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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. I. Structure

    DEFF Research Database (Denmark)

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

    2007-01-01

    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...

  2. 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...

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

    Science.gov (United States)

    Enevoldsen, A. D.; Hansen, F. Y.; Diama, A.; Taub, H.; Dimeo, R. M.; Neumann, D. A.; Copley, J. R. D.

    2007-03-01

    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 the dynamics of these monolayers they used both the disk chopper spectrometer (DCS) and the high flux backscattering spectrometer (HFBS) at the National Institute of Standards and Technology. These instruments made it possible to study dynamical processes such as molecular diffusive motions and vibrations on very different time scales: 1-40ps (DCS) and 0.1-4ns (HFBS). The MD simulations were done on corresponding time scales and were used to interpret the neutron spectra. The authors found that the dynamics of the two monolayers are qualitatively similar on the respective time scales and that there are only small quantitative differences that can be understood in terms of the different masses and moments of inertia of the two molecules. In the course of this study, the authors developed a procedure to separate out the low-frequency vibrational modes in the spectra, thereby facilitating an 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.

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

    Science.gov (United States)

    Enevoldsen, A. D.; Hansen, F. Y.; Diama, A.; Criswell, L.; Taub, H.

    2007-03-01

    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) 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 91K 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 temperature. The neutron diffraction data show that the translational order in the squalane monolayer is significantly less than in the tetracosane monolayer. The authors' MD simulations suggest that this is caused by a distortion of the squalane molecules upon adsorption on the graphite surface. When the molecules are allowed to relax on the surface, they distort such that all six methyl groups point away from the surface. This results in a reduction in the monolayer's translational order characterized by a decrease in its coherence length and hence a broadening of the diffraction peaks. The MD simulations also show that the melting mechanism in the squalane monolayer is the same footprint reduction mechanism found in the tetracosane monolayer, where a chain melting drives the lattice melting.

  5. Simulated Effects of Odd-Alkane Impurities in a Hexane Monolayer on Graphite

    OpenAIRE

    Pint, Cary L.; Roth, Michael W.

    2005-01-01

    We present the results of molecular dynamics simulations of odd alkane impurities present within the hexane (even alkane) monolayer. We simulate various temperatures at ca. 3%, 5%, 10%, and 15% impurities of propane, pentane, heptane, nonane, and undecane, each having a low-temperature solid phase belonging to a different space group as compared to hexane, to study the effects of impurities on the various phases and phase transitions for hexane monolayers that are well-characterized through p...

  6. A Comparison of the Monolayer Dynamics of the Branched Alkane Squalane and the Normal Alkane Tetracosane Adsorbed on Graphite

    Science.gov (United States)

    Enevoldsen, A. D.; Hansen, F. Y.; Diama, A.; Taub, H.

    2004-03-01

    Squalane is a branched alkane (C_30H_62) with 24 carbon atoms in its backbone, like the normal alkane tetracosane ( n-C_24H_50), and six symmetrically placed methyl side groups. In general, branched alkanes such as squalane are better lubricants than n-alkanes. We have studied the dynamics of the squalane and tetracosane monolayers by quasielastic neutron scattering and molecular dynamics (MD) simulations on two different time scales. Both experiments and simulations showed that diffusion at 260 K is about 2.5 times faster in the squalane than in the tetracosane system. It is somewhat surprising that the diffusion in a system with a branched alkane is faster than with a normal alkane. A possible explanation is that the squalane molecule does not bind as strongly to the surface as tetracosane, because the MD simulations have shown that the adsorbed molecules have a distorted backbone. This may also explain why the slow intramolecular motions associated with conformational changes are seen at lower temperatures in the squalane than the tetracosane monolayer where they are only observed near melting.

  7. Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation

    DEFF Research Database (Denmark)

    Diama, A.; Matthies, B.; Herwig, K. W.;

    2009-01-01

    We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C24H50 denoted as C24) and dotriacontane (n-C32H66 denoted as C32) adsorbed on a graphite basal-plane surface. Our...... show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously...

  8. Intramolecular diffusive motion in alkane monolayers studied by high-resolution quasielastic neutron scattering and molecular dynamics simulations

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Criswell, L.; Fuhrmann, D;

    2004-01-01

    Molecular dynamics simulations of a tetracosane (n-C24H50) monolayer adsorbed on a graphite basal-plane surface show that there are diffusive motions associated with the creation and annihilation of gauche defects occurring on a time scale of similar to0.1-4 ns. We present evidence that these rel...

  9. Structure and Phase Transitions of Monolayers of Intermediate-length n-alkanes on Graphite Studied by Neutron Diffraction and Molecular Dynamics Simulation

    Energy Technology Data Exchange (ETDEWEB)

    Taub, H. [University of Missouri, Columbia; Hansen, F.Y. [Technical University of Denmark; Diama, Amand [National University of the Ivory Coast; Matthies, Blake [Goodyear Tire and Rubber Company, The; Criswell, Leah [University of Missouri, Columbia; Mo, Haiding [Advanced Optowave Corporation; Bai, M [University of Missouri, Columbia; Herwig, Kenneth W [ORNL

    2009-01-01

    We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C(24)H(50) denoted as C24) and dotriacontane (n-C(32)H(66) denoted as C32) adsorbed on a graphite basal-plane surface. Our measurements indicate that the two monolayer films differ principally in the transition temperatures between phases. At the lowest temperatures, both C24 and C32 form a crystalline monolayer phase with a rectangular-centered (RC) structure. The two sublattices of the RC structure each consists of parallel rows of molecules in their all-trans conformation aligned with their long axis parallel to the surface and forming so-called lamellas of width approximately equal to the all-trans length of the molecule. The RC structure is uniaxially commensurate with the graphite surface in its [110] direction such that the distance between molecular rows in a lamella is 4.26 A=sqrt[3a(g)], where a(g)=2.46 A is the lattice constant of the graphite basal plane. Molecules in adjacent rows of a lamella alternate in orientation between the carbon skeletal plane being parallel and perpendicular to the graphite surface. Upon heating, the crystalline monolayers transform to a 'smectic' phase in which the inter-row spacing within a lamella expands by approximately 10% and the molecules are predominantly oriented with the carbon skeletal plane parallel to the graphite surface. In the smectic phase, the MD simulations show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously.

  10. Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation.

    Science.gov (United States)

    Diama, A; Matthies, B; Herwig, K W; Hansen, F Y; Criswell, L; Mo, H; Bai, M; Taub, H

    2009-08-28

    We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C(24)H(50) denoted as C24) and dotriacontane (n-C(32)H(66) denoted as C32) adsorbed on a graphite basal-plane surface. Our measurements indicate that the two monolayer films differ principally in the transition temperatures between phases. At the lowest temperatures, both C24 and C32 form a crystalline monolayer phase with a rectangular-centered (RC) structure. The two sublattices of the RC structure each consists of parallel rows of molecules in their all-trans conformation aligned with their long axis parallel to the surface and forming so-called lamellas of width approximately equal to the all-trans length of the molecule. The RC structure is uniaxially commensurate with the graphite surface in its [110] direction such that the distance between molecular rows in a lamella is 4.26 A=sqrt[3a(g)], where a(g)=2.46 A is the lattice constant of the graphite basal plane. Molecules in adjacent rows of a lamella alternate in orientation between the carbon skeletal plane being parallel and perpendicular to the graphite surface. Upon heating, the crystalline monolayers transform to a "smectic" phase in which the inter-row spacing within a lamella expands by approximately 10% and the molecules are predominantly oriented with the carbon skeletal plane parallel to the graphite surface. In the smectic phase, the MD simulations show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously.

  11. Interaction of hydrocarbon monolayer surfaces across n-alkanes: A steric repulsion

    Science.gov (United States)

    Herder, Christina E.; Ninham, Barry W.; Christenson, Hugo K.

    1989-05-01

    We present results of force measurements between hydrocarbon monolayer surfaces across n-alkanes (hexane, decane, and tetradecane). The interaction is qualitatively different from that of any previously studied system and, in particular, bears no resemblance to an oscillatory solvation force. Instead, the force is repulsive from about 2.5 nm, with the exception of a shallow minimum just outside a force maximum at 0.8-0.9 nm. At smaller separations the force becomes attractive and there is a weak adhesion at contact. We suggest that the force law is due to a steric effect—a repulsive interaction originating in restrictions on chain conformations of the alkanes at small surface separations. This interaction is accessible via simple mean-field theories. The similarity of the liquid-liquid and liquid-surface interactions allows this to dominate over solvation effects. The results are of significance for interaggregate interactions in lamellar liquid crystals, microemulsions, and surfactant-stabilized dispersions.

  12. On the inclusion of alkanes into the monolayer of aliphatic alcohols at the water/alkane vapor interface: a quantum chemical approach.

    Science.gov (United States)

    Vysotsky, Yuri B; Fomina, Elena S; Belyaeva, Elena A; Fainerman, Valentin B; Vollhardt, Dieter

    2013-02-14

    In the framework of the quantum chemical semiempirical PM3 method thermodynamic and structural parameters of the formation and clusterization of aliphatic alcohols C(n)H(2n+1)OH (n(OH) = 8-16) at 298 K at the water/alkane vapor C(n)H(2n+2), (n(CH(3)) = 6-16) interface were calculated. The dependencies of enthalpy, entropy and Gibbs' energy of clusterization per one monomer molecule of 2D films on the alkyl chain length of corresponding alcohols and alkanes, the molar fraction of alkanes in the monolayers and the immersion degree of alcohol molecules into the water phase were shown to be linear or stepwise. The threshold of spontaneous clusterization of aliphatic alcohols at the water/alkane vapor interface was 10-11 carbon atoms at 298 K which is in line with experimental data at the air/water interface. It is shown that the presence of alkane vapor does not influence the process of alcohol monolayer formation. The structure of these monolayers is analogous to those obtained at the air/water interface in agreement with experimental data. The inclusion of alkane molecules into the amphiphilic monolayer at the water/alkane vapor interface is possible for amphiphiles with the spontaneous clusterization threshold at the air/water interface (n(s)(0)) of at least 16 methylene units in the alkyl chain, and it does not depend on the molar fraction of alkanes in the corresponding monolayer. The inclusion of alkanes from the vapor phase into the amphiphilic monolayer also requires that the difference between the alkyl chain lengths of alcohols and alkanes is not larger than n(s)(0) - 15 and n(s)(0) - 14 for the 2D film 1 and 2D film 2, respectively.

  13. 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

    Molecular dynamics (MD) simulations and neutron diffraction experiments have been performed on n-dotriacontane (n-C32D66) monolayers adsorbed on a graphite basal-plane surface. The diffraction experiments show little change in the crystalline monolayer structure up to a temperature of similar to ...

  14. Theoretical study of the rhenium–alkane interaction in transition metal–alkane σ-complexes

    OpenAIRE

    Cobar, Erika A.; Khaliullin, Rustam Z.; Bergman, Robert G.; Head-Gordon, Martin

    2007-01-01

    Metal–alkane binding energies have been calculated for [CpRe(CO)2](alkane) and [(CO)2M(C5H4)CC(C5H4)M(CO)2](alkane), where M = Re or Mn. Calculated binding energies were found to increase with the number of metal–alkane interaction sites. In all cases examined, the manganese–alkane binding energies were predicted to be significantly lower than those for the analogous rhenium–alkane complexes. The metal (Mn or Re)–alkane interaction was predicted to be primarily one of charge transfer, both fr...

  15. 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.

  16. Neutron diffraction and quasielastic neutron scattering studies of films of intermediate-length alkanes adsorbed on a graphite surface

    Science.gov (United States)

    Diama, Armand

    Over the past several years, we have conducted a variety of elastic neutron diffraction and quasielastic neutron scattering experiments to study the structure and the dynamics of films of two intermediate-length alkane molecules (C nH2n+2), adsorbed on a graphite basal-plane surface. The two molecules are the normal alkane n-tetracosane [n-CH 3(CH2)22CH3] and the branched alkane squalane (C30H62 or 2, 6, 10, 15, 19, 23-hexamethyltetracosane) whose carbon backbone is the same length as teteracosane. The temperature dependence of the monolayer structure of tetracosane and squalane was investigated using elastic neutron diffraction and evidence of two phase transitions was observed. Both the low-coverage tetracosane (C 24H50) and squalane (C30H62) monolayers have crystalline-to-"smectic" and "smectic"-to-isotropic fluid phase transitions upon heating. The diffusive motion in the tetracosane and squalane monolayers has been investigated by quasielastic neutron scattering. Two different quasielastic neutron scattering spectrometers at the Center for Neutron Research, National Institute of Standards and Technology (NIST) have been used. The spectrometers differ in both their dynamic range and energy resolution allowing molecular motions to be investigated on time scales in the range 10-13--10 -9 s. On these time scales, we observe evidence of translational, rotational, and intermolecular diffusive motions in the tetracosane and squalane monolayers. We conclude that the molecular diffusive motion in the two monolayers is qualitatively similar. Thus, despite the three methyl sidegroups at each end of the squalane molecule, its monolayer structure, phase transitions, and dynamics are qualitatively similar to that of a monolayer of the unbranched tetracosane molecules. With the higher resolution spectrometer at NIST, we have also investigated the molecular diffusive motion in multilayer tetracosane films. The analysis of our measurements indicates slower diffusive motion in

  17. 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 e...

  18. 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.

  19. A simulation study on the thermal and wetting behavior of alkane thiol SAM on gold (111) surface

    Institute of Scientific and Technical Information of China (English)

    J. Meena Devi

    2014-01-01

    Molecular dynamics simulations have been performed to investigate the structural, thermal and wetting properties of self-assembled monolayer (SAM) of alkane thiol on gold surface. The specific heat capacity of the gold SAM surface was found to linearly increase with the temperature in the range 100-300 K. It was found to drop down at 400 K and this decrease might be attributed to the disorder of the SAM chains. Hydration of gold SAM surface for two different terminal groups, namely methyl (hydrophobic), and hydroxy (hydrophilic) was studied at room temperature. The difference in their wetting behavior and the structure of their interfacial water were examined from the estimation of the z density profile, radial distribution function, hydrogen bonds and orientation of water dipoles in the interfacial region. The present simulation results suggest that the wetting behavior of the gold SAM surface can be modified by altering the terminal functional group of the SAM chains.

  20. Hydrogen-hydrogen bonds in highly branched alkanes and in alkane complexes: A DFT, ab initio, QTAIM, and ELF study.

    Science.gov (United States)

    Monteiro, Norberto K V; Firme, Caio L

    2014-03-06

    The hydrogen-hydrogen (H-H) bond or hydrogen-hydrogen bonding is formed by the interaction between a pair of identical or similar hydrogen atoms that are close to electrical neutrality and it yields a stabilizing contribution to the overall molecular energy. This work provides new, important information regarding hydrogen-hydrogen bonds. We report that stability of alkane complexes and boiling point of alkanes are directly related to H-H bond, which means that intermolecular interactions between alkane chains are directional H-H bond, not nondirectional induced dipole-induced dipole. Moreover, we show the existence of intramolecular H-H bonds in highly branched alkanes playing a secondary role in their increased stabilities in comparison with linear or less branched isomers. These results were accomplished by different approaches: density functional theory (DFT), ab initio, quantum theory of atoms in molecules (QTAIM), and electron localization function (ELF).

  1. Composition index of n-alkanes and paleoenvironmental study in sediments of the Arctic

    Institute of Scientific and Technical Information of China (English)

    Lu Bing; Zhou Huaiyang; Wang Zipan; Lu Douding

    2001-01-01

    This paper reports different concentration patterns of n-alkanes distribution in the sediments from the Chukchi Sea, the Bering Sea in the Arctic. Factor statistical analysis method is used for studying the source of n-alkanes and paleoenviroment. The result shows that n-alkanes is in the range of nC15~nC33 and n-alkane distribution patterns are characterized by two modes. The first mode belongs to the higher molecular with MH being nC25~ nC27, CPI> 1 and with remarkable odd-even dominance.They are of terrigenous plant origin. The second one belongs to lower carbon range with MH being nC17 ~nC20, CPI> 1 and with indistinct odd-even dominance. Therefore they are contributed by marine biological inputs. The contribution of land origin is larger than that of marine source. Pr/Ph is lower than 1 in the investigated area, which indicates the depositional environment of reducing reaction with lower oxygen. The result of factor analysis has good agreement with composition characteristics of n-alkanes in the sediment.

  2. Monte Carlo studies of model Langmuir monolayers.

    Science.gov (United States)

    Opps, S B; Yang, B; Gray, C G; Sullivan, D E

    2001-04-01

    This paper examines some of the basic properties of a model Langmuir monolayer, consisting of surfactant molecules deposited onto a water subphase. The surfactants are modeled as rigid rods composed of a head and tail segment of diameters sigma(hh) and sigma(tt), respectively. The tails consist of n(t) approximately 4-7 effective monomers representing methylene groups. These rigid rods interact via site-site Lennard-Jones potentials with different interaction parameters for the tail-tail, head-tail, and head-head interactions. In a previous paper, we studied the ground-state properties of this system using a Landau approach. In the present paper, Monte Carlo simulations were performed in the canonical ensemble to elucidate the finite-temperature behavior of this system. Simulation techniques, incorporating a system of dynamic filters, allow us to decrease CPU time with negligible statistical error. This paper focuses on several of the key parameters, such as density, head-tail diameter mismatch, and chain length, responsible for driving transitions from uniformly tilted to untilted phases and between different tilt-ordered phases. Upon varying the density of the system, with sigma(hh)=sigma(tt), we observe a transition from a tilted (NNN)-condensed phase to an untilted-liquid phase and, upon comparison with recent experiments with fatty acid-alcohol and fatty acid-ester mixtures [M. C. Shih, M. K. Durbin, A. Malik, P. Zschack, and P. Dutta, J. Chem. Phys. 101, 9132 (1994); E. Teer, C. M. Knobler, C. Lautz, S. Wurlitzer, J. Kildae, and T. M. Fischer, J. Chem. Phys. 106, 1913 (1997)], we identify this as the L'(2)/Ov-L1 phase boundary. By varying the head-tail diameter ratio, we observe a decrease in T(c) with increasing mismatch. However, as the chain length was increased we observed that the transition temperatures increased and differences in T(c) due to head-tail diameter mismatch were diminished. In most of the present research, the water was treated as a hard

  3. 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.

  4. Interaction of SynaptotagminⅠ with Phospholipid Membrane: A Monolayer Study

    Institute of Scientific and Technical Information of China (English)

    贺雨虹; 隋森芳

    2002-01-01

    Synaptotagmin Ⅰ(sytⅠ) is an abundant integral membrane protein of the synaptic vesicle and the C2A domain is an important functional domain in the cytoplasmic part of sytⅠ. C2A prefers to interact with plasmic membranes of neuron cells in vivo and such interaction is closely related to the sytⅠ physiological function as a Ca2+ sensor in the Ca2+-regulated neurotransmitter release. However, the interaction nature between C2A and phospholipids is not well understood. Monolayers at an air/water interface were used to study the interaction between C2A and a phospholipid membrane. The results show that C2A preferentially inserts into the negatively charged phosphatidylserine monolayer and Ca2+ ions are required for the interaction. Electrostatic force is mostly responsible for the insertion of C2A into dipalmitoyl phosphatidylserine monolayers.

  5. 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.

  6. 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.

  7. 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

  8. Studies on the Physical Properties of Alkanes Using Edge-adjacency Information Topological Index

    Institute of Scientific and Technical Information of China (English)

    Cai Hua NI; Xian Yu ZENG; He HUANG

    2005-01-01

    Edge-adjacency index and information topological index for 82 molecules of alkanes have been constructed and calculated. The topological indices were used to correlate with seven physical properties of the alkanes. Some empirical equations were obtained through regression.The regression and calculation results show a good agreement of the topological indices and the properties.

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

    Energy Technology Data Exchange (ETDEWEB)

    Salamifar, Seyed Ehsan [Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran (Iran, Islamic Republic of); Mehrgardi, Masoud Ayatollahi [Department of Chemistry, University of Isfahan, Isfahan (Iran, Islamic Republic of); Kazemi, Sayed Habib [Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan (Iran, Islamic Republic of); Mousavi, Mir Fazllollah, E-mail: mousavim@modares.ac.i [Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran (Iran, Islamic Republic of)

    2010-12-30

    Electron transfer (ET) kinetics through n-dodecanethiol (C{sub 12}SH) 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){sub 6}{sup 4-/3-}) and ferrocenemethanol/ferrociniummethanol (FMC{sup 0/+}) through the C{sub 12}SH monolayer yielding standard tunneling rate constant (k{sub ET}{sup 0}) of (4 {+-} 1) x 10{sup -11} and (3 {+-} 1) x 10{sup -10} cm s{sup -1} for Fe(CN){sub 6}{sup 4-/3-} and FMC{sup 0/+} respectively. Decay tunneling constants ({beta}) of 0.97 and 0.96 A{sup -1} for saturated alkane thiol chains were obtained using Fe(CN){sub 6}{sup 4-} and FMC respectively. Also, it was found that methylene blue (MB) molecules are effectively immobilized on the C{sub 12}SH 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 k{sub BI} = (5 {+-} 1) x 10{sup 6} and (4 {+-} 2) x 10{sup 7} cm{sup 3} mol{sup -1} s{sup -1} for the bimolecular ET and k{sub ET/MB}{sup 0}=(1{+-}0.3)x10{sup -3} and (7 {+-} 3) x 10{sup -2} s{sup -1} for the standard tunneling rate constant of ET using Fe(CN){sub 6}{sup 4-/3-} and FMC{sup 0/+} probes respectively.

  10. Theoretical and experimental study of the vibrational excitations in ethane monolayers adsorbed on graphite (0001) surfaces

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Taub, H.

    1987-01-01

    The collective vibrational excitations of two different crystalline monolayer phases of ethane (C2H6) adsorbed on the graphite (0001) surface have been investigated theoretically and experimentally. The monolayer phases studied are the commensurate 7/8 ×4 structure in which the ethane molecules lie...

  11. Length dependence of the thermal conductance of alkane-based single-molecule junctions: An ab initio study

    Science.gov (United States)

    Klöckner, J. C.; Bürkle, M.; Cuevas, J. C.; Pauly, F.

    2016-11-01

    Motivated by recent experiments, we present here a systematic ab initio study of the length dependence of the thermal conductance of single-molecule junctions. We make use of a combination of density functional theory with nonequilibrium Green's function techniques to investigate the length dependence of the phonon transport in single-alkane chains, contacted with gold electrodes via both thiol and amine anchoring groups. Additionally, we study the effect of the substitution of the hydrogen atoms in the alkane chains by heavier fluorine atoms to form polytetrafluoroethylenes. Our results demonstrate that (i) the room-temperature thermal conductance is fairly length independent for chains with more than 5 methylene units and (ii) the efficiency of the thermal transport is strongly influenced by the strength of the phononic metal-molecule coupling. Our study sheds light on the phonon transport in molecular junctions, and it provides clear guidelines for the design of molecular junctions for thermal management.

