that replace this type of molecules by inhomogeneous molecules that have LC character. We will replace the aromatic rings by units of 1,3,4-oxadiazole and study the effects of these new components of the transition temperatures and the Thermodynamic characteristics of n- alkanes in these two LC's phases. have been investigated by inverse gas chromatography. The transition temperatures obtained by GC are in good agreement with those found by DSC. The results are interpreted in terms of parameters “b” and related thermodynamic quantities

  6. Magnetic field effect study of solvent hole deprotonation in x-irradiated liquid n-alkanes

    International Nuclear Information System (INIS)

    Complete text of publication follows. Solvent radical cations, or holes, are the key intermediates in many radiation chemical processes. Because of their short life span (ns to tens of ns), normal molecular ion mobility and the lack of specific optical spectra the holes of n-alkanes are difficult to study using conventional spectroscopic techniques. A suitable alternative is spin chemistry methods taking advantage of the hole being a partner of a spin--correlated radical ion pair. In this work stationary magnetic field effect including MARY spectroscopy was applied to study proton transfer from holes to alcohols in n-alkanes. Reactions with additives were registered as line broadening in experimental MARY spectra reflecting short time scale evolution of the pair. An extensive scan for n-alkanes from C6 to C16 and alcohols from MeOH to t-BuOH with careful provisions for solvent purity yielded diffusion-controlled rates of the pair decay for all alkane/alcohol combinations. Surprisingly, no correlation was found between the rate and the AE(PA) of the expected proton transfer reaction, extrapolated from gas phase data. One possible explanation is that the differences in sizes and charge distributions of the two cations can make a substantial (and hardly accountable) solvation contribution to the driving force of the reaction even in these non-polar solvents. Another option is that other reaction channels like interaction with the radical anion partner of the pair are possible. To clarify the matter normal magnetic effect reflecting the effective hyperfine coupling of the radical ions was employed. Providing radical anions with effective couplings significantly lower and higher than those of the solvent hole helped ascribe the observed magnetic field effects and MARY spectra. Substitution of the hole with a stable radical cation not prone to proton loss under these conditions showed that it is solvent hole that is attacked by the alcohol. The counter ion does not

  7. Added Alkane Allows Thermal Thinning of Supramolecular Columns by Forming Superlattice-An X-ray and Neutron Study.

    Science.gov (United States)

    Yen, Ming-Huei; Chaiprapa, Jitrin; Zeng, Xiangbing; Liu, Yongsong; Cseh, Liliana; Mehl, Georg H; Ungar, Goran

    2016-05-11

    We report a columnar superlattice formed by blends of dendron-like Li 3,4,5-tris(n-alkoxy)benzoates with n-alkanes. Without the alkane, the wedge-shaped molecules form liquid crystal columns with 3 dendrons in a supramolecular disk. The same structure exists in the blend, but on heating one dendron is expelled from the disks in every third column and is replaced by the alkane. This superlattice of unequal columns is confirmed by complementary X-ray and neutron diffraction studies. Lateral thermal expansion of dendrons normally leads to the expulsion of excess molecules from the column, reducing the column diameter. However, in the already narrow columns of pure Li salt, expulsion of one of only three dendrons in a disk is not viable. The added alkane facilitates the expulsion, as it replaces the missing dendron. Replacing the alkane with a functional compound can potentially lead to active nanoarrays with relatively large periodicity by using only small molecules. PMID:27101731

  8. The study on the primary processes of radiation chemistry in liquid alkanes by means of picosecond pulse radiolysis

    International Nuclear Information System (INIS)

    The primary processes of radiation chemistry in liquid alkanes were studied by using picosecond pulse radiolysis. Especially, the geminate ion recombination, the formation process of excited states and ion-molecular reaction of radical cations were directly observed and the primary processes were discussed. Also, future picosecond and femtosecond pulse radiolysis to elucidate the unsolved problem in the primary processes was discussed. (author)

  9. Pulse radiolysis of alkanes: A time-resolved electron paramagnetic resonance study

    International Nuclear Information System (INIS)

    Time-resolved spin-echo-detected electron paramagnetic resonance (EPR) was applied to examine short-lived alkyl radicals formed in pulse radiolysis of liquid alkanes. It was found that the ratio of yields of penultimate and interior radicals in n-alkanes at the instant of their generation is temperature-independent and is ca. 1.25 times greater than the statistical quantity. This higher-than-statistical production of penultimate radicals indicates that the fast ion molecule reactions involving radical cations are a significant route of radical generation. The analysis of spin-echo kinetics in n-alkanes suggests that the alkyl radicals are emissively polarized in spur reactions. this initial polarization rapidly increases with shortening of the aliphatic chain. Another finding is that a long-chain structure of these radicals results in much higher rate of Heisenberg spin exchange relative to the recombination rate. The relative yields of hydrogen abstraction and fragmentation for various branched alkanes are estimated. It is concluded that the fragmentation occurs prior to the formation of radicals in an excited precursor species. Effects of phenolic and alkene additives in radiolysis of n-alkanes are examined. It is demonstrated that phenoxy radicals are produced in dissociative capture of electrons and alkane holes. Another route is a reaction of phenols with free hydrogen atoms. A rapid transfer of singlet correlation from the geminate radical ion pairs is responsible for unusual polarization patterns in the phenoxy and cyclohexadienyl radicals. The significance of these results in the context of cross-linking in polyethylene and higher paraffins is discussed. 56 refs

  10. Studies of the structure and properties of organic monolayers, multilayers and superlattices

    International Nuclear Information System (INIS)

    Organic monolayers and multilayers are both scientifically fascinating and technologically promising; they are, however, both complex systems and relatively inaccessible to experimental probes. In this progress report, we describe our x-ray diffraction studies, which have given us substantial new information about the structures and phase transitions in monolayers on the surface of water; our use of these monolayers as a unique probe of the dynamics of wetting and spreading; and our studies of monolayer mechanical properties using a simple but effective technique available to anyone using the Wilhelmy method to measure surface tension. 20 refs., 11 figs

  11. Raman study of local ordering processes of solid n-alkanes

    Science.gov (United States)

    Hacura, A.; Zimnicka, B.; Wrzalik, R.

    2016-02-01

    The microphase separation of n-alkanes with different chain length was investigated by Raman spectroscopy for binary mixture rapidly quenched from the melt. The process was observed as a function of time. The first several minutes after solidification were crucial for the demixing process. For a few weeks old sample the orientational order parameters and were calculated based on the analysis of polarized spectra recorded in the area of the formed domains. The measured values are significantly greater than zero (from 0.17 to 0.32), which indicates the mutual parallel arrangement of the molecules in the domains composed of n-alkanes of the same chain length.

  12. Oxygen Monolayers Adsorbed on Graphite Studied by Neutron Scattering

    DEFF Research Database (Denmark)

    Nielsen, Mourits; McTague, J. P.

    1979-01-01

    The phase diagram of absorbed films of O2 molecules on (002) surfaces of graphite has been measured in the range of densities from submonolayer to 1.6 monolayer. This system is particularly interesting because it orders magnetically below 11.9 K for dense monolayer and higher coverages. This...

  13. A molecular dynamics study of nanofracture in monolayer boron nitride

    International Nuclear Information System (INIS)

    In this paper, we use molecular dynamics (MD) modeling to study the fracture properties of monolayer hexagonal boron nitride (h-BN) under mixed mode I and II loading. We investigate the impact of crack edge chirality, crack tip configuration and loading phase angle on the crack propagation path and critical stress intensity factors. The MD results predict that under all the loading phase angles cracks prefer to propagate along a zigzag direction and the critical stress intensity factors of zigzag cracks are higher than those of armchair cracks. Under mixed mode loading, the h-BN sheets can undergo out-of-plane deformations due to the buckling induced by compressive stresses. The out-of-plane deformations can be significant when mode II loading is dominant. An excessive amount of out-of-plane deformation can induce buckling cracks. Depending on the loading phase angle and crack configurations, buckling cracks can nucleate before or after the propagation of the original cracks

  14. Study of Liquid Alkanes Production from Biomass-Derived Carbohydrates by Aldol-Condensation and Hydrogenation Processes

    Directory of Open Access Journals (Sweden)

    Navadol Laosiripojana

    2010-10-01

    Full Text Available This research aims to synthesis liquid alkanes from biomass-derived hydroxyl methyl furfural (HMF and furfural by aldol-condensation and hydrogenation processes over several catalysts i.e. TiO2, TiO2-ZrO2, Pd/Al2O3 and Pd/CeO2. It was found that the catalysts make significant impact on the selectivity and yield of alkanes product. It is noted that Pd/Al2O3 provided the highest alkane yield and selectivity. The aldol-condensation and hydrogenation of HMF over Pd/Al2O3 provide high C12 selectivity whereas the aldol-condensation and hydrogenation of furfural over Pd/Al2O3 provide high C8 selectivity. The effects of reaction temperature, reaction pressure and reaction time were then studied. The effect of inlet furfural to acetone molar ratio was also determined. It was also found that the optimized conditions to maximize the yield of alkane production from the aldol-condensation/hydrogenation of HMF and furfural are (i at 53oC and 24 hr for aldol-condenstation of HMF, (ii 80oC and 24 hr for aldol-condenstation of furfural, and (iii 120oC for 6 hr with HMF to acetone molar ratio of 3:1 and furfural to acetone molar ratio of 4:1 in the presence of Pd/Al2O3 (calcined at 500oC for hydrogenation reaction.

  15. Semifluorinated Alkane Eye Drops for Treatment of Dry Eye Disease—A Prospective, Multicenter Noninterventional Study

    Science.gov (United States)

    Scherer, Dieter; Krösser, Sonja; Beckert, Michael; Cursiefen, Claus; Kaercher, Thomas

    2015-01-01

    Abstract Purpose: Evaporation of the tear film is heavily discussed as one core reason for dry eye disease (DED). Subsequently, new artificial tear products are developed that specifically target this pathomechanism. Perfluorohexyloctane (F6H8, NovaTears®) from the family of semifluorinated alkanes is a novel substance that has been approved as a medical device, as a nonblurring wetting agent for the ocular surface. Methods: Thirty patients with hyperevaporative dry eye received F6H8 during a prospective, multicenter, observational 6-week study. Patients were advised to apply 1 drop 4 times daily in both eyes. Parameters assessed included best corrected visual acuity, intraocular pressure, Schirmer I test, tear fluid, tear film breakup time (TFBUT), corneal staining, meibum secretion, and Ocular Surface Disease Index (OSDI©). Results: From the 30 patients recruited, 25 completed the trial per protocol. Four patients discontinued F6H8 and 1 patient did not present for follow-up. F6H8 treatment led to significant reduction of corneal staining and significant increase of Schirmer I and TFBUT. In addition, OSDI score dropped significantly from a mean of 55 (±23.0) to 34 (±22.4). Visual acuity and ocular pressure did not change. Conclusions: This prospective observational study shows significant beneficial effects in patients suffering from evaporative DED, using F6H8 in all the relevant parameters tested. The decrease of the OSDI by a mean of 21 points was particularly remarkable and clearly exceeds minimal, clinical important differences for mild or moderate and severe disease. Overall, F6H8 (NovaTears) seems to be safe and effective in treating mild to moderate hyperevaporative DED. PMID:26296040

  16. Cyclic voltammetry and scanning electrochemical microscopy studies of methylene blue immobilized on the self-assembled monolayer of n-dodecanethiol

    International Nuclear Information System (INIS)

    Electron transfer (ET) kinetics through n-dodecanethiol (C12SH) self-assembled monolayer on gold electrode was studied using cyclic voltammetry (CV), scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). An SECM model for compensating pinhole contribution, was used to measure the ET kinetics of solution-phase probes of ferrocyanide/ferricyanide (Fe(CN)64-/3-) and ferrocenemethanol/ferrociniummethanol (FMC0/+) through the C12SH monolayer yielding standard tunneling rate constant (kET0) of (4 ± 1) x 10-11 and (3 ± 1) x 10-10 cm s-1 for Fe(CN)64-/3- and FMC0/+ respectively. Decay tunneling constants (β) of 0.97 and 0.96 A-1 for saturated alkane thiol chains were obtained using Fe(CN)64- and FMC respectively. Also, it was found that methylene blue (MB) molecules are effectively immobilized on the C12SH monolayer and can mediate the ET between the solution-phase probes and underlying gold substrate. SECM-mediated model was used to simultaneously measure the bimolecular ET between the solution-phase probes and the monolayer-immobilized MB molecules, as well as tunneling ET between the monolayer-immobilized MB molecules and the underlying gold electrode, allowing the measurement of kBI = (5 ± 1) x 106 and (4 ± 2) x 107 cm3 mol-1 s-1 for the bimolecular ET and kET/MB0=(1±0.3)x10-3 and (7 ± 3) x 10-2 s-1 for the standard tunneling rate constant of ET using Fe(CN)64-/3- and FMC0/+ probes respectively.

  17. Structural and Kinetic Studies of Novel Cytochrome P450 Small-Alkane Hydroxylases

    Energy Technology Data Exchange (ETDEWEB)

    Arnold, Frances H.

    2012-02-27

    The goals of this project are to investigate (1) the kinetics and stabilities of engineered cytochrome P450 (P450) small alkane hydroxylases and their evolutionary intermediates, (2) the structural basis for catalytic proficiency on small alkanes of these engineered P450s, and (3) the changes in redox control resulting from protein engineering. To reach these goals, we have established new methods for determining the kinetics and stabilities of multicomponent P450s such as CYP153A6. Using these, we were able to determine that CYP153A6 is proficient for hydroxylation of alkanes as small as ethane, an activity that has never been observed previously in any natural P450. To elucidate the structures of the engineered P450s, we obtained x-ray diffraction data for two variants in the P450PMO (propane monooxygenase) lineage and a preliminary structure for the most evolved variant. This structure shows changes in the substrate binding regions of the enzyme and a reduction in active site volume that are consistent with the observed changes in substrate specificity from fatty acids in the native enzyme to small alkanes in P450PMO. We also constructed semi-rational designed libraries mutating only residues in the enzyme active site that in one round of mutagenesis and screening produced variants that achieved nearly half of the activity of the most evolved enzymes of the P450PMO lineage. Finally, we found that changes in redox properties of the laboratory-evolved P450 alkane hydroxylases did not reflect the improvement in their electron transfer efficiency. The heme redox potential remained constant throughout evolution, while activity increased and coupling efficiency improved from 10% to 90%. The lack of correlation between heme redox potential and enzyme activity and coupling efficiency led us to search for other enzyme properties that could be better predictors for activity towards small alkanes, specifically methane. We investigated the oxidation potential of the radical

  18. A Novel Topological Index for the Studies on Structure-Properties of Alkanes

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A novel topological index derived from eccentric connectivity index has been proposed. The new topological index and eccentric connectivity index were correlated with eight physical properties such as the boiling point, critical temperature, critical pressure, critical volume, evaporation heat, density, heat capaci- ty, surface tension, and three thermodynamic properties such as standard enthalpy, standard entropy and standard formation free energy of alkanes. A series of empiric equations for calculating the properties were obtained. Correlation coefficients of nine properties were more than 0. 99 . Regression analysis and calcula- tion results indicated that the topological indices were well correlated with the physico-chemical properties of alkanes, and the novel topological index was far superior to eccentric connectivity index in the correlation.

  19. Electrochemical Studies of Glutathione Monolayer Assembled on A Polycrystalline Gold Electrode

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The glutathione (GSH) monolayer and complex monolayer of GSH-metallic ion on polycrys-talline gold electrode were studied by using K3Fe(CN)6 as the redox probe. As for the GSH monolayer, itwas found that the metallic ions could open the ion-gate in the monolayer dramatically in the order La3+>Pb2+>> Ba2+> Ca2+ whereas Zn2+ ion closed the ion-gate. The complexes of GSH-metallic ions were ca-pable of self-assembling the different kind of monolayer. All the differences were related to the structuralconfiguration of the anchored GSH molecule, which changed with the different metallic ions or pH.

  20. Study of the ionization of alkane-electron scavenger reactant mixtures irradiated by 60Co gamma rays

    International Nuclear Information System (INIS)

    This study deals with ionization of alkane-electron scavenger reactant mixtures, irradiated by 60Co γ-rays. It is shown that the extrapolated free-ion yields (extrapolated yield method) decrease with the reactant concentration. On the basis of ONSAGER model and theoretical treatment of MOZUMDER, the cross sections of epithermal electron attachment in hexane, cyclohexane, 2,2-dimethylbutane, cyclopentane, 2,2,4-trimethylpentane for CCl4, C7F14, C6H5Br, C6H5Cl, C6F14, (C6H5)2 are determined. A comparison between gas-phase and liquid-phase cross sections is established

  1. Exploring Ag(111) Substrate for Epitaxially Growing Monolayer Stanene: A First-Principles Study

    Science.gov (United States)

    Gao, Junfeng; Zhang, Gang; Zhang, Yong-Wei

    2016-07-01

    Stanene, a two-dimensional topological insulator composed of Sn atoms in a hexagonal lattice, is a promising contender to Si in nanoelectronics. Currently it is still a significant challenge to achieve large-area, high-quality monolayer stanene. We explore the potential of Ag(111) surface as an ideal substrate for the epitaxial growth of monolayer stanene. Using first-principles calculations, we study the stability of the structure of stanene in different epitaxial relations with respect to Ag(111) surface, and also the diffusion behavior of Sn adatom on Ag(111) surface. Our study reveals that: (1) the hexagonal structure of stanene monolayer is well reserved on Ag(111) surface; (2) the height of epitaxial stanene monolayer is comparable to the step height of the substrate, enabling the growth to cross the surface step and achieve a large-area stanene; (3) the perfect lattice structure of free-standing stanene can be achieved once the epitaxial stanene monolayer is detached from Ag(111) surface; and finally (4) the diffusion barrier of Sn adatom on Ag(111) surface is found to be only 0.041 eV, allowing the epitaxial growth of stanene monolayer even at low temperatures. Our above revelations strongly suggest that Ag(111) surface is an ideal candidate for growing large-area, high-quality monolayer stanene.

  2. Interactions of gas molecules with monolayer MoSe2: A first principle study

    Science.gov (United States)

    Sharma, Munish; Jamdagni, Pooja; Kumar, Ashok; Ahluwalia, P. K.

    2016-05-01

    We present a first principle study of interaction of toxic gas molecules (NO, NO2 and SO2) with monolayer MoSe2. The predicted order of sensitivity of gas molecule is NO2 > SO2 > NO. Adsorbed molecules strongly influence the electronic behaviour of monolayer MoSe2 by inducing impurity levels in the vicinity of Fermi energy. NO and SO2 is found to induce p-type doping effect while semiconductor to metallic transitions occur on NO2 adsorption. Our findings may guide the experimentalist for fabricating sensor devices based on MoSe2 monolayer.

  3. Reactions of C$_2$({\\it a}$^3Pi_u$) with selected saturated alkanes: A temperature dependence study

    CERN Document Server

    Hu, Renzhi; Chen, Yang

    2010-01-01

    We present a temperature dependence study on the gas phase reactions of the C$_2$({\\it a}$^3Pi_u$) radical with a selected series of saturated alkanes (C$_2$H$_6$, C$_3$H$_8$, n-C$_4$H$_10$, i-C$_4$H$_10$, and n-C$_6$H$_14$) by means of pulsed laser photolysis/laser-induced fluorescence technique. The bimolecular rate constants for these reactions were obtained between 298 and 673 K. A pronounced negative temperature effect was observed for n-C$_4$H$_10$, i-C$_4$H$_10$, and n-C$_6$H$_14$ and interpreted in terms of steric hindrance of the more reactive secondary or tertiary C-H bonds by less reactive CH$_3$ groups. Detailed analysis of our experimental results reveals quantitatively the temperature dependence of reactivities for the primary, secondary, and tertiary C-H bonds in these saturated alkanes and further lends support to a mechanism of hydrogen abstraction.

  4. Molecular dynamics studies of the melting of butane and hexane monolayers adsorbed on the basal-plane surface of graphite

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Newton, J. C.; Taub, H.

    1993-01-01

    The effect of molecular steric properties on the melting of quasi-two-dimensional solids is investigated by comparing results of molecular dynamics simulations of the melting of butane and hexane monolayers adsorbed on the basal-plane surface of graphite. These molecules differ only in their length......, being members of the n-alkane series [CH3(CH2)n−2CH3] where n=4 for butane and n=6 for hexane. The simulations employ a skeletal model, which does not include the hydrogen atoms explicitly, to represent the intermolecular and molecule–substrate interactions. Nearest-neighbor intramolecular bonds are...... fixed in length, but the molecular flexibility is preserved by allowing the bend and dihedral torsion angles to vary. The simulations show a qualitatively different melting behavior for the butane and hexane monolayers consistent with neutron and x-ray scattering experiments. The melting of the low...

  5. Structural study of monolayer cobalt phthalocyanine adsorbed on graphite

    CERN Document Server

    Scheffler, M; Baumann, D; Schlegel, R; Hänke, T; Toader, M; Büchner, B; Hietschold, M; Hess, C

    2014-01-01

    We present microscopic investigations on the two-dimensional arrangement of cobalt phthalocyanine molecules on a graphite (HOPG) substrate in the low coverage regime. The initial growth and ordering of molecular layers is revealed in high resolution scanning tunneling microscopy (STM). On low coverages single molecules orient mostly along one of the substrate lattice directions, while they form chains at slightly higher coverage. Structures with two different unit cells can be found from the first monolayer on. A theoretical model based on potential energy calculations is presented, which relates the two phases to the driving ordering forces.

  6. Carbon Isotopes of Alkanes in Hydrothermal Abiotic Organic Synthesis Processes at High Temperatures and Pressures: An Experimental Study

    Science.gov (United States)

    Fu, Qi; Socki, Richard A.; Niles, Paul B.

    2010-01-01

    Observation of methane in the Martian atmosphere has been reported by different detection techniques [1-4]. With more evidence showing extensive water-rock interaction in Martian history [5-7], abiotic formation by Fischer-Tropsch Type (FTT) synthesis during serpentization reactions may be one possible process responsible for methane generation on Mars [8, 9]. While the experimental studies performed to date leave little doubt that chemical reactions exist for the abiotic synthesis of organic compounds by mineral surface-catalyzed reactions [10-12], little is known about the reaction pathways by which CO2 and/or CO are reduced under hydrothermal conditions. Carbon and hydrogen isotope measurements of alkanes have been used as an effective tool to constrain the origin and reaction pathways of hydrocarbon formation. Alkanes generated by thermal breakdown of high molecular weight organic compounds have carbon and hydrogen isotopic signatures completely distinct from those formed abiotically [13-15]. Recent experimental studies, however, showed that different abiogenic hydrocarbon formation processes (e.g., polymerization vs. depolymerization) may have different carbon and hydrogen isotopic patterns [16]. Results from previous experiments studying decomposition of higher molecular weight organic compounds (lignite) also suggested that pressure could be a crucial factor affecting fractionation of carbon isotopes [17]. Under high pressure conditions, no experimental data are available describing fractionation of carbon isotope during mineral catalyzed FTT synthesis. Thus, hydrothermal experiments present an excellent opportunity to provide the requisite carbon isotope data. Such data can also be used to identify reaction pathways of abiotic organic synthesis under experimental conditions.

  7. Efficient Hydrogenolysis of Alkanes at Low Temperature and Pressure Using Tantalum Hydride on MCM-41, and a Quantum Chemical Study

    KAUST Repository

    Polshettiwar, Vivek

    2012-02-10

    Hydrogenolysis of hydrocarbons is of considerable technological importance for applications such as the hydroprocessing of petrochemical feedstocks to generate high-value and useful chemicals and fuels. We studied the catalytic activity of tantalum hydride supported on MCM-41 for the hydrogenolysis of alkanes at low temperature and low atmospheric pressure in a dynamic reactor. The reactions proceed with good turnover numbers, and the catalyst could be reused for several times, which makes the overall catalytic process sustainable. We derived the plausible mechanism by using DFT calculations and identified the preferred pathways by the analysis of potential energy surface. Our results and the proposed reaction mechanism demonstrate the viability of the "catalyst-by-design" approach. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Phase separation in the organic solid state: simultaneous Synchrotron SAXS / DSC studies of unstable n-alkane blends

    International Nuclear Information System (INIS)

    Full text: Blends of normal alkanes form lamellar structures, when quenched from the melt, in which the separation of the individual chains may be controlled by the chain-length difference, molar composition, isotopic substitution and confinement. We have performed simultaneous synchrotron small-angle X-ray scattering and differential scanning calorimetry studies on 2:1 C28H58:C36D74 mixtures as a function of cooling protocol. Their simultaneous collection enables the temperature-dependent nanostructural changes to be correlated with phase transitions. The data are further complemented by small-angle neutron scattering highlighting the separation of the individual chains via isotopic contrast and optical microscopy indicating changes occurring on the macroscopic scale. Copyright (2005) Australian Institute of Physics

  9. Evaporating Drops of Alkane Mixtures

    CERN Document Server

    Gu'ena, G; Poulard, C; Cazabat, Anne-Marie; Gu\\'{e}na, Geoffroy; Poulard, Christophe

    2005-01-01

    Alkane mixtures are model systems where the influence of surface tension gradients during the spreading and the evaporation of wetting drops can be easily studied. The surface tension gradients are mainly induced by concentration gradients, mass diffusion being a stabilising process. Depending on the relative concentration of the mixture, a rich pattern of behaviours is obtained.

  10. Study of Liquid Alkanes Production from Biomass-Derived Carbohydrates by Aldol-Condensation and Hydrogenation Processes

    OpenAIRE

    Navadol Laosiripojana; Verawat Champreda; Wassana Dedsuksophon

    2010-01-01

    This research aims to synthesis liquid alkanes from biomass-derived hydroxyl methyl furfural (HMF) and furfural by aldol-condensation and hydrogenation processes over several catalysts i.e. TiO2, TiO2-ZrO2, Pd/Al2O3 and Pd/CeO2. It was found that the catalysts make significant impact on the selectivity and yield of alkanes product. It is noted that Pd/Al2O3 provided the highest alkane yield and selectivity. The aldol-condensation and hydrogenation of HMF over Pd/Al2O3 provide high C12 selecti...

  11. High-resolution ellipsometric study of an n-alkane film, dotriacontane, adsorbed on a SiO2 surface

    DEFF Research Database (Denmark)

    Volkmann, U.G.; Pino, M.; Altamirano, L.A.;

    2002-01-01

    alkane/SiO2 interfacial region differs qualitatively from that which occurs in the surface freezing effect at the bulk alkane fluid/vapor interface. In that case, there is again a perpendicular film phase adjacent to the air interface but no parallel film phase intervenes between it and the bulk alkane...... present at higher coverages. In addition, we have performed high-resolution ellipsometry and stray-light measurements on dotriacontane films deposited from solution onto highly oriented pyrolytic graphite substrates. After film deposition, these substrates proved to be less stable in air than SiO2....

  12. Spectroscopic studies of large sheets of graphene oxide and reduced graphene oxide monolayers prepared by Langmuir-Blodgett technique

    Energy Technology Data Exchange (ETDEWEB)

    Sutar, D.S. [Central Surface Analytical Facility, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India); Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India); Narayanam, Pavan K.; Singh, Gulbagh; Botcha, V. Divakar; Talwar, S.S. [Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India); Srinivasa, R.S. [Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India); Major, S.S., E-mail: syed@iitb.ac.in [Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India)

    2012-07-01

    Graphene oxide (GO) sheets prepared by chemical exfoliation were spread at the air-water interface and transferred to silicon substrates by Langmuir-Blodgett technique as closely spaced monolayers of 20-40 {mu}m size. Hydrazine exposure followed by annealing in vacuum and argon ambient results in the formation of reduced graphene oxide (RGO) monolayers, without significantly affecting the overall morphology of the sheets. The monolayer character of both GO and RGO sheets was ascertained by atomic force microscopy. X-ray photoelectron spectroscopy supported by Fourier transform infrared spectroscopy revealed that the reduction process results in a significant decrease in oxygen functionalities, accompanied by a substantial decrease in the ratio of non-graphitic to graphitic (sp{sup 2} bonded) carbon in the monolayers from 1.2 to 0.35. Raman spectra of GO and RGO monolayers have shown that during the reduction process, the G-band shifts by 8-12 cm{sup -1} and the ratio of the intensities of D-band to G-band, I(D)/I(G) decreases from 1.3 {+-} 0.3 to 0.8 {+-} 0.2, which is in tune with the smaller non-graphitic carbon content of RGO monolayers. The significant decrease in I(D)/I(G) has been explained by assuming that substantial order is present in precursor GO monolayers as well as RGO monolayers obtained by solid state reduction. - Highlights: Black-Right-Pointing-Pointer Graphene oxide (GO) monolayers were deoxygenated to form reduced GO (RGO). Black-Right-Pointing-Pointer GO monolayers are 20-40 {mu}m in size, which does not change during reduction. Black-Right-Pointing-Pointer Reduction process does not affect the morphological stability of monolayers. Black-Right-Pointing-Pointer RGO monolayers show substantial decrease in non-graphitic carbon content. Black-Right-Pointing-Pointer Raman studies indicate presence of order in both GO and RGO monolayers.

  13. A molecular dynamics study of the effect of thermal boundary conductance on thermal transport of ideal crystal of n-alkanes with different number of carbon atoms

    Science.gov (United States)

    Rastgarkafshgarkolaei, Rouzbeh; Zeng, Yi; Khodadadi, J. M.

    2016-05-01

    Phase change materials such as n-alkanes that exhibit desirable characteristics such as high latent heat, chemical stability, and negligible supercooling are widely used in thermal energy storage applications. However, n-alkanes have the drawback of low thermal conductivity values. The low thermal conductivity of n-alkanes is linked to formation of randomly oriented nano-domains of molecules in their solid structure that is responsible for excessive phonon scattering at the grain boundaries. Thus, understanding the thermal boundary conductance at the grain boundaries can be crucial for improving the effectiveness of thermal storage systems. The concept of the ideal crystal is proposed in this paper, which describes a simplified model such that all the nano-domains of long-chain n-alkanes are artificially aligned perfectly in one direction. In order to study thermal transport of the ideal crystal of long-chain n-alkanes, four (4) systems (C20H42, C24H50, C26H54, and C30H62) are investigated by the molecular dynamics simulations. Thermal boundary conductance between the layers of ideal crystals is determined using both non-equilibrium molecular dynamics (NEMD) and equilibrium molecular dynamics (EMD) simulations. Both NEMD and EMD simulations exhibit no significant change in thermal conductance with the molecular length. However, the values obtained from the EMD simulations are less than the values from NEMD simulations with the ratio being nearly three (3) in most cases. This difference is due to the nature of EMD simulations where all the phonons are assumed to be in equilibrium at the interface. Thermal conductivity of the n-alkanes in three structures including liquid, solid, and ideal crystal is investigated utilizing NEMD simulations. Our results exhibit a very slight rise in thermal conductivity values as the number of carbon atoms of the chain increases. The key understanding is that thermal transport can be significantly altered by how the molecules and the

  14. Ab-initio study on the possible doping strategies for MoS$_2$ monolayers

    OpenAIRE

    Dolui, Kapildeb; Rungger, Ivan; Pemmaraju, Chaitanya Das; Sanvito, Stefano

    2013-01-01

    Density functional theory is used to systematically study the electronic and magnetic properties of doped MoS$_2$ monolayers, where the dopants are incorporated both via S/Mo substitution or as adsorbates. Among the possible substitutional dopants at the Mo site, Nb is identified as suitable p-type dopant, while Re is the donor with the lowest activation energy. When dopants are simply adsorbed on a monolayer we find that alkali metals shift the Fermi energy into the MoS$_2$ conduction band, ...

  15. Phases of phosphatidyl ethanolamine monolayers studied by synchrotron x-ray scattering

    DEFF Research Database (Denmark)

    Helm, C.A.; Tippmann-Krayer, P.; Möhwald, H.;

    1991-01-01

    For the first time, phospholid monolayers at the air/water interface have been studied by x-ray diffraction and reflection all along the isotherm from the laterally isotropic fluid (the so-called LE phase) to the ordered phases. The model used to analyze the data, and the accuracy of the paramete...

  16. Synthesis of Novel Amphiphilic Azobenzenes and X-ray Scattering Studies of Their Langmuir Monolayers

    DEFF Research Database (Denmark)

    Sørensen, Thomas Just; Kjær, Kristian; Breiby, Dag Werner;

    2008-01-01

    air-water interface, the amphiphilic azobenzenes form noncrystalline but stable Langmuir films that display an unusual reversible monolayer collapse close to 35 mN/m. The structures and phase transitions were studied by X-ray reflectivity (XR) and grazing-incidence X-ray diffraction, both utilizing...

  17. Formaldehyde molecule adsorption on the doped monolayer MoS2: A first-principles study

    Science.gov (United States)

    Ma, Dongwei; Ju, Weiwei; Li, Tingxian; Yang, Gui; He, Chaozheng; Ma, Benyuan; Tang, Yanan; Lu, Zhansheng; Yang, Zongxian

    2016-05-01

    Based on first-principles calculations, formaldehyde (H2CO) adsorption on the pristine monolayer MoS2 and that doped with Cl, P, or Si was theoretically studied to explore the potential of the MoS2 sheets as H2CO gas sensors. It is found that under Mo-rich conditions it is viable for Cl to be filled into the S vacancies acting as n-type dopant and for P and Si acting as p-type dopants. The results on the H2CO adsorption on the pristine and the Cl-doped monolayer MoS2 indicate that both are insensitive to H2CO. In contrast, H2CO exhibits strong adsorption on the P or Si-doped monolayer MoS2. And there are large electron transfer from the P or Si-doped monolayer MoS2 to the H2CO and obvious change in the electronic densities of states of both systems induced by the H2CO adsorption. These suggest that P and Si can be appropriate dopants filled into MoS2 sheets for detecting H2CO molecule.

  18. Thermodynamic study of alkane-α,ω-diamines - evidence of odd-even pattern of sublimation properties

    Czech Academy of Sciences Publication Activity Database

    Fulem, Michal; Růžička, K.; Červinka, C.; Bazyleva, A.; Della Gatta, G.

    2014-01-01

    Roč. 371, Jun (2014), s. 93-105. ISSN 0378-3812 Institutional support: RVO:68378271 Keywords : alkane-diamines * odd–even effect * vapor pressure * sublimation and vaporization thermodynamic properties * statistical thermodynamic s Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.200, year: 2014

  19. Metathesis of alkanes and related reactions

    KAUST Repository

    Basset, Jean-Marie

    2010-02-16

    (Figure Presented) The transformation of alkanes remains a difficult challenge because of the relative inertness of the C-H and C-C bonds. The rewards for asserting synthetic control over unfunctionalized, saturated hydrocarbons are considerable, however, because converting short alkanes into longer chain analogues is usually a value-adding process. Alkane metathesis is a novel catalytic and direct transformation of two molecules of a given alkane into its lower and higher homologues; moreover, the process proceeds at relatively low temperature (ambient conditions or higher). It was discovered through the use of a silica-supported tantalum hydride, (=SiO)2TaH, a multifunctional catalyst with a single site of action. This reaction completes the story of the metathesis reactions discovered over the past 40 years: olefin metathesis, alkyne metathesis, and ene-yne cyclizations. In this Account, we examine the fundamental mechanistic aspects of alkane metathesis as well as the novel reactions that have been derived from its study. The silica-supported tantalum hydride catalyst was developed as the result of systematic and meticulous studies of the interaction between oxide supports and organometallic complexes, a field of study denoted surface organometallic chemistry (SOMC). A careful examination of this surface-supported tantalum hydride led to the later discovery of aluminasupported tungsten hydride, W(H)3/Al 2O3, which proved to be an even better catalyst for alkane metathesis. Supported tantalum and tungsten hydrides are highly unsaturated, electron-deficient species that are very reactive toward the C-H and C-C bonds of alkanes. They show a great versatility in various other reactions, such as cross-metathesis between methane and alkanes, cross-metathesis between toluene and ethane, or even methane nonoxidative coupling. Moreover, tungsten hydride exhibits a specific ability in the transformation of isobutane into 2,3-dimethylbutane as well as in the metathesis of

  20. Catalytic activation of alkanes on noble metal-loaded zeolites : experimental studies and simulation of the dehydroalkylation of toluene with ethane

    OpenAIRE

    Rezai, Alireza

    2012-01-01

    With the recent progress in chemical reaction engineering and highly active, multi-functional catalysts, the activation of relatively inert alkanes may be achieved. The direct use of short-chain alkanes, especially methane and ethane, as basic chemical feedstocks represents an attractive alternative to alkenes. Significant reserves of alkanes are found in nature in the form of wet natural gas, whereas alkenes have to be synthesized via other chemical reactions. The activation of alkanes can b...

  1. Lithium halide monolayers: Structural, electronic and optical properties by first principles study

    Science.gov (United States)

    Safari, Mandana; Maskaneh, Pegah; Moghadam, Atousa Dashti; Jalilian, Jaafar

    2016-09-01

    Using first principle study, we investigate the structural, electronic and optical properties of lithium halide monolayers (LiF, LiCl, LiBr). In contrast to graphene and other graphene-like structures that form hexagonal rings in plane, these compounds can form and stabilize in cubic shape interestingly. The type of band structure in these insulators is identified as indirect type and ionic nature of their bonds are illustrated as well. The optical properties demonstrate extremely transparent feature for them as a result of wide band gap in the visible range; also their electron transitions are indicated for achieving a better vision on the absorption mechanism in these kinds of monolayers.

  2. Wedge energy bands of monolayer black phosphorus: a first-principles study.

    Science.gov (United States)

    Park, Minwoo; Bae, Hyeonhu; Lee, Seunghan; Yang, Li; Lee, Hoonkyung

    2016-08-01

    On the basis of first-principles calculations, we present intriguing electronic properties of halogen-striped functionalized monolayer black phosphorus. The halogen-striped monolayer black phosphorus is found to have a wedge energy band with the energy-momentum relation of [Formula: see text] when the stripe-stripe distance is smaller than ~40 Å. Our tight-binding study shows that the wedge energy band occurs when 2-atom basis 1D lattices are periodically repeated aligned with each other in a 2D lattice. We also discuss the possible applications of this wedge energy band in electron supercollimation with high mobility or severely anisotropic electronic transport, which can be used for the development of optics-like nano-electronics. PMID:27299467

  3. Possible doping strategies for MoS 2 monolayers: An ab initio study

    KAUST Repository

    Dolui, Kapildeb

    2013-08-14

    Density functional theory is used to systematically study the electronic properties of doped MoS2 monolayers, where the dopants are incorporated both via S/Mo substitution or as adsorbates. Among the possible substitutional dopants at the Mo site, Nb is identified as suitable p-type dopant, while Re is the donor with the lowest activation energy. When dopants are simply adsorbed on a monolayer we find that alkali metals shift the Fermi energy into the MoS2 conduction band, making the system n type. Finally, the adsorption of charged molecules is considered, mimicking an ionic liquid environment. We find that molecules adsorption can lead to both n- and p-type conductivity, depending on the charge polarity of the adsorbed species. © 2013 American Physical Society.

  4. Wedge energy bands of monolayer black phosphorus: a first-principles study

    Science.gov (United States)

    Park, Minwoo; Bae, Hyeonhu; Lee, Seunghan; Yang, Li; Lee, Hoonkyung

    2016-08-01

    On the basis of first-principles calculations, we present intriguing electronic properties of halogen-striped functionalized monolayer black phosphorus. The halogen-striped monolayer black phosphorus is found to have a wedge energy band with the energy-momentum relation of E\\propto {{p}y} when the stripe–stripe distance is smaller than ~40 Å. Our tight-binding study shows that the wedge energy band occurs when 2-atom basis 1D lattices are periodically repeated aligned with each other in a 2D lattice. We also discuss the possible applications of this wedge energy band in electron supercollimation with high mobility or severely anisotropic electronic transport, which can be used for the development of optics-like nano-electronics.

  5. Alkane dimers interaction

    DEFF Research Database (Denmark)

    Ferrighi, Lara; Madsen, Georg Kent Hellerup; Hammer, Bjørk

    The interaction energies of a series of n-alkane dimers, from methane to decane, have been investigated with Density Functional Theory (DFT), using the MGGA-M06-L density functional. The results are compared both to the available wavefunction-based values as well as to dispersion corrected DFT...

  6. Experimental and modeling study of the low-temperature oxidation of large alkanes

    CERN Document Server

    Biet, Joffrey; Warth, Valérie; Glaude, Pierre-Alexandre; Battin-Leclerc, Frédérique

    2008-01-01

    This paper presents an experimental and modeling study of the oxidation of large linear akanes (from C10) representative from diesel fuel from low to intermediate temperature (550-1100 K) including the negative temperature coefficient (NTC) zone. The experimental study has been performed in a jet-stirred reactor at atmospheric pressure for n-decane and a n-decane/n-hexadecane blend. Detailed kinetic mechanisms have been developed using computer-aided generation (EXGAS) with improved rules for writing reactions of primary products. These mechanisms have allowed a correct simulation of the experimental results obtained. Data from the literature for the oxidation of n-decane, in a jet-stirred reactor at 10 bar and in shock tubes, and of n-dodecane in a pressurized flow reactor have also been correctly modeled. A considerable improvement of the prediction of the formation of products is obtained compared to our previous models. Flow rates and sensitivity analyses have been performed in order to better understand ...

  7. Contribution to study of the thermodynamics properties of mixtures containing 2-methoxy-2-methylpropane, alkanol, alkane

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Experimental enthalpies for the mixtures MTBE + pentanol + hexane and pentanol + hexane were measured. • No experimental ternary values were found in the currently available literature. • Excess molar enthalpies are positive over the whole range of composition. • The ternary contribution is also positive with the exception of a range located around the rich compositions of 1-pentanol. - Abstract: Excess molar enthalpies for the ternary system {x1 2-methoxy-2-methylpropane (MTBE) + x2 1-pentanol + (1 − x1 − x2) hexane} and the involved binary mixture {x 1-pentanol + (1 − x) hexane}, have been measured at T = 298.15 K and atmospheric pressure over the whole composition range. We are not aware of the existence of previous experimental measurement of the excess enthalpy for the ternary mixture under study in the literature currently available. Values of the excess molar enthalpies were measured using a Calvet microcalorimeter. The results were fitted by means of different variable degree polynomials. The ternary contribution to the excess enthalpy was correlated with the equation due to Verdes et al. (2004), and the equation proposed by Myers–Scott (1963) was used to fit the experimental binary mixture measured in this work. Smooth representations of the results are presented and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. The excess molar enthalpies for the binary and ternary system are positive over the whole range of composition. The binary mixture {x 1-pentanol + (1 − x) hexane} is asymmetric, with its maximum displace toward a high mole fraction of decane. The ternary contribution is also positive with the exception of a range located around the rich compositions of 1-pentanol, and the representation is asymmetric. Additionally, the group contribution model of the UNIFAC model, in the versions of Larsen et al. (1987) [18] and Gmehling et al. (1993) [19] was used to estimate

  8. Self Assembly of Mixed Monolayers of Mercaptoundecylferrocene and Undecanethiol studied by STM

    International Nuclear Information System (INIS)

    Mixed monolayers of mercaptoundecylferrocene and undecanethiol were deposited from solution by coadsorption and by a two-step insertion method, using the alkanethiol monolayer as insulating matrix. The resulting layers were characterized by UHV-STM, showing molecular resolution. For insertion-processed samples, a mesh-like surface structure of ferrocenes was observed, due to the preferential incorporation of molecules along domain boundaries and defect sites of the alkanethiol monolayer. For monolayers in the intermediate coverage regime, a crystalline phase was observed

  9. Study of relaxation process of dipalmitoyl phosphatidylcholine monolayers at air-water interface: Effect of electrostatic energy

    Science.gov (United States)

    Ou-Yang, Wei; Weis, Martin; Manaka, Takaaki; Iwamoto, Mitsumasa

    2011-04-01

    The instability of organic monolayer composed of polar molecules at the air-water interface has been a spotlight in interface science for many decades. However, the effect of electrostatic energy contribution to the free energy in the system is still not understood. Herein, we investigate the mechanical and electrical properties by studying the isobaric relaxation process of a dipalmitoyl phosphatidylcholine monolayer on water subphase with various concentrations of divalent ions to reveal the effect of electrostatic energy on thermodynamics and kinetics of the collapse mechanism. Our results demonstrate that electrical energy among the dipolar molecules plays an important role in the stability of monolayer and enhances the formation of micelles into subphase under high pressure. In addition, to confirm the electrostatic energy contribution, the well-known thermal effect on the stability of the film is compared. Hence, the general description of the monolayer free energy with contribution of electrostatic energy is suggested to describe the phase transition.

  10. Interfacial structures of self-assembled monolayers of 2-pyridinethiol on Au(111) studied by in situ scanning tunneling microscopy

    International Nuclear Information System (INIS)

    In situ Scanning Tunneling Microscopy (STM) operating under electrochemical condition was used to study self-assembled monolayers of 2-pyridinethiol (2-PySH) on Au(111) in perchloric acid solution. Each molecule appeared as two spots, presumably originated from adsorption through S and N atoms of 2-pyridinethiolate with a vertical orientation on the Au(111) surface. The ordered 2-pyridinethiolate monolayers exhibited a p(4 x √7R-40.9deg) structure, which was constructed by alternative arrangements of two types of molecular rows with differently rotated molecules. In situ STM also revealed that the monolayer consisted of molecularly ordered domains with the p(4 x √7R-40.9deg) structure, its mirror structure defined as a p(4 x √7R-19.1deg), and their rotational structures. Detailed interfacial structures and molecularly ordered domains of the 2-pyridinethiolate monolayer have been elucidated by in situ STM imaging in aqueous solution. (author)

  11. Electronic and magnetic properties of dopant atoms in SnSe monolayer: a first-principles study

    CERN Document Server

    Wang, Qingxia; Fu, Xiaonan; Qiao, Chong; Xia, Congxin; Jia, Yu

    2015-01-01

    SnSe monolayer with orthorhombic Pnma GeS structure is an important two-dimensional (2D) indirect band gap material at room temperature. Based on first-principles density functional theory calculations, we present systematic studies on the electronic and magnetic properties of X (X = Ga, In, As, Sb) atoms doped SnSe monolayer. The calculated electronic structures show that Ga-doped system maintains semiconducting property while In-doped SnSe monolayer is half-metal. The As- and Sb- doped SnSe systems present the characteristics of n-type semiconductor. Moreover, all considered substitutional doping cases induce magnetic ground states with the magnetic moment of 1{\\mu}B. In addition, the calculated formation energies also show that four types of doped systems are thermodynamic stable. These results provide a new route for the potential applications of doped SnSe monolayer in 2D photoelectronic and magnetic semiconductor devices.

  12. Positional order in Langmuir monolayers: An X-ray diffraction study

    DEFF Research Database (Denmark)

    Kaganer, V.M.; Brezesinski, G.; Möhwald, H.;

    1999-01-01

    The structural phase transition from the hexagonal to a distorted-hexagonal (centered rectangular) phase (the LS-S transition) in Langmuir monolayers of octadecanol is studied in a grazing incidence x-ray diffraction experiment. We find algebraic decay of positional correlations, which suggests...... solid-like order in both phases at the distances accessible in the present x-ray diffraction experiment. The transition is accompanied by strong positional disorder, which is evident from the drastic increase of the exponent eta to values eta>2 close to the transition. Remarkably, on approaching...

  13. Towards strain gauges based on a self-assembled nanoparticle monolayer-SAXS study

    International Nuclear Information System (INIS)

    An in situ small-angle x-ray scattering study of the nanoparticle displacement in a self-assembled monolayer as a function of a supporting membrane strain is presented. The average nanoparticle spacing is 6.7 nm in the unstrained state and increases in the applied force direction, following linearly the membrane strain which reaches the maximum value of 11%. The experimental results suggest a continuous mutual shift of the nanoparticles and their gradual separation with the growing stress rather than nanoparticle islands formation. No measurable shift of the nanoparticles was observed in the direction perpendicular to the applied stress.

  14. Products of Chemistry: Alkanes: Abundant, Pervasive, Important, and Essential.

    Science.gov (United States)

    Seymour, Raymond B.

    1989-01-01

    Discusses the history and commercialization of alkanes. Examines the nomenclature and uses of alkanes. Studies polymerization and several types of polyethylenes: low-density, high-density, low-molecular-weight, cross-linked, linear low-density, and ultrahigh-molecular-weight. Includes a glossary of hydrocarbon terms. (MVL)

  15. Perforated monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Regen, S.L.

    1992-12-01

    Goal of this research program is to create ultrathin organic membranes that possess uniform and adjustable pores ( < 7[angstrom] diameter). Such membranes are expected to possess high permeation selectivity (permselectivity) and high permeability, and to provide the basis for energy-efficient methods of molecular separation. Work carried out has demonstrated feasibility of using perforated monolayer''-based composites as molecular sieve membranes. Specifically, composite membranes derived from Langmuir-Blodgett multilayers of the calix[6]arene-based surfactant shown below plus poly[l-(trimethylsilyl)-l-propyne] (PTMSP) were found to exhibit sieving behavior towards He, N[sub 2] and SF[sub 6]. Results of derivative studies that have also been completed are also described in this report.

  16. STM study of morphology and electron transport features in cytochrome c and nanocluster molecule monolayers.

    Science.gov (United States)

    Khomutov, G B; Belovolova, L V; Gubin, S P; Khanin, V V; Obydenov, A Yu; Sergeev-Cherenkov, A N; Soldatov, E S; Trifonov, A S

    2002-01-01

    The morphology and electron tunneling through single cytochrome c and nanocluster Pt(5)(CO)(7)[P(C(6)H(5))](4) molecules organized as monolayer Langmuir-Blodgett (LB) films on graphite substrate have been studied experimentally using scanning tunneling microscopy (STM) and spectroscopy techniques with sub-nanometer spatial resolution in a double barrier tunnel junction configuration STM tip-monomolecular film-conducting substrate at ambient conditions. STM images of the films revealed globular structures with characteristic diameters (approximately 3.5 nm for the protein molecule and approximately 1.2 nm for the nanocluster). The spectroscopic study by recording the tunneling current-bias voltage (I-V) curves revealed tunneling I-V characteristics with features as steps of different width and heights that are dependent on the STM tip position over the molecule in the monolayer, giving evidence for sequential discrete electron-tunneling effects with the combination of the single electron Coulomb-charging energy and the electronic energy level separation (molecular spectrum) in such immobilized metalloprotein and nanocluster structures that can be of interest for the development of bioelectronic and hybrid functional nanosystems. PMID:11786369

  17. Electronic and vibrational properties of graphene monolayers with iron adatoms: A density functional theory study

    International Nuclear Information System (INIS)

    Highlights: • Periodic density functional calculations were performed on graphene monolayers with and without an iron adatom. • Densities of states, charge transfers, and overlap populations were used to elucidate the effects of weak iron adsorption on graphene compared to CO adsorption on Pt. • Infrared intensities and normal mode analysis verify weak iron adsorption on graphene by studying the shift in prominent vibrational modes and changes in lattice dynamics. - Abstract: Periodic density functional calculations on graphene monolayers with and without an iron adatom have been used to elucidate iron-graphene adsorption and its effects on graphene electronic and vibrational properties. Density-of-states calculations and charge density contour plots reveal charge transfer from the iron s orbitals to the d orbitals, in agreement with past reports. Adsorbed iron atoms covalently bind to the graphene substrate, verified by the strong hybridization of iron d-states with the graphene bands in the energy region just below the Fermi level. This adsorption is weak and compared to the well-analyzed CO adsorption on Pt: It is indicated by its small adsorption energy and the minimal change of the substrate geometry due to the presence of the iron adatoms. Graphene vibrational spectra are analyzed though a systematic variation of the graphene supercell size. The shifts of graphene most prominent infrared active vibrational modes due to iron adsorption are explored using normal mode eigenvectors

  18. First principles kinetic Monte Carlo study on the growth patterns of WSe2 monolayer

    Science.gov (United States)

    Nie, Yifan; Liang, Chaoping; Zhang, Kehao; Zhao, Rui; Eichfeld, Sarah M.; Cha, Pil-Ryung; Colombo, Luigi; Robinson, Joshua A.; Wallace, Robert M.; Cho, Kyeongjae

    2016-06-01

    The control of domain morphology and defect level of synthesized transition metal dichalcogenides (TMDs) is of crucial importance for their device applications. However, current TMDs synthesis by chemical vapor deposition and molecular beam epitaxy is in an early stage of development, where much of the understanding of the process-property relationships is highly empirical. In this work, we use a kinetic Monte Carlo coupled with first principles calculations to study one specific case of the deposition of monolayer WSe2 on graphene, which can be expanded to the entire TMD family. Monolayer WSe2 domains are investigated as a function of incident flux, temperature and precursor ratio. The quality of the grown WSe2 domains is analyzed by the stoichiometry and defect density. A phase diagram of domain morphology is developed in the space of flux and the precursor stoichiometry, in which the triangular compact, fractal and dendritic domains are identified. The phase diagram has inspired a new synthesis strategy for large TMD domains with improved quality.

  19. Electronic and vibrational properties of graphene monolayers with iron adatoms: A density functional theory study

    Energy Technology Data Exchange (ETDEWEB)

    Dimakis, Nicholas, E-mail: dimakis@utpa.edu [Department of Physics and Geology, University of Texas-Pan American, Edinburg, TX (United States); Navarro, Nestor E. [Department of Chemistry, University of Texas-Pan American, Edinburg, TX (United States); Velazquez, Julian; Salgado, Andres [Department of Physics and Geology, University of Texas-Pan American, Edinburg, TX (United States)

    2015-04-15

    Highlights: • Periodic density functional calculations were performed on graphene monolayers with and without an iron adatom. • Densities of states, charge transfers, and overlap populations were used to elucidate the effects of weak iron adsorption on graphene compared to CO adsorption on Pt. • Infrared intensities and normal mode analysis verify weak iron adsorption on graphene by studying the shift in prominent vibrational modes and changes in lattice dynamics. - Abstract: Periodic density functional calculations on graphene monolayers with and without an iron adatom have been used to elucidate iron-graphene adsorption and its effects on graphene electronic and vibrational properties. Density-of-states calculations and charge density contour plots reveal charge transfer from the iron s orbitals to the d orbitals, in agreement with past reports. Adsorbed iron atoms covalently bind to the graphene substrate, verified by the strong hybridization of iron d-states with the graphene bands in the energy region just below the Fermi level. This adsorption is weak and compared to the well-analyzed CO adsorption on Pt: It is indicated by its small adsorption energy and the minimal change of the substrate geometry due to the presence of the iron adatoms. Graphene vibrational spectra are analyzed though a systematic variation of the graphene supercell size. The shifts of graphene most prominent infrared active vibrational modes due to iron adsorption are explored using normal mode eigenvectors.

  20. Radical formation in the [MeReO3]-catalyzed aqueous peroxidative oxidation of alkanes: a theoretical mechanistic study.

    Science.gov (United States)

    Kuznetsov, Maxim L; Pombeiro, Armando J L

    2009-01-01

    Plausible mechanisms of radical formation in the catalytic system [MeReO(3)]/H(2)O(2)/H(2)O-CH(3)CN for the oxidation of alkanes to alcohols and ketones, via radical pathways, are investigated extensively at the density functional theory level. The most favorable route is based on the monoperoxo complex [MeReO(2)(O(2))(H(2)O)] and includes the formation of an H(2)O(2) adduct, water-assisted H-transfer from H(2)O(2) to the peroxo ligand, and generation of HOO(*). The thus formed reduced Re(VI) complex [MeReO(2)(OOH)(H(2)O)] reacts with H(2)O(2), resulting, upon water-assisted H-transfer and O-OH bond homolysis, in the regeneration of the oxo-Re(VII) catalyst and formation of the HO(*) radical that reacts further with the alkane. Water plays a crucial role by (i) stabilizing transition states for the proton migrations and providing easy intramolecular H-transfers in the absence of any N,O-ligands and (ii) saturating the Re coordination sphere what leads to a decrease of the activation barrier for the formation of HOO(*). The activation energy of the radical formation calculated for [MeReO(3)] (17.7 kcal/mol) is compatible with that determined experimentally [Shul'pin et al. J. Chem. Soc., Perkin Trans. 2 2001, 1351 .] for oxo-V-based catalytic systems (17 +/- 2 kcal/mol), and the overall type of mechanism proposed for such V catalysts is also effective for [MeReO(3)]. PMID:19049432

  1. A note on the use of ellipsometry for studying the kinetics of formation of self-assembled monolayers

    Indian Academy of Sciences (India)

    Murali Sastry

    2000-06-01

    Ellipsometry is currently one of the most important techniques for characterization of the deposition and growth mode of ultra thin organic films. However, it is well known that for thicknesses normally encountered in organic monolayer films, as would occur for example in self-assembled monolayers, ellipsometry cannot be used to simultaneously determine the thickness and refractive index of the monolayer film. Current practice is to assume a reasonable value for the film refractive index and calculate an effective ‘ellipsometric thickness’. This communication seeks to show that the alternative approach of assuming a thickness for the monolayer (determined by the length of the molecule) and calculating the effective film refractive index lends itself to easier and more meaningful physical interpretation. The Lorentz–Lorenz formula is then used to transform the effective refractive index into a surface coverage and hence to an effective mass coverage. The methodology advanced is applied to the kinetics of formation of a self-assembled monolayer of a well-studied molecule, octadecanethiol on Au.

  2. Reflectance spectroscopy of organic compounds: 1. Alkanes

    Science.gov (United States)

    Clark, R.N.; Curchin, J.M.; Hoefen, T.M.; Swayze, G.A.

    2009-01-01

    Reflectance spectra of the organic compounds comprising the alkane series are presented from the ultraviolet to midinfrared, 0.35 to 15.5 /??m. Alkanes are hydrocarbon molecules containing only single carbon-carbon bonds, and are found naturally on the Earth and in the atmospheres of the giant planets and Saturn's moon, Titan. This paper presents the spectral properties of the alkanes as the first in a series of papers to build a spectral database of organic compounds for use in remote sensing studies. Applications range from mapping the environment on the Earth, to the search for organic molecules and life in the solar system and throughout the. universe. We show that the spectral reflectance properties of organic compounds are rich, with major diagnostic spectral features throughout the spectral range studied. Little to no spectral change was observed as a function of temperature and only small shifts and changes in the width of absorption bands were observed between liquids and solids, making remote detection of spectral properties throughout the solar system simpler. Some high molecular weight organic compounds contain single-bonded carbon chains and have spectra similar to alkanes even ' when they fall into other families. Small spectral differences are often present allowing discrimination among some compounds, further illustrating the need to catalog spectral properties for accurate remote sensing identification with spectroscopy.

  3. Growth of n-alkane films on a single-crystal substrate

    DEFF Research Database (Denmark)

    Wu, Z. U.; Ehrlich, S. N.; Matthies, B.; Herwig, K. W.; Dai, P.; Volkmann, U. G.; Hansen, Flemming Yssing; Taub, H.

    The structure and growth mode of alkane films (n-C/sub n/H/sub 2n+2/; n=4, 6, 7) adsorbed on a Ag(111) surface have been investigated by synchrotron X-ray scattering. New models are proposed for the butane (n=4) and hexane (n=6) monolayer and butane bilayer structures. Specular reflectivity scans...

  4. Growth of n-alkane films on a single-crystal substrate

    DEFF Research Database (Denmark)

    Wu, Z. U.; Ehrlich, S. N.; Matthies, B.;

    2001-01-01

    The structure and growth mode of alkane films (n-C/sub n/H/sub 2n+2/; n=4, 6, 7) adsorbed on a Ag(111) surface have been investigated by synchrotron X-ray scattering. New models are proposed for the butane (n=4) and hexane (n=6) monolayer and butane bilayer structures. Specular reflectivity scans...

  5. Samarium(III) picrate tetraethylene glycol complex: Photoluminescence study and active material in monolayer electroluminescent

    International Nuclear Information System (INIS)

    A mononuclear Sm(III) complex involving Pic and EO4 (where Pic=picrate anion and EO4=tetraethylene glycol) has been studied. It shows a bright-orange emission when used as active material in a monolayer electroluminescent device of ITO/EO4-Sm-Pic/Al. The crystal structure of the complex consists of [Sm(Pic)2(H2O)(EO4)]+ cation and [Pic]- anion. The Sm(III) ion is coordinated with nine oxygen atoms from one EO4 ligand in a pentadentate mode, two Pic anions each in bidentate and monodentate modes, and one water molecule. Both the terminal alcohol groups of the acyclic EO4 ligand were involved in the O-H...O hydrogen bonding by infinite one-dimensional (1D) chain within a symmetry direction [0 1 0]. The photoluminescence (PL) spectrum of the thin film shows the typical spectral features of the Sm(III) ion (4G5/2→6H7/2 transitions). The root-mean-square (rms) of the roughness of thin film is 30.605 nm and indicates that the formation of the monolayer electroluminescent device is not uniform and retains a high crystallinity. Typical semiconductor current-voltage (I-V) property was also observed in this device with threshold and turn voltages of 2.8 and 6.2 V, respectively. The [Sm(Pic)2(H2O)(EO4)](Pic).H2O complex can be applied as a luminescent center in OLED for bright-orange emission. - Highlights: → The [Sm(Pic)2(H2O)(EO4)](Pic).H2O complex is crystallized in triclinic with space group P-1. → The complex is applied as a emissive center in monolayer device structure of ITO/EO4-Sm-Pic/Al. → The photoluminescence spectrum of the crystalline and thin film shows a bright-orange emission. → The current-voltage property showed the turn on voltage of 6.2 V.

  6. Density functional study of CaN monolayer on Si(001)

    Science.gov (United States)

    Saati asr, Maryam; Zahedifar, Maedeh; Hashemifar, S. Javad; Akbarzadeh, Hadi

    2016-01-01

    In this work, the first-principles computations are performed to study the structural and magnetic properties of CaN/Si(001) interface. Bulk CaN in the zinc-blende (ZB) structure is argued to be an ionic magnetic compound with a total spin moment of 1 μB per formula unit, originated from the p electrons of N ions. Various interface configurations of a ZB CaN monolayer on Si (001) surface are investigated and the lowest energy and the highest spin polarized interfaces are extracted. Then the minimum energy path between the lowest energy and the highest spin polarized interfaces are calculated by using the nudged elastic band method and it is argued that both these systems are unstable toward a nonmagnetic interface with a rock-salt arrangement of Ca and N atoms.