  12. Numerical and experimental studies of ethanol flames and autoignition theory for higher alkanes

    Science.gov (United States)

    Saxena, Priyank

    In order to enhance the fuel efficiency of an engine and to control pollutant formation, an improved understanding of the combustion chemistry of the fuels at a fundamental level is paramount. This knowledge can be gained by developing detailed reaction mechanisms of the fuels for various combustion processes and by studying combustion analytically employing reduced-chemistry descriptions. There is a need for small detailed reaction mechanisms for alkane and alcohol fuels with reduced uncertainties in their combustion chemistry that are computationally cheaper in multidimensional CFD calculations. Detailed mechanisms are the starting points in identifying reduced-chemistry descriptions of combustion processes to study problems analytically. This research includes numerical, experimental and analytical studies. The first part of the dissertation consists of numerical and experimental studies of ethanol flames. Although ethanol has gained popularity as a possible low-pollution source of renewable energy, significant uncertainties remain in its combustion chemistry. To begin to address ethanol combustion, first a relatively small detailed reaction mechanism, commonly known as the San Diego Mech, is developed for the combustion of hydrogen, carbon monoxide, formaldehyde, methane, methanol, ethane, ethylene, and acetylene, in air or oxygen-inert mixtures. This mechanism is tested for autoignition, premixed-flame burning velocities, and structures and extinction of diffusion flames and of partially premixed flames of many of these fuels. The reduction in uncertainties in the combustion chemistry can best be achieved by consistently updating a reaction mechanism with reaction rate data for the elementary steps based on newer studies in literature and by testing it against as many experimental conditions as available. The results of such a testing for abovementioned fuels are reported here along with the modifications of reaction-rate parameters of the most important

  13. Comparative study of alkali-vapour cells with alkane-, alkeneand 1-nonadecylbenzene-based antirelaxation wall coatings

    Energy Technology Data Exchange (ETDEWEB)

    Balabas, M V; Tretiak, O Yu [Department of Physics, Saint-Petersburg State University (Russian Federation)

    2013-12-31

    The dependence of both longitudinal and transverse relaxation times of ground-state magnetic polarisation in alkali atoms on the coating temperature is experimentally studied for the first time in a rubidium-vapour cell with 1-nonadecylbenzene antirelaxation coating of inner walls. The comparison of these times with the relaxation times in a caesium-vapour cell with alkane wall coatings is presented. It is found that within the studied temperature range (294 – 340K) the transverse relaxation time decreases with increasing temperature of alkene and 1-nonadecylbenzene coatings. For the alkane coating such a dependence was not explicitly found. The longitudinal relaxation time begins to decrease in all cases when passing a certain critical temperature of the coating material. It is found that the unsaturated radical structure of the coating material molecules strongly affects its antirelaxation properties. (optical pumping)

  14. 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.

  15. Monte Carlo study of electron transport in monolayer silicene

    Science.gov (United States)

    Borowik, Piotr; Thobel, Jean-Luc; Adamowicz, Leszek

    2016-11-01

    Electron mobility and diffusion coefficients in monolayer silicene are calculated by Monte Carlo simulations using simplified band structure with linear energy bands. Results demonstrate reasonable agreement with the full-band Monte Carlo method in low applied electric field conditions. Negative differential resistivity is observed and an explanation of the origin of this effect is proposed. Electron mobility and diffusion coefficients are studied in low applied electric field conditions. We demonstrate that a comparison of these parameter values can provide a good check that the calculation is correct. Low-field mobility in silicene exhibits {T}-3 temperature dependence for nondegenerate electron gas conditions and {T}-1 for higher electron concentrations, when degenerate conditions are imposed. It is demonstrated that to explain the relation between mobility and temperature in nondegenerate electron gas the linearity of the band structure has to be taken into account. It is also found that electron-electron scattering only slightly modifies low-field electron mobility in degenerate electron gas conditions.

  16. 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

  17. 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.

  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. Comparative Study of Protein Immobilization Properties on Calixarene Monolayers

    Directory of Open Access Journals (Sweden)

    Kwangnak Koh

    2007-06-01

    Full Text Available Three calix[4]arene (Cal-4 derivatives of which contain ethylester (1,carboxylic acid (2, and crownether (3 at the lower rim with a common reactive thiol at theupper rim were synthesized and constructed to self-assembled monolayers (SAMs on Aufilms. After spectroscopic characterization of monolayers, the interaction between Cal-4and surface confined bovine serum albumin (BSA in the SAMs was analyzed by surfaceplasmon resonance (SPR. The estimated surface concentration of BSA on the Cal-4 SAMwith crownether group was the highest among the three Cal-4 derivatives. Anti-hIgG andhIgG pair was employed for the investigation of protein-protein interaction. Molecularinteraction between anti-hIgG and hIgG can be detected in a concentration range of 10pg/mL to 200 pg/mL on the Cal-4 derivative 3 SAM modified SPR chip.

  20. Electrochemical Impedance Study of Schiff Base by Means of Self-assembled Monolayer

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In this work, the self-assembled monolayer of Schiff base was first investigated using electrochemical impedance spectroscopy (ELS). The complexation of Cu2+ with the Schiff base was also detected with EIS method. The approximate linear relationship between Cu2+ and the reaction resistance (Rr) was observed. All the results suggest that the electrochemical property of Schiff base could be studied conveniently by means of forming self-assembled monolayer.

  1. Study on folds of monolayer sandwiched-in different thickness terranes

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The paper discussed the limitation of ‘Dominant wavelength theory’. The theoretical model and nonhomogeneous differential equation of fold and deformation of a monolayer sandwiched-in limited and different thickness terranes are proposed by using mechanics of elasticity. In addition, the ′Dominant wavelength theory’ is proved by the experimental folding in elastic materials. The folds of a monolayer sandwiched-in limited and different thickness terranes are studied inside and are explored in the field.

  2. First-principles study of the magnetism of Ni-doped MoS2 monolayer

    Science.gov (United States)

    Luo, Min; Hao Shen, Yu; Hao Chu, Jun

    2016-09-01

    The magnetic properties of Ni-doped monolayer MoS2 are investigated using the density function theory. The results show that two Ni-doped systems of the nearest-neighbor configuration are ferromagnetic. The p-d hybridization between the Ni dopant and its neighboring S atoms results in the splitting of energy levels near the Fermi energy. These results suggest the p-d hybridization mechanism for the magnetism of the Ni-doped MoS2 monolayer. The magnetic moment disappears with increasing Ni-Ni distance. Our studies predict the nearest two-Ni-doped MoS2 monolayers to be candidates for thin dilute magnetic semiconductors. Moreover, the formation energy calculations indicate that it would be easier to incorporate Ni atoms into a S-rich MoS2 monolayer in the experiment.

  3. Mössbauer studies of alkane ω-hydroxylase: Evidence for a diiron cluster in an integral-membrane enzyme

    OpenAIRE

    Shanklin, John; Achim, Catalina; Schmidt, Hermann; Fox, Brian G.; Münck, Eckard

    1997-01-01

    The gene encoding the alkane ω-hydroxylase (AlkB; EC 1.14.15.3) from Pseudomonas oleovorans was expressed in Escherichia coli. The integral-membrane protein was purified as nearly homogeneous protein vesicles by differential ultracentrifugation and HPLC cation exchange chromatography without the detergent solubilization normally required for membrane proteins. Purified AlkB had specific activity of up to 5 units/mg for octane-dependent NADPH consumption. Mössbauer studies of AlkB showed that ...

  4. 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.

  5. Study of the aggregation of human insulin Langmuir monolayer.

    Science.gov (United States)

    Liu, Wei; Johnson, Sheba; Micic, Miodrag; Orbulescu, Jhony; Whyte, Jeffrey; Garcia, Andrew R; Leblanc, Roger M

    2012-02-21

    The human insulin (HI) Langmuir monolayer at the air-water interface was systematically investigated in the presence and absence of Zn(II) ions in the subphase. HI samples were dissolved in acidic (pH 2) and basic (pH 9) aqueous solutions and then spread at the air-water interface. Spectroscopic data of aqueous solutions of HI show a difference in HI conformation at different pH values. Moreover, the dynamics of the insulin protein showed a dependence on the concentration of Zn(II) ions. In the absence of Zn(II) ions in the subphase, the acidic and basic solutions showed similar behavior at the air-water interface. In the presence of Zn(II) ions in the subphase, the surface pressure-area and surface potential-area isotherms suggest that HI may aggregate at the air-water interface. It was observed that increasing the concentration of Zn(II) ions in the acidic (pH 2) aqueous solution of HI led to an increase of the area at a specific surface pressure. It was also seen that the conformation of HI in the basic (pH 9) medium had a reverse effect (decrease in the surface area) with the increase of the concentration of Zn(II) ions in solution. From the compression-decompression cycles we can conclude that the aggregated HI film at air-water interface is not stable and tends to restore a monolayer of monomers. These results were confirmed from UV-vis and fluorescence spectroscopy analysis. Infrared reflection-absorption and circular dichroism spectroscopy techniques were used to determine the secondary structure and orientation changes of HI by zinc ions. Generally, the aggregation process leads to a conformation change from α-helix to β-strand and β-turn, and at the air-water interface, the aggregation process was likewise seen to induce specific orientations for HI in the acidic and basic media. A proposed surface orientation model is presented here as an explanation to the experimental data, shedding light for further research on the behavior of insulin as a Langmuir

  6. 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.

  7. Nanorheology of Liquid Alkanes

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, S.A., Cochran, H.D., Cummings, P.T. [Tennessee Univ., Knoxville, TN (United States). Dept. of Chemical Engineering], [Oak Ridge National Lab., TN (United States)

    1997-09-01

    We report molecular dynamics simulations of liquid alkanes, squalane and tetracosane, confined between moving walls to which butane chains are tethered, effectively screening the details of the wall. As in an experiment, heat is removed by thermostatting the tethered molecules. Results obtained at high strain rates, typical of practical applications, suggest little or no difference between the bulk rheology and confined flow, and the occurrence of a high degree of slip at the wall-fluid interface at the conditions studied. At relatively low velocities and high densities, tetracosane shows the formation of fully-extended chains at certain wall spacings.

  8. Fluctuations in a ferrofluid monolayer: an integral equation study.

    Science.gov (United States)

    Luo, Liang; Klapp, Sabine H L

    2009-07-21

    Using integral equation theory in the reference hypernetted chain (RHNC) approximation we investigate the structure and phase behavior of a monolayer of dipolar spheres. The dipole orientations of the particles fluctuate within the plane. The resulting angle dependence of the correlation functions is treated via an expansion in two-dimensional rotational invariants. For homogeneous, isotropic states the RHNC correlation functions turn out to be in good agreement with Monte Carlo simulation data. We then use the RHNC theory combined with a stability (fluctuation) analysis to identify precursors of the low-temperature behavior. As expected, the fluctuations point to pair and cluster formation in the range of low and moderate densities. At high densities, there is no clear indication for a ferroelectric transition, contrary to what is found in three-dimensional dipolar fluids. The stability analysis rather indicates an alignment of chains supplemented by local crystal-like order.

  9. Liquid-liquid interfaces of semifluorinated alkane diblock copolymers with water, alkanes, and perfluorinated alkanes.

    Science.gov (United States)

    Pierce, Flint; Tsige, Mesfin; Perahia, Dvora; Grest, Gary S

    2008-12-18

    The liquid-liquid interface between semifluorinated alkane diblock copolymers of the form F3C(CF2)n-1-(CH2)m-1CH3 and water, protonated alkanes, and perfluorinated alkanes are studied by fully atomistic molecular dynamics simulations. A modified version of the OPLS-AA (Optimized Parameter for Liquid Simulation All-Atom) force field of Jorgensen et al. has been used to study the interfacial behavior of semifluorinated diblocks. Aqueous interfaces are found to be sharp, with correspondingly large values of the interfacial tension. Due to the reduced hydrophobicity of the protonated block compared to the fluorinated block, hydrogen enhancement is observed at the interface. Water dipoles in the interfacial region are found to be oriented nearly parallel to the liquid-liquid interface. A number of protonated alkanes and perfluorinated alkanes are found to be mutually miscible with the semifluorinated diblocks. For these liquids, interdiffusion follows the expected Fickian behavior, and concentration-dependent diffusivities are determined.

  10. Comparative Study on Single-Molecule Junctions of Alkane- and Benzene-Based Molecules with Carboxylic Acid/Aldehyde as the Anchoring Groups

    Science.gov (United States)

    Chen, Fang; Peng, Lin-Lu; Hong, Ze-Wen; Mao, Jin-Chuan; Zheng, Ju-Fang; Shao, Yong; Niu, Zhen-Jiang; Zhou, Xiao-Shun

    2016-08-01

    We have measured the alkane and benzene-based molecules with aldehyde and carboxylic acid as anchoring groups by using the electrochemical jump-to-contact scanning tunneling microscopy break junction (ECSTM-BJ) approach. The results show that molecule with benzene backbone has better peak shape and intensity than those with alkane backbone. Typically, high junction formation probability for same anchoring group (aldehyde and carboxylic acid) with benzene backbone is found, which contributes to the stronger attractive interaction between Cu and molecules with benzene backbone. The present work shows the import role of backbone in junction, which can guide the design molecule to form effective junction for studying molecular electronics.

  11. Titanium Trisulfide Monolayer as a Potential Thermoelectric Material: A First-Principles-Based Boltzmann Transport Study.

    Science.gov (United States)

    Zhang, Jie; Liu, Xiaolin; Wen, Yanwei; Shi, Lu; Chen, Rong; Liu, Huijun; Shan, Bin

    2017-01-25

    Good electronic transport capacity and low lattice thermal conductivity are beneficial for thermoelectric applications. In this study, the potential use as a thermoelectric material for the recently synthesized two-dimensional TiS3 monolayer is explored by applying first-principles method combined with Boltzmann transport theory. Our work demonstrates that carrier transport in the TiS3 sheet is orientation-dependent, caused by the difference in charge density distribution at band edges. Due to a variety of Ti-S bonds with longer lengths, we find that the TiS3 monolayer shows thermal conductivity much lower compared with that of transition-metal dichalcogenides such as MoS2. Combined with a high power factor along the y-direction, a considerable n-type ZT value (3.1) can be achieved at moderate carrier concentration, suggesting that the TiS3 monolayer is a good candidate for thermoelectric applications.

  12. Structural stability study of protein monolayers in air

    Science.gov (United States)

    Pompa, P. P.; Biasco, A.; Cingolani, R.; Rinaldi, R.; Verbeet, M. Ph.; Canters, G. W.

    2004-03-01

    The assessment of the folding and of the structural stability of a protein in air, upon immobilization in the solid state, represents a critical point from both a fundamental point of view and for the development of solid state nanobioelectronics. The recent demonstrations by Rinaldi et al. [R. Rinaldi et al., Adv. Mater. 14, 1453 (2002); Appl. Phys. Lett. 82, 472 (2003); Ann. (N.Y.) Acad. Sci. 1006, 187 (2003)] of protein-based solid state devices and transistors working in air have raised an intriguing question about the behavior of a biomolecule under nonphysiological conditions. The operation principle of the realized devices is based on the physiological electron transfer function of the metalloprotein azurin. This means that azurin should retain its shape and functionality also in the solid state when utilized in air and at room temperature. In this Brief Report, we prove this claim by analyzing the conformational state of the azurin monolayers developed for such devices by means of intrinsic fluorescence spectroscopy. We show that the immobilization of azurins in the solid state under nonliquid conditions, by means of a specific chemisorption process, does not necessarily lead to protein denaturation. This result is of great importance because it opens up interesting perspectives for the development of solid state hybrid nanodevices for electronic applications requiring nonliquid environments.

  13. Improved Alkane Production in Nitrogen-Fixing and Halotolerant Cyanobacteria via Abiotic Stresses and Genetic Manipulation of Alkane Synthetic Genes.

    Science.gov (United States)

    Kageyama, Hakuto; Waditee-Sirisattha, Rungaroon; Sirisattha, Sophon; Tanaka, Yoshito; Mahakhant, Aparat; Takabe, Teruhiro

    2015-07-01

    Cyanobacteria possess the unique capacity to produce alkane. In this study, effects of nitrogen deficiency and salt stress on biosynthesis of alkanes were investigated in three kinds of cyanobacteria. Intracellular alkane accumulation was increased in nitrogen-fixing cyanobacterium Anabaena sp. PCC7120, but decreased in non-diazotrophic cyanobacterium Synechococcus elongatus PCC7942 and constant in a halotolerant cyanobacterium Aphanothece halophytica under nitrogen-deficient condition. We also found that salt stress increased alkane accumulation in Anabaena sp. PCC7120 and A. halophytica. The expression levels of two alkane synthetic genes were not upregulated significantly under nitrogen deficiency or salt stress in Anabaena sp. PCC7120. The transformant Anabaena sp. PCC7120 cells with additional alkane synthetic gene set from A. halophytica increased intracellular alkane accumulation level compared to control cells. These results provide a prospect to improve bioproduction of alkanes in nitrogen-fixing halotolerant cyanobacteria via abiotic stresses and genetic engineering.

  14. 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.

  15. Lupane-type pentacyclic triterpenes in Langmuir monolayers: a synchrotron radiation scattering study.

    Science.gov (United States)

    Broniatowski, Marcin; Flasiński, Michał; Wydro, Paweł

    2012-03-20

    Lupane-type pentacyclic triterpenes (lupeol, betulin, and betulinic acid) are natural products isolated from various plant sources. The terpenes exhibit a vast spectrum of biological activity and are applied in therapies for different diseases, among which the anticancer, anti-HIV, antihypercholesteremic, and antiinflammatory are the most promising. These chemicals possess amphiphilic structure and were proved to interact strongly with biomembranes, which can be the key stage in their mechanism of action. In our studies, we applied Langmuir monolayers as versatile models of biomembranes. It turned out that the three investigated terpenes are capable of stable monolayer formation; however, these monolayers differ profoundly regarding their physicochemical characteristics. In our research, we applied the Langmuir technique (surface pressure-mean molecular area (π-A) isotherm registration) coupled with Brewster angle microscopy (BAM), but the main focus was on the synchrotron radiation scattering method, grazing incidence X-ray diffraction (GIXD), which provides information on the amphiphilic molecule ordering in the angström scale. It was proved that all the investigated terpenes form crystalline phases in their monolayers. In the case of lupeol, only the closely packed upright phase was observed, whereas for betulin and betulinic acid, the phase situation was more complex. Betulinic acid molecules can be organized in an upright phase, which is crystalline, and in a tilted phase, which is amorphous. The betulin film is a conglomerate of an upright crystalline monolayer phase, tilted amorphous monolayer phase, and a crystalline tilted bilayer. In our paper, we discuss the factors leading to the formation of the observed phases and the implications of our results to the therapeutic applications of the native lupane-type triterpenes.

  16. 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.

  17. In situ detection of anaerobic alkane metabolites in subsurface environments.

    Science.gov (United States)

    Agrawal, Akhil; Gieg, Lisa M

    2013-01-01

    Alkanes comprise a substantial fraction of crude oil and refined fuels. As such, they are prevalent within deep subsurface fossil fuel deposits and in shallow subsurface environments such as aquifers that are contaminated with hydrocarbons. These environments are typically anaerobic, and host diverse microbial communities that can potentially use alkanes as substrates. Anaerobic alkane biodegradation has been reported to occur under nitrate-reducing, sulfate-reducing, and methanogenic conditions. Elucidating the pathways of anaerobic alkane metabolism has been of interest in order to understand how microbes can be used to remediate contaminated sites. Alkane activation primarily occurs by addition to fumarate, yielding alkylsuccinates, unique anaerobic metabolites that can be used to indicate in situ anaerobic alkane metabolism. These metabolites have been detected in hydrocarbon-contaminated shallow aquifers, offering strong evidence for intrinsic anaerobic bioremediation. Recently, studies have also revealed that alkylsuccinates are present in oil and coal seam production waters, indicating that anaerobic microbial communities can utilize alkanes in these deeper subsurface environments. In many crude oil reservoirs, the in situ anaerobic metabolism of hydrocarbons such as alkanes may be contributing to modern-day detrimental effects such as oilfield souring, or may lead to more beneficial technologies such as enhanced energy recovery from mature oilfields. In this review, we briefly describe the key metabolic pathways for anaerobic alkane (including n-alkanes, isoalkanes, and cyclic alkanes) metabolism and highlight several field reports wherein alkylsuccinates have provided evidence for anaerobic in situ alkane metabolism in shallow and deep subsurface environments.

  18. In situ detection of anaerobic alkane metabolites in subsurface environments

    Directory of Open Access Journals (Sweden)

    Lisa eGieg

    2013-06-01

    Full Text Available Alkanes comprise a substantial fraction of crude oil and refined fuels. As such, they are prevalent within deep subsurface fossil fuel deposits and in shallow subsurface environments such as aquifers that are contaminated with hydrocarbons. These environments are typically anaerobic, and host diverse microbial communities that can potentially use alkanes as substrates. Anaerobic alkane biodegradation has been reported to occur under nitrate-reducing, sulfate-reducing, and methanogenic conditions. Elucidating the pathways of anaerobic alkane metabolism has been of interest in order to understand how microbes can be used to remediate contaminated sites. Alkane activation primarily occurs by addition to fumarate, yielding alkylsuccinates, unique anaerobic metabolites that can be used to indicate in situ anaerobic alkane metabolism. These metabolites have been detected in hydrocarbon-contaminated shallow aquifers, offering strong evidence for intrinsic anaerobic bioremediation. Recently, studies have also revealed that alkylsuccinates are present in oil and coal seam production waters, indicating that anaerobic microbial communities can utilize alkanes in these deeper subsurface environments. In many crude oil reservoirs, the in situ anaerobic metabolism of hydrocarbons such as alkanes may be contibuting to modern-day detrimental effects such as oilfield souring, or may lead to more benefical technologies such as enhanced energy recovery from mature oilfields. In this review, we briefly describe the key metabolic pathways for anaerobic alkane (including n-alkanes, isoalkanes, and cyclic alkanes metabolism and highlight several field reports wherein alkylsuccinates have provided evidence for anaerobic in situ alkane metabolism in shallow and deep subsurface environments.

  19. 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.

  20. Evaporating Drops of Alkane Mixtures

    OpenAIRE

    Guéna, Geoffroy; Poulard, Christophe; Cazabat, Anne-Marie

    2005-01-01

    22 pages 9 figures; 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.

  1. 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

    . At the 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...

  2. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers

    NARCIS (Netherlands)

    Badali, D. S.; Gengler, R. Y. N.; Miller, R. J. D.

    2016-01-01

    A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the "medium" energy regime (1-10

  3. Microbial biosynthesis of alkanes.

    Science.gov (United States)

    Schirmer, Andreas; Rude, Mathew A; Li, Xuezhi; Popova, Emanuela; del Cardayre, Stephen B

    2010-07-30

    Alkanes, the major constituents of gasoline, diesel, and jet fuel, are naturally produced by diverse species; however, the genetics and biochemistry behind this biology have remained elusive. Here we describe the discovery of an alkane biosynthesis pathway from cyanobacteria. The pathway consists of an acyl-acyl carrier protein reductase and an aldehyde decarbonylase, which together convert intermediates of fatty acid metabolism to alkanes and alkenes. The aldehyde decarbonylase is related to the broadly functional nonheme diiron enzymes. Heterologous expression of the alkane operon in Escherichia coli leads to the production and secretion of C13 to C17 mixtures of alkanes and alkenes. These genes and enzymes can now be leveraged for the simple and direct conversion of renewable raw materials to fungible hydrocarbon fuels.

  4. 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.

  5. Study of polystyrene-poly(ethylene oxide) diblock copolymer monolayers as barriers to protein adsorption

    Science.gov (United States)

    Jogikalmath, Gangadhar

    Protein adsorption resistant surfaces find use in many biomedical applications, such as catheters, dialysis devices and biosensors that involve blood contacting surfaces. To ensure long-term functioning of a device in an environment containing protein, there is a need to produce homogeneous surfaces that are resistant to protein adsorption. A polymer brush covered surface, produced by either physical adsorption or chemical grafting of hydrophilic polymers to surfaces, is one of the approaches used in creating such surfaces. High grafting densities needed to make an effective barrier are usually not realized in chemical grafting/adsorption from solution, due to self-exclusion of surface grafted molecules. In this dissertation polymer brush surfaces formed by chemically grafted PEO molecules and transferred monolayers of PS-b-PEO diblock copolymers are investigated using atomic force microscopy (AFM), surface plasmon resonance (SPR) and surface pressure measurement techniques. An AFM adhesion mapping technique was used to evaluate the surface heterogeneity of chemically modified PEO and transferred diblock copolymer monolayer surfaces. The behavior of PS-b-PEO molecules at the air-water interface was studied using Langmuir trough. The stability of transferred diblock copolymer monolayers was investigated using AFM. Using SPR, protein adsorption to the diblock copolymer layers was investigated as a function of protein size (using HSA and ferritin) as a function of grafting density of PEO in the monolayer. It was seen that a lower density of the PS-b-PEO monolayer was sufficient to prevent ferritin adsorption (larger protein) while a higher density brush layer was required to achieve complete prevention of HSA adsorption to the surface. The effect of mobility of the polymer brush layer on protein adsorption prevention was analyzed using SPR and surface pressure measurements. It was seen that the copolymer monolayer (at the air-buffer interface) rearranged itself to

  6. Interactions of doxorubicin with self-assembled monolayer-modified electrodes: electrochemical, surface plasmon resonance (SPR), and gravimetric studies.