  7. Transepithelial transport of aliphatic carboxylic acids studied in Madin Darby canine kidney (MDCK) cell monolayers

    International Nuclear Information System (INIS)

    Transport of 14C-labeled acetic, propionic (PA), butyric, valeric, heptanoic (HA), and octanoic (OA) acids across the Madin Darby canine kidney (MDCK) epithelial cell monolayer grown on a porous polycarbonate membrane was studied in Hanks' balanced salt solution (HBSS) at 37 degrees C in both apical-to-basolateral and basolateral-to-apical directions. At micromolar concentrations of solutes, metabolic decomposition was significant as evidenced by [14C]CO2 production during the OA transport. The apparent permeability (Pe) indicates that as lipophilicity increases, diffusion across the unstirred boundary layer becomes rate limiting. In support of this notion, transport of OA and HA was enhanced by agitation, showed an activation energy of 3.7 kcal/mol for OA, and resulted in identical Pe values for both transport directions. Analysis of Pe changes with varying alkyl chain length resulted in a delta G of -0.68 +/- 0.09 kcal/mol for -CH2-group transfer from an aqueous phase to the MDCK cells. When the intercellular tight junctions were opened by the divalent chelator EGTA in Ca2+/Mg2(+)-free HBSS, transport of the fluid-phase marker Lucifer yellow greatly increased because of paracellular leakage. PA transport also showed a significant increase, but OA transport was independent of EGTA. Although albumin also undergoes paracellular transport in the presence of EGTA and OA binds strongly to albumin, OA transport in EGTA solution was unchanged by albumin. These observations indicate that transmembrane transport is the major mechanism for lipophilic substances. The present study, together with earlier work on the transport of polar substances, shows that the MDCK cell monolayer is an excellent model of the transepithelial transport barrier

  8. Transepithelial transport of aliphatic carboxylic acids studied in Madin Darby canine kidney (MDCK) cell monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Cho, M.J.; Adson, A.; Kezdy, F.J. (Upjohn Company, Kalamazoo, MI (USA))

    1990-04-01

    Transport of 14C-labeled acetic, propionic (PA), butyric, valeric, heptanoic (HA), and octanoic (OA) acids across the Madin Darby canine kidney (MDCK) epithelial cell monolayer grown on a porous polycarbonate membrane was studied in Hanks' balanced salt solution (HBSS) at 37{degrees}C in both apical-to-basolateral and basolateral-to-apical directions. At micromolar concentrations of solutes, metabolic decomposition was significant as evidenced by (14C)CO2 production during the OA transport. The apparent permeability (Pe) indicates that as lipophilicity increases, diffusion across the unstirred boundary layer becomes rate limiting. In support of this notion, transport of OA and HA was enhanced by agitation, showed an activation energy of 3.7 kcal/mol for OA, and resulted in identical Pe values for both transport directions. Analysis of Pe changes with varying alkyl chain length resulted in a delta G of -0.68 +/- 0.09 kcal/mol for -CH2-group transfer from an aqueous phase to the MDCK cells. When the intercellular tight junctions were opened by the divalent chelator EGTA in Ca2+/Mg2(+)-free HBSS, transport of the fluid-phase marker Lucifer yellow greatly increased because of paracellular leakage. PA transport also showed a significant increase, but OA transport was independent of EGTA. Although albumin also undergoes paracellular transport in the presence of EGTA and OA binds strongly to albumin, OA transport in EGTA solution was unchanged by albumin. These observations indicate that transmembrane transport is the major mechanism for lipophilic substances. The present study, together with earlier work on the transport of polar substances, shows that the MDCK cell monolayer is an excellent model of the transepithelial transport barrier.

  9. Kinetic studies on the interactions between glycolipid biosurfactant assembled monolayers and various classes of immunoglobulins using surface plasmon resonance.

    Science.gov (United States)

    Ito, Seya; Imura, Tomohiro; Fukuoka, Tokuma; Morita, Tomotake; Sakai, Hideki; Abe, Masahiko; Kitamoto, Dai

    2007-08-01

    Kinetic studies on the interactions between self-assembled monolayers of mannosylerythritol lipids (MELs), which are glycolipid biosurfactants abundantly produced by microorganisms, and various classes of immunoglobulins including human IgG, IgA, and IgM were performed using surface plasmon resonance (SPR). The effect of the MEL structure on the binding behavior of HIgG was examined. Assembled monolayers of MEL-A having two acetyl groups on the headgroup gave a high affinity (K(d)=1.7x10(-6)M) toward HIgG, while those of MEL-B or MEL-C having only one acetyl group at C-6' or C-4' position gave little affinity. Our kinetic analysis revealed that the binding manner of HIgG, HIgA (K(d)=2.4x10(-7)M), and HIgM (K(d)=2.2x10(-7)M) to the assembled monolayers of MEL-A is not the monovalent mode but the bivalent mode, and both the first and second rate association constants (k(a1), k(a2)) increase with an increase in the number of antibody binding sites, while those for dissociation (k(d1), k(d2)) changed little. Moreover, we succeeded in directly observing great amounts of HIgG, HIgA, and HIgM bound to MEL-A monolayers using atomic force microscopy (AFM). Finally, we found that MEL-A assembled monolayer binds toward various IgG derived from mouse, pig, rabbit, horse, goat, rat, and bovine as well as human IgG (HIgG), and the only exception was sheep IgG. These results clearly demonstrate that MEL-A assembled monolayers would be useful as noble affinity ligand system for various immunoglobulins. PMID:17428643

  10. Computational Study of Metal Contacts to Monolayer Transition-Metal Dichalcogenide Semiconductors

    Science.gov (United States)

    Kang, Jiahao; Liu, Wei; Sarkar, Deblina; Jena, Debdeep; Banerjee, Kaustav

    2014-07-01

    Among various 2D materials, monolayer transition-metal dichalcogenide (mTMD) semiconductors with intrinsic band gaps (1-2 eV) are considered promising candidates for channel materials in next-generation transistors. Low-resistance metal contacts to mTMDs are crucial because currently they limit mTMD device performances. Hence, a comprehensive understanding of the atomistic nature of metal contacts to these 2D crystals is a fundamental challenge, which is not adequately addressed at present. In this paper, we report a systematic study of metal-mTMD contacts with different geometries (top contacts and edge contacts) by ab initio density-functional theory calculations, integrated with Mulliken population analysis and a semiempirical van der Waals dispersion potential model (which is critical for 2D materials and not well treated before). Particularly, In, Ti, Au, and Pd, contacts to monolayer MoS2 and WSe2 as well as Mo-MoS2 and W-WSe2 contacts are evaluated and categorized, based on their tunnel barriers, Schottky barriers, and orbital overlaps. Moreover, going beyond Schottky theory, new physics in such contact interfaces is revealed, such as the metallization of mTMDs and abnormal Fermi level pinning. Among the top contacts to MoS2, Ti and Mo show great potential to form favorable top contacts, which are both n-type contacts, while for top contacts to WSe2, W or Pd exhibits the most advantages as an n- or p-type contact, respectively. Moreover, we find that edge contacts can be highly advantageous compared to top contacts in terms of electron injection efficiency. Our formalism and the results provide guidelines that would be invaluable for designing novel 2D semiconductor devices.

  11. Neutron scattering study of 36 Ar monolayer films adsorbed on graphite

    DEFF Research Database (Denmark)

    Taub, H.; da Costa Carneiro, Kim; Kjems, Jørgen;

    1977-01-01

    scattered from 36 Ar monolayers in the nominally in-plane configuration can be reasonably well described at low temperatures by a 2D harmonic-phonon model while the scattering in the out-of-plane configuration seems to be best represented in terms of a resonant coupling of the monolayer film to out......-of-plane collective motions of the graphite substrate. There is some evidence of renormalization of the in-plane transverse modes of the monolayer at higher temperatures; however, the in-plane longitudinal modes and the out-of-plane modes do not appear to be similarly affected....

  12. Revisiting the Kinetics and Thermodynamics of the Low-Temperature Oxidation Pathways of Alkanes: A Case Study of the Three Pentane Isomers

    KAUST Repository

    Bugler, John

    2015-07-16

    © 2015 American Chemical Society. This paper describes our developing understanding of low-temperature oxidation kinetics. We have investigated the ignition of the three pentane isomers in a rapid compression machine over a wide range of temperatures and pressures, including conditions of negative temperature coefficient behavior. The pentane isomers are small alkanes, yet have structures that are complex enough to allow for the application of their kinetic and thermochemical rules to larger molecules. Updates to the thermochemistry of the species important in the low-temperature oxidation of hydrocarbons have been made based on a thorough literature review. An evaluation of recent quantum-chemically derived rate coefficients from the literature pertinent to important low-temperature oxidation reaction classes has been performed, and new rate rules are recommended for these classes. Several reaction classes have also been included to determine their importance with regard to simulation results, and we have found that they should be included when developing future chemical kinetic mechanisms. A comparison of the model simulations with pressure-time histories from experiments in a rapid compression machine shows very good agreement for both ignition delay time and pressure rise for both the first- and second-stage ignition events. We show that revisions to both the thermochemistry and the kinetics are required in order to replicate experiments well. A broader validation of the models with ignition delay times from shock tubes and a rapid compression machine is presented in an accompanying paper. The results of this study enhance our understanding of the combustion of straight- and branched-chained alkanes.

  13. Long-chain alkane production by the yeast Saccharomyces cerevisiae.

    Science.gov (United States)

    Buijs, Nicolaas A; Zhou, Yongjin J; Siewers, Verena; Nielsen, Jens

    2015-06-01

    In the past decade industrial-scale production of renewable transportation biofuels has been developed as an alternative to fossil fuels, with ethanol as the most prominent biofuel and yeast as the production organism of choice. However, ethanol is a less efficient substitute fuel for heavy-duty and maritime transportation as well as aviation due to its low energy density. Therefore, new types of biofuels, such as alkanes, are being developed that can be used as drop-in fuels and can substitute gasoline, diesel, and kerosene. Here, we describe for the first time the heterologous biosynthesis of long-chain alkanes by the yeast Saccharomyces cerevisiae. We show that elimination of the hexadecenal dehydrogenase Hfd1 and expression of a redox system are essential for alkane biosynthesis in yeast. Deletion of HFD1 together with expression of an alkane biosynthesis pathway resulted in the production of the alkanes tridecane, pentadecane, and heptadecane. Our study provides a proof of principle for producing long-chain alkanes in the industrial workhorse S. cerevisiae, which was so far limited to bacteria. We anticipate that these findings will be a key factor for further yeast engineering to enable industrial production of alkane based drop-in biofuels, which can allow the biofuel industry to diversify beyond bioethanol. PMID:25545362

  14. Distribution and sources of n-alkanes in surface sediments of Taihu Lake, China

    Directory of Open Access Journals (Sweden)

    Yu Yunlong

    2016-03-01

    Full Text Available The last study on n-alkanes in surface sediments of Taihu Lake was in 2000, only 13 surface sediment samples were analysed, in order to have a comprehensive and up-to-date understanding of n-alkanes in the surface sediments of Taihu Lake, 41 surface sediment samples were analyzed by GC-MS. C10 to C37 were detected, the total concentrations of n-alkanes ranged from 2109 ng g−1 to 9096 ng g−1 (dry weight. There was strong odd carbon predominance in long chain n-alkanes and even carbon predominance in short chain n-alkanes. When this finding was combined with the analysis results of wax n-alkanes (WaxCn, carbon preference index (CPI, unresolved complex mixture (UCM, hopanes and steranes, it was considered that the long chain n-alkanes were mainly from terrigenous higher plants, and that the short chain n-alkanes mainly originated from bacteria and algae in the lake, compared with previous studies, there were no obvious anthropogenic petrogenic inputs. Terrestrial and aquatic hydrocarbons ratio (TAR and C21−/C25+ indicated that terrigenous input was higher than aquatic sources and the nearshore n-alkanes were mainly from land-derived sources. Moreover, the distribution of short chain n-alkanes presented a relatively uniform pattern, while the long chain n-alkanes presented a trend that concentrations dropped from nearshore places to the middle of lake.

  15. Abnormal carbon and hydrogen isotopes of alkane gases from the Qingshen gas field, Songliao Basin, China, suggesting abiogenic alkanes?

    Science.gov (United States)

    Liu, Quanyou; Dai, Jinxing; Jin, Zhijun; Li, Jian; Wu, Xiaoqi; Meng, Qingqiang; Yang, Chun; Zhou, Qinghua; Feng, Zihui; Zhu, Dongya

    2016-01-01

    It is great debate that the alkane gases of abiogenic origin would constitute a major portion of the commercial accumulation of the Qingshen gas field, Songliao Basin, China. In this study, abiogenic gases characterized by heavy δ13C1 values, reversal of the usual carbon isotopic trend of C1-C5 alkanes, very narrow variation in δ2HC1 values, and low CH4/3He ratios associated with high R/Ra values (>1) were identified. The hydrocarbon gas in the Qingshen gas field is a mixture of thermogenic alkanes derived from Cretaceous mudstone (type I kerogen) or Jurassic coal (type III kerogen) and abiogenic alkanes (mainly CH4) from mantle degassing. A quantitative estimation of abiogenic alkanes contribution to the Qingshen gas field is made based on a δ13C1 vs. δ13C2 plot: about 30-40% of alkane gases in the Qingshen gas field, along with its helium, are estimated to be derived from the mantle via magmatic activity. Particularly, the abiogenic formation of CH4 generated from the reduction of CO2 by hydrothermal activity may contribute. Our study suggests that abiogenic alkane gases in certain geological settings could be more widespread than previously thought, and may accumulate into economic reservoirs.

  16. Cholesterol Depletion from a Ceramide/Cholesterol Mixed Monolayer: A Brewster Angle Microscope Study

    KAUST Repository

    Mandal, Pritam

    2016-06-01

    Cholesterol is crucial to the mechanical properties of cell membranes that are important to cells’ behavior. Its depletion from the cell membranes could be dramatic. Among cyclodextrins (CDs), methyl beta cyclodextrin (MβCD) is the most efficient to deplete cholesterol (Chol) from biomembranes. Here, we focus on the depletion of cholesterol from a C16 ceramide/cholesterol (C16-Cer/Chol) mixed monolayer using MβCD. While the removal of cholesterol by MβCD depends on the cholesterol concentration in most mixed lipid monolayers, it does not depend very much on the concentration of cholesterol in C16-Cer/Chol monolayers. The surface pressure decay during depletion were described by a stretched exponential that suggested that the cholesterol molecules are unable to diffuse laterally and behave like static traps for the MβCD molecules. Cholesterol depletion causes morphology changes of domains but these disrupted monolayers domains seem to reform even when cholesterol level was low.

  17. X-ray diffraction and molecular-dynamics studies: Structural analysis of phases in diglyceride monolayers

    DEFF Research Database (Denmark)

    Peters, Günther H.J.; Larsen, Niels Bent; Bjørnholm, T.;

    1998-01-01

    We report a detailed structural analysis of the phases of 1,2-sn-dipalmitoylglycerol Langmuir monolayers at room temperature. Pressure-induced transitions have been investigated by combination of molecular-dynamics simulations and grazing-incidence x-ray diffraction (XRD). The diglyceride film un...... indicate that in the simulated monolayer the finite size with periodic boundary conditions imposes a higher degree of order....

  18. X-ray grazing incidence studies of the 2D crystallization of monolayers of 1-alcohols at the air water interface

    DEFF Research Database (Denmark)

    Legrand, J.F.; Renault, A.; Konovalov, O.; Chevigny, E.; Als-Nielsen, J.; Grübel, G.; Berge, B.

    1994-01-01

    A new undulator producing an X-ray beam of high brilliance has been used at the European Synchrotron Radiation Facility (ESRF, Beamline-9, Troika) for investigating the structure of two-dimensional crystals of 1-tetradecanol, 1-dodecanol, 1-decanol and 1-nonanol. These fatty alcohols with...... relatively short chains crystallize in a hexagonal structure akin to that of alkanes in the Rotator II phase. The high flux obtained under grazing incidence conditions has permitted a detailed investigation to be made of the in-plane (Q(x)) and out-of-plane (Q(z)) diffraction from the monolayers. When...... chain molecules do not remain perfectly perpendicular to the water surface....

  19. Design of BAs-AlN monolayered honeycomb heterojunction structures: A first-principles study

    Science.gov (United States)

    Camacho-Mojica, Dulce C.; López-Urías, Florentino

    2016-04-01

    BAs and AlN are semiconductor materials with an indirect and direct gap respectively in the bulk phase. Recently, electronic calculations have demonstrated that a single-layer or few layers of BAs and AlN exhibit a graphite-like structure with interesting electronic properties. In this work, infinite sheets single-layer heterojunction structures based on alternated strips with honeycomb BAs and AlN layers are investigated using first-principles density functional theory calculations. Optimized geometries, density of states, band-gaps, formation energies, and wave functions are studied for different strip widths joined along zigzag and armchair edges. Results in optimized heterojunction geometries revealed that BAs narrow strips exhibit a corrugation effect due to a lattice mismatch. It was found that zigzag heterojunctions are more energetically favored than armchair heterojunctions. Furthermore, the formation energy presents a maximum at the point where the heterojunction becomes a planar structure. Electronic charge density results yielded a more ionic behavior in Alsbnd N bonds than the Bsbnd As bonds in accordance with monolayer results. It was observed that the conduction band minimum for both heterojunctions exhibit confined states located mainly at the entire AlN strips whereas the valence band maximum exhibits confined states located mainly at BAs strips. We expect that the present investigation will motivate more experimental and theoretical studies on new layered materials made of III-V semiconductors.

  20. A structure study of copper oxide for monolayer dispersion of anatase supported

    International Nuclear Information System (INIS)

    The monolayer dispersion of copper oxide on the surface of anatase and its effect on the properties have been studied by X-ray photoelectron spectroscopy (XPS) and X-ray extended absorption fine structure (EXAFS). XPS results give an utmost dispersion capacity of 7.2 mg/gTiO2. Strong interactions between copper oxide and anatase can be seen from EXAFS results. The structure of the supported CuO species is strongly dependent on the amount of CuO loading. When the content of CuO loading is below the utmost dispersion capacity, the surface of CuO/TiO2 is dominated by the highly dispersed CuO species having no -Cu-O-Cu- chains. The copper ion is located in an octahedral coordination environment, and the Cu-O coordination distance is much longer than that in pure crystalline CuO. When CuO loading is exceeds the utmost dispersion capacity, crystalline CuO is formed on the surface of CuO/TiO2. From the result of the structure study, it is Cu-O octahedral coordination and coordination distance change in comparison with pure crystalline CuO on the surface CuO/TiO2 that have catalytic activity

  1. A comparison study of oxygen reduction on the supported Pt, Pd, Au monolayer on WC(0001)

    Science.gov (United States)

    Zhang, Xilin; Lu, Zhansheng; Yang, Zongxian

    2016-07-01

    Using the first principles methods, the geometric and electronic structures of the metal monolayers supported on WC(0001) surfaces (MML/WC(0001) (M = Pt, Pd, and Au)) and their catalytic activity toward the oxygen reduction reaction (ORR) were comparatively studied. Both the kinetics and the density of states results demonstrated that the direct dissociation of O2 on all three MML/WC(0001) surfaces are almost impossible. Yet the barriers of the formation and dissociation of OOH on AuML/WC(0001) are much smaller than those on the PtML/WC(0001) and the PdML/WC(0001) surfaces, implying that the AuML/WC(0001) exhibits the highest catalytic activity for ORR via a combination of 2e- hydrogenation of O2 and 4e- dissociation of OOH. The rate-limiting step barrier of 0.83 eV for the hydrogenation of OH forming H2O is also comparable to that on the traditional Pt-based catalysts. The deactivation mechanism of PtML/WC(0001) and the performance of PdML/WC(0001) for ORR were identified. The present study is conductive to designing new efficient catalyst without using of the precious Pt for efficiently promoting ORR.

  2. Hydrogen isotopic compositions of individual alkanes as a new approach to petroleum correlation: case studies from the Western Canada Sedimentary Basin

    Energy Technology Data Exchange (ETDEWEB)

    Maowen Li; Obermajer, M.; Chunqing Jiang; Snowdon, L.R.; Fowler, M.G. [Geological Survey of Canada, Calgary (Canada); Yongsong Huang [Brown University, Providence, RI (United States). Department of Geological Science

    2001-07-01

    Isotopic compositions of carbon-bound hydrogen in individual n-alkanes and acyclic isoprenoid alkanes, from a number of crude oil samples, were measured using gas chromatography-thermal conversion-isotope ratio mass spectrometry. The precision of this technique is better than 3 per cent for most alkanes, compared to the large range of {delta}D variation among the samples (up to 160 per cent). The oils were selected from major genetic oil families in the Western Canada Sedimentary Basin, with source rocks ranging in age from Ordovician (and possibly Cambrian) to Cretaceous. The hydrogen isotopic composition of alkanes in crude oils is controlled by three factors: isotopic compositions of biosynthetic precursors, source water {delta}D values, and postdepositional processes. The inherited difference in the lipid's biosynthetic origins and/or pathways is reflected by a small hydrogen isotopic variability within n-alkanes, but much larger differences in the {delta}D values between n-alkanes and pristane/phytane. The shift toward lighter hydrogen isotopic compositions from Paleozoic to Upper Cretaceous oils in the WCSB reflects a special depositional setting and/or a minor contribution of terrestrial organic matter. The strong influence of source water {delta}D values is demonstrated by the distinctively lower {delta}D values of lacustrine oils than marine oils, and also by the high values for oils with source rocks deposited in evaporative environments. Thermal maturation may alter the {delta}D values of the alkanes in the oil to some extent, but secondary oil migration does not appear to have had any significant impact. The fact that oils derived from source rocks that could be of Cambrian age still retain a strong signature of the hydrogen isotopic compositions of source organic matter, and source water, indicates that {delta}D values are very useful for oil-source correlation and for paleoenvironmental reconstructions. (author)

  3. Theoretical study of polyiodide formation and stability on monolayer and bilayer graphene.

    Science.gov (United States)

    Tristant, Damien; Puech, Pascal; Gerber, Iann C

    2015-11-28

    The presence of polyiodide complexes have been reported several times when carbon-based materials were doped by iodine molecules, but their formation mechanism remains unclear. By using first-principles calculations that include nonlocal correlation effects by means of a van der Waals density functional approach, we propose that the formation of triiodide (I3(-)) and pentaiodide (I5(-)) is due to a large density of iodine molecules (I2) in interaction with a carbonaceous substrate. As soon as the concentration of surface iodine reaches a threshold value of 12.5% for a graphene monolayer and 6.25% for a bilayer, these complexes spontaneously appear. The corresponding structural and energetic aspects, electronic structures and vibrational frequencies support this statement. An upshift of the Dirac point from the Fermi level with values of 0.45 and 0.52 eV is observed for adsorbed complexes on graphene and intercalated complexes between two layers, respectively. For doped-graphene, it corresponds to a graphene hole density of around 1.1 × 10(13) cm(-2), in quantitative agreement with experiments. Additionally, we have studied the thermal stability at room temperature of these adsorbed ions on graphene by means of ab initio molecular dynamics, which also shows successful p-doping with polyiodide complexes. PMID:26497888

  4. Reveal of small alkanes and isomers using calculated core and valence binding energy spectra and total momentum cross sections

    OpenAIRE

    Yang, Zejin; Wang, Feng

    2013-01-01

    The present study revealed quantum mechanically that the C1s binding energy spectra of the small alkanes (upto six carbons) provide a clear picture of isomeric chemical shift in linear alkanes and branched isomers, whereas the valence binding energy spectra contain more sensitive information regarding the length of the carbon chains. Total momentum cross sections of the alkanes exhibit the information of the chain length as well as constitutional isomers of the small alkanes. The C1s binding ...

  5. Probing the Structure of Liquids with 129Xe NMR Spectroscopy: n-Alkanes, Cycloalkanes, and Branched Alkanes

    OpenAIRE

    Morgado, Pedro; Bonifácio, Rui; Martins, Luís F. G.; Filipe, Eduardo J. M.

    2013-01-01

    The liquid organization of linear, branched, and cyclic alkanes was studied using atomic 129Xe as a NMR probe. 129Xe chemical shifts have been experimentally determined for xenon dissolved in a total of 21 alkanes. In order to allow the comparison of the different solvents at similar thermodynamic conditions, the measurements were performed over a wide range of temperatures, from the melting point of the solvent up to 350 K. The results were rationalized in terms of the dens...

  6. Hydrogen Bonding to Alkanes: Computational Evidence

    DEFF Research Database (Denmark)

    Hammerum, Steen; Olesen, Solveig Gaarn

    2009-01-01

    The structural, vibrational, and energetic properties of adducts of alkanes and strong cationic proton donors were studied with composite ab initio calculations. Hydrogen bonding in [D-H+ H-alkyl] adducts contributes to a significant degree to the interactions between the two components, which is...... substantiated by NBO and AIM results. The hydrogen bonds manifest themselves in the same manner as conventional hydrogen bonds, D-H bond elongation, D-H vibrational stretching frequency red shift and intensity increase, and adduct stabilization. The alkane adducts also exhibit elongation of the C-H bonds...... involved and a concurrent red shift, which is rationalized in terms of charge-transfer interactions that cause simultaneous weakening of both the O-H and C-H bonds. Like other dihydrogen-bonded adducts, the adducts possess a bent structure and asymmetric bifurcated hydrogen bonds. The hydrogen bonds are...

  7. Ordered water monolayer on ionic model substrates studied by molecular dynamics simulations

    International Nuclear Information System (INIS)

    The molecular behaviors of interfacial water molecules at the solid/liquid interface are of a fundamental significance in a diverse set of technical and scientific contexts, thus have drawn extensive attentions. On certain surfaces, the water monolayer may exhibit an ordered feature, which may result in the novel wetting phenomenon. In this article, based on the molecular dynamics simulations, we make a detailed structure analysis of the ordered water monolayer on ionic model surface with graphene-like hexagonal lattices under various charges and unit cell sizes. We carefully analyze the water density profiles and potential of mean force, which are the origin of the special hexagonal ordered water structures near the solid surface. The number of hydrogen bonds of the ordered water monolayer near the solid surface is carefully investigated. (authors)

  8. Study on transport properties of silicene monolayer under external field using NEGF method

    Energy Technology Data Exchange (ETDEWEB)

    Syaputra, Marhamni, E-mail: marhamni@students.itb.ac.id; Wella, Sasfan Arman; Wungu, Triati Dewi Kencana; Purqon, Acep; Suprijadi [Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung Jalan Ganesa 10 Bandung, 40132 Indonesia (Indonesia)

    2015-09-30

    We investigate the current-voltage (I-V) characteristics of a pristine monolayer silicene using non-equilibrium Green function (NEGF) method combining with density functional theory (DFT). This method succeeded in showing the relationship of I and V on silicene corresponding to the electronic characteristics such as density of states. The external field perpendicular to the silicene monolayer affects in increasing of the current. Under 0.2 eV external field, the current reaches the maximum peak at Vb = 0.3 eV with the increase is about 60% from what it is in zero external field.

  9. Study on transport properties of silicene monolayer under external field using NEGF method

    International Nuclear Information System (INIS)

    We investigate the current-voltage (I-V) characteristics of a pristine monolayer silicene using non-equilibrium Green function (NEGF) method combining with density functional theory (DFT). This method succeeded in showing the relationship of I and V on silicene corresponding to the electronic characteristics such as density of states. The external field perpendicular to the silicene monolayer affects in increasing of the current. Under 0.2 eV external field, the current reaches the maximum peak at Vb = 0.3 eV with the increase is about 60% from what it is in zero external field

  10. Surface and liquid-crystalline properties of FmHnFm triblock semifluorinated n-alkanes.

    Science.gov (United States)

    Chachaj-Brekiesz, Anna; Górska, Natalia; Osiecka, Natalia; Makyła-Juzak, Katarzyna; Dynarowicz-Łątka, Patrycja

    2016-05-01

    A series of triblock semifluorinated n-alkanes of the general formula: F(CF2)m(CH2)n(CF2)mF, (in short FmHnFm), where m=10, 12, and n=6, 8, and 12 have been synthesized and employed for liquid crystalline studies and Langmuir monolayer characterization. Differential scanning calorimetry (DSC) measurements together with texture observation with polarizing microscope (POM) revealed the presence of liquid crystalline smectic phases for all the investigated homologs. The behavior of the studied molecules spread at the free water surface has also been investigated. Our results show for the first time that these unusual film-forming materials, which are completely hydrophobic in nature and do not possess any polar group in their structure, are surface active and form insoluble (Langmuir) monolayers at the air/water interface. Due to the fact that these molecules are chemically inert and, similar to the semifluorinated diblocks, are not toxic, they may be destined for biomedical uses as gas carriers and contrast agents, as well as in drug delivery systems. PMID:26952494

  11. A Comparative Study of Genome-Wide Transcriptional Profiles of Primary Hepatocytes in Collagen Sandwich and Monolayer Cultures

    OpenAIRE

    Kim, Yeonhee; Lasher, Christopher D; Milford, Logan M.; Murali, T.M.; Rajagopalan, Padmavathy

    2010-01-01

    Two commonly used culture systems in hepatic tissue engineering are the collagen sandwich (CS) and monolayers of cells. In this study, genome-wide gene expression profiles of primary hepatocytes were measured over an 8-day period for each cell culture system using Affymetrix GeneChips and compared via gene set enrichment analysis to elicit biologically meaningful information at the level of gene sets. Our results demonstrate that gene expression in hepatocytes in CS cultures steadily and comp...

  12. Discrimination of abiogenic and biogenic alkane gases

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    We have combined the analytical data of the carbon isotope distribution pattern, R/Ra and CH4/3He values of abiogenic and biogenic (referring to the thermogenic and bacterial or microbial) alkane gases in China with those of alkane gases from USA, Russia, Germany, Australia and other countries. Four discrimination criteria are derived from this comparative study: 1) Carbon isotopic composition is generally greater than -30‰ for abiogenic methane and less than -30‰ for biogenic methane; 2) Abiogenic alkane gases have a carbon isotopic reversal trend (δ 13C1> δ 13C2> δ 13C3> δ 13C4) with δ 13C1>-30‰ in general; 3) Gases with R/Ra >0.5 and δ 13C11 δ 13C2>0 are of abiogenic origin; 4) Gases (meth- ane) with CH4/3He≤106 are of abiogenic origin, whereas gases with CH4/3He≥1011 are of biogenic origin.

  13. Data reduction and analysis programs for neutron reflection studies of monolayer adsorption at interfaces

    International Nuclear Information System (INIS)

    Data reduction and analysis programs for neutron reflectivity data from monolayer adsorption at interfaces are described. The application of model fitting to the reflectivity data, and the determination of partial structure factors within the kinematic approximation are discussed. Recent data for the adsorption of surfactants at the air-solution interface are used to illustrate the programs described. (author)

  14. An atomic force microcopy study of the mechanical and electricalproperties of monolayer films of molecules with aromatic end groups

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Liang; Park, J.Y.; Ma, H.; Jen, A.K.-Y.; Salmeron, M.

    2007-09-06

    The effect of intermolecular {pi}-{pi} stacking on the electrical and mechanical properties of monolayer films molecules containing aromatic groups was studied using atomic force microscopy. Two types of aromatic molecules, (4-mercaptophenyl) anthrylacetylene (MPAA) and (4-mercaptophenyl)-phenylacetylene (MPPA) were used as model systems with different {pi}-{pi} stacking strength. Monolayer films of these molecules on Au(111) surfaces exhibited conductivities differing by more than one order of magnitude, MPAA being the most conductive and MPPA the least conductive. The response to compressive loads by the AFM tip was also found to be very different for both molecules. In MPAA films distinct molecular conductivity changes are observed upon mechanical perturbation. This effect however was not observed on the MPPA film, where intermolecular {pi}-{pi} interactions are likely weaker.

  15. Solar photothermochemical alkane reverse combustion.

    Science.gov (United States)

    Chanmanee, Wilaiwan; Islam, Mohammad Fakrul; Dennis, Brian H; MacDonnell, Frederick M

    2016-03-01

    A one-step, gas-phase photothermocatalytic process for the synthesis of hydrocarbons, including liquid alkanes, aromatics, and oxygenates, with carbon numbers (Cn) up to C13, from CO2 and water is demonstrated in a flow photoreactor operating at elevated temperatures (180-200 °C) and pressures (1-6 bar) using a 5% cobalt on TiO2 catalyst and under UV irradiation. A parametric study of temperature, pressure, and partial pressure ratio revealed that temperatures in excess of 160 °C are needed to obtain the higher Cn products in quantity and that the product distribution shifts toward higher Cn products with increasing pressure. In the best run so far, over 13% by mass of the products were C5+ hydrocarbons and some of these, i.e., octane, are drop-in replacements for existing liquid hydrocarbons fuels. Dioxygen was detected in yields ranging between 64% and 150%. In principle, this tandem photochemical-thermochemical process, fitted with a photocatalyst better matched to the solar spectrum, could provide a cheap and direct method to produce liquid hydrocarbons from CO2 and water via a solar process which uses concentrated sunlight for both photochemical excitation to generate high-energy intermediates and heat to drive important thermochemical carbon-chain-forming reactions. PMID:26903631

  16. Microelectrode array in mixed alkanethiol self-assembled monolayers: Electrochemical studies

    International Nuclear Information System (INIS)

    We report an efficient alternative to obtain recessed microelectrodes device on gold electrode surface, in which mixed self-assembled monolayer of long and short carbon alkanethiol chains was used for this purpose. Development of the modified electrodes included the chemical adsorption of 11-mercaptoundecanoic acid and 2-mercaptoethanol solution, as well as their mixtures, on gold surface, resulting in the final mixed self-assembled monolayer configuration. For comparison, the electrochemical performance of self-assembled monolayer of 11-mercaptoundecanoic acid, 3-mercaptopropionic acid, 4-mercapto-1-butanol and 6-mercapto-1-hexanol modified electrodes was also investigated. It was verified that, in the mixed self-assembled monolayer, the 11-mercaptoundecanoic acid acts as a barrier for electron transfer while the short alkanethiol chair is deposited in an island-like shape through which electrons can be freely transferred to ions in solution, allowing electrochemical reactions to occur. The performance of the modified electrodes toward microelectrode behavior was investigated via cyclic voltammetry and electrochemical impedance spectroscopy measurements using [Fe(CN)6]3−/4− redox couple as a probe. In this case, sigmoidal voltammetric responses were obtained, very similar to those observed for microelectrodes. Such behavior reinforces the proposition of electron transfer through the short alkanethiol chain layer and surface blockage by the long chain one. Electrochemical impedance results allowed calculated the mean radius value of each microelectrode disks of 3.8 μm with about 22 μm interval between them. The microelectrode environment provided by the mixed self-assembled monolayer can be conveniently used to provide an efficient catalytic conversion in biosensing applications.

  17. Markedly different adsorption behaviors of gas molecules on defective monolayer MoS2: a first-principles study.

    Science.gov (United States)

    Li, Hongxing; Huang, Min; Cao, Gengyu

    2016-06-01

    Sulfur vacancy (SV) is one of the most typical defects in two-dimensional monolayer MoS2, leading to reactive sites. We presented a systematic study of the adsorption behaviors of gas molecules, CO2, N2, H2O, CO, NH3, NO, O2, H2 and NO2, on monolayer MoS2 with single SV by first-principles calculations. It was found that CO2, N2 and H2O molecules physisorbed at the proximity of single SV. Our adsorption energy calculations and charge transfer analysis showed that the interactions between CO2, N2 and H2O molecules and defective MoS2 are stronger than the cases of CO2, N2 and H2O molecules adsorbed on pristine MoS2, respectively. The defective MoS2 based gas sensors may be more sensitive to CO2, N2 and H2O molecules than pristine MoS2 based ones. CO, NO, O2 and NH3 molecules were found to chemisorb at the S vacancy site and thus modify the electronic properties of defective monolayer MoS2. Magnetism was induced upon adsorption of NO molecules and the defective states induced by S vacancy can be completely removed upon adsorption of O2 molecules, which may provide some helpful information for designing new MoS2 based nanoelectronic devices in future. The H2 and NO2 molecules were found to dissociate at S vacancy. The dissociation of NO2 molecules resulted in O atoms located at the S vacancy site and NO molecules physisorbed on O-doped MoS2. The calculated results showed that NO2 molecules can help heal the S vacancy of the MoS2 monolayer. PMID:27198064

  18. X-ray Reflectivity Studies of cPLA?-C2 Domains Adsorbed onto Langmuir Monolayers of SOPC

    Energy Technology Data Exchange (ETDEWEB)

    Raghothamachar,B.; Dudley, M.; Dalmau, R.; Schlesser, R.; Sitar, Z.

    2005-01-01

    X-ray reflectivity is used to study the interaction of C2 domains of cytosolic phospholipase A2 (cPLA{sub 2{alpha}}-C2) with a Langmuir monolayer of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) supported on a buffered aqueous solution containing Ca{sup 2+}. The reflectivity is analyzed in terms of the known crystallographic structure of cPLA2{alpha}-C2 domains and a slab model representing the lipid layer to yield an electron density profile of the lipid layer and bound C2 domains. This new method of analysis determines the angular orientation and penetration depth of the cPLA{sub 2{alpha}}-C2 domains bound to the SOPC monolayer, information not available from the standard slab model analysis of x-ray reflectivity. The best-fit orientation places the protein-bound Ca{sup 2+} ions within 1 Angstrom of the lipid phosphate group (with an accuracy of {+-}3 Angstroms). Hydrophobic residues of the calcium-binding loops CBL1 and CBL3 penetrate deepest into the lipid layer, with a 2 Angstrom penetration into the tailgroup region. X-ray measurements with and without the C2 domain indicate that there is a loss of electrons in the headgroup region of the lipid monolayer upon binding of the domains. We suggest that this is due to a loss of water molecules bound to the headgroup. Control experiments with a non-calcium buffer and with domain mutants confirm that the cPLA{sub 2{alpha}}-C2 binding to the SOPC monolayer is Ca{sup 2+}-dependent and that the hydrophobic residues in the calcium-binding loops are critical for membrane binding. These results indicate that an entropic component (due to water loss) as well as electrostatic and hydrophobic interactions contributes to the binding mechanism.

  19. The anaerobic degradation of gaseous, nonmethane alkanes — From in situ processes to microorganisms

    OpenAIRE

    Florin Musat

    2015-01-01

    The short chain, gaseous alkanes ethane, propane, n- and iso-butane are released in significant amounts into the atmosphere, where they contribute to tropospheric chemistry and ozone formation. Biodegradation of gaseous alkanes by aerobic microorganisms, mostly bacteria and fungi isolated from terrestrial environments, has been known for several decades. The first indications for short chain alkane anaerobic degradation were provided by geochemical studies of deep-sea environments around hydr...

  20. Effects of n-alkanes on the morphology of lipid bilayers. A freeze-fracture and negative stain analysis.

    Science.gov (United States)

    McIntosh, T J; Costello, M J

    1981-07-20

    The effect of n-alkanes on the ultrastructure of lipid bilayers has been investigated using freeze-fracture and negative stain electron microscopy. It has been found that the morphology of bilayers containing the long alkane tetradecane is quite different from bilayers containing the short alkane hexane. The smooth fracture faces of gel and liquid crystalline state bilayers are unmodified by tetradecane. However, hexane dramatically alters the hydrophobic bilayer interior, producing large (20 to 50 nm) mounds and depressions in the fracture faces. The fracture steps in these multilayer preparations containing hexane are variable in thickness and often considerably wider than the corresponding fracture steps in multilayers which contain tetradecane or are solvent-free. Alkanes also modify the structure of the P beta' or 'banded' phase of phosphatidylcholine bilayers. The incorporation of tetradecane removes the banded structure from both the bilayer's hydrophilic surface, as viewed by negative staining, and the bilayer's hydrophobic interior, as viewed by the freeze-fracture technique. These results are consistent with X-ray diffraction data which imply that long alkanes are primarily located between adjacent lipid hydrocarbon chains in each monolayer of the bilayer, while short alkanes can partition into the geometric center of the bilayer between apposing monolayers. PMID:6168283

  1. Phase Equilibria of Mixtures Containing Glycol and n-Alkane: Experimental Study of Infinite Dilution Activity Coefficients and Modeling Using the Cubic-Plus-Association Equation of State

    DEFF Research Database (Denmark)

    Afzal, Waheed; Breil, Martin Peter; Théveneau, Pascal;

    2009-01-01

    In this work, we report the infinite dilution activity coefficients for four n-alkanes (n-pentane, n-hexane, n-heptane, and n-octane) in monoethylene glycol in the temperature range from 298 to 334 K and at atmospheric pressure. Experimental data were measured using a previously described inert gas...

  2. The Interface between Gd and Monolayer MoS2: A First-Principles Study

    KAUST Repository

    Zhang, Xuejing

    2014-12-08

    We analyze the electronic structure of interfaces between two-, four- and six-layer Gd(0001) and monolayer MoS2 by first-principles calculations. Strong chemical bonds shift the Fermi energy of MoS2 upwards into the conduction band. At the surface and interface the Gd f states shift to lower energy and new surface/interface Gd d states appear at the Fermi energy, which are strongly hybridized with the Mo 4d states and thus lead to a high spin-polarization (ferromagnetically ordered Mo magnetic moments of 0.15 μB). Gd therefore is an interesting candidate for spin injection into monolayer MoS2.

  3. A study of calixarene self-assembled monolayers on gold metal surfaces

    Czech Academy of Sciences Publication Activity Database

    Šustrová, Barbora; Mareček, Vladimír; Štulík, Karel

    Ústí nad Labem: BEST servis, 2010 - (Navrátil, T.; Barek, J.), s. 172-176 ISBN 978-80-254-6710-7. [Modern Electroanalytical Methods /30./. Jetřichovice (CZ), 24.05.2010-28.05.2010] R&D Projects: GA AV ČR IAA400400806 Institutional research plan: CEZ:AV0Z40400503 Keywords : calix[4]arene * self-assembled monolayer (SAM) * gold electrode Subject RIV: CG - Electrochemistry

  4. Effects of Oxygen Contamination on Monolayer GeSe: A computational study

    OpenAIRE

    de Oliveira, I. S. S.; Longuinhos, R.

    2016-01-01

    Natural oxidation is a common degradation mechanism of both mechanical and electronic properties for most of the new two-dimensional materials. From another perspective, controlled oxidation is an option to tune material properties, expanding possibilities for real-world applications. Understanding the electronic structure modifications induced by oxidation is highly desirable for new materials like monolayer GeSe, which is a new candidate for near-infrared photodetectors. By means of first-p...

  5. Numerical study of the conductivity of graphene monolayer within the effective field theory approach

    OpenAIRE

    Buividovich, P. V.; Luschevskaya, E. V.; Pavlovsky, O. V.; Polikarpov, M. I.; Ulybyshev, M. V.

    2012-01-01

    We report on the direct numerical measurements of the conductivity of graphene monolayer. Our numerical simulations are performed in the effective lattice field theory with noncompact 3 + 1-dimensional Abelian lattice gauge fields and 2 + 1-dimensional staggered lattice fermions. The conductivity is obtained from the Green-Kubo relations using the Maximum Entropy Method. We find that in a phase with spontaneously broken sublattice symmetry the conductivity rapidly decreases. For the largest v...

  6. Distribution and sources of n-alkanes in surface sediments of Taihu Lake, China

    OpenAIRE

    Yu Yunlong; Li Yuanyuan; Guo Zhigang; Zou Hua

    2016-01-01

    The last study on n-alkanes in surface sediments of Taihu Lake was in 2000, only 13 surface sediment samples were analysed, in order to have a comprehensive and up-to-date understanding of n-alkanes in the surface sediments of Taihu Lake, 41 surface sediment samples were analyzed by GC-MS. C10 to C37 were detected, the total concentrations of n-alkanes ranged from 2109 ng g−1 to 9096 ng g−1 (dry weight). There was strong odd carbon predominance in long chain n-alkanes and even carbon predomin...

  7. Theoretical study of the interaction of electron donor and acceptor molecules with monolayer WS2

    International Nuclear Information System (INIS)

    With the aim of understanding recent experimental data concerning molecular doping in WS2-based FET gas sensors, we have investigated the interaction of NH3 and H2O molecules with monolayer WS2, by means of first-principles calculations. The structural relaxations and total energy calculations are performed to determine the preferential binding configurations and it is found that both NH3 and H2O molecules are physisorbed on monolayer WS2. The Bader analysis combined with the plane-averaged differential charge density results indicate that NH3 acts as the electron donor, while H2O acts as the electron acceptor, leading to n- and p-type doping of WS2, respectively. The charge transfer mechanism is discussed in light of the mixing of the molecular highest occupied molecular orbital and lowest unoccupied molecular orbital with the underlying WS2 orbitals. In addition, the modification of the work function is found to be almost linearly dependent on the total charge transfer. The modification of the work function and the carrier concentration can be obtained by tuning the molecule coverages, without destroying the band structure of monolayer WS2. The electrical sensitivities to the gas adsorption make WS2 a gas sensor that promises wide-ranging applications. (paper)

  8. Resonant diffusion of normal alkanes in zeolites: Effect of the zeolite structure and alkane molecule vibrations

    CERN Document Server

    Tsekov, R

    2015-01-01

    Diffusion of normal alkanes in one-dimensional zeolites is theoretically studied on the basis of the stochastic equation formalism. The calculated diffusion coefficient accounts for the vibrations of the diffusing molecule and zeolite framework, molecule-zeolite interaction, and specific structure of the zeolite. It is shown that when the interaction potential is predominantly determined by the zeolite pore structure, the diffusion coefficient varies periodically with the number of carbon atoms of the alkane molecule, a phenomenon called resonant diffusion. A criterion for observable resonance is obtained from the balance between the interaction potentials of the molecule due to the atomic and pore structures of the zeolite. It shows that the diffusion is not resonant in zeolites without pore structure, such as ZSM-12. Moreover, even in zeolites with developed pore structure no resonant dependence of the diffusion constant can be detected if the pore structure energy barriers are not at least three times high...

  9. Study of fibrinogen adsorption on self-assembled monolayers on Au(1 1 1) by atomic force microscopy

    International Nuclear Information System (INIS)

    The adsorption of plasma protein fibrinogen on the self-assembled monolayers (SAMs) of n-hexadecyl mercaptan and citrate was investigated with atomic force microscopy (AFM). On the basis of the preparation of these two flat SAMs on Au(1 1 1), high-resolution AFM images of bovine fibrinogen were obtained with different protein concentrations. The results indicated that the surface chemical composition significantly affected the adsorption behavior of fibrinogen. Since fibrinogen plays a key role in the regulation of both haemostasis and thrombosis, high-resolution AFM imaging on SAMs is expected to be an effective approach to study the haemocompatibility of materials with different surface chemistry

  10. Study of Alkylthiolate Self-assembled Monolayers on Au(111) Using a Semilocal meta-GGA Density Functional

    DEFF Research Database (Denmark)

    Ferrighi, Lara; Pan, Yun-xiang; Grönbeck, Henrik;

    2012-01-01

    We present a density functional theory study of the structure and stability of self-assembled monolayers (SAMs) of alkylthiolate on Au(111) as a function of the alkyl chain length. The most favorable structure of the SAMs involves an RS–Au–SR complex (S being sulfur, R being an alkyl chain) formed...... particular, the use of M06-L yields an increased stability of the SAMs with increasing alkyl chain length and an increased attractive interaction between RS–Au–SR complexes at shorter distances....

  11. Atomic force microscopy study of the adsorption of protein molecules on transferred Langmuir monolayer

    International Nuclear Information System (INIS)

    Ordered protein films have been obtained by the adsorption of protein molecules on a Langmuir monolayer, which had previously formed on a silicon substrate, using the Langmuir-Blodgett and molecular self-organization methods. A mixture of cholesterol with dipalmitoylphosphatidylcholine (DPPC) and a polymer-cellulose acetopivalinate-were used as immobilization materials. Protein molecules (catalase and alkaline phosphatase) immobilized on solid substrates have been investigated by atomic force micros-copy. It was shown that the developed combined technique provides a deposition of homogeneous ultrathin protein films with a high degree of filling.

  12. Experimental Study of the Temperature Dependence of Substrate Coverage in Ionic Self-Assembled Monolayers

    Science.gov (United States)

    Simpson, Brian; Abudayyeh, Mohammad; Ali, Md; Hamrick, Alena; Mazilu, Dan; Mazilu, Irina

    2014-03-01

    We investigate the temperature dependence of the surface coverage of thin films consisting of silica nanoparticles deposited on glass substrates via the ISAM (ionically self-assembled monolayers) technique. Variables such as the concentration and pH of the silica colloidal suspension and polyelectrolyte solution, dipping time, and particle size among others are controlled, and the thin films are deposited on substrates under a range of temperature values. The samples are analyzed using scanning electron microscopy. The surface coverage is estimated by employing a pixel-count comparison of grayscale values in the SEM micrographs and compared to analytical results obtained using a cooperative sequential adsorption model. Presentor.

  13. Structure of solid monolayers and multilayers of -hexane on graphite

    Indian Academy of Sciences (India)

    M Krishnan; S Balasubramanian; S Clarke

    2003-10-01

    We present all-atom molecular dynamics simulations of -hexane on the basal plane of graphite at monolayer and multilayer coverages. In keeping with experimental data, we find the presence of ordered adsorbed layers both at single monolayer coverage and when the adsorbed layer coexists with excess liquid adsorbate. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate lattice to a fully commensurate structure on increasing the coverage from a monolayer to a multilayer. The zig-zag backbone planes of all the alkane molecules lie parallel to the graphite surface at the multilayer coverage, while a few molecules are observed to attain the perpendicular orientation at monolayer coverage.

  14. Electrochemical and Photoelectrochemical Study of Self-assembled Monolayer of Phytic Acid on Brass

    Institute of Scientific and Technical Information of China (English)

    XU Qun-Jie; WAN Zong-Yue; ZHOU Guo-Ding; YIN Ren-He; CAO Wei-Min; LIN Chang-Jian

    2008-01-01

    Phytic acid is an environment-friendly reagent for processing metals.The anticorrosion and inhibiting mechanism for phytic acid monolayers self-assembled on a brass (HSn70-1) electrode has been investigated by using electrochemical and photocurrent response methods.The electrochemical measurements indicate that phytic acid is liable to form surface complexes on the brass electrode,and the self-assembled monolayers (SAM) change the structure of the electric double-layer and shift the potential of zero charge positively.The photochemical measurement indicates that the brass electrode shows a p-type photoresponse owing to the formation of a Cu2O layer on its surface,and the presence of SAM weakens significantly the photoresponse,suggesting an excellent effect on anticorrosion,which is consistent with the EIS and polarization curve measurements.Adsorption of phytic acid was found to be typical of chemisorption,which can be reasonably described on the basis of the Langmuir isotherm.

  15. Catalytic conversion of light alkanes

    Energy Technology Data Exchange (ETDEWEB)

    Lyons, J.E.

    1992-06-30

    The second Quarterly Report of 1992 on the Catalytic Conversion of Light Alkanes reviews the work done between April 1, 1992 and June 31, 1992 on the Cooperative Agreement. The mission of this work is to devise a new catalyst which can be used in a simple economic process to convert the light alkanes in natural gas to oxygenate products that can either be used as clean-burning, high octane liquid fuels, as fuel components or as precursors to liquid hydrocarbon uwspomdon fuel. During the past quarter we have continued to design, prepare, characterize and test novel catalysts for the mild selective reaction of light hydrocarbons with air or oxygen to produce alcohols directly. These catalysts are designed to form active metal oxo (MO) species and to be uniquely active for the homolytic cleavage of the carbon-hydrogen bonds in light alkanes producing intermediates which can form alcohols. We continue to investigate three molecular environments for the active catalytic species that we are trying to generate: electron-deficient macrocycles (PHASE I), polyoxometallates (PHASE II), and regular oxidic lattices including zeolites and related structures as well as other molecular surface structures having metal oxo groups (PHASE I).

  16. Collapsed States of Langmuir Monolayers.

    Science.gov (United States)

    Phan, Minh Dinh; Lee, Jumi; Shin, Kwanwoo

    2016-05-01

    Langmuir monolayers of amphiphilic molecules at an air-water interface can be compressed laterally to achieve high surface density. However, compression beyond a certain threshold causes the monolayer to become unstable, which may lead to the formation of collapsed states with topographical differences that are associated with the structures and mechanical properties of the constituent molecules of the monolayer. The mechanisms and collapsed structures can differ owing to differences in experimental conditions, i.e., temperature, ion-content, the pH of subphase, or compression rate; in addition, the type of constituent molecules, i.e., biological lipids or chemical surfactants, has an effect. In this review, we compare studies concerning several aspects of collapse, from basic concepts and theoretical mechanisms to experimental visualization of the monolayer topography. In addition, techniques often employed to study this subject are discussed in this review. PMID:27086998

  17. a Heat Capacity Study of Para-Hydrogen Monolayers on Graphite.

    Science.gov (United States)

    Motteler, Frederick Clark

    The heat capacity of monolayer p-H(,2) adsorbed on graphite foam has been measured over the 0.0631(ANGSTROM)(' -2) to 0.0891(ANGSTROM)('-2) density range and the 2 to 25(DEGREES)K temperature range. Specific heat peaks are observed over almost the entire density range and are similar to those observed for ('4)He and ('3)He monolayers on graphite for similar densities. Low density data (0.0631(ANGSTROM)('-2) to 0.0727(ANGSTROM)(' -2)) contains a heat capacity peak attributed to the commensurate order-disorder transition. At commensurate density. 0.0637(ANGSTROM)(' -2), the peak attains a maximum height of C/Nk(,b) = 11.7 at 21.4(DEGREES)K and may be characterized by the critical exponent (alpha) = 0.33. For temperatures below the order -disorder transition, the commensurate monolayer heat capacity is characterized by Einstein like behavior with (theta)(,E) = 53.4(DEGREES)K. High density data (0.0787(ANGSTROM)('-2) to 0.0815(ANGSTROM)(' -2)) contains a heat capacity peak attributed to the disordering of a close packed triangular incommensurate solid. The incommensurate solid is characterized by its Debye like heat capacity behavior. The density region between the commensurate structure and incommensurate solid (0.0707(ANGSTROM)('-2) to 0.772(ANGSTROM)(' -2)) contains two heat capacity peaks. At about 20(DEGREES)K there is broad rounded remnant of the order-disorder peak. At lower temperatures (6 to 9(DEGREES)K) there is a small, but very sharp heat capacity peak. The peak attains a maximum height of C/Nk(,b) = 0.89 at a density of 0.0727(ANGSTROM)(' -2) and a temperature of 9.54(DEGREES)K. The remnant of the order-disorder transition seen in p-H(,2) data, together with re-examination of ('4)He data indicates that a shoulder-like remnant intersects the melting line. The melting peak of ('4)He undergoes significant change at the intersection point. The low temperature intermediate density region is consistent with a striped phase of domain walls. The sharp low

  18. Electronic and vibrational properties of graphene monolayers with iron adatoms: A density functional theory study

    Science.gov (United States)

    Dimakis, Nicholas; Navarro, Nestor E.; Velazquez, Julian; Salgado, Andres

    2015-04-01

    Periodic density functional calculations on graphene monolayers with and without an iron adatom have been used to elucidate iron-graphene adsorption and its effects on graphene electronic and vibrational properties. Density-of-states calculations and charge density contour plots reveal charge transfer from the iron s orbitals to the d orbitals, in agreement with past reports. Adsorbed iron atoms covalently bind to the graphene substrate, verified by the strong hybridization of iron d-states with the graphene bands in the energy region just below the Fermi level. This adsorption is weak and compared to the well-analyzed CO adsorption on Pt: It is indicated by its small adsorption energy and the minimal change of the substrate geometry due to the presence of the iron adatoms. Graphene vibrational spectra are analyzed though a systematic variation of the graphene supercell size. The shifts of graphene most prominent infrared active vibrational modes due to iron adsorption are explored using normal mode eigenvectors.

  19. Bandgap engineering of monolayer MoS2 under strain: A DFT study

    Science.gov (United States)

    Li, Can; Fan, Bowen; Li, Weiyi; Wen, Luowei; Liu, Yan; Wang, Tao; Sheng, Kuang; Yin, You

    2015-06-01

    In this paper, density functional theory calculations are used to investigate the monolayer MoS2 in terms of the strain by analyzing the structure parameters: the bandgap, the density of states (DOS) and the Milliken charges. The calculations indicate that an increasing external stain tends to depress the ripple structure with a shorter S-S interlayer spacing and to enlarge the length of the Mo-S bond. Tensile strain dramatically alteres the bandgap; however, compressive strain almost does not. The change in the bandgap is explained by an analysis of the DOS, the partial density of states (PDOS), the structure parameters and the Mulliken charge distribution. The effects of strain on the Mulliken charge and the length of the Mo-S band cause bandgap differences under tensile and compressive strain.

  20. First-principle study of hydrogenation on monolayer MoS2

    Science.gov (United States)

    Xu, Yong; Li, Yin; Chen, Xi; Zhang, Chunfang; Zhang, Ru; Lu, Pengfei

    2016-07-01

    The structural and electronic properties of hydrogenation on 1H-MoS2 and 1T-MoS2 have been systematically explored by using density functional theory (DFT) calculations. Our calculated results indicate an energetically favorable chemical interaction between H and MoS2 monolayer for H adsorption when increasing concentration of H atoms. For 1H-MoS2, single H atom adsorption creates midgap approaching the fermi level which increases the n-type carrier concentration effectively. As a consequence, its electrical conductivity is expected to increase significantly. For 1T-MoS2, H atoms adsorption can lead to the opening of a direct gap of 0.13eV compared to the metallic pristine 1T-MoS2.

  1. Tethered chains in poor solvent conditions: An experimental study involving Langmuir diblock copolymer monolayers

    International Nuclear Information System (INIS)

    We have employed Langmuir monolayers of highly asymmetric polydimethylsiloxane-polystyrene (PDMS-PS) diblock copolymers on dioctyl phthalate (DOP) at temperatures ranging from 22 to -35thinsp degree C as a model system for tethered chains in poor solvent conditions. The thicknesses of the tethered PS layers extending into the DOP subphase, measured by neutron reflection, decrease with decreasing temperature (T) over this entire range. However, the variation with T becomes weak below -20thinsp degree C. At the lowest T, the layer thicknesses are 55%endash 75% of the values at the theta condition (Tθ=22thinsp degree C). The contraction of the layer with decreasing T is determined as a function of surface density and molecular weight, and these data are compared to universal scaling forms. The PS segments are depleted from the near surface region over the entire T range, with the thickness of the depletion layer increasing slightly with decreasing T. The free energy of the surface layer is probed by surface tension measurements. With decreasing T, negative surface pressures are observed at low coverages for both PDMS-PS and PDMS monolayers, indicating metastability toward lateral phase separation. Evidence for a transition from a dispersed phase to a condensed phase with decreasing T was observed in the reflectivity for very low PDMS-PS coverage. At high coverage where the submerged blocks are strongly interacting at 22thinsp degree C, only a modest decrease in surface pressure is observed over the experimental range of T despite the strong contraction. This latter result is discussed in terms of the relative contributions of enthalpic and entropic effects to the surface pressure. copyright 1999 American Institute of Physics

  2. Langmuir monolayers and Differential Scanning Calorimetry for the study of the interactions between camptothecin drugs and biomembrane models.

    Science.gov (United States)

    Casadó, Ana; Giuffrida, M Chiara; Sagristá, M Lluïsa; Castelli, Francesco; Pujol, Montserrat; Alsina, M Asunción; Mora, Margarita

    2016-02-01

    CPT-11 and SN-38 are camptothecins with strong antitumor activity. Nevertheless, their severe side effects and the chemical instability of their lactone ring have questioned the usual forms for its administration and have focused the current research on the development of new suitable pharmaceutical formulations. This work presents a biophysical study of the interfacial interactions of CPT-11 and SN-38 with membrane mimetic models by using monolayer techniques and Differential Scanning Calorimetry. The aim is to get new insights for the understanding of the bilayer mechanics after drug incorporation and to optimize the design of drug delivery systems based on the formation of stable bilayer structures. Moreover, from our knowledge, the molecular interactions between camptothecins and phospholipids have not been investigated in detail, despite their importance in the context of drug action. The results show that neither CPT-11 nor SN-38 disturbs the structure of the complex liposome bilayers, despite their different solubility, that CPT-11, positively charged in its piperidine group, interacts electrostatically with DOPS, making stable the incorporation of a high percentage of CPT-11 into liposomes and that SN-38 establishes weak repulsive interactions with lipid molecules that modify the compressibility of the bilayer without affecting significantly neither the lipid collapse pressure nor the miscibility pattern of drug-lipid mixed monolayers. The suitability of a binary and a ternary lipid mixture for encapsulating SN-38 and CPT-11, respectively, has been demonstrated. PMID:26656185

  3. Molecular dynamics study of temperature-dependent ripples in monolayer and bilayer graphene on 6H-SiC surfaces

    Institute of Scientific and Technical Information of China (English)

    Tang Chao; Wei Xiao-Lin; Tan Xin; Peng Xiang-Yang; Sun Li-Zhong; Zhong Jian-Xin

    2012-01-01

    Using classical molecular dynamics and a simulated annealing technique,we show that microscopic corrugations occur in monolayer and bilayer graphene on 6H-SiC substrates.From an analysis of the atomic configurations,two types of microscopic corrugations are identified,namely periodic ripples at room temperature and random ripples at high temperature.Two different kinds of ripple morphologies,each with a periodic structure,occur in the monolayer graphene due to the existence of a coincidence lattice between graphene and the SiC terminated surface (Si- or C-terminated surface).The effect of temperature on microscopic ripple morphology is shown through analysing the roughness of the graphene.A temperature-dependent multiple bonding conjugation is also shown by the broad distribution of the carbon-carbon bond length and the bond angle in the rippled graphene on the SiC surface.These results provide atomic-level information about the rippled graphene layers on the two polar faces of the 6H-SiC substrate,which is useful not only for a better understanding of the stability and structural properties of graphene,but also for the study of the electronic properties of graphene-based devices.

  4. Reactivation of coked H-ZSM-5 by treatment with hydrogen and alkanes

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, F.; Ernst, H. [Univ. of Leipzig (Germany); Geidel, E. [Univ. of Hamburg (Germany); Schoedel, R. [Leuna-Werke GmbH (Germany)

    1996-11-01

    The conversion of methanol to hydrocarbons on zeolite H-ZSM-5, in particular the long-term stability of the catalyst, was studied under different reaction conditions. Whereas no significant change in the product distribution was observed, hydrogen and alkane-containing recycle gases show lower deactivation rates than nitrogen. In addition, spent catalysts were partially reactivated by alkane treatment, increasing the time on stream before an oxidative regeneration procedure is required. Lower alkanes such as propane and isobutane yield the best results. The influence of hydrogen-containing gases on the deactivation rate and on the nature of coke on zeolite H-ZSM-5 indicates dissociative adsorption of hydrogen and alkanes on a few sites with enhanced activity. Surface hydrogen species formed by adsorption of alkanes are assumed to make possible the hydrocracking of carbonaceous deposits. 20 refs., 6 figs., 2 tabs.

  5. Photoluminescence study of the substitution of Cd by Zn during the growth by atomic layer epitaxy of alternate CdSe and ZnSe monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Hernández-Calderón, I. [Physics Department,Cinvestav, Ave. IPN2508, 07360, México City, DF. (Mexico); Salcedo-Reyes, J. C. [Thin Films Group, Physics Department, Pontificia Universidad Javeriana, Cr. 7 No. 43-82, Ed. 53, Lab. 404, Bogotá, D.C. (Colombia)

    2014-05-15

    We present a study of the substitution of Cd atoms by Zn atoms during the growth of alternate ZnSe and CdSe compound monolayers (ML) by atomic layer epitaxy (ALE) as a function of substrate temperature. Samples contained two quantum wells (QWs), each one made of alternate CdSe and ZnSe monolayers with total thickness of 12 ML but different growth parameters. The QWs were studied by low temperature photoluminescence (PL) spectroscopy. We show that the Cd content of underlying CdSe layers is affected by the exposure of the quantum well film to the Zn flux during the growth of ZnSe monolayers. The amount of Cd of the quantum well film decreases with higher exposures to the Zn flux. A brief discussion about the difficulties to grow the Zn{sub 0.5}Cd{sub 0.5}Se ordered alloy (CuAu-I type) by ALE is presented.

  6. Photoluminescence study of the substitution of Cd by Zn during the growth by atomic layer epitaxy of alternate CdSe and ZnSe monolayers

    International Nuclear Information System (INIS)

    We present a study of the substitution of Cd atoms by Zn atoms during the growth of alternate ZnSe and CdSe compound monolayers (ML) by atomic layer epitaxy (ALE) as a function of substrate temperature. Samples contained two quantum wells (QWs), each one made of alternate CdSe and ZnSe monolayers with total thickness of 12 ML but different growth parameters. The QWs were studied by low temperature photoluminescence (PL) spectroscopy. We show that the Cd content of underlying CdSe layers is affected by the exposure of the quantum well film to the Zn flux during the growth of ZnSe monolayers. The amount of Cd of the quantum well film decreases with higher exposures to the Zn flux. A brief discussion about the difficulties to grow the Zn0.5Cd0.5Se ordered alloy (CuAu-I type) by ALE is presented

  7. Catalytic isomerization of light alkanes

    OpenAIRE

    Løften, Thomas

    2004-01-01

    In recent years the levels of sulfur and benzene in the gasoline pool have been reduced, and in the future there may also be new regulations on vapor pressure and the level of aromatics and olefins as well. The limitations on vapor pressure and aromatics will lead to reduced use of C4 and reformate respectively. The branched isomers of C5 and C6 alkanes have high octane numbers compared to the straight chain isomers, and are consequently valuable additives to the gasoline pool. To maintain th...