    Science.gov (United States)

    Nieciecka, Dorota; Krysinski, Pawel

    2011-02-01

    We present the results on the partitioning of doxorubicin (DOX), a potent anticancer drug, through the model membrane system, self-assembled monolayers (SAMs) on gold electrodes. The monolayers were formed from alkanethiols of comparable length with different ω-terminal groups facing the aqueous electrolyte: the hydrophobic -CH(3) groups for the case of dodecanethiol SAMs or hydrophilic -OH groups of mercaptoundecanol SAMs. The electrochemical experiments combined with the surface plasmon resonance (SPR) and gravimetric studies show that doxorubicin is likely adsorbed onto the surface of hydrophilic monolayer, while for the case of the hydrophobic one the drug mostly penetrates the monolayer moiety. The adsorption of the drug hinders further penetration of doxorubicin into the monolayer moiety.

  7. X-ray diffraction studies of organic monolayers on the surface of water

    Energy Technology Data Exchange (ETDEWEB)

    Dutta, P.; Peng, J.B.; Lin, B.; Ketterson, J.B.; Prakash, M.; Georgopoulos, P.; Ehrlich, S.

    1987-05-25

    We have used synchrotron radiation to study organic monolayers on water (''Langmuir films''). At high monolayer pressures, lead stearate (Pb(C/sub 17/H/sub 35/COO)/sub 2/) shows a powder peak at 1.60 A/sup -1/, implying an area per unit cell of 17.8 A/sup 2/ if the lattice is triangular. The correlation length is about 250 A. Lignoceric acid (C/sub 23/H/sub 47/COOH) shows a similar peak even though no heavy ions are attached. When the pressure is reduced, the peak in lead stearate does not observably move or broaden; below the ''knee'' in the isotherm, however, the peak height decreases slowly with increasing area, implying a first-order melting transition.

  8. 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.

  9. 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.

  10. Studies on Absorption and Tansport of Limoninoids from Fructus Evodiae in Caco-2 Cell Monolayer Model

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Objective To study the intestinal absorption and transepithelial transport of three limoninoids: evodol (EVO), limonin (LIM), and shihulimonin A (SHIA), isolated from Fructus Evodiae [the unripe fruit of Evodia rutaecarpa and Evodia rutaecarpa var. bodinieri] in the human intestine. Methods The in vitro cultured human colon carcinoma cell line, Caco-2 cell monolayer model, was applied to studying the absorption and transepithelial transport of the three limoninoids from apical (AP) to basolateral (BL) side and from BL to AP side. The three limoninoids were measured by reversed-phase high performance liquid chromatography coupled with ultraviolet absorption detector. Transport parameters and apparent permeability coefficients (Papp) were then calculated and compared with those of Propranolol as a control substance of high permeability and Atenolol as a control substance of poor permeability. Results The Papp value of EVO and LIM from AP to BL side for absorption and transport were 1.78 × 10-5 cm/s and 1.16 × 10-5 cm/s, respectively, which was comparable to that of Propranolol with Papp 2.18 × 10-5 cm/s. Conclusion The absorption and transport of both EVO and LIM are main passive diffusion as the dominating process in Caco-2 cell monolayer model, and they were estimated to be high absorbed compounds. SHIA in Caco-2 cell monolayer model may be involved in metabolism in the transport processes.

  11. Revealing fibrinogen monolayer conformations at different pHs: electrokinetic and colloid deposition studies.

    Science.gov (United States)

    Nattich-Rak, Małgorzata; Adamczyk, Zbigniew; Wasilewska, Monika; Sadowska, Marta

    2015-07-01

    Adsorption mechanism of human fibrinogen on mica at different pHs is studied using the streaming potential and colloid deposition measurements. The fibrinogen monolayers are produced by a controlled adsorption under diffusion transport at pH of 3.5 and 7.4. Initially, the electrokinetic properties of these monolayers and their stability for various ionic strength are determined. It is shown that at pH 3.5 fibrinogen adsorbs irreversibly on mica for ionic strength range of 4×10(-4) to 0.15 M. At pH 7.4, a partial desorption is observed for ionic strength below 10(-2) M. This is attributed to the desorption of the end-on oriented molecules whereas the side-on adsorbed molecules remain irreversibly bound at all ionic strengths. The orientation of molecules and monolayer structure is evaluated by the colloid deposition measurements involving negatively charged polystyrene latex microspheres, 820 nm in diameter. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential is observed. At pH 3.5 measurable deposition of latex is observed even at low ionic strength where the approach distance of latex particles exceeded 70 nm. At pH 7.4 this critical distance is 23 nm. This confirms that fibrinogen monolayers formed at both pHs are characterized by the presence of the side-on and end-on oriented molecules that prevail at higher coverage range. It is also shown that positive charge is located at the end parts of the αA chains of the adsorbed fibrinogen molecules. Therefore, it is concluded that the colloid deposition method is an efficient tool for revealing protein adsorption mechanisms at solid/electrolyte interfaces.

  12. A comparative study for Hydrogen storage in metal decorated graphyne nanotubes and graphyne monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Jinlian [Department of Physics, Xiangtan University, Xiangtan, Hunan 411105 (China); Guo, Yanhua [College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009 (China); Zhang, Yun; Tang, Yingru [Department of Physics, Xiangtan University, Xiangtan, Hunan 411105 (China); Cao, Juexian, E-mail: jxcao@xtu.edu.cn [Department of Physics, Xiangtan University, Xiangtan, Hunan 411105 (China); Beijing Computational Science Research Center, Beijing 100084 (China)

    2015-11-15

    A comparative study for hydrogen storage in metal decorated graphyne nanotubes and graphyne monolayers has been investigated within the framework of first-principle calculations. Our results show that the binding energies of Li, Ca, Sc, Ti on graphyne nanotubes are stronger than that on graphyne monolayers. Such strong binding would prevent the formation of metal clusters on graphyne nanotubes. From the charge transfer and partial density of states, it is found that the curvature effect of nanotubes plays an important role for the strong binding strength of metal on graphyne nanotubes. And the hydrogen storage capacity is 4.82 wt%, 5.08 wt%, 4.88 wt%, 4.76 wt% for Li, Ca, Sc, Ti decorated graphyne nanotubes that promise a potential material for storing hydrogen. - Graphical abstract: Metal atoms (Li, Ca, Sc and Ti) can strongly bind to graphyne nanotubes to avoid the formation of metal clusters, and a capacity of Ca@graphyne nanotube is 5.08 wt% which is close to the requirement of DOE in 2015. Twenty-four hydrogen molecules absorb to Ti-decorated graphyne nanotube. - Highlights: • The binding strength for metal on graphyne nanotubes is much stronger than that on γ-graphyne monolayer. • Metal atoms can strongly bind to the curving triangle acetylenes rings to avoid the formation of metal clusters. • A capacity of Ca@graphyne nanotube is 5.08 wt% which is close to the requirement of DOE in 2015.

  13. 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

    to the interface. At still higher coverages and at temperatures below the bulk melting point at T-b=341 K, solid bulk particles coexist on top of the "perpendicular film." For higher temperatures in the range T-bT-s, a uniformly thick fluid film wets to the parallel film phase. This structure of the alkane/SiO2...

  14. Mechanic studies of monolayer formation on H-Si(111) surfaces

    NARCIS (Netherlands)

    Rijksen, B.M.G.

    2012-01-01

    Covalently attached organic monolayers on silicon surfaces form thermally and chemically stable platforms for (bio)functionalization of the surface. Recent advances in monolayer formation – yielding increases in monolayer quality and the complete exclusion of oxygen at modified surfaces &ndash

  15. 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.

  16. 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

  17. 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...

  18. Infrared Absorption Spectroscopic Study on Reaction between Self-Assembled Monolayers and Atmospheric-Pressure Plasma

    Directory of Open Access Journals (Sweden)

    Masanori Shinohara

    2015-01-01

    Full Text Available Plasma is becoming increasingly adopted in bioapplications such as plasma medicine and agriculture. This study investigates the interaction between plasma and molecules in living tissues, focusing on plasma-protein interactions. To this end, the reaction of air-pressure air plasma with NH2-terminated self-assembled monolayer is investigated by infrared spectroscopy in multiple internal reflection geometry. The atmospheric-pressure plasma decomposed the NH2 components, the characteristic units of proteins. The decomposition is attributed to water clusters generated in the plasma, indicating that protein decomposition by plasma requires humid air.

  19. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers.

    Science.gov (United States)

    Badali, D S; Gengler, R Y N; Miller, R J D

    2016-05-01

    A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the "medium" energy regime (1-10 kV). An extremely compact design, in combination with low bunch charges, allows for high quality diffraction in a lensless geometry. The measured and simulated characteristics of the experimental system reveal sub-picosecond temporal resolution, while demonstrating the ability to produce high quality diffraction patterns from atomically thin samples.

  20. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers

    Directory of Open Access Journals (Sweden)

    D. S. Badali

    2016-05-01

    Full Text Available A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the “medium” energy regime (1–10 kV. An extremely compact design, in combination with low bunch charges, allows for high quality diffraction in a lensless geometry. The measured and simulated characteristics of the experimental system reveal sub-picosecond temporal resolution, while demonstrating the ability to produce high quality diffraction patterns from atomically thin samples.

  1. Alkane dimers interaction

    DEFF Research Database (Denmark)

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

    2010-01-01

    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...

  2. Sub-monolayers of carbon on alpha-iron facets: an ab-initio study

    CERN Document Server

    Riikonen, S; Nieminen, R M

    2010-01-01

    Motivated by recent in situ studies of carbon nanotube growth from large transition-metal nanoparticles, we study various alpha-iron (ferrite) facets at different carbon concentrations using ab initio methods. The studied (110), (100) and (111) facets show qualitatively different behaviour when carbon concentration changes. In particular, adsorbed carbon atoms repel each other on the (110) facet, resulting in carbon dimer and graphitic material formation. Carbon on the (100) facet forms stable structures at concentrations of about 0.5 monolayer and at 1.0 monolayer this facet becomes unstable due to a frustration of the top layer iron atoms. The stability of the (111) facet is weakly affected by the amount of adsorbed carbon and its stability increases further with respect to the (100) facet with increasing carbon concentration. The exchange of carbon atoms between the surface and sub-surface regions on the (111) facet is easier than on the other facets and the formation of carbon dimers is exothermic. These ...

  3. Topological properties of phosphorene-like monolayer group V semiconductor compounds: a first-principles study

    CERN Document Server

    Yu, Weiyang; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu

    2015-01-01

    To broaden the scope of layered group V semiconductors, we propose a class of phosphorenelike monolayer group V semiconductor compounds, such as PN, AsP, SbP and BiP with black-phosphorus-like alpha-phase and blue-phosphorus-like beta-phase, respectively. Using first-principles density functional theory calculations, we study yet unrealized structural phases of these compounds. We find the black-phosphorus-like alpha-phase to be almost equally stable as the blue-phosphorus-like beta-phase. alpha-phase compounds display a direct band gap, while beta-phase compounds display an indirect band gap. Both alpha-phase and beta-phase monolayers depends sensitively on the in-layer strain, as is studied with alpha- and beta- AsP and BiP. Further more, We find that alpha-BiP presents an intriguing topological state when gained a compress from -8% to -10%, offering an unprecedented tunability in structural and electronic properties of BiP compound.

  4. Flash kinetics in liquefied noble gases: Studies of alkane activation and ligand dynamics at rhodium carbonyl centers, and a search for xenon-carbene adducts

    Energy Technology Data Exchange (ETDEWEB)

    Yeston, Jake Simon [Univ. of California, Berkeley, CA (United States)

    2001-01-01

    A general introduction is given to place the subsequent chapters in context for the nonspecialist. Results are presented from a low temperature infrared (IR) flash kinetic study of C-H bond activation via photoinduced reaction of Cp*Rh(CO)2 (1) with linear and cyclic alkanes in liquid krypton and liquid xenon solution. No reaction was observed with methane; for all other hydrocarbons studied, the rate law supports fragmentation of the overall reaction into an alkane binding step followed by an oxidative addition step. For the binding step, larger alkanes within each series (linear and cyclic) interact more strongly than smaller alkanes with the Rh center. The second step, oxidative addition of the C-H bond across Rh, exhibits very little variance in the series of linear alkanes, while in the cyclic series the rate decreases with increasing alkane size. Results are presented from an IR flash kinetic study of the photoinduced chemistry of Tp*Rh(CO)2 (5; Tp* = hydridotris(3,5-dimethylpyrazolyl)borato) in liquid xenon solution at –50 °C. IR spectra of the solution taken 2 μs after 308 nm photolysis exhibit two transient bands at 1972-1980 cm-1 and 1992-2000 cm-1, respectively. These bands were assigned to (η3-Tp*)Rh(CO)•Xe and (η2-Tp*)Rh(CO)•Xe solvates on the basis of companion studies using Bp*Rh(CO)2 (9; Bp* = dihydridobis(3,5-dimethyl pyrazolyl)borato). Preliminary kinetic data for reaction of 5 with cyclohexane in xenon solution indicate that both transient bands still appear and that their rates of decay correlate with formation of the product Tp*Rh(CO)(C6H11)(H). The preparation and reactivity of the new complex Bp*Rh(CO)(pyridine) (11) are described. The complex reacts with CH3I to yield the novel Rh carbene hydride complex HB(Me2pz)2Rh(H)(I)(C5H5N)(C(O)Me) (12), resulting from formal addition of CH

  5. Molecular Simulation study of Alkyl Monolayers on Si(III) Surface

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The structure of eight-carbon monolayers on the H-terminated Si(III) surface was investigated by molecular simulation method. The best substitution percent 50% for octene or octyne-derived monolayer can be obtained using molecular mechanics calculation. And the densely packed, well-ordered monolayer on Si(III) surface can be shown through energy minimization in the suitable-size simulation cell.

  6. 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.

  7. The insertion of human apolipoprotein H into phospholipid membranes: a monolayer study.

    Science.gov (United States)

    Wang, S X; Cai, G P; Sui, S F

    1998-10-15

    Apolipoprotein H (ApoH) is a plasma glycoprotein isolated from human serum. The interactions of ApoH with lipid membrane were reported to be essential for its physiological and pathogenic roles. In this paper we studied the ability of ApoH to insert into phospholipid membranes using the monolayer approach. The results show that ApoH is surface active and can insert into the lipid monolayers. The insertion ability of ApoH is stronger when a higher content of negatively charged lipids is present in the membrane. The acidic-pH and low-ionic-strength conditions will also enhance ApoH insertion, but these factors may not have much influence on the final insertion ability of ApoH, suggesting that, in the mechanism of ApoH insertion, not only electrostatic forces, but also hydrophobic interactions, are evidently involved. Modification by heat inactivation and reduction/alkylation does not change the critical insertion pressure (pic) of ApoH, suggesting a stable domain, maybe a linear sequence motif, but not the native three-dimensional structure of ApoH, is responsible for its insertion. The extent to which insertion of ApoH into phospholipid membranes may facilitate the 'immune cleaning' of plasma liposomes is discussed.

  8. Theoretical Study of Monolayer and Double-Layer Waveguide Love Wave Sensors for Achieving High Sensitivity.

    Science.gov (United States)

    Li, Shuangming; Wan, Ying; Fan, Chunhai; Su, Yan

    2017-03-22

    Love wave sensors have been widely used for sensing applications. In this work, we introduce the theoretical analysis of the monolayer and double-layer waveguide Love wave sensors. The velocity, particle displacement and energy distribution of Love waves were analyzed. Using the variations of the energy repartition, the sensitivity coefficients of Love wave sensors were calculated. To achieve a higher sensitivity coefficient, a thin gold layer was added as the second waveguide on top of the silicon dioxide (SiO₂) waveguide-based, 36 degree-rotated, Y-cut, X-propagating lithium tantalate (36° YX LiTaO₃) Love wave sensor. The Love wave velocity was significantly reduced by the added gold layer, and the flow of wave energy into the waveguide layer from the substrate was enhanced. By using the double-layer structure, almost a 72-fold enhancement in the sensitivity coefficient was achieved compared to the monolayer structure. Additionally, the thickness of the SiO₂ layer was also reduced with the application of the gold layer, resulting in easier device fabrication. This study allows for the possibility of designing and realizing robust Love wave sensors with high sensitivity and a low limit of detection.

  9. Adsorption of alkyltrimethylammonium bromides at water/alkane interfaces: competitive adsorption of alkanes and surfactants.

    Science.gov (United States)

    Fainerman, V B; Mucic, N; Pradines, V; Aksenenko, E V; Miller, R

    2013-11-12

    The adsorption of members of the homologous series of alkyl trimethylammonium bromides (C(n)TAB) is studied at water/alkane interfaces by drop profile analysis tensiometry. The results are discussed in terms of a competitive adsorption process of alkane and surfactant molecules. A thermodynamic model, derived originally for the adsorption of surfactant mixtures, is adapted such that it describes a competitive adsorption of the surfactant molecules from the aqueous phase and alkane molecules from the oil phase. This new model involves the interspecies attraction coefficient, which mutually increases the adsorption activities of the alkane and C(n)TAB. The effects of the alkyl chain length n of C(n)TABs and the influence of the number of C atoms in the alkane chain are discussed, and the physical quantities are compared to those determined at the aqueous solution/air interface. The new theoretical model for aqueous solution/oil interfaces is also compared to a theory that does not consider the adsorption of alkane. The proposed new model demonstrates good agreement with the experimental data.

  10. Green synthesis and anti-inflammatory studies of a series of 1,1-bis(heteroaryl)alkane derivatives.

    Science.gov (United States)

    Jaratjaroonphong, Jaray; Tuengpanya, Surisa; Saeeng, Rungnapha; Udompong, Sarinporn; Srisook, Klaokwan

    2014-08-18

    Molecular iodine has been used as an efficient catalyst for a double Friedel-Crafts reaction of various heteroarenes, i.e. 2-methylfuran, 2-ethylfuran, 2-methylthiophene, pyrrole, N-methylpyrrole and indole, using aldehydes as alkylating agents under "open-flask" conditions with toluene or water as the reaction media. In the presence of 10 mol% iodine in toluene at room temperature, both aliphatic and aromatic aldehydes reacted smoothly to give the corresponding bis(heteroaryl)alkanes in good to excellent yields. Interestingly, with water as the solvent, the bis(heteroaryl)alkane adducts were obtained in moderate to good yields. The use of mild reaction conditions, low catalyst loadings, and eco-friendly reagents in a single step synthesis are the advantages of the present procedure. In an effort to discover novel non-steroidal anti-inflammatory agents, the synthesized bis(heteroaryl)alkanes were evaluated for the anti-inflammatory activity in the lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage model. These compounds (50 μM) significantly inhibited NO production and did not exhibit significant cytotoxic effects on macrophage cells. Among them, bis[(5-methyl)2-furyl](4-nitrophenyl) methane exhibited the most potent inhibition of NO with IC50 value of 42.4 ± 1.9, which is similar to that of the positive control, aminoguanidine (43.3 ± 2.5 μM). Thus, the bis[(5-methyl)2-furyl](4-nitrophenyl) methane could be considered a lead compound for the development of novel anti-inflammatory agents.

  11. Systematic study of aggregation structure and thermal behavior of a series of unique H-shape alkane molecules.

    Science.gov (United States)

    Yamamoto, Hiroko; Tashiro, Kohji; Nemoto, Norio; Motoyama, Yukihiro; Takahashi, Yoshiaki

    2011-08-11

    The H-shape alkanes of various arm lengths have been synthesized successfully through the Grignard reaction. The detailed investigation of these novel compounds may allow us to widen the topological chemistry field furthermore. The molecular form and molecular packing structure in the crystal lattice have been revealed successfully on the basis of X-ray structure analysis as well as the analysis of Raman longitudinal acoustic modes (LAM) sensitive to the alkyl zigzag chain segments. The molecular conformation in the crystal lattice is deformed markedly from the originally imagined H-shape. In the cases of C3HOH to C6HOH, for example, the molecules are packed in a complicated manner and the OH···O hydrogen bonds govern the whole intermolecular interactions mainly. Since the alkyl segmental length is not very long, the conformational change is not very drastic, i.e., the small configurational entropy. Synergic effect of the hydrogen bonds and the small configurational entropy gives the higher melting point as known from the thermal data. On the other hand, in the cases of C10HOH and C12HOH, one of the long alkyl chain arms is found to be bent by 90° so that all of the alky chain segments of planar-zigzag conformation can be packed as closely as possible, and the intermolecular OH···O hydrogen bonds are also formed effectively without any mistake. As a result, the contribution of nonbonded intra- and intermolecular van der Waals interactions between the trans-zigzag alkyl chain segments become major, and the coupling of this enthalpy effect with the larger configurational entropy effect of the molecular shape results in the decrement of the melting point which approaches gradually that of longer n-alkane compound. In this way a sensitive balance between the nonbonded van der Waals interactions, the OH···O hydrogen bonds, as well as the configurational entropy effect gives the characteristic thermal behavior of the H-shape compounds. The thus

  12. 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.

  13. Insights into rapid climate change: A high resolution, compound-specific n-alkane δD study of the 8.2 ka event (Tenaghi Philippon, Greece)

    Science.gov (United States)

    Schemmel, F.; Niedermeyer, E.; Schwab, V.; Pross, J.; Mulch, A.

    2013-12-01

    Despite being characterized as remarkably stable, the Holocene climate has experienced a number of abrupt, relatively short-term climate changes. Arguably the most prominent climate perturbation, the 8.2 ka event, was caused by the catastrophic drainage of the ice-dammed Laurentide ice-lake into the North Atlantic, leading to a severe weakening of thermohaline circulation, causing a decline in temperature and significant changes in atmospheric circulation in the Northern Hemisphere, especially in the North Atlantic realm and Europe. Being located between the climate systems of the higher and lower latitudes, the Mediterranean region is particularly susceptible to rapid climate change. Available proxy data and climate models provide first-order insight into the impact of the 8.2 ka event in this area but often lack the temporal resolution to supply information about changes in seasonality, hence severely hindering the understanding of rapid climate changes and revealing the need for high resolution terrestrial archives. Here, we present a multi-proxy, high resolution stable isotope study across the 8.2 ka event on a peat core from the classical site of Tenaghi Philippon (NE Greece). We aim to characterize the effects of changing temperature and rainfall patterns by using compound-specific δD values of the long-chain n-alkanes as a proxy for terrestrial (summer) precipitation. We compare changes in hydrogen isotopic composition to the concentration of the long-chain n-alkanes as well as to δ13Cbulk measurements of the organic material and high-resolution palynomorphic data from the same core. Analysis of 35 samples of telmatic peat shows significant decreases in concentration of the long-chain n-alkanes along with strong positive shifts in δD (over 40 ‰ in δDC29) during the 8.2 ka event. The general trend of δD of the n-Alkanes n-C27, n-C29 and n-C31 coincides with changes in δ13Cbulk, and to some degree reflects changes in moisture availability. We attribute

  14. Case studies on the formation of chalcogenide self-assembled monolayers on surfaces and dissociative processes

    Directory of Open Access Journals (Sweden)

    Yongfeng Tong

    2016-02-01

    Full Text Available This report examines the assembly of chalcogenide organic molecules on various surfaces, focusing on cases when chemisorption is accompanied by carbon–chalcogen atom-bond scission. In the case of alkane and benzyl chalcogenides, this induces formation of a chalcogenized interface layer. This process can occur during the initial stages of adsorption and then, after passivation of the surface, molecular adsorption can proceed. The characteristics of the chalcogenized interface layer can be significantly different from the metal layer and can affect various properties such as electron conduction. For chalcogenophenes, the carbon–chalcogen atom-bond breaking can lead to opening of the ring and adsorption of an alkene chalcogenide. Such a disruption of the π-electron system affects charge transport along the chains. Awareness about these effects is of importance from the point of view of molecular electronics. We discuss some recent studies based on X-ray photoelectron spectroscopy that shed light on these aspects for a series of such organic molecules.

  15. Electrochemical Study of Biotin-Modified Self-Assembled Monolayers: Recommendations for Robust Preparation

    Directory of Open Access Journals (Sweden)

    Richard J.C. Brown

    2006-01-01

    Full Text Available The development of the underpinning methodology for the production of robust, well-formed, and densely packed biotin-HPDP functionalised gold surfaces, the crucial first step in immobilising bimolecules on surfaces, is described. Self-assembled monolayers (SAMs with biotin end-groups were prepared on polycrystalline gold surfaces according to a published method. The layers formed were studied using cyclic voltammetry to determine the composition of the layer and its quality. Crystal impedance spectroscopy was also applied as a complimentary indicator of the composition of the layer.For the first time, the effect of assembly time on the properties of the layer was studied along with the composition of the layer and the ability of the precursor molecule to self-assemble by oxidative addition.

  16. 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...

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

    Science.gov (United States)

    Cho, M J; Adson, A; Kezdy, F J

    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.

  18. 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...

  19. Novel transparent zirconium-based hybrid material with multilayered nanostructures: studies of surface dewettability toward alkane liquids.

    Science.gov (United States)

    Masheder, Benjamin; Urata, Chihiro; Cheng, Dalton F; Hozumi, Atsushi

    2013-01-01

    We have successfully prepared unique inorganic-organic hybrid materials that demonstrate excellent transparency and dewettability toward various alkane liquids (n-hexadecane, n-dodecane and n-decane) without relying on conventional surface roughening and perfluorination. Such coatings were made using a novel family of hybrid materials generated by substituting carboxylic acids, with a range of alkyl chain lengths (CH(3)(CH(2))(x-2)COOH where x = total carbon number, i.e., 10, 12, 14, 16, 18, 22, or 24, into zirconium (Zr) tetra-propoxide complexes. This precursor was then mixed with acetic acid and spincast to produce transparent thin Zr-carboxylic acid (ZrCA(x)) hybrid films using a nonhydrolytic sol-gel process. Fourier transform infrared spectroscopy provided proof of Zr-O-Zr network formation in the films upon casting and also followed changes to the physical nature (liquid-like or solid-like) of the alkyl chain assemblies depending upon alkyl chain length. X-ray diffractometry revealed that the hybrid films prepared using the longer chain carboxylic acids (ZrCA(x≥18)) spontaneously self-assembled into lamella structures with d-spacings ranging from 29.5 to 32.7 Angstroms, depending on the length of the alkyl chain. On the other hand the remaining films (ZrCA(xoleophobicity among the seven hybrid films. In particular, small volume alkane droplets (5 μL) could be easily set in motion to move across and off ZrCA(14) film surfaces without pinning at low tilt angles (~6°).

  20. Do n-alkane biomarkers in soils/sediments reflect the δ²H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research.

    Science.gov (United States)

    Zech, Michael; Zech, Roland; Rozanski, Kazimierz; Gleixner, Gerd; Zech, Wolfgang

    2015-01-01

    During the last decade compound-specific deuterium ((2)H) analysis of plant leaf wax-derived n-alkanes has become a promising and popular tool in paleoclimate research. This is based on the widely accepted assumption that n-alkanes in soils and sediments generally reflect δ(2)H of precipitation (δ(2)H(prec)). Recently, several authors suggested that δ(2)H of n-alkanes (δ(2)H(n-alkanes)) can also be used as a proxy in paleoaltimetry studies. Here, we present results from a δ(2)H transect study (∼1500 to 4000 m above sea level [a.s.l.]) carried out on precipitation and soil samples taken from the humid southern slopes of Mt. Kilimanjaro. Contrary to earlier suggestions, a distinct altitude effect in δ(2)H(prec) is present above ∼2000 m a.s.l., that is, δ(2)H(prec) values become more negative with increasing altitude. The compound-specific δ(2)H values of nC27 and nC29 do not confirm this altitudinal trend, but rather become more positive both in the O-layers (organic layers) and the Ah-horizons (mineral topsoils). Although our δ(2)H(n-alkane) results are in agreement with previously published results from the southern slopes of Mt. Kilimanjaro [Peterse F, van der Meer M, Schouten S, Jia G, Ossebaar J, Blokker J, Sinninghe Damsté J. Assessment of soil n-alkane δD and branched tetraether membrane lipid distributions as tools for paleoelevation reconstruction. Biogeosciences. 2009;6:2799-2807], a re-interpretation is required given that the δ(2)H(n-alkane) results do not reflect the δ(2)H(prec) results. The theoretical framework for this re-interpretation is based on the evaporative isotopic enrichment of leaf water associated with the transpiration process. Modelling results show that relative humidity, decreasing considerably along the southern slopes of Mt. Kilimanjaro (from 78% in ∼2000 m a.s.l. to 51% in 4000 m a.s.l.), strongly controls δ(2)H(leaf water). The modelled (2)H leaf water enrichment along the altitudinal transect matches well the

  1. 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...

  2. 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.

  3. Studies of Self-assembled Monolayers Formed by Imidazoline on Iron Surface by SEM and SECM

    Institute of Scientific and Technical Information of China (English)

    Xiu Yu LIU; Shen Hao CHEN; Shuai MIAO; Su Xiang WU; Li Xia SHEN; Yuan Xing CAI; Hong Yan ZHAI

    2006-01-01

    The self-assembled monolayers (SAMs) of imidazoline (IM) on the iron surface were characterized by scanning electron microscope (SEM) and scanning electrochemical microscopy(SECM). The results showed that SAMs were an effective inhibition film for iron.

  4. Studies on the interactions between parabens and lipid membrane components in monolayers at the air/aqueous solution interface.

    Science.gov (United States)

    Flasiński, Michał; Gawryś, Maciej; Broniatowski, Marcin; Wydro, Paweł

    2016-04-01

    The interactions between parabens (PBs) and lipid components of mammalian and bacterial cell membranes were investigated in model systems of Langmuir monolayers. Me-, Et-, Pr- and Bu-paraben studied in this paper are frequently applied as cosmetics and food preservatives, since they possess broad antimicrobial activity. The mode of PB action is connected with their incorporation into the membrane of bacterial organisms, however; it is not known what is the role of the respective lipid species in this mechanism. This problem is crucial to understand the differences in paraben activity toward individual microorganisms and to shed the light onto the problem of PB cytotoxicity reported in studies on mammalian cells. In this paper, the mentioned aspects were investigated with application of the Langmuir monolayer technique complemented with BAM and GIXD. Our experiments revealed that the influence of PBs depends on their chemical structure, solution concentration and on the class of lipid. The strongest modification of the monolayer characteristics, leading to its collapse at low surface pressure, occurred in the presence of BuPB, having the largest chain. PBs interact preferentially with the monolayers possessing low degree of condensation, whereas for LC state, the effect was weaker and observed only as modification of the 2D unit cells. In the model systems, PBs interact with phospholipids characteristic for mammalian membranes (phosphatidylcholine) stronger than with bacterial (phosphatidylglycerol and cardiolipin). This strong influence of parabens on the model systems composed of animal lipids may explain cytotoxic activity of these preservatives.

  5. Anisotropic mechanical properties and Stone-Wales defects in graphene monolayer: A theoretical study

    Energy Technology Data Exchange (ETDEWEB)

    Fan, B.B. [School of Materials Science and Engineering, Zhengzhou University, Henan 450001 (China); Yang, X.B. [Department of Physics, South China University of Technology, Guangzhou 510640 (China); Zhang, R., E-mail: zhangray@zzu.edu.c [School of Materials Science and Engineering, Zhengzhou University, Henan 450001 (China); Zhengzhou Institute of Aeronautical Industry Management, Henan 450046 (China)

    2010-06-14

    We investigate the mechanical properties of graphene monolayer via the density functional theoretical (DFT) method. We find that the strain energies are anisotropic for the graphene under large strain. We attribute the anisotropic feature to the anisotropic sp{sup 2} hybridization in the hexagonal lattice. We further identify that the formation energies of Stone-Wales (SW) defects in the graphene monolayer are determined by the defect concentration and also the direction of applied tensile strain, correlating with the anisotropic feature.

  6. Isolating the non-polar contributions to the intermolecular potential for water-alkane interactions.

    Science.gov (United States)

    Ballal, Deepti; Venkataraman, Pradeep; Fouad, Wael A; Cox, Kenneth R; Chapman, Walter G

    2014-08-14

    Intermolecular potential models for water and alkanes describe pure component properties fairly well, but fail to reproduce properties of water-alkane mixtures. Understanding interactions between water and non-polar molecules like alkanes is important not only for the hydrocarbon industry but has implications to biological processes as well. Although non-polar solutes in water have been widely studied, much less work has focused on water in non-polar solvents. In this study we calculate the solubility of water in different alkanes (methane to dodecane) at ambient conditions where the water content in alkanes is very low so that the non-polar water-alkane interactions determine solubility. Only the alkane-rich phase is simulated since the fugacity of water in the water rich phase is calculated from an accurate equation of state. Using the SPC/E model for water and TraPPE model for alkanes along with Lorentz-Berthelot mixing rules for the cross parameters produces a water solubility that is an order of magnitude lower than the experimental value. It is found that an effective water Lennard-Jones energy ε(W)/k = 220 K is required to match the experimental water solubility in TraPPE alkanes. This number is much higher than used in most simulation water models (SPC/E-ε(W)/k = 78.2 K). It is surprising that the interaction energy obtained here is also higher than the water-alkane interaction energy predicted by studies on solubility of alkanes in water. The reason for this high water-alkane interaction energy is not completely understood. Some factors that might contribute to the large interaction energy, such as polarizability of alkanes, octupole moment of methane, and clustering of water at low concentrations in alkanes, are examined. It is found that, though important, these factors do not completely explain the anomalously strong attraction between alkanes and water observed experimentally.

  7. 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.

  8. How to reduce resistance to movement of alkane liquid drops across tilted surfaces without relying on surface roughening and perfluorination.

    Science.gov (United States)

    Urata, Chihiro; Masheder, Benjamin; Cheng, Dalton F; Hozumi, Atsushi

    2012-12-21

    Alkylsilane-derived monolayer-covered surfaces generally display a reasonably good level of hydrophobicity but poor oleophobicity. Here, we demonstrate that the physical attributes of alkylsilane-derived surfaces (liquid-like or solid-like) are dependent on the alkyl chain length and density, and these factors subsequently have significant influence upon the dynamic dewetting behavior toward alkanes (C(n)H(2n+2), where n = 7-16). In this study, we prepared and characterized hybrid films through a simple sol-gel process based on the cohydrolysis and co-condensation of a mixture of a range of alkyltriethoxysilanes (C(n)H(2n+1)Si(OEt)(3), where n = 3, 6, 8, 10, 12, 14, 16, and 18) and tetramethoxysilane (TMOS). Surprisingly, when the carbon number (C(n)) of alkyl chain was 10 and below, the produced hybrid films were all smooth, highly transparent, and showed negligible contact angle (CA) hysteresis. On these hybrid surfaces, 5 μL drops of alkanes (n-hexadecane, n-dodecane, and n-decane) could move easily at low tilt angles (oleophobicity. Therefore, the critical C(n) of alkyl chain used for determining final dynamic dewetting behavior against alkane liquids was 12. Furthermore, our hybrid surfaces exhibited excellent antifingerprint properties, particularly demonstrating low adhesion and easy removal from the surface.

  9. Dynamics of monolayers adsorbed at the solid-liquid interface

    Energy Technology Data Exchange (ETDEWEB)

    Clarke, Stuart M. [BP Institute, Department of Chemistry, Univ. of Cambridge (United Kingdom); Inaba, Akira [Department of Chemistry, Osaka Univ., Osaka (Japan); Arnold, Thomas [Physical and Theoretical Chemistry Laboratory, Univ. of Oxford (United Kingdom); Thomas, Robert K.; Castro, Miguel A. [Instituto de Ciencia de Materiale de Sevilla, Avda. Americo Vespucio (Spain)

    2001-03-01

    Recently we have demonstrated, using a variety of techniques including calorimetry and neutron diffraction, the existence of translationally ordered two-dimensional phases of short chain n-alkanes (CnH2n+2) on the surface of graphite. Dodecane (n=12) is unusual in that it is found from diffraction experiments to adopt a structure with parallel molecules, similar to that seen for the odd alkanes, and exhibits a monolayer phase transition at 281 K, before the layer melts at 286 K. This additional transition is reminiscent of the rotator phase transitions seen in the longer bulk alkanes. In this work we present elastic incoherent neutron scattering (EISF) data which probe the dynamics of the monolayer and clearly demonstrate that the adsorbed layer is indeed far from static but has a high degree of rotational mobility. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    Camacho-Mojica, Dulce C.; López-Urías, Florentino, E-mail: flo@ipicyt.edu.mx

    2016-04-15

    Graphical abstract: Single-layer honeycomb heterojunction structures based on alternated and coupled ribbons of BAs and AlN 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 ribbon widths joined along the zigzag and armchair edges. Optimized heterojunction geometries results revealed that BAs narrow ribbons exhibit a corrugation effect at the interface due to a lattice mismatch. From formation energy calculations, it was found that zigzag heterojunctions are more stable than the armchair heterojunctions. - Highlights: • We design new 2D-semiconductor heterojunction nanostructures. • Monolayers formed by alternated strips (heterojunctions) of aluminum-nitride and boron-arsenide, with graphene-like structure are explored by DFT method. • Due to the lattice mismatch, an effect of corrugation was observed in heterojunctions AlN and BAs. • Electronic band gaps are strongly dependent on width and chirality (zigzag or armchair) of the strips. • Formation energy calculations revealed that zigzag heterojunctions are more stable than the armchair heterojunctions. - Abstract: 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

  11. First-principle studies of electronic structure and magnetic excitations in FeSe monolayer

    Science.gov (United States)

    Bazhirov, Timur; Cohen, Marvin L.

    2013-03-01

    Recent experimental advances made it possible to study single-layered superconducting systems of iron-based compounds. The results show evidence of significant enhancement of superconducting properties compared to the bulk case. We use first-principle pseudopotential density functional theory techniques and the local spin-density approximation to study the electronic properties of an FeSe monolayer in different spin configurations. The results show that the experimental shape of the Fermi surface is best described by a checkerboard antiferromagnetic (AFM) spin arrangement. To explore the underlying pairing mechanism, we study the evolution of the non-magnetic to the AFM-ordered structures under constrained magnetization, and we estimate the electronic coupling to magnetic excitations involving transfer and increase of iron magnetic moments and compare it to the electron-phonon coupling. Finally, we simulate the substrate-induced interaction by using uniform charge doping and show that the latter can lead to an increase in the density of states at the Fermi level and possibly produce higher superconducting transition temperatures. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility

  12. Wetting transitions of simple liquid films adsorbed on selfassembled monolayer substrates: an ellipsometric study

    Science.gov (United States)

    Batchelder, D. N.; Cheng, Y. L.; Evans, S. D.; Henderson, J. R.

    We report on an ellipsometric experimental study designed to explore the relevance of the wetting phase diagram predicted by liquid state physics of basic models, to the wide class of simple organic liquid films that adsorb from saturated vapour onto planar substrates at room temperature. The wetting properties are explored by measuring adsorption isotherms in the approach to saturation, in particular, for adsorption of n -hexane on a variety of specially constructed substrates (self-assembled monolayers) spanning a wide range of surface energy, and by carrying out the microscopic equivalent of contact angle experiments at saturation. We locate a wetting transition, which in our case is continuous, and then study its properties in detail. The general prediction of the wetting phase diagram, that wetting transitions should be ubiquitous in nature and readily located via control over the substrate field, is supported by our data, but the quantitative nature of the thick film adsorption regime is not in agreement with Lifshitz theory. This conclusion supports the work of a variety of earlier related studies, but contrasts with recent results for adsorption onto the surface of water. In addition, the correlation length determined from our complete wetting adsorption isotherms is mesoscopic, suggesting that equilibrium statistical mechanics of simple models of inhomogeneous fluids cannot explain the data.

  13. Studies on the formation of long-chain dicarboxylic acids from pure n-alkanes by a mutant of Canadida tropicalis

    Energy Technology Data Exchange (ETDEWEB)

    Hill, F.F.; Venn, I.; Lukas, K.L.

    1986-05-01

    Individual n-alkanes, from C/sub 11/-C/sub 16/, were metabolized by a mutant of Candida tropicalis. This strain was selected for its inability to grow in the presence of dodecanedioic acid and dodecane as the sole carbon source. Transformations were studied in fed-batch cultures. Undecane was only poorly transformed, but from dodecane to hexadecane high transformation yields were achieved. Maximum yield of acid-precipitable long-chain dioic acids was obtained with tridecane as substrate. All the products were mixtures of different acids. Besides the ..cap alpha..,..omega..-alkanedioic acids, the 3-hydroxy derivatives of longchain ..cap alpha..,..omega..-alkanedioic acids and dioic acids with a shortened carbon chain were found.

  14. Slow Diffusive Motions in a Monolayer of Tetracosane Molecules Adsorbed on Graphite

    DEFF Research Database (Denmark)

    Taub, H.; Hansen, Flemming Yssing; Criswell, L.;

    2004-01-01

    Monolayers of intermediate-length alkane molecules such as tetracosane (n-C24H50 or C24) serve as prototypes for studying the interfacial dynamics of more complex polymers, including bilayer lipid membranes. Using high-resolution quasielastic neutron scattering (QNS) and exfoliated graphite...... to a temperature of similar to230 K, we observe the QNS energy width to be dispersionless, consistent with molecular dynamics simulations showing rotational motion of the molecules about their long axis. At 260 K, the QNS energy width begins to increase with wave vector transfer, suggesting onset of nonuniaxial...... rotational motion and bounded translational motion. We continue to observe QNS up to the monolayer melting temperature at similar to340 K where our simulations indicate that the only motion slow enough to be visible within our energy window results from the creation of gauche defects in the molecules....

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

    Institute of Scientific and Technical Information of China (English)

    Fen-LanZi; Xiao-haiCai; 等

    2001-01-01

    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 7.2mg/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 sturcture study,it is Cu-O octahedral Coordination and coordination distance change in comparation with pure crystalline Cuo on the surface CuO/TiO2 that have catalytic activity.

  16. Anomalous Lithium Adsorption Propensity of Monolayer Carbonaceous Materials: A Density Functional Study

    Indian Academy of Sciences (India)

    SWATI PANIGRAHI; DEIVASIGAMANI UMADEVI; G NARAHARI SASTRY

    2016-10-01

    Interaction between lithium and carbonaceous materials has gained a lot of importance in lithium battery industry as an important source of energy and storage. The size, dimension, curvature and chirality of the carbonaceous materials are found to be very important factors in controlling the sequential binding oflithium. The propensity of lithium binding to the monolayer carbonaceous materials has been studied using Density functional theory (DFT). Structural and energetical parameters of the complexes have been analyzed through interaction energy, sequential energy, Mulliken population analysis and spin density distribution. Spindensity of odd Li doped systems reveals the preferences for addition of further lithium atoms on the surface. Upon analyzing the interaction energy in armchair carbon nanotubes (A-CNTs) and zigzag carbon nanotubes (Z-CNTs), it has been observed that external and internal surfaces of CNTs have contrasting binding preferences for sequential addition of Li atoms. Internal surface is found to be more feasible site for lithium adsorption than the external surface. This current study provides fundamental understanding of the mechanism of lithium adsorption in lithium battery.

  17. 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.

  18. Monte Carlo study of fractional (1 1 1) monolayers of EuTe

    CERN Document Server

    Holl, S; Giebultowicz, T; Krenn, H

    2000-01-01

    The magnetic properties depending on the temperature and magnetic field of few (1 1 1) monolayers of antiferromagnetic EuTe are analyzed by means of Monte Carlo simulations. We apply a classical Heisenberg as well as a XY model Hamiltonian with ferromagnetic nearest neighbor (J sub 1 =0.06 K) and antiferromagnetic next-nearest-neighbor (J sub 2 =-0.16 K) exchange constants. Furthermore, dipolar interaction is included which links the spin space to real space and therefore introduces the easy plane anisotropy. Structures consisting of incomplete sets of monolayers, e.g. two perfect monolayers and a finite island as the third monolayer, are investigated. We analyze the atomic spin patterns and compare these results with total magnetization and neutron diffraction experiments. It is emphasized that EuTe in the reduced dimensional limit of few odd numbers of monolayers exhibits a field-induced uniaxial anisotropy, even in the frame of isotropic Heisenberg exchange interaction. A concomitant field-parallel ferrima...

  19. 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.

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

    Science.gov (United States)

    Bugler, John; Somers, Kieran P; Silke, Emma J; Curran, Henry J

    2015-07-16

    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.

  1. 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.

  2. 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.

  3. Stability and Electronic Properties of Hydrogenated MoS2 Monolayer: A First-Principles Study.

    Science.gov (United States)

    Zhang, Weibin; Zhang, Zhijun; Yang, Woochul

    2015-10-01

    First-principles total energy studies are used to investigate the stability of hydrogenated MoS2 monolayer (MoS2-Hx) (x = 1-8), which is a compound with different numbers of H atoms adsorbed on the MoS2 surface. Energetically, the S-top side of the MoS2 is found to be the most favorable for H-adsorption. H2S and graphene are well-known to be stable, and MoS2-Hx is predicted to be even more stable because its binding energy is lower than that of H2S and its formation energy and adsorption energy are lower than those of graphene. The analysis of the electronic density distribution and the orbital hybrid also shows that MoS2-Hx forms stable structures. In addition, the influence of the number of the adsorbed H-atoms in the MoS2-Hx on the electronic structure of the compound is also investigated. The MoS2-Hx band structure exhibits a dispersion and the MoS2-Hx band gap gradually decreases from 1.72 eV to 0 eV as the number of adsorbed H atoms increases. The corresponding work function increases as a result of the strengthening of the dipole moment formed between the H atoms that are adsorbed and the hydrogenated MoS2.

  4. [Establishment of Caco-2 cell monolayer model with collagen coating 6-well plates for study of traditional Chinese medicine prescription].

    Science.gov (United States)

    Yang, Yan-Fang; Wu, Ni; Yang, Xiu-Wei

    2014-02-01

    Caco-2 cell monolayer model is widely utilized in drug absorption study and 12-well transwellTM plates were commonly used to study the absorption of different kinds of natural products. To establish a stable method for the study of traditional Chinese medicine prescription, 6-well plates were chosen because of the larger well volumes than 12-well plates. To study the impacts of collagen kinds, coating density as well as coating time on the cell culture, the transepithelial electrical resistance of Caco-2 cell monolayers grown on different collagen coating transwells was determined, and the permeations of propranolol and atenolol as standard markers were detected with HPLC. The results showed that the kinds of collagen, the different coating densities and coating time of rat tail collagen had no significant influences on the Caco-2 cell monolayer integrality and absorption capacity. 6-well plates coated with 2 micro g Scm-2 rat tail collagen for 1 hour were enough reliable and suitable for the study of traditional Chinese medicine prescription in vitro.

  5. Immobilization of rhodium complexes at thiolate monolayers on gold surfaces : Catalytic and structural studies

    NARCIS (Netherlands)

    Belser, T; Stöhr, Meike; Pfaltz, A

    2005-01-01

    Chiral rhodium-diphosphine complexes have been incorporated into self-assembled thiolate monolayers (SAMS) on gold colloids. Catalysts of this type are of interest because they combine properties of homogeneous and heterogeneous systems. In addition, it should be possible to influence the catalytic

  6. Monolayers of CF4 Adsorbed on Graphite, Studied by Synchrotron X-Ray Diffraction

    DEFF Research Database (Denmark)

    Kjær, Kristian; Nielsen, Mourits; Bohr, Jakob;

    1982-01-01

    With synchrotron x-ray diffraction we have measured the phase diagram of CF4 monolayers adsorbed on the graphite substrate UCAR-ZYX. We have found four two-dimensional crystalline phases including the 2×2 commensurate structure. Between this and the denser incommensurate hexagonal phase we find...