  8. Magnetic monolayers on semiconducting substrates. An in situ FMR study of Fe-based heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Zakeri Lori, K.

    2007-10-18

    The growth, magnetic anisotropy, g-factor, and magnetization of Fe monolayers grown on GaAs(001), InAs(001), and InP(001) are investigated by a combination of in situ ferromagnetic resonance and SQUID magnetometry as a function of temperature and film thickness. The effect of stress caused by the lattice mismatch and the surface reconstruction on the magnetic anisotropy is quantified. An in-plane spin reorientation transition as a function of film thickness is observed at room temperature for all systems. A magneto-elastic model is used to explain the direction of the easy axis, the spin reorientation transition, and the contributions to the magnetic anisotropy terms using the stress components measured directly by in situ IV-low-energy electron diffraction. While the model gives a quantitative explanation of the out-of-plane magnetic anisotropy, changes of the electronic interface structure have to be taken into account for the in-plane magnetic anisotropy. The influence of Ag and Au buffer and cap layers on the magnetic anisotropy terms are determined. The temperature dependence of the total magnetic anisotropy, as well as the surface-interface and volume contribution to the magnetic anisotropy are determined for Fe monolayers on GaAs(001). It is demonstrated that the temperature dependence of the magnetic anisotropy is correlated with the temperature dependence of the magnetization according to the Callen-Callen model. The temperature dependence of the volume contribution to the perpendicular magnetic anisotropy is fully explained by the temperature dependence of the magneto-elastic anisotropy. A temperature-driven morphological transformation occurring at a temperature higher than 550 K depending on the film thickness is observed. The thin Fe3Si binary Heusler structure epitaxially grown on MgO(001) is investigated. In addition to the structural properties, magnetic anisotropy, magnetization, g-factor, spin, and orbital magnetism, the magnetic relaxation

  9. First-principles study of B, C, N and F doped graphene-like MgO monolayer

    Science.gov (United States)

    Wu, Ping; Huang, Min; Cheng, Wenjing; Tang, Fuling

    2016-07-01

    Based on the first-principles calculations, we have investigated the stable geometries, electronic and magnetic properties of the graphene-like MgO monolayer with O atom substituted by B, C, N, and F atoms. The formation energy decreases in the order of B>C>N>F, which may be influenced by the different electronegativities. The band gaps of p-type doped MgO monolayers are tunable due to the emergence of impurity states within the band gap, while F-doped MgO monolayer realizes the transition from semiconductor to metal. The results show that p-type doped MgO monolayer exhibit magnetic behaviors due to polarizations of dopants and surrounding Mg or O atoms near the dopants, while no magnetism is observed in the case of F doped MgO monolayer. These results are potentially useful for spintronic applications and the development of magnetic nanostructures.

  10. Quasielastic neutron scattering and molecular dynamics simulation studies of the melting transition in butane and hexane monolayers adsorbed on graphite

    DEFF Research Database (Denmark)

    Hervig, K.W.; Wu, Z.; Dai, P.;

    1997-01-01

    on an exfoliated graphite substrate, For butane, quasielastic scattering broader than the experimental energy resolution width of 70 mu eV appears abruptly at the monolayer melting point of T-m = 116 K, whereas, for the hexane monolayer, it appears 20 K below the melting transition (T-m = 170 K). To facilitate...... neutron diffraction experiments. Butane melts abruptly to a liquid phase where the molecules in the trans conformation translationally diffuse while rotating about their center of mass. In the case of the hexane monolayer, the MD simulations show that the appearance of quasielastic scattering below T-m......Quasielastic neutron scattering experiments and molecular dynamics (MD) simulations have been used to investigate molecular diffusive motion near the melting transition of monolayers of flexible rod-shaped molecules. The experiments were conducted on butane and hexane monolayers adsorbed...

  11. Comparative Study of Electroless Copper Film on Different Self-Assembled Monolayers Modified ABS Substrate

    Directory of Open Access Journals (Sweden)

    Jiushuai Xu

    2014-04-01

    Full Text Available Copper films were grown on (3-Mercaptopropyltrimethoxysilane (MPTMS, (3-Aminopropyltriethoxysilane (APTES and 6-(3-(triethoxysilylpropylamino-1,3,5- triazine-2,4-dithiol monosodium (TES self-assembled monolayers (SAMs modified acrylonitrile-butadiene-styrene (ABS substrate via electroless copper plating. The copper films were examined using scanning electron microscopy (SEM and X-ray diffraction (XRD. Their individual deposition rate and contact angle were also investigated to compare the properties of SAMs and electroless copper films. The results indicated that the formation of copper nuclei on the TES-SAMs modified ABS substrate was faster than those on the MPTMS-SAMs and APTES-SAMs modified ABS substrate. SEM images revealed that the copper film on TES-SAM modified ABS substrate was smooth and uniform, and the density of copper nuclei was much higher. Compared with that of TES-SAMs modified resin, the coverage of copper nuclei on MPTMS and APTES modified ABS substrate was very limited and the copper particle size was too big. The adhesion property test demonstrated that all the SAMs enhanced the interfacial interaction between copper plating and ABS substrate. XRD analysis showed that the copper film deposited on SAM-modified ABS substrate had a structure with Cu(111 preferred orientation, and the copper film deposited on TES-SAMs modified ABS substrate is better than that deposited on MPTMS-SAMs or APTES-SAMs modified ABS resins in electromigrtion resistance.

  12. Lipophilization of ascorbic acid: a monolayer study and biological and antileishmanial activities.

    Science.gov (United States)

    Kharrat, Nadia; Aissa, Imen; Sghaier, Manel; Bouaziz, Mohamed; Sellami, Mohamed; Laouini, Dhafer; Gargouri, Youssef

    2014-09-17

    Ascorbyl lipophilic derivatives (Asc-C2 to Asc-C(18:1)) were synthesized in a good yield using lipase from Staphylococcus xylosus produced in our laboratory and immobilized onto silica aerogel. Results showed that esterification had little effect on radical-scavenging capacity of purified ascorbyl esters using DPPH assay in ethanol. However, long chain fatty acid esters displayed higher protection of target lipids from oxidation. Moreover, compared to ascorbic acid, synthesized derivatives exhibited an antibacterial effect. Furthermore, ascorbyl derivatives were evaluated, for the first time, for their antileishmanial effects against visceral (Leishmania infantum) and cutaneous parasites (Leishmania major). Among all the tested compounds, only Asc-C10, Asc-C12, and Asc-C(18:1) exhibited antileishmanial activities. The interaction of ascorbyl esters with a phospholipid monolayer showed that only medium and unsaturated long chain (Asc-C10 to Asc-C(18:1)) derivative esters were found to interact efficiently with mimetic membrane of leishmania. These properties would make ascorbyl derivatives good candidates to be used in cosmetic and pharmaceutical lipophilic formulations. PMID:25148258

  13. Comparing the accuracy of high-dimensional neural network potentials and the systematic molecular fragmentation method: A benchmark study for all-trans alkanes.

    Science.gov (United States)

    Gastegger, Michael; Kauffmann, Clemens; Behler, Jörg; Marquetand, Philipp

    2016-05-21

    Many approaches, which have been developed to express the potential energy of large systems, exploit the locality of the atomic interactions. A prominent example is the fragmentation methods in which the quantum chemical calculations are carried out for overlapping small fragments of a given molecule that are then combined in a second step to yield the system's total energy. Here we compare the accuracy of the systematic molecular fragmentation approach with the performance of high-dimensional neural network (HDNN) potentials introduced by Behler and Parrinello. HDNN potentials are similar in spirit to the fragmentation approach in that the total energy is constructed as a sum of environment-dependent atomic energies, which are derived indirectly from electronic structure calculations. As a benchmark set, we use all-trans alkanes containing up to eleven carbon atoms at the coupled cluster level of theory. These molecules have been chosen because they allow to extrapolate reliable reference energies for very long chains, enabling an assessment of the energies obtained by both methods for alkanes including up to 10 000 carbon atoms. We find that both methods predict high-quality energies with the HDNN potentials yielding smaller errors with respect to the coupled cluster reference. PMID:27208939

  14. Comparing the accuracy of high-dimensional neural network potentials and the systematic molecular fragmentation method: A benchmark study for all-trans alkanes

    Science.gov (United States)

    Gastegger, Michael; Kauffmann, Clemens; Behler, Jörg; Marquetand, Philipp

    2016-05-01

    Many approaches, which have been developed to express the potential energy of large systems, exploit the locality of the atomic interactions. A prominent example is the fragmentation methods in which the quantum chemical calculations are carried out for overlapping small fragments of a given molecule that are then combined in a second step to yield the system's total energy. Here we compare the accuracy of the systematic molecular fragmentation approach with the performance of high-dimensional neural network (HDNN) potentials introduced by Behler and Parrinello. HDNN potentials are similar in spirit to the fragmentation approach in that the total energy is constructed as a sum of environment-dependent atomic energies, which are derived indirectly from electronic structure calculations. As a benchmark set, we use all-trans alkanes containing up to eleven carbon atoms at the coupled cluster level of theory. These molecules have been chosen because they allow to extrapolate reliable reference energies for very long chains, enabling an assessment of the energies obtained by both methods for alkanes including up to 10 000 carbon atoms. We find that both methods predict high-quality energies with the HDNN potentials yielding smaller errors with respect to the coupled cluster reference.

  15. Modeling Study of Hydrogen/Oxygen and n-alkane/Oxygen Counterflow Diffusion Flames%氢、碳氢燃料对向扩散火焰

    Institute of Scientific and Technical Information of China (English)

    汪小卫; 蔡国飙; Vigor Yang

    2011-01-01

    A comprehensive analysis of hydrogen/oxygen and hydrocarbon/oxygen counterflow diffusion flames has been conducted using corresponding detailed reaction mechanisms. The hydrocarbon fuels contain n-alkanes from CH4 to C16H34. The basic diffusion flame structures are demonstrated, analyzed, and compared. The effects of pressure, and strain rate on the flame behavior and energy-release rate for each fuel are examined systematically. The detailed chemical kinetic reaction mechanisms from Lawrence Livermore National Laboratory (LLNL) are employed, and the largest one of them contains 2115 species and 8157 reversible reactions. The results indicate for all of the fuels the flame thickness and heat release rate correlate well with the square root of the pressure multiplied by the strain rate. Under the condition of any strain rate and pressure, H2 has thicker flame than hydrocarbons, while the hydrocarbons have the similar temperature and main products distributions and almost have the same flame thickness and heat release rate. The result indicates that the fuels composed with these hydrocarbons will still have the same flame properties as any pure n-alkane fuel.

  16. Cholesterol strongly affects the organization of lipid monolayers studied as models of the milk fat globule membrane: Condensing effect and change in the lipid domain morphology.

    Science.gov (United States)

    Murthy, Appala Venkata Ramana; Guyomarc'h, Fanny; Paboeuf, Gilles; Vié, Véronique; Lopez, Christelle

    2015-10-01

    The biological membrane that surrounds the milk fat globules exhibits phase separation of polar lipids that is poorly known. The objective of this study was to investigate the role played by cholesterol in the organization of monolayers prepared as models of the milk fat globule membrane (MFGM). Differential scanning calorimetry and X-ray diffraction experiments allowed characterization of the gel to liquid crystalline phase transition temperature of lipids, Tm ~35°C, in vesicles prepared with a MFGM lipid extract. For temperature below Tm, atomic force microscopy revealed phase separation of lipids at 30 mN·m(-1) in Langmuir-Blodgett monolayers of the MFGM lipid extract. The high Tm lipids form liquid condensed (LC) domains that protrude by about 1.5 nm from the continuous liquid expanded (LE) phase. Cholesterol was added to the MFGM extract up to 30% of polar lipids (cholesterol/milk sphingomyelin (MSM) molar ratio of 50/50). Compression isotherms evidenced the condensing effect of the cholesterol onto the MFGM lipid monolayers. Topography of the monolayers showed a decrease in the area of the LC domains and in the height difference H between the LC domains and the continuous LE phase, as the cholesterol content increased in the MFGM lipid monolayers. These results were interpreted in terms of nucleation effects of cholesterol and decrease of the line tension between LC domains and LE phase in the MFGM lipid monolayers. This study revealed the major structural role of cholesterol in the MFGM that could be involved in biological functions of this interface (e.g. mechanisms of milk fat globule digestion). PMID:26087463

  17. Unfolding of cytochrome c immobilized on self-assembled monolayers. An electrochemical study

    International Nuclear Information System (INIS)

    Highlights: → Denaturation involves intermediate and partially unfolded forms. → An unfolded species displaying the haem with Fe coordinated by two His is observed. → Under unfolding conditions the nature of the SAM influences conformation of protein. → Concentration of the unfolding agent affects redox properties of immobilized protein. - Abstract: The electron transfer (ET) process of progressively unfolded bovine cytochrome c immobilized on different self-assembled monolayers (SAMs) was investigated. Insight is gained on the role of the SAM surface on the functionality of the partially unfolded and non-native forms of the adsorbed protein. Direct electrochemical measurements were performed on cytochrome c adsorbed on mercaptopyridine (MP) and mixed 11-mercapto-1-undecanoic acid/11-mercapto-1-undecanol (MUA/MU) at varying temperature, in the presence of urea as unfolding agent. Under strongly unfolding conditions, a non-native form of cytochrome c, in which the methionine ligand is replaced by a histidine, was observed on both MP and MUA/MU SAMs. The Eo' of the native form, in which the haem is axially coordinated by methionine and histidine, slightly shifts to negative values upon increasing urea concentration. However, the non-native bis-histidinate species shows a much lower Eo' value (by approximately 0.4 V) which is by far enthalpic in origin and largely determined by axial ligand swapping. Analysis of the reduction enthalpies and entropies and of the ET rate constants indicate that the nature of the SAM (hydrophilic or anionic) results in changes in the conformational rearrangement of the cytochrome c under unfolding conditions.

  18. Unfolding of cytochrome c immobilized on self-assembled monolayers. An electrochemical study

    Energy Technology Data Exchange (ETDEWEB)

    Monari, Stefano; Ranieri, Antonio; Bortolotti, Carlo Augusto; Peressini, Silvia [Department of Chemistry, University of Modena and Reggio Emilia, via Campi 183, 41125 Modena (Italy); Tavagnacco, Claudio [Department of Chemistry, University of Trieste, via Giorgieri 1, 34127 Trieste (Italy); Borsari, Marco, E-mail: marco.borsari@unimore.it [Department of Chemistry, University of Modena and Reggio Emilia, via Campi 183, 41125 Modena (Italy)

    2011-08-01

    Highlights: > Denaturation involves intermediate and partially unfolded forms. > An unfolded species displaying the haem with Fe coordinated by two His is observed. > Under unfolding conditions the nature of the SAM influences conformation of protein. > Concentration of the unfolding agent affects redox properties of immobilized protein. - Abstract: The electron transfer (ET) process of progressively unfolded bovine cytochrome c immobilized on different self-assembled monolayers (SAMs) was investigated. Insight is gained on the role of the SAM surface on the functionality of the partially unfolded and non-native forms of the adsorbed protein. Direct electrochemical measurements were performed on cytochrome c adsorbed on mercaptopyridine (MP) and mixed 11-mercapto-1-undecanoic acid/11-mercapto-1-undecanol (MUA/MU) at varying temperature, in the presence of urea as unfolding agent. Under strongly unfolding conditions, a non-native form of cytochrome c, in which the methionine ligand is replaced by a histidine, was observed on both MP and MUA/MU SAMs. The E{sup o}' of the native form, in which the haem is axially coordinated by methionine and histidine, slightly shifts to negative values upon increasing urea concentration. However, the non-native bis-histidinate species shows a much lower E{sup o}' value (by approximately 0.4 V) which is by far enthalpic in origin and largely determined by axial ligand swapping. Analysis of the reduction enthalpies and entropies and of the ET rate constants indicate that the nature of the SAM (hydrophilic or anionic) results in changes in the conformational rearrangement of the cytochrome c under unfolding conditions.

  19. 单分子膜研究的方法及现状%Ways and Currmt Situation of Monolayer Studies

    Institute of Scientific and Technical Information of China (English)

    胡杰; 朱谱新

    2001-01-01

    单分子膜一般是将两亲性物质溶解在铺展溶剂中制成铺晨溶液,然后铺展在底液上而得的。在其性质的研究中,测定表面压—面积关系曲线是最基本、也是最重要的一种研究手段。但是,仅有表面压—面积曲线所能了解的信息是远远不够的,因此必须结合另一些手段进行研究,测定表面粘度就是其中很重要的一种。而随着现代光谱仪器的更新、发展,光学方法已日益成为单分子膜研究的一个重要途径。%Monolayers are generally formed at air/weater interface byspreadng proper solutions in which amphiprotic substances ste ressolved. A large number of studies bave been carried out in order to understand the peoperties and structures of the onolayers. Of the researching metiods, the pressurearea curve is the most foumdamental and importamt. The other techniques involve measurement of surface viscosity and optical properties of monolayers. With advancing and developing of spectrometes, sensitive maging techniques have been opening up new prospect for a better understanding of the physics of themonolayers.

  20. A raft-associated species of phosphatidylethanolamine interacts with cholesterol comparably to sphingomyelin. A Langmuir-Blodgett monolayer study.

    Directory of Open Access Journals (Sweden)

    Michal Grzybek

    Full Text Available BACKGROUND: Specific interactions between sphingomyelin (SM and cholesterol (Ch are commonly believed to play a key role in the formation of rafts in the biological membranes. A weakness of this model is the implication that these microdomains are confined to the outer bilayer leaflet. The cytoplasmic leaflet, which contains the bulk of phosphatidylethanolamine (PE, phosphatidylserine (PS and phosphatidylinositol (PI, is thought also to harbour half of the membrane cholesterol. Moreover, SLPE (1-stearoyl-2-linoleoyl-sn-glycero-3-phosphatidyl-ethanolamine has recently been shown to be enriched in isolated detergent-resistant membranes (DRM, and this enrichment was independent of the method of isolation of DRM. METHODOLOGY/PRINCIPAL FINDINGS: Here we present quantitative evidence coming from Langmuir-Blodgett monolayer experiments that SLPE forms complex with Ch similar to that between SM and Ch. The energies of these interactions as calculated form the monolayer studies are highly negative. FRAP analysis showed that NBD-Ch recovery was similar in liposomes composed of DOPC/Ch SM or SLPE but not DPPE, providing further evidence that SLPE may form an l(o phase in the presence of high Ch concentration. Experiments on the solubility of DOPC liposomes containing DPPE/Ch (1ratio1, SM/Ch (1ratio1 or SLPE/Ch (1ratio1 showed the presence of Triton X-100 insoluble floating fraction (TIFF in the case of SM/Ch or SLPE/Ch but not in DPPE/Ch containing liposomes. Quantitative determination of particular lipid species in the TIFF fraction confirms the conclusion that SLPE (or similar PE species could be an important constituent of the inner leaflet raft. CONCLUSION: Such interactions suggest a possible existence of inner-leaflet nanoscale assemblies composed of cholesterol complexes with SLPE or similar unsaturated PE species.

  1. Enrichment and Characterization of a Psychrotolerant Consortium Degrading Crude Oil Alkanes Under Methanogenic Conditions.

    Science.gov (United States)

    Ding, Chen; Ma, Tingting; Hu, Anyi; Dai, Lirong; He, Qiao; Cheng, Lei; Zhang, Hui

    2015-08-01

    Anaerobic alkane degradation via methanogenesis has been intensively studied under mesophilic and thermophilic conditions. While there is a paucity of information on the ability and composition of anaerobic alkane-degrading microbial communities under low temperature conditions. In this study, we investigated the ability of consortium Y15, enriched from Shengli oilfield, to degrade hydrocarbons under different temperature conditions (5-35 °C). The consortium could use hexadecane over a low temperature range (15-30 °C). No growth was detected below 10 °C and above 35 °C, indicating the presence of cold-tolerant species capable of alkane degradation. The preferential degradation of short chain n-alkanes from crude oil was observed by this consortium. The structure and dynamics of the microbial communities were examined using terminal restriction fragment length polymorphism (T-RFLP) fingerprinting and Sanger sequencing of 16S rRNA genes. The core archaeal communities were mainly composed of aceticlastic Methanosaeta spp. Syntrophaceae-related microorganisms were always detected during consecutive transfers and dominated the bacterial communities, sharing 94-96 % sequence similarity with Smithella propionica strain LYP(T). Phylogenetic analysis of Syntrophaceae-related clones in diverse methanogenic alkane-degrading cultures revealed that most of them were clustered into three sublineages. Syntrophaceae clones retrieved from this study were mainly clustered into sublineage I, which may represent psychrotolerant, syntrophic alkane degraders. These results indicate the wide geographic distribution and ecological function of syntrophic alkane degraders. PMID:25783218

  2. Supplementary Material: Computational Study of Quasi-2D Liquid State in Free Standing Platinum, Silver, Gold, and Copper Monolayers

    OpenAIRE

    Yang, Li-ming; Ganz, Ariel B.; Dornfeld, Matthew; Ganz, Eric

    2016-01-01

    Supplementary files for Condensed Matter 2016, 1(1), 1; doi:10.3390/condmat1010001; http://www.mdpi.com/ 2410-3896/1/1/1. Captions: Video S1. (Pt 2400 K 5 ps) 5 ps Molecular Dynamics Movie of Pt Freestanding Monolayer at 2400 K.  Video S2.  (Ag 1050K 6 ps) 6 ps Molecular Dynamics Movie of Ag Freestanding Monolayer at 1050 K. Video S3. (Au 1600K 4ps) 4 ps Molecular Dynamics Movie of Au Freestanding Monolayer at 1600 K. ...

  3. Effect of alkane chain length and counterion on the freezing transition of cationic surfactant adsorbed film at alkane mixture - water interfaces.

    Science.gov (United States)

    Tokiwa, Yuhei; Sakamoto, Hiroyasu; Takiue, Takanori; Aratono, Makoto; Matsubara, Hiroki

    2015-05-21

    Penetration of alkane molecules into the adsorbed film gives rise to a surface freezing transition of cationic surfactant at the alkane-water interface. To examine the effect of the alkane chain length and counterion on the surface freezing, we employed interfacial tensiometry and ellipsometry to study the interface of cetyltrimethylammonium bromide and cetyltrimethylammonium chloride aqueous solutions against dodecane, tetradecane, hexadecane, and their mixtures. Applying theoretical equations to the experimental results obtained, we found that the alkane molecules that have the same chain length as the surfactant adsorb preferentially into the surface freezing film. Furthermore, we demonstrated that the freezing transition temperature of cationic surfactant adsorbed film was independent of the kind of counterion. PMID:25932500

  4. Hematite nanoparticle monolayers on mica electrokinetic characteristics.

    Science.gov (United States)

    Morga, Maria; Adamczyk, Zbigniew; Oćwieja, Magdalena

    2012-11-15

    Electrokinetic properties of α-Fe(2)O(3) (hematite) nanoparticle monolayers on mica were thoroughly characterized using the streaming potential method. Hematite suspensions were obtained by acidic hydrolysis of ferric chloride. The average size of particles (hydrodynamic diameter), determined by dynamic light scattering (DLS) and AFM, was 22 nm (pH=5.5, I=10(-2)M). The hematite monolayers on mica were produced under diffusion-controlled transport from the suspensions of various bulk concentration. The monolayer coverage, quantitatively determined by AFM and SEM, was regulated within broad limits by adjusting the nanoparticle deposition time. This allowed one to uniquely express zeta potential of hematite monolayers, determined by the streaming potential measurements, in terms of the particle coverage. Such dependencies, obtained for various pH, were successfully interpreted in terms of the three-dimensional electrokinetic model. A universal calibrating graph was produced enabling one to determine hematite monolayer coverage from the measured value of the streaming potential. The influence of the ionic strength, varied between 10(-4) and 10(-2)M, on the zeta potential of hematite monolayers was also studied. Additionally, the stability of monolayers (desorption kinetics) was determined under in situ conditions using the streaming potential method. Our experimental data prove that it is feasible to produce uniform and stable hematite particle monolayers of well-controlled coverage. Such monolayers may find practical applications as universal substrates for protein immobilization (biosensors) and in electrocatalytic applications. PMID:22921408

  5. [Distribution Characteristics and Source Apportionment of n-Alkanes in Water from Yellow River in Henan Section].

    Science.gov (United States)

    Feng, Jing-lan; Xi, Nan-nan; Zhang, Fei; Liu, Shu-hui; Sun, Jian-hui

    2016-03-15

    To investigate the distributions and possible sources of n-alkanes in water and suspended particulate matter from Yellow River in Henan section, 26 water and suspended particulate matter samples were collected in August 2010 and 22 n-alkanes (C₁₄-C₃₆) were quantitatively determined by gas chromatography-mass spectrometer (GC-MS). Potential sources of n-alkanes were analyzed using different characteristic parameters. The results indicated that total concentrations of 22 n-alkanes were 521-5,843 ng · L⁻¹ with a mean concentration of 1,409 ng · L⁻¹, while the total amounts of n-alkanes in the suspended particulate matter were 463-11,142 ng · L⁻¹ with a mean value of 1,951 ng · L⁻¹. The composition profiles of n-alkanes in water showed unimodal distribution with a peak at C₂₅ in water. However, the composition characteristics of n-alkanes in SPM were of bimodal type, but still with the advantage of high carbon hydrocarbons peak at C₂₅. Results of characteristic parameters including CPI, TAR, OEP and % WaxCn showed that n-alkanes in the studied area were derived mainly from combustion of fossil fuel, while terrestrial higher plant played a role in the existence of n-alkanes in water and suspended particulate matter from Yellow River in Henan section. PMID:27337879

  6. Theoretical study of the adsorption of a PTCDA monolayer on S-passivated GaAs(l 0 0)

    International Nuclear Information System (INIS)

    This work investigates the adsorption of a PTCDA (3,4,9,10-perylene tetracarboxylic dianhydride) monolayer on a 2 x 1 S-passivated GaAs(1 0 0) surface with density functional based tight binding (DFTB) calculations. The structure of the first monolayer is discussed within the restricted class of surface unit cells including a single PTCDA molecule, and the calculated current-voltage characteristics are used to predict the electronic transport properties of the hybrid system

  7. Effect of vacancies on structural, electronic and optical properties of monolayer MoS2: A first-principles study

    International Nuclear Information System (INIS)

    Highlights: • VMo induces an outward relaxation, whereas VS induces inward relaxation. • Monolayer MoS2 has changed from direct to indirect band gap after introduction of VMo0. • VMo induces acceptor-like level, whereas VS induces donor-like level. • Band gaps get smaller and defect levels get deeper as charge states of V increase. • Dielectric constants of defective monolayer MoS2 are larger than that of perfect one. - Abstract: Effects of vacancies on structural, electronic and optical properties of monolayer MoS2 were investigated using first-principles plane-wave pseudopotential method based on density functional theory. Results show that the band structure and band gap of perfect monolayer MoS2 are in good agreement with the available experimental and theoretical data. Structural analysis indicates that ions surrounding Mo vacancies show an outward relaxation, while that ions surrounding S vacancies exhibit slightly inward relaxation. Electronic analysis implies that the band gaps of defective monolayer MoS2 are smaller than that of perfect one. After introduction of neutral S-vacancy, monolayer MoS2 has changed from direct to indirect band gap. Mo vacancies bring about acceptor-like levels and p-type conductivities, whereas S vacancies lead to donor-like levels and n-type conductivities. With the increasing charge states of vacancies, the band gaps get smaller and the defect energy levels become deeper. Moreover, as the charge states of vacancies increase, the static dielectric constants of monolayer MoS2 with Mo vacancies decrease, whereas the static dielectric constants of monolayer MoS2 with S vacancies increase

  8. Modeling the solubilities of high molecular weight n-alkanes in supercritical carbon dioxide

    OpenAIRE

    Jha, Sujit Kumar; Madras, Giridhar

    2004-01-01

    The Peng-Robinson equation of state with quadratic mixing rules and a single adjustable parameter was used to model the solubilities of various high molecular weight solid n-alkanes in supercritical carbon dioxide. The key conclusion of the study is that the adjustable parameter, $k_{ij}$, varies linearly with the number of carbon atoms in the main chain of the n-alkane. Thus, the model can be used to predict the solubilities of various high molecular weight solid n-alkanes in supercritical c...

  9. Thermodynamic and structural study of two-dimensional melting within monolayers or rare gases or methane physically adsorbed upon the surface of layer-like solids

    International Nuclear Information System (INIS)

    The 2D (two-dimensional) melting of monolayers of rare gases or methane physically adsorbed on the basal face of lamellar solids (graphite, boron nitride and lamellar halides) has been studied. Two different experimental measurements have been made: i) adsorption isotherms; ii) neutron diffraction spectra. The main part of this report deals with the 2D liquid-incommensurate solid transition within monolayers of rare gases or methane adsorbed on the basal face of lamellar halides. This transition is first order. It is observed only if certain conditions of dimensional incompatibility between the substrate and the absorbate are fulfilled. It is little affected by the structure of the underlying substrate. A number of thermodynamic parameters associated with it, are constants once properly scaled. These constants agree well with theoretical estimates for 6-12 Lennard Jones particles adsorbed on a smooth surface. For the monolayer of Xe adsorbed on graphite the temperature of the tricritical point above which melting becomes a continuous transition has been measured. The isotope effect associated with 2D melting has been investigated by comparing the behaviour of monolayers of CH4 and CD4 adsorbed on boron nitride. The vapor pressure of Xe has been determined in the temperature range 101-120 K. (author)

  10. Surface plasmon Raman scattering studies of liquid crystal anchoring on liquid-crystal-based self-assembled monolayers.

    Science.gov (United States)

    Critchley, Kevin; Cheadle, Edward M; Zhang, Hao-Li; Baldwin, Kurt J; Liu, Quanying; Cheng, Yaling; Fukushima, Hitoshi; Tamaki, Takashi; Batchelder, David N; Bushby, Richard J; Evans, Stephen D

    2009-11-26

    We studied the anchoring of 6CB on a series of self-assembled monolayers (SAMs) with a functional group that mimics that of the nematic liquid crystal (LC). The SAMs were first characterized by wetting, Fourier-transform infrared spectroscopy, and surface potential measurements. We found that, in two of these SAMs, the end group dipoles were oriented close to the normal of the surface and that these promoted homeotropic anchoring. In the case of the other SAM, the dipole was oriented parallel to the surface, and planar anchoring was obtained. Raman scattering by adsorbates on thin metal films is enhanced by the electromagnetic fields of surface plasmon polaritons (SPPs). Despite the inherent polarization of SPPs, there have been few reports in which SPP Raman scattering has been used to study molecular orientation. We have developed optical instrumentation to provide efficient excitation and collection of SPP Raman scattered light using attenuated total reflection geometry. The Kretschmann prism coupling configuration was used to excite SPPs on thin (500 A) gold films with adsorbed SAMs of alkanethiols in contact with thin films (50 microm) of the nematic liquid crystal 4'-hexylbiphenyl-4-carbonitrile (6CB, Merck). The anchoring and orientational wetting of the LC 6CB at the interface with omega-functionalized SAMs was studied using this arrangement. In agreement with the results of previous studies, a high-energy surface (-COOH) was found to promote planar anchoring, whereas a low-energy surface (-CF(3)) was found to induce homeotropic anchoring. PMID:19921953

  11. Application of metal-modified silica gels as sorbents for alkane-thiols

    International Nuclear Information System (INIS)

    In order to elaborate high effective method of purification of industry wastes from alkane-thiols the sorption properties of silica gels modified by ions of heavy metals are studied. The optimal conditions of sorption are defined.

  12. Scorpionate complexes as catalysts for alkane functionalization

    OpenAIRE

    Martins, Luísa M. D. R. S.

    2009-01-01

    A survey of the scorpionate tris(pyrazolyl)methane complexes synthesized by our group is presented, as well as their structural features and catalytic applications toward the funtionalization of linear and cyclic light alkanes.

  13. Supported organoiridium catalysts for alkane dehydrogenation

    Energy Technology Data Exchange (ETDEWEB)

    Baker, R. Thomas; Sattelberger, Alfred P.; Li, Hongbo

    2013-09-03

    Solid supported organoiridium catalysts, a process for preparing such solid supported organoiridium catalysts, and the use of such solid supported organoiridium catalysts in dehydrogenation reactions of alkanes is provided. The catalysts can be easily recovered and recycled.

  14. A DNA self-assembled monolayer for the specific attachment of unmodified double- or single-stranded DNA.

    OpenAIRE

    Bamdad, C

    1998-01-01

    A novel method for DNA surface immobilization and a paradigm for the attachment of unmodified DNA of any length or sequence are described herein. The development of a DNA self-assembled monolayer (DNA-SAM) that incorporates a DNA-thiol into a monolayer of inert alkane thiolates is reported. This DNA-SAM specifically hybridized complementary oligonucleotides while resisting the nonspecific adsorption of noncomplementary DNA and irrelevant proteins. Duplex DNA, having a single-stranded "capture...

  15. Solvation of alkane and alcohol molecules. Energy contributions

    OpenAIRE

    Pais, A. A. C. C.; Sousa, A.; Eusébio, M. E.; Redinha, J. S.

    2001-01-01

    In this work we conduct a systematic ab initio study of the solvation of small alkane, monoalcohol and diol molecules, in polar solvents with different properties. A choice of basis set suitable for the type of compounds under study is presented. The various components of the solvent–solute interaction and the cavitation energy are treated individually and their variation with chain length and introduction of hydroxy groups assessed. The use of solute molecules in which controlled changes are...

  16. Nanodimentional Aggregates In Organic Monolayers Studied With Atomic Force Microscopy (AFM) And Fluorescence Lifetime Imaging Microscopy (FLIM)

    Science.gov (United States)

    Ivanov, George R.; Burov, Julian

    2007-04-01

    Organic monolayers from a fluorescently labeled phospholipid (DPPE-NBD) were deposited on solid supports under special conditions that form stable nanometer wide bilayers cylinders that protrude from the monolayer. This molecule was frequently used in sensor applications due to its sensitivity to environment changes. The proposed configuration should provide both fast response times (ultra thin film) and increased sensitivity (greatly increased surface area). AFM can clearly distinguish between the different phases. The height difference between the solid-expanded and the liquid-expanded phase was measured to be 1.4 nm while the bilayer thickness was 5.6 nm. The solid domains show a 20 % decrease in fluorescence lifetime in comparison to the monolayer as measured by FLIM. This difference in lifetimes is explained in the model of fluorescence self quenching in the solid phase due to the molecules being closer to each other.

  17. A study of the inhibiton of copper corrosion by triethyl phosphate and triphenyl phosphate self-assembled monolayers

    Directory of Open Access Journals (Sweden)

    HOUYI MA

    2006-02-01

    Full Text Available Two kinds of phosphates, triethyl phosphate (TEP and triphenyl phosphate (TPP, were used to form self-assembled monolayers for the inhibition of the corrosion of copper in 0.2 mol dm–3 NaCl solution. Electrochemical impedance spectroscopy (EIS was applied to investigate the inhibition effects. The results showed that their inhibition ability first increased with increasing immersion time in ethanolic solutions of the corresponding compounds. However, when the immersion time was increased over some critical point, the inhibition effect decreased. For the same immersion time, the inhibition effect of the TPP monolayer was more pronounced than that of the TEP monolayer. Thus, ab initio calculations were used to interpret the relationship between the inhibition effects and the structures of the compounds.

  18. The influence of extraframework aluminum on H-FAU catalyzed cracking of light alkanes

    OpenAIRE

    Narbeshuber, T.F.; Brait, A.; Seshan, K.; Lercher, J.A.

    1996-01-01

    The conversion of light linear and branched alkanes on two faujasite samples containing different concentrations of free Brønsted acid sites and extraframework alumina (EFAL) was studied between 733 K and 813 K. Protolytic cracking and bimolecular hydride transfer proceeded solely on Brønsted acid sites. For cracking of n-alkanes, the variation of the concentration of extraframework aluminum did not affect the catalytic activity per accessible Brønsted acid site. The activity to dehydrogenati...

  19. MONOLAYER BEHAVIOR OF SOME STEREOREGULAR POLY(METHACRYLATES)

    NARCIS (Netherlands)

    BRINKHUIS, RHG; SCHOUTEN, AJ

    1992-01-01

    The monolayer behavior of some poly(methacrylates) with short ester side chains (methyl, ethyl, and isobutyl) is studied as a function of the tacticity. In all cases, the isotactic polymers are observed to form expanded monolayers, whereas the syndiotactic materials yield more condensed monolayers.

  20. Molecular ordering and phase transitions in alkanol monolayers at the water-hexane interface

    International Nuclear Information System (INIS)

    The interface between bulk water and bulk hexane solutions of n-alkanols (H(CH2)mOH, where m=20, 22, 24, or 30) is studied with x-ray reflectivity, x-ray off-specular diffuse scattering, and interfacial tension measurements. The alkanols adsorb to the interface to form a monolayer. The highest density, lowest temperature monolayers contain alkanol molecules with progressive disordering of the chain from the -CH2OH to the -CH3 group. In the terminal half of the chain that includes the -CH3 group the chain density is similar to that observed in bulk liquid alkanes just above their freezing temperature. The density in the alkanol headgroup region is 10% greater than either bulk water or the ordered headgroup region found in alkanol monolayers at the water-vapor interface. We conjecture that this higher density is a result of water penetration into the headgroup region of the disordered monolayer. A ratio of 1:3 water to alkanol molecules is consistent with our data. We also place an upper limit of one hexane to five or six alkanol molecules mixed into the alkyl chain region of the monolayer. In contrast, H(CH2)30OH at the water-vapor interface forms a close-packed, ordered phase of nearly rigid rods. Interfacial tension measurements as a function of temperature reveal a phase transition at the water-hexane interface with a significant change in interfacial excess entropy. This transition is between a low temperature interface that is nearly fully covered with alkanols to a higher temperature interface with a much lower density of alkanols. The transition for the shorter alkanols appears to be first order whereas the transition for the longer alkanols appears to be weakly first order or second order. The x-ray data are consistent with the presence of monolayer domains at the interface and determine the domain coverage (fraction of interface covered by alkanol domains) as a function of temperature. This temperature dependence is consistent with a theoretical model for a

  1. Experimental proof for resonant diffusion of normal alkanes in LTL and ZSM-12 zeolites

    CERN Document Server

    Yoo, K; Smirniotis, P G

    2015-01-01

    The intra-crystalline diffusion of normal alkanes in LTL and ZSM-12 zeolite was experimentally studied via gravimetric measurements performed at different temperatures. A periodic dependence of the diffusion coefficient on the number of carbon atoms in alkane was detected, which is an experimental proof for resonant diffusion. The present observations were described on the base of the existing theory of the resonant diffusion and several important parameters of the alkane-zeolite interaction and zeolite vibrations were obtained. In the considered temperature region the diffusion coefficient follows the Arrhenius law with periodic dependences of the pre-exponential factor and activation energy on the number of carbon atoms in alkanes. A compensation effect of simultaneous increases of the pre-exponential factor and the activation energy was also established.

  2. Short-time Evolution of Alkane-in-Water Nanoemulsions

    OpenAIRE

    Urbina-Villalba, German; Rahn-Chique, Kareem

    2013-01-01

    The stability of alkane-in-water nanoemulsions during the sub-stationary regime is studied by means of Emulsion Stability Simulations (ESS). The effects of Ostwald ripening, flocculation, coalescence, gravity, and hydration forc- es are considered. According to these calculations flocculation and coalescence are predominant during the first few seconds after the preparation of the emulsion. This favors the generation of a right-skewed Drop Size Distribu- tion (DSD). As the system evolves, the...

  3. Study on surface acid-base property of carboxylic acid-terminated self-assembled monolayers by cyclic voltammetry and electro-chemical impedance spectroscopy

    Institute of Scientific and Technical Information of China (English)

    罗立强; 程志亮; 杨秀荣; 汪尔康

    2000-01-01

    Cyclic voltammetry and electrochemical impedance spectroscopy were used to study the surface acid-base property of carboxylic acid-terminated self-assembled monolayers (SAMs). A carboxylic acid-terminated thiol, such as thioctic acid (1,2-dithiolane-3-pentanoic acid), was self-assembled on gold electrodes. Electron transfer between the bulk solution and the SAM modified electrode was studied at different pH using Fe(CN)63 as a probe. The surface pK. of thioctic acid was determined by cyclic voltammetry and electrochemical impedance spectroscopy to be 5.6±0.1 and 5.8±0.1, respectively. The method is compared with other methods of monolayer pK.measurement.

  4. Graphic model for calculating the entropy of С11Н24 alkanes with allowance for multiple non-valence interactions through three atoms along the chain of a molecule

    Science.gov (United States)

    Nilov, D. Yu.; Smolyakov, V. M.

    2016-08-01

    A fourteen-constant graphic scheme is proposed for evaluating the thermodynamic properties of branched paraffin hydrocarbons. Absolute entropy S f, 298 gas of 159 alkanes, of which 157 alkanes have yet to be studied experimentally, are calculated using 105 experimental data S f, 298 K, gas for alkanes CН4-С32Н66.

  5. Reveal of small alkanes and isomers using calculated core and valence binding energy spectra and total momentum cross sections

    CERN Document Server

    Yang, Zejin

    2013-01-01

    The present study revealed quantum mechanically that the C1s binding energy spectra of the small alkanes (upto six carbons) provide a clear picture of isomeric chemical shift in linear alkanes and branched isomers, whereas the valence binding energy spectra contain more sensitive information regarding the length of the carbon chains. Total momentum cross sections of the alkanes exhibit the information of the chain length as well as constitutional isomers of the small alkanes. The C1s binding energies of small alkanes (including isomers) are position specific and the terminal carbons have the lowest energies. The length of an alkane chain does not apparently affect the C1s energies so that the terminal carbons (289.11 eV) of pentane are almost the same as those of hexane. The valence binding energy spectra of the alkanes are characterized by inner valence and outer valence regions which are separated by an energy gap at approximately 17 eV. The intensities of the total momentum cross sections of the alkanes ar...

  6. Diversity of alkane hydroxylase systems in the environment; Diversite des systemes alcane hydroxylase dans l'environnement

    Energy Technology Data Exchange (ETDEWEB)

    Van Beilen, J.B.; Li, Z.; Duetz, W.A.; Smits, T.H.M.; Witholt, B. [Institute of Biotechnology, ETH-Honggerberg, Zurich (Switzerland); Smits, T.H.M. [Environnement Naturel, Architectural et Construt - ENAC/ISTE/LBE, EPFL, Lausanne (Switzerland)

    2003-08-01

    The first step in the aerobic degradation of alkanes by bacteria, yeasts, and fungi is catalyzed by oxygenases. These enzymes, which introduce oxygen atoms derived from molecular oxygen into the alkane substrate, play an important role in oil bio-remediation and in the co-metabolic degradation of compounds such as trichloroethylene and fuel oxygenates. In addition, they are useful bio-catalysts and important models for a difficult chemical reaction: the regio- and stereo-specific activation of C-H bonds. Several unrelated enzyme classes catalyze the oxidation of alkanes. Alkane-degrading yeast strains contain multiple alkane hydroxylases belonging to the P450 super-family, while many bacteria contain enzymes related to the Pseudomonas putida GPo1 membrane-bound alkane hydroxylase system. Short-chain alkanes are probably oxidized by alkane hydroxylases related to the soluble and particulate methane mono-oxygenases. Only the membrane-bound enzymes have been studied with respect to their prevalence in environments such as soils or aquifers. (authors)

  7. A study of the electron transfer inhibition on a charged self-assembled monolayer modified gold electrode by odd random phase multisine electrochemical impedance spectroscopy

    International Nuclear Information System (INIS)

    The interest of self-assembled monolayers (SAM) comes from their wide range of very specific technological applications. The SAMs having a terminal charged group are of great importance as model surfaces for electron transfer studies. The electron transfer for highly charged electroactive ions at a SAM modified electrode involves an electrostatic interaction. The present work studies a negatively charged SAM of 2-mercaptobenzimidazole-5-sulfonate (MBIS). The adsorption of the molecule on polycrystalline gold is described by X-ray photoelectron spectroscopy (XPS) and the reductive desorption of MBIS. The behavior of the MBIS monolayer towards the electron transfer of the ferri/ferrocyanide reaction is investigated by cyclic voltammetry and odd random phase multisine electrochemical impedance spectroscopy (ORP-EIS). This technique ensures reliable experiments and enables a statistically founded modeling. The combined electrochemical and surface study allows the investigation of the characteristics and electrochemical properties of the MBIS monolayer formed on polycrystalline gold to provide a quantitative modeling, which is physically and statistically validated. The major contribution of this work is the use of ORP-EIS and XPS to understand how the interaction between a charged SAM and electroactive ions affects the electron transfer

  8. Phase transitions in diglyceride monolayers studied by computer simulations, pressure-area isotherms and x-ray diffraction

    DEFF Research Database (Denmark)

    Peters, Günther H.J.; Toxværd, S.; Larsen, N.B.;

    1994-01-01

    1,2-sn-diglyceride monolayers exhibit unique and complex phase transitions as a function of surface pressure. The dynamical response of the layer on expanding the film has been investigated by computer simulations, (π-A) isotherms and grazing-incidence X-ray diffraction. Good agreement is found b...

  9. Elastic properties of surfactant monolayers at liquid-liquid interfaces: A molecular dynamics study

    DEFF Research Database (Denmark)

    Laradji, Mohamed; Mouritsen, Ole G.

    2000-01-01

    Using a simple molecular model based on the Lennard-Jones potential, we systematically study the elastic properties of liquid-liquid interfaces containing surfactant molecules by means of extensive and large-scale molecular dynamics simulations. The main elastic constants of the interface, corres...

  10. Effect of Dispersion on Surface Interactions of Cobalt(II) Octaethylporphyrin Monolayer on Au(111) and HOPG(0001) Substrates: a Comparative First Principles Study

    Energy Technology Data Exchange (ETDEWEB)

    Chilukuri, Bhaskar; Mazur, Ursula; Hipps, Kerry W.

    2014-07-21

    A density functional theory study of a cobalt(II) octaethylporphyrin (CoOEP) monolayer on Au(111) and HOPG(0001) surfaces was performed under periodic boundary conditions. Calculations with and without dispersion corrections are performed and the effect of van der Waals forces on the interface properties is analyzed. Calculations have determined that the CoOEP molecule tends to bind at the 3-fold and the 6-fold center sites on Au(111) and HOPG(0001), respectively. Geometric optimizations at the center binding sites have indicated that the porphyrin molecules (in the monolayer) lie flat on both substrates. Calculations also reveal that the CoOEP monolayer binds slightly more strongly to Au(111) than to HOPG(0001). Charge density difference plots disclose that charge is redistributed mostly around the porphyrin plane and the first layer of the substrates. Dispersion interactions cause a larger substrate to molecule charge pushback on Au(111) than on HOPG. CoOEP adsorption tends to lower the work functions of either substrate, qualitatively agreeing with the experimental photoelectron spectroscopic data. Comparison of the density of states (DOS) of the isolated CoOEP molecule with that on gold and HOPG substrates showed significant band shifts around the Fermi energy due to intermolecular orbital hybridization. Simulated STM images were plotted with the Tersoff–Hamann approach using the local density of states, which also agree with the experimental results. This study elucidates the role of dispersion for better describing porphyrin–substrate interactions. A DFT based overview of geometric, adsorption and electronic properties of a porphyrin monolayer on conductive surfaces is presented.

  11. X-ray reflectivity studies of cPLA2alpha-C2 domains adsorbed onto Langmuir monolayers of SOPC

    Science.gov (United States)

    Malkova, Sarka

    X-ray reflectivity is used to study the interaction of the C2 domain of cytosolic phospholipase A2 with a Langmuir monolayer of SOPC supported on a buffered aqueous solution containing Ca2+. The reflectivity is analyzed in terms of the known crystallographic structure of cPLA2alpha-C2 domains and a slab model representing the lipid layer to yield an electron density profile of the lipid layer and bound C2 domains. This new method of analysis determines the angular orientation and penetration depth of the cPLA2alpha-C2 domains bound to the monolayers, information not possible to obtain from the standard slab model analysis of x-ray reflectivity data. In the best fit orientation, the protein bound Ca 2+ ions are placed within 1 A of the lipid phosphate group (with an accuracy of +/-3 A). Hydrophobic residues of the calcium binding loops CBL1 and CBL3 penetrate deepest into the lipid layer, with a 2 A penetration into the tailgroup region. X-ray measurements with and without the C2 domain indicate a loss of water bound to the headgroup upon binding of the C2 domains. Control experiments with a non-calcium buffer and with domain mutants confirm that the cPLA2alpha-C2 binding to the SOPC monolayer is Ca2+ dependent and that the hydrophobic residues in the calcium binding loops are critical for membrane binding. These results indicate that an entropic component (due to water loss) as well as electrostatic and hydrophobic interactions contribute to the binding mechanism. Labeling the protein domain is not required for these studies. The conditions necessary to measure x-ray reflectivity from Langmuir monolayers of unsaturated lipids with negligible x-ray damage are demonstrated.

  12. Crumpling deformation regimes of monolayer graphene on substrate: a molecular mechanics study

    International Nuclear Information System (INIS)

    Experiments and simulations demonstrating reversible and repeatable crumpling of graphene warrant a detailed understanding of the underlying mechanisms of graphene crumple formation, especially for design of tailored nanostructures. To systematically study the formation of crumples in graphene, we use a simple molecular dynamics model, and perform a series of simulations to characterize the finite number of deformation regimes of graphene on substrate after compression. We formulate a quantitative measure of predicting these deformations based on observed results of the simulations and distinguish graphene crumpling considered in this study from others. In our study, graphene is placed on a model substrate while controlling and varying the interfacial energy between graphene and substrate and the substrate roughness through a set of particles embedded in the substrate. We find that a critical value of interfacial adhesion energy marks a transition point that separates two deformation regimes of graphene on substrate under uniaxial compression. The interface between graphene and substrate plays a major role in the formation of crumples, and we show that the choice of substrate can help in designing desired topologies in graphene. (paper)

  13. Theoretical model study of dynamic ferromagnetic susceptibility in mono-layer graphene

    Science.gov (United States)

    Sahu, Sivabrata; Parashar, S. K. S.; Rout, G. C.

    2016-04-01

    We report here a microscopic theoretical study of dynamic ferromagnetic spin susceptibility of electrons for graphene systems, which deal with a tight-binding model Hamiltonian consisting of the hopping of electrons up to third-nearest-neighbors, impurity and substrate effects besides Coulomb interaction of electrons at A-and B- sub- lattices. The spin susceptibility involves four two-particle Green's functions, which are calculated by Zubarev's Green's function technique. The up and down electron occupancies at A and B sub-lattices are computed numerically and self-consistently. The temperature dependent susceptibility shows a pronounced peak at Curie temperature for critical Coulomb interaction Uc = 2.2t1.

  14. Eukaryotic expression system Pichia pastoris affects the lipase catalytic properties: a monolayer study.

    Directory of Open Access Journals (Sweden)

    Madiha Bou Ali

    Full Text Available Recombinant DNA methods are being widely used to express proteins in both prokaryotic and eukaryotic cells for both fundamental and applied research purposes. Expressed protein must be well characterized to be sure that it retains the same properties as the native one, especially when expressed protein will be used in the pharmaceutical field. In this aim, interfacial and kinetic properties of native, untagged recombinant and tagged recombinant forms of a pancreatic lipase were compared using the monomolecular film technique. Turkey pancreatic lipase (TPL was chosen as model. A kinetic study on the dependence of the stereoselectivity of these three forms on the surface pressure was performed using three dicaprin isomers spread in the form of monomolecular films at the air-water interface. The heterologous expression and the N-His-tag extension were found to modify the pressure preference and decrease the catalytic hydrolysis rate of three dicaprin isomers. Besides, the heterologous expression was found to change the TPL regioselectivity without affecting its stereospecificity contrary to the N-tag extension which retained that regioselectivity and changed the stereospecificity at high surface pressures. The study of parameters, termed Recombinant expression Effects on Catalysis (REC, N-Tag Effects on Catalysis (TEC, and N-Tag and Recombinant expression Effects on Catalysis (TREC showed that the heterologous expression effects on the catalytic properties of the TPL were more deleterious than the presence of an N-terminal tag extension.

  15. Experimental Investigation Of Microbially Induced Corrosion Of Test Samples And Effect Of Self-assembled Hydrophobic Monolayers. Exposure Of Test Samples To Continuous Microbial Cultures, Chemical Analysis, And Biochemical Studies

    CERN Document Server

    Laurinavichius, K S

    1998-01-01

    Experimental Investigation Of Microbially Induced Corrosion Of Test Samples And Effect Of Self-assembled Hydrophobic Monolayers. Exposure Of Test Samples To Continuous Microbial Cultures, Chemical Analysis, And Biochemical Studies

  16. Scanning tunneling microscopy studies of organic monolayers adsorbed on the rhodium(111) crystal surface

    Energy Technology Data Exchange (ETDEWEB)

    Cernota, Paul D.

    1999-08-01

    Scanning Tunneling Microscopy studies were carried out on ordered overlayers on the (111) surface of rhodium. These adsorbates include carbon monoxide (CO), cyclohexane, cyclohexene, 1,4-cyclohexadiene, para-xylene, and meta-xylene. Coadsorbate systems included: CO with ethylidyne, CO with para- and meta-xylene, and para-xylene with meta-xylene. In the case of CO, the structure of the low coverage (2x2) overlayer has been observed. The symmetry of the unit cell in this layer suggests that the CO is adsorbed in the 3-fold hollow sites. There were also two higher coverage surface structures with ({radical}7x{radical}7) unit cells. One of these is composed of trimers of CO and has three CO molecules in each unit cell. The other structure has an additional CO molecule, making a total of four. This extra CO sits on a top site.

  17. Energetics, diffusion, and magnetic properties of cobalt atom in a monolayer graphene: An ab initio study

    International Nuclear Information System (INIS)

    We use ab initio methods to study the binding, diffusion, and magnetic properties of cobalt atom embedded in graphene vacancies. We investigate the diffusion of Co-monovacancy (Co-MV) and Co-divacancy (Co-DV) defect complexes, and determine the minimum energy path (MEP), as well as the activation energy barrier of migration. We obtained similar activation energy barriers, of ∼5.8 eV, for Co-MV and Co-DV diffusion, respectively. Our calculations also suggest that, at electron–irradiation energy of 200 keV as used in a related experiment, the maximum energy transfer to the Co atom, of approximately 9.0 eV is sufficiently high to break metal-carbon bonding. The incident electron energy is also high enough to displace graphene's carbon atoms from their lattice positions. The breaking of metal-carbon bonding and the displacement of graphene atoms may act to facilitate the migration of Co. We conclude therefore that the detrapping and diffusion of cobalt as observed experimentally is likely to be radiation-induced, similar to what has been observed for Au and Fe in electron-irradiated graphene. Furthermore, we show that Co migration in graphene is such that its magnetic moment varies along the diffusion path. The magnetic moment of Co is consistently higher in Co-DV diffusion when compared to that of Co-MV diffusion

  18. Oxidative dehydrogenation of light alkanes

    Energy Technology Data Exchange (ETDEWEB)

    Meiswinkel, A.; Thaller, C.; Bock, M.; Alvarado, L. [Linde AG, Pullach (Germany); Hartmann, D.; Veen, A.C. van; Lercher, J.A. [Technische Univ. Muenchen (Germany)

    2012-07-01

    The demand of light olefins increases steadily and the current steam cracking production is highly energy demanding. This motivates the development of alternative production processes like the oxidative dehydrogenation (ODH) of light alkanes operating at comparably low temperatures. Multi-component oxides are reported to show excellent catalytic performance in the ODH. Especially, MoVTeNbO oxides present high activity and selectivity in ODH of ethane. Synthesis of MoVTeNb oxides was done by a hydrothermal method. Qualitative and quantitative phase analysis were performed by X-ray diffraction and Rietveld refinement. Surface compositions were determined by Low energy ion scattering (LEIS). Catalytic tests were carried out in a fixed bed plug flow reactor using ethane and oxygen diluted in helium, as gaseous feed. Based on laboratory investigations a first upscale to a bench-top-pilot unit was performed in order to evaluate the large scale and long term feasibility of the process under technically relevant conditions. MoVTeNb oxides show high activity combined with excellent selectivity in the ODH of ethane to ethylene (S > 95% at X < 40%). Phase analysis reveals the presence of M1, M2 and amorphous phases. Literature reports the crystalline M1 phase as essential for the performance. Indeed, the crystalline M1 phase impacts on the activity via exposing V on the surface being apparently vital to achieve an active material. A correlation of the apparent activation energy with the surface vanadium composition of the catalysts is noticed, however, surprisingly with no major impact on the ethene selectivity. As this material was identified as most promising for a technical application a scale up from less than 1g to 50g of catalyst was performed in a bench-top-pilot unit. The reaction has a significant adiabatic temperature rise and the handling of the reaction heat is a major challenge for process engineering. Furthermore different diluent media such as Helium, Nitrogen

  19. Enzymes and Genes Involved in Aerobic Alkane Degradation

    Directory of Open Access Journals (Sweden)

    ZongzeShao

    2013-05-01

    Full Text Available Alkanes are major constituents of crude oil. They are also present at low concentrations in diverse non-contaminated because many living organisms produce them as chemo-attractants or as protecting agents against water loss. Alkane degradation is a widespread phenomenon in nature. The numerous microorganisms, both prokaryotic and eukaryotic, capable of utilizing alkanes as a carbon and energy source, have been isolated and characterized. This review summarizes the current knowledge of how bacteria metabolize alkanes aerobically, with a particular emphasis on the oxidation of long-chain alkanes, including factors that are responsible for chemotaxis to alkanes , transport across cell membrane of alkanes , the regulation of alkane degradation gene and initial oxidation.

  20. Study of the ability of self-assembled N-vinylcarbazole monolayers to protect copper against corrosion

    Directory of Open Access Journals (Sweden)

    NAI-XING WANG

    2002-10-01

    Full Text Available N-Vinylcarbazole (NVC monolayers were self-assembled on copper surfaces. The electrochemical properties of the copper surfaces modified by NVC self-assembled monolayers (SAMs were investigated using polarization and electrochemical impedance spectroscopic (EIS methods. The polarization measurements indicated that the NVC SAMs could reduce the rates of the anodic and cathodic reaction on the surface of copper electrodes in 0.5 mol dm-3 NaCl solution. The EIS results showed the NVC formed a closely packed film that was able to inhibit copper corrosion. X-Ray photoelectron spectroscopy (XPS analysis of the copper samples and atomic adsorption analysis of the solution showed that the copper surfaces were covered by NVC SAMs, and the adsorption of NVC on the copper surfaces was accompanied with dissolution of Cu into the solution.

  1. Transport mechanisms and wetting dynamics in molecularly thin films of long-chain alkanes at solid/vapour interface : relation to the solid-liquid phase transition

    OpenAIRE

    Lazar, Paul

    2005-01-01

    Wetting and phase transitions play a very important role our daily life. Molecularly thin films of long-chain alkanes at solid/vapour interfaces (e.g. C30H62 on silicon wafers) are very good model systems for studying the relation between wetting behaviour and (bulk) phase transitions. Immediately above the bulk melting temperature the alkanes wet partially the surface (drops). In this temperature range the substrate surface is covered with a molecularly thin ordered, solid-like alkane film (...

  2. Molecular organization of antifungal antibiotic amphotericin B in lipid monolayers studied by means of Fluorescence Lifetime Imaging Microscopy

    OpenAIRE

    Gruszecki, Wieslaw I.; Luchowski, Rafał; Gagoś, Mariusz; Arczewska, Marta; Sarkar, Pabak; Hereć, Monika; Myśliwa-Kurdziel, Beata; Strzałka, Kazimierz; Gryczynski, Ignacy; Gryczynski, Zygmunt

    2009-01-01

    Abstract Amphotericin B (AmB) is a life-saving polyene antibiotic used to treat deep-seated mycotic infections. Both the mode of therapeutic action as well as toxic side effects are directly dependent on molecular organization of the drug. Binding of AmB to lipid monolayers formed with dipalmitoylphosphatidylcholine, pure and containing 40 mol% cholesterol or ergosterol, the sterols of human and fungi respectively, has been examined by means of Fluorescence Lifetime Imaging Microsc...

  3. A Study of the Modification of the Gold Electrode Surface with a Calix[4]arene Self-Assembled Monolayer

    Czech Academy of Sciences Publication Activity Database

    Šustrová, Barbora; Štulík, Karel; Mareček, Vladimír; Janda, Pavel

    2010-01-01

    Roč. 22, 17-18 (2010), s. 2051-2057. ISSN 1040-0397. [International Conference on Modern Electroanalytical Methods. Prague, 09.12.2009-14.12.2009] R&D Projects: GA AV ČR IAA400400806 Institutional research plan: CEZ:AV0Z40400503 Keywords : Calix[4]arene * Self-assembled monolayer (SAM) * ionophores Subject RIV: CG - Electrochemistry Impact factor: 2.721, year: 2010

  4. Scanning probe microscopies for the creation and characterization of interfacial architectures: Studies of alkyl thiolate monolayers at gold

    Energy Technology Data Exchange (ETDEWEB)

    Green, J.

    1997-01-10

    Scanning probe microscopy (SPM) offers access to the structural and material properties of interfaces, and when combined with macroscopic characterization techniques results in a powerful interfacial development tool. However, the relative infancy of SPM techniques has dictated that initial investigations concentrate on model interfacial systems as benchmarks for testing the control and characterization capabilities of SPM. One such family of model interfacial systems results from the spontaneous adsorption of alkyl thiols to gold. This dissertation examines the application of SPM to the investigation of the interfacial properties of these alkyl thiolate monolayers. Structural investigations result in a proposed explanation for counterintuitive correlations between substrate roughness and heterogeneous electron transfer barrier properties. Frictional measurements are used for characterization of the surface free energy of a series of end-group functionalized monolayers, as well as for the material properties of monolayers composed of varying chain length alkyl thiols. Additional investigations used these characterization techniques to monitor the real-time evolution of chemical and electrochemical surface reactions. The results of these investigations demonstrates the value of SPM technology to the compositional mapping of surfaces, elucidation of interfacial defects, creation of molecularly sized chemically heterogeneous architectures, as well as to the monitoring of surface reactions. However, it is the future which will demonstrate the usefulness of SPM technology to the advancement of science and technology.

  5. 40 CFR 721.10163 - Chloro fluoro alkane (generic).

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Chloro fluoro alkane (generic). 721... Substances § 721.10163 Chloro fluoro alkane (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as chloro fluoro alkane (PMN...

  6. 40 CFR 721.536 - Halogenated phenyl alkane.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Halogenated phenyl alkane. 721.536... Substances § 721.536 Halogenated phenyl alkane. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halogenated phenyl alkane (PMN P-89-867)...

  7. Diamondoid monolayers as electron emitters

    Science.gov (United States)

    Yang, Wanli; Fabbri, Jason D.; Melosh, Nicholas A.; Hussain, Zahid; Shen, Zhi-Xun

    2012-04-10

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  8. Alkane dehydrogenation over supported chromium oxide catalysts

    NARCIS (Netherlands)

    Weckhuysen, B.M.; Schoonheydt, R.A.

    1999-01-01

    The dehydrogenation of alkanes over supported chromium oxide catalysts in the absence of oxygen is of high interest for the industrial production of propene and isobutene. In this review, a critical overview is given of the current knowledge nowadays available about chromium-based dehydrogenation ca

  9. Liszt och Alkan: Den virtuosa pianoetyden : Övningsstycke eller muterat monster?

    OpenAIRE

    Rådén, Anders

    1999-01-01

    Anders Rådén: Liszt & Alkan: the virtuoso piano study – practice study or monstrous mutation? Uppsala: Musikvetenskap, 1998. C-uppsats (60 p). The purpose of this essay is to analyse a selection of studies by Franz Liszt (1811-1886) and Charles- Valentin Alkan (1813-1888). Can they be definedas practice studies, or are they reshaped in such a manner, as to establish a larger form reminiscent of the concert study? First of all, typical study characteristics of this time period are determin...

  10. Self-assembled monolayers of radical molecules physisorbed on HOPG(0 0 0 1) substrate studied by scanning tunnelling microscopy and electron paramagnetic resonance techniques

    International Nuclear Information System (INIS)

    In this paper, we present a combined STM and EPR study on the adsorption and self-organization of monolayers formed from 2-(14-Carboxytetradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxy (16DS) and 4',4'-Dimethylspiro(5α-cholestane-3,2'-oxazolidin)-3'-yloxy (CSL) adsorbed on a highly oriented pyrolitic graphite HOPG(0 0 0 1) substrate. Both 16DS and CSL molecules are persistent free radicals containing a paramagnetic doxyl group. The STM measurements of 16DS on HOPG(0 0 0 1) were performed at the liquid-solid interface while the studies of CSL on HOPG(0 0 0 1) were carried out under ultrahigh vacuum conditions. It was found that the 16DS molecules on the HOPG(0 0 0 1) surface form a highly-ordered monolayer with a domain structure. The high-resolution STM images show structural details of 16DS molecules on HOPG(0 0 0 1) revealing the paramagnetic doxyl group. In contrast, CSL molecules on HOPG(0 0 0 1) form a well-ordered monolayer without domain structure. The EPR results indicate that both compounds deposited on HOPG(0 0 0 1) substrate are not reduced and retain their paramagnetic character. We believe that the molecular systems described can be used in single spin detection experiments using an electron spin noise-scanning tunnelling microscopy (ESN-STM) technique. In particular, the possibility of obtaining contrast spin signals from the paramagnetic and diamagnetic parts of molecules increases the significance of our results.

  11. Use of Self-Assembling Monolayers to Control Interface Bonding in a Model Study of Interfacial Fracture

    Energy Technology Data Exchange (ETDEWEB)

    Kent, M.S.; Matheson, A.; Reedy, E.D.; Yim, H.

    1999-03-05

    The relationships between the extent of interfacial bonding, energy dissipation mechanisms, and fracture toughness in a glassy adhesive/inorganic solid joint are not well understood. We address this subject with a model system involving an epoxy adhesive on a polished silicon wafer containing its native oxide. The extent of interfacial bonding, and the wetting behavior of the epoxy, is varied continuously using self-assembling monolayers (SAMs) of octadecyltrichlorosilane (ODTS). The epoxy interacts strongly with the bare silicon oxide surface, but forms only a very weak interface with the methylated tails of the ODTS monolayer. We examine the fracture behavior of such joints as a function of the coverage of ODTS in the napkin-ring geometry. Various characterization methods are applied to the ODTS-coated surface before application of the epoxy, and to both surfaces after fracture. The fracture data are discussed with respect to the wetting of the liquid epoxy on the ODTS-coated substrates, the locus of failure, and the energy dissipation mechanisms. Our goal is to understand how energy is dissipated during fracture as a function of interface strength.

  12. A comparative study of transport properties of monolayer graphene and AlGaN-GaN heterostructure

    International Nuclear Information System (INIS)

    The electronic transport properties of monolayer graphene are presented with an Ensemble Monte Carlo method where a rejection technique is used to account for the occupancy of the final states after scattering. Acoustic and optic phonon scatterings are considered for intrinsic graphene and in addition, ionized impurity and surface roughness scatterings are considered for the case of dirty graphene. The effect of screening is considered in the ionized impurity scattering of electrons. The time dependence of drift velocity of carriers is obtained where overshoot and undershoot effects are observed for certain values of applied field and material parameters for intrinsic graphene. The field dependence of drift velocity of carriers showed negative differential resistance and disappeared as acoustic scattering becomes dominant for intrinsic graphene. The variation of electron mobility with temperature is calculated for intrinsic (suspended) and dirty monolayer graphene sheets separately and they are compared. These are also compared with the mobility of two dimensional electrons at an AlGaN/GaN heterostructure. It is observed that interface roughness may become very effective in limiting the mobility of electrons in graphene

  13. Kinetic studies of attachment and re-orientation of octyltriethoxysilane for formation of self-assembled monolayer on a silica substrate.

    Science.gov (United States)

    Hasan, Abshar; Pandey, Lalit M

    2016-11-01

    The present study deals with kinetic studies of the chemical modification for synthesizing a hydrophobic silica surface. Surface silanization (modification) via formation of Self-Assembled Monolayer (SAM) using a short chain triethoxyoctylsilane (TEOS) was carried out under inert atmosphere at room temperature. Fourier transmission infrared (FTIR) spectroscopy, water contact angle (WCA) and atomic force microscopy (AFM) were employed to investigate surface modification. FTIR analysis in the range from 900-1200cm(-1) and 2850-3000cm(-1) confirmed surface modification and re-orientation of the attached molecules. Kinetic studies of TEOS SAM formation were fitted by Exponential Association function. Kinetic fitting of FTIR data in the range from 900-1200cm(-1) revealed a very fast attachment of TEOS molecules resulting in total surface coverage within 16min whereas re-orientation rate was slow and continued till 512min. Further, change in orientation from lying-down to standing-up state was supported by contact angle analysis. AFM images initially showed small islands of ~20nm, which in-fill with time indicating formation of a smooth monolayer. Our findings indicate that formation of octyl SAM is fast process and completes within 8.5h in contrary to reported 24h in conventional SAM formation protocols. The kinetic fitting data can be explored to design a nanopatterned surface for a specific application. PMID:27524037

  14. Monolayer MXenes: promising half-metals and spin gapless semiconductors

    Science.gov (United States)

    Gao, Guoying; Ding, Guangqian; Li, Jie; Yao, Kailun; Wu, Menghao; Qian, Meichun

    2016-04-01

    Half-metals and spin gapless semiconductors are promising candidates for spintronic applications due to the complete (100%) spin polarization of electrons around the Fermi level. Based on recent experimental and theoretical findings of graphene-like monolayer transition metal carbides and nitrides (also known as MXenes), we demonstrate using first-principles calculations that monolayers Ti2C and Ti2N exhibit nearly half-metallic ferromagnetism with the magnetic moments of 1.91 and 1.00μB per formula unit, respectively, while monolayer V2C is a metal with unstable antiferromagnetism, and monolayer V2N is a nonmagnetic metal. Interestingly, under a biaxial strain, there is a phase transition from a nearly half-metal to truly half-metal, spin gapless semiconductor, and metal for monolayer Ti2C. Monolayer Ti2N is still a nearly half-metal under a suitable biaxial strain. Large magnetic moments can be induced by the biaxial tensile and compressive strains for monolayer V2C and V2N, respectively. We also show that the structures of these four monolayer MXenes are stable according to the calculated formation energy and phonon spectrum. Our investigations suggest that, unlike monolayer graphene, monolayer MXenes Ti2C and Ti2N without vacancy, doping or external electric field exhibit intrinsic magnetism, especially the half-metallic ferromagnetism and spin gapless semiconductivity, which will stimulate further studies on possible spintronic applications for new two-dimensional materials of MXenes.

  15. The synergetic effect of starch and alpha amylase on the biodegradation of n-alkanes.

    Science.gov (United States)

    Karimi, M; Biria, D

    2016-06-01

    The impact of adding soluble starch on biodegradation of n-alkanes (C10-C14) by Bacillus subtilis TB1 was investigated. Gas chromatography was employed to measure the residual hydrocarbons in the system. It was observed that the efficiency of biodegradation improved with the presence of starch and the obtained residual hydrocarbons in the system were 53% less than the samples without starch. The produced bacterial enzymes were studied through electrophoresis and reverse zymography for explaining the observations. The results indicated that the produced amylase by the bacteria can degrade hydrocarbons and the same was obtained by the application of a commercial alpha amylase sample. In addition, in silico docking of alpha-amylase with n-alkanes with different molecular weights was studied by Molegro virtual docker which showed high negative binding energies and further substantiated the experimental observations. Overall, the findings confirmed the catalytic effect of alpha amylase on n-alkanes degradation. PMID:26971168

  16. RNAi silencing of a cytochrome P450 monooxygenase disrupts the ability of a filamentous fungus, Graphium sp. to grow on short-chain gaseous alkanes and ethers

    Science.gov (United States)

    Graphium sp. (ATCC 58400), a filamentous fungus, is one of the few eukaryotes that grows on short-chain alkanes and ethers. In this study, we investigated the genetic underpinnings that enable this fungus to catalyze the first step in the alkane and ether oxidation pathway. A gene, CYP52L1, was iden...

  17. Fe monolayers on InAs(0 0 1): An in situ study of surface, interface and volume magnetic anisotropy

    International Nuclear Information System (INIS)

    The magnetic anisotropy of epitaxial Fe films with thicknesses in the range of 2-142 monolayers (ML) grown on {4x2} reconstructed InAs(0 0 1) was investigated by in situ ferromagnetic resonance. The easy magnetization direction was found to be parallel to the [11-bar 0]-direction for Fe films below 4 ML, while it rotates by 450 toward the [100]-direction. It is observed that both surface-interface and volume contribution to the perpendicular anisotropy favor an easy axis perpendicular to the film plane. The cubic surface-interface anisotropy is relatively large with easy axes along -directions in contrast to the volume contribution which favors easy axes along the -directions. The volume contribution is found to be larger than the Fe bulk cubic anisotropy. A thickness independent uniaxial anisotropy has been found in films with a thickness of 2 up to 142 ML.

  18. Large perpendicular magnetic anisotropy of single Co atom on MgO monolayer: A first-principles study

    International Nuclear Information System (INIS)

    Realizing the magnetic bit with a single atom is the ultimate goal for magnetic storage. Based on density functional theory, the magnetic anisotropy (MA) of single Co atom on MgO monolayer has been investigated. Results show that this two dimensional system possesses a large perpendicular MA, about 5.8 meV per Co atom. Besides, there exists remarkable unquenched orbital moments for different magnetization directions, which can be attributed to the reduction of coordination number in two dimensional system and is responsible for the enhanced MA. The Bloch pseudo-wavefunction and band structure of Co d-orbitals have been calculated to elucidate the origin of the perpendicular MA

  19. Studies of the epitaxial monolayer NbSe2 by ultra-low-temperature scanning tunnelling microscope

    Science.gov (United States)

    Ji, Shuai-Hua

    Monolayer NbSe2 has been successfully synthesized by molecular beam epitaxy on the graphitized SiC(0001) surface. Wide substrate temperature window from 200°C to 650°C for the epitaxial growth has been observed. The polycrystalline nature of the epitaxial sheet, which is caused by the weak Van der Waals interaction with substrate, has been evidenced by reflection high-energy electron diffraction and locally by scanning tunnelling microscope. Under the high temperature growth condition, grain size could reach as large as hundreds of nanometers. The shape of grain boundary is strongly depended on the misaligned angle between adjacent grains. Mainly, three type grain boundaries have been identified at the atomic scale by the local scanning probe. The BCS-like superconducting gap and the spatial fluctuation of order parameter have been revealed by ultra-low temperature scanning tunnelling microscope in the sub-Kelvin range.

  20. Zitterbewegung in monolayer silicene in a magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Romera, E. [Departamento de Física Atómica, Molecular y Nuclear and Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Roldán, J.B. [Departamento de Electrónica y Tecnología de Computadores and CITIC, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Santos, F. de los [Departamento de Electromagnetismo y Física de la Materia, and Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain)

    2014-07-04

    We study the Zitterbewegung in monolayer silicene under a perpendicular magnetic field. Using an effective Hamiltonian, we have investigated the autocorrelation function and the density currents in this material. Moreover, we have analyzed other types of periodicities of the system (classical and revival times). Finally, the above results are compared with their counterparts in two other monolayer materials subject to a magnetic field: graphene and MoS{sub 2}. - Highlights: • We study Zitterbewegung in monolayer silicene in a magnetic field. • We have analyzed other types of periodicities in silicene. • The above results are compared with other monolayer materials (graphene and MoS{sub 2})

  1. A theoretical and experimental XAS study of monolayer dispersive supported CuO/γ-Al2O3 catalysts

    International Nuclear Information System (INIS)

    The local structures of supported CuO/γ-Al2O3 monolayer dispersive catalysts with different CuO loadings have been investigated by EXAFS and multiple scattering XANES simulations. The EXAFS results show that the first nearest neighbors around the Cu atoms in the CuO/γ-Al2O3 catalysts are similar to that of the polycrystalline CuO powder, which is independent of the CuO loadings. Moreover, the Cu K-XANES FEFF8 calculations for CuO reveal that the monolayer-dispersed CuO species are of small distorted (CuO4) mn+ clusters, which is mainly composed of a distorted CuO6 octahedron incorporated in the surface octahedral vacant sites of the γ-Al2O3 support. We consider that the CuO species for the CuO/γ-Al2O3 catalysts with loadings of 0.4 and 0.8 mmol/100 m2 are distorted (CuO4) mn+ clusters composed mainly of a distorted CuO6 octahedron incorporated in the surface octahedral vacant sites of the γ-Al2O3 support after calcinations at high temperature in air for a few hours. On the contrary, for the CuO/γ-Al2O3 with loading of 1.2 mmol/100 m2, the local structure of Cu atoms in CuO/γ-Al2O3 is similar to that of polycrystalline CuO powder

  2. Studies of the surface structures of molecular crystals and of adsorbed molecular monolayers on the (111) crystal faces of platinum and silver by low-energy electron diffraction

    International Nuclear Information System (INIS)

    The structures of molecular crystal surfaces were investigated for the first time by the use of low-energy electron diffraction (LEED). The experimental results from a variety of molecular crystals were examined and compared as a first step towards understanding the properties of these surfaces on a microscopic level. The method of sample preparation employed, vapor deposition onto metal single-crystal substrates at low temperatures in ultrahigh vacuum, allowed concurrent study of the structures of adsorbed monolayers on metal surfaces and of the growth processes of molecular films on metal substrates. The systems investigated were ice, ammonia, naphthalene, benzene, the n-paraffins (C3 to C8), cyclohexane, trioxane, acetic acid, propionic acid, methanol, and methylamine adsorbed and condensed on both Pt(111) and Ag(111) surfaces. Electron-beam-induced damage of the molecular surfaces was observed after electron exposures of 10-4 A sec cm-2 at 20 eV. Aromatic molecular crystal samples were more resistant to damage than samples of saturated molecules. The quality and orientation of the grown molecular crystal films were influenced by substrate preparation and growth conditions. Forty ordered monolayer structures were observed. 110 figures, 22 tables, 162 references

  3. Effects of Odd–Even Side Chain Length of Alkyl-Substituted Diphenylbithiophenes on First Monolayer Thin Film Packing Structure

    KAUST Repository

    Akkerman, Hylke B.

    2013-07-31

    Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5′bis(4-alkylphenyl)-2,2′-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified SiO2 surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd-even effect in the strength of the intermolecular electronic coupling. © 2013 American Chemical Society.

  4. Nucleation, growth and habit modification of n-alkanes and homologous mixtures in the absence and presence of flow improving additives

    CERN Document Server

    Taggart, A M

    1996-01-01

    A detailed study has been performed on the nucleation, growth and habit modification of n-alkanes and homologous mixtures in the absence and presence of flow improving additives in an attempt to gain a clearer appreciation of the interaction mechanisms behind wax / additive crystallisation. Kinetic and structural assessment of melt phase n-alkanes illustrate the different crystallographic forms present within the homologous series. Studies demonstrate the alternating behaviour of the even and odd numbered homologues which converges as a function of increasing molecular weight. Greater crystal lattice stabilities were found for those n-alkanes which have an even carbon number and which crystallise into the triclinic crystal structure. Solid state phase behaviour of the n-alkanes was found to vary depending on the number and parity of n. Nucleation kinetic studies of n-alkanes and homologous mixtures from model diesel fuel solvents (dodecane, m-xylene, decalin, pristane and a dewaxed fuel) are assessed using tu...

  5. Positronium in solid phases of n-alkane binary mixtures

    International Nuclear Information System (INIS)

    Highlights: • Rotator phase in even alkanes CnH2n+2 with n ⩽ 20 appears in mixed samples only. • Interlamellar gap width is the same for shorter chain alkane concentration x and 1 − x. • Excess electron trapping diminishes with broadening of alkane chain distribution Δn. - Abstract: Binary mixtures of even-numbered normal alkanes CnH2n+2 and Cn+2H2n+6 with n ⩽ 18 were investigated by positron annihilation spectroscopy. Formation of the rotator phase was observed in mixed structures, while no such a phase in neat alkanes in this range of n was found. Phase diagrams for n = 18 and n = 16 are very similar to the diagrams for binary mixtures of odd-numbered alkanes. The effect of positronium formation with trapped excess electrons weakens with decreasing n, at low n values the time constant of Ps rise contains the component much shorter than 1 h

  6. Effect of molecular packing on radiolytic processes of n-alkanes

    International Nuclear Information System (INIS)

    Complete text of publication follows. Effects of packing arrangements on both ionic (viz., the proton transfer from alkane radical cations to alkane molecules) and radical (viz., intermolecular radical site transfer) are being discussed. Structurally determined acceptor site selectivity in the proton transfer from alkane radical cations to alkane molecules, i.e. acceptor site selectivity resulting from donor site selectivity in combination with accessibility differences due to structural factors has been studied in γ-irradiated heptane/octane/1-chlorohexane and heptane/decane/1-chloroheptane mixed crystals. In such crystals, heptane radical cations are in the extended all-trans conformation and proton donation (from ground-state cations) takes place selectively from planar chain-end C-H bonds in these (matrix) cations to secondary C-H bonds in the alkane solute molecules. In heptane/octane/1-chlorohexane crystals, penultimate C-H bonds in octane, which as deduced from studies on γ-irradiated CCl3F/alkanes have the greatest propensity to act as proton acceptor, are also structurally very much favored over interior C-H bonds as proton acceptor resulting in very high selectivity with respect to this site. In heptane/decane/1-chloroheptane crystals accessibility factors of secondary C-H bonds in decane to planar chain-end C-H bonds in heptane radical cations are in the order C2 3 > C4 > C5 and protonation occurs in the order C2 > C3 > C4 > C5, providing evidence for both intrinsic (preference for penultimate position) and structurally-determined acceptor site selectivity. With respect to radical transformation by intermolecular radical site transfer, the accessibility of secondary C-H bonds to primary radical sites in γ-irradiated neat n-alkanes depends critically on their crystalline structure. On the basis of this information, EPR studies on the nature of undecyl radicals in γ-irradiated CCl3F/undecane as a function of undecane concentration have allowed us to

  7. n-Alkane biosynthetic hydrogen isotope fractionation is not constant throughout the growing season in the riparian tree Salix viminalis

    Science.gov (United States)

    Newberry, Sarah L.; Kahmen, Ansgar; Dennis, Paul; Grant, Alastair

    2015-09-01

    Compound-specific δ2H values of leaf wax n-alkanes have emerged as a potentially powerful paleohydrological proxy. Research suggests terrestrial plant n-alkane δ2H values are strongly correlated with meteoric water δ2H values, and may provide information on temperature, relative humidity, evaporation, and precipitation. This is based upon several assumptions, including that biosynthetic fractionation of n-alkanes during synthesis is constant within a single species. Here we present a multi-isotope study of the n-alkanes of riparian Salix viminalis growing in Norwich, UK. We measured n-alkane δ2H, leaf water δ2H, xylem water δ2H, and bulk foliar δ13C and evaluated the variability of n-alkane δ2H values and net biosynthetic fractionation (εlw-wax) over a whole growing season. S. viminalis n-alkane δ2H values decreased by 40‰ between the start of the growing season in April and the time when they stabilized in July. Variation in leaf and xylem water δ2H did not explain this variability. εlw-wax varied from -116‰ during leaf expansion in April to -156‰ during the stable phase. This suggests that differential biosynthetic fractionation was responsible for the strong seasonal trends in S. viminalis n-alkane δ2H values. We suggest that variability in εlw-wax is driven by seasonal differences in the carbohydrate source and thus the NADPH used in n-alkane biosynthesis, with stored carbohydrates utilized during spring and recent occurring growing season assimilates used later in the season. This is further supported by bulk foliar δ13C values, which are 13C-enriched during the period of leaf flush, relative to the end of the growing season. Our results challenge the assumption that biosynthetic fractionation is constant for a given species, and suggest that 2H-enriched stored assimilates are an important source for n-alkane biosynthesis early in the growing season. These findings have implications for the interpretation of sedimentary n-alkanes and call

  8. Phase-Specific Diffusivity of DPPG Monolayers

    Science.gov (United States)

    Dewitt, Joel; Thapa, Prem; Flanders, Bret

    2004-03-01

    The primary role of lung surfactant is to reduce the alveolar surface tension during exhalation in a reversible manner. Failure to do so results in respiratory distress syndrome. Model lung surfactants provide simplified systems for studying the mechanisms that underlie this essential role of alveolar surfactant. Dipalmitoyl-phosphatidylglycerol (DPPG) monolayers exhibit reversible folding when compressed to a critical surface tension. This process may exemplify how the compression-expansion cycle attains reversibility and, thus, requires penetrating study. The buckling theory for reversible collapse provides a promising though untested description of this process, but poor knowledge of domain boundary widths in DPPG monolayers impedes the evaluation of this theory as a model for the observed behavior. In turn, the measurement of the domain boundary widths requires knowledge of the phase-specific viscosities of the monolayer. In this study, multi-particle tracking has been used to determine the phase-specific diffusion coefficients of polystyrene spheres embedded in DPPG monolayers. By invoking a Stokes-Einstein relationship that is appropriate for spheres diffusing in a viscous surfactant, the phase specific viscosities of the monolayers have been estimated. The rationale for this work is that this knowledge will promote the quantitative evaluation of buckling as a model for reversible folding and, thus, promote growth in understanding of the folding mechanism in model lung surfactants.

  9. Ordering of alkane isomers by means of connectivity indices

    Directory of Open Access Journals (Sweden)

    ANKA NEDIC

    2002-02-01

    Full Text Available The connectivity index of an organic molecule whose molecular graph is G is defined as C(l = S(dudu1, where du is the degree of the vertex u in G, where the summation goes over all pairs of adjacent vertices of G and where l is a pertinently chosen exponent. The usual value of l is –1/2, in which case c = C(–1/2 is referred to as the Randic index. The ordering of isomeric alkanes according to c follows the extent of branching of the carbon-atom skeleton. We now study the ordering of the constitutional isomers of alkanes with 6 through 10 carbon atoms with respect to C( l for various values of the parameter l. This ordering significantly depends on l. The difference between the orderings with respect to c and with respect to C( l is measured by a function D and the l-dependence of D was established.

  10. Identification of Novel Genes Involved in Long-Chain n-Alkane Degradation by Acinetobacter sp. Strain DSM 17874▿

    Science.gov (United States)

    Throne-Holst, Mimmi; Wentzel, Alexander; Ellingsen, Trond E.; Kotlar, Hans-Kristian; Zotchev, Sergey B.

    2007-01-01

    Acinetobacter sp. strain DSM 17874 is capable of utilizing n-alkanes with chain lengths ranging from that of decane (C10H22) to that of tetracontane (C40H82) as a sole carbon source. Two genes encoding AlkB-type alkane hydroxylase homologues, designated alkMa and alkMb, have been shown to be involved in the degradation of n-alkanes with chain lengths of from 10 to 20 C atoms in this strain. Here, we describe a novel high-throughput screening method and the screening of a transposon mutant library to identify genes involved in the degradation of n-alkanes with C chain lengths longer than 20, which are solid at 30°C, the optimal growth temperature for Acinetobacter sp. strain DSM 17874. A library consisting of approximately 6,800 Acinetobacter sp. strain DSM 17874 transposon mutants was constructed and screened for mutants unable to grow on dotriacontane (C32H66) while simultaneously showing wild-type growth characteristics on shorter-chain n-alkanes. For 23 such mutants isolated, the genes inactivated by transposon insertion were identified. Targeted inactivation and complementation studies of one of these genes, designated almA and encoding a putative flavin-binding monooxygenase, confirmed its involvement in the strain's metabolism of long-chain n-alkanes. To our knowledge, almA represents the first cloned gene shown to be involved in the bacterial degradation of long-chain n-alkanes of 32 C's and longer. Genes encoding AlmA homologues were also identified in other long-chain n-alkane-degrading Acinetobacter strains. PMID:17400787

  11. Study of the selective abstration reaction of the hydrogen atom in the radiolysis and photolysis of alkane mixture at 77 K

    International Nuclear Information System (INIS)

    The occurence of the selective abstraction reaction of the solute hydrogen atom by hydrogen atom produced during radiolysis or photolysis of the systems such as neopentane/cyclo-hexane/HI, neopentane/2,3 dimethylbutane, n-pentane/HI/cyclo-hexane and cyclo-hexane/HI/n-pentane, at 77 K is studied. Experiments have been undertaken on the kinetics nature of the active species, the H atom, during radiolysis and photolysis of the neopentane/cyclo-hexane/HI system at 77 K, presenting competitive reactions. Studies have also been made on the occurrence of the selective abstraction reaction in inverted systems, in which the concentrations of the components of a system are so much altered that the solute becomes the solvent and vice-versa, in the other system. By means of photolysis at 77 K, it has been observed that for the two systems constitued by the cyclo-hexane and n-pentane the selective abstraction reaction occurs. However, for radiolysis of that same two systems it has been observed that only the hydrogen atom abstraction reaction corresponding to the solvent occurs. (Author)

  12. Nonradiative Electron-Hole Recombination Rate Is Greatly Reduced by Defects in Monolayer Black Phosphorus: Ab Initio Time Domain Study.

    Science.gov (United States)

    Long, Run; Fang, Weihai; Akimov, Alexey V

    2016-02-18

    We report ab initio time-domain simulations of nonradiative electron-hole recombination and electronic dephasing in ideal and defect-containing monolayer black phosphorus (MBP). Our calculations predict that the presence of phosphorus divacancy in MBP (MBP-DV) substantially reduces the nonradiative recombination rate, with time scales on the order of 1.57 ns. The luminescence line width in ideal MBP of 150 meV is 2.5 times larger than MBP-DV at room temperature, and is in excellent agreement with experiment. We find that the electron-hole recombination in ideal MBP is driven by the 450 cm(-1) vibrational mode, whereas the recombination in the MBP-DV system is driven by a broad range of vibrational modes. The reduced electron-phonon coupling and increased bandgap in MBP-DV rationalize slower recombination in this material, suggesting that electron-phonon energy losses in MBP can be minimized by creating suitable defects in semiconductor device material. PMID:26821943

  13. Black phosphorene/monolayer transition-metal dichalcogenides as two dimensional van der Waals heterostructures: a first-principles study.

    Science.gov (United States)

    You, Baiqing; Wang, Xiaocha; Zheng, Zhida; Mi, Wenbo

    2016-03-14

    The electronic structure of black phosphorene (BP)/monolayer 1H-XT2 (X = Mo, W; T = S, Se, Te) two dimensional (2D) van der Waals heterostructures have been calculated by the first-principles method. It is found that the electronic band structures of both BP and XT2 are preserved in the combined van der Waals heterostructures. The WSe2/BP van der Waals heterostructure demonstrates a type-I band alignment, but the MoS2/BP, MoSe2/BP, MoTe2/BP, WS2/BP and WTe2/BP van der Waals heterostructures demonstrate a type-II band alignment. In particular, the n-type XT2/p-type BP van der Waals heterostructures can be applied in p-n diode and logical devices. Strong spin splitting appears in all of the heterostructures when considering the spin orbital coupling. Our results play a significant role in the prediction of novel 2D van der Waals heterostructures that have potential applications in spin-filter devices, spin field effect transistors, optoelectronic devices, etc. PMID:26899350

  14. Transcriptional response of Desulfatibacillum alkenivorans AK-01 to growth on alkanes: insights from RT-qPCR and microarray analyses.

    Science.gov (United States)

    Herath, Anjumala; Wawrik, Boris; Qin, Yujia; Zhou, Jizhong; Callaghan, Amy V

    2016-05-01

    Microbial transformation ofn-alkanes in anaerobic ecosystems plays a pivotal role in biogeochemical carbon cycling and bioremediation, but the requisite genetic machinery is not well elucidated.Desulfatibacillum alkenivoransAK-01 utilizesn-alkanes (C13to C18) and contains two genomic loci encoding alkylsuccinate synthase (ASS) gene clusters. ASS catalyzes alkane addition to fumarate to form methylalkylsuccinic acids. We hypothesized that the genes in the two clusters would be differentially expressed depending on the alkane substrate utilized for growth. RT-qPCR was used to investigateass-gene expression across AK-01's known substrate range, and microarray-based transcriptomic analysis served to investigate whole-cell responses to growth onn-hexadecane versus hexadecanoate. RT-qPCR revealed induction ofassgene cluster 1 during growth on all tested alkane substrates, and the transcriptional start sites in cluster 1 were determined via 5'RACE. Induction ofassgene cluster 2 was not observed under the tested conditions. Transcriptomic analysis indicated that the upregulation of genes potentially involved in methylalkylsuccinate metabolism, including methylmalonyl-CoA mutase and a putative carboxyl transferase. These findings provide new directions for studying the transcriptional regulation of genes involved in alkane addition to fumarate, fumarate recycling and the processing of methylalkylsuccinates with regard to isolates, enrichment cultures and ecological datasets. PMID:27009900

  15. Long chain n-alkanes and their carbon isotopes in lichen species from western Hubei Province: implication for geological records

    Institute of Scientific and Technical Information of China (English)

    Xianyu HUANG; Jiantao XUE; Shouyu GUO

    2012-01-01

    Five coticolous lichen samples were collected from western Hubei Province of China to analyze the long chain n-alkanes and their carbon isotope compositions.The n-alkanes range in carbon number from C17 to C33 with strong odd-over-even predominance between C21and C33.Lichens are dominated by n-C29 in the samples of Dajiuhu,Shennongjia Mountain,but by both n-C23 and n-C29 at Qizimei Mountain.This difference may result from the different environmental conditions in these two sites.The δ13C values of long chain n-alkanes in lichen samples show the signature of C3 plants.Based on compoundspecific carbon isotopic values and previous results,we state that alkane homologs > C23 mainly originate from the symbiotic fungi,while symbiotic algae only contribute trace amount of long chain alkanes.Of great interesting is the occurrence of long chain 3-methylalkanes in the Qizimei samples.These anteiso compounds range from C24 to C32,displaying obvious even-over-odd predominance.This study reveals that the association of long chain 3-methylalkanes with n-C23 alkane might be used as proxies to reconstruct the paleoecological implications of lichens in Earth history.

  16. Analysis of alkane-dependent methanogenic community derived from production water of a high-temperature petroleum reservoir

    Energy Technology Data Exchange (ETDEWEB)

    Mbadinga, Serge Maurice; Li, Kai-Ping; Zhou, Lei; Wang, Li-Ying; Yang, Shi-Zhong; Liu, Jin-Feng; Mu, Bo-Zhong [East China Univ. of Science and Technology, Shanghai (China). State Key Lab. of Bioreactor Engineering and Inst. of Applied Chemistry; Gu, Ji-Dong [Hong Kong Univ. (China). School of Biological Sciences

    2012-10-15

    Microbial assemblage in an n-alkanes-dependent thermophilic methanogenic enrichment cultures derived from production waters of a high-temperature petroleum reservoir was investigated in this study. Substantially higher amounts of methane were generated from the enrichment cultures incubated at 55 C for 528 days with a mixture of long-chain n-alkanes (C{sub 15}-C{sub 20}). Stoichiometric estimation showed that alkanes-dependent methanogenesis accounted for about 19.8% of the total amount of methane expected. Hydrogen was occasionally detected together with methane in the gas phase of the cultures. Chemical analysis of the liquid cultures resulted only in low concentrations of acetate and formate. Phylogenetic analysis of the enrichment revealed the presence of several bacterial taxa related to Firmicutes, Thermodesulfobiaceae, Thermotogaceae, Nitrospiraceae, Dictyoglomaceae, Candidate division OP8 and others without close cultured representatives, and Archaea predominantly related to uncultured members in the order Archaeoglobales and CO{sub 2}-reducing methanogens. Screening of genomic DNA retrieved from the alkanes-amended enrichment cultures also suggested the presence of new alkylsuccinate synthase alpha-subunit (assA) homologues. These findings suggest the presence of poorly characterized (putative) anaerobic n-alkanes degraders in the thermophilic methanogenic enrichment cultures. Our results indicate that methanogenesis of alkanes under thermophilic condition is likely to proceed via syntrophic acetate and/or formate oxidation linked with hydrogenotrophic methanogenesis. (orig.)

  17. Polychlorinated Alkanes in Fish from Norwegian Freshwater

    OpenAIRE

    Borgen, Anders R.; Martin Schlabach; Roland Kallenborn; Eirik Fjeld

    2002-01-01

    Short-chain polychlorinated alkanes (sPCAs) have been measured in freshwater fish samples from different lakes all over Norway and from the Norwegian Arctic. The analyses were performed with high-resolution GC coupled to high-resolution MS in electron capture negative ion mode. The species investigated were trout, Arctic char, and burbot (Lota lota). Muscle tissue in the lake trout and Arctic char, and liver in burbot, were selected for analyses because of their high lipid content. ∑sPCA conc...

  18. Numerical study of transport properties in monolayer graphene-based double-barrier(well) structures under a time-periodic potential

    Science.gov (United States)

    Chen, Hai Yang

    2014-05-01

    We have analyzed the effect of various system parameters and external time-dependent field on the transport properties of monolayer graphene-based double-barrier(well) structures under a time-periodic potential. Results indicate that the Klein tunneling still exists. Besides, the transmission probability, conductivity, shot noise, and Fano factor exhibit various types of oscillatory behavior with changes in the system parameters, and they are either improved or suppressed in the presence of the time-periodic potential. We have also discussed the reasons underlying these phenomena. The results obtained in this study demonstrate that the transport properties can be controlled by manipulating the structural parameters of the system and the external field strength.

  19. Fabrication and study of organic solar cells composed of P3HT/PCBM blend with monolayers of P(VDF-TrFE)

    Science.gov (United States)

    Carrasco, Hector; Vedrine, Josee; Luis Rosa Collaboration

    2014-03-01

    Organic polymeric materials that are conducting provide an added facility in device fabrication, particularly in solar cell applications. In this work, we study the electrical and morphological properties of bulk hetero-junction solar cells fabricated with poly (3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric-acid-methyl ester (PCBM) blends, when a monolayer of the ferroelectric polymer poly[(vinylidenefluoride-co-trifluoroethylene] [P(VDF-TrFE)] is deposited between ITO conductor and bulk heterojunction. The bulk heterojunction and ferroelectric films are annealed at 140 °C under vacuum atmosphere to improve their crystallinity, which may assist in enhanced charge transfer. We measure device photovoltaic properties with changing blend thickness, while keeping the ferroelectric layer constant.. The current-voltage characteristics are measured and compared for the different film thicknesses. AFM techniques are used to analyze their morphological and conductive properties.

  20. Extremely large perpendicular magnetic anisotropy of an Fe(001) surface capped by 5d transition metal monolayers: A density functional study

    Science.gov (United States)

    Odkhuu, D.; Rhim, S. H.; Park, N.; Hong, S. C.

    2013-11-01

    Significant enhancement of the magnetocrystalline anisotropy (MCA) of an Fe(001) surface capped by 4d and 5d transition metal monolayers is presented in this study using first principles density functional calculations. In particular, an extremely large perpendicular MCA of +10 meV/Ir was found in Ir-capped Fe(001), which originates not from the Fe but from the large spin-orbit coupling of the Ir atoms. From the spin-channel decomposition of the MCA matrix and electronic structure analyses, we find that strong 3d-5d band hybridization in the minority spin state is responsible for the sign changes of the MCA from parallel to perpendicular.

  1. Nanoscale observation of delayering in alkane films

    DEFF Research Database (Denmark)

    Bai, M.; Knorr, K.; Simpson, M.J.;

    2007-01-01

    Tapping-mode Atomic Force Microscopy and synchrotron X-ray scattering measurements on dotriacontane ( n-C32H66 or C-32) films adsorbed on SiO2- coated Si( 100) wafers reveal a narrow temperature range near the bulk C32 melting point T-b in which a monolayer phase of C32 molecules oriented perpend...

  2. The influence of extraframework aluminum on H-FAU catalyzed cracking of light alkanes

    NARCIS (Netherlands)

    Narbeshuber, T.F.; Brait, A.; Seshan, K.; Lercher, J.A.

    1996-01-01

    The conversion of light linear and branched alkanes on two faujasite samples containing different concentrations of free Brønsted acid sites and extraframework alumina (EFAL) was studied between 733 K and 813 K. Protolytic cracking and bimolecular hydride transfer proceeded solely on Brønsted acid s

  3. Calculations of gamma-ray spectral profiles of linear alkanes in the positron annihilation process

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Xiaoguang [Molecular Model Discovery Laboratory, Department of Chemistry and Biotechnology, School of Science, Faculty of Science, Engineering and Technology, Swinburne University of Technology, PO Box 218, Hawthorn, Victoria, 3122 (Australia); School of Physics and Optoelectronic Engineering, Ludong University, Shandong, Yantai, 264025 (China); Wang, Feng, E-mail: fwang@swin.edu.au [Molecular Model Discovery Laboratory, Department of Chemistry and Biotechnology, School of Science, Faculty of Science, Engineering and Technology, Swinburne University of Technology, PO Box 218, Hawthorn, Victoria, 3122 (Australia)

    2014-10-15

    Highlights: • The study calculates gamma-ray profiles for linear alkanes (n up to 12) quantum mechanically;. • “Profile quality” has been defined as the root-mean square deviation (RMSD) between the theoretical and the experimental results in the entire region of the profile. • Excellent agreement with measurements suggests that the theory model is applicable to predict other alkanes such as heptane (C{sub 7}H{sub 16}) etc. • The study suggested that gamma-ray spectra may be more sensitive to study smaller alkanes (and their isomers), rather than larger alkanes (i.e., n > 12). - Abstract: The positron–electron annihilation gamma-ray spectra of linear alkanes C{sub n}H{sub 2n+2} (n = 1–12) have been studied systematically. A profile quality (PQ) parameter, χ, is introduced to assess the agreement between the obtained theoretical profiles and the experimental measurements in the entire region of energy shift of the spectra. Together with the Doppler shift (Δε) of the gamma-ray spectra, the two parameters, χ and Δε, are able to provide a more comprehensive assessment of the calculated gamma-ray spectra with respect to available experiment. Applying the recently developed docking model, the present study determines the positrophilic electrons for individual alkanes from which the gamma-ray spectral profiles are calculated. The results achieve an excellent agreement with experiment, not only with respect to the Doppler shift, but also with respect to the gamma-ray profiles in the photon energy region up to 5 keV. The study further calculates the gamma-ray spectra of other linear alkanes in the series without available experimental measurements, such as heptane (C{sub 7}H{sub 16}), octane (C{sub 8}H{sub 18}), decane (C{sub 10}H{sub 22}) and undecane (C{sub 11}H{sub 24}). The results obtained show a dominance of the positrophilic electrons in the lowest occupied valence orbital (LOVO) in the positron–electron annihilation process, in agreement with

  4. Emergence of chirality in hexagonally packed monolayers of hexapentyloxytriphenylene on Au(111): a joint experimental and theoretical study.

    Science.gov (United States)

    Sleczkowski, Piotr; Katsonis, Nathalie; Kapitanchuk, Oleksiy; Marchenko, Alexandr; Mathevet, Fabrice; Croset, Bernard; Lacaze, Emmanuelle

    2014-11-11

    We investigate the expression of chirality in a monolayer formed spontaneously by 2,3,6,7,10,11-pentyloxytriphenylene (H5T) on Au(111). We resolve its interface morphology by combining scanning tunneling microscopy (STM) with theoretical calculations of intermolecular and interfacial interaction potentials. We observe two commensurate structures. While both of them belong to a hexagonal space group, analogical to the triangular symmetry of the molecule and the hexagonal symmetry of the substrate surface, they surprisingly reveal a 2D chiral character. The corresponding breaking of symmetry arises for two reasons. First it is due to the establishment of a large molecular density on the substrate, which leads to a rotation of the molecules with respect to the molecular network crystallographic axes to avoid steric repulsion between neighboring alkoxy chains. Second it is due to the molecule-substrate interactions, leading to commensurable large crystallographic cells associated with the large size of the molecule. As a consequence, molecular networks disoriented with respect to the high symmetry directions of the substrate are induced. The high simplicity of the intermolecular and molecule-substrate van der Waals interactions leading to these observations suggests a generic character for this kind of symmetry breaking. We demonstrate that, for similar molecular densities, only two kinds of molecular networks are stabilized by the molecule-substrate interactions. The most stable network favors the interfacial interactions between terminal alkoxy tails and Au(111). The metastable one favors a specific orientation of the triphenylene core with its symmetry axes collinear to the Au⟨110⟩. This specific orientation of the triphenylene cores with respect to Au(111) appears associated with an energy advantage larger by at least 0.26 eV with respect to the disoriented core. PMID:25317696

  5. Gas-phase reactions of the bare Th2+ and U2+ ions with small alkanes, CH4, C2H6, and C3H8: experimental and theoretical study of elementary organoactinide chemistry.

    Science.gov (United States)

    Di Santo, Emanuela; Santos, Marta; Michelini, Maria C; Marçalo, Joaquim; Russo, Nino; Gibson, John K

    2011-02-16

    The gas-phase reactions of two dipositive actinide ions, Th(2+) and U(2+), with CH(4), C(2)H(6), and C(3)H(8) were studied by both experiment and theory. Fourier transform ion cyclotron resonance mass spectrometry was employed to study the bimolecular ion-molecule reactions; the potential energy profiles (PEPs) for the reactions, both observed and nonobserved, were computed by density functional theory (DFT). The experiments revealed that Th(2+) reacts with all three alkanes, including CH(4) to produce ThCH(2)(2+), whereas U(2+) reacts with C(2)H(6) and C(3)H(8), with different product distributions than for Th(2+). The comparative reactivities of Th(2+) and U(2+) toward CH(4) are well explained by the computed PEPs. The PEPs for the reactions with C(2)H(6) effectively rationalize the observed reaction products, ThC(2)H(2)(2+) and UC(2)H(4)(2+). For C(3)H(8) several reaction products were experimentally observed; these and additional potential reaction pathways were computed. The DFT results for the reactions with C(3)H(8) are consistent with the observed reactions and the different products observed for Th(2+) and U(2+); however, several exothermic products which emerge from energetically favorable PEPs were not experimentally observed. The comparison between experiment and theory reveals that DFT can effectively exclude unfavorable reaction pathways, due to energetic barriers and/or endothermic products, and can predict energetic differences in similar reaction pathways for different ions. However, and not surprisingly, a simple evaluation of the PEP features is insufficient to reliably exclude energetically favorable pathways. The computed PEPs, which all proceed by insertion, were used to evaluate the relationship between the energetics of the bare Th(2+) and U(2+) ions and the energies for C-H and C-C activation. It was found that the computed energetics for insertion are entirely consistent with the empirical model which relates insertion efficiency to the

  6. Langmuir monolayer formation of metal complexes from polymerizable amphiphilic ligands

    NARCIS (Netherlands)

    Werkman, PJ; Schouten, AJ

    1996-01-01

    The monolayer behaviour of 4-(10,12-pentacosadiynoicamidomethyl)-pyridine at the air-water interface was studied by measuring the surface pressure-area isotherms. The amphiphile formed stable monolayers with a clear liquid-expanded (LE) to liquid-condensed phase transition at various temperatures. U

  7. Feasibility limits and performance of an absorption cooling machine using light alkane mixtures

    International Nuclear Information System (INIS)

    The performance of a heat-driven vapor absorption chiller with various alkane mixtures as working pairs was studied. A Thermodynamic analysis showed that under specified operating conditions and with a generator temperature below 130 °C, temperature achievable with a simple flat plate collector when solar energy is expected as the driving heat source, the application of some of the proposed alkane mixtures is not feasible. Simulations using ASPEN Plus flow sheeting program are then done with the selected working pairs. All simulations were done specifying the Peng-Robinson equation of state as the property method. A parametric study was carried out allowing the investigation of the generator temperature effect on the system performance and the comparison between performances released with each working pair. Results revealed that a water-cooled absorption machine using the C3H8/n-C9H20 pair as working fluid releases the best performances from a heat driving temperature level of about 100 °C. - Highlights: • Performance of an absorption chiller with various alkane mixtures was studied. • Some of the proposed alkane mixtures is not feasible. • Only the n-C4/n-C6 mixture may be considered for air-cooled machine. • In case of water cooling, C3/n-C9 and n-C4/n-C9 give the best COP

  8. Saturated-liquid heat capacity calculation of alkanes

    OpenAIRE

    JOVAN D. JOVANOVIC; DUSAN K. GROZDANIC

    2005-01-01

    An empirical model for the calculation of the heat capacity of alkanes is recommended. This model was tested and compared to known models (LuriaâBenson and RizickaâDomalski) using 68 sets with 1155 literature experimental heat capacity data of 39 alkanes. The obtained results indicate that the newmodel is slightly better tha the existing models, especially near the critical point.

  9. 40 CFR 721.3435 - Butoxy-substituted ether alkane.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Butoxy-substituted ether alkane. 721... Substances § 721.3435 Butoxy-substituted ether alkane. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as butoxy-substituted ether...

  10. Shale gas opportunities. Dehydrogenation of light alkanes

    Energy Technology Data Exchange (ETDEWEB)

    Patcas, F.C.; Dieterle, M.; Rezai, A.; Asprion, N. [BASF SE, Ludwigshafen (Germany)

    2013-11-01

    The discovery and use of shale gas in North America has become a game changer for the chemical industry by access to a cheaper feedstock compared to conventional oil. Increased number of ethane crackers spurred increasing interest in light alkanes dehydrogenation. Several companies have announced their interest in new propane dehydrogenation units in North America. BASF is developing light alkanes dehydrogenation technologies for two decades now. BASF developed jointly with Linde the isothermal C3 dehydrogenation process. The latest dehydrogenation catalyst development at BASF focused on a supported and steam resistant Pt-Sn catalyst which yielded excellent selectivity and activity. Intense research work both internally as well as in cooperation with universities contributed to the understanding of the relationship between the surface structure and catalyst performances like activity, selectivity and coking resistance. Using such type of catalysts BASF developed an autothermal propane dehydrogenation as well as a butane dehydrogenation process. The most recent catalyst development was a dehydrogenation catalyst coated on a honeycomb monolith to improve catalyst usage and pressure drop. This will probably be the first industrial usage of catalytic monoliths in a chemical synthesis process. (orig.) (Published in summary form only)

  11. EXAFS in total reflection (reflEXAFS) for the study of organometallic Pd(II) thiol complexes based self-assembled monolayers on gold

    International Nuclear Information System (INIS)

    Graphical abstract: The molecular structure and organization of organometallic Pd(II) thiolates SAMs and multilayers on Au/Si(1 1 1) were investigated by reflEXAFS. For SAMs, S-Au bond lengths, Pd-S-Au bond angles and molecular orientations were assessed. Research highlights: → Organometallic Pt(II) thiolates deposited as SAMs and multilayers on gold. → Molecular structure and organization of SAMs and multilayers studied by reflEXAFS. → SAMs S-Au bond lengths, Pd-S-Au bond angles and molecular orientations are assessed. - Abstract: The molecular structure and organization of self-assembled monolayers (SAMs) and multilayer films grafted onto Au/Si(1 1 1) surfaces of mononuclear transition metal dialkynyl bridged Pd(II) complexes trans-[HS-Pd(PBu3)2-SH] (1), trans-[HS-Pd(PBu3)2(-C≡C-C6H5)] (2) and of the binuclear complex trans, trans-[HS-Pd(PBu3)2(-C≡C-C6H4-C6H4-C≡C-Pd(PBu3)2-SH] (3), have been investigated by extended X-ray absorption fine structure spectroscopy in total reflection conditions (reflEXAFS). ReflEXAFS analysis of the data lead to determine the local structure around Pd atoms, assessing the square-planar geometry around the transition metal in the multilayers case, preserved in the monolayer regime. The investigation on the SAMs also provided the assessment of the S-Au bond length and Pd-S-Au bond angle and on the molecular orientation on the gold substrate of the complexes, confirmed by quantum chemical calculations.

  12. Hydrocarbon metabolism by Brevibacterium erythrogenes: normal and branched alkanes.

    Science.gov (United States)

    Pirnik, M P; Atlas, R M; Bartha, R

    1974-09-01

    Branched- and straight-chain alkanes are metabolized by Brevibacterium erythrogenes by means of two distinct pathways. Normal alkanes (e.g., n-pentadecane) are degraded, after terminal oxidation, by the beta-oxidation system operational in fatty acid catabolism. Branched alkanes like pristane (2,6,10,14-tetramethylpentadecane) and 2-methylundecane are degraded as dicarboxylic acids, which also undergo beta-oxidation. Pristane-derived intermediates are observed to accumulate, with time, as a series of dicarboxylic acids. This dicarboxylic acid pathway is not observed in the presence of normal alkanes. Release of (14)CO(2) from [1-(14)C]pristane is delayed, or entirely inhibited, in the presence of n-hexadecane, whereas CO(2) release from n-hexadecane remains unaffected. These results suggest an inducible dicarboxylic acid pathway for degradation of branched-chain alkanes. PMID:4852318

  13. Low temperature carrier transport study of monolayer MoS2 field effect transistors prepared by chemical vapor deposition under an atmospheric pressure

    International Nuclear Information System (INIS)

    Large size monolayer Molybdenum disulphide (MoS2) was successfully grown by chemical vapor deposition method under an atmospheric pressure. The electrical transport properties of the fabricated back-gate monolayer MoS2 field effect transistors (FETs) were investigated under low temperatures; a peak field effect mobility of 59 cm2V−1s−1 was achieved. With the assist of Raman measurement under low temperature, this work identified the mobility limiting factor for the monolayer MoS2 FETs: homopolar phonon scattering under low temperature and electron-polar optical phonon scattering at room temperature

  14. Low temperature carrier transport study of monolayer MoS{sub 2} field effect transistors prepared by chemical vapor deposition under an atmospheric pressure

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xinke, E-mail: xkliu@szu.edu.cn, E-mail: wujing026@gmail.com; He, Jiazhu; Tang, Dan; Lu, Youming; Zhu, Deliang; Liu, Wenjun; Cao, Peijiang; Han, Sun [College of Materials Science and Engineering, Shenzhen Engineering Laboratory for Advanced Technology of Ceramics, Nanshan District Key Lab for Biopolymer and Safety Evaluation, Shenzhen University, 3688 Nanhai Ave, Shenzhen 518060 (China); Liu, Qiang; Wen, Jiao; Yu, Wenjie [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, CAS, 865 Chang Ning Road, Shanghai 200050 (China); Liu, Wenjun [State Key Laboratory of ASIC and System, Department of Microelectronics, Fudan University, 220 Handan Road, Shanghai 200433 (China); Wu, Jing, E-mail: xkliu@szu.edu.cn, E-mail: wujing026@gmail.com [Department of Physics, National University of Singapore, 21 Lower Kent Ridge Road, 117576 Singapore (Singapore); He, Zhubing [Department of Materials Science and Engineering, South University of Science and Technology of China, 1088 Xueyuan Road, Shenzhen 518055 (China); Ang, Kah-Wee [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore (Singapore)

    2015-09-28

    Large size monolayer Molybdenum disulphide (MoS{sub 2}) was successfully grown by chemical vapor deposition method under an atmospheric pressure. The electrical transport properties of the fabricated back-gate monolayer MoS{sub 2} field effect transistors (FETs) were investigated under low temperatures; a peak field effect mobility of 59 cm{sup 2}V{sup −1}s{sup −1} was achieved. With the assist of Raman measurement under low temperature, this work identified the mobility limiting factor for the monolayer MoS{sub 2} FETs: homopolar phonon scattering under low temperature and electron-polar optical phonon scattering at room temperature.

  15. Effect of biaxial strain and external electric field on electronic properties of MoS2 monolayer: A first-principle study

    Science.gov (United States)

    Nguyen, Chuong V.; Hieu, Nguyen N.

    2016-04-01

    In this work, making use of density functional theory (DFT) computations, we systematically investigate the effect of biaxial strain engineering and external electric field applied perpendicular to the layers on the band gaps and electronic properties of monolayer MoS2. The direct-to-indirect band gaps and semiconductor-to-metal transition are observed in monolayer MoS2 when strain and electric field are applied in our calculation. We show that when the biaxial strain and external electric field are introduced, the electronic properties including band gaps of monolayer MoS2 can be reduced to zero. Our results provide many useful insights for the wide applications of monolayer MoS2 in electronics and optoelectronics.

  16. Effects of ambient conditions on adsorbed surfactant and polymer monolayers

    International Nuclear Information System (INIS)

    The physical properties of surfactant-coated and polyelectrolyte-coated surfaces in adhesive contact in air have been studied using the surface forces apparatus technique. Various physisorbed monolayers with different head groups and chains (or polymer segments) were prepared both by adsorption form solution (self-assembly) and by the Langmuir-Blodgett deposition technique. The results show that many monolayer properties depend on the atmospheric conditions such as the relative humidity or presence of organic vapors and that these properties can further change when two monolayer-coated surfaces are brought into contact. These properties include monolayer composition and structure, thickness and compressibility, fluidity and phase state (i.e., whether solid, gel, or liquid), and the adhesion between two monolayer-coated surfaces. In addition, we find that both out-of-plane and in-plane (lateral) phase transitions can be induced in certain adsorbed monolayers when they are subjected to a compressive stress. The results provide new insights into molecular ordering and dynamics in physisorbed monolayers and how monolayers are affected when they are exposed to vapors or when they interact with other surfaces. 18 refs., 13 figs., 4 tabs

  17. Non-rotator phases in phospholipid monolayers?

    DEFF Research Database (Denmark)

    Kenn, R.M.; Kjær, K.; Möhwald, H.

    Monolayers of diacylphosphatidylethanolamines at the air/water interface are studied by grazing incidence X-ray diffraction. The results prove the existence of phases which show analogies with the rotator phases of single-chain surfactants: hexagonal tail lattice with no tilt; rectangular lattice...

  18. 2-Mercaptobenzothiazole monolayers on zinc and silver surfaces for anticorrosion

    International Nuclear Information System (INIS)

    Anticorrosive behaviors of 2-mercaptobenzothiazole (MBT) self-assembled monolayers (SAMs) on silver and zinc electrodes were comparatively studied by means of electrochemical impedance spectroscopy (EIS). The promising inhibition effect of the MBT for silver and zinc from corrosion had been confirmed. The adsorption geometries of MBT monolayers on zinc and silver electrodes were observed by surface enhanced Raman scattering (SERS) technique. The SERS spectra implied that monolayers of MBT could be self-assembled on Ag surface through S10 and N3 atoms and the molecular plane should be tilted with respect to the surface. On Zn surface, MBT molecules formed monolayers via both S atoms and the other moieties of the molecule away from the surface. From the in situ electrochemical SERS results it can be found that MBT monolayers on both Ag and Zn surfaces experienced the changes of adsorption fashions as the potential shifting to more negative direction

  19. Investigating C4 Grass Contributions to N-alkane Based Paleoclimate Reconstructions

    Science.gov (United States)

    Doman, C. E.; Enders, S. K.; Chadwick, O.; Freeman, K. H.

    2014-12-01

    Plant wax n-alkanes are long-chain, saturated hydrocarbons contained within the protective waxy cuticle on leaves. These lipids are pervasive and persistent in soils and sediments and thus are ideal biomarkers of ancient terrestrial organic matter. In ecosystems dominated by C3 plants, the relationship between the carbon isotopic value of whole leaves and lipids is fairly well documented, but this relationship has not been fully investigated for plants that use C4 photosynthesis. In both cases, it is unclear if the isotopic relationships are sensitive to environmental conditions, or reflect inherited characteristics. This study used a natural climate gradient on the Kohala peninsula of Hawaii to investigate relationships between climate and the δ13C and δ2H values of n-alkanes in C3 and C4 plants. δ13C of C3 leaves and lipids decreased 5 ‰ from the driest to the wettest sites, consistent with published data. Carbon isotope values of C4 plants showed no relationship to moisture up to 1000 mm mean annual precipitation (MAP). Above this threshold, δ 13C values were around 10‰ more depleted, likely due to a combination of canopy effects and C4 grasses growing in an uncharacteristically wet and cold environment. In C3 plants, the fractionation between leaf and lipid carbon isotopes did not vary with MAP, which allows estimations of δ13C leaf to be made from alkanes preserved in ancient sediments. Along this transect, C3 plants produce around twice the quantity of n-alkanes as C4 grasses. C4 grasses produce longer carbon chains. As a result, n-alkanes in the geologic record will be biased towards C3 plants, but the presence of alkanes C33 and C35 indicate the contributions of C4 grasses. In both C3 and C4 plants, average chain length increased with mean annual precipitation, but the taxonomic differences in chain length were greater than environmental differences. Hydrogen isotopes of n-alkanes show no trends with MAP, but do show clear differences between plant

  20. Microbial communities in methane- and short chain alkane-rich hydrothermal sediments of Guaymas Basin

    Directory of Open Access Journals (Sweden)

    Frederick eDowell

    2016-01-01

    Full Text Available The hydrothermal sediments of Guaymas Basin, an active spreading center in the Gulf of California (Mexico, are rich in porewater methane, short-chain alkanes, sulfate and sulfide, and provide a model system to explore habitat preferences of microorganisms, including sulfate-dependent, methane- and short chain alkane-oxidizing microbial communities. In this study, sediments (above 60˚C covered with sulfur-oxidizing microbial mats surrounding a hydrothermal mound (termed Mat Mound were characterized by porewater geochemistry of methane, C2-C6 short-chain alkanes, sulfate, sulfide, sulfate reduction rate measurements, in-situ temperature gradients, bacterial and archaeal 16S rRNA gene clone libraries and V6 tag pyrosequencing. The most abundantly detected groups in the Mat mound sediments include anaerobic methane-oxidizing archaea of the ANME-1 lineage and its sister clade ANME-1Guaymas, the uncultured bacterial groups SEEP-SRB2 within the Deltaproteobacteria and the separately branching HotSeep-1 Group; these uncultured bacteria are candidates for sulfate-reducing alkane oxidation and for sulfate-reducing syntrophy with ANME archaea. The archaeal dataset indicates distinct habitat preferences for ANME-1, ANME-1-Guaymas and ANME-2 archaea in Guaymas Basin hydrothermal sediments. The bacterial groups SEEP-SRB2 and HotSeep-1 co-occur with ANME-1 and ANME-1Guaymas in hydrothermally active sediments underneath microbial mats in Guaymas Basin. We propose the working hypothesis that this mixed bacterial and archaeal community catalyzes the oxidation of both methane and short-chain alkanes, and constitutes a microbial community signature that is characteristic for hydrothermal and/or cold seep sediments containing both substrates.

  1. Study of Fused Thiophene Based Organic Semiconductors and Interfacial Self-Assembled Monolayer (SAM) for Thin-Film Transistor (TFT) Application

    Science.gov (United States)

    Youn, Jangdae

    In this thesis, the molecular packing motifs of our newly designed fused thiophenes, benzo[d,d]thieno[3,2-b;4,5-b]dithiophene (BTDT) derivatives, were studied by utilizing grazing incidence wide angle X-ray scattering (GIWAXS). Considering the potential of fused thiophene molecules as an environmentally stable, high performance semiconductor building block, it must be an important groundwork to investigate their thin film structures in relation to molecular structures, single crystal structures, and organic thin-film transistors (OTFT) performances. OTFT device performance is not only determined by semiconductor materials, but also influenced by the interfacial properties. Since there are three major components in TFT structures---electrodes, semiconductors, and dielectrics, two types of major interfaces exist. One is the semiconductor-electrode interface, and the other is the semiconductor-dielectric interface. Both of these interfaces have critical roles for TFT operation. For example, the semiconductor-electrode interface determines the charge injection barrier. Before charge carriers go through the electrode (source)-semiconductor-electrode (drain) pathways, the energy gaps between the work function of the electrodes and the HOMO energy of the semiconductor materials must be overcome for hole injection, or the energy gap between the metal work function of the electrodes and the LUMO energy of the semiconductor materials must be overcome for electron injection. These charge injection barriers are largely determined by the energetic structure of the semiconductor material and work function of the electrode. However, the size of energy gap can be modified by introducing an organic self-assembled monolayer (SAM) on the surface of metal electrode. In addition, the structure of semiconductor films, especially within several monolayers right above the electrode, is greatly influenced by the SAM, and it changes charge injection property of OTFT devices. In this thesis

  2. Exfoliating biocompatible ferromagnetic Cr-trihalide monolayers.

    Science.gov (United States)

    Liu, Junyi; Sun, Qiang; Kawazoe, Yoshiyuki; Jena, Puru

    2016-03-23

    In addition to spintronics another motivation for exploring ferromagnetic two-dimensional materials is for biomedical applications such as magnetic labeling and hyperthermia treatment of tumors. Unfortunately, the widely studied Mn-containing monolayer is not biocompatible, although it is ferromagnetic. Here using first principles calculations combined with Monte Carlo simulations based on the Ising model, we systematically study a class of 2D ferromagnetic monolayers CrX3 (X = Cl, Br, I). The feasibility of exfoliation from their layered bulk phase is confirmed by the small cleavage energy and high in-plane stiffness. Spin-polarized calculations, combined with self-consistently determined Hubbard U that accounts for strong correlation energy, demonstrate that CrX3 (X = Cl, Br, I) monolayers are ferromagnetic and that Cr is trivalent and carries a magnetic moment of 3 μB; the resulting Cr(3+) ions are biocompatible. The corresponding Curie temperatures for CrCl3, CrBr3 and CrI3 are found to be 66, 86, and 107 K, respectively, which can be increased to 323, 314, and 293 K by hole doping. The biocompatibility and ferromagnetism render these Cr-containing trihalide monolayers unique for applications. PMID:26452203

  3. Oxidation of long-chain alkanes by Acetobacter rancens

    International Nuclear Information System (INIS)

    The degradation of hexadecane and tetradecane by Acetobacter rancens CCM 1774 was investigated. It was found that this strain is able to grow to a limited extent on hexadecane as a carbon source. The occurrence of n-alkanoic acids and alcohols among the reaction products of growing as well as resting cells indicates a monoterminal degradation of long-chain alkanes. Both alkane-grown and glucose-grown resting cells exhibited alkane oxidizing activities which were not influenced by chloramphenicol. This suggested a constitutive nature of the appropriate enzymes. (orig.)

  4. Alkanes-filled photonic crystal fibers as sensor transducers

    Science.gov (United States)

    Marć, P.; Przybysz, N.; Stasiewicz, K.; Jaroszewicz, L. R.

    2015-09-01

    In this paper we propose alkanes-filled PCFs as the new class of transducers for optical fiber sensors. We investigated experimentally thermo-optic properties of a commercially available LMA8 partially filled with different alkanes with a higher number of carbon atoms. A partially filled PCF spliced with standard SMFs constitutes one of the newest type transducer. We have selected a group of eight alkanes which have melting points in different temperatures. An analysis of temperature spectral characteristics of these samples will allow to design an optical fiber sensor with different temperature thresholds at specific wavelengths.

  5. UNIQUAC interaction parameters for alkane/amine systems determined by Molecular Mechanics

    DEFF Research Database (Denmark)

    Jonsdottir, Svava Osk; Klein, R. A.; Rasmussen, Kjeld

    UNIQUAC interaction parameters have been successfully determined for three alkane/primary amine systems using a Molecular Mechanics method called the Consistent Force Field. Interaction parameters for alkane/alkane and alkane/ketone systems had been determined previously using this method and in...