  7. Melting of short 1-alcohol monolayers on water: Thermodynamics and x-ray scattering studies

    DEFF Research Database (Denmark)

    Berge, B.; Konovalov, O.; Lajzerowicz, J.

    1994-01-01

    From surface tension measurements we extract the melting entropy Delta S-2D of fatty-alcohol monolayers on water. Delta S-2D is found to be 4(kB)/mol lower than in the bulk. Because of the role of the conformational entropy, the melting transition is discontinuous for long chains, but tends...

  8. Microcomputer interface for computer-controlled enzyme kinetic studies with the monolayer technique

    NARCIS (Netherlands)

    Haas, G. de; Donné-Op den Kelder, G.M.; Wildt, H. van der

    1984-01-01

    Abstract A microcomputer interface for computer-assisted monolayer experiments was developed, tested, and used for analysis of the enzymatic hydrolysis by pancreatic phospholipases A2 (EC 3.1.1.4) of 1,2-didodecanoyl-sn-glycero-3-sulfate monitored under constant surface pressure. The interface descr

  9. Selective electrophilic activation of alkanes

    Energy Technology Data Exchange (ETDEWEB)

    Sommer, J.; Bukala, J. (Universite Louis Pasteur, Strasbourg (France))

    1993-07-01

    One major drawback for the direct use of alkanes as chemicals is their chemical inertness toward most of the usual reagents. For this reason, costly, large-scale refinery operations such as catalytic reforming and vapocracking are needed, which necessitate the use of noble metal catalysts and/or high temperature to activate the strong C-H and C-C bonds and yield the primary chemical building blocks such as ethylene, propylene, butadiene, benzene, toluene, and xylene. In response to the challenge to use more economically a larger share of alkanes, and increasing number of research groups are working on the activation functionalization processes of the saturated hydrocarbon C-H bond. The goal is to overcome smoothly and selectively the chemical inertness of the starting (paraffinic) material. A book and special issue have been published recently on this subject. Protonated alkanes are reaction intermediates in superacid-catalyzed protolysis. Protonation occurs on all C-C and C-H [sigma]-bonds independently of the further reactivity of the protonated alkane as confirmed by using [sup 2]H labeled superacids. Direct and selective C-H bond protolysis is limited to tertiary alkanes whereas linear alkanes undergo less selective C-C bond cleavage. 31 refs., 3 figs.

  10. Interactions of a Tetrazine Derivative with Biomembrane Constituents: A Langmuir Monolayer Study.

    Science.gov (United States)

    Nakahara, Hiromichi; Hagimori, Masayori; Mukai, Takahiro; Shibata, Osamu

    2016-07-05

    Tetrazine (Tz) is expected to be used for bioimaging and as an analytical reagent. It is known to react very fast with trans-cyclooctene under water in organic chemistry. Here, to understand the interaction between Tz and biomembrane constituents, we first investigated the interfacial behavior of a newly synthesized Tz derivative comprising a C18-saturated hydrocarbon chain (rTz-C18) using a Langmuir monolayer spread at the air-water interface. Surface pressure (π)-molecular area (A) and surface potential (ΔV)-A isotherms were measured for monolayers of rTz-C18 and biomembrane constituents such as dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), dipalmitoyl phosphatidylethanolamine (DPPE), palmitoyl sphingomyelin (PSM), and cholesterol (Ch). The lateral interaction between rTz-C18 and the lipids was thermodynamically elucidated from the excess Gibbs free energy of mixing and two-dimensional phase diagram. The binary monolayers except for the Ch system indicated high miscibility or affinity. In particular, rTz-C18 was found to interact more strongly with DPPE, which is a major constituent of the inner surface of cell membranes. The phase behavior and morphology upon monolayer compression were investigated by using Brewster angle microscopy (BAM), fluorescence microscopy (FM), and atomic force microscopy (AFM). The BAM and FM images of the DPPC/rTz-C18, DPPG/rTz-C18, and PSM/rTz-C18 systems exhibited a coexistence state of two different liquid-condensed domains derived mainly from monolayers of phospholipids and phospholipids-rTz-C18. From these morphological observations, it is worthy to note that rTz-C18 is possible to interact with a limited amount of the lipids except for DPPE.

  11. Structural insights into diversity and n-alkane biodegradation mechanisms of alkane hydroxylases

    OpenAIRE

    Yurui eJi; Guannan eMao; Yingying eWang; Mark eBartlam

    2013-01-01

    Environmental microbes utilize four degradation pathways for the oxidation of n-alkanes. Although the enzymes degrading n-alkanes in different microbes may vary, enzymes functioning in the first step in the aerobic degradation of alkanes all belong to the alkane hydroxylases. Alkane hydroxylases are a class of enzymes that insert oxygen atoms derived from molecular oxygen into different sites of the alkane terminus (or termini) depending on the type of enzymes. In this review, we summarize th...

  12. Study of PEGylated lipid layers as a model for PEGylated liposome surfaces: molecular dynamics simulation and Langmuir monolayer studies.

    Science.gov (United States)

    Stepniewski, Michał; Pasenkiewicz-Gierula, Marta; Róg, Tomasz; Danne, Reinis; Orlowski, Adam; Karttunen, Mikko; Urtti, Arto; Yliperttula, Marjo; Vuorimaa, Elina; Bunker, Alex

    2011-06-21

    We have combined Langmuir monolayer film experiments and all-atom molecular dynamics (MD) simulation of a bilayer to study the surface structure of a PEGylated liposome and its interaction with the ionic environment present under physiological conditions. Lipids that form both gel and liquid-crystalline membranes have been used in our study. By varying the salt concentration in the Langmuir film experiment and including salt at the physiological level in the simulation, we have studied the effect of salt ions present in the blood plasma on the structure of the poly(ethylene glycol) (PEG) layer. We have also studied the interaction between the PEG layer and the lipid bilayer in both the liquid-crystalline and gel states. The MD simulation shows two clear results: (a) The Na(+) ions form close interactions with the PEG oxygens, with the PEG chains forming loops around them and (b) PEG penetrates the lipid core of the membrane for the case of a liquid-crystalline membrane but is excluded from the tighter structure of the gel membrane. The Langmuir monolayer results indicate that the salt concentration affects the PEGylated lipid system, and these results can be interpreted in a fashion that is in agreement with the results of our MD simulation. We conclude that the currently accepted picture of the PEG surface layer acting as a generic neutral hydrophilic polymer entirely outside the membrane, with its effect explained through steric interactions, is not sufficient. The phenomena we have observed may affect both the interaction between the liposome and bloodstream proteins and the liquid-crystalline-gel transition and is thus relevant to nanotechnological drug delivery device design.

  13. A Quantitative Study of Tethered Chains in Various Solution Conditions Using Langmuir Diblock Copolymer Monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Kent, Michael S.

    1999-08-13

    This article summarizes our investigations of tethered chain systems using Langmuir monolayer of polydimethysiloxane-poly styrene (PDMS-PS) diblock copolymers on organic liquids. In this system, the PDMS block adsorbs to the air surface while the PS block dangles into the subphase liquid. The air surface can be made either repulsive or attractive for the tethered PS chain segments by choosing a subphase liquid which has a surface tension lower or greater than that of PS, respectively. The segment profile of the PS block is determined by neutron reflection as a function of the surface density, the molecular weights of the PS and PDMS blocks, and the solution conditions. We cover the range of reduced surface density (SIGMA) characteristic of the large body of data in the literature for systems of chains tethered onto solid surfaces from dilute solution in good or theta solvent conditions (SIGMA < 12). We emphasize quantitative comparisons with analytical profile forms and scaling predictions. We find that the strong-stretching limit invoked in analytical SCF and scaling theories is not valid over this Z range. On the other hand, over a large portion of this range (SIGMA < 5) tethered layers are well described by a renormalization group theory addressing weakly interacting or noninteracting chains. Simultaneous with the study of the profile form, the free energy of the chains is examined through the surface tension. A strong increase in the surface pressure is observed with increasing surface density which determines the maximum surface density which can be achieved. This apparently nonequilibrium effect is attributed to steric interactions and limited lateral interpenetration. This effect may explain several outstanding discrepancies regarding the adsorption of end-functionalized chains and diblock copolymers onto solid surfaces.

  14. 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.

  15. Reconstitution of plant alkane biosynthesis in yeast demonstrates that Arabidopsis ECERIFERUM1 and ECERIFERUM3 are core components of a very-long-chain alkane synthesis complex.

    Science.gov (United States)

    Bernard, Amélie; Domergue, Frédéric; Pascal, Stéphanie; Jetter, Reinhard; Renne, Charlotte; Faure, Jean-Denis; Haslam, Richard P; Napier, Johnathan A; Lessire, René; Joubès, Jérôme

    2012-07-01

    In land plants, very-long-chain (VLC) alkanes are major components of cuticular waxes that cover aerial organs, mainly acting as a waterproof barrier to prevent nonstomatal water loss. Although thoroughly investigated, plant alkane synthesis remains largely undiscovered. The Arabidopsis thaliana ECERIFERUM1 (CER1) protein has been recognized as an essential element of wax alkane synthesis; nevertheless, its function remains elusive. In this study, a screen for CER1 physical interaction partners was performed. The screen revealed that CER1 interacts with the wax-associated protein ECERIFERUM3 (CER3) and endoplasmic reticulum-localized cytochrome b5 isoforms (CYTB5s). The functional relevance of these interactions was assayed through an iterative approach using yeast as a heterologous expression system. In a yeast strain manipulated to produce VLC acyl-CoAs, a strict CER1 and CER3 coexpression resulted in VLC alkane synthesis. The additional presence of CYTB5s was found to enhance CER1/CER3 alkane production. Site-directed mutagenesis showed that CER1 His clusters are essential for alkane synthesis, whereas those of CER3 are not, suggesting that CYTB5s are specific CER1 cofactors. Collectively, our study reports the identification of plant alkane synthesis enzymatic components and supports a new model for alkane production in which CER1 interacts with both CER3 and CYTB5 to catalyze the redox-dependent synthesis of VLC alkanes from VLC acyl-CoAs.

  16. 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.

  17. The work function of sub-monolayer cesium-covered gold: A photoelectronspectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    LaRue, J.L.; White, J.D.; Nahler, N.H.; Liu, Z.; Sun, Y.; Pianetta, P.A.; Auerbach, D.J.; Wodtke, A.M.; /SLAC, SSRL /UC, Santa Barbara, Chem. Dept.

    2008-06-13

    Using visible and X-ray photoelectron spectroscopy we measured the work function of a Au(111) surface at a well-defined sub-monolayer coverage of Cs. For a Cs coverage producing a photoemission maximum with a He-Ne laser, the work function is 1.61 {+-} 0.08 eV consistent with previous assumptions used to analyze vibrationally promoted electron emission. A discussion of possible Cs layer structures is also presented.

  18. First-principles study on magnetism of Ru monolayer under an external electric field

    Science.gov (United States)

    Kitaoka, Yukie; Imamura, Hiroshi

    Electric field control of magnetic properties such as magnetic moment and magnetic anisotropy has been attracted. For the 4 d TM films, on the other hand, it was recently reported that the ferromagnetism Pd thin-film is induced by application of an external electric field otherwise Pd thin-film shows paramagnetic. However, little attention has been paid to the magnetism of other 4 d TMs. Here, we investigate the magnetism of the free-standing Ru monolayer and that on MgO(001) substrate under an external electric field by using first-principles FLAPW method. We found that the free-standing Ru monolayer is ferromagnet with magnetic moment of 1.50 ¥muB /atom. The MA energy is 3.45 meV/atom, indicating perpendicular MA, at zero electric field (E=0) and increases up to 3.84 meV/atom by application of E=1 (V/¥AA). The Ru monolayer on MgO(001) substrate is also ferromagnet with magnetic moment of 0.89 ¥muB /atom. The MA energy is 1.49 meV/atom, indicating perpendicular MA, at E=0 and decreases to 1.33 meV/atom by application of E=1 (V/¥AA).

  19. 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

    surfaces at low temperatures) are observed to decrease smoothly above 40 K, falling from 100 to 15 Å at 80 K. Little if any positional order remains at temperatures where the nearest-neighbor distance in the monolayer matches that of a registered √3×√3 phase. The spectrum of neutrons inelastically......Diffraction of neutrons from 36 Ar monolayers adsorbed on graphite basal planes indicates that an ordered, two-dimensional (2D) triangular lattice is formed at low temperature. The lattice constant is found to be slightly larger than that of the bulk 3D solid but significantly smaller than...... that of a registered √3×√3 overlayer. Thermal expansion of the monolayer is anomalously large; up to 60 K the linear expansion is 4.5 times greater than in the 3D solid. There is no evidence of a sharp melting transition. Instead, the positional correlations (which extend to the full dimensions of the crystallite...

  20. Discrimination of abiogenic and biogenic alkane gases

    Institute of Scientific and Technical Information of China (English)

    DAI JinXing; MI JingKui; LI ZhiSheng; HU AnPing; YANG Chun; ZHOU QingHua; SHUAI YanHua; ZHANG Ying; MA ChengHua; ZOU CaiNeng; ZHANG ShuiChang; LI Jian; NI YunYan; HU GuoYi; LUO Xia; TAO ShiZhen; ZHU GuangYou

    2008-01-01

    We have combined the analytical data of the carbon isotope distribution pattern, R/Ra and cliche values of abiogenic and biogenic (referring to the therrnogenic 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 (Δ13c1>Δ13c2>Δ13c3>Δ13c4) with Δ13c1>-30‰ in general; 3) Gases with R/Ra>0.5 and Δ13c1- Δ13c2>0 are of abiogenic origin; 4) Gases (methane) with CH4/3He≤106 are of abiogenic origin, whereas gases with CH4/3He≥1011 are of biogenic origin.

  1. 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.

  2. 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.

  3. High-Yield Excited Triplet States in Pentacene Self-Assembled Monolayers on Gold Nanoparticles through Singlet Exciton Fission.

    Science.gov (United States)

    Kato, Daiki; Sakai, Hayato; Tkachenko, Nikolai V; Hasobe, Taku

    2016-04-18

    One of the major drawbacks of organic-dye-modified self-assembled monolayers on metal nanoparticles when employed for efficient use of light energy is the fact that singlet excited states on dye molecules can be easily deactivated by means of energy transfer to the metal surface. In this study, a series of 6,13-bis(triisopropylsilylethynyl)pentacene-alkanethiolate monolayer protected gold nanoparticles with different particle sizes and alkane chain lengths were successfully synthesized and were employed for the efficient generation of excited triplet states of the pentacene derivatives by singlet fission. Time-resolved transient absorption measurements revealed the formation of excited triplet states in high yield (172±26 %) by suppressing energy transfer to the gold surface.

  4. Study of two grafting methods for obtaining a 3-aminopropyltriethoxysilane monolayer on silica surface.

    Science.gov (United States)

    Simon, A; Cohen-Bouhacina, T; Porté, M C; Aimé, J P; Baquey, C

    2002-07-15

    In order to establish a 3-aminopropyltriethoxysilane (APTES) grafting procedure with limited number of APTESs noncovalently linked to the silica surface, two different methods of grafting (in acid-aqueous solution and in anhydrous solution) were compared. The grafted surface state was investigated by atomic force microscopy (AFM). The stability of the grafting was checked at different temperatures by AFM. Continuous and plane APTES grafted surfaces were successfully prepared using both grafting preparations. The grafting in an anhydrous solution behaves homogeneously and stably compared to the grafting in an acid-aqueous solution. Moreover, with anhydrous solution, results showed that a unique monolayer of APTES was grafted.

  5. First-principles study of the contractive reconstruction of gold and silver monolayers on gold, silver and aluminum

    Energy Technology Data Exchange (ETDEWEB)

    Takeuchi, Noboru.

    1990-11-16

    Using first-principles calculations in conjunction with modeling techniques, the author has investigated the structures of Au and Ag monolayers on a number of metal surfaces. Au(100) has a c(26 {times} 68) surface unit cell and the reconstruction has been interpreted as the top layer transforming to a contracted hexagonal-close-packed layer, superimposed on the square lattice of the underlying substrate atoms. Similar reconstructions have been observed on the 5d fcc metals Ir and Pt, but not in the 4d Rh, Pd, and Ag. The author studied the energetics of a monolayer of Au and Ag using first-principles calculations. The author found that it is energetically favorable for both Au and Ag to transform from a square to hexagonal arrangement and to contract to a higher surface density, but Au gains substantially more energy than Ag. This is true both for a monolayer in isolation as well as on top of a jellium surface. The author also calculated the mismatch energy (energy loss when the top layer loses registry with the substrate) for Au and Ag, and found that Ag has a slightly higher mismatch energy. The first-principles results thus offer a strong indication that Au(100) can reconstruct but Ag will not. The reconstruction is further studied with a 2 dimensional Frenkel-Kontorowa model, with parameters extracted from the total energy calculations. The author found that it is indeed energetically favorable for the top layer of Au(100), but not for Ag, to transform to a hexagonal-close-packed structure and contract. 85 refs., 34 figs., 8 tabs.

  6. 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.

  7. From monomer to monolayer: a global optimisation study of (ZnO)n nanoclusters on the Ag surface.

    Science.gov (United States)

    Demiroglu, Ilker; Woodley, Scott M; Sokol, Alexey A; Bromley, Stefan T

    2014-12-21

    We employ global optimisation to investigate how oxide nanoclusters of increasing size can best adapt their structure to lower the system energy when interacting with a realistic extended metal support. Specifically, we focus on the (ZnO)@Ag(111) system where experiment has shown that the infinite Ag(111)-supported ZnO monolayer limit corresponds to an epitaxially 7 : 8 matched graphene-like (Zn(3)O(3))-based hexagonal sheet. Using a two-stage search method based on classical interatomic potentials and then on more accurate density functional theory, we report global minina candidate structures for Ag-supported (ZnO)n cluster with sizes ranging from n = 1-24. Comparison with the respective global minina structure of free space (ZnO)n clusters reveals that the surface interaction plays a decisive role in determining the lowest energy Ag-supported (ZnO)n cluster structures. Whereas free space (ZnO)n clusters tend to adopt cage-like bubble structures as they grow larger, Ag-supported (ZnO)n clusters of increasing size become progressively more like planar cuts from the infinite graphene-like ZnO single monolayer. This energetic favourability for planar hexagonal Ag-supported clusters over their 3D counterparts can be partly rationalised by the ZnO-Ag(111) epitaxial matching and the increased number of close interactions with the Ag surface. Detailed analysis shows that this tendency can also be attributed to the capacity of 2D clusters to distort to improve their interaction with the Ag surface relative to more rigid 3D bubble cluster isomers. For the larger sized clusters we find that the adsorption energies and most stable structural types appear to be rather converged confirming that our study makes a bridge between the Ag-supported ZnO monomer and the infinite Ag-supported ZnO monolayer.

  8. 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.

  9. CO oxidation catalyzed by silicon carbide (SiC) monolayer: A theoretical study.

    Science.gov (United States)

    Wang, Nan; Tian, Yu; Zhao, Jingxiang; Jin, Peng

    2016-05-01

    Developing metal-free catalysts for CO oxidation has been a key scientific issue in solving the growing environmental problems caused by CO emission. In this work, the potential of the silicon carbide (SiC) monolayer as a metal-free catalyst for CO oxidation was systematically explored by means of density functional theory (DFT) computations. Our results revealed that CO oxidation reaction can easily proceed on SiC nanosheet, and a three-step mechanism was proposed: (1) the coadsorption of CO and O2 molecules, followed by (2) the formation of the first CO2 molecule, and (3) the recovery of catalyst by a second CO molecule. The last step is the rate-determining one of the whole catalytic reaction with the highest barrier of 0.65eV. Remarkably, larger curvature is found to have a negative effect on the catalytic performance of SiC nanosheet for CO oxidation. Therefore, our results suggested that flat SiC monolayer is a promising metal-free catalyst for CO oxidation.

  10. 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 g...

  11. Variation in n-Alkane Distributions of Modern Plants: Questioning Applications of n-Alkanes in Chemotaxonomy and Paleoecology

    Science.gov (United States)

    Bush, R. T.; McInerney, F. A.

    2010-12-01

    Long chain n-alkanes (n-C21 to n-C37) are synthesized as part of the epicuticular leaf wax of terrestrial plants and are among the most recognizable and widely used plant biomarkers. n-Alkane distributions have been utilized in previous studies on modern plant chemotaxonomy, testing whether taxa can be identified based on characteristic n-alkane profiles. Dominant n-alkanes (e.g. n-C27 or n-C31) have also been ascribed to major plant groups (e.g. trees or grasses respectively) and have been used in paleoecology studies to reconstruct fluctuations in plant functional types. However, many of these studies have been based on relatively few modern plant data; with the wealth of modern n-alkane studies, a more comprehensive analysis of n-alkanes in modern plants is now possible and can inform the usefulness of n-alkane distributions as paleoecological indicators. The work presented here is a combination of measurements made using plant leaves collected from the Chicago Botanic Garden and a compilation of published literature data from six continents. We categorized plants by type: angiosperms, gymnosperms, woody plants, forbs, grasses, ferns and pteridophytes, and mosses. We then quantified n-alkane distribution parameters such as carbon preference index (CPI), average chain length (ACL), and dispersion (a measure of the spread of the profile over multiple chain lengths) and used these to compare plant groups. Among all plants, one of the emergent correlations is a decrease in dispersion with increasing CPI. Within and among plant groups, n-alkane distributions show a very large range of variation, and the results show little or no correspondence between broad plant groups and a single dominant n-alkane or a ratio of n-alkanes. These findings are true both when data from six continents are combined and when plants from a given region are compared (North America). We also compared the n-alkane distributions of woody angiosperms, woody gymnosperms, and grasses with one

  12. The adsorption of CO and NO on the MoS{sub 2} monolayer doped with Au, Pt, Pd, or Ni: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Dongwei, E-mail: dwmachina@126.com [School of Physics, Anyang Normal University, Anyang 455000 (China); Ju, Weiwei [College of Physics and Engineering, Henan University of Science and Technology, Luoyang 471023 (China); Li, Tingxian; Zhang, Xiwei [School of Physics, Anyang Normal University, Anyang 455000 (China); He, Chaozheng, E-mail: hecz2013@nynu.edu.cn [Physics and Electronic Engineering College, Nanyang Normal University, Nanyang 473061 (China); Ma, Benyuan [Physics and Electronic Engineering College, Nanyang Normal University, Nanyang 473061 (China); Lu, Zhansheng; Yang, Zongxian [College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007 (China)

    2016-10-15

    Graphical abstract: The MoS{sub 2} monolayers doped with Au, Pt, Pd, or Ni show enhanced adsorption and sensitivity toward CO or NO molecule. - Highlights: • CO and NO adsorption on the doped MoS{sub 2} monolayers is theoretically studied. • CO and NO are chemisorbed on the doped MoS{sub 2} monolayers. • Charge transfer can be observed between the adsorbed molecule and the substrates. • Molecular adsorption can induce the change in electronic structures of the doped MoS{sub 2} monolayers. - Abstract: By performing the first-principles calculation, the adsorption of CO and NO molecules on the Au, Pt, Pd, or Ni doped MoS{sub 2} monolayer has been studied. The interaction between CO or NO with the doped MoS{sub 2} monolayer is strong and belongs to the chemisorption, as evidenced by the large adsorption energy and the short distance between the adsorbed molecules and the dopants. The charge transfer and the electronic property induced by the molecule adsorption are discussed. It is found that for both CO and NO adsorption, for all the cases charge transfer between the substrates and the adsorbed molecules has been observed. For NO, the adsorption obviously induces new impurity states in the band gap or the redistribution of the original impurity states. These can lead to the change of the transport properties of the doped MoS{sub 2} monolayer, by which the adsorbed CO or NO can be detected. The present work shows that introducing appropriate dopants may be a feasible method to improve the performance of MoS{sub 2}-based gas sensors.

  13. Electrochemical studies of cystine modified self-assembled monolayer for Escherichia coli detection

    Energy Technology Data Exchange (ETDEWEB)

    Pandey, Chandra Mouli; Sumana, Gajjala [Department of Science and Technology Centre on Biomolecular Electronics, Biomedical Instrumentation Section, Materials Physics and Engineering Division, National Physical Laboratory (Council of Scientific and Industrial Research), Dr. K. S. Krishnan Marg, New Delhi 110012 (India); Sood, K.N. [Electron Microscope Section, Division of Material Characterization, National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012 (India); Malhotra, B.D., E-mail: bansi.malhotra@gmail.co [Department of Science and Technology Centre on Biomolecular Electronics, Biomedical Instrumentation Section, Materials Physics and Engineering Division, National Physical Laboratory (Council of Scientific and Industrial Research), Dr. K. S. Krishnan Marg, New Delhi 110012 (India)

    2010-11-30

    An electrochemical DNA biosensor based on cystine modified self-assembled monolayer (cys-SAM) onto gold electrode (AuE) has been fabricated for Escherichia coli (E. coli) detection. This biosensing electrode has been characterized using scanning electron microscopy (SEM), FT-IR spectroscopy, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Under the optimum conditions, this DNA biosensor can be used to detect complementary target DNA concentration in the range of 1 x 10{sup -6} M to 1 x 10{sup -20} M within 60 s of hybridization time at 25 {sup o}C and has been found to be stable for about four months when stored at 4 {sup o}C.

  14. Binding of Na+ and K+ to the Headgroup of Palmitic Acid Monolayers Studied by Vibrational Sum Frequency Generation Spectroscopy

    Science.gov (United States)

    Huang, Zishuai; Allen, Heather C.

    2012-06-01

    Alkali cations are critical in biological systems due to their electrical interaction with cell membranes. While Na+ and K+ share similar chemical and physical properties, they can exhibit differences when interacting with biological membranes. These phenomena may be modeled using a Langmuir monolayer of surfactant on alkali chloride solutions. Vibrational sum frequency generation (VSFG) spectroscopy is an interface specific technique that is widely employed to study molecular organization at surfaces and interfaces. VSFG spectroscopy was used to probe the CO2- vibrational mode for the carboxylic acid headgroup of palmitic acid (PA) spread on the surface of NaCl and KCl solutions in the vibrational region between 1400 and 1500 cm-1. The ability of Na+ and K+ to bind with the carboxylic headgroup of PA is revealed by observing peak positions (˜1410 cm-1 and ˜1470 cm-1) and relative intensity for the CO2- peaks. These results are compared and discussed with perspective toward elucidating interfacial PA headgroup organization. The time evolution for the PA CO2- peaks is also monitored after monolayer spreading via VSFG and these results are presented as well.

  15. 植物表皮蜡中链烷含量测定方法的研究%Study on the Determining Method on n-Alkane in the Cuticular Wax of Plants

    Institute of Scientific and Technical Information of China (English)

    张英俊; 栂村恭子; 秋山典昭; 大槻和夫

    2002-01-01

    植物细胞壁中链烷含量测定分析研究的目的是不降低测定分析精度的同时,节约时间和费用以便将来用于大量样品的分析.本研究首次把链烷分析提纯过程中省略用作纯化的硅胶,直接将含有链烷但未经硅胶提纯的原提取液注入气相色谱仪中测定,将世界通用的两种链烷分析法作为对照.结果表明,硅胶能否省略应根据不同牧草而定.本实验中所用的三种牧草,以省略硅胶而简化的链烷分析可用于多年生黑麦草和芒,而不能用于日本结缕草中链烷的测定.%Based on saving cost and time, and increasing the turnover rate in the determination of n-alkane concentrations so as to facilitate the application of the n-alkane technique in large-scale studies of herbage intake were the goal of the study on the modifications of the chemical analytical procedure to be described in this paper. The simplification,eliminating silica gel and injecting the raw extracts into the gas chromatography column,were evaluated of three pasture species: Miscanthus sinensis,Zoysia japonica and Lolium perenne in 2000.The simplified procedure of the n-alkane determination was compared with other two ordinary procedures.The results showed that a simplified procedure by eliminating silica gel and injecting the raw extracts into the gas chromatography column could be used for the n-alkane determination of Miscanthus sinensis and Lolium perenne. However, the n-alkane concentrations of Zoysia japonica without purification by silica gel were not able to get correctly, for the peak of contaminated substances interfered to the peak of C34.Though the samples used in this experiment were supposed to be insufficient to the final conclusion,it is indicated that the procedure simplification should be used cautiously in the different herbage analysis,too.

  16. 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...

  17. Alkane inducible proteins in Geobacillus thermoleovorans B23

    Directory of Open Access Journals (Sweden)

    Kato Tomohisa

    2009-03-01

    Full Text Available Abstract Background Initial step of β-oxidation is catalyzed by acyl-CoA dehydrogenase in prokaryotes and mitochondria, while acyl-CoA oxidase primarily functions in the peroxisomes of eukaryotes. Oxidase reaction accompanies emission of toxic by-product reactive oxygen molecules including superoxide anion, and superoxide dismutase and catalase activities are essential to detoxify them in the peroxisomes. Although there is an argument about whether primitive life was born and evolved under high temperature conditions, thermophilic archaea apparently share living systems with both bacteria and eukaryotes. We hypothesized that alkane degradation pathways in thermophilic microorganisms could be premature and useful to understand their evolution. Results An extremely thermophilic and alkane degrading Geobacillus thermoleovorans B23 was previously isolated from a deep subsurface oil reservoir in Japan. In the present study, we identified novel membrane proteins (P16, P21 and superoxide dismutase (P24 whose production levels were significantly increased upon alkane degradation. Unlike other bacteria acyl-CoA oxidase and catalase activities were also increased in strain B23 by addition of alkane. Conclusion We first suggested that peroxisomal β-oxidation system exists in bacteria. This eukaryotic-type alkane degradation pathway in thermophilic bacterial cells might be a vestige of primitive living cell systems that had evolved into eukaryotes.

  18. Alkane desaturation by concerted double hydrogen atom transfer to benzyne.

    Science.gov (United States)

    Niu, Dawen; Willoughby, Patrick H; Woods, Brian P; Baire, Beeraiah; Hoye, Thomas R

    2013-09-26

    The removal of two vicinal hydrogen atoms from an alkane to produce an alkene is a challenge for synthetic chemists. In nature, desaturases and acetylenases are adept at achieving this essential oxidative functionalization reaction, for example during the biosynthesis of unsaturated fatty acids, eicosanoids, gibberellins and carotenoids. Alkane-to-alkene conversion almost always involves one or more chemical intermediates in a multistep reaction pathway; these may be either isolable species (such as alcohols or alkyl halides) or reactive intermediates (such as carbocations, alkyl radicals, or σ-alkyl-metal species). Here we report a desaturation reaction of simple, unactivated alkanes that is mechanistically unique. We show that benzynes are capable of the concerted removal of two vicinal hydrogen atoms from a hydrocarbon. The discovery of this exothermic, net redox process was enabled by the simple thermal generation of reactive benzyne intermediates through the hexadehydro-Diels-Alder cycloisomerization reaction of triyne substrates. We are not aware of any single-step, bimolecular reaction in which two hydrogen atoms are simultaneously transferred from a saturated alkane. Computational studies indicate a preferred geometry with eclipsed vicinal C-H bonds in the alkane donor.

  19. 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

  20. Epitaxial nucleation and growth of n-alkane crystals on graphite

    NARCIS (Netherlands)

    Leunissen, M.E.; Graswinckel, W.S.; Enckevort, W.J.P. van; Vlieg, E.

    2004-01-01

    To study the heteroepitaxial growth of apolar organic compounds on apolar inorganic substrates, the n-alkanes dotriacontane (C32H66) and tritriacontane (C33H68), dissolved in n-heptane, were deposited onto the (0001) face of highly oriented pyrolytic graphite (HOPG). It was found that both n-alkanes

  1. Stabilization of H sub II phases by low levels of diglycerides and alkanes: An NMR, calorimetric, and X-ray diffraction study

    Energy Technology Data Exchange (ETDEWEB)

    Siegel, D.P; Banschbach, J.; Yeagle, P.L. (Procter Gamble Company, Cincinnati, OH (USA))

    1989-06-13

    Traces of hydrophobic molecules like diglycerides and alkanes substantially reduce the lamellar/inverted hexagonal phase transition temperature of phospholipid systems. Two different mechanisms of which impurities can stabilize nonbilayer phases have been proposed. Each requires a different location for impurity molecules within the H{sub II}-phase unit cell. Here, {sup 2}H, NMR, {sup 31}P NMR, X-ray diffraction, and DSC were used to probe the environment of perdeuterated alkanes and chain-perdeuterated 1,2-dipalmitoylglycerol (DPG-d{sub 62}) in L{sub {alpha}}- and H{sub II}-phase lattices. The host phospholipids were dioleoylphosphatidylcholine (DOPC) and monomethylated dioleoylphosphatidylethanolamine (DOPE-Me), and the samples contained several mole percent of perdeuterated additives. The data collected here generally support the two proposed mechanisms of H{sub II} stabilization. The authors data are consistent with localization of perdeuterated alkane molecules to the periphery of H{sub II} tubes and to the hydrophobic interstices between H{sub II} tubes. X-ray diffraction data show that DPG decreases the lattice constant of the H{sub II} phase at constant temperature. These can modulate the phase behavior of biomembrane lipids. Such modulation may be involved in the control of dynamic processes in biomembranes.

  2. 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).

  3. 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

    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 on an ex......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...... comparison with experiment, quasielastic spectra calculated from the MD simulations were analyzed using the same models and fitting algorithms as for the neutron spectra. This combination of techniques gives a microscopic picture of the melting process in these two monolayers which is consistent with earlier...

  4. Studies on Mixed Monolayers and Langmuir-Blodgett Films of Schiff-Base Complex Cu(SBC(18))(2) and Calix

    Science.gov (United States)

    Pang, Shufeng; Ye, Zhifeng; Li, Chun; Liang, Yingqiu

    2001-08-15

    Mixed monolayers of Schiff-base complex Cu(SBC(18))(2) with an octadecyl hydrocarbon chain and Calix[4]arene without a long alkyl chain at an air/water interface were studied in ultrapure water at different temperatures. Interface behavior and thermodynamic estimation of the mixed monolayer indicate that a strong intermolecular interaction exists between the mixed components (Cu(SBC(18))(2) and calix[4]arene) and the two-dimensional miscibility decreases with the molar fraction of Cu(SBC(18))(2). It is noticeable that the calix[4]arene monolayer can be transferred successfully onto solid substrates due to the introduction of Cu(SBC(18))(2). FTIR transmission and UV-Vis absorption spectra of mixed LB films provide further evidence of molecular interaction between the headgroups. Copyright 2001 Academic Press.

  5. Infrared Spectroscopic Investigation on CH Bond Acidity in Cationic Alkanes

    Science.gov (United States)

    Matsuda, Yoshiyuki; Xie, Min; Fujii, Asuka

    2016-06-01

    We have demonstrated large enhancements of CH bond acidities in alcohol, ether, and amine cations through infrared predissociation spectroscopy based on the vacuum ultraviolet photoionization detection. In this study, we investigate for the cationic alkanes (pentane, hexane, and heptane) with different alkyl chain lengths. The σ electrons are ejected in the ionization of alkanes, while nonbonding electrons are ejected in ionization of alcohols, ethers, and amines. Nevertheless, the acidity enhancements of CH in these cationic alkanes have also been demonstrated by infrared spectroscopy. The correlations of their CH bond acidities with the alkyl chain lengths as well as the mechanisms of their acidity enhancements will be discussed by comparison of infrared spectra and theoretical calculations.

  6. 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.

  7. Scanning tunneling microscopy study of organic molecules and self-assembled monolayers

    Science.gov (United States)

    Park, Hayn

    In this dissertation I present my findings on alkanethiol self-assembled monolayers (SAM) on Au(111), as well as investigations of the self-assembly and electron transport properties of a custom-synthesized organic molecule (bis-phenyloxazole: BPO) chosen for its interesting physical and electronic structure. Utilizing scanning tunneling microscopy (STM) techniques, we observed unique molecular structures at the boundaries of single-species alkanethiol SAM domains, and propose packing arrangements for the observed structures. We also found evidence for island formation in alkanethiol SAMs; these islands were dynamic and exhibited ordered packing of the adsorbed molecules. For codeposited two-species (dodecanethiol, octanethiol) SAMs, we observed preferential insertion of the longer molecules at domain boundaries, edges, and defect sites, and found that they tended to segregate into separate domains. Scanning tunneling spectroscopy (STS) of the inserted dodecanethiol molecules revealed evidence of conduction resonances within the HOMO-LUMO gap. We explored the charge transport and self-assembly properties of the BPO molecules on a Au(111) surface. The molecules self-assembled into a novel columnar structure after annealing in vacuum. We compare tunneling spectroscopy results to ab initio computations of the molecular orbitals.

  8. 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.

  9. Comparative study of electroless copper film on different self-assembled monolayers modified ABS substrate.

    Science.gov (United States)

    Xu, Jiushuai; Fan, Ruibin; Wang, Jiaolong; Jia, Mengke; Xiong, Xuanrui; Wang, Fang

    2014-04-15

    Copper films were grown on (3-Mercaptopropyl)trimethoxysilane (MPTMS), (3-Aminopropyl)triethoxysilane (APTES) and 6-(3-(triethoxysilyl)propylamino)-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.

  10. pH-regulated release of dopamine from well-ordered self-assembled monolayers: electrochemical studies.

    Science.gov (United States)

    Kazemi, Sayed Habib; Alizadeh, Abdolhamid; Mohamadi, Rahim; Khodaei, Mohammad Mahdi; Kordestani, Davood

    2013-12-01

    In the present work, gold electrode modified with novel aldehyde-terminated self-assembled monolayers (SAMs) was used for controllable load and release of dopamine molecules by pH triggering. Electrochemical techniques including cyclic voltammetry (CV) and electrochemcial impedance spectroscopy (EIS) were employed to investigate the SAMs characteristic on the gold electrode surface. The electrochemical experiments indicated Faradaic behavior for the electrode surface after its modification with dopamine. Notably, it was observed that decreasing the conditioning pH, results in a decrease of peak currents, presumably due to the hydrolysis of the terminal imine bonds and releasing the dopamine moiety into the solution. Moreover, the preliminary kinetics studies were done for dopamine release from the SAMs surface as a model to design future drug delivery systems. Finally, the rate constant of dopamine release from the SAMs modified surface estimated to be 0.167 day(-1) at pH=3.

  11. Comparison of Electronic and Optical Properties of GaN Monolayer and Bulk Structure: a First Principle Study

    Science.gov (United States)

    Imran, Muhammad; Hussain, Fayyaz; Rashid, Muhammad; Ullah, Hafeez; Sattar, Atif; Iqbal, Faisal; Ahmad, Ejaz

    2016-03-01

    The semiconducting two-dimensional (2D) architectures materials have potential applications in electronics and optics. The design and search of new 2D materials have attracted extensive attention recently. In this study, first principle calculation has been done on 2D gallium nitride (GaN) monolayer with respect to its formation and binding energies. The electronic and optical properties are also investigated. It is found that the single isolated GaN sheet is forming mainly ionic GaN bonds despite a slightly weaker GaN interaction as compared with its bulk counterpart. The dielectric constant value of 2D GaN is smaller as compared to 3D GaN due to less effective electronic screening effect in the layer, which is accompanied by lesser optical adsorption range and suggested to be a promising candidate in electronic and optoelectronic devices.

  12. Packing of ganglioside-phospholipid monolayers

    DEFF Research Database (Denmark)

    Majewski, J.; Kuhl, T.L.; Kjær, K.

    2001-01-01

    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...... polymer groups. Indeed, the lack of packing disruptions by the oligosaccharide groups indicates that protein-GM, interactions, including binding, insertion, chain fluidization, and domain formation (lipid rafts), can be studied in 2-D monolayers using scattering techniques....

  13. Modeling Stimuli-Responsive Nanoparticle Monolayer

    Science.gov (United States)

    Yong, Xin

    2015-03-01

    Using dissipative particle dynamics (DPD), we model a monolayer formed at the water-oil interface, which comprises stimuli-responsive nanoparticles. The solid core of the nanoparticle encompasses beads arranged in an fcc lattice structure and its surface is uniformly grafted with stimuli-responsive polymer chains. The surface-active nanoparticles adsorb to the interface from the suspension to minimize total energy of the system and create a monolayer covering the interface. We investigate the monolayer formation by characterizing the detailed adsorption kinetics. We explore the microstructure of the monolayer at different surface coverage, including the particle crowding and ordering, and elucidate the response of monolayer to external stimuli. The collective behavior of the particles within the monolayer is demonstrated quantitatively by vector-vector autocorrelation functions. This study provides a fundamental understanding of the interfacial behavior of stimuli-responsive nanoparticles.

  14. Unidimensional diffusion of long n-alkanes in nanoporous channels.

    Science.gov (United States)

    Jobic, Hervé; Farago, Bela

    2008-11-07

    The diffusion of long n-alkanes confined in silicalite zeolite has been studied with the neutron spin-echo technique. Since only isotropic diffusion has been measured so far with this technique, we derive the intermediate scattering functions for one-dimensional (1D) and single-file diffusion. The 1D diffusion model explains the results obtained for long n-alkanes in the intersecting channel system of silicalite. A redistribution of the molecules is observed at high temperatures, supporting the presence of internal barriers within the zeolite crystals.

  15. Why fluorination of the polar heads reverses the positive sign of the dipole potential of Langmuir monolayers: a vibrational sum frequency spectroscopic study.

    Science.gov (United States)

    Karageorgiev, Peter; Petrov, Jordan G; Motschmann, Hubert; Moehwald, Helmuth

    2013-04-16

    Natural nonionic amphiphiles forming monolayers, bilayers, micelles, or biomembranes create a positive dipole potential at the boundary with water. In a series of papers we have reported on Langmuir monolayers with CF3 terminals of the polar heads, which show a negative surface dipole potential ΔV (Petrov , J. G.; Andreeva, T. D.; Kurt, D. K.; Möhwald, H. J. Phys. Chem. B 2005, 109, 14102). Here we use vibrational sum frequency spectroscopy (SF) to study the origin of the opposite ΔV signs of Langmuir films of CH3(CH2)20COCH2CH3 (ethyl ether, EE) and CH3(CH2)20COCH2CF3 (fluorinated ethyl ether, FEE). The vibrational sum frequency spectra are recorded at the same film density of the S-phase of the EE and FEE monolayers and analyzed in the spectral regions of OH, COC, CH3, and CF3 stretching vibrations because these functional groups could be responsible for the different dipole potentials. We compare the rearrangement of the pure water surface by EE and FEE monolayers and the conformations of EE and FEE polar heads. The analysis is performed according to the three-capacitor model of the dipole potential of Langmuir monolayers (Demchak, R. T.; Fort, T., Jr. J. Colloid Interface Sci. 1974, 46, 191). The results show that reversal of the ΔV sign caused by fluorination of the polar heads originates from the upward-oriented CF3 terminals of the FEE heads, whose negative normal dipole moment component determines the negative dipole potential of the FEE monolayer.

  16. Monolayer and Brewster angle microscopy study of human serum albumin-dipalmitoyl phosphatidyl choline mixtures at the air-water interface.

    Science.gov (United States)

    Toimil, Paula; Prieto, Gerardo; Miñones, José; Trillo, José M; Sarmiento, Félix

    2012-04-01

    The aim of this study is to deepen the understanding of the behavior of human serum albumin (HSA) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixed monolayers. For this purpose, different amounts of DPPC were spread at 25°C on the water surface containing a monolayer of HSA. Surface film balance and Brewster angle microscopy techniques have been used to analyze the structural and energetic characteristics (structure, topography, thickness, miscibility and interactions) of these mixtures. HSA/DPPC mixed monolayers exhibit two phase transitions evidenced by two discontinuities in the corresponding π-A isotherms and by two minimum values in the compressional modulus (C(s)(-1))-surface pressure (π) curves. The plot of the molecular areas occupied by the mixed monolayers as function of the mass fraction of DPPC shows the absence of deviations from linearity, a typical behavior for ideal or inmiscible system. This result was confirmed from the values calculated for the free energy of excess (ΔG(exc)), which are practically zero whatever the composition of the mixtures and the surface pressures at which ΔG(exc) values were calculated. In addition, relative thickness values of HSA/DPPC mixed monolayers showed the existence of an exclusion surface pressure (π(exc)), below which the monolayer is composed of a mixture of both components, while above π(exc) the HSA molecules are squeezed out the interface, but not totally. In fact, although in this region DPPC domains predominate at the interface, the existence of protein molecules in a packing "loops" configuration can be observed in BAM images. Moreover, relative thickness measurements confirm this hypothesis.

  17. Alkane biohydroxylation: Interests, constraints and future developments.

    Science.gov (United States)

    Soussan, Laurence; Pen, Nakry; Belleville, Marie-Pierre; Marcano, José Sanchez; Paolucci-Jeanjean, Delphine

    2016-03-20

    Alkanes constitute one of the vastest reserves of raw materials for the production of fine chemicals. This paper focuses on recent advances in alkane biohydroxylation, i.e. the bioactivation of alkanes into their corresponding alcohols. Enzyme and whole-cell biocatalysts have been reviewed. Process considerations to implement such biocatalysts in bioreactors at large scale by coupling the bioconversion with cofactor regeneration and product removal are also discussed.

  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. Enhanced production of n-alkanes in Escherichia coli by spatial organization of biosynthetic pathway enzymes.

    Science.gov (United States)

    Rahmana, Ziaur; Sung, Bong Hyun; Yi, Ji-Yeun; Bui, Le Minh; Lee, Jun Hyoung; Kim, Sun Chang

    2014-12-20

    Alkanes chemically mimic hydrocarbons found in petroleum, and their demand as biofuels is steadily increasing. Biologically, n-alkanes are produced from fatty acyl-ACPs by acyl-ACP reductases (AARs) and aldehyde deformylating oxygenases (ADOs). One of the major impediments in n-alkane biosynthesis is the low catalytic turnover rates of ADOs. Here, we studied n-alkane biosynthesis in Escherichia coli using a chimeric ADO-AAR fusion protein or zinc finger protein-guided ADO/AAR assembly on DNA scaffolds to control their stoichiometric ratios and spatial arrangements. Bacterial production of n-alkanes with the ADO-AAR fusion protein was increased 4.8-fold (24 mg/L) over a control strain expressing ADO and AAR separately. Optimal n-alkane biosynthesis was achieved when the ADO:AAR binding site ratio on a DNA scaffold was 3:1, yielding an 8.8-fold increase (44 mg/L) over the control strain. Our findings indicate that the spatial organization of alkane-producing enzymes is critical for efficient n-alkane biosynthesis in E. coli.

  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. Cloning and expression of three ladA-type alkane monooxygenase genes from an extremely thermophilic alkane-degrading bacterium Geobacillus thermoleovorans B23.

    Science.gov (United States)

    Boonmak, Chanita; Takahashi, Yasunori; Morikawa, Masaaki

    2014-05-01

    An extremely thermophilic bacterium, Geobacillus thermoleovorans B23, is capable of degrading a broad range of alkanes (with carbon chain lengths ranging between C11 and C32) at 70 °C. Whole-genome sequence analysis revealed that unlike most alkane-degrading bacteria, strain B23 does not possess an alkB-type alkane monooxygenase gene. Instead, it possesses a cluster of three ladA-type genes, ladAαB23, ladAβB23, and ladB B23, on its chromosome, whose protein products share significant amino acid sequence identities, 49.8, 34.4, and 22.7 %, respectively, with that of ladA alkane monooxygenase gene found on a plasmid of Geobacillus thermodetrificans NG 80-2. Each of the three genes, ladAαB23, ladAβB23, and ladB B23, was heterologously expressed individually in an alkB1 deletion mutant strain, Pseudomonas fluorescens KOB2Δ1. It was found that all three genes were functional in P. fluorescens KOB2Δ1, and partially restored alkane degradation activity. In this study, we suggest that G. thermoleovorans B23 utilizes multiple LadA-type alkane monooxygenases for the degradation of a broad range of alkanes.

  2. Biochemistry of Short-Chain Alkanes (Tissue-Specific Biosynthesis of n-Heptane in Pinus jeffreyi).

    Science.gov (United States)

    Savage, T. J.; Hamilton, B. S.; Croteau, R.