  6. Late Quaternary environmental changes inferred from n-alkane evidence in coastal area of southern Hainan Island, China

    Science.gov (United States)

    Wang, Mengyuan; Zheng, Zhuo

    2016-04-01

    The studied core was a coastal core in Hainan Island, China. It is in length of 49.01m and divided into four Units (MIS 1~MIS 6) according to lithology description. The Optically Stimulated Luminescence (OSL) attributes the sediments from Unit 3 to the Oxygen Isotope Stage of MIS 5e (Unit 3b and 3c) and 5d (Unit 3a). To interpret the origination of organic carbons and to reconstruct paleovegetation changes, n-alkane, δ13C and TOC have been used in the present research. The result of n-alkanes distribution indicates a series of changes of sedimentary environment and terrestrial input. The shallow water facies at Unit 2, 3a and 4 is mainly characterized by short carbon chain n-alkanes and relatively low concentration. Contrasting with that of deep-water marine facies of MIS 5e (Unit 3b), the n-alkane pattern is typical bimodal and the main peaks are both in short and long carbon chains. During Unit 3b-1 (MIS 5e), more terrestrial original n-alkanes contribute to the concentration of TOC than oceanic. Organic matter source is mainly terrestrial origination. Total organic matter input mechanism of TLG-01 correlates with sediment grain size (average grain size). Total organic carbon input is enhanced with the increasing of fine grain size component. The variation of CPI (25-33) value in this study correlates with hydrological energy. The highest CPI (25-33) value is shown in the high sea level period of MIS 5e, comparing with that in MIS 5d and MIS 1. High CPI value corresponds to high TOC and average grain size (Φ) value. In the weak hydrological energy sedimentary environment, more terrestrial organic matter, together with TOC, deposit in the study area. ACL (25-33) index display higher values in the interglacial period (MIS 5 and MIS 1) than MIS 3 (sediments weathered during MIS 2) and MIS 6. Paq proxy, together with δ13C, estimates the mangrove growing depth in MIS 5e. The correlation between δ13C and each carbon chain alkane state stabilize and turbulence of

  7. Methyl ketones in high altitude Ecuadorian Andosols confirm excellent conservation of plant-specific n-alkane patterns

    Science.gov (United States)

    Jansen, B.; Nierop, K. G. J.

    2009-04-01

    Montane forest composition and specifically the position of the upper forest line (UFL) is very sensitive to climate change and human interference. As a consequence, reconstructions of past altitudinal UFL dynamics and forest species composition are crucial instruments to infer relationships between climate change and vegetation dynamics, and assess the impact of (pre)historic human settlement. One of the most detailed methods available to date to reconstruct past vegetation dynamics is the analysis of fossil pollen. Unfortunately, fossil pollen analysis does not distinguish beyond family or generic level in most cases, while its spatial resolution is limited amongst others by windblown dispersal of pollen, affecting the accuracy of pollen based reconstructions of UFL positions. To overcome these limitations, we developed a new method based on the analysis of plant-specific groups of biomarkers preserved in suitable archives, such as peat deposits, that are unravelled into the plant species of origin by the newly developed VERHIB model. In a study of UFL positions in the Northern Ecuadorian Andes we found longer chain-length n-alkanes, (C19-C35) to occur in plant-specific patterns in the dominant vegetation in the area as well as preliminary soil and peat samples. A crucial factor in determining the applicability of these n-alkanes as biomarkers for past vegetation is their preservation in soils and peat deposits. Therefore, we investigated the preservation of C19-C35 n-alkanes in a peat core and in five excavations along an altitudinal transect (3500-3860 m.a.s.l) in the study area. We were able to establish that n-methyl ketones are the main degradation product of the n-alkanes in question, while the degradation of the n-alkanes was the main source of the n-methyl ketones. This allowed us to use the relationship between the concentrations and carbon chain length patterns of n-alkanes and n-methyl ketones to assess possible (selective) degradation of the n-alkanes

  8. Arbuscular mycorrhizal wheat inoculation promotes alkane and polycyclic aromatic hydrocarbon biodegradation: Microcosm experiment on aged-contaminated soil.

    Science.gov (United States)

    Ingrid, Lenoir; Lounès-Hadj Sahraoui, Anissa; Frédéric, Laruelle; Yolande, Dalpé; Joël, Fontaine

    2016-06-01

    Very few studies reported the potential of arbuscular mycorrhizal symbiosis to dissipate hydrocarbons in aged polluted soils. The present work aims to study the efficiency of arbuscular mycorrhizal colonized wheat plants in the dissipation of alkanes and polycyclic aromatic hydrocarbons (PAHs). Our results demonstrated that the inoculation of wheat with Rhizophagus irregularis allowed a better dissipation of PAHs and alkanes after 16 weeks of culture by comparison to non-inoculated condition. These dissipations observed in the inoculated soil resulted from several processes: (i) a light adsorption on roots (0.5% for PAHs), (ii) a bioaccumulation in roots (5.7% for PAHs and 6.6% for alkanes), (iii) a transfer in shoots (0.4 for PAHs and 0.5% for alkanes) and mainly a biodegradation. Whereas PAHs and alkanes degradation rates were respectively estimated to 12 and 47% with non-inoculated wheat, their degradation rates reached 18 and 48% with inoculated wheat. The mycorrhizal inoculation induced an increase of Gram-positive and Gram-negative bacteria by 56 and 37% compared to the non-inoculated wheat. Moreover, an increase of peroxidase activity was assessed in mycorrhizal roots. Taken together, our findings suggested that mycorrhization led to a better hydrocarbon biodegradation in the aged-contaminated soil thanks to a stimulation of telluric bacteria and hydrocarbon metabolization in mycorrhizal roots. PMID:26995451

  9. Enhanced translocation and growth of Rhodococcus erythropolis PR4 in the alkane phase of aqueous-alkane two phase cultures were mediated by GroEL2 overexpression.

    Science.gov (United States)

    Takihara, Hayato; Ogihara, Jun; Yoshida, Takao; Okuda, Shujiro; Nakajima, Mutsuyasu; Iwabuchi, Noriyuki; Sunairi, Michio

    2014-01-01

    We previously reported that R. erythropolis PR4 translocated from the aqueous to the alkane phase, and then grew in two phase cultures to which long-chain alkanes had been added. This was considered to be beneficial for bioremediation. In the present study, we investigated the proteins involved in the translocation of R. erythropolis PR4. The results of our proteogenomic analysis suggested that GroEL2 was upregulated more in cells that translocated inside of the pristane (C19) phase than in those located at the aqueous-alkane interface attached to the n-dodecane (C12) surface. PR4 (pK4-EL2-1) and PR4 (pK4-ΔEL2-1) strains were constructed to confirm the effects of the upregulation of GroEL2 in translocated cells. The expression of GroEL2 in PR4 (pK4-EL2-1) was 15.5-fold higher than that in PR4 (pK4-ΔEL2-1) in two phase cultures containing C12. The growth and cell surface lipophilicity of PR4 were enhanced by the introduction of pK4-EL2-1. These results suggested that the plasmid overexpression of groEL2 in PR4 (pK4-EL2-1) led to changes in cell localization, enhanced growth, and increased cell surface lipophilicity. Thus, we concluded that the overexpression of GroEL2 may play an important role in increasing the organic solvent tolerance of R. erythropolis PR4 in aqueous-alkane two phase cultures. PMID:25311591

  10. n-alkane distribution coupled with organic carbon isotope composition in the shell bar section, Qarhan paleolake, Qaidam basin, NE Tibetan Plateau

    Institute of Scientific and Technical Information of China (English)

    Yang PU; Hucai ZHANG; Guoliang LEI; Fengqin CHANG; Mingsheng YANG; Xianyu HUANG

    2009-01-01

    Lipids extracted from lacustrine deposits in the paleolake Qarhan of the Qaidam basin in the northeastern Tibetan Plateau were determined by conventional gas chromatography-mass spectrometry. Several series of biomarkers were identified, mainly including n-alkanes, n-alkan-2-ones, n-alkanoic acids, branched alkanes, triter-penoids and steroids, indicative of various biogenic contributions. On the basis of cluster analysis, the n-C15, n-C17, n-C19 alkanes were proposed to be derived from algae and/or photosynthetic bacteria, the n-C21 n-C23, n-C25 homologues from aquatic plants, and the n-C29, n-C31 homologues from vascular plants. In contrast, the n-C27 alkane is not categorized in the n-C29 and n-C31 group of alkanes, probably due to more complex origins including both aquatic and vascular plants, and/or differential biodegradation. Stratigraphically, layers-2, 4 and 5 were found to show a close relationship in n-alkane distribution, associated with a positive shift in carbon isotope composition of bulk organic matter (δ13Corg), inferring a cold/dry period. Layers-1 and 6 were clustered together in association with a negative δ13Corg excursion, probably indicating a relatively warm/humid climate. The potential coupling between the n-alkane distributions and δ13Corg, suggests a consequence of vegetation change in response to climate change, with the late MIS3 being shown to be unstable, thought to be the climatic optimum in the Tibetan Plateau. Our results suggest that the cluster analysis used in this study probably provides an effective and authentic method to investigate the n-alkane distribution in paleolake sediments.

  11. Binary self-assembled monolayers of alkanethiols on gold: deposition from solution versus microcontact printing and the study of surface nanobubbles.

    Science.gov (United States)

    Bayat, Haider; Tranchida, Davide; Song, Bo; Walczyk, Wiktoria; Sperotto, Elena; Schönherr, Holger

    2011-02-15

    The coadsorption of alkanethiols on noble metals has been recognized for a long time as a suitable means of affording surfaces with systematically varied wettability and other properties. In this article, we report on a comparative study of the composition of the mixed self-assembled monolayers (SAMs) obtained (i) by the coadsorption of octadecanethiol (ODT) and 16-mercaptohexadecanoic acid (MHDA) from ethanol and chloroform onto gold substrates and (ii) by microcontact printing using poly(dimethyl siloxane) (PDMS) stamps. SAMs prepared by coadsorption from solution showed a preferential adsorption of ODT for both solvents, but this trend was reversed in microcontact-printed SAMs when using chloroform as a solvent, as evidenced by contact angle and Fourier transform infrared (FTIR) spectroscopy measurements. An approximately linear relationship between the static contact angle and the degree of swelling with different solvents was observed, which suggests that the surface composition can be controlled by the interaction of the solvent and the PDMS elastomer. The altered preference is attributed to the different partitioning of the two thiols into solvent-swelled PDMS, as shown by (1)H NMR spectroscopy. Finally, molecularly mixed binary SAMs on ODT and MHDA on template-stripped gold were applied to study the effect of surface nanobubbles on wettability by atomic force microscopy (AFM). With a decreasing macroscopic contact angle measured through water, the nanoscopic contact angle was found to decrease as well. PMID:21117682

  12. A surface enhanced Raman spectroscopy study of aminothiophenol and aminothiophenol-C{sub 60} self-assembled monolayers: Evolution of Raman modes with experimental parameters

    Energy Technology Data Exchange (ETDEWEB)

    Delafosse, G.; Patrone, L. [CNRS, IM2NP (UMR 7334), Faculte des Sciences et Techniques, Avenue Escadrille Normandie Niemen - Case 142, 13397 Marseille Cedex 20 (France); Aix-Marseille Universite, IM2NP, Campus de Saint-Jerome - Case 142, F-13397 Marseille Cedex 20 (France); Institut Superieur de l' Electronique et du Numerique, IM2NP, Maison des Technologies, Place Georges Pompidou, F-83000 Toulon (France); Merlen, A. [CNRS, IM2NP (UMR 7334), Faculte des Sciences et Techniques, Avenue Escadrille Normandie Niemen - Case 142, 13397 Marseille Cedex 20 (France); Universite du Sud Toulon-Var, IM2NP, Batiment R, BP 132, F-83957 La Garde Cedex (France); Clair, S. [CNRS, IM2NP (UMR 7334), Faculte des Sciences et Techniques, Avenue Escadrille Normandie Niemen - Case 142, 13397 Marseille Cedex 20 (France); Aix-Marseille Universite, IM2NP, Campus de Saint-Jerome - Case 142, F-13397 Marseille Cedex 20 (France)

    2012-05-21

    P-aminothiophenol (PATP) is a well-known molecule for the preparation of self-assembled monolayers on gold via its thiol functional group. After adsorption, it has been demonstrated that this molecule is anchored to gold through its thiol group, and standing nearly upright at the surface with the amino functional group on top. This molecule has been extensively studied by surface enhanced Raman spectroscopy but its exact SERS spectrum remains unclear. Here, we demonstrate that it can be strongly affected by at least two experimental parameters: laser power and layer density. Those features are discussed in terms of a dimerization of the PATP molecules. The free amino group affords the adsorption of other molecules such as C{sub 60}. In this case, a complex multilayer system is formed and the question of its precise characterisation remains a key point. In this article, we demonstrate that surface enhanced Raman spectroscopy combined with x ray photoelectron spectroscopy can bring very important information about the organization of such a self-assembled multilayer on gold. In our study, the strong evolution of Raman modes after C{sub 60} adsorption suggests a change in the organization of aminothiophenol molecules during C{sub 60} adsorption. These changes, also observed when the aminothiophenol layer is annealed in toluene, do not prevent the adsorption of C{sub 60} molecules.

  13. The uptake of tritium-labelled carnitine by monolayer cultures of human fetal muscle and its potential as a label in cytotoxicity studies

    International Nuclear Information System (INIS)

    As a novel approach to the investigation of immune responses directed against muscle antigens in inflammatory muscle disease, the use of tritium-labelled carnitine as a selective marker for myotubes in monolayer cultures was investigated. Tritium-labelled carnitine was incubated either with monolayer cultures of human fetal muscle or with syngeneic monolayer cultures of human fetal fibroblasts. The rate of uptake and loss of tritium-labelled carnitine by muscle cultures was compared with that shown by fibroblast cultures; values for the ratio Ksub(m)/Vsub(max) were 3.1 for muscle cultures and 0.46 for fibroblast cultures. Freeze-dried radioautographs of muscle monolayers, previously incubated with tritium-labelled carnitine confirmed the specific intra-tubular localization of the label. Fetal muscle monolayers, previously incubated with tritium-labelled carnitine, were used as targets in long-term cytotoxicity experiments into lymphocyte-mediated myotoxicity. Peripheral blood lymphocytes from patients with inflammatory muscle disease were shown to be myotoxic, but lymphocytes from normal individuals or those with non-inflammatory muscle disease were not. Carnitine-based measures of myotoxicity closely followed the clinical activity of the disease in one patient and the test shows considerable potential as a means of assessing myotube killing by lymphocytes on a per-cell basis. (author)

  14. Thermodynamic and structural studies of mixed monolayers: Mutual mixing of DPPC and DPPG with DoTAP at the air-water interface

    International Nuclear Information System (INIS)

    Phospholipid monomolecular films at the air-water interface are useful model membranes to understand miscibility among various components. Surface pressure (π)-area (A) isotherms of pure and mixed monolayers of dioleoyltrimethylammonium propane (DoTAP)-dipalmitoylphosphatidylcholine (DPPC) and DoTAP-dipalmitoyphosphatidylglycerol (DPPG) were constructed using a surface balance. DPPC and DPPG produced isotherms as expected and reported earlier. DoTAP, an unsaturated lipid, demonstrated a continuous π-A isotherm. Associative interactions were identified in DPPC-DoTAP mixtures compared to the pure components, while DPPG-DoTAP mixtures showed repulsive interaction up to an equimolar ratio. Compression moduli of the monolayers revealed that DPPC-DoTAP mixtures had increasing stability with increasing surface pressure, but addition of DoTAP to DPPG showed instability at low and intermediate concentrations. In both cases increased stability was returned at higher XDoTAP values and surface pressures. Lipid monolayer film thickness values, determined on a gold coated glass substrate by surface plasmon resonance spectroscopy (SPR), indicated a systematic change in height profile for DPPC-DoTAP mixtures with increasing XDoTAP. However, DPPG-DoTAP mixed monolayer systems demonstrated a biphasic response. The SPR data were in excellent agreement with our interpretation of the structure of solid supported lipid monolayers.

  15. At what chain length do unbranched alkanes prefer folded conformations?

    CERN Document Server

    Byrd, Jason N; Montgomery, John A

    2013-01-01

    Short unbranched alkanes are known to prefer linear conformations, while long unbranched alkanes are folded. It is not known with certainty at what chain length the linear conformation is no longer the global minimum. To clarify this point, we use {\\it ab initio} and density functional methods to compute the relative energies of the linear and hairpin alkane conformers for increasing chain lengths. Extensive electronic structure calculations are performed to obtain optimized geometries, harmonic frequencies and accurate single point energies for the selected alkane conformers from octane through octadecane. Benchmark CCSD(T)/cc-pVTZ single point calculations are performed for chains through tetradecane, while approximate methods are required for the longer chains up to octadecane. Using frozen natural orbitals to unambiguously truncate the virtual orbital space we are able to compute composite CCSD FNO(T) single point energies for all the chain lengths. This approximate composite method has significant comput...

  16. Alkane oxidation by Pseudomonas oleovorans : genes and proteins

    NARCIS (Netherlands)

    van Beilen, Jan Berthold

    1994-01-01

    This thesis deals with the molecular genetics and biochemistry of oxidation of medium chainlength alkanes by P. oleovorans, as part of a program to develop biotechnological processes, based on oxygenases.

  17. Coverage dependent organic-metal interaction studied by high-resolution core level spectroscopy: SnPc (sub)monolayers on Ag(1 1 1)

    Energy Technology Data Exchange (ETDEWEB)

    Haeming, M.; Scheuermann, C. [Experimentelle Physik II, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Schoell, A. [Experimentelle Physik II, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Forschungszentrum Karlsruhe, Gemeinschaftslabor fuer Nanoanalytik, D-76021 Karlsruhe (Germany)], E-mail: achim.schoell@physik.uni-wuerzburg.de; Reinert, F. [Experimentelle Physik II, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Forschungszentrum Karlsruhe, Gemeinschaftslabor fuer Nanoanalytik, D-76021 Karlsruhe (Germany); Umbach, E. [Experimentelle Physik II, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Forschungszentrum Karlsruhe and Karlsruhe Institute of Technology, Weberstrasse 5, D-76021 Karlsruhe (Germany)

    2009-08-15

    We study the electronic structure of tin-phthalocyanine (SnPc) molecules adsorbed on a Ag(1 1 1) surface by high-resolution photoelectron spectroscopy. We particularly address the effect of different SnPc coverages on the interaction and charge transfer at the interface. The results give evidence for a covalent molecule-substrate interaction, which is temperature and coverage dependent. The valence and core level spectra as well as the work function measurements allow us monitoring subtle differences in the strength of the interface interaction, thus demonstrating the sensitivity of the methods. The results consistently show the effect of charge exchange between substrate and molecules which obviously leads to a net charge transfer into the SnPc molecules, and which is increased with decreasing coverage. Surprisingly, the Sn3d core levels are neither effected by variations of charge transfer and interaction strength, nor by a possible 'Sn-up' or 'Sn-down' orientation, which have been observed for sub-monolayers.

  18. Surface sealing using self-assembled monolayers and its effect on metal diffusion in porous low-k dielectrics studied using monoenergetic positron beams

    Science.gov (United States)

    Uedono, Akira; Armini, Silvia; Zhang, Yu; Kakizaki, Takeaki; Krause-Rehberg, Reinhard; Anwand, Wolfgang; Wagner, Andreas

    2016-04-01

    Surface sealing effects on the diffusion of metal atoms in porous organosilicate glass (OSG) films were studied by monoenergetic positron beams. For a Cu(5 nm)/MnN(3 nm)/OSG(130 nm) sample fabricated with pore stuffing, C4F8 plasma etch, unstuffing, and a self-assembled monolayer (SAM) sealing process, it was found that pores with cubic pore side lengths of 1.1 and 3.1 nm coexisted in the OSG film. For the sample without the SAM sealing process, metal (Cu and Mn) atoms diffused from the top Cu/MnN layer into the OSG film and were trapped by the pores. As a result, almost all pore interiors were covered with those metals. For the sample damaged by an Ar/C4F8 plasma etch treatment before the SAM sealing process, SAMs diffused into the OSG film, and they were preferentially trapped by larger pores. The cubic pore side length in these pores containing self-assembled molecules was estimated to be 0.7 nm. Through this work, we have demonstrated that monoenergetic positron beams are a powerful tool for characterizing capped porous films and the trapping of atoms and molecules by pores.

  19. Transepithelial permeability studies of flavan-3-ol-C-glucosides and procyanidin dimers and trimers across the Caco-2 cell monolayer.

    Science.gov (United States)

    Hemmersbach, Sarah; Brauer, Susanne S; Hüwel, Sabine; Galla, Hans-Joachim; Humpf, Hans-Ulrich

    2013-08-21

    In this study the permeability of two flavanol-C-glucosides (FCglcs) and five dimeric and trimeric flavan-3-ols, namely, procyanidins (PCs), was investigated with the human colon carcinoma cell line (Caco-2) model. These compounds can be found especially in cocoa, and they are of great interest due to their assumed beneficial health effects. Transepithelial electrical resistance (TEER) and capacitance were measured online with a CellZscope device prior to and during the whole experiment to guarantee the maintenance of the barrier properties. The transport experiments with pure, single compounds (50-300 μM) from apical to basolateral side showed slight permeation of PCs A2, B2, and B5 and cinnamtannin B1 (CB1) as well as (-)-catechin-6-C-glucoside (C6Cglc) and (-)-catechin-8-C-glucoside (C8Cglc) of about 0.02-0.2% after 24 h. Transport of PC C1 could not be detected. Inhibition of P-glycoprotein (Pgp) increased the permeation of PC B2 and CB1 to the basolateral side, which indicates that Pgp counteracts the transport of these compounds. Metabolites (epicatechin, 3'- and 4'-O-epicatechin) in very small amounts were detectable only for PC B2. These are the first data concerning the permeability of flavan-3-ol-C-glucosides across the Caco-2 cell monolayer. PMID:23885956

  20. A graph theoretical method for partial ordering of alkanes

    OpenAIRE

    Vukičević, Damir; Sedlar, Jelena; Rajtmajer, Sarah Michelle

    2007-01-01

    The topological Zagreb index M-1 introduces an ordering on the set of alkanes. Recently, modified Zagreb indices M-lambda(1) have been proposed, and it is noted that they differently order alkanes. In this paper, the level of consistency between these orders is analyzed. A new partial order > as the intersection of all partial orders M-lambda(1) (where m is at least 2) is introduced and its properties are analyzed.

  1. Structure and solvation forces in confined films of alkanes

    OpenAIRE

    Dijkstra, Marjolein

    1998-01-01

    We compute by computer simulations the solvation force of a system of linear and branched alkanes confined in a slab geometry. The solvation force for linear decane oscillates with distance with a periodicity close to the width of the molecules. The branched alkanes, 2- methylundecane and 2-methylheptane, show a similar oscillatory behaviour, however the oscillations are decreased with a factor of about three and show a long-range attractive force. In addition, we show that the critical tempe...

  2. Alkane Biosynthesis Genes in Cyanobacteria and Their Transcriptional Organization

    OpenAIRE

    Stephan eKlähn; Desiree eBaumgartner; Ulrike ePfreundt; Karsten eVoigt; Verena eSchoen; Claudia eSteglich; Hess, Wolfgang R

    2014-01-01

    In cyanobacteria, alkanes are synthesized from a fatty acyl-ACP by two enzymes, acyl-acyl carrier protein reductase (AAR) and aldehyde deformylating oxygenase (ADO). Despite the great interest in the exploitation for biofuel production, nothing is known about the transcriptional organization of their genes or the physiological function of alkane synthesis. The comparison of 115 microarray datasets indicates the relatively constitutive expression of aar and ado genes. The analysis of 181 avail...

  3. New perspectives for the isomerization of light n-alkanes

    OpenAIRE

    Hubaut, Robert; Rives, Alain; Kuang, Wenxing; Fournier, Michel

    2005-01-01

    Isomerization of light n-alkanes into the high-octane number branched alkanes is an important challenge for petroleum refining industry. According to the literature, such a transformation needs two different active centres: one having a hydrogenating/dehydrogenating ability and another, a protonic acid function. From this point of view, heteropolyacids (HPAs) in mixing with one or more transition metal appear promising. Mechanical mixtures of alumina-supported platinum or of mixed palladium (...

  4. Phonons in bulk and monolayer HfS2 and possibility of phonon-mediated superconductivity: A first-principles study

    Science.gov (United States)

    Chen, Jianyong

    2016-07-01

    Using density functional perturbation theory (DFPT) with Born effective charges included, we calculate in detail the phonons of bulk and monolayer HfS2. Our calculated phonon frequencies and LO-TO splitting agree well with experimental data. The variation of phonon frequencies from bulk to monolayer can be accounted for in terms of the delicate balance of the long- and short-range force constants. The ultimate strength under biaxial tensile strain is explored for the first time. Monolayer HfS2 can suffer only no more than 6% tensile strain. Our important finding is that the phonon gap appears when goes to single layer from bulk and can be tuned by biaxial tension. By analysing the Eliashberg function we conclude that HfS2 cannot turn to superconductivity by electron-phonon interaction.

  5. Structural and electronic properties of multilayer graphene on monolayer hexagonal boron nitride/nickel (111) interface system: A van der Waals density functional study

    Science.gov (United States)

    Yelgel, Celal

    2016-02-01

    The structural and electronic properties of multilayer graphene adsorbed on monolayer hexagonal boron nitride (h-BN)/Ni(111) interface system are investigated using the density functional theory with a recently developed non-local van der Waals density functional (rvv10). The most energetically favourable configuration for a monolayer h-BN/Ni(111) interface is found to be N atom atop the Ni atoms and B atom in fcc site with the interlayer distance of 2.04 Å and adsorption energy of 302 meV/BN. Our results show that increasing graphene layers on a monolayer h-BN/Ni(111) interface leads to a weakening of the interfacial interaction between the monolayer h-BN and Ni(111) surface. The adsorption energy of graphene layers on the h-BN/Ni(111) interface is found to be in the range of the 50-120 meV/C atom as the vertical distance from h-BN to the bottommost graphene layers decreases. With the adsorption of a multilayer graphene on the monolayer h-BN/Ni(111) interface system, the band gap of 0.12 eV and 0.25 eV opening in monolayer graphene and bilayer graphene near the K point is found with an upward shifting of the Fermi level. However, a stacking-sensitive band gap is opened in trilayer graphene. We obtain the band gap of 0.35 eV close to the K point with forming a Mexican hat band structure for ABC-stacked trilayer graphene.

  6. Positronium in solid phases of n-alkane binary mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Zgardzińska, B.; Goworek, T.

    2015-09-08

    Highlights: • Rotator phase in even alkanes C{sub n}H{sub 2n+2} with n ⩽ 20 appears in mixed samples only. • Interlamellar gap width is the same for shorter chain alkane concentration x and 1 − x. • Excess electron trapping diminishes with broadening of alkane chain distribution Δn. - Abstract: Binary mixtures of even-numbered normal alkanes C{sub n}H{sub 2n+2} and C{sub n+2}H{sub 2n+6} with n ⩽ 18 were investigated by positron annihilation spectroscopy. Formation of the rotator phase was observed in mixed structures, while no such a phase in neat alkanes in this range of n was found. Phase diagrams for n = 18 and n = 16 are very similar to the diagrams for binary mixtures of odd-numbered alkanes. The effect of positronium formation with trapped excess electrons weakens with decreasing n, at low n values the time constant of Ps rise contains the component much shorter than 1 h.

  7. Superposition-additive approach in the description of thermodynamic parameters of formation and clusterization of substituted alkanes at the air/water interface.

    Science.gov (United States)

    Vysotsky, Yu B; Belyaeva, E A; Fomina, E S; Vasylyev, A O; Vollhardt, D; Fainerman, V B; Aksenenko, E V; Miller, R

    2012-12-01

    The superposition-additive approach developed previously was shown to be applicable for the calculations of the thermodynamic parameters of formation and atomization of conjugate systems, their dipole polarizability, molecular diamagnetic susceptibility, π-electronic ring currents, etc. In the present work, the applicability of this approach for the calculation of the thermodynamic parameters of formation and clusterization at the water/air interface of alkanes, fatty alcohols, thioalcohols, amines, nitriles, fatty acids (C(n)H(2n+1)X, X is the functional group) and cis-unsaturated carboxylic acids (C(n)H(2n-1)COOH) is studied. Using the proposed approach the thermodynamic quantities determined agree well with the available data, either calculated using the semiempirical (PM3) quantum chemical method, or obtained in experiments. In particular, for enthalpy and Gibbs' energy of the formation of substituted alkane monomers from the elementary substances, and their absolute entropy, the standard deviations of the values calculated according to the superposition-additive scheme with the mutual superimposition domain C(n-2)H(2n-4) (n is the number of carbon atoms in the alkyl chain) from the results of PM3 calculations for alkanes, alcohols, thioalcohols, amines, fatty acids, nitriles and cis-unsaturated carboxylic acids are respectively: 0.05, 0.004, 2.87, 0.02, 0.01, 0.77, and 0.01 kJ/mol for enthalpy; 2.32, 5.26, 4.49, 0.53, 1.22, 1.02, 5.30 J/(molK) for absolute entropy; 0.69, 1.56, 3.82, 0.15, 0.37, 0.69, 1.58 kJ/mol for Gibbs' energy, whereas the deviations from the experimental data are: 0.52, 5.75, 1.40, 1.00, 4.86 kJ/mol; 0.52, 0.63, 1.40, 6.11, 2.21 J/(molK); 2.52, 5.76, 1.58, 1.78, 4.86 kJ/mol, respectively (for nitriles and cis-unsaturated carboxylic acids experimental data are not available). The proposed approach provides also quite accurate estimates of enthalpy, entropy and Gibbs' energy of boiling and melting, critical temperatures and standard heat

  8. Effect of Rhamnolipid (Biosurfactant) Structure on Solubilization and Biodegradation of n-Alkanes

    OpenAIRE

    Zhang, Y.; Miller, R M

    1995-01-01

    A study to quantify the effect of rhamnolipid biosurfactant structure on the degradation of alkanes by a variety of Pseudomonas isolates was conducted. Two dirhamnolipids were studied, a methyl ester form (dR-Me) and an acid form (dR-A). These rhamnolipids have different properties with respect to interfacial tension, solubility, and charge. For example, the interfacial tension between hexadecane and water was decreased to

  9. Evidence from carbon isotope measurements for biological origins of individual longchain n-alkanes in sediments from the Nansha Sea, China

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Carbon isotopes are measured for individual long-chain n-alkanes in sediments from the Nansha Sea. The features of carbon isotopic compositions of individual n-alkanes and their origins are studied. The results show that the long-chain n-aikanes have a light carbon isotopic composition and a genetic feature of mixing sources, and low-latitude higher plants and microbes are considered to be their main end member sources. Based on the abundances and carbon isotopic compositions of individual n-alkanes, the fractional contributions of the two end member sources to individual n-aikanes are quantitatively calculated by using a mixing model. The obtained data indicate that the fractional contributions of the two biological sources are different in the three samples. A trend is that the contribution of microbes increases with the depth. These results provide the theory basis and quantitatively studied method for carbon isotopic applied research of individual n-alkanes.

  10. Melting mechanism in monolayers of flexible rod-shaped molecules

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Taub, H.

    1992-01-01

    The melting of butane and hexane monolayers adsorbed on a graphite basal-plane surface has been studied by molecular-dynamics simulations and experimentally by neutron diffraction. The simulation results are qualitatively consistent with the observed diffraction patterns and suggest a general...... mechanism for melting in monolayers of flexible rod-shaped molecules. Melting requires the formation of vacancies in the monolayer by molecular motion perpendicular to the surface. This ‘‘footprint reduction’’ mechanism implies that strictly two-dimensional theories of melting are inapplicable...

  11. Experimental Investigation of Microbially Induced Corrosion of Test Samples and Effect of Self-Assembled Hydrophobic Monolayers. Exposure of Test Samples to Continuous Microbial Cultures, Chemical Analysis, and Biochemical Studies

    Energy Technology Data Exchange (ETDEWEB)

    Laurinavichius, K.S.

    1998-09-30

    The study of biocorrosion of aluminum and beryllium samples were performed under conditions of continuous fermentation of thermophilic anaerobic microorganisms of different groups. This allowed us to examine the effect of various types of metabolic reactions of reduction-oxidation proceeding at different pH and temperatures under highly reduced conditions on aluminum and beryllium corrosion and effect of self-assembled hydrophobic monolayers.

  12. The interaction of bioactive peptides with an immobilized phosphatidylcholine monolayer.

    OpenAIRE

    Mozsolits, H; Lee, T. H.; Wirth, H J; Perlmutter, P; Aguilar, M I

    1999-01-01

    The interaction of three bioactive peptides, bombesin, beta-endorphin, and glucagon with a phosphatidylcholine monolayer that was immobilized to porous silica particles and packed into a stainless steel column cartridge, has been studied using dynamic elution techniques. This immobilized lipid monolayer provides a biophysical model system with which to study the binding of peptides to a lipid membrane. In particular, the influence of temperature and methanol concentration on the affinity of e...

  13. Crossed-beam DC slice imaging of fluorine atom reactions with linear alkanes

    International Nuclear Information System (INIS)

    We report the reaction dynamics of F atom with selected alkanes studied by crossed beam scattering with DC slice ion imaging. The target alkanes are propane, n-butane, and n-pentane. The product alkyl radicals are probed by 157 nm single photon ionization following reaction at a collision energy of ∼10 kcal mol−1. The analyzed data are compared with the corresponding theoretical studies. Reduced translational energy distributions for each system show similar trends with little of the reaction exoergicity appearing in translation. However, the pentane reaction shows a somewhat smaller fraction of available energy in translation than the other two, suggesting greater energy channeled into pentyl internal degrees of freedom. The center-of-mass angular distributions all show backscattering as well as sharp forward scattering that decreases in relative intensity with the size of the molecule. Possible reasons for these trends are discussed

  14. Crossed-beam DC slice imaging of fluorine atom reactions with linear alkanes

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Yuanyuan; Kamasah, Alexander; Joalland, Baptiste; Suits, Arthur G., E-mail: asuits@chem.wayne.edu [Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202 (United States)

    2015-05-14

    We report the reaction dynamics of F atom with selected alkanes studied by crossed beam scattering with DC slice ion imaging. The target alkanes are propane, n-butane, and n-pentane. The product alkyl radicals are probed by 157 nm single photon ionization following reaction at a collision energy of ∼10 kcal mol{sup −1}. The analyzed data are compared with the corresponding theoretical studies. Reduced translational energy distributions for each system show similar trends with little of the reaction exoergicity appearing in translation. However, the pentane reaction shows a somewhat smaller fraction of available energy in translation than the other two, suggesting greater energy channeled into pentyl internal degrees of freedom. The center-of-mass angular distributions all show backscattering as well as sharp forward scattering that decreases in relative intensity with the size of the molecule. Possible reasons for these trends are discussed.

  15. Electromelting of Confined Monolayer Ice

    OpenAIRE

    Qiu, Hu; Guo, Wanlin

    2013-01-01

    In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to field-induced disruption of the water-wall interaction induced well-ordered network of hydrogen bond. This electromelting ...

  16. Effect of chain length on the adhesion behaviour of n-alkanethiol self-assembled monolayers on Au(1 1 1): An atomic force microscopy study

    Indian Academy of Sciences (India)

    S Subramanian; S Sampath

    2005-10-01

    The effect of chain length on the adhesion behaviour of n-alkanethiols CH3(CH2) SH, where = 5, 6, 7, 9, 10, 11, 14 and 15 has been followed by carrying out pull-off force measurement using atomic force microscopy (AFM). The self-assembled monolayers on Au(111) surface has been characterized by reflection absorption infra-red spectroscopy (RAIRS) and contact mode AFM. It is observed that the work of adhesion is independent of thiol chain length though the standard deviation is high for short chain length thiol-based monolayers. This may be attributed to the relatively more deformable nature of the short chain thiol films due to their heterogeneity in the monolayer structure than the long chain ones. This, in turn, increases the contact area/volume between the AFM tip and the monolayer, and hence the force of adhesion. However, in the presence of water, the force of adhesion is lower than that observed in air reflecting the effects of capillary forces/polar components associated with the surface energy.

  17. Electronic structures and elastic properties of monolayer and bilayer transition metal dichalcogenides MX2 (M = Mo, W; X = O, S, Se, Te): A comparative first-principles study

    Science.gov (United States)

    Zeng, Fan; Zhang, Wei-Bing; Tang, Bi-Yu

    2015-09-01

    First-principle calculations with different exchange-correlation functionals, including LDA, PBE, and vdW-DF functional in the form of optB88-vdW, have been performed to investigate the electronic and elastic properties of two-dimensional transition metal dichalcogenides (TMDCs) with the formula of MX2(M = Mo, W; X = O, S, Se, Te) in both monolayer and bilayer structures. The calculated band structures show a direct band gap for monolayer TMDCs at the K point except for MoO2 and WO2. When the monolayers are stacked into a bilayer, the reduced indirect band gaps are found except for bilayer WTe2, in which the direct gap is still present at the K point. The calculated in-plane Young moduli are comparable to that of graphene, which promises possible application of TMDCs in future flexible and stretchable electronic devices. We also evaluated the performance of different functionals including LDA, PBE, and optB88-vdW in describing elastic moduli of TMDCs and found that LDA seems to be the most qualified method. Moreover, our calculations suggest that the Young moduli for bilayers are insensitive to stacking orders and the mechanical coupling between monolayers seems to be negligible. Project supported by the Construct Program of the Key Discipline in Hunan Province, China and Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province, China.

  18. Tunable electronic and magnetic properties of a MoS2 monolayer with vacancies under elastic planar strain: Ab initio study

    Science.gov (United States)

    Salami, N.; Shokri, A. A.; Elahi, S. M.

    2016-03-01

    Electronic and magnetic properties of a molybdenum disulfide (MoS2) monolayer with some intrinsic and extrinsic vacancies are investigated using ab initio method in the presence of planar strain distributions. The calculations are carried out within the density functional theory (DFT) as implemented in SIESTA package. By using fully relaxed structures and applying a full spin-polarized description to the system, we concentrate on created magnetic moment due to the vacancies under different planar strains. The results show that the extrinsic MoS6 vacancy induces a net magnetic moment of 6.00 μB per supercell. Also, it is found that the pure MoS2 monolayer for the most cases does not show any magnetic properties under the planar strain. While the net magnetic moment of MoS2 monolayer with the vacancies enhances as the planar tensile strain is applied. The tunable magnetic moment of MoS2 monolayer may be utilized for the development of spintronic and flexible electronic nano-devices.

  19. Collective cell motion in endothelial monolayers

    International Nuclear Information System (INIS)

    Collective cell motility is an important aspect of several developmental and pathophysiological processes. Despite its importance, the mechanisms that allow cells to be both motile and adhere to one another are poorly understood. In this study we establish statistical properties of the random streaming behavior of endothelial monolayer cultures. To understand the reported empirical findings, we expand the widely used cellular Potts model to include active cell motility. For spontaneous directed motility we assume a positive feedback between cell displacements and cell polarity. The resulting model is studied with computer simulations and is shown to exhibit behavior compatible with experimental findings. In particular, in monolayer cultures both the speed and persistence of cell motion decreases, transient cell chains move together as groups and velocity correlations extend over several cell diameters. As active cell motility is ubiquitous both in vitro and in vivo, our model is expected to be a generally applicable representation of cellular behavior

  20. Studies of endothelial monolayer formation on irradiated poly-L-lactide acid with ions of different stopping power and velocity

    Science.gov (United States)

    Arbeitman, Claudia R.; del Grosso, Mariela F.; Ibañez, Irene L.; Behar, Moni; Grasselli, Mariano; Bermúdez, Gerardo García

    2015-12-01

    In this work we study cell viability, proliferation and morphology of bovine aortic endothelial cells (BAEC) cultured on poly-L-lactide acid (PLLA) modified by heavy ion irradiation. In a previous study comparing ions beams with the same stopping power we observed an increase in cell density and a better cell morphology at higher ion velocities. In the present work we continued this study using heavy ions beam with different stopping power and ion velocities. To this end thin films of 50 μm thickness were irradiated with 2 MeV/u and 0.10 MeV/u ion beams provided the Tandar (Buenos Aires, Argentina) and Tandetron (Porto Alegre, Brazil) accelerators, respectively. The results suggest that a more dense and elongated cell shapes, similar to the BAEC cells on the internal surface of bovine aorta, was obtained for stopping power of 18.2-22.1 MeV cm2 mg-1 and ion velocity of 2 MeV/u. On the other hand, for low ion velocity 0.10 MeV/u the cells present a more globular shapes.

  1. Electron Trapping by Polar Molecules in Alkane Liquids: Cluster Chemistry in Dilute Solution

    CERN Document Server

    Shkrob, I A; Shkrob, Ilya A.; Sauer, Myran C.

    2005-01-01

    Monomers and small clusters of such molecules can reversibly trap conduction band electrons in dilute alkane solutions. The dynamics and energetics of this trapping have been studied using pulse radiolysis - transient absorption spectroscopy and time-resolved photoconductivity. Binding energies, thermal detrapping rates, and absorption spectra of excess electrons attached to monomer and multimer solute traps are obtained and possible structures for these species are discussed. "Dipole coagulation" (stepwise growth of the solute cluster around the cavity electron) predicted by Mozumder in 1972 is observed. Acetonitrile monomer is shown to solvate the electron by its methyl group, just like the alkane solvent does. The electron is dipole-bound to the CN group; the latter points away from the cavity. The resulting negatively charged species has a binding energy of 0.4 eV and absorbs in the infrared. Molecules of straight-chain aliphatic alcohols solvate the excess electron by their OH groups; at equilibrium, the...

  2. Measurement of thermodiffusion coefficient in n-alkane binary mixtures: composition dependence.

    Science.gov (United States)

    Madariaga, J A; Santamaría, C; Bou-Ali, M Mounir; Urteaga, P; Alonso De Mezquia, D

    2010-05-27

    In this work, we have measured the thermodiffusion coefficient of different n-alkane binary mixtures at several concentrations using the thermogravitational technique. In particular, we have studied the n-dodecane/n-heptane system as a function of composition and other systems covering a large range of mass differences and concentration at 25 degrees C and 1 atm. The results show that for any concentration the thermodiffusion coefficient of n-alkane mixtures is proportional to the mass difference between the components and to the ratio of the thermal expansion coefficient and viscosity of the mixture. The obtained equation allows us to determine the infinite dilution values of the thermodiffusion coefficient. We compare these values with recent experimental results in dilute polymer solutions and analyze the Brenner theory of thermodiffusion. Finally, it is shown that the thermodiffusion coefficient depends linearly with the mass fraction, and it can be calculated from the viscosity and thermal expansion of the pure components. PMID:20429569

  3. Calculations of gamma-ray spectral profiles of linear alkanes in the positron annihilation process

    CERN Document Server

    Ma, X G

    2014-01-01

    The positron-electron annihilation gamma-ray spectra of linear alkanes CnH2n+2 (n=1-12) have been studied systematically. A profile quality (PQ) parameter, is introduced to assess the agreement between the obtained theoretical profiles and the experimental measurements in the entire region of energy shift of the spectra. Together with the Doppler shift of the gamma-ray spectra, the two parameters,PQ and Doppler shift, are able to provide a more comprehensive assessment of the calculated gamma-ray spectra with respect to available experiment. Applying the recently developed docking model, the present study determines the positrophilic electrons for individual alkanes from which the gamma-ray spectral profiles are calculated. The results achieve an excellent agreement with experiment, not only with respect to the Doppler shift, but also with respect to the gamma-ray profiles in the photon energy region up to 5 keV. The study further calculates the gamma-ray spectra of other linear alkanes in the series without ...

  4. Studies on the synthesis of sterol carrier protein-2 in rat adrenocortical cells in monolayer culture. Regulation by ACTH and dibutyryl cyclic 3',5'-AMP

    International Nuclear Information System (INIS)

    The effects of ACTH or dibutyryl cyclic AMP (Bt2cAMP) on the synthesis of sterol carrier protein-2 (SCP2) have been studied in rat adrenocortical cells in monolayer culture. Radiolabeling of total cellular proteins with [35S]methionine and immunoprecipitation with antibodies directed against rat liver SCP2, followed by polyacrylamide gel electrophoresis and fluorography, showed a 3-4-fold increase in the rate of synthesis of SCP2 in cells treated for 48 h with ACTH (1 microM) or Bt2cAMP (0.1 mM). The induction of SCP2 synthesis depended upon the concentrations of ACTH or Bt2cAMP with an ED50 of 8 and 100 nM, respectively, and increased linearly with time between 12 and 48 h of treatment. Immunoprecipitation of SCP2 synthesized in a rabbit reticulocyte in vitro translation system programmed with RNA isolated from cells treated with ACTH or Bt2cAMP revealed increased synthesis of SCP2 compared to RNA from control cells. The immunoprecipitable rat adrenal SCP2, synthesized in a cell-free translation system, showed mobility corresponding to Mr of 14,400 upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis and was clearly larger than immunodetectable SCP2 synthesized in cultured adrenal cells (Mr = 11,300). The electrophoretic mobilities of rat liver SCP2 synthesized in cultured cells and in a cell-free translation system were the same as the respective forms from rat adrenal

  5. Massive endocytosis driven by lipidic forces originating in the outer plasmalemmal monolayer: a new approach to membrane recycling and lipid domains

    OpenAIRE

    Fine, Michael; Llaguno, Marc C.; Lariccia, Vincenzo; Lin, Mei-Jung; Yaradanakul, Alp; Hilgemann, Donald W.

    2011-01-01

    The roles that lipids play in endocytosis are the subject of debate. Using electrical and imaging methods, we describe massive endocytosis (MEND) in baby hamster kidney (BHK) and HEK293 cells when the outer plasma membrane monolayer is perturbed by the nonionic detergents, Triton X-100 (TX100) and NP-40. Some alkane detergents, the amphipathic drugs, edelfosine and tamoxifen, and the phospholipase inhibitor, U73122, are also effective. Uptake of the membrane tracer, FM 4–64, into vesicles and...

  6. Electrostatic cluster formation in lipid monolayers

    OpenAIRE

    Ellenbroek, Wouter G.; Wang, Yu-Hsiu; Christian, David A.; Discher, Dennis E.; Janmey, Paul A.; Liu, Andrea J.

    2010-01-01

    We study phase separation in mixed monolayers of neutral and highly negatively charged lipids, induced by the addition of divalent positively charged counterions. We find good agreement between experiments on mixtures of pip2 and sopc and simulations of a simplified model in which only the essential electrostatic interactions are retained. Thus, our results support an interpretation of pip2 clustering as governed primarily by electrostatic interactions, in which divalent ions such as calcium ...

  7. Laser-Induced Spallation of Microsphere Monolayers

    OpenAIRE

    Hiraiwa, Morgan; Stossel, Melicent; Khanolkar, Amey; Wang, Junlan; Boechler, Nicholas

    2016-01-01

    The detachment of a semi-ordered monolayer of polystyrene microspheres adhered to an aluminum-coated glass substrate is studied using a laser-induced spallation technique. The microsphere-substrate adhesion force is estimated from substrate surface displacement measurements obtained using optical interferometry, and a rigid-body model that accounts for the inertia of the microspheres. The estimated adhesion force is compared with estimates obtained from interferometric measurement of the out-...

  8. Significance of medium chainn-alkanes as accompanying compounds in hemipteran defensive secretions: An investigation based on the defensive secretion ofCoridius janus.

    Science.gov (United States)

    Gunawardena, N E; Herath, H M

    1991-12-01

    A mixture oftrans-2-hexenal;n-tridecane (60:40, w/w), the natural combination present in the defensive secretion ofCoridius janus (Hemiptera; Pentatomidae) was shown by comparison with similar aldehyde mixtures having longer and shorter chainn-alkanes, to be the optimal combination as a fumigant and a repellent against three test insect species,Anoplolepis longipes, Sitotroga cerealella, andCulex quinquefasciatus. Toxic values obtained for the three insects, respectively: 1/LC50, 1.72, 4.54, and 6.66 ppm while repellencies were 63%, 50%, and 69%. This study revealed that amongt-2-hexenal:n-alkane combinations those with medium carbon chains,viz C-11 and C-12, also possessed high toxicities and repellencies comparable to that of the natural combination while those with shorter and longern-alkanes possessed lower activity. Toxicities and repellencies ofn-alkane series were only moderate to low showing highest toxic values forn-tridecane at 1/LC50, 0.39, 2.32, and 2.32 ppm and repellencies at 31%, 30%, and 32% for the three test insects, respectively. This series, nevertheless, showed similar variation, medium length chains, C-11, C-12, and C-13 showing comparatively higher activity than other alkanes of shorter and longer chains. This study also revealed that the fumigant property of both alkane and aldehyde are of equal importance while repellency is heavily dependent on the aldehyde. PMID:24258638

  9. Saccharomyces cerevisiae SHSY detoxifies petroleum n-alkanes by an induced CYP52A58 and an enhanced order in cell surface hydrophobicity.

    Science.gov (United States)

    Hanano, Abdulsamie; Shaban, Mouhnad; Almousally, Ibrahem; Al-Ktaifani, Mahmoud

    2015-09-01

    Environmental hydrocarbon contamination has a serious hazard to human health. Alkanes, the major component of hydrocarbons, can be consumed by various species of yeast. We previously identified a new strain SHSY of Saccharomyces cerevisiae with a remarkable ability to utilize the petroleum crude-oil (PCO) in aqueous solution. The current study demonstrated that the n-alkanes-assimilation activity of S. cerevisiae SHSY was related to an induced microsomal protein of 59 kDa approximately. The identified ORF encoded a protein of 517 amino acids and shared 93% sequence identity with an alkane-inducible hydroxylase CYP52A53 isolated from Scheffersomyces stipitis CBS. It was therefore referred as CYP52A58. The catalytic activity of the recombinant CYP52A58 was confirmed by the hydroxylation of n-alkanes, it showed an optimal mono-terminal hydroxylation activity toward n-hexadecane. Moreover, the ability of the yeast to use n-alkanes was accompanied with an increasing level in cell wall mannoproteins. Two differential protein bands were detected in the mannoproteins extracted from PCO-grown yeast. In parallel, a significant increase in the fatty acids content with a high degree of unsaturation was subsequently detected in the PCO-grown yeast. This study characterizes a safe and potential microorganism to remove n-alkanes from the aquatic environment. PMID:25434275

  10. Phospholipid interactions in model membrane systems. I. Experiments on monolayers.

    OpenAIRE

    Mingins, J; Stigter, D; Dill, K A

    1992-01-01

    We study the lateral headgroup interactions among phosphatidylcholine (PC) molecules and among phosphatidylethanolamine (PE) molecules in monolayers and extend our previous models. In this paper, we present an extensive set of pressure-area isotherms and surface potential experiments on monolayers of phospholipids ranging from 14 to 22 carbons in length at the n-heptane/water interface, over a wide range of temperature, salt concentration, and pH on the acid side. The pressure data presented ...

  11. Biodegradation of Variable-Chain-Length Alkanes at Low Temperatures by a Psychrotrophic Rhodococcus sp.

    OpenAIRE

    Whyte, Lyle G.; Hawari, Jalal; Zhou, Edward; Bourbonnière, Luc; Inniss, William E.; Greer, Charles W

    1998-01-01

    The psychrotroph Rhodococcus sp. strain Q15 was examined for its ability to degrade individual n-alkanes and diesel fuel at low temperatures, and its alkane catabolic pathway was investigated by biochemical and genetic techniques. At 0 and 5°C, Q15 mineralized the short-chain alkanes dodecane and hexadecane to a greater extent than that observed for the long-chain alkanes octacosane and dotriacontane. Q15 utilized a broad range of aliphatics (C10 to C21 alkanes, branched alkanes, and a substi...

  12. Diffusion of methane and other alkanes in metal-organic frameworks for natural gas storage

    Energy Technology Data Exchange (ETDEWEB)

    Borah, B; Zhang, HD; Snurr, RQ

    2015-03-03

    Diffusion of methane, ethane, propane and n-butane was studied within the micropores of several metal organic frameworks (MOFs) of varying topologies, including the MOFs PCN-14, NU-125, NU-1100 and DUT-49. Diffusion coefficients of the pure components, as well as methane/ethane, methane/ propane and methane/butane binary mixtures, were calculated using molecular dynamics simulations to understand the effect of the longer alkanes on uptake of natural gas in MOB. The calculated self diffusion coefficients of all four components are on the order of 10(-8) m(2)/s. The diffusion coefficients of the pure components decrease as a function of chain length in all of the MOFs studied and show different behaviour as a function of loading in different MOB. The self-diffusivities follow the trend DPCN-14 < DNU-125 approximate to DNU-1100 < DDUT-49, which is exactly the reverse order of the densities of the MOFs: PCN-14 > NU-125 approximate to NU-1100 > DUT-49. By comparing the diffusion of pure methane and methane mixtures vvith the higher alkancs, it is observed that the diffusivity of methane is unaffected by the presence of the higher alkanes in the MOFs considered, indicating that the diffusion path of methane is not blocked by the higher alkanes present in natural gas. (C) 2014 Elsevier Ltd. All rights reserved.

  13. Metabolism of Hydrocarbons in n-Alkane-Utilizing Anaerobic Bacteria.

    Science.gov (United States)

    Wilkes, Heinz; Buckel, Wolfgang; Golding, Bernard T; Rabus, Ralf

    2016-01-01

    The glycyl radical enzyme-catalyzed addition of n-alkanes to fumarate creates a C-C-bond between two concomitantly formed stereogenic carbon centers. The configurations of the two diastereoisomers of the product resulting from n-hexane activation by the n-alkane-utilizing denitrifying bacterium strain HxN1, i.e. (1-methylpentyl)succinate, were assigned as (2S,1'R) and (2R,1'R). Experiments with stereospecifically deuterated n-(2,5-2H2)hexanes revealed that exclusively the pro-S hydrogen atom is abstracted from C2 of the n-alkane by the enzyme and later transferred back to C3 of the alkylsuccinate formed. These results indicate that the alkylsuccinate-forming reaction proceeds with an inversion of configuration at the carbon atom (C2) of the n-alkane forming the new C-C-bond, and thus stereochemically resembles a SN2-type reaction. Therefore, the reaction may occur in a concerted manner, which may avoid the highly energetic hex-2-yl radical as an intermediate. The reaction is associated with a significant primary kinetic isotope effect (kH/kD ≥3) for hydrogen, indicating that the homolytic C-H-bond cleavage is involved in the first irreversible step of the reaction mechanism. The (1-methylalkyl)succinate synthases of n-alkane-utilizing anaerobic bacteria apparently have very broad substrate ranges enabling them to activate not only aliphatic but also alkyl-aromatic hydrocarbons. Thus, two denitrifiers and one sulfate reducer were shown to convert the nongrowth substrate toluene to benzylsuccinate and further to the dead-end product benzoyl-CoA. For this purpose, however, the modified β-oxidation pathway known from alkylbenzene-utilizing bacteria was not employed, but rather the pathway used for n-alkane degradation involving CoA ligation, carbon skeleton rearrangement and decarboxylation. Furthermore, various n-alkane- and alkylbenzene-utilizing denitrifiers and sulfate reducers were found to be capable of forming benzyl alcohols from diverse alkylbenzenes

  14. Tribological properties of OTS self-assembled monolayers

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs)were prepared on the substrates of silicon and glass. The tribological properties were tested with a self-made point-contact pure sliding micro tribometer. The effect of humidity on the tribological properties of both OTS SAMs and the naked substrates were studied. When the substrate is covered by OTS monolayer, the friction coefficient is reduced from 0.5 to 0.1 and the stick-slip phenomenon is weakened. OTS monolayer can keep its friction coefficient steady in a wide range of humidity, because it is highly hydrophobic and thus not sensitive to humidity. In addition, the OTS monolayer has a considerable anti-wear ability.

  15. Young's modulus of a solid two-dimensional Langmuir monolayer

    Science.gov (United States)

    Bercegol, H.; Meunier, J.

    1992-03-01

    LANGMUIR monolayers-films of amphiphilic molecules at the surface of water-exhibit many phases1,2. Some of these behave like two-dimensional solids on experimental timescales, but previous measurements of the shear modulus of these 'solid' monolayers3-5 have yielded a value too small to be compatible with a two-dimensional crystal. The interpretation of these is complicated, however, by the likelihood of inhomogeneities in the films, which are probably assemblies of microscopic crystalline domains. Here we describe measurements of the Young's modulus of an isolated "solid' domain of NBD-stearic acid monolayers. We obtain a value large enough to be compatible with the modulus of a two-dimensional crystal6-8. This suggests that Langmuir monolayers should provide model systems for studies of melting in two dimensions6-8.

  16. Epitaxial growth by monolayer restricted galvanic displacement

    Directory of Open Access Journals (Sweden)

    Vasilić Rastko

    2012-01-01

    Full Text Available The development of a new method for epitaxial growth of metals in solution by galvanic displacement of layers pre-deposited by underpotential deposition (UPD was discussed and experimentally illustrated throughout the lecture. Cyclic voltammetry (CV and scanning tunneling microscopy (STM are employed to carry out and monitor a “quasi-perfect”, two-dimensional growth of Ag on Au(111, Cu on Ag(111, and Cu on Au(111 by repetitive galvanic displacement of underpotentially deposited monolayers. A comparative study emphasizes the displacement stoichiometry as an efficient tool for thickness control during the deposition process and as a key parameter that affects the deposit morphology. The excellent quality of layers deposited by monolayer-restricted galvanic displacement is manifested by a steady UPD voltammetry and ascertained by a flat and uniform surface morphology maintained during the entire growth process.

  17. Growth factor controls on the distribution and carbon isotope composition of n-alkanes in leaf wax

    Science.gov (United States)

    Jia, C.; Xie, S.; Huang, X.

    2012-12-01

    Cuticular wax plays pivotal physiological and ecological roles in the interactions between plants and the environments in which they grow. Plant-derived long-chain alkanes are more resistant to decay than other biochemical polymers. n-Alkane distributions (Carbon Preference Index (CPI) values and Average Chain Length (ACL) values) and carbon isotopic values are used widely in palaeoenvironmental reconstruction. However, there is little information available on how growth stages of the plant might influence the abundance of n-alkanes in the natural environment. In this study, we analyzed n-alkane distributions and carbon isotope data from two tree species (Cinnamomum camphora (L.) Presl. and Liquidambar formosana Hance) collected monthly from 2009 to 2011 in Nanwang Shan, Wuhan, Hubei Province. CPI values for n-alkanes from C. camphora remained stable in autumn and winter but fluctuated dramatically during spring and autumn each year. Positive correlations between CPI values and the relative content of (C27+C29) were observed in both sun and shade leaves of C. camphora from April to July. In L. formosana, CPI values decreased gradually from April to December. A similar trend was observed in all three years suggesting that growth stages rather than temperature or relative humidity affected the CPI values on a seasonal timescale. In the samples of L. formosana ACL values were negatively correlated with CPI values in the growing season (from April to July) and positively correlated with CPI values in the other seasons. The δ13C values of C29 and C31 n-alkanes displayed more negative carbon isotopic values in autumn and winter compared with leaves sampled at the start of the growing season from both trees. The δ13C values of C29 and C31 n-alkanes of L. formosana decreased from April to December. These results demonstrate the importance of elucidating the growing factors that influence the distribution and δ13C values of alkanes in modern leaves prior to using CPI

  18. Fossil Leaves and Fossil Leaf n-Alkanes: Reconstructing the First Closed Canopied Rainforests

    Science.gov (United States)

    Graham, H. V.; Freeman, K. H.

    2013-12-01

    characteristics associated with canopy effect. A biomass flux-weighted model of alkane chain-length distribution and δ13Cleaf indicate n-alkanes extracted from bulk rock are consistent with inputs integrated over time from plants represented by fossil leaves. In a modern rainforest, we found leaf lipid amounts markedly higher in the shaded and moist understory, consistent with studies that show alkanes proffer fungal protection. Shade tolerance is associated with higher plant orders and, consistent with this, literature data for modern plants from 30 plant orders shows alkane production in asterids and rosids is 2 to 3 times greater than in basal angiosperms or gymnosperms. The lower clades tend to contain greater amounts of terpenoids and novel benzylisoquinoline alkaloids, rather than alkanes. For our three fossil floras, alkane abundance is strongly influenced by depositional setting, with preservation best in the lacustrine setting. Within each site, abundance patterns are potentially influenced by both taxonomic affiliation and by canopy structure as measured by δ13Cleaf values, and such relationships shed light on the combined influences of plant evolution, canopy structure and the function of biochemical resources on the geochemical record of the first rainforests.

  19. Mixed azide-terminated monolayers: a platform for modifying electrode surfaces.

    Science.gov (United States)

    Collman, James P; Devaraj, Neal K; Eberspacher, Todd P A; Chidsey, Christopher E D

    2006-03-14

    We have prepared and characterized mixed self-assembled monolayers (SAM) on gold electrodes from azido alkane thiols and various omega-functionalized alkane thiols. In the presence of copper(I) catalysts, these azide-modified surfaces are shown to react rapidly and quantitatively with terminal acetylenes forming 1,2,3-triazoles, via "click" chemistry. The initial azide substituents can be identified and monitored using both grazing-angle infrared (IR) and X-ray photoelectron spectrosopies. Acetylenes possessing redox-active ferrocene substituents react with the azide-terminated mixed SAMs and electrochemical measurements of the ferrocene-modified SAM electrodes have been used to quantify the redox centers attached to these platforms. Time-resolved electrochemical measurements have enabled us to follow the formation of these ferrocene centers and thus to measure the rate of the surface "click" reaction. Under optimal conditions this well-behaved second-order reaction takes place with a rate constant of 1 x 10(3) M(-)(1) s(-)(1). Typical reaction times of several minutes were realized using micromolar concentrations of acetylene. These techniques have been used to construct well-characterized, covalently modified monolayers that can be employed as functional electrode surfaces. PMID:16519441

  20. Raman analysis of bond conformations in the rotator state and premelting of normal alkanes.

    Science.gov (United States)

    Kotula, Anthony P; Walker, Angela R Hight; Migler, Kalman B

    2016-06-14

    We perform Raman spectroscopic measurements on normal alkanes (CnH2n+2) to quantify the n dependence of the conformational disorder that occurs below the melt temperature. We employ a three-state spectral analysis method originally developed for semi-crystalline polyethylene that posits crystalline, amorphous, and non-crystalline consecutive trans (NCCT) conformations to extract their respective mass fractions. For the alkanes studied that melt via a rotator phase (21 ≤n≤ 37), we find that conformational disorder can be quantified by the loss of NCCT mass fraction, which systematically decreases with increasing chain length. For those that melt directly via the crystal phase (n≥ 40), we observe NCCT conformational mass fractions that are independent of chain length but whose disordered mass fraction increases with length. These complement prior IR measurements which measure disorder via gauche conformations, but have not been able to measure the mass fraction of this disorder as a function of n. An interesting feature of the three-state analysis when applied to alkanes is that the measured fraction of disordered chain conformations in the rotator phase of (10 to 30)% greatly exceeds the mass fraction of gauche bonds (1 to 7)% as measured from IR; we reconcile this difference through DFT calculations. PMID:27174157

  1. Induction and development of the oil emulsifying system in an alkane oxidizing Rhodococcus species

    International Nuclear Information System (INIS)

    There is a potential use of oil emulsifying bacteria for the clean-up of oil-contaminated natural environments, and oil transport and storage systems. The control mechanisms of the emulsifying abilities in these bacteria are important in relation to the optimization of such processes. A study was conducted to investigate the physiological criteria for the formation of the emulsifying activity in Rhodococcus sp. strain 094, which forms a hydrophobic cell surface when cultivated on alkanes, permitting oil-associated exponential growth. The ability of this bacteria to produce oil emulsifying agents is clearly inducible by crude oil or a number of single hydrophobic compounds. Before the cells are able to emulsify the oil, they must pass through a relatively short induction period followed by a longer period of synthesis of hydrophobic surface parts, coinciding with cell proliferation. The latter is due to the required coordination with new cell wall synthesis. If the cells are allowed to produce sufficient amounts of hydrophobic cell surface parts, they commence to emulsify the oil efficiently when the hydrophobic factor is released from the cell surface as part of their change to a more hydrophillic state. All the positive inducers were hydrophobic alkyl derivatives, and with one exception, also substrate for growth. Many of the better inducers were alkanes, and would require an alkane oxidizing system to be used by the cells. 14 ref., 2 tabs., 3 figs

  2. Nanoencapsulation of n-alkanes with poly(styrene-co-ethylacrylate) shells for thermal energy storage

    International Nuclear Information System (INIS)

    Highlights: • Four series of nanocapsules containing n-alkanes were synthesized in poly(styrene-co-ethylacrylate). • The emulsion co-polymerization technique was used. • Influence of core:shell ratio on encapsulation and thermal properties reported. - Abstract: In this work, we synthesized a series of four nanocapsules containing n-alkanes (CnH2n+2), namely tetradecane, pentadecane, hexadecane, and heptadecane, in poly(styrene-co-ethylacrylate) using an emulsion copolymerization method. The nanocapsules were characterized according to their geometric profiles, phase transition temperatures, phase transition heats, mean particle sizes, and chemical stabilities by means of scanning electron microscopy, differential scanning calorimetry, thermal gravimetric analysis and Fourier transform infrared spectroscopy. Furthermore, we also focused on the effect of the core/shell mass ratio on the phase change properties of the nanocapsules. We found that microcapsules were synthesized successfully and that the best core/shell mass ratio was 3:1 for this study. These results indicate that encapsulated n-alkanes with poly(styrene-co-ethylacrylate) have an excellent potential for energy storage

  3. Structures of a 17,19-hexatriacontadiyne and sashlike polydiacetylene monolayer on MoS2(0001) studied by UHV-STM

    International Nuclear Information System (INIS)

    We have observed a 17,19-hexatriacontadiyne (HTDY) monolayer on MoS2(0001) and sashlike polydiacetylene atomic sash (AS) molecules derived from the monolayer by scanning tunnelling microscopy under ultrahigh vacuum. HTDY molecules adsorbed at 150 K start to move around on the surface above 240 K to form relatively unstable columnar structures. The column is converted into the AS by UV irradiation. In most AS molecules on MoS2(0001), the alkyl chains are in all-trans conformation but their carbon planes are tilted to the polydiacetylene backbone. This conformer, which is one of the most stable structures for an isolated AS molecule, appears on MoS2(0001) because of very weak molecule-substrate interactions

  4. Monolayer arrangement of fatty hydroxystearic acids on graphite: Influence of hydroxyl groups

    Energy Technology Data Exchange (ETDEWEB)

    Medina, S. [Laboratorio de Rayos-X, Centro de Investigación Tecnología e Innovación, de la Universidad de Sevilla (CITIUS), Universidad de Sevilla, Avenida Reina Mercedes, 4B. 41012, Sevilla (Spain); Benítez, J.J.; Castro, M.A. [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain); Cerrillos, C. [Servicio de Microscopía, Centro de Investigación Tecnología e Innovación, de la Universidad de Sevilla (CITIUS), Universidad de Sevilla, Avenida Reina Mercedes, 4B. 41012, Sevilla (Spain); Millán, C. [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain); Alba, M.D., E-mail: alba@icmse.csic.es [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain)

    2013-07-31

    Previous studies have indicated that long-chain linear carboxylic acids form commensurate packed crystalline monolayers on graphite even at temperatures above their melting point. This study examines the effect on the monolayer formation and structure of adding one or more secondary hydroxyl, functional groups to the stearic acid skeleton (namely, 12-hydroxystearic and 9,10-dihydroxystearic acid). Moreover, a comparative study of the monolayer formation on recompressed and monocrystalline graphite has been performed through X-ray diffraction (XRD) and Scanning Tunneling Microscopy (STM), respectively. The Differential Scanning Calorimetry (DSC) and XRD data were used to confirm the formation of solid monolayers and XRD data have provided a detailed structural analysis of the monolayers in good correspondence with obtained STM images. DSC and XRD have demonstrated that, in stearic acid and 12-hydroxystearic acid adsorbed onto graphite, the monolayer melted at a higher temperature than the bulk form of the carboxylic acid. However, no difference was observed between the melting point of the monolayer and the bulk form for 9,10-dihydroxystearic acid adsorbed onto graphite. STM results indicated that all acids on the surface have a rectangular p2 monolayer structure, whose lattice parameters were uniaxially commensurate on the a-axis. This structure does not correlate with the initial structure of the pure compounds after dissolving, but it is conditioned to favor a) hydrogen bond formation between the carboxylic groups and b) formation of hydrogen bonds between secondary hydroxyl groups, if spatially permissible. Therefore, the presence of hydroxyl functional groups affects the secondary structure and behavior of stearic acid in the monolayer. - Highlights: • Hydroxyl functional groups affect structure and behavior of acids in the monolayer. • Acids on the surface have a rectangular p2 monolayer structure. • Lattice parameters of acids are uniaxially

  5. Effect of temperature on the adsorption of short alkanes in the zeolite ssz-13-adapting adsorption isotherms to microporous materials

    NARCIS (Netherlands)

    Jiang, Tao; Göltl, Florian; Bulo, Rosa E.; Sautet, Philippe

    2014-01-01

    Understanding the diffusion and adsorption of hydrocarbons in zeolites is a highly important topic in the field of catalysis in micro-and mesoporous materials. Especially, the properties of alkanes in zeolites have been studied extensively. A theoretical description of these processes is challenging

  6. Packing properties 1-alkanols and alkanes in a phospholipid membrane

    DEFF Research Database (Denmark)

    Westh, Peter

    2006-01-01

    We have used vibrating tube densitometry to investigate the packing properties of four alkanes and a homologous series of ten alcohols in fluid-phase membranes of dimyristoyl phosphatidylcholine (DMPC). It was found that the volume change of transferring these compounds from their pure states into...... the membrane, Vm(puremem), was positive for small (C4-C6) 1-alkanols while it was negative for larger alcohols and all alkanes. The magnitude of Vm(puremem) ranged from about +4 cm3/mol for alcohols with an alkyl chain about half the length of the fatty acids of DMPC, to -10 to -15 cm3/mol for the...... alkanes and long chain alcohols. On the basis of these observations, previously published information on the structure of the membrane-solute complexes and the free volume properties of (pure) phospholipid membranes, we suggest that two effects dominate the packing properties of hydrophobic solutes in...

  7. High Temperature Chemical Kinetic Combustion Modeling of Lightly Methylated Alkanes

    Energy Technology Data Exchange (ETDEWEB)

    Sarathy, S M; Westbrook, C K; Pitz, W J; Mehl, M

    2011-03-01

    Conventional petroleum jet and diesel fuels, as well as alternative Fischer-Tropsch (FT) fuels and hydrotreated renewable jet (HRJ) fuels, contain high molecular weight lightly branched alkanes (i.e., methylalkanes) and straight chain alkanes (n-alkanes). Improving the combustion of these fuels in practical applications requires a fundamental understanding of large hydrocarbon combustion chemistry. This research project presents a detailed high temperature chemical kinetic mechanism for n-octane and three lightly branched isomers octane (i.e., 2-methylheptane, 3-methylheptane, and 2,5-dimethylhexane). The model is validated against experimental data from a variety of fundamental combustion devices. This new model is used to show how the location and number of methyl branches affects fuel reactivity including laminar flame speed and species formation.

  8. A Quick Estimate of the Correlation Energy for Alkanes

    Institute of Scientific and Technical Information of China (English)

    黎书华; 李伟; 马晶

    2003-01-01

    Within the localized molecular orbital description, the intraand interorbital pair correlation energies calculated with the coupled cluster doubles (CCD) theory have been obtained for methane, ethane, propane, butane, isobutane, pentane,isopentane and neopentane using the 6-31G* basis set. The results showed the quantitative transferability of pair correlation energies and gross orbital correlation energies within this series of molecules. Based on the gross orbital correlation energies of five sample alkanes (butane, isobutane, pentane,isopentane and neopentane), we have derived a simple linear relationship to estimate the CCD correlation energy for an arbitrary large alkane. The correlation energy predicted by this simple relationship remarkably recovers more than 98.9% of the exact CCD correlation energy for a number of alkanes containing six to eight carbon atoms. The relative stability of less branched isomers can be correctly predicted.

  9. Exploring atomic defects in molybdenum disulphide monolayers

    KAUST Repository

    Hong, Jinhua

    2015-02-19

    Defects usually play an important role in tailoring various properties of two-dimensional materials. Defects in two-dimensional monolayer molybdenum disulphide may be responsible for large variation of electric and optical properties. Here we present a comprehensive joint experiment-theory investigation of point defects in monolayer molybdenum disulphide prepared by mechanical exfoliation, physical and chemical vapour deposition. Defect species are systematically identified and their concentrations determined by aberration-corrected scanning transmission electron microscopy, and also studied by ab-initio calculation. Defect density up to 3.5 × 10 13 cm \\'2 is found and the dominant category of defects changes from sulphur vacancy in mechanical exfoliation and chemical vapour deposition samples to molybdenum antisite in physical vapour deposition samples. Influence of defects on electronic structure and charge-carrier mobility are predicted by calculation and observed by electric transport measurement. In light of these results, the growth of ultra-high-quality monolayer molybdenum disulphide appears a primary task for the community pursuing high-performance electronic devices.

  10. High Quality Factor Mechanical Resonators Based on WSe2 Monolayers.

    Science.gov (United States)

    Morell, Nicolas; Reserbat-Plantey, Antoine; Tsioutsios, Ioannis; Schädler, Kevin G; Dubin, François; Koppens, Frank H L; Bachtold, Adrian

    2016-08-10

    Suspended monolayer transition metal dichalcogenides (TMD) are membranes that combine ultralow mass and exceptional optical properties, making them intriguing materials for opto-mechanical applications. However, the low measured quality factor of TMD resonators has been a roadblock so far. Here, we report an ultrasensitive optical readout of monolayer TMD resonators that allows us to reveal their mechanical properties at cryogenic temperatures. We find that the quality factor of monolayer WSe2 resonators greatly increases below room temperature, reaching values as high as 1.6 × 10(4) at liquid nitrogen temperature and 4.7 × 10(4) at liquid helium temperature. This surpasses the quality factor of monolayer graphene resonators with similar surface areas. Upon cooling the resonator, the resonant frequency increases significantly due to the thermal contraction of the WSe2 lattice. These measurements allow us to experimentally study the thermal expansion coefficient of WSe2 monolayers for the first time. High Q-factors are also found in resonators based on MoS2 and MoSe2 monolayers. The high quality-factor found in this work opens new possibilities for coupling mechanical vibrational states to two-dimensional excitons, valley pseudospins, and single quantum emitters and for quantum opto-mechanical experiments based on the Casimir interaction. PMID:27459399

  11. BIODEGRADATION AND GAS-EXCHANGE OF GASEOUS ALKANES IN MODEL ESTUARINE ECOSYSTEMS

    Science.gov (United States)

    Gas exchange-biodegradation experiments conducted in model estuarine ecosystems indicate that the ease of degradation of gaseious normal alkanes increases with chain length. The behavior of gaseous perhalogenated alkanes can be explained by gas exchange alone with no degradation....

  12. On the relation between Zenkevich and Wiener indices of alkanes

    Directory of Open Access Journals (Sweden)

    ZARKO BOSKOVIC

    2004-04-01

    Full Text Available A relatively complicated relation was found to exist between the quantity U, recently introduced by Zenkevich (providing a measure of internal molecular energy, and the Wiener index W (measuring molecular surface area and intermolecular forces. We now report a detailed analysis of this relation and show that, in the case of alkanes, its main features are reproduced by the formula U = –aW + b + gn1; where n1 is the number of methyl groups, and a, b and g are constants, depending only on the number of carbon atoms. Thus, for isomeric alkanes with the same number of methyl groups, U and W are linearly correlated.

  13. Squeezing molecularly thin alkane lubrication films: Layering transistions and wear

    DEFF Research Database (Denmark)

    Sivebæk, Ion Marius; Samoilov, V. N.; Persson, B. N. J.

    2004-01-01

    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, C(3)H(8); C(4)H(10); C(8)H(18); C(9)H(20); C(10)H......(22); C(12)H(26), and C(14)H(30) 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...

  14. Squeezing molecular thin alkane lubrication films: layering transition and wear

    OpenAIRE

    Sivebæk, Ion Marius; Samoilov, V. N.; Persson, B. N. J.

    2003-01-01

    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. In most cases 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....

  15. Regioselective alkane hydroxylation with a mutant AlkB enzyme

    Energy Technology Data Exchange (ETDEWEB)

    Koch, Daniel J.; Arnold, Frances H.

    2012-11-13

    AlkB from Pseudomonas putida was engineered using in-vivo directed evolution to hydroxylate small chain alkanes. Mutant AlkB-BMO1 hydroxylates propane and butane at the terminal carbon at a rate greater than the wild-type to form 1-propanol and 1-butanol, respectively. Mutant AlkB-BMO2 similarly hydroxylates propane and butane at the terminal carbon at a rate greater than the wild-type to form 1-propanol and 1-butanol, respectively. These biocatalysts are highly active for small chain alkane substrates and their regioselectivity is retained in whole-cell biotransformations.

  16. Electromelting of Confined Monolayer Ice

    CERN Document Server

    Qiu, Hu

    2013-01-01

    In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to field-induced disruption of the water-wall interaction induced well-ordered network of hydrogen bond. This electromelting process should add an important new ingredient to the physics of water.

  17. Positional order in Langmuir monolayers

    DEFF Research Database (Denmark)

    Kaganer, V.M.; Brezesinski, G.; Möhwald, H.; Howes, P.B.; Kjær, K.

    1998-01-01

    We find that a structural solid-solid phase transition in a two-dimensional Langmuir film is accompanied by strong positional disorder. Specifically, we find by a grazing-incidence x-ray diffraction experiment that in monolayers of octadecanol both the hexagonal phase LS and the centered rectangu......We find that a structural solid-solid phase transition in a two-dimensional Langmuir film is accompanied by strong positional disorder. Specifically, we find by a grazing-incidence x-ray diffraction experiment that in monolayers of octadecanol both the hexagonal phase LS and the centered...

  18. Cation effect of ammonium imide based ionic liquids in alcohols extraction from alcohol-alkane azeotropic mixtures

    International Nuclear Information System (INIS)

    Highlights: • Six ternary liquid+liquid equilibriums alkane + alcohol + IL were studied. • The influence of IL cation structure was evaluated. • The ethanol extraction ability from alkanes was determined for each IL. • Determination of solute distribution ratio and selectivity was required. • Experimental data correlation was realized by NRTL model. -- Abstract: During recent last years, outstanding properties of ionic liquids such as low melting point, large liquid range and negligible volatility have turned them into possible volatile organic solvents replacers to break alcohol-alkane azeotropic mixtures. On this basis, two ionic liquids, butyltrimethylammoniumbis(trifluoromethylsulfonyl)imide, [BTMA][NTf2], and tributylmethylammoniumbis(trifluoromethylsulfonyl)imide, [TBMA][NTf2], were studied through ternary liquid+liquid equilibrium (LLE) of {alkane(1) + alcohol (2) + IL(3)} at T = 298.15 K and atmospheric pressure in order to consider the effect of ionic liquid cation alkyl chain length on the extraction process. The ILs capability as azeotrope breakers was determined by the calculation of parameters such as solute distribution ratio, β, and selectivity, S and this capability was compared with other bis (trifluoromethylsulfonyl)imide based ionic liquids from literature. The consistency of tie-line data was ascertained by applying the Othmer–Tobias and Hand equations. Finally, the experimental LLE were correlated by the Non Random Two Liquid (NRTL) thermodynamic model

  19. 40 CFR 721.4464 - Mixture of hydrofluoro alkanes and hydrofluoro alkene.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Mixture of hydrofluoro alkanes and... Specific Chemical Substances § 721.4464 Mixture of hydrofluoro alkanes and hydrofluoro alkene. (a) Chemical... as a mixture of hydrofluoro alkanes and hydrofluoro alkene (PMNs P-96-945/946/947/948) are subject...

  20. 40 CFR 721.9300 - Reaction products of substituted hydroxy-alkanes and polyalkylpolyisocyanatocarbomono- cycle.

    Science.gov (United States)

    2010-07-01

    ... hydroxy-alkanes and polyalkylpolyisocyanatocarbomono- cycle. 721.9300 Section 721.9300 Protection of... substituted hydroxy-alkanes and polyalkylpolyisocyanatocarbomono- cycle. (a) Chemical substance and... products of substituted hydroxy-alkanes and polyal- kylpoly-isocyanato-carbo-mono-cycle (PMN P-91-75)...

  1. Selective conversion of butane into liquid hydrocarbon fuels on alkane metathesis catalysts

    KAUST Repository

    Szeto, Kaï Chung

    2012-01-01

    We report a selective direct conversion of n-butane into higher molecular weight alkanes (C 5+) by alkane metathesis reaction catalysed by silica-alumina supported tungsten or tantalum hydrides at moderate temperature and pressure. The product is unprecedented, asymmetrically distributed towards heavier alkanes. This journal is © 2012 The Royal Society of Chemistry.

  2. Leaf physiological processes strongly affect δH2 values of leaf wax n-alkanes in C3 and C4 grasses.

    Science.gov (United States)

    Gamarra, Bruno; Sachse, Dirk; Kahmen, Ansgar

    2013-04-01

    Leaf wax n-alkanes are naturally synthesized saturated hydrocarbons. They are synthesized as part of plant leaf cuticle as a mechanism to prevent water losses. Two of the most important features of n-alkanes are their enormous environmental persistence and terrestrial ubiquity making them a solid and reliable long-term and large-scale biomarker. Their hydrogen isotopic composition (δH2) of leaf wax n-alkanes has been traditionally related to precipitation. Leaf wax n-alkanes and their δH2 values have thus been celebrated as biomarkers to reconstruct hydrological changes. δH2 values of leaf wax n-alkanes are yet to be fully comprehended. They are basically determined by three mechanisms: (1) The δH2 value of the plant source water (2) leaf water evaporative enrichment in H2 and (3) biosynthetic fractionation and depletion in H2during their biosynthesis from leaf water. Out of these three, the exact degree by which the evaporative H2-enrichment of leaf water influences the δH2 values of leaf wax n-alkanes is still unknown. We conducted an experiment where we tested and quantified the effects of leaf water evaporative H2-enrichment on the leaf wax n-alkane δH2 values of different grass species. We grew 12 C3 and C4 grass species under controlled environmental conditions in growth chambers. The plants were exposed to 3 different levels of air relative humidity (45, 65 and 85%). These treatments were to generate different degrees of leaf water H2-enrichment in the plants. The goal of our experiment was to determine by what degree the different levels of leaf water H2-enrichment influence the δH2 values of the different C3 and C4 grass species. Additional measurements of gas exchange, evapotranspiration and leaf length and area accompanied the isotopic analysis in order to explain species variability. Our experiments showed that leaf water evaporative H2-enrichment has a critical impact on leaf wax n-alkane δH2 values of all studied plants. The magnitude was

  3. Surface energetics of freely suspended fluid molecular monolayer and multilayer smectic liquid crystal films

    OpenAIRE

    Nguyen, Zoom Hoang; Park, Cheol Soo; Pang, Jinzhong; Clark, Noel A.

    2012-01-01

    A study of the surface energetics of the thinnest substrate-free liquid films, fluid molecular monolayer and multilayer smectic liquid crystal films suspended in air, is reported. In films having monolayer and multilayer domains, the monolayer areas contract, contrary to predictions from the van der Waals disjoining pressure of thin uniform slabs. This discrepancy is accounted for by modeling the environmental asymmetry of the surface layers in multilayer films, leading to the possibility tha...

  4. Monolayers of lysolecithins and analogs

    NARCIS (Netherlands)

    Eibl, H.; Demel, R.A.; Deenen, L.L.M. van

    1969-01-01

    1) The interfacial characteristics of lysolecithins are highly dependent on chain length and unsaturation of the fatty acid chain. (Stearoyl) and (oleoyl) lysolecithins form stable monolayers with high collapse pressures (35 dynes/cm) whereas (palmitoyl) (myristoyl), and (linoleoyl) lysolecithin mon

  5. Positional order in Langmuir monolayers

    DEFF Research Database (Denmark)

    Kaganer, V.M.; Brezesinski, G.; Möhwald, H.;

    1998-01-01

    We find that a structural solid-solid phase transition in a two-dimensional Langmuir film is accompanied by strong positional disorder. Specifically, we find by a grazing-incidence x-ray diffraction experiment that in monolayers of octadecanol both the hexagonal phase LS and the centered...

  6. Oxygenation of alkanes with hydrogen peroxide catalysed by osmium complexes

    OpenAIRE

    Shulpin, Georgiy B.; Süss-Fink, Georg; Shulpina, Lidia S.

    2006-01-01

    Efficient oxidation of alkanes, including methane and ethane, with H2O2 in the presence of catalytic amount of an Os complex in MeCN (addition of nitrogen-containing heterocycles significantly enhances the yield of the products) or in MeCO2H gives the corresponding ketones and alcohols.

  7. MODELING OF ALKANE EMISSIONS FROM A WOOD STAIN

    Science.gov (United States)

    The article discusses full-scale residential house tests to evaluate the effects of organic emissions from a wood finishing product--wood stain--on indoor air quality (IAQ). The test house concentrations of three alkane species, nonane, decane, and undecane, were measured as a fu...

  8. Integrated process for preparing a carboxylic acid from an alkane

    Energy Technology Data Exchange (ETDEWEB)

    Benderly, Abraham (Elkins Park, PA); Chadda, Nitin (Radnor, PA); Sevon, Douglass (Fairless Hills, PA)

    2011-12-20

    The present invention relates to an integrated process for producing unsaturated carboxylic acids from the corresponding C.sub.2-C.sub.4 alkane. The process begins with performance of thermally integrated dehydrogenation reactions which convert a C.sub.2-C.sub.4 alkane to its corresponding C.sub.2-C.sub.4 alkene, and which involve exothermically converting a portion of an alkane to its corresponding alkene by oxidative dehydrogenation in an exothermic reaction zone, in the presence of oxygen and a suitable catalyst, and then feeding the products of the exothermic reaction zone to an endothermic reaction zone wherein at least a portion of the remaining unconverted alkane is endothermically dehydrogenated to form an additional quantity of the same corresponding alkene, in the presence of carbon dioxide and an other suitable catalyst. The alkene products of the thermally integrated dehydrogenation reactions are then provided to a catalytic vapor phase partial oxidation process for conversion of the alkene to the corresponding unsaturated carboxylic acid or nitrile. Unreacted alkene and carbon dioxide are recovered from the oxidation product stream and recycled back to the thermally integrated dehydrogenation reactions.

  9. A superoleophobic textile repellent towards impacting drops of alkanes

    Science.gov (United States)

    Artus, Georg R. J.; Zimmermann, Jan; Reifler, Felix A.; Brewer, Stuart A.; Seeger, Stefan

    2012-02-01

    A commercially available polyester fabric has been rendered superoleophobic by coating with silicone nanofilaments and subsequent plasma fluorination. The treated samples show outstanding oil-repellency. They achieve the highest possible oil-repellency grade of 8, repel impacting drops of alkanes and show a plastron layer in hexadecane. The oil repellency is shown to depend on the topography of the silicone nanofilament coating.

  10. Broadband ultra-high transmission of terahertz radiation through monolayer MoS$_{2}$

    CERN Document Server

    Deng, Xue-Yong; Su, Fu-Hai; Liu, Nian-Hua; Liu, Jiang-Tao

    2015-01-01

    In this study, terahertz (THz) absorption and transmission of monolayer MoS$_{2}$ was calculated under different carrier concentrations. Results showed that the THz absorption of monolayer MoS$_{2}$ is very small even under high carrier concentrations and large incident angle. Equivalent loss of the THz absorption is the total sum of reflection and absorption that is one to three grades lower than that of graphene. The monolayer MoS$_{2}$ transmission is much larger than that of the traditional GaAs and InAs two-dimensional electron gas. The field-effect tubular structure formed by the monolayer MoS$_{2}$-insulation-layer-graphene is investigated. In this structure the THz absorption of graphene to reach saturation under low voltage. Meantime, the maximum THz absorption of monolayer MoS$_{2}$ was limited to approximately 5\\%. Thus, monolayer MoS$_{2}$ is a kind of ideal THz Transparent Electrodes.

  11. Scanning tunneling microscopy study of the c(4x4) structure formation in the sub-monolayer Sb/Si(100) system

    International Nuclear Information System (INIS)

    Upon Sb desorption from a Sb-saturated Si(100) surface, the c(4x4) structure formed at about 0.25 monolayer Sb coverage. The c(4x4) reconstruction has been found to develop best when the surface is slightly contaminated, plausibly, by carbon. The Si(100)-c(4x4)-Sb surface shows up in the high-resolution filled state scanning tunneling microscopy images as being very similar to that of the recently reported c(4x4)-Si reconstruction. Here the main features of the Si(100)-c(4x4)-Sb structure are identified and the possible atomic arrangement is discussed. (author)

  12. What makes the T c of monolayer FeSe on SrTiO3 so high: a sign-problem-free quantum Monte Carlo study

    OpenAIRE

    Li, Zi-Xiang; Wang, Fa; Yao, Hong; Lee, Dung-Hai

    2016-01-01

    Monolayer FeSe films grown on SrTiO3 (STO) substrate show superconducting gap-opening temperatures ( \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{\\mathrm{c}}$$\\end{document} T c ) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based superconductor...

  13. Studies of metal ion binding by apo-metallothioneins attached onto preformed self-assembled monolayers using a highly sensitive surface plasmon resonance spectrometer

    OpenAIRE

    Zhang, Yintang; Xu, Maotian; Wang, Yanju; Toledo, Freddy; Zhou, Feimeng

    2007-01-01

    The use of a flow-injection surface plasmon resonance (FI-SPR) spectrometer equipped with a bicell detector or a position-sensitive device for determining coordination of heavy metal ions (Cd2+ and Hg2+) by surface-confined apo-metallothionein (apo-MT) molecules is described. To facilitate the formation of a compact MT adsorbate layer with a uniform surface orientation, MT molecules were attached onto a preformed alkanethiol self-assembled monolayer. The method resorts to the generation of ap...

  14. Progressive degradation of crude oil n-alkanes coupled to methane production under mesophilic and thermophilic conditions.

    Directory of Open Access Journals (Sweden)

    Lei Cheng

    Full Text Available Although methanogenic degradation of hydrocarbons has become a well-known process, little is known about which crude oil tend to be degraded at different temperatures and how the microbial community is responded. In this study, we assessed the methanogenic crude oil degradation capacity of oily sludge microbes enriched from the Shengli oilfield under mesophilic and thermophilic conditions. The microbial communities were investigated by terminal restriction fragment length polymorphism (T-RFLP analysis of 16S rRNA genes combined with cloning and sequencing. Enrichment incubation demonstrated the microbial oxidation of crude oil coupled to methane production at 35 and 55°C, which generated 3.7±0.3 and 2.8±0.3 mmol of methane per gram oil, respectively. Gas chromatography-mass spectrometry (GC-MS analysis revealed that crude oil n-alkanes were obviously degraded, and high molecular weight n-alkanes were preferentially removed over relatively shorter-chain n-alkanes. Phylogenetic analysis revealed the concurrence of acetoclastic Methanosaeta and hydrogenotrophic methanogens but different methanogenic community structures under the two temperature conditions. Candidate divisions of JS1 and WWE 1, Proteobacteria (mainly consisting of Syntrophaceae, Desulfobacteraceae and Syntrophorhabdus and Firmicutes (mainly consisting of Desulfotomaculum were supposed to be involved with n-alkane degradation in the mesophilic conditions. By contrast, the different bacterial phylotypes affiliated with Caldisericales, "Shengli Cluster" and Synergistetes dominated the thermophilic consortium, which was most likely to be associated with thermophilic crude oil degradation. This study revealed that the oily sludge in Shengli oilfield harbors diverse uncultured microbes with great potential in methanogenic crude oil degradation over a wide temperature range, which extend our previous understanding of methanogenic degradation of crude oil alkanes.

  15. Dislocations in Monolayers and Semiconductors.

    Science.gov (United States)

    Ren, Qiang

    1995-01-01

    Four different aspects of the properties of dislocations in monolayer and semiconductors have been investigated: (i) Using atomic relaxation techniques, dislocation dipoles of various sizes and orientations have been studied for monolayers with the Lennard-Jones potential (LJP) and the nearest-neighbour piecewise linear force (PLF) interactions. In the WP system the lower energy vacancy dipoles have over a wide range of angles an energy which is mainly a function of the vacancy content of the dipole. There is a competition between the elastic forces and the topological constraints which favour a five-fold coordinate vacancy (FCV) at the centre of each core. For the short range PLF system the lattice usually compresses upon the introduction of a dislocation, a consequence of the soft core of the interaction potential, and interstitial dipoles are lower in energy. For the long range LJP system the dislocations are mobile whereas for the PLF system they are pinned. The relevance of these results to existing theories of melting are discussed. (ii) Using generalized stacking-fault (GSF) energies obtained from first-principles density-functional calculations, a zero-temperature model for dislocations in silicon is constructed within the framework of a Peierls-Nabarro (PN) model. Core widths, core energies, PN pinning energies, and stresses are calculated for various possible perfect and imperfect dislocations. Both shuffle and glide sets are considered. 90^circ partials are shown to have a lower Peierls stress (PS) than 30 ^circ partials in accord with experiment. (iii) We have also studied by atomic relaxation techniques the properties of dislocations in silicon, modelled by the empirical potential of Stillinger and Weber. In order to compare with the preceding calculation no reconstruction is allowed. We find no evidence of dissociation in the shuffle dislocations. Within this model shuffle dislocations glide along their slipping planes. On the other hand, glide sets

  16. Production of liquid alkanes by controlling reactivity of sorbitol hydrogenation with a Ni/HZSM-5 catalyst in water

    International Nuclear Information System (INIS)

    Graphical abstract: MCM-41-modified Ni/HZSM-5 catalyst was developed by impregnation method with high catalytic performance for sorbitol hydrogenation in water. Appropriate amount of MCM-41 addition can distinctly promote the improvement in the surface structure and modulation of acidic sites of the catalyst. The scission of C–O bond in the sorbitol molecule into liquid alkanes was easily carried out on the catalyst containing more Lewis acidic sites. - Highlights: • Ni/HZSM-5 promoted with MCM-41 is active for sorbitol hydrogenation to liquid alkanes. • Lewis acidic sites of Ni/HZSM-5 can be modulated by pure silica MCM-41. • MCM-41 added can distinctly decrease carbon deposition on the catalyst surface. - Abstract: Liquid fuels derived from renewable biomass are of great importance on the potential substitution for diminishing fossil fuels. The conversion of sorbitol (a product of biomass-derived glucose hydrogenation) into liquid alkanes such as pentane and hexane over the Ni/HZSM-5 catalysts with or without MCM-41 addition was investigated in the presence of hydrogen in water medium. The production distribution of sorbitol hydrogenation can be controlled by adjusting the acidity of the catalyst. The scission of C–C bond in the sorbitol molecule into light C1–C4 alkanes was mainly carried out over Ni/HZSM-5 containing strong Brønsted acid sites, while C–O bond scission into heavier alkanes was dominated over the catalysts added by MCM-41 containing weak Lewis acid sites. The sorbitol conversion and total liquid alkanes selectivity were found to be 67.1% and 98.7% over 2%Ni/HZSM-5 modified by 40 wt% of MCM-41, whereas the corresponding value was 40% and 35.6% over 2%Ni/HZSM-5 in the absence of MCM-41. The effect of MCM-41 on the structure, acidity, and reducibility of Ni/HZSM-5 was investigated by using XRD, Py-IR, IR, and H2-TPR. Meanwhile, the resistance of carbon deposition over the catalyst modified by MCM-41 was studied by using TG

  17. Secondary organic aerosol composition from C12 alkanes.

    Science.gov (United States)

    Schilling Fahnestock, Katherine A; Yee, Lindsay D; Loza, Christine L; Coggon, Matthew M; Schwantes, Rebecca; Zhang, Xuan; Dalleska, Nathan F; Seinfeld, John H

    2015-05-14

    The effects of structure, NOx conditions, relative humidity, and aerosol acidity on the chemical composition of secondary organic aerosol (SOA) are reported for the photooxidation of three C12 alkanes: n-dodecane, cyclododecane, and hexylcyclohexane. Acidity was modified through seed particle composition: NaCl, (NH4)2SO4, and (NH4)2SO4 + H2SO4. Off-line analysis of SOA was carried out by solvent extraction and gas chromatography-mass spectrometry (GC/MS) and direct analysis in real-time mass spectrometry. We report here 750 individual masses of SOA products identified from these three alkane systems and 324 isomers resolved by GC/MS analysis. The chemical compositions for each alkane system provide compelling evidence of particle-phase chemistry, including reactions leading to oligomer formation. Major oligomeric species for alkane SOA are peroxyhemiacetals, hemiacetals, esters, and aldol condensation products. Furans, dihydrofurans, hydroxycarbonyls, and their corresponding imine analogues are important participants in these oligomer-producing reactions. Imines are formed in the particle phase from the reaction of the ammonium sulfate seed aerosol with carbonyl-bearing compounds present in all the SOA systems. Under high-NO conditions, organonitrate products can lead to an increase of aerosol volume concentration by up to a factor of 5 over that in low-NO conditions. Structure was found to play a key role in determining the degree of functionalization and fragmentation of the parent alkane, influencing the mean molecular weight of the SOA produced and the mean atomic O:C ratio. PMID:24814371

  18. The influence of chromatin structure on the frequency of radiation-induced DNA strand breaks: a study using nuclear and nucleoid monolayers

    International Nuclear Information System (INIS)

    To assess the influence of chromatin structure on the frequency of radiation-induced DNA strand breaks, the alkaline unwinding technique was applied to nuclear and nucleoid monolayers. These chromatin substrates were prepared by treating human fibroblasts grown as monolayers with the nonionic detergent Triton X-100 and varying concentrations of cations. The chromatin structure was modified either by a stepwise removal of DNA-bound proteins by extraction in increasing concentrations of monovalent salt, or by the addition or deletion of mono- and divalent cations to condense or decondense the chromatin, respectively. It was found that the stepwise removal of DNA-bound proteins from the chromatin dramatically increased the frequency of radiation-induced DNA strand breaks. The DNA-bound proteins showed a qualitative difference in their ability to protect the DNA where proteins removed by salt concentrations above 1.0 M exerted the greatest protection. Furthermore, the frequency of radiation-induced DNA strand breaks was found to be 6 times lower in condensed chromatin than in decondensed chromatin and about 80 times lower than in protein-depleted chromatin. It is concluded that the presence of DNA-bound proteins and the folding of the chromatin into higher-order structures protect the DNA against radiation-induced strand breaks

  19. Use of self assembled monolayers at variable coverage to control interface bonding in a model study of interfacial fracture: Pure shear loading

    Energy Technology Data Exchange (ETDEWEB)

    KENT,MICHAEL S.; YIM,HYUN; MATHESON,AARON J.; COGDILL,C.; NELSON,GERALD C.; REEDY JR.,EARL DAVID

    2000-05-16

    The relationships between fundamental interfacial interactions, energy dissipation mechanisms, and fracture stress or fracture toughness in a glassy thermoset/inorganic solid joint are not well understood. This subject is addressed with a model system involving an epoxy adhesive on a polished silicon wafer containing its native oxide. The proportions of physical and chemical interactions at the interface, and the in-plane distribution, are varied using self-assembling monolayers of octadecyltrichlorosilane (ODTS). The epoxy interacts strongly with the bare silicon oxide surface, but forms only a very weak interface with the methylated tails of the ODTS monolayer. The fracture stress is examined as a function of ODTS coverage in the napkin-ring (pure shear) loading geometry. The relationship between fracture stress and ODTS coverage is catastrophic, with a large change in fracture stress occurring over a narrow range of ODTS coverage. This transition in fracture stress does not correspond to a wetting transition of the epoxy. Rather, the transition in fracture stress corresponds to the onset of deformation in the epoxy, or the transition from brittle to ductile fracture. The authors postulate that the transition in fracture stress occurs when the local stress that the interface can support becomes comparable to the yield stress of the epoxy. The fracture results are independent of whether the ODTS deposition occurs by island growth (T{sub dep} = 10 C) or by homogeneous growth (T{sub dep} = 24 C).

  20. Electrochemical, high-resolution photoemission spectroscopy and vdW-DFT study of the thermal stability of benzenethiol and benzeneselenol monolayers on Au(111).

    Science.gov (United States)

    Cometto, F P; Patrito, E M; Paredes Olivera, P; Zampieri, G; Ascolani, H

    2012-09-25

    The preparation and thermal stability of benzenethiol and benzeneselenol self-assembled monolayers (SAMs) grown on Au(111) have been investigated by electrochemical experiments and high-resolution photoemission spectroscopy. Both techniques confirm the formation of monolayers with high packing densities (θ = 0.27-0.29 ML) and good degrees of order in both cases. Despite many similarities between the two SAMs, the thermal desorption is distinctly different: whereas the benzenethiol SAM desorbs in a single steplike process, the desorption of the benzeneselenol SAM occurs with a much lower activation energy and involves the cleavage of some Se-C bonds and a change in molecular configuration from standing up to lying down. This behavior is explained by considering the different nature of the bonding of the headgroup with the metal surface and with the phenyl ring. Density functional theory calculations show that the breakage of the Se-C bond has a lower activation energy barrier than the breakage of the S-C bond. PMID:22946792

  1. Image Charge Effects in the Wetting Behavior of Alkanes on Water with Accounting for Water Solubility

    Directory of Open Access Journals (Sweden)

    Kirill A. Emelyanenko

    2016-03-01

    Full Text Available Different types of surface forces, acting in the films of pentane, hexane, and heptane on water are discussed. It is shown that an important contribution to the surface forces originates from the solubility of water in alkanes. The equations for the distribution of electric potential inside the film are derived within the Debye-Hückel approximation, taking into account the polarization of the film boundaries by discrete charges at water-alkane interface and by the dipoles of water molecules dissolved in the film. On the basis of above equations we estimate the image charge contribution to the surface forces, excess free energy, isotherms of water adsorption in alkane film, and the total isotherms of disjoining pressure in alkane film. The results indicate the essential influence of water/alkane interface charging on the disjoining pressure in alkane films, and the wettability of water surface by different alkanes is discussed.

  2. Packing of ganglioside-phospholipid monolayers

    DEFF Research Database (Denmark)

    Majewski, J.; Kuhl, T.L.; Kjær, K.; Smith, G.S.

    2001-01-01

    Using synchrotron grazing-incidence x-ray diffraction (GIXD) and reflectivity, the in-plane and out-of-plane structure of mixed ganglioside-phospholipid monolayers was investigated at the air-water interface. Mixed monolayers of 0, 5, 10, 20, and 100 mol% ganglioside GM, and the phospholipid...... DPPE monolayer and does not distort the hexagonal in-plane unit cell or out-of-plane two-dimensional (2-D) packing compared with a pure DPPE monolayer. The oligosaccharide headgroups were found to extend normally from the monolayer surface, and the incorporation of these glycolipids into DPPE...... monolayers did not affect hydrocarbon tail packing (fluidization or condensation of the hydrocarbon region). This is in contrast to previous investigations of lipopolymer-lipid mixtures, where the packing structure of phospholipid monolayers was greatly altered by the inclusion of lipids bearing hydrophilic...

  3. Ionically self-assembled monolayers (ISAMs)

    Science.gov (United States)

    Janik, John

    2001-04-01

    Ionically self-assembled monolayers (ISAMs), fabricated by alternate adsorption of cationic and anionic components, yield exceptionally homogeneous thin films with sub-nanometer control of the thickness and relative special location of the component materials. Using organic electrochromic materials such as polyaniline, we report studies of electrochromic responses in ISAM films. Reversible changes in the absorption spectrum are observed with the application of voltages on the order of 1.0 V. Measurements are made using both liquid electrolytes and in all-solid state devices incorporating solid polyelectrolytes such as poly(2-acylamido 2-methyl propane sulfonic acid) (PAMPS).

  4. Critical wetting of n-alkanes on water; Mouillage critique des alcanes sur l`eau

    Energy Technology Data Exchange (ETDEWEB)

    Ragil, K.

    1996-10-18

    This study concerns the wetting properties of n-alkanes on water under thermodynamic equilibrium conditions, a problem that is interesting for the petroleum industry as well as for the fundamental understanding of wetting phenomena. An experimental study using ellipsometry reveals that pentane on water undergoes a continuous or critical wetting transition at a temperature equal to 53.1 deg. C. This is the first experimental observation of such a transition, confirming theoretical predictions made on this subject over ten years. This transition is characterized by a continuous and reversible evolution of the thickness of the film of pentane with temperature from a thick (but finite film) to a macroscopic film. The critical wetting transition occurs when the Hamaker constant of the system, which gives the net interaction between the two interfaces bounding the wetting layer of pentane in terms of the van der Waals forces, changes sign. A theoretical approach based on the Cahn-Landau theory, which takes into account long range forces (van der Waals forces), enables us to explain the mechanism of the critical wetting transition and to show that a first-order wetting transition should precede it. Because of their similar dispersive properties, linear alkanes could all be able to show such a succession of transitions. An ellipsometry study performed on a brine/hexane/vapor system confirms that a discontinuous transition from a thin microscopic film to a thick but finite adsorbed film takes place. THis study demonstrates that the wetting of alkanes on water is determined by subtle interplay between short range and long range forces, which can lead to an intermediary state between partial and complete wetting. (author)

  5. Structural Effects on the Langmuir Monolayers of Calix[4]arene Induced by Lower Rim Aromatic Substitution

    Institute of Scientific and Technical Information of China (English)

    HE Wei-Jiang; QIU Lin; LI Jun-Bai; ZHANG Yu; GUO Zi-Jian; ZHU Long-Gen

    2006-01-01

    The Langmuir monolayer properties of lower rim aromatically substituted calix[4]arenes, 5,11,17,23-tetra-tertbutyl-25,27-bis(2-naphth-1'-ylacetylaminoethoxy)-26,28-dihydroxylcalix[4]arene (BNAEC), 5,11,17,23-tetra-tertbutyl-25,27-bis(2-benzoylamino ethoxy)-26,28-dihydroxylcalix[4]arene (BBAEC) and 5,11,17,23-tetra-tert-butyl-25,27-bis(2-cinnamoylaminoethoxy)-26,28-dihydroxylcalix[4]arene (BCAEC), have been studied. Film balance measurements and Brewster angle microscopy (BAM) observation demonstrate that all the compounds can form Langmuir monolayers with different molecular limiting areas. BNAEC or BBAEC monolayer is able to form condensed domains during compression, while BCAEC monolayer can never form condensed domain. BNAEC monolayer is more readily to form condensed domain than BBAEC monolayer. Moreover, BNAEC monolayer can form the total condensed phase during compression even when T=28 ℃, while BBAEC monolayer can not when T> 10 ℃. The results imply that different lower rim aromatic substitutions affect essentially the intermolecular interaction and molecular packing in the monolayer at air/water interface.

  6. Equivalent aqueous phase modulation of domain segregation in myelin monolayers and bilayer vesicles

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, R.G. [Universidad Nacional de Cordoba, Cordoba, CO (Argentina)

    2012-07-01

    Full text: Purified myelin can be spread as monomolecular films at the air/aqueous interface. These films were visualized by fluorescence and Brewster angle microscopy, showing phase coexistence at low and medium surface pressures (<20-30 mN/m). Beyond this threshold, the film becomes homogeneous or not, depending on the aqueous sub phase composition. Pure water as well as sucrose, glycerol, dimethylsulfoxide, and dimethylformamide solutions (20% in water) produced monolayers that become homogeneous at high surface pressures; on the other hand, the presence of salts (NaCl, CaCl{sub 2}) in Ringers and physiological solution leads to phase domain microheterogeneity over the whole compression isotherm. These results show that surface heterogeneity is favored by the ionic milieu. The modulation of the phase-mixing behavior in monolayers is paralleled by the behavior of multilamellar vesicles as determined by small-angle and wide-angle x-ray scattering. The correspondence of the behavior of monolayers and multilayers is achieved only at high surface pressures near the equilibrium adsorption surface pressure; at lower surface pressures, the correspondence breaks down. The equilibrium surface tension on all sub phases corresponds to that of the air/alkane interface (27 mN/m), independently on the surface tension of the clean sub phase. (author)

  7. Ultralow effective work function surfaces using diamondoid monolayers

    Science.gov (United States)

    Narasimha, Karthik Thimmavajjula; Ge, Chenhao; Fabbri, Jason D.; Clay, William; Tkachenko, Boryslav A.; Fokin, Andrey A.; Schreiner, Peter R.; Dahl, Jeremy E.; Carlson, Robert M. K.; Shen, Z. X.; Melosh, Nicholas A.

    2016-03-01

    Electron emission is critical for a host of modern fabrication and analysis applications including mass spectrometry, electron imaging and nanopatterning. Here, we report that monolayers of diamondoids effectively confer dramatically enhanced field emission properties to metal surfaces. We attribute the improved emission to a significant reduction of the work function rather than a geometric enhancement. This effect depends on the particular diamondoid isomer, with [121]tetramantane-2-thiol reducing gold's work function from ∼5.1 eV to 1.60 ± 0.3 eV, corresponding to an increase in current by a factor of over 13,000. This reduction in work function is the largest reported for any organic species and also the largest for any air-stable compound. This effect was not observed for sp3-hybridized alkanes, nor for smaller diamondoid molecules. The magnitude of the enhancement, molecule specificity and elimination of gold metal rearrangement precludes geometric factors as the dominant contribution. Instead, we attribute this effect to the stable radical cation of diamondoids. Our computed enhancement due to a positively charged radical cation was in agreement with the measured work functions to within ±0.3 eV, suggesting a new paradigm for low-work-function coatings based on the design of nanoparticles with stable radical cations.

  8. Orientational ordering of adsorbed monolayers

    International Nuclear Information System (INIS)

    The authors set up a model for the adsorption energy for a closed-packed hexagonal monolayer deposited on a substrate surface of the same structure, but different lattice constant, as a function of the epitaxy angle between the principal axis. The surface substrate potential is expressed in the form of symmetry and periodic potential with symmetry and periodicity of the substrate surface. The particular case of lead underpotentially deposited on Ag(111) is examined

  9. Transfer of CVD-grown monolayer graphene onto arbitrary substrates.

    Science.gov (United States)

    Suk, Ji Won; Kitt, Alexander; Magnuson, Carl W; Hao, Yufeng; Ahmed, Samir; An, Jinho; Swan, Anna K; Goldberg, Bennett B; Ruoff, Rodney S

    2011-09-27

    Reproducible dry and wet transfer techniques were developed to improve the transfer of large-area monolayer graphene grown on copper foils by chemical vapor deposition (CVD). The techniques reported here allow transfer onto three different classes of substrates: substrates covered with shallow depressions, perforated substrates, and flat substrates. A novel dry transfer technique was used to make graphene-sealed microchambers without trapping liquid inside. The dry transfer technique utilizes a polydimethylsiloxane frame that attaches to the poly(methyl methacrylate) spun over the graphene film, and the monolayer graphene was transferred onto shallow depressions with 300 nm depth. The improved wet transfer onto perforated substrates with 2.7 μm diameter holes yields 98% coverage of holes covered with continuous films, allowing the ready use of Raman spectroscopy and transmission electron microscopy to study the intrinsic properties of CVD-grown monolayer graphene. Additionally, monolayer graphene transferred onto flat substrates has fewer cracks and tears, as well as lower sheet resistance than previous transfer techniques. Monolayer graphene films transferred onto glass had a sheet resistance of ∼980 Ω/sq and a transmittance of 97.6%. These transfer techniques open up possibilities for the fabrication of various graphene devices with unique configurations and enhanced performance. PMID:21894965

  10. Magnetic and Structural Phases of Monolayer 02 on Graphite

    DEFF Research Database (Denmark)

    McTague, J. P.; Nielsen, Mourits

    1976-01-01

    Neutron diffraction studies of O2 thin films physisorbed on the basal plane of graphite show three distinct two-dimensional crystalline phases, all incommensurate with the substrate lattice. The low-temperature monolayer phase has a distorted triangular structure analogous to the closest-packed p......Neutron diffraction studies of O2 thin films physisorbed on the basal plane of graphite show three distinct two-dimensional crystalline phases, all incommensurate with the substrate lattice. The low-temperature monolayer phase has a distorted triangular structure analogous to the closest...

  11. Resonance Raman spectra of phthalocyanine monolayers on different supports. A normal mode analysis of zinc phthalocyanine by means of the MNDO method

    NARCIS (Netherlands)

    Palys, Barbara J.; Ham, van den Dirk M.W.; Briels, Wim; Feil, Dirk

    1995-01-01

    Resonance Raman spectra of monolayers of transition metal phthalocyanines reveal specific interaction with the support. To elucidate its mechanism, Raman spectra of zinc phthalocyanine monolayers were studied. The analysis was based largely on the results of MNDO calculations. Calculated wavenumbers

  12. Flash Points of Secondary Alcohol and n-Alkane Mixtures.

    Science.gov (United States)

    Esina, Zoya N; Miroshnikov, Alexander M; Korchuganova, Margarita R

    2015-11-19

    The flash point is one of the most important characteristics used to assess the ignition hazard of mixtures of flammable liquids. To determine the flash points of mixtures of secondary alcohols with n-alkanes, it is necessary to calculate the activity coefficients. In this paper, we use a model that allows us to obtain enthalpy of fusion and enthalpy of vaporization data of the pure components to calculate the liquid-solid equilibrium (LSE) and vapor-liquid equilibrium (VLE). Enthalpy of fusion and enthalpy of vaporization data of secondary alcohols in the literature are limited; thus, the prediction of these characteristics was performed using the method of thermodynamic similarity. Additionally, the empirical models provided the critical temperatures and boiling temperatures of the secondary alcohols. The modeled melting enthalpy and enthalpy of vaporization as well as the calculated LSE and VLE flash points were determined for the secondary alcohol and n-alkane mixtures. PMID:26491811

  13. SYNCHROTRON X-RAY OBSERVATIONS OF A MONOLAYER TEMPLATE FOR MINERALIZATION

    International Nuclear Information System (INIS)

    Mineral nucleation at a Langmuir film interface has been studied by synchrotron x-ray scattering. Diluted calcium bicarbonate solutions were used as subphases for arachidic and stearic acid monolayers, compressed in a Langmuir trough. Self-assembly of the monolayer template is observed directly, and subsequent crystal growth monitored in-situ

  14. The effect of gauche molecular conformations on the phase diagram of a Langmuir monolayer

    NARCIS (Netherlands)

    Zangi, R; Rice, SA

    2003-01-01

    Experimental and simulation studies have shown that the gauche conformational degrees of freedom of long-chain amphiphile molecules assembled in a dense Langmuir monolayer play an important role in determining the structures of the several phases that the monolayer supports. Nevertheless, for simpli

  15. Rate effects on layering of a confined linear alkane

    OpenAIRE

    Bureau, Lionel

    2007-01-01

    We perform drainage experiments of a linear alkane fluid (n-hexadecane) down to molecular thicknesses, and focus on the role played by the confinement rate. We show that molecular layering is strongly influenced by the velocity at which the confining walls are approached: under high enough shear rates, the confined medium behaves as a structureless liquid of enhanced viscosity for film thickness below $\\sim$10 nm. Our results also lead us to conclude that a rapidly confined film can be quench...

  16. Active coke: Carbonaceous materials as catalysts for alkane dehydrogenation

    OpenAIRE

    McGregor, J.; Huang, Z; Parrott, E.; Zeitler, J.; Nguyen, K.; Rawson, J.; Carley, A; Hansen, T.; Tessonnier, J.; Su, D.; Teschner, D; Vass, E.; Knop-Gericke, A.; Schlögl, R.; Gladden, L.

    2010-01-01

    The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes are of significant industrial importance. In this work both carbonaceous materials deposited on VOx/Al2O3 catalysts during reaction and unsupported carbon nanofibres (CNFs) are shown to be active for the dehydrogenation of butane in the absence of gas-phase oxygen. Their activity in these reactions is shown to be dependent upon their structure, with different reaction temperatures yielding structurally dif...

  17. Chromium oxide catalysts in the dehydrogenation of alkanes

    OpenAIRE

    Airaksinen, Sanna

    2005-01-01

    Light alkenes, such as propene and butenes, are important intermediates in the manufacture of fuel components and chemicals. The direct catalytic dehydrogenation of the corresponding alkanes is a selective way to produce these alkenes and is frequently carried out using chromia/alumina catalysts. The aim of this work was to obtain structure–activity information, which could be utilised in the optimisation of this catalytic system. The properties of chromia/alumina catalysts were investigated ...

  18. Alkane biosynthesis genes in cyanobacteria and their transcriptional organization

    Directory of Open Access Journals (Sweden)

    Stephan eKlähn

    2014-07-01

    Full Text Available In cyanobacteria, alkanes are synthesized from a fatty acyl-ACP by two enzymes, acyl-acyl carrier protein reductase (AAR and aldehyde deformylating oxygenase (ADO. Despite the great interest in the exploitation for biofuel production, nothing is known about the transcriptional organization of their genes or the physiological function of alkane synthesis. The comparison of 115 microarray datasets indicates the relatively constitutive expression of aar and ado genes. The analysis of 181 available genomes showed that in 90% of the genomes both genes are present, likely indicating their physiological relevance. In 61% of them they cluster together with genes encoding acetyl-CoA carboxyl transferase and a short chain dehydrogenase, strengthening the link to fatty acid metabolism and in 76% of the genomes they are located in tandem, suggesting constraints on the gene arrangement. However, contrary to the expectations for an operon, we found in Synechocystis sp. PCC 6803 specific promoters for the two genes, sll0208 (ado and sll0209 (aar, that give rise to monocistronic transcripts. Moreover, the upstream located ado gene is driven by a proximal as well as a second, distal, promoter, from which a third transcript, the ~160 nt sRNA SyR9 is transcribed. Thus, the transcriptional organization of the alkane biosynthesis genes in Synechocystis sp. PCC 6803 is of substantial complexity. We verified all three promoters to function independently from each other and show a similar promoter arrangement also in the more distant Nodularia spumigena, Trichodesmium erythraeum, Anabaena sp. PCC 7120, Prochlorococcus MIT9313 and MED4. The presence of separate regulatory elements and the dominance of monocistronic mRNAs suggest the possible autonomous regulation of ado and aar. The complex transcriptional organization of the alkane synthesis gene cluster has possible metabolic implications and should be considered when manipulating the expression of these genes in

  19. Direct hydrodeoxygenation of raw woody biomass into liquid alkanes

    OpenAIRE

    Qineng Xia, Zongjia Chen, Yi Shao, Xueqing Gong, Haifeng Wang, Xiaohui Liu, Stewart F. Parker, Xue Han, Sihai Yang & Yanqin Wang

    2016-01-01

    Being the only sustainable source of organic carbon, biomass is playing an ever-increasingly important role in our energy landscape. The conversion of renewable lignocellulosic biomass into liquid fuels is particularly attractive but extremely challenging due to the inertness and complexity of lignocellulose. Here we describe the direct hydrodeoxygenation of raw woods into liquid alkanes with mass yields up to 28.1 wt% over a multifunctional Pt/NbOPO4 catalyst in cyclohexane. T...

  20. Pairwise-additive hydrophobic effect for alkanes in water

    OpenAIRE

    Wu, Jianzhong; Prausnitz, John M.

    2008-01-01

    Pairwise additivity of the hydrophobic effect is indicated by reliable experimental Henry's constants for a large number of linear and branched low-molecular-weight alkanes in water. Pairwise additivity suggests that the hydrophobic effect is primarily a local phenomenon and that the hydrophobic interaction may be represented by a semiempirical force field. By representing the hydrophobic potential between two methane molecules as a linear function of the overlap volume of the hydration layer...

  1. Frictional transition from superlubric islands to pinned monolayers.

    Science.gov (United States)

    Pierno, Matteo; Bruschi, Lorenzo; Mistura, Giampaolo; Paolicelli, Guido; di Bona, Alessandro; Valeri, Sergio; Guerra, Roberto; Vanossi, Andrea; Tosatti, Erio

    2015-08-01

    The inertial sliding of physisorbed submonolayer islands on crystal surfaces contains unexpected information on the exceptionally smooth sliding state associated with incommensurate superlubricity and on the mechanisms of its disappearance. Here, in a joint quartz crystal microbalance and molecular dynamics simulation case study of Xe on Cu(111), we show how superlubricity emerges in the large size limit of naturally incommensurate Xe islands. As coverage approaches a full monolayer, theory also predicts an abrupt adhesion-driven two-dimensional density compression on the order of several per cent, implying a hysteretic jump from superlubric free islands to a pressurized commensurate immobile monolayer. This scenario is fully supported by the quartz crystal microbalance data, which show remarkably large slip times with increasing submonolayer coverage, signalling superlubricity, followed by a dramatic drop to zero for the dense commensurate monolayer. Careful analysis of this variety of island sliding phenomena will be essential in future applications of friction at crystal/adsorbate interfaces. PMID:26006001

  2. Influence of compost amendments on the diversity of alkane degrading bacteria in hydrocarbon contaminated soils

    Directory of Open Access Journals (Sweden)

    MichaelSchloter

    2014-03-01

    Full Text Available Alkane degrading microorganisms play an important role for bioremediation of petrogenic contaminated environments. In this study, we investigated the effects of compost addition on the diversity of alkane monooxygenase gene (alkB harboring bacteria in oil-contaminated soil originated from an industrial zone in Celje, Slovenia, to improve our understanding about the bacterial community involved in alkane degradation and the effects of amendments. Soil without any amendments (control soil and soil amended with compost of different maturation stages, i 1 year and ii 2 weeks, were incubated under controlled conditions in a microcosm experiment and sampled after 0, 6, 12 and 36 weeks of incubation. By using quantitative real-time PCR higher number of alkB genes could be detected in soil samples with compost compared to the control soil after 6, 12 and 36 weeks mainly if the less maturated compost was added. To get an insight into the composition of the alkB harboring microbial communities, we performed next generation sequencing of alkB gene fragment amplicons. Richness and diversity of alkB gene harboring prokaryotes was higher in soil mixed with compost compared to control soil after 6, 12 and 36 weeks again with stronger effects of the less maturated compost. Comparison of communities detected in different samples and time points based on principle component analysis revealed that the addition of compost in general stimulated the abundance of alkB harboring Actinobacteria during the experiment independent from the maturation stage of the compost compared to the control soils. In addition alkB harboring proteobacteria like Shewanella or Hydrocarboniphaga as well as proteobacteria of the genus Agrobacterium responded positively to the addition of compost to soil The amendment of the less maturated compost resulted in addition in a large increase of alkB harboring bacteria of the Cytophaga group (Microscilla mainly at the early sampling

  3. Comparison of Mechanisms of Alkane Metabolism under Sulfate-Reducing Conditions among Two Bacterial Isolates and a Bacterial Consortium

    OpenAIRE

    Callaghan, Amy V.; Gieg, Lisa M.; Kropp, Kevin G.; Suflita, Joseph M.; Young, Lily Y.

    2006-01-01

    Recent studies have demonstrated that fumarate addition and carboxylation are two possible mechanisms of anaerobic alkane degradation. In the present study, we surveyed metabolites formed during growth on hexadecane by the sulfate-reducing isolates AK-01 and Hxd3 and by a mixed sulfate-reducing consortium. The cultures were incubated with either protonated or fully deuterated hexadecane; the sulfate-reducing consortium was also incubated with [1,2-13C2]hexadecane. All cultures were extracted,...

  4. Cold-tolerant alkane-degrading Rhodococcus species from Antarctica

    Energy Technology Data Exchange (ETDEWEB)

    Bej, A.K.; Saul, D.; Aislabie, J.

    2000-07-01

    Bioremediation is a possible mechanism for clean-up of hydrocarbon-contaminated soils in the Antarctic. Microbes indigenous to the Antarctic are required that degrade the hydrocarbon contaminants found in the soil, and that are able to survive and maintain activity under in situ conditions. Alkane-degrading bacteria previously isolated from oil-contaminated soil from around Scott Base, Antarctica, grew on a number of n-alkanes from hexane (C6) through to eicosane (C20) and the branched alkane pristane. Mineralization of {sup 14}C-dodecane was demonstrated with four strains. Representative isolates were identified as Rhodococcus species using 16S rDNA sequence analysis. Rhodococcus spp. strains 5/14 and 7/1 grew at -2 C but numbers of viable cells declined when incubated t 37 C. Both strains appear to have the major cold-shock gene cspA. Partial nucleotide sequence analyses of the PCR-amplified cspA open reading frame from Rhodococcus spp. strains 5/14 and 7/1 were approximately 60% identical to cspA from Escherichia coli.

  5. Modeling SOA production from the oxidation of intermediate volatility alkanes

    Science.gov (United States)

    Aumont, B.; Mouchel-Vallon, C.; Camredon, M.; Lee-Taylor, J.; Madronich, S.

    2012-12-01

    Secondary Organic Aerosols (SOA) production and ageing is a multigenerational oxidation process involving the formation of successive organic compounds with higher oxidation degree and lower vapour pressure. This process was investigated using the explicit oxidation model GECKO-A (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere). Results for the C8-C24 n-alkane series show the expected trends, i.e. (i) SOA yield grows with the carbon backbone of the parent hydrocarbon, (ii) SOA yields decreases with the decreasing pre-existing organic aerosol concentration, (iii) the number of generations required to describe SOA production increases when the pre-existing organic aerosol concentration decreases. Most SOA contributors were found to be not oxidized enough to be categorized as highly oxygenated organic aerosols (OOA) but reduced enough to be categorized as hydrocarbon like organic aerosols (HOA). Branched alkanes are more prone to fragment in the early stage of the oxidation than their corresponding linear analogues. Fragmentation is expected to alter both the yield and the mean oxidation state of the SOA. Here, GECKO-A is applied to generate highly detailed oxidation schemes for various series of branched and cyclised alkanes. Branching and cyclisation effects on SOA yields and oxidation states will be examined.

  6. Hydrogen isotope composition of leaf wax n-alkanes in Arabidopsis lines with different transpiration rates

    Science.gov (United States)

    Pedentchouk, N.; Lawson, T.; Eley, Y.; McAusland, L.

    2012-04-01

    Stable isotopic compositions of oxygen and hydrogen are used widely to investigate modern and ancient water cycles. The D/H composition of organic compounds derived from terrestrial plants has recently attracted significant attention as a proxy for palaeohydrology. However, the role of various plant physiological and biochemical factors in controlling the D/H signature of leaf wax lipids in extant plants remains unclear. The focus of this study is to investigate the effect of plant transpiration on the D/H composition of n-alkanes in terrestrial plants. This experiment includes 4 varieties of Arabidopsis thaliana that differ with respect to stomatal density and stomatal geometry. All 4 varieties were grown indoors under identical temperature, relative humidity, light and watering regimes and then sampled for leaf wax and leaf water stable isotopic measurements. During growth, stomatal conductance to carbon dioxide and water vapour were also determined. We found that the plants varied significantly in terms of their transpiration rates. Transpiration rates were significantly higher in Arabidopsis ost1 and ost1-1 varieties (2.4 and 3.2 mmol m-2 s-1, respectively) than in Arabidopsis RbohD and Col-0 (1.5 and 1.4). However, hydrogen isotope measurements of n-alkanes extracted from leaf waxes revealed a very different pattern. Varieties ost1, ost1-1, and RbohD have very similar deltaD values of n-C29 alkane (-125, -128, and -127 per mil), whereas the deltaD value of Col-0 is more negative (-137 per mil). The initial results of this work suggest that plant transpiration is decoupled from the D/H composition of n-alkanes. In other words, physical processes that affect water vapour movement between the plant and its environment apparently cannot account for the stable hydrogen isotope composition of organic compounds that comprise leaf waxes. Additional, perhaps biochemical, processes that affect hydrogen isotope fractionation during photosynthesis might need to be invoked

  7. C60 fullerene promotes lung monolayer collapse

    OpenAIRE

    Barnoud, Jonathan; Urbini, Laura; Monticelli, Luca

    2015-01-01

    Airborne nanometre-sized pollutants are responsible for various respiratory diseases. Such pollutants can reach the gas-exchange surface in the alveoli, which is lined with a monolayer of lung surfactant. The relationship between physiological effects of pollutants and molecular-level interactions is largely unknown. Here, we determine the effects of carbon nanoparticles on the properties of a model of lung monolayer using molecular simulations. We simulate phase-separated lipid monolayers in...