    1996-01-01

    Short-chain (C7-C11) alkanes accumulate as the volatile component of oleoresin (pitch) in several pine species native to western North America. To establish the tissue most amenable for use in detailed studies of short-chain alkane biosynthesis, we examined the tissue specificity of alkane accumulation and biosynthesis in Pinus jeffreyi Grev. & Balf. Short-chain alkane accumulation was highly tissue specific in both 2-year-old saplings and mature trees; heart-wood xylem accumulated alkanes up to 7.1 mg g-1 dry weight, whereas needles and other young green tissue contained oleoresin with monoterpenoid, rather than paraffinic, volatiles. These tissue-specific differences in oleoresin composition appear to be a result of tissue-specific rates of alkane and monoterpene biosynthesis; incubation of xylem tissue with [14C]sucrose resulted in accumulation of radiolabel in alkanes but not monoterpenes, whereas incubation of foliar tissue with 14CO2 resulted in the accumulation of radiolabel in monoterpenes but not alkanes. Furthermore, incubation of xylem sections with [14C]acetate resulted in incorporation of radiolabel into alkanes at rates up to 1.7 nmol h-1 g-1 fresh weight, a rate that exceeds most biosynthetic rates reported with other plant systems for the incorporation of this basic precursor into natural products. This suggests that P. jeffreyi may provide a suitable model for elucidating the enzymology and molecular biology of short-chain alkane biosynthesis.

  3. The genome sequence of Desulfatibacillum alkenivorans AK-01: a blueprint for anaerobic alkane oxidation.

    Science.gov (United States)

    Callaghan, A V; Morris, B E L; Pereira, I A C; McInerney, M J; Austin, R N; Groves, J T; Kukor, J J; Suflita, J M; Young, L Y; Zylstra, G J; Wawrik, B

    2012-01-01

    Desulfatibacillum alkenivorans AK-01 serves as a model organism for anaerobic alkane biodegradation because of its distinctive biochemistry and metabolic versatility. The D. alkenivorans genome provides a blueprint for understanding the genetic systems involved in alkane metabolism including substrate activation, CoA ligation, carbon-skeleton rearrangement and decarboxylation. Genomic analysis suggested a route to regenerate the fumarate needed for alkane activation via methylmalonyl-CoA and predicted the capability for syntrophic alkane metabolism, which was experimentally verified. Pathways involved in the oxidation of alkanes, alcohols, organic acids and n-saturated fatty acids coupled to sulfate reduction and the ability to grow chemolithoautotrophically were predicted. A complement of genes for motility and oxygen detoxification suggests that D. alkenivorans may be physiologically adapted to a wide range of environmental conditions. The D. alkenivorans genome serves as a platform for further study of anaerobic, hydrocarbon-oxidizing microorganisms and their roles in bioremediation, energy recovery and global carbon cycling.

  4. Utilization of n-alkanes by a newly isolated strain of Acinetobacter venetianus: the role of two AlkB-type alkane hydroxylases.

    Science.gov (United States)

    Throne-Holst, Mimmi; Markussen, Sidsel; Winnberg, Asgeir; Ellingsen, Trond E; Kotlar, Hans-Kristian; Zotchev, Sergey B

    2006-09-01

    A bacterial strain capable of utilizing n-alkanes with chain lengths ranging from decane (C10H22) to tetracontane (C40H82) as a sole carbon source was isolated using a system for screening microorganisms able to grow on paraffin (mixed long-chain n-alkanes). The isolate, identified according to its 16S rRNA sequence as Acinetobacter venetianus, was designated A. venetianus 6A2. Two DNA fragments encoding parts of AlkB-type alkane hydroxylase homologues, designated alkMa and alkMb, were polymerase chain reaction-amplified from the genome of A. venetianus 6A2. To study the roles of these two alkM paralogues in n-alkane utilization in A. venetianus 6A2, we constructed alkMa, alkMb, and alkMa/alkMb disruption mutants. Studies on the growth patterns of the disruption mutants using n-alkanes with different chain lengths as sole carbon source demonstrated central roles for the alkMa and alkMb genes in utilization of C10 to C18 n-alkanes. Comparative analysis of these patterns also suggested different substrate preferences for AlkMa and AlkMb in n-alkane utilization. Because both single and double mutants were able to grow on n-alkanes with chain lengths of C20 and longer, we concluded that yet another enzyme(s) for the utilization of these n-alkanes must exist in A. venetianus 6A2.

  5. Alkane-Based Urethane Potting Compounds

    Science.gov (United States)

    Morris, D. E.

    1986-01-01

    New low viscosity urethanes easily mixed, molded, and outgassed. Alkane-based urethanes resist hydrolysis and oxidation and have excellent dielectric properties. Low-viscosity alkane-based urethane prepolymer prepared by one-step reaction of either isophorone diisocyanate or methyl-bis (4-cyclohexyl isocyanate) with hydrogenated, hydroxy-terminated polybutadiene (HTPBD).

  6. Lateral pressure profiles in lipid monolayers

    NARCIS (Netherlands)

    Baoukina, Svetlana; Marrink, Siewert J.; Tieleman, D. Peter

    2010-01-01

    We have used molecular dynamics simulations with coarse-grained and atomistic models to study the lateral pressure profiles in lipid monolayers. We first consider simple oil/air and oil/water interfaces, and then proceed to lipid monolayers at air/water and oil/water interfaces. The results are qual

  7. 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.

  8. Diffusion of squalene in n-alkanes and squalane.

    Science.gov (United States)

    Kowert, Bruce A; Watson, Michael B; Dang, Nhan C

    2014-02-27

    Squalene, an intermediate in the biosynthesis of cholesterol, has a 24-carbon backbone with six methyl groups and six isolated double bonds. Capillary flow techniques have been used to determine its translational diffusion constant, D, at room temperature in squalane, n-C16, and three n-C8-squalane mixtures. The D values have a weaker dependence on viscosity, η, than predicted by the Stokes-Einstein relation, D = kBT/(6πηr). A fit to the modified relation, D/T = ASE/η(p), gives p = 0.820 ± 0.028; p = 1 for the Stokes-Einstein limit. The translational motion of squalene appears to be much like that of n-alkane solutes with comparable chain lengths; their D values show similar deviations from the Stokes-Einstein model. The n-alkane with the same carbon chain length as squalene, n-C24, has a near-equal p value of 0.844 ± 0.018 in n-alkane solvents. The values of the hydrodynamic radius, r, for n-C24, squalene, and other n-alkane solutes decrease as the viscosity increases and have a common dependence on the van der Waals volumes of the solute and solvent. The possibility of studying squalene in lipid droplets and membranes is discussed.

  9. A theoretical study of the electrical contact between metallic and semiconducting phases in monolayer MoS2

    Science.gov (United States)

    Paz, Wendel S.; Palacios, J. J.

    2017-03-01

    We present a theoretical study of the electrical contact between the two most common crystallographic phases of MoS2 monolayer crystals: the stable semiconducting 2H phase and the metastable metallic 1T phase. A density functional theory (DFT) study of the electronic structure of interface between the two phases shows a higher Schottky barrier for electrons than for holes for the undoped 2H phase. Charge transfer from the 1T to the 2H phase occurs, but, as expected for a one-dimensional contact, the generated dipole potential decays away from the interface and the naive Schottky-Mott band-alignment picture is recovered away from the interface. The decay length of the dipole potential turns out to be larger for the zigzag interface than for the armchair interface due to the different penetration of the edge states into the bulk. Tight-binding quantum transport calculations aided by the DFT results generically confirm a low contact resistance in the range of ≈200-400 Ωμm, as experimentally reported. Furthermore, the contact resistance is predicted to be smaller at the armchair interface for electron injection and, on the contrary, smaller for hole injection at the zigzag interface.

  10. Adsorption of gas molecules on Cu impurities embedded monolayer MoS{sub 2}: A first- principles study

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, B.; Li, C.Y. [Hubei Nuclear Solid Physics Key Laboratory, Department of Physics, Wuhan University, Wuhan 430072 (China); Liu, L.L. [Key Lab for Special Functional Materials of Ministry of Eduaction, Henan Province, Henan University, Kaifeng 475004 (China); Zhou, B.; Zhang, Q.K. [Hubei Nuclear Solid Physics Key Laboratory, Department of Physics, Wuhan University, Wuhan 430072 (China); Chen, Z.Q., E-mail: chenzq@whu.edu.cn [Hubei Nuclear Solid Physics Key Laboratory, Department of Physics, Wuhan University, Wuhan 430072 (China); Tang, Z., E-mail: ztang@ee.ecnu.edu.cn [Key Laboratory of Polar Materials and Devices, Ministry of Education of China, East China Normal University, Shanghai 200241 (China)

    2016-09-30

    Highlights: • Embedded Cu atom is strongly constrained on the sulfur vacancy of monolayer MoS{sub 2}. • Transition-metal Cu atom can break the chemical inactivation of MoS{sub 2} surface. • MoS{sub 2}-Cu system is a promising for future application in gas molecules sensing. - Abstract: Adsorption of small gas molecules (O{sub 2}, NO, NO{sub 2} and NH{sub 3}) on transition-metal Cu atom embedded monolayer MoS{sub 2} was investigated by first-principles calculations based on the density-functional theory (DFT). The embedded Cu atom is strongly constrained on the sulfur vacancy of monolayer MoS{sub 2} with a high diffusion barrier. The stable adsorption geometry, charge transfer and electronic structures of these gas molecules on monolayer MoS{sub 2} embedded with transition-metal Cu atom are discussed in detail. It is found that the monolayer MoS{sub 2} with embedded Cu atom can effectively capture these gas molecules with high adsorption energy. The NH{sub 3} molecule acts as electron donor after adsorption, which is different from the other gas molecules (O{sub 2}, NO, and NO{sub 2}). The results suggest that MoS{sub 2}-Cu system may be promising for future applications in gas molecules sensing and catalysis, which is similar to those of the transition-metal embedded graphene.

  11. Crystallization features of normal alkanes in confined geometry.

    Science.gov (United States)

    Su, Yunlan; Liu, Guoming; Xie, Baoquan; Fu, Dongsheng; Wang, Dujin

    2014-01-21

    How polymers crystallize can greatly affect their thermal and mechanical properties, which influence the practical applications of these materials. Polymeric materials, such as block copolymers, graft polymers, and polymer blends, have complex molecular structures. Due to the multiple hierarchical structures and different size domains in polymer systems, confined hard environments for polymer crystallization exist widely in these materials. The confined geometry is closely related to both the phase metastability and lifetime of polymer. This affects the phase miscibility, microphase separation, and crystallization behaviors and determines both the performance of polymer materials and how easily these materials can be processed. Furthermore, the size effect of metastable states needs to be clarified in polymers. However, scientists find it difficult to propose a quantitative formula to describe the transition dynamics of metastable states in these complex systems. Normal alkanes [CnH2n+2, n-alkanes], especially linear saturated hydrocarbons, can provide a well-defined model system for studying the complex crystallization behaviors of polymer materials, surfactants, and lipids. Therefore, a deeper investigation of normal alkane phase behavior in confinement will help scientists to understand the crystalline phase transition and ultimate properties of many polymeric materials, especially polyolefins. In this Account, we provide an in-depth look at the research concerning the confined crystallization behavior of n-alkanes and binary mixtures in microcapsules by our laboratory and others. Since 2006, our group has developed a technique for synthesizing nearly monodispersed n-alkane containing microcapsules with controllable size and surface porous morphology. We applied an in situ polymerization method, using melamine-formaldehyde resin as shell material and nonionic surfactants as emulsifiers. The solid shell of microcapsules can provide a stable three-dimensional (3-D

  12. Studies on the Electrochemical Behaviour of Hydroquinone at L-cysteine Self-Assembled Monolayers Modified Gold Electrode

    Directory of Open Access Journals (Sweden)

    Dan Du

    2002-02-01

    Full Text Available L-Cysteine is combined onto gold electrode to form a self-assembled monolayers modified electrode (L-Cys/Au SAMs by taking advantage of strong sulfur-gold interaction. ATR-FTIR, SEM, cyclic voltammetry (CV and impedance were used for the characterization of the film. It shows excellent stability upon voltametric scanning and a good voltametric response towards hydroquinone with the potential ranged from 0.8 to –0.2 V (vs.SCE in 0.5M HAc-NaAc buffer solution (pH 4.8. The oxidation potential of hydroquinone on the modified electrode shifted negatively about 330 mV as compared with the bare gold electrode. The plot of catalytic current vs.its concentration has a good linear relation in the range of 2.0×10-6~2.0×10-4M with the correlation coefficient of 0.9986 and the detection limit of 4.0×10-7M by different pulse voltammetry (DPV. Mechanism for the electrocatalytical process has been studied.

  13. Full membrane spanning self-assembled monolayers as model systems for UHV-based studies of cell-penetrating peptides

    Energy Technology Data Exchange (ETDEWEB)

    Franz, Johannes [Max Planck Institute for Polymer Research, Mainz (Germany); Graham, Daniel J. [Univ. of Washington, Seattle, WA (United States). NESAC/BIO; Schmüser, Lars [Max Planck Institute for Polymer Research, Mainz (Germany); Baio, Joe E. [Oregon State Univ., Corvallis, OR (United States); Lelle, Marco [Max Planck Institute for Polymer Research, Mainz (Germany); Peneva, Kalina [Max Planck Institute for Polymer Research, Mainz (Germany); Müllen, Klaus [Max Planck Institute for Polymer Research, Mainz (Germany); Castner, David G. [Univ. of Washington, Seattle, WA (United States). NESAC/BIO; Bonn, Mischa [Max Planck Institute for Polymer Research, Mainz (Germany); Weidner, Tobias [Max Planck Institute for Polymer Research, Mainz (Germany)

    2015-03-01

    Biophysical studies of the interaction of peptides with model membranes provide a simple yet effective approach to understand the transport of peptides and peptide based drug carriers across the cell membrane. Therein, the authors discuss the use of self-assembled monolayers fabricated from the full membrane-spanning thiol (FMST) 3-((14-((4'-((5-methyl-1-phenyl-35-(phytanyl)oxy-6,9,12,15,18,21,24,27,30,33,37-undecaoxa-2,3-dithiahenpentacontan-51-yl)oxy)-[1,1'-biphenyl]-4-yl)oxy)tetradecyl)oxy)-2-(phytanyl)oxy glycerol for ultrahigh vacuum (UHV) based experiments. UHV-based methods such as electron spectroscopy and mass spectrometry can provide important information about how peptides bind and interact with membranes, especially with the hydrophobic core of a lipid bilayer. Moreover, near-edge x-ray absorption fine structure spectra and x-ray photoelectron spectroscopy (XPS) data showed that FMST forms UHV-stable and ordered films on gold. XPS and time of flight secondary ion mass spectrometry depth profiles indicated that a proline-rich amphipathic cell-penetrating peptide, known as sweet arrow peptide is located at the outer perimeter of the model membrane.

  14. Study of the helium cross-section of unsymmetric disulfide self-assembled monolayers on Au(111)

    Science.gov (United States)

    Albayrak, Erol; Karabuga, Semistan; Bracco, Gianangelo; Danışman, M. Fatih

    2016-12-01

    We have investigated the formation of self-assembled monolayers (SAMs) of 11-hydroxyundecyl decyl disulfide (CH3-(CH2)9-S-S-(CH2)11-OH, HDD) and 11-hydroxyundecyl octadecyl disulfide (CH3-(CH2)17-S-S-(CH2)11-OH, HOD) produced by supersonic molecular beam deposition (SMBD). The study has been carried out by means of helium diffraction at very low film coverage. In this regime helium single molecule cross sections have been estimated in a temperature range between 100 K and 450 K. The results show a different behavior above 300 K that has been interpreted as the starting of mobility with the formation of two thiolate moieties either linked by a gold adatom or distant enough to prevent cross section overlapping. Finally, helium diffraction patterns measured at 80 K for the SAMs grown at 200 K are discussed and the results support the proposed hypothesis of molecular dissociation based on the cross section data.

  15. Comparative Study of Monolayer and Bilayer Epitaxial Graphene Field-Effect Transistors on SiC Substrates

    Institute of Scientific and Technical Information of China (English)

    Ze-Zhao He; Ke-Wu Yang; Cui Yu; Qing-Bin Liu; Jing-Jing Wang; Xu-Bo Song; Ting-Ting Han

    2016-01-01

    Monolayer and bilayer graphenes have generated tremendous excitement as the potentially useful electronic materials due to their unique features.We report on monolayer and bilayer epitaxial graphene field-effect transistors (GFETs) fabricated on SiC substrates.Compared with monolayer GFETs,the bilayer GFETs exhibit a significant improvement in dc characteristics,including increasing current density IDS,improved transconductance gm,reduced sheet resistance Ron,and current saturation.The improved electrical properties and tunable bandgap in the bilayer graphene lead to the excellent dc performance of the bilayer GFETs.Furthermore,the improved dc characteristics enhance a better rf performance for bilayer graphene devices,demonstrating that the quasifree-standing bilayer graphene on SiC substrates has a great application potential for the future graphene-based electronics.

  16. 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.

  17. Study of gas-liquid partitioning of alkane solutes in several organic solvents by using principal component analysis and linear solvation energy relationships

    Energy Technology Data Exchange (ETDEWEB)

    Castells, Cecilia B.; Reta, Mario R

    2003-07-17

    Principal component analysis (PCA) was used to extract the number of factors which can describe the 737 gas-liquid partition coefficients of five linear, four branched, and two cyclic alkanes in 67 common solvents. Based on the reconstruction of partition coefficient data matrix, we concluded that the experimental dataset could readily be reduced to two relevant factors. Using only these two factors, there were no errors larger than 3%, 7 cases had errors larger than 2%, and in 34 cases, errors were between 1 and 2%. n-Hexane and ethylcyclohexane were chosen as the test factors, and all other partition coefficients were expressed in terms of these two test factors. Prediction of the logarithmic partition coefficient of these alkanes in seven chemically different solvents, which were originally excluded from the data matrix, was excellent: the root mean square error was 0.064, only in 11 cases the errors were larger than 1%, and only 3 had errors larger than 4%. Linear solvation energy relationships (LSERs) using both theoretical and empirical solvent parameters were used to explain the molecular interactions responsible for partition. Several combinations of parameters were tried but the standard deviations were not less than 0.31. This could be attributed to the model itself, imprecisions in the data matrix or in some of the LSER parameters. Solvent cohesive parameters and surface tension in combination with polarity-polarizability or dispersion parameters perform the best. Finally, the two principal component factors were rotated onto the most relevant physicochemical parameters that control the gas-liquid partitioning phenomena.

  18. Chain length dependence of the thermodynamic properties of linear and cyclic alkanes and polymers.

    Science.gov (United States)

    Huang, Dinghai; Simon, Sindee L; McKenna, Gregory B

    2005-02-22

    The specific heat capacity was measured with step-scan differential scanning calorimetry for linear alkanes from pentane (C(5)H(12)) to nonadecane (C(19)H(40)), for several cyclic alkanes, for linear and cyclic polyethylenes, and for a linear and a cyclic polystyrene. For the linear alkanes, the specific heat capacity in the equilibrium liquid state decreases as chain length increases; above a carbon number N of 10 (decane) the specific heat asymptotes to a constant value. For the cyclic alkanes, the heat capacity in the equilibrium liquid state is lower than that of the corresponding linear chains and increases with increasing chain length. At high enough molecular weights, the heat capacities of cyclic and linear molecules are expected to be equal, and this is found to be the case for the polyethylenes and polystyrenes studied. In addition, the thermal properties of the solid-liquid and the solid-solid transitions are examined for the linear and cyclic alkanes; solid-solid transitions are observed only in the odd-numbered alkanes. The thermal expansion coefficients and the specific volumes of the linear and cyclic alkanes are also calculated from literature data and compared with the trends in the specific heats.

  19. Structure and dynamics of monolayer films of squalane molecules adsorbed on a solid surface

    Science.gov (United States)

    D. T Enevoldsen, A.; Hansen, F. Y.; Diama, A.; Taub, H.

    2003-03-01

    Squalane is a branched alkane (C_30H_62). It consists of a straight chain with 24 carbon atoms, as in tetracosane (C_24H_50), and has six methyl side groups. Branched polymers such as squalane are thought to be better lubricants than n-alkanes. At low temperature, our molecular dynamics (MD) simulations show that the molecules form an ordered monolayer which melts at approximately 325 K compared to the tetracosane monolayer melting point of ˜ 340 K. Our MD simulations indicate the same melting mechanism in the squalane monolayer that was found previously for tetracosane (F. Y. Hansen and H. Taub, Phys. Rev. Lett. 69, 652 (1992).) They also show that the adsorbed molecules are distorted from an all-trans carbon backbone in contrast to what was found for tetracosane. This may explain why the Bragg diffraction peaks were observed to be broader for the squalane monolayer than for tetracosane (D. Fuhrmann, A. P. Graham, L. Criswell, H. Mo, B. Matthies, K. W. Herwig, and H. Taub, Surf. Sci. 482-485, 77 (2001).). The diffusive motion in a squalane monolayer has been investigated by both quasielastic neutron scattering and MD simulations and compared to the dynamics in tetracosane monolayers. Focus will be on differences in the dynamics.

  20. 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.

  1. Molecular-dynamics study of the dynamical excitations in commensurate monolayer films of nitrogen molecules on graphite: A test of the corrugation in the nitrogen-graphite potential

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Bruch, Ludwig Walter

    1995-01-01

    The dynamical excitations in a commensurate monolayer solid of N2 molecules adsorbed on graphite have been studied using molecular-dynamics simulations. Velocity and rotational correlation functions as well as coherent intermediate scattering functions and dynamical structure factors have been ca...... demonstrated from the time dependence of the mean-square displacement of the molecules and the two-dimensional diffusion coefficient is estimated to be 2–3×10-5 cm2/s at 75–80 K.......The dynamical excitations in a commensurate monolayer solid of N2 molecules adsorbed on graphite have been studied using molecular-dynamics simulations. Velocity and rotational correlation functions as well as coherent intermediate scattering functions and dynamical structure factors have been...

  2. n-alkane profiles of engine lubricating oil and particulate matter by molecular sieve extraction.

    Science.gov (United States)

    Caravaggio, Gianni A; Charland, Jean-Pierre; Macdonald, Penny; Graham, Lisa

    2007-05-15

    As part of the Canadian Atmospheric Fine Particle Research Program to obtain reliable primary source emission profiles, a molecular sieve method was developed to reliably determine n-alkanes in lubricating oils, vehicle emissions, and mobile source dominated ambient particulate matter (PM). This work was also initiated to better calculate carbon preference index values (CPI: the ratio of the sums of odd over even n-alkanes), a parameter for estimating anthropogenic versus biogenic contributions in PM. n-Alkanes in lubricating oil and mobile source dominated PM are difficult to identify and quantify by gas chromatography due to the presence of similar components that cannot be fully resolved. This results in a hump, the unresolved complex mixture (UCM) that leads to incorrect n-alkane concentrations and CPI values. The sieve method yielded better chromatography, unambiguous identification of n-alkanes and allowed examination of differences between n-alkane profiles in light (LDV) and heavy duty vehicle (HDV) lubricating oils that would have been otherwise difficult. These profile differences made it possible to relate the LDV profile to that of the PM samples collected during a tunnel study in August 2001 near Vancouver (British Columbia, Canada). The n-alkane PM data revealed that longer sampling times result in a negative artifact, i.e., the desorption of the more volatile n-alkanes from the filters. Furthermore, the sieve procedure yielded n-alkane data that allowed calculation of accurate CPI values for lubricating oils and PM samples. Finally, this method may prove helpful in estimating the respective diesel and gasoline contributions to ambient PM.