  8. Whole-cell bio-oxidation of n-dodecane using the alkane hydroxylase system of P. putida GPo1 expressed in E. coli

    DEFF Research Database (Denmark)

    Grant, Chris; Woodley, John; Baganz, Frank

    2011-01-01

    The alkane-1-monoxygenase (alkB) complex of Pseudomonas putida GPo1 has been extensively studied in the past and shown to be capable of oxidising aliphatic C5–C12 alkanes to primary alcohols both in the wild-type organism by growth on C5–C12 alkanes as sole carbon source and in vitro. Despite this......, successful n-dodecane oxidation for the production of 1-dodecanol or dodecanoic acid has proven elusive in the past when using alkB-expressing recombinants. This article demonstrates, for the first time in vivo, by using the Escherichia coli GEC137 pGEc47ΔJ strain, that n-dodecane oxidation using this enzyme...

  9. Equation of state modeling of the phase equilibria of asymmetric CO2+n-alkane binary systems using mixing rules cubic with respect to mole fraction

    DEFF Research Database (Denmark)

    Cismondi, Martin; Mollerup, Jørgen M.; Zabaloy, Marcelo S.

    2010-01-01

    available interaction parameters) in modern equations of state.In particular, the phase equilibria of binary mixtures containing CO2 and heavy n-alkanes have been studied by an important number of authors and using different types of models, achieving only partially accurate results and realizing the...... for the first time a quite successful complete description of asymmetric CO2+n-alkane binary systems, with n-alkane carbon number from 14 to 22....... a great diversity of mixtures. Nevertheless, the models for representing phase equilibria and physico-chemical properties of asymmetric systems may require more flexible mixing rules than the classical quadratic van der Waals (vdW) mixing rules or their equivalent (with regard to the number of...

  10. Phase transformations in binary colloidal monolayers.

    Science.gov (United States)

    Yang, Ye; Fu, Lin; Marcoux, Catherine; Socolar, Joshua E S; Charbonneau, Patrick; Yellen, Benjamin B

    2015-03-28

    Phase transformations can be difficult to characterize at the microscopic level due to the inability to directly observe individual atomic motions. Model colloidal systems, by contrast, permit the direct observation of individual particle dynamics and of collective rearrangements, which allows for real-space characterization of phase transitions. Here, we study a quasi-two-dimensional, binary colloidal alloy that exhibits liquid-solid and solid-solid phase transitions, focusing on the kinetics of a diffusionless transformation between two crystal phases. Experiments are conducted on a monolayer of magnetic and nonmagnetic spheres suspended in a thin layer of ferrofluid and exposed to a tunable magnetic field. A theoretical model of hard spheres with point dipoles at their centers is used to guide the choice of experimental parameters and characterize the underlying materials physics. When the applied field is normal to the fluid layer, a checkerboard crystal forms; when the angle between the field and the normal is sufficiently large, a striped crystal assembles. As the field is slowly tilted away from the normal, we find that the transformation pathway between the two phases depends strongly on crystal orientation, field strength, and degree of confinement of the monolayer. In some cases, the pathway occurs by smooth magnetostrictive shear, while in others it involves the sudden formation of martensitic plates. PMID:25677504

  11. Predicting Two-Dimensional Silicon Carbide Monolayers.

    Science.gov (United States)

    Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I

    2015-10-27

    Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics. PMID:26394207

  12. Utilização dos componentes da cera das plantas, em especial os n-alcanos, em estudos de nutrição de ruminantes The utilization of plant wax components, especially n-alkanes, in ruminants nutrition studies

    Directory of Open Access Journals (Sweden)

    Dimas Estrásulas de Oliveira

    2000-06-01

    Full Text Available A utilização de métodos indiretos para estimar o consumo e a digestibilidade dos alimentos por ruminantes é bastante importante, porque pode representar uma economia de tempo, dinheiro e trabalho em relação aos experimentos convencionais e, também, por permitir tais estimativas sob condições extensivas de pastejo. Dentre esses métodos, sobressai-se o dos indicadores fecais. Várias substâncias têm sido utilizadas para esse fim. Este artigo é uma revisão de alguns aspectos sobre o uso de n-alcanos como indicadores em estudos de nutrição de ruminantes.The indirect methods used to estimate the intake and digestibility of feedstuffs by ruminants are very important because these methods represent an economy of time, money and work, in relation to conventional trials. Also, they permit estimates in grazing conditions. Among these methods, the faecal markers stand out and lots of substances have been used. This paper is a review about the use of n-alkanes as markers in ruminant nutrition studies.

  13. Equilibrating nanoparticle monolayers using wetting films.

    Science.gov (United States)

    Pontoni, Diego; Alvine, Kyle J; Checco, Antonio; Gang, Oleg; Ocko, Benjamin M; Pershan, Peter S

    2009-01-01

    Monolayers of bimodal gold nanoparticles on silicon are investigated by a combination of microscopy (dry monolayers) and x-ray diffraction (dry and wet monolayers). In the presence of an excess of small particles, the nanoscale packing structure closely resembles the small-particle-rich scenario of the structural crossover transition that has been predicted and also observed with micron-scale hard-sphere colloids. Structural morphology is monitored in situ during monolayer dissolution and reassembly within the thin liquid wetting film. This approach allows investigation of size and solvent effects on nanoparticles in quasi-two-dimensional confinement. PMID:19257214

  14. (Liquid + liquid) extraction of methanol from alkanes using dialkylphosphate-based ionic liquids as solvents

    International Nuclear Information System (INIS)

    Highlights: • Several ILs were studied as solvents to extract methanol from alkanes. • LLE data for ternary systems were measured at T = 298.2 K and atmospheric pressure. • LLE data for ternary systems were successfully correlated by using the NRTL model. • Results of solute distribution ratio and selectivity were compared with literature. • The [MMIM][DMP] showed the best extraction effectiveness in the studied ILs. - Abstract: In this work, the feasibility of ionic liquids (ILs), 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), and 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]), as solvents for the extraction of methanol from its mixtures with hexane and heptane was analyzed. The knowledge of (liquid + liquid) equilibria (LLE) of these mixtures is necessary for the design of the extraction separation process. Hence, the LLE data for the ternary systems, {methanol + hexane + ([MMIM][DMP], or [EMIM][DEP], or [BMIM][DBP])}, and {methanol + heptane + ([MMIM][DMP], or [EMIM][DEP], or [BMIM][DBP])}, were measured at T = 298.2 K and atmospheric pressure. The experimental results were correlated with the thermodynamic nonrandom two-liquid (NRTL) model. The solute distribution ratios of methanol and methanol/alkane selectivities, derived from the experimental LLE data, were calculated and analyzed to evaluate the capability of the studied ILs to accomplish the separation target. Meanwhile, these capabilities were also compared with that of other ILs obtained from the literature

  15. Citrate-reduced silver hydrosol modified with omega-mercaptoalkanoic acids self-assembled monolayers as a substrate for surface-enhanced resonance Raman scattering. A study with cytochrome c

    NARCIS (Netherlands)

    Bonifacio, A.; Sneppen, van der L.; Gooijer, C.; Zwan, van der G.

    2004-01-01

    A new citrate-reduced silver hydrosol coated with omega-mercaptoalkanoic acids (mercaptopropionic and mercaptoundecanoic acids) self-assembled monolayers was prepared and characterized with surface-enhanced Raman spectroscopy. The structure and the quality of the coating monolayers are discussed and

  16. Nucleation, growth and habit modification of n-alkanes and homologous mixtures in the absence and presence of flow improving additives

    International Nuclear Information System (INIS)

    A detailed study has been performed on the nucleation, growth and habit modification of n-alkanes and homologous mixtures in the absence and presence of flow improving additives in an attempt to gain a clearer appreciation of the interaction mechanisms behind wax / additive crystallisation. Kinetic and structural assessment of melt phase n-alkanes illustrate the different crystallographic forms present within the homologous series. Studies demonstrate the alternating behaviour of the even and odd numbered homologues which converges as a function of increasing molecular weight. Greater crystal lattice stabilities were found for those n-alkanes which have an even carbon number and which crystallise into the triclinic crystal structure. Solid state phase behaviour of the n-alkanes was found to vary depending on the number and parity of n. Nucleation kinetic studies of n-alkanes and homologous mixtures from model diesel fuel solvents (dodecane, m-xylene, decalin, pristane and a dewaxed fuel) are assessed using turbidity as the method of crystallite detection. Saturation temperatures are found to be related to both alkane structure and molecular chain length for all solvent systems. N-alkane solubilities are lower for n-alkane like solvents. The width of the meta stable zone varies as a function of solvent in order of dodecane ≅ pristane 19H40 and solvent m-xylene. Wax precipitation from distillate fuels in the presence of flow improving additives (di-alkyl di-amino xylene, phthalic acid and sulphobenzene acid derivatives and high molecular weight polymers) reveal responsive wax crystal nucleator and growth inhibitor additives. The crystal morphology of heptacosane, C27H56 to simulate a model wax crystal is assessed in addition to its response to blocker 'tailor made' additives: methyl substituted C27H56 and di-alkyl substituted phenyl additives [additive (A) and (B)]. Pure C27H56 reveals a thin lozenge shaped platelet. All additives studied induce growth inhibition

  17. Mg2+-Dependent Control of the Spatial Arrangement of Rhodococcus erythropolis PR4 Cells in Aqueous-Alkane Two Phase Culture Containing n-Dodecane

    Science.gov (United States)

    Takihara, Hayato; Akase, Yumiko; Sunairi, Michio; Iwabuchi, Noriyuki

    2016-01-01

    We recently reported that a close relationship exists between alkane carbon-chain length, cell growth, and translocation frequency in Rhodococcus. In the present study, we examined the regulation of the spatial arrangement of cells in aqueous-alkane two phase cultures. An analysis of the effects of minerals on cell localization revealed that changes in the concentration of MgSO4 in two phase cultures containing n-dodecane (C12) altered cell localization from translocation to adhesion and vice versa. Our results indicate that the spatial arrangement of cells in two phase culture systems is controlled through the regulation of MgSO4 concentrations. PMID:27180641

  18. Role of Sn in the Regeneration of Pt/γ-Al2O3 Light Alkane Dehydrogenation Catalysts

    OpenAIRE

    Pham, Hien N.; Sattler, Jesper J. H. B.; Weckhuysen, Bert M.; Datye, Abhaya K.

    2016-01-01

    Alumina-supported Pt is one of the major industrial catalysts for light alkane dehydrogenation. This catalyst loses activity during reaction, with coke formation often considered as the reason for deactivation. As we show in this study, the amount and nature of carbon deposits do not directly correlate with the loss of activity. Rather, it is the transformation of subnanometer Pt species into larger Pt nanoparticles that appears to be responsible for the loss of catalytic activity. Surprising...

  19. Ionic channels and nerve membrane constituents. Tetrodotoxin-like interaction of saxitoxin with cholesterol monolayers.

    Science.gov (United States)

    Villegas, R; Barnola, F V

    1972-01-01

    Saxitoxin (STX) and tetrodotoxin (TTX) have the same striking property of blocking the Na(+) channels in the axolemma. Experiments with nerve plasma membrane components of the squid Dosidicus gigas have shown that TTX interacts with cholesterol monolayers. Similar experiments were carried out with STX. The effect of STX on the surface pressure-area diagrams of lipid monolayers and on the fluorescence emission spectra of sonicated nerve membranes was studied. The results indicate a TTX-like interaction of STX with cholesterol monolayers. The expansion of the monolayers caused by 10(-6)M STX was 2.2 A(2)/cholesterol molecule at 25 degrees C. From surface pressure measurements at constant cholesterol area (39 A(2)/molecule) in media with various STX concentrations, it was calculated that the STX/cholesterol surface concentration ratio is 0.54. The apparent dissociation constant of the STX-cholesterol monolayer complex is 4.0 x 10(-7)M. The STX/cholesterol ratio and the apparent dissociation constant are similar to those determined for TTX. The presence of other lipids in the monolayers affects the STX-cholesterol association. The interactions of STX and TTX with cholesterol monolayers suggest (a) that cholesterol molecules may be part of the nerve membrane Na(+) channels, or (b) that the toxin receptor at the nerve membrane shares similar chemical features with the cholesterol monolayers. PMID:5007264

  20. Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED

    International Nuclear Information System (INIS)

    The room temperature self-assembly and ordering of (5,15-diphenylporphyrinato)nickel(II) (NiDPP) on the Ag(111) and Ag/Si(111)-(√3 × √3)R30° surfaces have been investigated using scanning tunnelling microscopy and low-energy electron diffraction. The self-assembled structures and lattice parameters of the NiDPP monolayer are shown to be extremely dependent on the reactivity of the substrate, and probable molecular binding sites are proposed. The NiDPP overlayer on Ag(111) grows from the substrate step edges, which results in a single-domain structure. This close-packed structure has an oblique unit cell and consists of molecular rows. The molecules in adjacent rows are rotated by approximately 17° with respect to each other. In turn, the NiDPP molecules form three equivalent domains on the Ag/Si(111)-(√3 × √3)R30° surface, which follow the three-fold symmetry of the substrate. The molecules adopt one of three equivalent orientations on the surface, acting as nucleation sites for these domains, due to the stronger molecule-substrate interaction compared to the case of the Ag(111). The results are explained in terms of the substrate reactivity and the lattice mismatch between the substrate and the molecular overlayer. (paper)

  1. In situ and real-time atomic force microscopy studies of the stability of oligothiophene langmuir-blodgett monolayers in liquid

    KAUST Repository

    Yin, Naining

    2014-03-20

    Oligothiophene thin films have been considered as promising material for molecular electronics due to their desirable electronic properties and high structural stability under ambient conditions. To ensure performance in devices the functional structures, such as individual ordered domains, must be stable under practical and operational conditions or environments including exposure to various media. This work investigates the structure of oligothiophene Langmuir-Blodgett (LB) films upon exposure to liquid media such as water, ethanol (EtOH), and mixed tetrahydrofuran (THF)/EtOH solutions. The LB films form islands ranging from 500 nm up to 1 μm consisting of densely packed oligothiophene molecules. These islands are surrounded by bare substrate and loosely packed adsorbates. In situ and time-dependent AFM images were acquired to reveal the structural evolution, from which degradation pathways and kinetics are extracted. Degradation of these LB films initiates and propagates from intraisland defect sites, such as cracks and pin holes, whereas the edges of islands remain intact on the surface. The observations appear to be in contrast to the known degradation mechanism among self-assembled monolayers, such as alkanethiols on gold, which initiates and progresses at domain boundaries. Rationale for the observed degradation processes will also be discussed. © 2014 American Chemical Society.

  2. Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED.

    Science.gov (United States)

    Murphy, B E; Krasnikov, S A; Cafolla, A A; Sergeeva, N N; Vinogradov, N A; Beggan, J P; Lübben, O; Senge, M O; Shvets, I V

    2012-02-01

    The room temperature self-assembly and ordering of (5,15-diphenylporphyrinato)nickel(II) (NiDPP) on the Ag(111) and Ag/Si(111)-(√3 × √3)R30° surfaces have been investigated using scanning tunnelling microscopy and low-energy electron diffraction. The self-assembled structures and lattice parameters of the NiDPP monolayer are shown to be extremely dependent on the reactivity of the substrate, and probable molecular binding sites are proposed. The NiDPP overlayer on Ag(111) grows from the substrate step edges, which results in a single-domain structure. This close-packed structure has an oblique unit cell and consists of molecular rows. The molecules in adjacent rows are rotated by approximately 17° with respect to each other. In turn, the NiDPP molecules form three equivalent domains on the Ag/Si(111)-(√3 × √3)R30° surface, which follow the three-fold symmetry of the substrate. The molecules adopt one of three equivalent orientations on the surface, acting as nucleation sites for these domains, due to the stronger molecule-substrate interaction compared to the case of the Ag(111). The results are explained in terms of the substrate reactivity and the lattice mismatch between the substrate and the molecular overlayer. PMID:22223550

  3. Self-Assembled Monolayers deposition in Supercritical Carbon Dioxide

    OpenAIRE

    Rabbia, Laurent; Perrut, Vincent; Pons, Patrick; Lellouchi, Djemel

    2009-01-01

    Self-Assembled Monolayers of organic molecules have been successfully deposited onto wafer surface in supercritical carbon dioxide. Deposition method and apparatus are described. The layers are characterized by AFM and water droplet contact angle. Interest of this technique compared to liquid and vapor phase is discussed and studied for surface conversion from hydrophilic to hydrophobic for different materials.

  4. Ultrafast shock compression of self-assembled monolayers: a molecular picture.

    Science.gov (United States)

    Patterson, James E; Dlott, Dana D

    2005-03-24

    Simulations of self-assembled monolayers (SAMs) are performed to interpret experimental measurements of ultrafast approximately 1 GPa (volume compression deltaV approximately 0.1) planar shock compression dynamics probed by vibrational sum-frequency generation (SFG) spectroscopy (Lagutchev, A. S.; Patterson, J. E.; Huang, W.; Dlott, D. D. J. Phys. Chem. B 2005, 109, XXXX). The SAMs investigated are octadecanethiol (ODT) and pentadecanethiol (PDT) on Au(111) and Ag(111) substrates, and benzyl mercaptan (BMT) on Au(111). In the alkane SAMs, SFG is sensitive to the instantaneous orientation of the terminal methyl; in BMT it is sensitive to the phenyl orientation. Computed structures of alkane SAMs are in good agreement with experiment. In alkanes, the energies of gauche defects increase with increasing number and depth below the methyl plane, with the exception of ODT/Au where both single and double gauche defects at the two uppermost dihedrals have similar energies. Simulations of isothermal uniaxial compression of SAM lattices show that chain and methyl tilting is predominant in PDT/Au, ODT/Ag and PDT/Ag, whereas single and double gauche defect formation is predominant in ODT/Au. Time-resolved shock data showing transient SFG signal loss of ODT/Au and PDT/Au are fit by calculations of the terminal group orientations as a function of deltaV and their contributions to the SFG hyperpolarizability. The highly elastic response of PDT/Au results from shock-generated methyl and chain tilting. The viscoelastic response of ODT/Au results from shock generation of single and double gauche defects. Isothermal compression simulations help explain and fit the time dependence of shock spectra but generally underestimate the magnitude of SFG signal loss because they do not include effects of high-strain-rate dynamics and shock front and surface irregularities. PMID:16863164

  5. Characterization of Particulate Matter Transport across the Lung-Surfactant Barrier using Langmuir Monolayers

    Science.gov (United States)

    Eaton, Jeremy; Dennin, Michael; Levine, Alex; George, Steven

    2014-03-01

    We investigate the transport of particulate matter acros the lung using a monolayer of bovine lung surfactant tagged with NBD in conjunction with alveolar lung cells below the air-water interface. The monolaye dynamically compressed and expanded to induce phase transitions as well as buckling and folding. Polystyrene spheres ranging from 20 to 500 nm in diameter were tagged with fluorescent molecules and deposited on the monolayer. We will present results of preliminary studies of the transport of beads from the air-water surface to the lung cells through the monolayer. Characterization of the transfer will focus on differential fluorescence microscopy to distinguish uncoated beads from beads from beads coated with surfactant monolayers. The presence or absence of surfactant associated with the beads provides insight into potential transfer mechanisms and will serve as an input into models of the bead transfer. We gladly acknowledge the support of NSF grant DMR-1309402.

  6. Measuring long chain alkanes in diesel engine exhaust by thermal desorption PTR-MS

    OpenAIRE

    Erickson, M. H.; Gueneron, M.; B. T. Jobson

    2014-01-01

    A method using thermal desorption sampling and analysis by proton transfer reaction mass spectrometry (PTR-MS) to measure long chain alkanes (C12–C18) and other larger organics associated with diesel engine exhaust emissions is described. Long chain alkanes undergo dissociative proton transfer reactions forming a series of fragment ions with formula CnH2n+1. The PTR-MS is insensitive to n-alkanes less than C8 but displays an increasing sensitivity for larger alkanes. Fragment ...

  7. Multifunctional self-assembled monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Zawodzinski, T.; Bar, G.; Rubin, S.; Uribe, F. [Los Alamos National Lab., NM (United States); Ferrais, J. [Texas Univ., Dallas, TX (United States)

    1996-06-01

    This is the final report of at three year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The specific goals of this research project were threefold: to develop multifunctional self-assembled monolayers, to understand the role of monolayer structure on the functioning of such systems, and to apply this knowledge to the development of electrochemical enzyme sensors. An array of molecules that can be used to attach electrochemically active biomolecules to gold surfaces has been synthesized. Several members of a class of electroactive compounds have been characterized and the factors controlling surface modification are beginning to be characterized. Enzymes have been attached to self-assembled molecules arranged on the gold surface, a critical step toward the ultimate goal of this project. Several alternative enzyme attachment strategies to achieve robust enzyme- modified surfaces have been explored. Several means of juxtaposing enzymes and mediators, electroactive compounds through which the enzyme can exchange electrons with the electrode surface, have also been investigated. Finally, the development of sensitive biosensors based on films loaded with nanoscale-supported gold particles that have surface modified with the self-assembled enzyme and mediator have been explored.

  8. Processing and Quality Evaluation of Additive Manufacturing Monolayer Specimens

    Directory of Open Access Journals (Sweden)

    Christiane Wendt

    2016-01-01

    Full Text Available Although its importance has increased significantly, Additive Manufacturing is not yet a fully accepted industrial manufacturing process for load-carrying parts. The future success of the process group depends on its standardization. This work proposes a methodology for the design, manufacturing, and quality evaluation of specimens manufactured by Fused Layer Modeling that are composed of only one layer (so-called monolayers. The processing methodology and properties of monolayers have not been studied systematically yet. A first systematic design of monolayers for mechanical testing is presented. Rectangular and circular monolayers adapted to the loads of tensile and compression testing are manufactured using different trajectory strategies. Frequently occurring macro- and microgeometrical defects are evaluated and categorized in order to optimize the part quality. This work also studies the effect of some manufacturing parameters such as the gap between print head and machine bed, trajectory strategy, bed leveling, and temperatures on part quality. The most suitable specimens are tested mechanically in tensile or compression tests. In the case of study, tensile strength values are only 8.6% lower than the values for reference tests on the unextruded filament. However, the properties deviate more strongly for compression tests which may be due to the selected specimen geometry.

  9. Ignition of alkane-rich FACE gasoline fuels and their surrogate mixtures

    KAUST Repository

    Sarathy, Mani

    2015-01-01

    Petroleum derived gasoline is the most used transportation fuel for light-duty vehicles. In order to better understand gasoline combustion, this study investigated the ignition propensity of two alkane-rich FACE (Fuels for Advanced Combustion Engines) gasoline test fuels and their corresponding PRF (primary reference fuel) blend in fundamental combustion experiments. Shock tube ignition delay times were measured in two separate facilities at pressures of 10, 20, and 40 bar, temperatures from 715 to 1500 K, and two equivalence ratios. Rapid compression machine ignition delay times were measured for fuel/air mixtures at pressures of 20 and 40 bar, temperatures from 632 to 745 K, and two equivalence ratios. Detailed hydrocarbon analysis was also performed on the FACE gasoline fuels, and the results were used to formulate multi-component gasoline surrogate mixtures. Detailed chemical kinetic modeling results are presented herein to provide insights into the relevance of utilizing PRF and multi-component surrogate mixtures to reproduce the ignition behavior of the alkane-rich FACE gasoline fuels. The two FACE gasoline fuels and their corresponding PRF mixture displayed similar ignition behavior at intermediate and high temperatures, but differences were observed at low temperatures. These trends were mimicked by corresponding surrogate mixture models, except for the amount of heat release in the first stage of a two-stage ignition events, when observed. © 2014 The Combustion Institute.

  10. Influence of alkane chain length on adsorption on an α-alumina surface by MD simulations

    International Nuclear Information System (INIS)

    Plasma surface techniques provide both an efficient and ecological tool for the functionalization of surfaces. Hence, a proper understanding of the plasma–surface interactions of precursors and radicals during the deposition process is of great importance. Especially during the initial deposition process, the deposition of molecules and fragments is difficult to investigate by experimental techniques and import insights can be obtained by molecular dynamics simulations. In this work, the reactive force field developed by the group of Kieffer at the University of Michigan was used to study the adsorption of single linear alkane chains on an α-alumina surface. The chain length was changed from 6 backbone carbon atoms to 16 carbon atoms, the deposition energy from 0.01 to 10 eV and the incidence angle from 0° to 60° with respect to the surface normal. Results show that the adsorption depends a lot on the ratio of deposition energy to alkane chain length and the incidence angle. More grazing incidence reduces the adsorption probability and a low ratio of energy to chain length increases it

  11. Alkane fluids confined and compressed by two smooth crystalline gold surfaces: Pure liquids and mixtures

    Science.gov (United States)

    Alvarez, Lina P. Merchan

    With the use of grand canonical molecular dynamics, we studied the slow compression(0.01m/s) of very thin liquid films made of equimolar mixtures of short and long alkane chains (hexane and hexadecane), and branched and unbranched alkanes (phytane and hexadecane). Besides comparing how these mixtures behave under constant speed compression, we will compare their properties with the behavior and structure of the pure systems undergoing the same type of slow compression. To understand the arrangement of the molecules inside the confinement, we present segmental and molecular density profiles, average length and orientation of the molecules inside well formed gaps. To observe the effects of the compression on the fluids, we present the number of confined molecules, the inlayer orientation, the solvation force and the inlayer diffusion coefficient, versus the thickness of the gap. We observe that pure hexadecane, although liquid at this temperature, starts presenting strong solid-like behavior when it is compressed to thicknesses under 30A, while pure hexane and pure phytane continue to behave liquid-like except at 13A when they show some weak solid-like features. When hexadecane is mixed with the short straight hexane, it remains liquid down to 28A at which point this mixture behaves solid-like with an enhanced alignment of the long molecules not seen in its pure form; but when hexade-cane is mixed with the branched phytane the system does not present the solid-like features seen when hexadecane is compressed pure.

  12. Influence of alkane chain length on adsorption on an α-alumina surface by MD simulations

    Energy Technology Data Exchange (ETDEWEB)

    Turgut, C. [Department of Science and Analysis of Materials (SAM), CRP-Gabriel Lippmann, L-4422 Belvaux (Luxembourg); Institut Jean Lamour (IJL) CNRS UMR 7198, Université de Lorraine, Faculté des Sciences et Technologies, BP 70239, F-54506 Vandoeuvre-les-Nancy Cedex (France); Pandiyan, S. [Department of Science and Analysis of Materials (SAM), CRP-Gabriel Lippmann, L-4422 Belvaux (Luxembourg); Mether, L. [Department of Physics, University of Helsinki, P.O. Box 43, FI-00014 (Finland); Belmahi, M. [Institut Jean Lamour (IJL) CNRS UMR 7198, Université de Lorraine, Faculté des Sciences et Technologies, BP 70239, F-54506 Vandoeuvre-les-Nancy Cedex (France); Nordlund, K. [Department of Physics, University of Helsinki, P.O. Box 43, FI-00014 (Finland); Philipp, P., E-mail: philipp@lippmann.lu [Department of Science and Analysis of Materials (SAM), CRP-Gabriel Lippmann, L-4422 Belvaux (Luxembourg)

    2015-06-01

    Plasma surface techniques provide both an efficient and ecological tool for the functionalization of surfaces. Hence, a proper understanding of the plasma–surface interactions of precursors and radicals during the deposition process is of great importance. Especially during the initial deposition process, the deposition of molecules and fragments is difficult to investigate by experimental techniques and import insights can be obtained by molecular dynamics simulations. In this work, the reactive force field developed by the group of Kieffer at the University of Michigan was used to study the adsorption of single linear alkane chains on an α-alumina surface. The chain length was changed from 6 backbone carbon atoms to 16 carbon atoms, the deposition energy from 0.01 to 10 eV and the incidence angle from 0° to 60° with respect to the surface normal. Results show that the adsorption depends a lot on the ratio of deposition energy to alkane chain length and the incidence angle. More grazing incidence reduces the adsorption probability and a low ratio of energy to chain length increases it.

  13. Cyanobacterial Alkanes Modulate Photosynthetic Cyclic Electron Flow to Assist Growth under Cold Stress.

    Science.gov (United States)

    Berla, Bertram M; Saha, Rajib; Maranas, Costas D; Pakrasi, Himadri B

    2015-01-01

    All cyanobacterial membranes contain diesel-range C15-C19 hydrocarbons at concentrations similar to chlorophyll. Recently, two universal but mutually exclusive hydrocarbon production pathways in cyanobacteria were discovered. We engineered a mutant of Synechocystis sp. PCC 6803 that produces no alkanes, which grew poorly at low temperatures. We analyzed this defect by assessing the redox kinetics of PSI. The mutant exhibited enhanced cyclic electron flow (CEF), especially at low temperature. CEF raises the ATP:NADPH ratio from photosynthesis and balances reductant requirements of biosynthesis with maintaining the redox poise of the electron transport chain. We conducted in silico flux balance analysis and showed that growth rate reaches a distinct maximum for an intermediate value of CEF equivalent to recycling 1 electron in 4 from PSI to the plastoquinone pool. Based on this analysis, we conclude that the lack of membrane alkanes causes higher CEF, perhaps for maintenance of redox poise. In turn, increased CEF reduces growth by forcing the cell to use less energy-efficient pathways, lowering the quantum efficiency of photosynthesis. This study highlights the unique and universal role of medium-chain hydrocarbons in cyanobacterial thylakoid membranes: they regulate redox balance and reductant partitioning in these oxygenic photosynthetic cells under stress. PMID:26459862

  14. Dehydrogenation of light alkanes over zeolites

    NARCIS (Netherlands)

    Narbeshuber, Thomas F.; Brait, Axel; Seshan, Kulathuiyer; Lercher, Johannes A.

    1997-01-01

    The conversion of light paraffins to olefins and the secondary reactions of the unsaturated compounds were investigated on H-ZSM5 and H-Y zeolites between 733 and 823 K. Steady state- and transient response-isotope tracing studies revealed that two mechanisms of dehydrogenation are operative. The ma

  15. A compound-specific n-alkane δ 13C and δD approach for assessing source and delivery processes of terrestrial organic matter within a forested watershed in northern Japan

    Science.gov (United States)

    Seki, Osamu; Nakatsuka, Takeshi; Shibata, Hideaki; Kawamura, Kimitaka

    2010-01-01

    We measured molecular distributions and compound-specific hydrogen (δD) and stable carbon isotopic ratios (δ 13C) of mid- and long-chain n-alkanes in forest soils, wetland peats and lake sediments within the Dorokawa watershed, Hokkaido, Japan, to better understand sources and processes associate with delivery of terrestrial organic matter into the lake sediments. δ 13C values of odd carbon numbered C 23-C 33n-alkanes ranged from -37.2‰ to -31.5‰, while δD values of these alkanes showed a large degree of variability that ranged from -244‰ to -180‰. Molecular distributions in combination with stable carbon isotopic compositions indicate a large contribution of C3 trees as the main source of n-alkanes in forested soils whereas n-alkanes in wetland soil are exclusively derived from marsh grass and/or moss. We found that the n-alkane δD values are much higher in forest soils than wetland peat. The higher δD values in forest samples could be explained by the enrichment of deuterium in leaf and soil waters due to increased evapotranspiration in the forest or differences in physiology of source plants between wetland and forest. A δ 13C vs. δD diagram of n-alkanes among forest, wetland and lake samples showed that C 25-C 31n-alkanes deposited in lake sediments are mainly derived from tree leaves due to the preferential transport of the forest soil organic matter over the wetland or an increased contribution of atmospheric input of tree leaf wax in the offshore sites. This study demonstrates that compound-specific δD analysis provides a useful approach for better understanding source and transport of terrestrial biomarkers in a C3 plant-dominated catchment.

  16. Stilling Waves with Ordered Molecular Monolayers

    Science.gov (United States)

    Vitz, Ed

    2008-01-01

    A demonstration of the damping effect of an oil monolayer on water waves is described. The history of this remarkable demonstration--with a 2000 (or more) year span--and a brief explanation in terms of the properties of water and the monolayer are presented. If a layer of olive oil, one molecule thick (about one-ten millionth of a centimeter), is…

  17. Packing of ganglioside-phospholipid monolayers

    DEFF Research Database (Denmark)

    Majewski, J.; Kuhl, T.L.; Kjær, K.;

    2001-01-01

    Using synchrotron grazing-incidence x-ray diffraction (GIXD) and reflectivity, the in-plane and out-of-plane structure of mixed ganglioside-phospholipid monolayers was investigated at the air-water interface. Mixed monolayers of 0, 5, 10, 20, and 100 mol% ganglioside GM, and the phospholipid dipa...

  18. Antiferromagnets Structure in Adsorbed O2 Monolayers

    DEFF Research Database (Denmark)

    Nielsen, Mourits; McTague, J. P.

    1977-01-01

    Neutron diffraction from monolayers of O2 adsorbed on graphite shows structural arrangements similar to the dense planes of bulk O2. At monolayer completion and above, a magnetic superlattice reflection shows well-developed antiferromagnetic order for T ⩽ 10 K. The submonolayer phase also shows...

  19. Cometabolism of Methyl tertiary Butyl Ether and Gaseous n-Alkanes by Pseudomonas mendocina KR-1 Grown on C5 to C8 n-Alkanes

    OpenAIRE

    Smith, Christy A.; O'Reilly, Kirk T.; Hyman, Michael R.

    2003-01-01

    Pseudomonas mendocina KR-1 grew well on toluene, n-alkanes (C5 to C8), and 1° alcohols (C2 to C8) but not on other aromatics, gaseous n-alkanes (C1 to C4), isoalkanes (C4 to C6), 2° alcohols (C3 to C8), methyl tertiary butyl ether (MTBE), or tertiary butyl alcohol (TBA). Cells grown under carbon-limited conditions on n-alkanes in the presence of MTBE (42 μmol) oxidized up to 94% of the added MTBE to TBA. Less than 3% of the added MTBE was oxidized to TBA when cells were grown on either 1° alc...

  20. The structure of percolating lipid monolayers.

    Science.gov (United States)

    Risović, D; Frka, S; Kozarac, Z

    2012-05-01

    The lattice structure and in plane molecular organization of Langmuir monolayer of amphiphilic material is usually determined from grazing incidence X-ray diffraction (GIXD) or neutron reflectivity. Here we present results of a different approach for determination of monolayer lattice structure based on application of fractal analysis and percolation theory in combination with Brewster angle microscopy. The considerations of compressibility modulus and fractal dimension dynamics provide information on percolation threshold and consequently by application of percolation theory on the lattice structure of a monolayer. We have applied this approach to determine the monolayer lattice structures of single chain and double chain lipids. The compressibility moduli were determined from measured π-A isotherms and fractal dimensions from corresponding BAM images. The monolayer lattice structures of stearic acid, 1-hexadecanol, DPPC and DPPA, obtained in this way conform to the corresponding lattice structures determined previously by other authors using GIXD. PMID:22209411

  1. Hydrocarbon activation by gas-phase lanthanide cations: interaction of Pr+, Eu+, and Gd+ with small alkanes, cycloalkanes, and alkenes

    International Nuclear Information System (INIS)

    The authors describe ion beam studies of the interaction of gas-phase lanthanide ions, praseodymium (Pr+), europium (Eu+), and gadolinium (Gd+), with small alkanes, cycloalkanes, alkenes, and several oxygen-containing compounds. Only Gd+ is seen to activate C-H and C-C bonds of alkanes. The ground state electronic configuration of Gd+ (4f75d16s1) is different from those of Pr+ (4f36s1) and Eu+ (4f76s1), leading to the conclusion that the f electrons play little part in the metal ion reactivity. Gd+ can be thought of as having two valence electrons, and indeed it reacts similarly to Sc+ and the other group 3 metal ions Y+ and La+, yielding products corresponding to elimination of hydrogen, alkanes, and alkenes. The elimination of neutral alkenes in the reaction of Gd+ with alkanes results in the formation of metal dialkyl or hydrido-alkyl complexes. This finding leads to estimates for the sum of two Gd+ σ bond dissociation energies of between 110 and 130 kcal/mol. Gd+ and Pr+ react readily with alkenes, yielding mostly dehydrogenation products along with smaller amounts of C-C bond cleavage products. Reactions of Gd+ and Pr+ with oxygen-containing species such as nitric oxide, formaldehyde, acetaldehyde, and acetone yield primarily the metal oxide ions and provide a lower limit for D(M+-O) of 179 kcal/mol, in good agreement with literature values of D(Pr+-O) = 188.4 +/- 5.2 kcal/mol and D(Gd+-0) = 181.0 +/- 4.4 kcal/mol. In keeping with the strong metal σ bonds, Gd+ is also seen to readily react with formaldehyde to eliminate CO and form GdH2+

  2. Thermodynamic modeling of saturated liquid compositions and densities for asymmetric binary systems composed of carbon dioxide, alkanes and alkanols

    International Nuclear Information System (INIS)

    Highlights: • Phase behavior of the binary systems containing largely different components. • Equation of state modeling of binary polar and non-polar systems by utilizing different mixing rules. • Three different mixing rules (one-parameter, two-parameters and Wong–Sandler) coupled with Peng–Robinson equation of state. • Two-parameter mixing rule shows promoting results compared to one-parameter mixing rule. • Wong–Sandler mixing rule is unable to predict saturated liquid densities with sufficient accuracy. - Abstract: The present study mainly focuses on the phase behavior modeling of asymmetric binary mixtures. Capability of different mixing rules and volume shift in the prediction of solubility and saturated liquid density has been investigated. Different binary systems of (alkane + alkanol), (alkane + alkane), (carbon dioxide + alkanol), and (carbon dioxide + alkane) are considered. The composition and the density of saturated liquid phase at equilibrium condition are the properties of interest. Considering composition and saturated liquid density of different binary systems, three main objectives are investigated. First, three different mixing rules (one-parameter, two parameters and Wong–Sandler) coupled with Peng–Robinson equation of state were used to predict the equilibrium properties. The Wong–Sandler mixing rule was utilized with the non-random two-liquid (NRTL) model. Binary interaction coefficients and NRTL model parameters were optimized using the Levenberg–Marquardt algorithm. Second, to improve the density prediction, the volume translation technique was applied. Finally, Two different approaches were considered to tune the equation of state; regression of experimental equilibrium compositions and densities separately and spontaneously. The modeling results show that there is no superior mixing rule which can predict the equilibrium properties for different systems. Two-parameter and Wong–Sandler mixing rule show promoting

  3. An in vitro and in silico study on the flavonoid-mediated modulation of the transport of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) through Caco-2 monolayers

    International Nuclear Information System (INIS)

    The present study describes the effect of different flavonoids on the absorption of the pro-carcinogen PhIP through Caco-2 monolayers and the development of an in silico model describing this process taking into account passive diffusion and active transport of PhIP. Various flavonoids stimulated the apical to basolateral PhIP transport. Using the in silico model for flavone, kaempferol and chrysoeriol, the apparent Ki value for inhibition of the active transport to the apical side was estimated to be below 53 μM and for morin, robinetin and taxifolin between 164 and 268 μM. For myricetin, luteolin, naringenin and quercetin, the apparent Ki values were determined more accurately and amounted to 37.3, 12.2, 11.7 and 5.6 μM respectively. Additional experiments revealed that the apical to basolateral PhIP transport was also increased in the presence of a typical BCRP or MRP inhibitor with apparent Ki values in the same range as those of the flavonoids. This observation together with the fact that flavonoids are known to be inhibitors of MRPs and BCRP, corroborates that inhibition of these apical membrane transporters is involved in the flavonoid-mediated increased apical to basolateral PhIP transport. Based on the apparent Ki values obtained, it is concluded that the flavonols, at the levels present in the regular Western diet, are capable of stimulating the transport of PhIP through Caco-2 monolayers from the apical to the basolateral compartment. This points to flavonoid-mediated stimulation of the bioavailability of PhIP and, thus, a possible adverse effect of these supposed beneficial food ingredients

  4. Quaternary (liquid + liquid) equilibrium data for the extraction of toluene from alkanes using the ionic liquid [EMim][MSO4

    International Nuclear Information System (INIS)

    Highlights: • EMim[MSO4] was proposed as solvent for the extraction of toluene from alkanes. • The quaternary system {heptane + cyclohexane + toluene + [EMim][MSO4]} was evaluated. • The extraction of toluene would be facilitated in the presence of one alkane. • Experimental LLE data were successfully correlated with the NRTL model. - Abstract: (Liquid + liquid) equilibrium (LLE) studies for the extraction of aromatics from alkanes present in the petroleum fractions are important to develop theoretical/semiempirical (liquid + liquid) equilibrium models, which are used in the design of extraction processes. In this work, the ionic liquid 1-ethyl-3-methylimidazolium methylsulfate, [EMim][MSO4], was evaluated as potential solvent for the separation of toluene from heptane and cyclohexane. The LLE data for the quaternary system {heptane (1) + cyclohexane (2) + toluene (3) + [EMim][MSO4] (4)} were experimentally determined at T = 298.15 K and atmospheric pressure. Moreover, the LLE data for the ternary systems {heptane or cyclohexane (1) + toluene (2) + [EMim][MSO4] (3)} were also determined. Solute distribution ratios and selectivities were calculated and analysed in order to evaluate the capability of the ionic liquid to accomplish the separation target. A comparison between the solute distribution ratios and selectivities for the quaternary and the ternary systems was also made. Finally, the experimental tie-line data were correlated with the NRTL model

  5. The Tunable Hybrid Surface Phonon and Plasmon Polariton Modes in Boron Nitride Nanotube and Graphene Monolayer Heterostructures

    OpenAIRE

    SUN, Yu; Zheng, Zheng; Cheng, Jiangtao; Liu, Jiansheng

    2014-01-01

    The hybrid modes incorporating surface phonon polariton (SPhP) modes in boron nitride nanotubes (BNNTs) and surface plasmon polariton (SPP) modes in graphene monolayers are theoretically studied. The combination of the 1D BNNTs and 2D graphene monolayer further improves the modal characteristics with electrical tunability. Superior to the graphene monolayers, the proposed heterostructures supports single mode transmission with lateral optical confinement. The modal characteristics can be shif...

  6. Defect-Tolerant Monolayer Transition Metal Dichalcogenides

    DEFF Research Database (Denmark)

    Pandey, Mohnish; Rasmussen, Filip Anselm; Kuhar, Korina;

    2016-01-01

    -principles investigation of defect tolerance in 29 monolayer transition metal dichalcogenides (TMDs) of interest for nanoscale optoelectronics. We find that the TMDs based on group VI and X metals form deep gap states upon creation of a chalcogen (S, Se, Te) vacancy, while the TMDs based on group IV metals form only...... shallow defect levels and are thus predicted to be defect-tolerant. Interestingly, all the defect sensitive TMDs have valence and conduction bands with a very similar orbital composition. This indicates a bonding/antibonding nature of the gap, which in turn suggests that dangling bonds will fall inside...... the gap. These ideas are made quantitative by introducing a descriptor that measures the degree of similarity of the conduction and valence band manifolds. Finally, the study is generalized to nonpolar nanoribbons of the TMDs where we find that only the defect sensitive materials form edge states within...

  7. Switchable polarization in an unzipped graphene oxide monolayer.

    Science.gov (United States)

    Noor-A-Alam, Mohammad; Shin, Young-Han

    2016-08-14

    Ferroelectricity in low-dimensional oxide materials is generally suppressed at the scale of a few nanometers, and has attracted considerable attention from both fundamental and technological aspects. Graphene is one of the thinnest materials (one atom thick). Therefore, engineering switchable polarization in non-polar pristine graphene could potentially lead to two-dimensional (2D) ferroelectric materials. In the present study, based on density functional theory, we show that an unzipped graphene oxide (UGO) monolayer can exhibit switchable polarization due to its foldable bonds between the oxygen atom and two carbon atoms underneath the oxygen. We find that a free standing UGO monolayer exhibits antiferroelectric switchable polarization. A UGO monolayer can be obtained as an intermediate product during the chemical exfoliation process of graphene. Interestingly, despite its dimensionality, our estimated polarization in a UGO monolayer is comparable to that in bulk ferroelectric materials (e.g., ferroelectric polymers). Our calculations could help realize antiferroelectric switchable polarization in 2D materials, which could find various potential applications in nanoscale devices such as sensors, actuators, and capacitors with high energy-storage density. PMID:27401944

  8. Topography and instability of monolayers near domain boundaries

    International Nuclear Information System (INIS)

    We theoretically study the topography of a biphasic surfactant monolayer in the vicinity of domain boundaries. The differing elastic properties of the two phases generally lead to a nonflat topography of 'mesas,' where domains of one phase are elevated with respect to the other phase. The mesas are steep but low, having heights of up to 10 nm. As the monolayer is laterally compressed, the mesas develop overhangs and eventually become unstable at a surface tension of about K(δc0)2 (δc0 being the difference in spontaneous curvature and K a bending modulus). In addition, the boundary is found to undergo a topography-induced rippling instability upon compression, if its line tension is smaller than about Kδc0. The effect of diffuse boundaries on these features and the topographic behavior near a critical point are also examined. We discuss the relevance of our findings to several experimental observations related to surfactant monolayers: (i) small topographic features recently found near domain boundaries; (ii) folding behavior observed in mixed phospholipid monolayers and model lung surfactants; (iii) roughening of domain boundaries seen under lateral compression; (iv) the absence of biphasic structures in tensionless surfactant films

  9. Omeprazole decreases magnesium transport across Caco-2 monolayers

    Institute of Scientific and Technical Information of China (English)

    Narongrit Thongon; Nateetip Krishnamra

    2011-01-01

    AIM: To elucidate the effect and underlying mechanisms of omeprazole action on Mg2+ transport across the intestinal epithelium. METHODS: Caco-2 monolayers were cultured in various dose omeprazole-containing media for 14 or 21 d before being inserted into a modified Ussing chamber apparatus to investigate the bi-directional Mg2+ transport and electrical parameters. Paracellular permeability of the monolayer was also observed by the dilution potential technique and a cation permeability study. An Arrhenius plot was performed to elucidate the activation energy of passive Mg2+ transport across the Caco-2 monolayers. RESULTS: Both apical to basolateral and basolateral to apical passive Mg2+ fluxes of omeprazole-treated epithelium were decreased in a dose- and time-dependent manner. Omeprazole also decreased the paracellular cation selectivity and changed the paracellular selective permeability profile of Caco-2 epithelium to Li+, Na+, K+, Rb+, and Cs+ from series Ⅶ to series Ⅵ of the Eisenman sequence. The Arrhenius plot revealed the higher activation energy for passive Mg2+ transport in omeprazoletreated epithelium than that of control epithelium, indicating that omeprazole affected the paracellular channel of Caco-2 epithelium in such a way that Mg2+ movement was impeded. CONCLUSION: Omeprazole decreased paracellular cation permeability and increased the activation energy for passive Mg2+ transport of Caco-2 monolayers that led to the suppression of passive Mg2+ absorption.

  10. Surface plasmon resonance for detecting clenbuterol: Influence of monolayer structure

    Science.gov (United States)

    Suherman; Morita, Kinichi; Kawaguchi, Toshikazu

    2015-03-01

    Surface plasmon resonance sensor equipped with a fabricated immunosensor chip is used for detecting clenbuterol in this study. Since clenbuterol is a small analyte, indirect competitive inhibition immunoassay is employed. For fabricating the immunosurface, the Au-chip was functionalized by succinimidyl-terminated alkanethiol, and the terminal N-hydroxysuccinimide group of the self-assembled monolayer was either replaced with clenbuterol or blocked with ethanolamine. Scanning tunneling microscope experiments and electrochemical measurements depicted the domain structures of the succinimide group of succinimidyl-terminated propanethiol monolayer. The surface concentration and the orientation of succinimide group was significantly dependent on the concentration of dithiobis(succinimidyl) propionate (DSP) used in fabricating the monolayer. Furthermore, the structure of monolayer significantly influenced both the surface concentration and the orientation of clenbuterol on the sensor surface. Consequently, high coverage and standing-up configuration of clenbuterol showed high affinity for clenbuterol antibody. However, high affinity constant exhibited by the sensor surface was coupled with a low sensitivity. By contrast, lowest concentration of DSP solution (0.1 mM) used in fabricating the immunosurface showed a detection sensitivity of 3 ppt - the highest reported sensitivity for clenbuterol. For regeneration the immunosurface, 0.1 M NaOH was used and the same sensor surface could be reused for performing >100 rapid immunoreaction.

  11. Coulomb excitations of monolayer germanene

    CERN Document Server

    Shih, Po-Hsin; Wu, Jhao-Ying; Shyu, Feng-Lin; Lin, Ming-Fa

    2016-01-01

    The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbital coupling and the buckled structure. The collective and single- particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e-h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e-h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes.

  12. Solid-Liquid equilibrium of n-alkanes using the Chain Delta Lattice Parameter model

    DEFF Research Database (Denmark)

    Coutinho, João A.P.; Andersen, Simon Ivar; Stenby, Erling Halfdan

    1996-01-01

    -liquid equilibrium of n-alkanes ranging from n-C_20 to n-C_40.The model is further modified to achieve a more correct temperature dependence because it severely underestimates the excess enthalpy. It is shown that the ratio of excess enthalpy and entropy for n-alkane solid solutions, as happens for other solid...

  13. Multiple sources of alkanes in Quaternary oceanic sediment of Antarctica

    Science.gov (United States)

    Kvenvolden, K.A.; Rapp, J.B.; Golan-Bac, M.; Hostettler, F.D.

    1987-01-01

    Normal alkanes (n-C13n-C36), isoprenoid hydrocarbons (i-C15, i-C16, i-C18, i-C19, and i-C20) triterpanes (C27C32), and (C27C29) are present in low concentrations offshore Antarctica in near-surface, Quaternary sediment of the Wilkes Land continental margin and of the western Ross Sea. The distributions of these hydrocarbons are interpreted relative to possible sources and processes. The hydrocarbons appear to be mixtures of primary and recycled material from marine and terrigenous sources. The n-alkanes are most abundant and are characterized by two distinct populations, one of probable marine origin and the other likely from terrigenous, vascular plant sources. Because the continent of Antarctica today is devoid of higher plants, the plant-derived hydrocarbons in these offshore sediments probably came from wind-blown material and recycled Antarctic sediment that contains land-plant remains from an earlier period of time. Isoprenoid hydrocarbons are partially recycled and mainly of marine origin; the dominance of pristane over phytane suggests oxic paleoenvironmental conditions. Both modern and ancient triterpanes and steranes are present, and the distribution of these indicates a mixture of primary and recycled bacterial, algal, and possible higher-plant materials. Although the sampled sediments were deposited during the Quaternary, they apparently contain a significant component of hydrocarbons of pre-Quaternary age. ?? 1987.

  14. Direct hydrodeoxygenation of raw woody biomass into liquid alkanes

    Science.gov (United States)

    Xia, Qineng; Chen, Zongjia; Shao, Yi; Gong, Xueqing; Wang, Haifeng; Liu, Xiaohui; Parker, Stewart F.; Han, Xue; Yang, Sihai; Wang, Yanqin

    2016-01-01

    Being the only sustainable source of organic carbon, biomass is playing an ever-increasingly important role in our energy landscape. The conversion of renewable lignocellulosic biomass into liquid fuels is particularly attractive but extremely challenging due to the inertness and complexity of lignocellulose. Here we describe the direct hydrodeoxygenation of raw woods into liquid alkanes with mass yields up to 28.1 wt% over a multifunctional Pt/NbOPO4 catalyst in cyclohexane. The superior performance of this catalyst allows simultaneous conversion of cellulose, hemicellulose and, more significantly, lignin fractions in the wood sawdust into hexane, pentane and alkylcyclohexanes, respectively. Investigation on the molecular mechanism reveals that a synergistic effect between Pt, NbOx species and acidic sites promotes this highly efficient hydrodeoxygenation of bulk lignocellulose. No chemical pretreatment of the raw woody biomass or separation is required for this one-pot process, which opens a general and energy-efficient route for converting raw lignocellulose into valuable alkanes. PMID:27025898

  15. Measurement of n-alkanals and hydroxyalkenals in biological samples.

    Science.gov (United States)

    Holley, A E; Walker, M K; Cheeseman, K H; Slater, T F

    1993-09-01

    A modified method was developed to measure nM levels of a range of n-alkanals and hydroxyalkenals in biological samples such as blood plasma and tissue homogenates and also in Folch lipid extracts of these samples. Butylated hydroxytoluene (BHT) and desferrioxamine (Desferal) were added to samples to prevent artifactual peroxidation. Aldehydes were reacted with 1,3-cyclohexanedione (CHD), cleaned up by solid-phase extraction on a Sep-Pak C18 cartridge and the fluorescent decahydroacridine derivatives resolved by reverse-phase high-performance liquid chromatography (HPLC) with gradient elution. A wider range of aldehydes was detected in lipid extracts of plasma and liver homogenate compared to whole (unextracted) samples. Human plasma contained nM levels of acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal. 4-Hydroxynonenal (0.93 nmol/g) and alkanals with two to six carbons (up to 7.36 nmol/g) were detected in rat liver. Recovery of aldehydes added to whole plasma or to lipid extracts of plasma was dependent on carbon chain length, varying from 95% for acetaldehyde to 8% for decanal. Recovery from biological samples was significantly less than that of standards taken through the Sep-Pak clean-up procedure, suggesting that aldehydes can bind to plasma protein and lipid components. PMID:8406128

  16. Radiation induced oxidation of liquid alkanes as a polymer model

    International Nuclear Information System (INIS)

    Radiation induced oxidation of liquid n-hexadecane (n-C16H34) and squalane (C30H62) as a polymer model has been investigated by the measurements of the gas evolution and O2 uptake, and analyses of the oxidation products. Low O2 uptake, [G(-O2) ∼ 6.0] in liquid alkanes, indicates that the oxidation reaction does not exhibit chain kinetics, which is a big contrast to the process observed in solid, G(-O2) >> 10. H2 is the main gas product. More than 90% of the consumed O2 are converted into the oxidation products in liquid phase, mainly carboxylic acids, which is also a big contrast to the results of the radiolysis of liquid cyclohexane in the presence of O2 and thermal oxidation of hexadecane at elevated temperatures, where ketones and alcohols are major products at the initial stage. In the presence of aromatic additives, energy and charge transfer to the additives taking place despite the presence of O2 reduce the H2 evolution and the acid formation in parallel. Although hydroaromatic compounds act as an energy and charge scavenger, they are selectively oxidized through the donation of hydrogen in cyclic alkyl part attached to the phenyl ring, leading to large O2 uptake and corresponding ketone formation. From the comparison of the G-values of the O2 uptake, it was found that the oxidation reactions of liquid alkanes reflect well the oxidation of amorphous part in polymers. (author)

  17. Radiation-induced synthesis of branched liquid alkanes

    International Nuclear Information System (INIS)

    The irradiation of gaseous alkane mixtures under circulation conditions was used for the synthesis of liquid branched hydrocarbons. Aurora-9B accelerator was used for irradiation with 500 keV electrons at 80 mA electron beam current, current power up to 40 kW. It was found that the synthesized liquid product was a mixture of alkanes with the average molecular weight higher than the molecular weight of the parent gas by a factor of 3-4. The resulting liquids were characterized by boiling range from 35 to 200 deg C in atmospheric distillation. The average degree of molecular branching in the synthesized liquids was evaluated on the basis of their knock resistance. The octane ratings of liquid mixtures were above 95 (motor octane number) or 103 (research octane number). The fractional composition and detonation properties of the synthesized liquids suggested the prevalence of C5-C11 isomers with highly branched structures in these liquids. Depending on irradiation conditions, 2,3-dimethylbutane, 2-methylpentane, or 3-methylpentane was predominant among hexanes. As a rule, 2,2,3-trimethylbutane and 2,3-dimethylpentane prevailed among heptanes

  18. Direct hydrodeoxygenation of raw woody biomass into liquid alkanes.

    Science.gov (United States)

    Xia, Qineng; Chen, Zongjia; Shao, Yi; Gong, Xueqing; Wang, Haifeng; Liu, Xiaohui; Parker, Stewart F; Han, Xue; Yang, Sihai; Wang, Yanqin

    2016-01-01

    Being the only sustainable source of organic carbon, biomass is playing an ever-increasingly important role in our energy landscape. The conversion of renewable lignocellulosic biomass into liquid fuels is particularly attractive but extremely challenging due to the inertness and complexity of lignocellulose. Here we describe the direct hydrodeoxygenation of raw woods into liquid alkanes with mass yields up to 28.1 wt% over a multifunctional Pt/NbOPO4 catalyst in cyclohexane. The superior performance of this catalyst allows simultaneous conversion of cellulose, hemicellulose and, more significantly, lignin fractions in the wood sawdust into hexane, pentane and alkylcyclohexanes, respectively. Investigation on the molecular mechanism reveals that a synergistic effect between Pt, NbOx species and acidic sites promotes this highly efficient hydrodeoxygenation of bulk lignocellulose. No chemical pretreatment of the raw woody biomass or separation is required for this one-pot process, which opens a general and energy-efficient route for converting raw lignocellulose into valuable alkanes. PMID:27025898

  19. Broadband ultra-high transmission of terahertz radiation through monolayer MoS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Xue-Yong [Nanoscale Science and Technology Laboratory, Institute for Advanced Study, Nanchang University, Nanchang 330031 (China); Materials Science and Engineering, Nanchang University, Nanchang 330031 (China); Deng, Xin-Hua [Department of Physics, Nanchang University, Nanchang 330031 (China); Su, Fu-Hai [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Liu, Nian-Hua; Liu, Jiang-Tao, E-mail: jtliu@semi.ac.cn [Nanoscale Science and Technology Laboratory, Institute for Advanced Study, Nanchang University, Nanchang 330031 (China); Department of Physics, Nanchang University, Nanchang 330031 (China)

    2015-12-14

    In this study, the terahertz (THz) absorption and transmission of monolayer MoS{sub 2} with different carrier concentrations were investigated theoretically. The calculation shows that the THz absorption of monolayer MoS{sub 2} is very low even under high carrier concentrations and large incident angles. The sum of reflection and absorption losses of monolayer MoS{sub 2} is lower than that of graphene by one to three orders of magnitude. The transmission of monolayer MoS{sub 2} is higher than that of two-dimensional electron gases in traditional GaAs and InAs. The field-effect tube structure formed by monolayer MoS{sub 2}-insulation-layer-graphene is also studied. The THz absorption of graphene can reach saturation under low voltage by tuning the voltage between MoS{sub 2} and graphene layers in the structure. The maximum THz absorption of monolayer MoS{sub 2} is approximately 5%. Thus, monolayer MoS{sub 2} is a promising candidate for THz transparent electrodes.

  20. Geomicrobiological linkages between short-chain alkane consumption and sulfate reduction rates in seep sediments.

    Directory of Open Access Journals (Sweden)

    Arpita eBose

    2013-12-01

    Full Text Available Marine hydrocarbon seeps are ecosystems that are rich in methane, and, in some cases, short-chain (C2-C5 and longer alkanes. C2-C4 alkanes such as ethane, propane and butane can be significant components of seeping fluids. Some sulfate-reducing microbes oxidize short-chain alkanes anaerobically, and may play an important role in both the competition for sulfate and the local carbon budget. To better understand the anaerobic oxidation of short-chain n-alkanes coupled with sulfate-reduction, hydrocarbon-rich sediments from the Gulf of Mexico were amended with artificial, sulfate-replete seawater and one of four n-alkanes (C1-C4 then incubated under strict anaerobic conditions. Measured rates of alkane oxidation and sulfate reduction closely follow stoichiometric predictions that assume the complete oxidation of alkanes to CO2 (though other sinks for alkane carbon likely exist. Changes in the δ13C of all the alkanes in the reactors show enrichment over the course of the incubation, with the C3 and C4 incubations showing the greatest enrichment (4.4‰ and 4.5‰ respectively. The concurrent depletion in the δ13C of dissolved inorganic carbon (DIC implies a transfer of carbon from the alkane to the DIC pool (-3.5 and -6.7‰ for C3 and C4 incubations, respectively. Microbial community analyses reveal that certain members of the class Deltaproteobacteria are selectively enriched as the incubations degrade C1-C4 alkanes. Phylogenetic analyses indicate that distinct phylotypes are enriched in the ethane reactors, while phylotypes in the propane and butane reactors align with previously identified C3-C4 alkane-oxidizing sulfate-reducers. These data further constrain the potential influence of alkane oxidation on sulfate reduction rates in cold hydrocarbon-rich sediments, provide insight into their contribution to local carbon cycling, and illustrate the extent to which short-chain alkanes can serve as electron donors and govern microbial community

  1. Morphological transitions in polymer monolayers under compression.

    Science.gov (United States)

    Srivastava, S; Basu, J K; Sprung, M; Wang, J

    2009-05-01

    We present a systematic investigation of morphological transitions in poly vinylacetate Langmuir monolayers. On compression, the polymer monolayer is converted to a continuous membrane with a thickness of approximately 2-3 nm. Above a certain surface concentration the monolayer, on water, undergoes a morphological transition-buckling, leading to formation of striped patterns of period of lambda(b) approximately 160 nm, as determined from in situ grazing incidence small angle x-ray scattering measurements. The obtained value is much smaller than what has been typically observed for Langmuir monolayers on water or thin films on soft substrates. Using existing theories for buckling of fluidlike films on fluid substrates, we obtain very low values of bending rigidity and Young's modulus of the polymer monolayer compared to that observed earlier for lipid or polymeric monolayers. Since buckling in these monolayers occurs only above a certain surface concentration, we have looked at the possibility that the buckling in these films occurs due to changes in their mechanical properties under compression. Using the model of Huang and Suo of buckling of solidlike films on viscoelastic substrates, we find values of the mechanical properties, which are much closer to the bulk values but still significantly lower. Although the reduction could be along the lines of what has been observed earlier for ultrathin polymer film or surface layers of polymers, the possibility of micromechanical effects also determining the buckling in such polymer monolayers cannot be ruled out. We have provided possible explanation of the buckling of the poly vinylacetate monolayers in terms of the change in isothermal compression modulus with surface concentration. PMID:19425809

  2. Chain length dependent alkane/β-cyclodextrin nonamphiphilic supramolecular building blocks.

    Science.gov (United States)

    Zhou, Chengcheng; Huang, Jianbin; Yan, Yun

    2016-02-01

    In this work we report the chain length dependent behavior of the nonamphiphilic supramolecular building blocks based on the host-guest inclusion complexes of alkanes and β-cyclodextrins (β-CD). (1)H NMR, ESI-MS, and SAXS measurements verified that upon increasing the chain length of alkanes, the building blocks for vesicle formation changed from channel type 2alkane@2β-CD via channel type alkane@2β-CD to non-channel type 2alkane@2β-CD. FT-IR and TGA experiments indicated that hydrogen bonding is the extensive driving force for vesicle formation. It revealed that water molecules are involved in vesicle formation in the form of structural water. Upon changing the chain length, the average number of water molecules associated with per building block is about 16-21, depending on the chain length. PMID:26660592

  3. Proton and hydrogen transport through two-dimensional monolayers

    Science.gov (United States)

    Seel, Max; Pandey, Ravindra

    2016-06-01

    Diffusion of protons and hydrogen atoms in representative two-dimensional materials is investigated. Specifically, density functional calculations were performed on graphene, hexagonal boron nitride (h-BN), phosphorene, silicene, and molybdenum disulfide (MoS2) monolayers to study the surface interaction and penetration barriers for protons and hydrogen atoms employing finite cluster models. The calculated barrier heights correlate approximately with the size of the opening formed by the three-fold open sites in the monolayers considered. They range from 1.56 eV (proton) and 4.61 eV (H) for graphene to 0.12 eV (proton) and 0.20 eV (H) for silicene. The results indicate that only graphene and h-BN monolayers have the potential for membranes with high selective permeability. The MoS2 monolayer behaves differently: protons and H atoms become trapped between the outer S layers in the Mo plane in a well with a depth of 1.56 eV (proton) and 1.5 eV (H atom), possibly explaining why no proton transport was detected, suggesting MoS2 as a hydrogen storage material instead. For graphene and h-BN, off-center proton penetration reduces the barrier to 1.38 eV for graphene and 0.11 eV for h-BN. Furthermore, Pt acting as a substrate was found to have a negligible effect on the barrier height. In defective graphene, the smallest barrier for proton diffusion (1.05 eV) is found for an oxygen-terminated defect. Therefore, it seems more likely that thermal protons can penetrate a monolayer of h-BN but not graphene and defects are necessary to facilitate the proton transport in graphene.

  4. Essential-Oil Constituents and Alkanes of Cephalaria ambrosioides Roem. & Schult. (Family Caprifoliaceae, Subfamily Dipsacaceae) and (Chemo)taxonomic Discernment of the Subfamilies Dipsacaceae and Morinaceae.

    Science.gov (United States)

    Vukićević, Dušan R; Stevanović, Dragana D; Genčić, Marija S; Blagojević, Polina D; Radulović, Niko S

    2016-02-01

    Herein, the results of the first study of the volatile and alkane profiles of Cephalaria ambrosioides Roem. & Schult. (Caprifoliaceae, subfamily Dipsacaceae) were reported. The GC-FID and GC/MS analyses of the essential oils hydrodistilled from leaves and stems (CA1) and flowers (CA2) of C. ambrosioides allowed the identification of 284 different components. The main compounds of the studied oil samples were palmitic acid (24.3 and 32.5% for CA1 and CA2, resp.), hexahydrofarnesyl acetone (1.4 and 10.8% for CA1 and CA2, resp.), (Z)-hex-3-en-1-ol (7.0 and genus Cephalaria and its infrageneric relations, especially concerning the subfamily Morinaceae (formerly a genus within Dipsacaceae). The results of multivariate statistical analyses (25 different essential-oil samples) supported the exclusion of Morina species from the Dipsacaceae subfamily. The relative abundances of alkanes from n-, iso-, and anteiso-series followed a (distorted) Gaussian-like distribution and suggested that the biosyntheses of n- and branched alkanes in C. ambrosioides are possibly not controlled by the same elongase. Also, the obtained results suggested that there was a difference in the biosynthesis/accumulation of alkanes in the vegetative and reproductive parts of C. ambrosioides. PMID:26880432

  5. Genes involved in alkane degradation in the Alcanivorax hongdengensis strain A-11-3

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Wanpeng [State Oceanic Administration, Xiamen (China). Key Lab. of Marine Biogenetic Resources; Xiamen Univ. (China). School of Life Sciences; Shao, Zongze [State Oceanic Administration, Xiamen (China). Key Lab. of Marine Biogenetic Resources

    2012-04-15

    Alcanivorax hongdengensis A-11-3 is a newly identified type strain isolated from the surface water of the Malacca and Singapore Straits that can degrade a wide range of alkanes. To understand the degradation mechanism of this strain, the genes encoding alkane hydroxylases were obtained by PCR screening and shotgun sequencing of a genomic fosmid library. Six genes involved in alkane degradation were found, including alkB1, alkB2, p450-1, p450-2, p450-3 and almA. Heterogeneous expression analysis confirmed their functions as alkane oxidases in Pseudomonas putida GPo12 (pGEc47{delta}B) or Pseudomonas fluorescens KOB2{delta}1. Q-PCR revealed that the transcription of alkB1 and alkB2 was enhanced in the presence of n-alkanes C{sub 12} to C{sub 24}; three p450 genes were up-regulated by C{sub 8}-C{sub 16} n-alkanes at different levels, whereas enhanced expression of almA was observed when strain A-11-3 grew with long-chain alkanes (C{sub 24} to C{sub 36}). In the case of branched alkanes, pristane significantly enhanced the expression of alkB1, p450-3 and almA. The six genes enable strain A-11-3 to degrade short (C{sub 8}) to long (C{sub 36}) alkanes that are straight or branched. The ability of A. hongdengensis A-11-3 to thrive in oil-polluted marine environments may be due to this strain's multiple systems for alkane degradation and its range of substrates. (orig.)

  6. 40 CFR 721.10178 - Distillates (Fischer-Tropsch), hydroisomerized middle, C10-13-branched alkane fraction.

    Science.gov (United States)

    2010-07-01

    ...), hydroisomerized middle, C10-13-branched alkane fraction. 721.10178 Section 721.10178 Protection of Environment...), hydroisomerized middle, C10-13-branched alkane fraction. (a) Chemical substance and significant new uses subject... middle, C10-13-branched alkane fraction (PMN P-04-319; CAS No. 642928-30-1) is subject to reporting...

  7. High quality sub-monolayer, monolayer, and bilayer graphene on Ru(0001)

    International Nuclear Information System (INIS)

    High quality sub-monolayer, monolayer, and bilayer graphene were grown on Ru(0001). For the sub-monolayer graphene, the size of graphene islands with zigzag edges can be controlled by the dose of ethylene exposure. By increasing the dose of ethylene to 100 Langmuir at a high substrate temperature (800 °C), high quality single-crystalline monolayer graphene was synthesized on Ru(0001). High quality bilayer graphene was formed by further increasing the dose of ethylene while reducing the cooling rate to 5 °C/min. Raman spectroscopy revealed the vibrational states of graphene, G and 2D peaks appeared only in the bilayer graphene, which demonstrates that it behaves as the intrinsic graphene. Our present work affords methods to produce high quality sub-monolayer, monolayer, and bilayer graphene, both for basic research and applications. (rapid communication)

  8. Topological Phase Diagrams of Bulk and Monolayer TiS2−xTex

    KAUST Repository

    Zhu, Zhiyong

    2013-02-12

    With the use of ab initio calculations, the topological phase diagrams of bulk and monolayer TiS2−xTex are established. Whereas bulk TiS2−xTex shows two strong topological phases [1;(000)] and [1;(001)] for 0.44monolayer is topologically nontrivial for 0.48monolayer, TiS2−xTex is a unique system for studying topological phases in three and two dimensions simultaneously.

  9. Diversity and abundance of n-alkane degrading bacteria in the near surface soils of a Chinese onshore oil and gas field

    Directory of Open Access Journals (Sweden)

    K. Zhao

    2012-10-01

    Full Text Available Alkane degrading bacteria have long been used as an important biological indicator for oil and gas prospecting, but their ecological characteristics in hydrocarbon microseep habitats are still poorly understood. In this study, the diversity and abundance of n-alkane degrading bacterial community in the near surface soils of a Chinese onshore oil and gas field were investigated using molecular techniques. Terminal restriction fragment length polymorphism (T-RFLP analyses in combination with cloning and sequencing of alkB genes revealed that trace amount of volatile hydrocarbons migrated from oil and gas reservoirs caused a shift of the n-alkane degrading bacterial community from Gram-positive bacteria (Mycobacterium and Rhodococcus to Gram-negative genotypes (Alcanivorax and Acinetobacter. Real-time PCR results furthermore showed that the abundance of alkB genes increased substantially in the surface soils underlying oil and gas reservoirs even though only low or undetectable concentrations of hydrocarbons were measured in these soils due to efficient microbial degradation. Our findings broadened the knowledge on the ecological characteristics of alkane degrading community in hydrocarbon microseeps and may provide a new approach for microbial prospecting for oil and gas (MPOG.

  10. Diversity and abundance of n-alkane degrading bacteria in the near surface soils of a Chinese onshore oil and gas field

    Science.gov (United States)

    Xu, K.; Tang, Y.; Ren, C.; Zhao, K.; Sun, Y.

    2012-10-01

    Alkane degrading bacteria have long been used as an important biological indicator for oil and gas prospecting, but their ecological characteristics in hydrocarbon microseep habitats are still poorly understood. In this study, the diversity and abundance of n-alkane degrading bacterial community in the near surface soils of a Chinese onshore oil and gas field were investigated using molecular techniques. Terminal restriction fragment length polymorphism (T-RFLP) analyses in combination with cloning and sequencing of alkB genes revealed that trace amount of volatile hydrocarbons migrated from oil and gas reservoirs caused a shift of the n-alkane degrading bacterial community from Gram-positive bacteria (Mycobacterium and Rhodococcus) to Gram-negative genotypes (Alcanivorax and Acinetobacter). Real-time PCR results furthermore showed that the abundance of alkB genes increased substantially in the surface soils underlying oil and gas reservoirs even though only low or undetectable concentrations of hydrocarbons were measured in these soils due to efficient microbial degradation. Our findings broadened the knowledge on the ecological characteristics of alkane degrading community in hydrocarbon microseeps and may provide a new approach for microbial prospecting for oil and gas (MPOG).

  11. Heterointerface Screening Effects between Organic Monolayers and Monolayer Transition Metal Dichalcogenides.

    Science.gov (United States)

    Zheng, Yu Jie; Huang, Yu Li; Chen, Yifeng; Zhao, Weijie; Eda, Goki; Spataru, Catalin D; Zhang, Wenjing; Chang, Yung-Huang; Li, Lain-Jong; Chi, Dongzhi; Quek, Su Ying; Wee, Andrew Thye Shen

    2016-02-23

    The nature and extent of electronic screening at heterointerfaces and their consequences on energy level alignment are of profound importance in numerous applications, such as solar cells, electronics etc. The increasing availability of two-dimensional (2D) transition metal dichalcogenides (TMDs) brings additional opportunities for them to be used as interlayers in "van der Waals (vdW) heterostructures" and organic/inorganic flexible devices. These innovations raise the question of the extent to which the 2D TMDs participate actively in dielectric screening at the interface. Here we study perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) monolayers adsorbed on single-layer tungsten diselenide (WSe2), bare graphite, and Au(111) surfaces, revealing a strong dependence of the PTCDA HOMO-LUMO gap on the electronic screening effects from the substrate. The monolayer WSe2 interlayer provides substantial, but not complete, screening at the organic/inorganic interface. Our results lay a foundation for the exploitation of the complex interfacial properties of hybrid systems based on TMD materials. PMID:26792247

  12. Mediated Electron Transfer at Redox Active Monolayers. Part 4: Kinetics of Redox Enzymes Coupled With Electron Mediators

    Directory of Open Access Journals (Sweden)

    Michael E.G. Lyons

    2003-01-01

    Full Text Available A detailed kinetic analysis of the pertinent physical processes underlying the operation of enzyme electrodes immobilized within alkane thiol self assembled monolayers is developed. These electrodes utilize a soluble mediator, which partitions into the monolayer, regenerates the active catalytic form of the enzyme and is re-oxidized at the underlying support electrode surface giving rise to a current which reflects kinetic events at the enzyme surface. Both the enzyme/substrate and enzyme mediator kinetics have been quantified fully in terms of a ping-pong mechanism for the former and Michaelis-Menten kinetics for the latter. The effect of substrate and mediator diffusion in solution have also been specifically considered and the latter processes have been shown to result in a complex expression for the reaction flux. Four limiting kinetic cases have been enumerated and simple expressions for the reaction flux in each of these rate limiting situations have been developed. Kinetic case diagrams have been presented as an aid to mechanistic diagnosis. The complicating effects of diffusive loss of reduced mediator from the enzyme layer have also been examined and the relation between the observed flux corresponding to reduced mediator oxidation at the support electrode and the substrate reaction flux in the enzyme layer have been quantified in terms of an efficiency factor. Results extracted from recently published practical realizations of immobilized monolayer enzyme systems have been discussed in the context of the proposed model analysis.

  13. Large Friction Anisotropy of a Polydiacetylene Monolayer

    International Nuclear Information System (INIS)

    Friction force microscopy measurements of a polydiacetylene monolayer film reveal a 300% friction anisotropy that is correlated with the film structure. The film consists of a monolayer of the red form of N-(2-ethanol)- 10,12 pentacosadiynamide, prepared on a Langmuir trough and deposited on a mica substrate. As confirmed by atomic force microscopy and fluorescence microscopy, the monolayer consists of domains of linearly oriented conjugated backbones with pendant hydrocarbon side chains above and below the backbones. Maximum friction occurs when the sliding direction is perpendicular to the backbone. We propose that the backbones impose anisotropic packing of the hydrocarbon side chains which leads to the observed friction anisotropy. Friction anisotropy is therefore a sensitive, optically-independent indicator of polymer backbone direction and monolayer structural properties

  14. Accurate Molecular Dimensions from Stearic Acid Monolayers.

    Science.gov (United States)

    Lane, Charles A.; And Others

    1984-01-01

    Discusses modifications in the fatty acid monolayer experiment to reduce the inaccurate moleculary data students usually obtain. Copies of the experimental procedure used and a Pascal computer program to work up the data are available from the authors. (JN)

  15. Shock tube measurements of the rate constants for seven large alkanes+OH

    KAUST Repository

    Badra, Jihad

    2015-01-01

    Reaction rate constants for seven large alkanes + hydroxyl (OH) radicals were measured behind reflected shock waves using OH laser absorption. The alkanes, n-hexane, 2-methyl-pentane, 3-methyl-pentane, 2,2-dimethyl-butane, 2,3-dimethyl-butane, 2-methyl-heptane, and 4-methyl-heptane, were selected to investigate the rates of site-specific H-abstraction by OH at secondary and tertiary carbons. Hydroxyl radicals were monitored using narrow-line-width ring-dye laser absorption of the R1(5) transition of the OH spectrum near 306.7 nm. The high sensitivity of the diagnostic enabled the use of low reactant concentrations and pseudo-first-order kinetics. Rate constants were measured at temperatures ranging from 880 K to 1440 K and pressures near 1.5 atm. High-temperature measurements of the rate constants for OH + n-hexane and OH + 2,2-dimethyl-butane are in agreement with earlier studies, and the rate constants of the five other alkanes with OH, we believe, are the first direct measurements at combustion temperatures. Using these measurements and the site-specific H-abstraction measurements of Sivaramakrishnan and Michael (2009) [1,2], general expressions for three secondary and two tertiary abstraction rates were determined as follows (the subscripts indicate the number of carbon atoms bonded to the next-nearest-neighbor carbon): S20=1.58×10-11exp(-1550K/T)cm3molecule-1s-1(887-1327K)S30=2.37×10-11exp(-1850K/T)cm3molecule-1s-1(887-1327K)S21=4.5×10-12exp(-793.7K/T)cm3molecule-1s-1(833-1440K)T100=2.85×10-11exp(-1138.3K/T)cm3molecule-1s-1(878-1375K)T101=7.16×10-12exp(-993K/T)cm3molecule-1s-1(883-1362K) © 2014 The Combustion Institute.

  16. Exciton Binding Energy of Monolayer WS2

    OpenAIRE

    Bairen Zhu; Xi Chen; Xiaodong Cui

    2015-01-01

    The optical properties of monolayer transition metal dichalcogenides (TMDC) feature prominent excitonic natures. Here we report an experimental approach toward measuring the exciton binding energy of monolayer WS2 with linear differential transmission spectroscopy and two-photon photoluminescence excitation spectroscopy (TP-PLE). TP-PLE measurements show the exciton binding energy of 0.71eV around K valley in the Brillouin zone. The trion binding energy of 34meV, two-photon absorption cross s...

  17. Structure of cholesterol/ceramide monolayer mixtures

    DEFF Research Database (Denmark)

    Scheffer, L.; Solomonov, I.; Weygand, M.J.; Kjær, K.; Leiserowitz, L.; Addadi, L.

    2005-01-01

    The structure of monolayers of cholesterol/ ceramide mixtures was investigated using grazing incidence x-ray diffraction, immunofluorescence, and atomic force microscopy techniques. Grazing incidence x-ray diffraction measurements showed the existence of a crystalline mixed phase of the two...... was determined and modeled. Immunolabeling was performed with an antibody specific to the cholesterol monohydrate crystalline arrangement. The antibody recognizes crystalline cholesterol monolayers, but does not interact with crystalline ceramide. Immunofluorescence and atomic force microscopy data...

  18. Kinetics and mechanism of alkane hydroperoxidation with tert-butyl hydroperoxide catalysed by a vanadate anion.

    Science.gov (United States)

    Shul'pin, Georgiy B; Kozlov, Yuriy N

    2003-07-01

    tert-Butyl hydroperoxide oxidizes alkanes in acetonitrile at 60 degrees C if the soluble vanadium(v) salt, n-Bu4NVO3, is used as a catalyst. Alkyl hydroperoxides are formed as main products which decompose during the course of the reaction to produce the more stable corresponding alcohols and ketones. Turnover numbers (ie. numbers of moles of products per one mole of a catalyst) attained 250. The kinetics and selectivity of the reaction have been studied. The mechanism proposed involves the formation of a complex between the V(V) species and t-BuOOH (K5 was estimated to be 5 dm3 mol(-1)) followed by decomposition of this complex (k6 = 0.2 s(-1)). The generated V(IV) species reacts with another t-BuOOH molecule to produce an active t-BuO* radical which attacks the hydrocarbon. PMID:12945701

  19. A Quantitative Structure Property Relationship for Prediction of Flash Point of Alkanes Using Molecular Connectivity Indices

    Institute of Scientific and Technical Information of China (English)

    Morteza Atabati; Reza Emamalizadeh

    2013-01-01

    Many structure-property/activity studies use graph theoretical indices,which are based on the topological properties of a molecule viewed as a graph.Since topological indices can be derived directly from the molecular structure without any experimental effort,they provide a simple and straightforward method for property prediction.In this work the flash point of alkanes was modeled by a set of molecular connectivity indices (x),modified molecular connectivity indices (mx(1)h) and valance molecular connectivity indices (mxv),with mxv calculated using the hydrogen perturbation.A stepwise Multiple Linear Regression (MLR) method was used to select the best indices.The predicted flash points are in good agreement with the experimental data,with the average absolute deviation 4.3 K.

  20. Soil n-alkane δD and Branched GDGTs Distributions Track Elevation-induced Precipitation and Temperature Changes along the South Central Andes (Argentina)

    Science.gov (United States)

    Nieto-Moreno, V.; Rohrmann, A.; van der Meer, M.; S Sinninghe Damsté, J.; Sachse, D.; Tofelde, S.; Niedermeyer, E. M.; Strecker, M. R.; Mulch, A.

    2015-12-01

    Orogenic surface uplift and topographic evolution of tectonically active mountain belts exert a strong impact on climatic teleconnections and Earth surface processes, including changes in global atmospheric circulation patterns, erosion rates, distribution of biomes, and precipitation patterns. Hence, quantifying the driving processes shaping the evolution of topography in ancient and active orogens is required in order to disentangle the dynamic interactions and feedbacks among surface uplift, climate, erosion and sedimentation. The south central Andes of Argentina provide a particularly suitable setting to study the interplay between the tectonic and climatic evolution of an actively subduction orogen over short and long time-scales. We present δD values of soil-derived n-alkane and brGDGTs distributions to assess their suitability for paleoelevation reconstructions in the southern central Andes. We collected soil samples from two different environmental and hydrological gradients, across the hillslope (26-28°S) and along a river-valley (22-24°S) of two individual mountain ranges. δD n-alkane and brGDGTs distributions are both linearly related with elevation and may be used for paleoaltimetry studies along the windward flanks of the south central Andes. δD n-alkane and brGDGT-derived temperature lapse rates broadly follow regional lapse rates along steep orographic fronts. The observed lapse rates are lower than the annual mean values of satellite-derived temperatures but approach those of temperature loggers along each transect. Instead, δD n-alkane lapse rates are in line with regional stream-water data. These linear relationships along the windward slopes break down when entering the internally drained part of the Puna plateau. Our data document that δD n-alkane and brGDGTs distributions can be used over time scales relevant for paleoclimate/-altimetry reconstructions but also stress that such reconstructions require knowledge of the depositional

  1. Mass spectrometric analysis of monolayer protected nanoparticles

    Science.gov (United States)

    Zhu, Zhengjiang

    Monolayer protected nanoparticles (NPs) include an inorganic core and a monolayer of organic ligands. The wide variety of core materials and the tunable surface monolayers make NPs promising materials for numerous applications. Concerns related to unforeseen human health and environmental impacts of NPs have also been raised. In this thesis, new analytical methods based on mass spectrometry are developed to understand the fate, transport, and biodistributions of NPs in the complex biological systems. A laser desorption/ionization mass spectrometry (LDI-MS) method has been developed to characterize the monolayers on NP surface. LDI-MS allows multiple NPs taken up by cells to be measured and quantified in a multiplexed fashion. The correlations between surface properties of NPs and cellular uptake have also been explored. LDI-MS is further coupled with inductively coupled plasma mass spectrometry (ICP-MS) to quantitatively measure monolayer stability of gold NPs (AuNPs) and quantum dots (QDs), respectively, in live cells. This label-free approach allows correlating monolayer structure and particle size with NP stability in various cellular environments. Finally, uptake, distribution, accumulation, and excretion of NPs in higher order organisms, such as fish and plants, have been investigated to understand the environmental impact of nanomaterials. The results indicate that surface chemistry is a primary determinant. NPs with hydrophilic surfaces are substantially less toxic and present a lower degree of bioaccumulation, making these nanomaterials attractive for sustainable nanotechnology.

  2. Modeling of Alkane Oxidation Using Constituents and Species

    Science.gov (United States)

    Bellan, Jasette; Harstad, Kenneth G.

    2010-01-01

    It is currently not possible to perform simulations of turbulent reactive flows due in particular to complex chemistry, which may contain thousands of reactions and hundreds of species. This complex chemistry results in additional differential equations, making the numerical solution of the equation set computationally prohibitive. Reducing the chemical kinetics mathematical description is one of several important goals in turbulent reactive flow modeling. A chemical kinetics reduction model is proposed for alkane oxidation in air that is based on a parallel methodology to that used in turbulence modeling in the context of the Large Eddy Simulation. The objective of kinetic modeling is to predict the heat release and temperature evolution. This kinetic mechanism is valid over a pressure range from atmospheric to 60 bar, temperatures from 600 K to 2,500 K, and equivalence ratios from 0.125 to 8. This range encompasses diesel, HCCI, and gas-turbine engines, including cold ignition. A computationally efficient kinetic reduction has been proposed for alkanes that has been illustrated for n-heptane using the LLNL heptane mechanism. This model is consistent with turbulence modeling in that scales were first categorized into either those modeled or those computed as progress variables. Species were identified as being either light or heavy. The heavy species were decomposed into defined 13 constituents, and their total molar density was shown to evolve in a quasi-steady manner. The light species behave either in a quasi-steady or unsteady manner. The modeled scales are the total constituent molar density, Nc, and the molar density of the quasi-steady light species. The progress variables are the total constituent molar density rate evolution and the molar densities of the unsteady light species. The unsteady equations for the light species contain contributions of the type gain/loss rates from the heavy species that are modeled consistent with the developed mathematical

  3. Insect attachment on crystalline bioinspired wax surfaces formed by alkanes of varying chain lengths

    Directory of Open Access Journals (Sweden)

    Elena Gorb

    2014-07-01

    Full Text Available The impeding effect of plant surfaces covered with three-dimensional wax on attachment and locomotion of insects has been shown previously in numerous experimental studies. The aim of this study was to examine the effect of different parameters of crystalline wax coverage on insect attachment. We performed traction experiments with the beetle Coccinella septempunctata and pull-off force measurements with artificial adhesive systems (tacky polydimethylsiloxane semi-spheres on bioinspired wax surfaces formed by four alkanes of varying chain lengths (C36H74, C40H82, C44H90, and C50H102. All these highly hydrophobic coatings were composed of crystals having similar morphologies but differing in size and distribution/density, and exhibited different surface roughness. The crystal size (length and thickness decreased with an increase of the chain length of the alkanes that formed these surfaces, whereas the density of the wax coverage, as well as the surface roughness, showed an opposite relationship. Traction tests demonstrated a significant, up to 30 fold, reduction of insect attachment forces on the wax surfaces when compared with the reference glass sample. Attachment of the beetles to the wax substrates probably relied solely on the performance of adhesive pads. We found no influence of the wax coatings on the subsequent attachment ability of beetles. The obtained data are explained by the reduction of the real contact between the setal tips of the insect adhesive pads and the wax surfaces due to the micro- and nanoscopic roughness introduced by wax crystals. Experiments with polydimethylsiloxane semi-spheres showed much higher forces on wax samples when compared to insect attachment forces measured on these surfaces. We explain these results by the differences in material properties between polydimethylsiloxane probes and tenent setae of C. septempunctata beetles. Among wax surfaces, force experiments showed stronger insect attachment and higher

  4. Involvement of an Alkane Hydroxylase System of Gordonia sp. Strain SoCg in Degradation of Solid n-Alkanes▿

    OpenAIRE

    Lo Piccolo, Luca; De Pasquale, Claudio; Fodale, Roberta; Puglia, Anna Maria; Quatrini, Paola

    2010-01-01

    Enzymes involved in oxidation of long-chain n-alkanes are still not well known, especially those in Gram-positive bacteria. This work describes the alkane degradation system of the n-alkane degrader actinobacterium Gordonia sp. strain SoCg, which is able to grow on n-alkanes from dodecane (C12) to hexatriacontane (C36) as the sole C source. SoCg harbors in its chromosome a single alk locus carrying six open reading frames (ORFs), which shows 78 to 79% identity with the alkane hydroxylase (AH)...

  5. Isolation and characterization of a novel n-alkane-degrading strain, Acinetobacter haemolyticus AR-46

    Energy Technology Data Exchange (ETDEWEB)

    Bihari, Z.; Balazs, M.; Bartos, P.; Kesserue, P.; Kiss, I.; Mecs, I. [Bay Zoltan Foundation for Applied Research, Szeged (Hungary). Inst. for Biotechnology; Pettko-Szandtner, A. [Hungarian Academy of Sciences, Szeged (Hungary). Inst. of Plant Biology; Csanadi, G. [Szeged Univ. (Hungary). Dept. of Biotechnology

    2007-03-15

    Strain AR-46, isolated and identified as Acinetobacter haemolyticus, evolutionally distant from the known hydrocarbon-degrading Acinetobacter spp., proved to have excellent long-chain n-alkane-degrading ability. This is the first detailed report on an n-alkane-utilizing strain belonging to this species. The preferred substrate is n-hexadecane, with an optimal temperature of 37 C under aerobic conditions. Five complete and two partial open reading frames were sequenced and correlated with the early steps of monoterminal oxidation-initiated n-alkane mineralization. The encoded protein sequences and the arrangement of these genes displayed high similarity to those found in Acinetobacter sp. M-1, but AR-46 seemed to have only one alkane hydroxylase gene, with a completely different induction profile. Unique behaviour was also observed in n-alkane bioavailability. Substrate uptake occurred through the hydrophobic surface of n-alkane droplet-adhered cells possessing long, thick fimbriae, which were presumed to play a major role in n-alkane solubilization. A majority of the cells was in detached form, with thick, but short fimbriae. These free cells were permanently hydrophilic, unlike the cells of other Acinetobacter strains. (orig.)

  6. ELECTROCATALYSIS ON SURFACES MODIFIED BY METAL MONOLAYERS DEPOSITED AT UNDERPOTENTIALS.

    Energy Technology Data Exchange (ETDEWEB)

    ADZIC,R.

    2000-12-01

    The remarkable catalytic properties of electrode surfaces modified by monolayer amounts of metal adatoms obtained by underpotential deposition (UPD) have been the subject of a large number of studies during the last couple of decades. This interest stems from the possibility of implementing strictly surface modifications of electrocatalysts in an elegant, well-controlled way, and these bi-metallic surfaces can serve as models for the design of new catalysts. In addition, some of these systems may have potential for practical applications. The UPD of metals, which in general involves the deposition of up to a monolayer of metal on a foreign substrate at potentials positive to the reversible thermodynamic potential, facilitates this type of surface modification, which can be performed repeatedly by potential control. Recent studies of these surfaces and their catalytic properties by new in situ surface structure sensitive techniques have greatly improved the understanding of these systems.

  7. Combined atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and quartz crystal microbalance (QCM) studies of glucose oxidase (GOx) immobilised onto self-assembled monolayer on the gold film

    International Nuclear Information System (INIS)

    In fabrication of biosensors, self-assembled monolayers (SAM) are an attractive method of immobilising enzymes at electrode surface since it allows precise control over the amount and spatial distribution of the immobilized enzyme. The covalent attachment of glucose oxidase (GOx) to a carboxylic terminated SAM chemisorbed onto gold films was achieved via carbodiimide activation of the carboxylic acids to a reactive intermediate susceptible to nucleophilic attack by amines on free lysine chains of the enzyme. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and quartz crystal microbalance (QCM) measurements were used for characterisation of GOx modified gold surfaces. Tapping mode AFM studies have revealed that GOx molecules form slightly disordered arrays of pentagonal or hexagonal clusters. Observed features of immobilised GOx are distributed as a submonolayer on the SAM surface which has allowed visualisation of native and unfolded enzyme structure. The presence of the SAM and enzyme on the gold surface was detected by XPS spectroscopy. Spectra show typical peaks for the C 1s, O 1s and N 1s regions. A kinetic study of the adsorption of GOx onto activated SAM using in-situ QCM allowed determination the amount of immobilised GOx on the layer and consequently the optimal immobilisation conditions. Performance parameters of the biosensor such as sensitivity to glucose concentration as a function of enzyme loading were evaluated amperometrically using the redox mediator p-benzoquinone

  8. Alkane, terpene and polycyclic aromatic hydrocarbon geochemistry of the Mackenzie River and Mackenzie shelf: Riverine contributions to Beaufort Sea coastal sediment

    Science.gov (United States)

    Yunker, Mark B.; Macdonald, Robie W.; Cretney, Walter J.; Fowler, Brian R.; McLaughlin, Fiona A.

    1993-07-01

    To study the largest source of river sediment to the Arctic Ocean, we have collected suspended particulates from the Mackenzie River in all seasons and sediments from the Mackenzie shelf between the river mouth and the shelf edge. These samples have been analyzed for alkanes, triterpenes and polycyclic aromatic hydrocarbons (PAHs). We found that naturally occurring hydrocarbons predominate in the river and on the shelf. These hydrocarbons include biogenic alkanes and triterpenes with a higher plant/peat origin, diagenetic PAHs from peat and plant detritus, petrogenic alkanes, triterpenes and PAHs from oil seeps and/or bitumens and combustion PAHs that are likely relict in peat deposits. Because these components vary independently, the season is found to strongly influence the concentration and composition of hydrocarbons in the Mackenzie River. While essentially the same pattern of alkanes, diagenetic hopanes and alkyl PAHs is observed in all river and most shelf sediment samples, alkane and triterpene concentration variations are strongly linked to the relative amount of higher plant/peat material. Polycyclic aromatic hydrocarbon molecular-mass profiles also appear to be tied primarily to varying proportions of peat, with an additional petrogenic component which is most likely associated with lithic material mobilized by the Mackenzie River at freshet. Consistent with the general lack of alkyl PAHs in peat, the higher PAHs found in the river are probably derived from forest and tundra fires. A few anthropogenic/pyrogenic compounds are manifest only at the shelf edge, probably due to a weakening of the river influence. We take this observation of pyrogenic PAHs and the pronounced source differences between two sediment samples collected at the shelf edge as evidence of a transition from dominance by the Mackenzie River to the geochemistry prevalent in Arctic regions far removed from major rivers.

  9. Comparison of bulk and compound-specific δ 13C analyses and determination of carbon sources to salt marsh sediments using n-alkane distributions (Maine, USA)

    Science.gov (United States)

    Tanner, Benjamin R.; Uhle, Maria E.; Mora, Claudia I.; Kelley, Joseph T.; Schuneman, Patrick J.; Lane, Chad S.; Allen, Evan S.

    2010-01-01

    Sources of sedimentary organic matter to a Morse River, Maine (USA) salt marsh over the last 3390 ± 60 RCYBP (Radiocarbon Years Before Present) are determined using distribution patterns of n-alkanes, bulk carbon isotopic analysis, and compound-specific carbon isotopic analysis. Marsh foraminiferal counts suggest a ubiquitous presence of high marsh and higher-high marsh deposits (dominated by Trochammina macrescens forma macrescens, Trochammina comprimata, and Trochammina inflata), implying deposition from ˜0.2 m to 0.5 m above mean high water. Distributions of n-alkanes show a primary contribution from higher plants, confirmed by an average chain length value of 27.5 for the core sediments, and carbon preference index values all >3. Many sample depths are dominated by the C 25 alkane. Salicornia depressa and Ruppia maritima have similar n-alkane distributions to many of the salt marsh sediments, and we suggest that one or both of these plants is either an important source to the biomass of the marsh through time, or that another unidentified higher plant source is contributing heavily to the sediment pool. Bacterial degradation or algal inputs to the marsh sediments appear to be minor. Compound-specific carbon isotopic analyses of the C 27 alkane are on average 7.2‰ depleted relative to bulk values, but the two records are strongly correlated ( R2 = 0.89), suggesting that marsh plants dominate the bulk carbon isotopic signal. Our study underscores the importance of using caution when applying mixing models of plant species to salt marsh sediments, especially when relatively few plants are included in the model.

  10. Compound-specific hydrogen isotope composition of n-alkanes in combustion residuals of fossil fuels

    Science.gov (United States)

    Bai, Huiling; Peng, Lin; Li, Zhongping; Liu, Xiaofeng; Song, Chongfang; Mu, Ling

    2014-11-01

    The hydrogen isotope compositions (δD) of n-alkanes present in the combustion residuals of fossil fuels (coal, gasoline, and diesel) were measured using GC-IRMS to distinguish between coal soot and vehicle exhaust. The n-alkane δD values of industrial and domestic coal soot ranged from -95.3‰ to -219.6‰ and -128.1‰ to -188.6‰, respectively, exhibiting similar tendencies. The δD values of the C15-C18n-alkanes in both types of coal soot were nearly consistent, and the δD values of the C19-C24n-alkanes exhibited a zigzag profile. The δD values of C16-C22n-alkanes in gasoline exhaust exhibited a saw-tooth distribution, decreased with the carbon number, and were more positive than the δD values of C16-C22n-alkanes in diesel exhaust, which increased with the carbon number. However, the δD values of the C23-C29n-alkanes in gasoline and diesel vehicle exhaust were mostly consistent. The weighted average δD values of the C16-C19n-alkanes in industrial and domestic coal soot were similar to the average δD values in gasoline and diesel vehicle exhausts; however, the average δD values of the C21-C29n-alkanes in vehicle exhausts were richer in D than those in coal soot.

  11. Fluorescently labeled pulmonary surfactant protein C in spread phospholipid monolayers.

    OpenAIRE

    Nag, K.; Perez-Gil, J.; Cruz, A; Keough, K M

    1996-01-01

    Pulmonary surfactant, a lipid-protein complex, secreted into the fluid lining of lungs prevents alveolar collapse at low lung volumes. Pulmonary surfactant protein C (SP-C), an acylated, hydrophobic, alpha-helical peptide, enhances the surface activity of pulmonary surfactant lipids. Fluorescein-labeled SP-C (F-SP-C) (3, 6, 12 wt%) in dipalmitoylphosphatidylcholine (DPPC), and DPPC:dipalmitoylphosphatidylglycerol (DPPG) [DPPC:DPPG 7:3 mol/mol] in spread monolayers was studied by epifluorescen...

  12. Performance Analysis of Strained Monolayer MoS$_{2}$ MOSFET

    OpenAIRE

    Sengupta, Amretashis; Ghosh, Ram Krishna; Mahapatra, Santanu

    2013-01-01

    We present a computational study on the impact of tensile/compressive uniaxial ($\\varepsilon_{xx}$) and biaxial ($\\varepsilon_{xx}=\\varepsilon_{yy}$) strain on monolayer MoS$_{2}$ NMOS and PMOS FETs. The material properties like band structure, carrier effective mass and the multi-band Hamiltonian of the channel, are evaluated using the Density Functional Theory (DFT). Using these parameters, self-consistent Poisson-Schr\\"{o}dinger solution under the Non-Equilibrium Green's Function (NEGF) fo...

  13. Self-assembled monolayers of alkylsiloxanes on SrTiO3 substrates

    OpenAIRE

    Kropman, Boike L.; Blank, Dave H. A.; Rogalla, Horst

    1997-01-01

    The formation and structure of alkyltrichlorosilanes on several types of SrTiO3 substrates have been studied. The silanes adsorb spontaneously from a hexadecane solution and form monolayers on all the substrates used. Characterization has been performed by atomic force microscopy, wettability, angle resolved X-ray photoelectron spectroscopy, reflection absorption infrared spectroscopy, and spectroscopic ellipsometry. It was found that highly ordered and densely packed monolayers were formed b...

  14. Effect of cimetidine and ranitidine on drug induced damage to gastric epithelial cell monolayers in vitro.

    OpenAIRE

    Romano, M.; Razandi, M; Ivey, K J

    1989-01-01

    The effect of the H2 blockers cimetidine and ranitidine on drug induced damage to gastric cell monolayers has been evaluated in conditions independent of systemic factors and their anti-acid properties. Monolayers of mucous cells from a human cell line MKN 28, obtained from a human gastric adenocarcinoma, have been studied. Cell damage has been assessed qualitatively by trypan blue dye exclusion test and quantitatively by 51Cr release assay. Cimetidine and ranitidine significantly protected c...

  15. Effect of Impurity Concentration on the Depth Profile of the Electric Field within Monolayer Thin Film

    Directory of Open Access Journals (Sweden)

    N.F. Habubi

    2012-06-01

    Full Text Available The effect of impurity concentration ratios on the depth profile of electric field within monolayer film is presented. SnO2 monolayer thin film material was prepared and doped with Co using spray chemical pyrolysis. The concentration ratios of impurity were 1 %, 3 %, 5 % and 7 %. The analysis utilizes matrix formulas based on Abele's formulas from the calculation of reflectance and transmittance. Present study gives an information to contamination sensitivity in optical coating issue.

  16. Quantum chemical study of hydroxylation of alkanes by hypofluorous acid

    Czech Academy of Sciences Publication Activity Database

    Ončák, Milan; Srnec, Martin; Zahradník, Rudolf

    2008-01-01

    Roč. 82, č. 4 (2008), s. 649-659. ISSN 0137-5083 Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z40550506 Keywords : electronic structure * nonheme iron * basis-set Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 0.518, year: 2008

  17. Investigation on degradation of long chain n-alkanes through single cell green algae

    Energy Technology Data Exchange (ETDEWEB)

    Schroeder, E.

    1980-01-01

    30 green algae stems of the chlorococcales order and one of the volvocales were investigated for their ability to oxidize alkanes and their degradation. It could be concluded from the results that chlorella vulgaris can oxidize alkanes by subterminal ways during photosynthesis or if glucose is available, i.e. that it only attackes in cooxidation and c. vulgaris alkanes apparently do not terminally (mono or diterminally) oxidize as oxidation products as no oxidation products of this type of degradation nor any indications in the fatty acid pattern of lipids was found.

  18. Adsorption of CF4 on graphite preplated with a monolayer of CF3Cl

    Science.gov (United States)

    Thomas, Petros; Velazquez, Daniel; Hess, George B.

    2011-03-01

    We report a study of the adsorption of CF4 on graphite preplated with a monolayer of CF3Cl, using infrared reflection absorption spectroscopy combined with ellipsometry. The saturated vapor pressure of CF3Cl is nearly 3 orders of magnitude smaller than that of CF4 at the same temperature, so the main control variables are the temperature and the pressure (or chemical potential) of CF4, together with the initial coverage of CF3Cl. The temperature range covered is 60-105 K. We find that, if the initial monolayer of CF3Cl is liquid, CF4 continuously displaces CF3Cl by substitution in the monolayer. If the initial monolayer of CF3Cl is solid, due to either lower temperature or compression, CF4 condenses as a second layer on the top of the CF3Cl layer, with only slight mixing with the original layer. This behavior persists to multiple layers of CF4.

  19. Assembly of oriented zeolite monolayers and thin films on polymeric surfaces via hydrogen bonding.

    Science.gov (United States)

    Zhou, Ming; Liu, Xiufeng; Zhang, Baoquan; Zhu, Huiming

    2008-10-21

    The b-oriented monolayers of microsized silicalite-1 crystals have been manually assembled on glass plate supported poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), chitosan, and poly(methyl methacrylate) (PMMA) thin films via hydrogen bonding with much enhanced binding strength and satisfactory degrees of coverage and close packing. The exerted pressure and rubbing time in the manual assembly do not affect the binding strength of the silicalite-1 monolayer on the glass plate supported polymeric film. This manual assembly has been further applied to fabricate zeolite monolayers on commercially available Plexiglas surfaces and b-oriented multilayered films of silicalite-1 crystals on glass plates. The assembly method established in this study provides a feasible way to produce zeolite monolayers on polymer-modified solid substrates and Plexiglas and to fabricate zeolite-polymer composite membranes by means of the layer-by-layer technique. PMID:18785711

  20. Effect of mycolic acid on surface activity of binary surfactant lipid monolayers.

    Science.gov (United States)

    Chimote, G; Banerjee, R

    2008-12-15

    In pulmonary tuberculosis, Mycobacterium tuberculosis lies in close physical proximity to alveolar surfactant. Cell walls of the mycobacteria contain loosely bound, detachable surface-active lipids. In this study, the effect of mycolic acid (MA), the most abundant mycobacterial cell wall lipid, on the surface activity of phospholipid mixtures from lung surfactant was investigated using Langmuir monolayers and atomic force microscopy (AFM). In the presence of mycolic acid, all the surfactant lipid mixtures attained high minimum surface tensions (between 20 and 40 mN/m) and decreased surface compressibility moduli acid. Mycolic acids could aggregate within surfactant lipid monolayers and result in disturbed monolayer surface activity. The extent of the effect of mycolic acid depended on the initial state of the monolayer, with fluid films of DPPC-POPC and DPPC-CHOL being least affected. The results imply inhibitory effects of mycolic acid toward lung surfactant lipids and could be a mechanism of lung surfactant dysfunction in pulmonary tuberculosis. PMID:18848703

  1. Platinum monolayer electrocatalysts for oxygen reduction: effect of substrates, and long-term stability

    Directory of Open Access Journals (Sweden)

    J. ZHANG

    2005-03-01

    Full Text Available We describe a novel concept for a Ptmonolayer electrocatalyst and present the results of our electrochemical, X-ray absorption spectroscopy, and scanning tunneling microscopy studies. The electrocatalysts were prepared by a new method for depositing Pt monolayers involving the galvanic displacement by Pt of an underpotentially deposited Cu monolayer on substrates of Au (111, Ir(111, Pd(111, Rh(111 and Ru(0001 single crylstals, and Pd nanoparticles. The kinetics of O2 reduction showed significant enhancement with Pt monolayers on Pd(111 and Pd nanoparticle surfaces in comparisonwith the reaction on Pt(111 and Pt nanoparticles, respectively. This increase in catalytic activity is attributed partly to the decreased formation of PtOH, as shown by in situ X-ray absorption spectroscopy. The results illustrate that placing a Pt monolayer on a suitable substrate of metal nanoparticles is an attractive way of designing better O2 reduction electrocatalysts with very low Pt contents.

  2. Defect passivation induced strong photoluminescence enhancement of rhombic monolayer MoS2.

    Science.gov (United States)

    Su, Weitao; Jin, Long; Qu, Xiaodan; Huo, Dexuan; Yang, Li

    2016-05-18

    Growing high quality monolayer MoS2 with strong photoluminescence (PL) is essential to produce light-emitting devices on the atomic scale. In this study we show that rhombic monolayer MoS2 with PL intensity 8 times stronger than those of chemical vapour deposition (CVD)-grown triangular and mechanically exfoliated (ME) monolayer MoS2 can be prepared by using CVD. Both Raman and PL measurements indicate low density of defects in rhombic monolayer MoS2 with enhanced PL intensity. Density functional theory (DFT) calculations show that passivation of defects in MoS2 removes trapping gap states, which may finally result in PL enhancement. PMID:27152375

  3. Structures and thermal properties of the N2 monolayer on Pb(1 1 1)

    International Nuclear Information System (INIS)

    The physisorption of N2 molecules has long been a model system of molecular adsorption. We present a low-energy electron diffraction (LEED) study of the adsorption structures and thermodynamics of monolayer N2 on Pb(1 1 1). The results indicate that the monolayer structure has a triangular incommensurate center-of-mass lattice, and that the N2-substrate interaction is weaker than that observed on other metal surfaces. The N2 monolayer undergoes a phase transition between an orientationally ordered phase (low-temperature) and an orientationally disordered phase at a temperature of 20 K. Potential energy and quasiharmonic calculations indicate that the weak N2-Pb(1 1 1) interaction is the main contributing factor for the difference in orientational order of incommensurate N2 monolayers on Pb(1 1 1) and other similar metal surfaces. (paper)

  4. Raman analysis of first monolayers of PTCDA on Ag(111)

    International Nuclear Information System (INIS)

    We present a Raman spectroscopic analysis of the bonding properties of organic molecules on Ag(111) surfaces as a model system for organic semiconductor/metal contacts. The planar molecule 3,4,9,10-perylene-tetracarboxylicacid-dianhydride (PTCDA) is used in the present study due to its high electronic mobility and thermal stability. Vibrational signatures of the first monolayer in direct contact with the metal, especially the modes at 1310 and 1575 cm-1, are found to be shifted to lower frequencies. First principles calculations result in corresponding mode patterns, which are essentially located in the centre of the molecule thus indicating the area, where major metal interaction takes place. Furthermore, upon annealing at 450 K the vibrational frequencies of the second monolayer are modified with respect to bulk PTCDA, which reflect particular changes of the bonding situation of this layer. For subsequent layers bulk-like behaviour is observed

  5. Electronic structure of graphene oxide and reduced graphene oxide monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Sutar, D. S. [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Central Surface Analytical Facility, Indian Institute of Technology Bombay, Mumbai 400076 (India); Singh, Gulbagh; Divakar Botcha, V. [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India)

    2012-09-03

    Graphene oxide (GO) monolayers obtained by Langmuir Blodgett route and suitably treated to obtain reduced graphene oxide (RGO) monolayers were studied by photoelectron spectroscopy. Upon reduction of GO to form RGO C1s x-ray photoelectron spectra showed increase in graphitic carbon content, while ultraviolet photoelectron spectra showed increase in intensity corresponding to C2p-{pi} electrons ({approx}3.5 eV). X-ray excited Auger transitions C(KVV) and plasmon energy loss of C1s photoelectrons have been analyzed to elucidate the valence band structure. The effective number of ({pi}+{sigma}) electrons as obtained from energy loss spectra was found to increase by {approx}28% on reduction of GO.

  6. Monolayer expansion induces an oxidative metabolism and ROS in chondrocytes

    International Nuclear Information System (INIS)

    This study tests the hypothesis that articular chondrocytes shift from a characteristically glycolytic to an oxidative energy metabolism during population expansion in monolayer. Bovine articular chondrocytes were cultured in monolayer under standard incubator conditions for up to 14 days. Cellular proliferation, oxygen consumption, lactate production, protein content, ROS generation and mitochondrial morphology were examined. Lactate release increased ∼5-fold within 1 week, but this was limited to ∼2-fold increase when normalized to cellular protein content. By contrast, per cell oxidative phosphorylation increased 98-fold in 1 week. The increase in oxidative phosphorylation was evident within 24 h, preceding cell proliferation and was associated with augmented reactive oxygen species generation. The autologous chondrocyte implantation procedure requires 14-21 days for population expansion. The alterations in metabolic phenotype we report within 7 days in vitro are thus pertinent to autologous chondrocyte implantation with significant implications for the chondrocyte functionality

  7. Microscopic dynamics of nanoparticle monolayers at air-water interface.

    Science.gov (United States)

    Bhattacharya, R; Basu, J K

    2013-04-15

    We present results of surface mechanical and particle tracking measurements of nanoparticles trapped at the air-water interface as a function of their areal density. We monitor both the surface pressure (Π) and isothermal compression modulus (ϵ) as well as the dynamics of nanoparticle clusters, using fluorescence confocal microscopy while they are compressed to very high density near the two dimensional close packing density Φ∼0.82. We observe non-monotonic variation in both ϵ and the dynamic heterogeneity, characterized by the dynamical susceptibility χ4 with Φ, in such high density monolayers. We provide insight into the underlying nature of such transitions in close packed high density nanoparticle monolayers in terms of the morphology and flexibility of these soft colloidal particles. We discuss the significance our results in the context of related studies on two dimensional granular or colloidal systems. PMID:23411354

  8. Surface investigation of chitosan film with fatty acid monolayers

    Directory of Open Access Journals (Sweden)

    Esam A. El-hefian

    2009-05-01

    Full Text Available The surface pressure- molecular area (-A isotherm curves of two fatty acids of different chain lengths, i.e. stearic (C18 and arachidic (C20 acids, were obtained by using Langmuir-Blodgett (LB technique. Results showed clear isotherm plots with limiting mean molecular area around 21 Å2 for both acids. However, the monolayer was found to collapse at higher than 33 mN m-1 and 21 mN m-1 for stearic acid and arachidic acid respectively. The effect of Langmuir-Blodgett monolayers of the acids was investigated by atomic force microscopy (AFM. Chitosan film, before and after dipping in water, was also studied by means of AFM so that it could be used for comparison. It was found that the surface of chitosan was more homogeneous and smoother after dipping in water. In addition, more homogeneous surfaces were achieved after transferring a layer of the fatty acid onto the substrate.

  9. Large Range Manipulation of Exciton Species in Monolayer WS2

    CERN Document Server

    Wei, Ke; Yang, Hang; Cheng, Xiangai; Jiang, Tian

    2016-01-01

    Unconventional emissions from exciton and trion in monolayer WS2 are studied by photoexcitation. Excited by 532nm laser beam, the carrier species in the monolayer WS2 are affected by the excess electrons escaping from photoionization of donor impurity, the concentration of which varies with different locations of the sample. Simply increasing the excitation power at room temperature, the excess electron and thus the intensity ratio of excited trion and exciton can be continuously tuned over a large range from 0.1 to 7.7. Furthermore, this intensity ratio can also be manipulated by varying temperature. However, in this way the resonance energy of the exciton and trion show red-shifts with increasing temperature due to electron-phonon coupling. The binding energy of the trion is determined to be ~23meV and independent to temperature, indicating strong Coulomb interaction of carriers in such 2D materials.

  10. Neutral amino acid transport across brain microvessel endothelial cell monolayers

    International Nuclear Information System (INIS)

    Brain microvessel endothelial cells (BMEC) which form the blood-brain barrier (BBB) possess an amino acid carrier specific for large neutral amino acids (LNAA). The carrier is important for facilitating the delivery of nutrient LNAA's and centrally acting drugs that are LNAA's, to the brain. Bovine BMEC's were isolated and grown up to complete monolayers on regenerated cellulose-membranes in primary culture. To study the transendothelial transport of leucine, the monolayers were placed in a side-by-side diffusion cell, and transport across the monolayers followed with [3H]-leucine. The transendothelial transport of leucine in this in vitro model was determined to be bidirectional, and time-, temperature-, and concentration-dependent. The transport of leucine was saturable and the apparent K/sub m/ and V/sub max/, 0.18 mM and 6.3 nmol/mg/min, respectively. Other LNAA's, including the centrally acting drugs, α-methyldopa, L-DOPA, α-methyl-tyrosine, and baclofen, inhibited leucine transport. The leucine carrier was also found to be stereospecific and not sensitive to inhibitors of active transport. These results are consistent with previous in vitro and in vivo studies. Primary cultures of BMEC's appear to be a potentially important tool for investigating at the cellular level, the transport mechanisms of the BBB

  11. Neutral amino acid transport across brain microvessel endothelial cell monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Audus, K.L.; Borchardt, R.T.

    1986-03-01

    Brain microvessel endothelial cells (BMEC) which form the blood-brain barrier (BBB) possess an amino acid carrier specific for large neutral amino acids (LNAA). The carrier is important for facilitating the delivery of nutrient LNAA's and centrally acting drugs that are LNAA's, to the brain. Bovine BMEC's were isolated and grown up to complete monolayers on regenerated cellulose-membranes in primary culture. To study the transendothelial transport of leucine, the monolayers were placed in a side-by-side diffusion cell, and transport across the monolayers followed with (/sup 3/H)-leucine. The transendothelial transport of leucine in this in vitro model was determined to be bidirectional, and time-, temperature-, and concentration-dependent. The transport of leucine was saturable and the apparent K/sub m/ and V/sub max/, 0.18 mM and 6.3 nmol/mg/min, respectively. Other LNAA's, including the centrally acting drugs, ..cap alpha..-methyldopa, L-DOPA, ..cap alpha..-methyl-tyrosine, and baclofen, inhibited leucine transport. The leucine carrier was also found to be stereospecific and not sensitive to inhibitors of active transport. These results are consistent with previous in vitro and in vivo studies. Primary cultures of BMEC's appear to be a potentially important tool for investigating at the cellular level, the transport mechanisms of the BBB.

  12. Wrinkle to fold transitions: Stress relaxation in lipid monolayers and other elastic thin films

    Science.gov (United States)

    Lee, Ka Yee C.

    2009-03-01

    Surfactants at air/water interfaces are often subjected to mechanical stresses as the interfaces they occupy are reduced in area. The most well characterized forms of stress relaxation in these systems are first order phase transitions. However, once chemical phase transitions have been exhausted, the monolayer undergoes global mechanical relaxations termed collapse. We have previously demonstrated that for lung surfactants, a mixture of lipids and proteins that coats the alveoli to reduce the work of breathing, collapse manifests itself as protrusions of folds into the subphase. These folds remain attached to the monolayer and reversibly reincorporated upon expansion. By studying different types of monolayers, we have shown that this folding transition in monolayers is not limited to lung surfactant films, but rather represents a much more general type of stress relaxation mechanism. Our study indicates that collapse modes are found most closely linked to in-plane rigidity. We characterize the rigidity of the monolayer by analyzing in-plane morphology on numerous length scales. More rigid monolayers collapse out-of-plane via a hard elastic mode similar to an elastic membrane, with the folded state being the final collapse state, while softer monolayers relax in-plane by shearing. For the hard elastic mode of collapse, we have further demonstrated experimentally and theoretically that the folded state is preceded by a wrinkled state, and similar wrinkle to fold transitions has been observed in elastic thin films ranging from 2 nm to 10 μm in thickness of completely different chemical nature (lung surfactant lipid monolayers, gold nanoparticle trilayers, and polyester sheets).

  13. The electronic structure and elastic property of monolayer and bilayer transition metal dichalcogenides MX$_2$ (M=Mo,W;X=O,S,Se,Te): A comparative first-principles study

    OpenAIRE

    Zeng, Fan; Zhang, Wei-Bing; Tang, Bi-Yu

    2015-01-01

    First-principle calculations with different exchange-correlation functionals, including LDA, PBE and vdW-DF functional in form of optB88-vdW, have been performed to investigate the electronic and elastic properties of two dimensional transition metal dichalcogenides(TMDCs) with the formula of MX$_2$(M=Mo,W; X=O,S,Se,Te) in both monolayer and bilayer structures. The calculated band structures show a direct band gap for monolayer TMDCs at the K point except for MoO$_2$ and WO$_2$. When the mono...

  14. CO catalytic oxidation on iron-embedded monolayer MoS2

    International Nuclear Information System (INIS)

    Highlights: • CO catalytic oxidation on the Fe-embedded monolayer MoS2 has been studied. • Fe atom can be strongly constrained at the S vacancy of monolayer MoS2. • Fe-embedded monolayer MoS2 shows high catalytic activity toward CO oxidation. - Abstract: Based on first-principles calculations, the CO catalytic oxidation on the Fe-embedded monolayer MoS2 (Fe-MoS2) was investigated. It is found that Fe atom can be strongly constrained at the S vacancy of monolayer MoS2 with a high diffusion barrier. The CO oxidation reaction proceeds via a two-step mechanism with the highest energy barrier of 0.51 eV, which is started by the Langmuir–Hinshelwood reaction and ended by the Eley–Rideal reaction. The high catalytic activity of the Fe-MoS2 system may be attributed to the charge transfer and the orbital hybridization between the adsorbates and the Fe atom. This study proposes that embedding transition-metals is a promising way for making the basal plane of monolayer MoS2 catalytically active

  15. CO catalytic oxidation on iron-embedded monolayer MoS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Dongwei, E-mail: dwmachina@126.com [School of Physics, Anyang Normal University, Anyang, Henan 455000 (China); Tang, Yanan [Department of Physics and Electronic Science, Zhengzhou Normal University, Zhengzhou, Henan 450044 (China); Yang, Gui; Zeng, Jun [School of Physics, Anyang Normal University, Anyang, Henan 455000 (China); He, Chaozheng [Physics and Electronic Engineering College, Nanyang Normal University, Nanyang 473061 (China); Lu, Zhansheng [College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, Henan 453007 (China)

    2015-02-15

    Highlights: • CO catalytic oxidation on the Fe-embedded monolayer MoS{sub 2} has been studied. • Fe atom can be strongly constrained at the S vacancy of monolayer MoS{sub 2}. • Fe-embedded monolayer MoS{sub 2} shows high catalytic activity toward CO oxidation. - Abstract: Based on first-principles calculations, the CO catalytic oxidation on the Fe-embedded monolayer MoS{sub 2} (Fe-MoS{sub 2}) was investigated. It is found that Fe atom can be strongly constrained at the S vacancy of monolayer MoS{sub 2} with a high diffusion barrier. The CO oxidation reaction proceeds via a two-step mechanism with the highest energy barrier of 0.51 eV, which is started by the Langmuir–Hinshelwood reaction and ended by the Eley–Rideal reaction. The high catalytic activity of the Fe-MoS{sub 2} system may be attributed to the charge transfer and the orbital hybridization between the adsorbates and the Fe atom. This study proposes that embedding transition-metals is a promising way for making the basal plane of monolayer MoS{sub 2} catalytically active.

  16. Aging of Transition Metal Dichalcogenide Monolayers.

    Science.gov (United States)

    Gao, Jian; Li, Baichang; Tan, Jiawei; Chow, Phil; Lu, Toh-Ming; Koratkar, Nikhil

    2016-02-23

    Two-dimensional sheets of transition metal dichalcogenides are an emerging class of atomically thin semiconductors that are considered to be "air-stable", similar to graphene. Here we report that, contrary to current understanding, chemical vapor deposited transition metal dichalcogenide monolayers exhibit poor long-term stability in air. After room-temperature exposure to the environment for several months, monolayers of molybdenum disulfide and tungsten disulfide undergo dramatic aging effects including extensive cracking, changes in morphology, and severe quenching of the direct gap photoluminescence. X-ray photoelectron and Auger electron spectroscopy reveal that this effect is related to gradual oxidation along the grain boundaries and the adsorption of organic contaminants. These results highlight important challenges associated with the utilization of transition metal dichalcogenide monolayers in electronic and optoelectronic devices. We also demonstrate a potential solution to this problem, featuring encapsulation of the monolayer sheet by a 10-20 nm thick optically transparent polymer (parylene C). This strategy is shown to successfully prevent the degradation of the monolayer material under accelerated aging (i.e., high-temperature, oxygen-rich) conditions. PMID:26808328

  17. Oxidation of alkanes with m-chloroperbenzoic acid catalyzed by iron(III) chloride and a polydentate amine

    OpenAIRE

    Shul’pin, Georgiy B.; Stoeckli-Evans, Helen; Mandelli, Dalmo; Kozlov, Yuriy N.; Tesouro Vallina, Ana; Woitiski, Camile B.; Jimenez, Ricardo S.; Carvalho, Wagner A.

    2009-01-01

    Tetradentate amine N,N′-bis(2-pyridylmethylene)-1,4-diaminodiphenyl ether (compound 1) dramatically accelerates the oxidation of alkanes with MCPBA in acetonitrile catalyzed by FeCl3, whereas N,N′-bis(2-pyrrolidinmethylene)-1,4-diaminodiphenyl ether (2) does not affect the reaction. The selectivity of the reaction in the presence of 1 is noticeably higher than that in its absence. On the basis of the kinetic study and selectivity parameters a mechanism has been proposed which includes the for...

  18. Characterization and Two-Dimensional Crystallization of Membrane Component AlkB of the Medium-Chain Alkane Hydroxylase System from Pseudomonas putida GPo1

    OpenAIRE

    Alonso, Hernan; Roujeinikova, Anna

    2012-01-01

    The alkane hydroxylase system of Pseudomonas putida GPo1 allows it to use alkanes as the sole source of carbon and energy. Bacterial alkane hydroxylases have tremendous potential as biocatalysts for the stereo- and regioselective transformation of a wide range of chemically inert unreactive alkanes into valuable reactive chemical precursors. We have produced and characterized the first 2-dimensional crystals of the integral membrane component of the P. putida alkane hydroxylase system, the no...

  19. Isolation and characterization of different bacterial strains for bioremediation of n-alkanes and polycyclic aromatic hydrocarbons.

    Science.gov (United States)

    Guermouche M'rassi, A; Bensalah, F; Gury, J; Duran, R

    2015-10-01

    Crude oil is a common environmental pollutant composed of a large number of both aromatic and aliphatic hydrocarbons. Biodegradation is carried out by microbial communities that are important in determining the fate of pollutants in the environment. The intrinsic biodegradability of the hydrocarbons and the distribution in the environment of competent degrading microorganisms are crucial information for the implementation of bioremediation processes. In the present study, the biodegradation capacities of various bacteria toward aliphatic and aromatic hydrocarbons were determined. The purpose of the study was to isolate and characterize hydrocarbon-degrading bacteria from contaminated soil of a refinery in Arzew, Algeria. A collection of 150 bacterial strains was obtained; the bacterial isolates were identified by 16S rRNA gene sequencing and their ability to degrade hydrocarbon compounds characterized. The isolated strains were mainly affiliated to the Gamma-Proteobacteria class. Among them, Pseudomonas spp. had the ability to metabolize high molecular weight hydrocarbon compounds such as pristane (C19) at 35.11 % by strain LGM22 and benzo[a] pyrene (C20) at 33.93 % by strain LGM11. Some strains were able to grow on all the hydrocarbons tested including octadecane, squalene, phenanthrene, and pyrene. Some strains were specialized degrading only few substrates. In contrast, the strain LGM2 designated as Pseudomonas sp. was found able to degrade both linear and branched alkanes as well as low and high poly-aromatic hydrocarbons (PAHs). The alkB gene involved in alkane degradation was detected in LGM2 and other Pseudomonas-related isolates. The capabilities of the isolated bacterial strains to degrade alkanes and PAHs should be of great practical significance in bioremediation of oil-contaminated environments. PMID:25813636

  20. MODELLING AND PARAMETER ESTIMATION IN REACTIVE CONTINUOUS MIXTURES: THE CATALYTIC CRACKING OF ALKANES. PART I

    OpenAIRE

    F. C. PEIXOTO; J. L. de Medeiros

    1999-01-01

    Fragmentation kinetics is employed to model a continuous reactive mixture. An explicit solution is found and experimental data on the catalytic cracking of a mixture of alkanes are used for deactivation and kinetic parameter estimation.