  3. Hydrothermal conversion of cellulose to alkanes with in-situ hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Yin, Sudong; Tan, Zhongchao [Department of Mechanical and Mechatronics Engineering, University of Waterloo (Canada)], Email: tanz@uwaterloo.ca

    2011-07-01

    A recently study examined the probability of hydrothermal conversion of cellulose to alkanes with in-situ H2 instead of external H2. This paper discusses the results of that study. The study researched the effects of volumetric ratios of initial input water to the reactor (W/R) and of selected catalysts on the alkane yields and composition. It was found that with the proper W/R ratios, the reforming of steam in the steam gas phase would automatically produce in-situ H2 and the key was to maintain the right balance of steam phase and liquid phase in the reactor. All the study results conclude that direct hydrothermal conversion of cellulose to alkanes with in-situ H2 is technically feasible. In addition, the application of this technology would protect the alkane bio-oil production biomass from the impact of unstable external supply of H2.

  4. Multiple alkane hydroxylase systems in a marine alkane degrader, Alcanivorax dieselolei B-5.

    Science.gov (United States)

    Liu, Chenli; Wang, Wanpeng; Wu, Yehui; Zhou, Zhongwen; Lai, Qiliang; Shao, Zongze

    2011-05-01

    Alcanivorax dieselolei strain B-5 is a marine bacterium that can utilize a broad range of n-alkanes (C(5) -C(36) ) as sole carbon source. However, the mechanisms responsible for this trait remain to be established. Here we report on the characterization of four alkane hydroxylases from A. dieselolei, including two homologues of AlkB (AlkB1 and AlkB2), a CYP153 homologue (P450), as well as an AlmA-like (AlmA) alkane hydroxylase. Heterologous expression of alkB1, alkB2, p450 and almA in Pseudomonas putida GPo12 (pGEc47ΔB) or P. fluorescens KOB2Δ1 verified their functions in alkane oxidation. Quantitative real-time RT-PCR analysis showed that these genes could be induced by alkanes ranging from C(8) to C(36) . Notably, the expression of the p450 and almA genes was only upregulated in the presence of medium-chain (C(8) -C(16) ) or long-chain (C(22) -C(36) ) n-alkanes, respectively; while alkB1 and alkB2 responded to both medium- and long-chain n-alkanes (C(12) -C(26) ). Moreover, branched alkanes (pristane and phytane) significantly elevated alkB1 and almA expression levels. Our findings demonstrate that the multiple alkane hydroxylase systems ensure the utilization of substrates of a broad chain length range.

  5. Adsorption of gas molecules on Cu impurities embedded monolayer MoS2: A first- principles study

    Science.gov (United States)

    Zhao, B.; Li, C. Y.; Liu, L. L.; Zhou, B.; Zhang, Q. K.; Chen, Z. Q.; Tang, Z.

    2016-09-01

    Adsorption of small gas molecules (O2, NO, NO2 and NH3) on transition-metal Cu atom embedded monolayer MoS2 was investigated by first-principles calculations based on the density-functional theory (DFT). The embedded Cu atom is strongly constrained on the sulfur vacancy of monolayer MoS2 with a high diffusion barrier. The stable adsorption geometry, charge transfer and electronic structures of these gas molecules on monolayer MoS2 embedded with transition-metal Cu atom are discussed in detail. It is found that the monolayer MoS2 with embedded Cu atom can effectively capture these gas molecules with high adsorption energy. The NH3 molecule acts as electron donor after adsorption, which is different from the other gas molecules (O2, NO, and NO2). The results suggest that MoS2-Cu system may be promising for future applications in gas molecules sensing and catalysis, which is similar to those of the transition-metal embedded graphene.

  6. 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 leng...

  7. 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...

  8. Phase behavior of mixed Ar-Kr, Ar-Xe and Kr-Xe monolayer films on graphite: a Monte Carlo study.

    Science.gov (United States)

    Patrykiejew, A

    2013-01-01

    Using Monte Carlo simulation methods in the grand canonical ensemble we have studied the behavior of mixed Ar-Kr, Ar-Xe and Kr-Xe monolayer films on the graphite basal plane. We have considered the adsorption of the lighter component, either argon or krypton, under the condition of a fixed chemical potential of the heavier component (krypton or xenon), as well as on the graphite surface with preadsorbed small amounts of a heavier noble gas. In both types of simulation the composition of the adsorbed layer is not conserved. We discuss the phase behavior of mixed films emerging from both types of 'computer experiment'. We also demonstrate that Monte Carlo simulation allows us to estimate the effects of preadsorbed xenon on the commensurate-incommensurate transition in the krypton monolayer film and gives the results that are in good quantitative agreement with experimental data.

  9. Supported organoiridium catalysts for alkane dehydrogenation

    Science.gov (United States)

    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.

  10. A new in vitro model to study cellular responses after thermomechanical damage in monolayer cultures.

    Directory of Open Access Journals (Sweden)

    Alice Hettler

    Full Text Available Although electrosurgical instruments are widely used in surgery to cut tissue layers or to achieve hemostasis by coagulation (electrocautery, only little information is available concerning the inflammatory or immune response towards the debris generated. Given the elevated local temperatures required for successful electrocautery, the remaining debris is likely to contain a plethora of compounds entirely novel to the intracorporal setting. A very common in vitro method to study cell migration after mechanical damage is the scratch assay, however, there is no established model for thermomechanical damage to characterise cellular reactions. In this study, we established a new in vitro model to investigate exposure to high temperature in a carefully controlled cell culture system. Heatable thermostat-controlled aluminium stamps were developed to induce local damage in primary human umbilical vein endothelial cells (HUVEC. The thermomechanical damage invoked is reproducibly locally confined, therefore allowing studies, under the same experimental conditions, of cells affected to various degrees as well as of unaffected cells. We show that the unaffected cells surrounding the thermomechanical damage zone are able to migrate into the damaged area, resulting in a complete closure of the 'wound' within 48 h. Initial studies have shown that there are significant morphological and biological differences in endothelial cells after thermomechanical damage compared to the mechanical damage inflicted by using the unheated stamp as a control. Accordingly, after thermomechanical damage, cell death as well as cell protection programs were activated. Mononuclear cells adhered in the area adjacent to thermomechanical damage, but not to the zone of mechanical damage. Therefore, our model can help to understand the differences in wound healing during the early phase of regeneration after thermomechanical vs. mechanical damage. Furthermore, this model lends itself

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

    Science.gov (United States)

    Al-Mulla, Talal; Qin, Zhao; Buehler, Markus J

    2015-09-04

    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.

  12. 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

  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. 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....... However, we found that the corresponding change in the bending rigidity is nonmonotonic. Specifically, we found that the bending rigidity decreases with increasing surfactant interfacial coverage for small surfactant interface coverages, but then it increases as the surfactant interface coverage...

  15. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Cernota, Paul Davis [Univ. of California, Berkeley, CA (United States)

    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 (√7x√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. 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.

  18. First-Principles Study of Structure Property Relationships of Monolayer (Hydroxy)Oxide-Metal Bifunctional Electrocatalysts

    DEFF Research Database (Denmark)

    Zeng, Zhenhua; Kubal, Joseph; Greeley, Jeffrey Philip

    2015-01-01

    In the present study, on the basis of detailed density functional theory (DFT) calculations, and using Ni hydroxy(oxide) films on Pt(111) and Au(111) electrodes as model systems, we describe a detailed structural and electrocatalytic analysis of hydrogen evolution (HER) at three-phase boundaries...... of information that is inaccessible by purely experimental means, and these structures, in turn, strongly suggest that a bifunctional reaction mechanism for alkaline HER will be operative at the interface between the films, the metal substrates, and the surrounding aqueous medium. This bifunctionality produces...... important changes in the calculated barriers of key elementary reaction steps, including water activation and dissociation, as compared to traditional monofunctional Pt surfaces. The successful identification of the structures of thin metal films and three-phase boundary catalysts is not only an important...

  19. Surface symmetry of monolayer titanium oxide on Mo(1 1 2) studied via fast atom diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Seifert, J., E-mail: jan.seifert@physik.hu-berlin.de; Winter, H.

    2013-11-15

    In studies on titanium oxide thin films we demonstrate the potential of Fast Atom Diffraction (FAD) and triangulation methods to derive the surface unit cell with enhanced surface sensitivity. Helium atoms with energies of 1–2 keV are scattered from the surface along low indexed surface directions under grazing angles of incidence. From the observed diffraction patterns, the lateral periodicity of the surface structures is derived. For low TiO{sub x} coverages a well-ordered c(2 × 4) superstructure and for higher coverage a p(8 × 2) film is observed. Based on FAD and triangulation methods for azimuthal rotation of the target the arrangement of topmost atoms in smaller sub-unit cells is revealed.

  20. The adsorption of CO and NO on the MoS2 monolayer doped with Au, Pt, Pd, or Ni: A first-principles study

    Science.gov (United States)

    Ma, Dongwei; Ju, Weiwei; Li, Tingxian; Zhang, Xiwei; He, Chaozheng; Ma, Benyuan; Lu, Zhansheng; Yang, Zongxian

    2016-10-01

    By performing the first-principles calculation, the adsorption of CO and NO molecules on the Au, Pt, Pd, or Ni doped MoS2 monolayer has been studied. The interaction between CO or NO with the doped MoS2 monolayer is strong and belongs to the chemisorption, as evidenced by the large adsorption energy and the short distance between the adsorbed molecules and the dopants. The charge transfer and the electronic property induced by the molecule adsorption are discussed. It is found that for both CO and NO adsorption, for all the cases charge transfer between the substrates and the adsorbed molecules has been observed. For NO, the adsorption obviously induces new impurity states in the band gap or the redistribution of the original impurity states. These can lead to the change of the transport properties of the doped MoS2 monolayer, by which the adsorbed CO or NO can be detected. The present work shows that introducing appropriate dopants may be a feasible method to improve the performance of MoS2-based gas sensors.

  1. The effects of nonmetal dopants on the electronic, optical and chemical performances of monolayer g-C3N4 by first-principles study

    Science.gov (United States)

    Lu, S.; Li, C.; Li, H. H.; Zhao, Y. F.; Gong, Y. Y.; Niu, L. Y.; Liu, X. J.; Wang, T.

    2017-01-01

    Doping is an effective means to alter the electronic behavior of materials by forming new chemical bond and relaxing the surrounding chemical bonds. With the aid of first-principle studies, the effects of a series of nonmetal (NM) dopants on the geometric, thermodynamic, electronic and optical performances of monolayer g-C3N4 have been investigated. Results shown that, all considered NM atoms except Br and I atoms can be introduced into the monolayer g-C3N4 on account of the thermal stability, the supercell parameter and film thickness have been altered by the newly formed Csbnd NM bonds and the relaxed chemical bonds around them, which have affected their electronic structure. The band gap values were altered less than ±0.14 eV. The optical absorption edge (and intensity) in visible light of all doped specimens red-shift 10-75 nm (and increase about 14%-71%) except for O- and S-doped specimens, and thus the NM dopants can enhance the visible-light response capability. Moreover, the highest occupied molecular orbital and lowest unoccupied molecular orbital of H-, B-, O-, S-, F- and As-doped specimens have been separated adequately, it can effectively separate the photogenerated e-/h+ pairs and enhance the photocatalytic efficiency. Finally, we have confirmed six high efficiency monolayer g-C3N4 based photocatalysts by doping H, B, O, S, F and As atoms.

  2. Vapour Liquid Equilibrium in Asymmetric Mixtures of n-Alkanes with Ethane

    OpenAIRE

    Duta, Anca

    2002-01-01

    The paper presents a vapour liquid equilibria study in binary mixtures of n-alkanes with high dimensional asymmetry. Each mixture contains ethane and alkanes higher than eicosane. Calculations were done using two equations of state, Peng-Robinson (PR) and Soave (SRK), in combination with van der Waals mixing rules, corrected with two interaction parameters. A limited temperature dependence of the interaction parameters was found. The correlations between the interaction parameters a...

  3. 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.

  4. Photocatalytic acceptorless alkane dehydrogenation: scope, mechanism, and conquering deactivation with carbon dioxide.

    Science.gov (United States)

    Chowdhury, Abhishek Dutta; Julis, Jennifer; Grabow, Kathleen; Hannebauer, Bernd; Bentrup, Ursula; Adam, Martin; Franke, Robert; Jackstell, Ralf; Beller, Matthias

    2015-01-01

    Alkane dehydrogenation is of special interest for basic science but also offers interesting opportunities for industry. The existing dehydrogenation methodologies make use of heterogeneous catalysts, which suffer from harsh reaction conditions and a lack of selectivity, whereas homogeneous methodologies rely mostly on unsolicited waste generation from hydrogen acceptors. Conversely, acceptorless photochemical alkane dehydrogenation in the presence of trans-Rh(PMe3 )2 (CO)Cl can be regarded as a more benign and atom efficient alternative. However, this methodology suffers from catalyst deactivation over time. Herein, we provide a detailed investigation of the trans-Rh(PMe3 )2 (CO)Cl-photocatalyzed alkane dehydrogenation using spectroscopic and theoretical investigations. These studies inspired us to utilize CO2 to prevent catalyst deactivation, which leads eventually to improved catalyst turnover numbers in the dehydrogenation of alkanes that include liquid organic hydrogen carriers.

  5. Evolution of an alkane-inducible biosensor for increased responsiveness to short-chain alkanes.

    Science.gov (United States)

    Reed, Ben; Blazeck, John; Alper, Hal

    2012-04-15

    Synthetic alkane-inducible biosensors have applications as detectors for environmental hydrocarbon contamination and as novel inducible expression systems with low-cost inducers. Here, we have assembled and evolved an alkane-responsive biosensor with a fluorescence output signal in Escherichia coli by utilizing regulatory machinery from Pseudomonas putida's alkane metabolism. Within our system, the transcriptional regulator, AlkSp, is activated by the presence of alkanes and binds to the P(alkB) promoter, stimulating transcription of a Green Fluorescent Protein reporter. Through two successive rounds of directed evolution via error prone PCR and fluorescence activated cell sorting, we isolated alkS mutants enabling up to a 5 fold increase in fluorescence output signal in response to short-chain alkanes such as hexane and pentane. Further characterization of selected mutants demonstrated altered responsiveness to a wide range of linear alkanes (pentane to dodecane). Sequence analysis highlighted the S470T mutation as a likely candidate responsible for increased effectiveness of the AlkS protein for short-chain alkanes. This work represents the first evolution of a synthetic biosensor system for alkanes.

  6. Structural Insights into Diversity and n-Alkane Biodegradation Mechanisms of Alkane Hydroxylases

    Directory of Open Access Journals (Sweden)

    Yurui eJi

    2013-03-01

    Full Text Available Environmental microbes utilize four degradation pathways for the oxidation of n-alkanes. Although the enzymes degrading n-alkanes in different microbes may vary, enzymes functioning in the first step in the aerobic degradation of alkanes all belong to the alkane hydroxylases. Alkane hydroxylases are a class of enzymes that insert oxygen atoms derived from molecular oxygen into different sites of the alkane terminus (or termini depending on the type of enzymes. In this review, we summarize the different types of alkane hydroxylases, their degrading steps and compare typical enzymes from various classes with regard to their three dimensional structures, in order to provide insights into how the enzymes mediate their different roles in the degradation of n-alkanes and what determines their different substrate ranges. Through the above analyses, the degrading mechanisms of enzymes can be elucidated and molecular biological methods can be utilized to expand their catalytic roles in the petrochemical industry or in bioremediation of oil-contaminated environments.

  7. Optimized modification of gold nanoparticles with a self-assembled monolayer for suppression of nonspecific binding in DNA assays

    Science.gov (United States)

    Esashika, Keiko; Saiki, Toshiharu

    2016-10-01

    Homogeneous DNA assays using gold nanoparticles (AuNPs) require the reduction of nonspecific binding between AuNPs to improve sensitivity in detecting the target molecule. In this study, we employed alkanethiol self-assembled monolayers (SAMs) for modifying the AuNP surface to attain both good dispersability and high hybridization efficiency. The alkanethiol SAMs enhance the repulsive interaction between AuNPs, reducing nonspecific binding and promoting the extension of surface-immobilized ssDNA into the solvent, thus enhancing the hybridization process. Introduction of oligoethylene glycol into the alkanethiol prevented nonspecific binding caused by the entanglement of alkane chains. Finally, the conditions were optimized by controlling the surface charge density through the introduction of a COOH group at the alkanethiol terminus, resulting in the complete blocking of nonspecific binding and the maintenance of high hybridization efficiency.

  8. Thermodynamics of the adsorption of organic molecules on graphitized carbon black modified with a monolayer of 5-hydroxy-6-methyluracil

    Science.gov (United States)

    Gus'kov, V. Yu.; Ivanov, S. P.; Shaikhitdinova, Yu. F.; Kudasheva, F. Kh.

    2016-10-01

    Thermodynamic characteristics of the adsorption of alkanes, alcohols, arenes, and esters on graphitized carbon black with a deposited monolayer (0.17%) of 5-hydroxy-6-methyluracil are studied by means of inverse gas chromatography at infinite dilution. It is established that size effects (violation of the additivity of molar changes in internal energy and the entropy of adsorption for pairs of molecules of one homologous series that differ by one methyl group) are observed when organic molecules are adsorbed on the surface of the resulting adsorbent. The size effects are similar to those observed when 1% 5-hydroxy-6-methyluracil is deposited on graphitized carbon black. It is concluded that the observed violation of additivity is associated with cavities in the supramolecular structure.

  9. 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.

  10. Systematic study of electronic structure and band alignment of monolayer transition metal dichalcogenides in Van der Waals heterostructures

    Science.gov (United States)

    Zhang, Chenxi; Gong, Cheng; Nie, Yifan; Min, Kyung-Ah; Liang, Chaoping; Oh, Young Jun; Zhang, Hengji; Wang, Weihua; Hong, Suklyun; Colombo, Luigi; Wallace, Robert M.; Cho, Kyeongjae

    2017-03-01

    Two-dimensional transition metal dichalcogenides (TMDs) are promising low-dimensional materials which can produce diverse electronic properties and band alignment in van der Waals heterostructures. Systematic density functional theory (DFT) calculations are performed for 24 different TMD monolayers and their bilayer heterostacks. DFT calculations show that monolayer TMDs can behave as semiconducting, metallic or semimetallic depending on their structures; we also calculated the band alignment of the TMDs to predict their alignment in van der Waals heterostacks. We have applied the charge equilibration model (CEM) to obtain a quantitative formula predicting the highest occupied state of any type of bilayer TMD heterostacks (552 pairs for 24 TMDs). The CEM predicted values agree quite well with the selected DFT simulation results. The quantitative prediction of the band alignment in the TMD heterostructures can provide an insightful guidance to the development of TMD-based devices.

  11. Achieving Uniform Monolayer Transition Metal Dichalcogenides Film on Silicon Wafer via Silanization Treatment: A Typical Study on WS2.

    Science.gov (United States)

    Chen, Ying; Gan, Lin; Li, Huiqiao; Ma, Ying; Zhai, Tianyou

    2017-02-01

    A silanization reaction is employed to improve the dispersion of precursors on a silicon wafer for a large-size uniform transition metal dichalcogenide (TMD) film synthesis and to achieve a highly crystalline monolayer WS2 film up to 1 cm(2) . The novel strategy is also verified for the synthesis of WSe2 and MoS2 uniform films, suggesting universality for TMD film fabrication.

  12. Graphic model for calculating the entropy of C11H24 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 CH4-C32H66.

  13. 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.

  14. 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...

  15. Separating and characterizing functional alkane degraders from crude-oil-contaminated sites via magnetic nanoparticle-mediated isolation.

    Science.gov (United States)

    Wang, Xinzi; Zhao, Xiaohui; Li, Hanbing; Jia, Jianli; Liu, Yueqiao; Ejenavi, Odafe; Ding, Aizhong; Sun, Yujiao; Zhang, Dayi

    Uncultivable microorganisms account for over 99% of all species on the planet, but their functions are yet not well characterized. Though many cultivable degraders for n-alkanes have been intensively investigated, the roles of functional n-alkane degraders remain hidden in the natural environment. This study introduces the novel magnetic nanoparticle-mediated isolation (MMI) technology in Nigerian soils and successfully separates functional microbes belonging to the families Oxalobacteraceae and Moraxellaceae, which are dominant and responsible for alkane metabolism in situ. The alkR-type n-alkane monooxygenase genes, instead of alkA- or alkP-type, were the key functional genes involved in the n-alkane degradation process. Further physiological investigation via a BIOLOG PM plate revealed some carbon (Tween 20, Tween 40 and Tween 80) and nitrogen (tyramine, l-glutamine and d-aspartic acid) sources promoting microbial respiration and n-alkane degradation. With further addition of promoter carbon or nitrogen sources, the separated functional alkane degraders significantly improved n-alkane biodegradation rates. This suggests that MMI is a promising technology for separating functional microbes from complex microbiota, with deeper insight into their ecological functions and influencing factors. The technique also broadens the application of the BIOLOG PM plate for physiological research on functional yet uncultivable microorganisms.

  16. Photopatterning of stable, low-density, self-assembled monolayers on gold.

    Science.gov (United States)

    Safazadeh, Leila; Berron, Brad J

    2015-03-10

    Photoinitiated thiol-yne chemistry is utilized as a click reaction for grafting of acid-terminated alkynes to thiol-terminated monolayers on a gold substrate to create stable, low-density monolayers. The resulting monolayers are compared with a well-packed 11-mercaptoundecanoic acid monolayer and the analogous low-density monolayers prepared through a solution phase synthetic approach. The overall structuring of the monolayer prepared by solid-phase grafting is characterized by contact angle goniometry and Fourier transform infrared spectroscopy. The results show that the product monolayer has an intermediate surface energy and a more disordered chemical structuring compared to a traditional well-packed self-assembled monolayer, showing a low-packing density of the chains at the monolayer surface. The monolayer's structure and electrochemical stability were studied by reductive desorption of the thiolates. The prepared low-density monolayers have a higher electrochemical stability than traditional well-packed monolayers, which results from the crystalline structure at the gold interface. This technique allows for simple, fast preparation of low-density monolayers of higher stability than well-packed monolayers. The use of a photomask to restrict light access to the substrate yielded these low-density monolayers in patterned regions defined by light exposure. This general thiol-yne approach is adaptable to a variety of analogous low-density monolayers with diverse chemical functionalities.

  17. Conformation of alkanes in the gas phase and pure liquids.

    Science.gov (United States)

    Thomas, Laura L; Christakis, Theodore J; Jorgensen, William L

    2006-10-26

    Monte Carlo (MC) statistical mechanics simulations have been carried out for the homologous alkane series of n-butane through n-dodecane in the gas phase and for the pure liquids at 298 K and 1 atm using the OPLS-AA force field. The study addresses potential cumulative deviations of computed properties and potential conformational differences between the gas phase and pure liquids, for example, from self-solvation in the gas phase. The average errors in comparison with experimental data for the computed densities and heats of vaporization are modest at 0.7% and 6.9%, respectively. Also, the invariant gas and liquid-phase results for average end-to-end distances and percentages of trans conformations for each nonterminal C-C bond assert that the conformer populations are not altered upon transfer from the gas phase to the pure liquid for the n-alkanes in this size range. Average end-to-end distances were also computed from the results of conformational searches and corroborated the MC findings. Quantitatively, the OPLS-AA result for the trans population of the C3-C4 bond in n-undecane is in close agreement with the findings from (13)C NMR experiments. Finally, previous work on determining the shortest n-alkane that does not have an all-trans global energy minimum has been extended. The smallest n-alkane with a hairpin geometry that is lower in energy than the all-trans conformer occurs for C(22)H(46) with OPLS-AA, though with a correction for GG sequences, the true turning point is likely in the C(16)-C(18) range.

  18. Recognition tunneling measurement of the conductance of DNA bases embedded in self-assembled monolayers.

    Science.gov (United States)

    Huang, Shuo; Chang, Shuai; He, Jin; Zhang, Peiming; Liang, Feng; Tuchband, Michael; Li, Shengqing; Lindsay, Stuart

    2010-12-09

    The DNA bases interact strongly with gold electrodes, complicating efforts to measure the tunneling conductance through hydrogen-bonded Watson Crick base pairs. When bases are embedded in a self-assembled alkane-thiol monolayer to minimize these interactions, new features appear in the tunneling data. These new features track the predictions of density-functional calculations quite well, suggesting that they reflect tunnel conductance through hydrogen-bonded base pairs.

  19. Molecular simulation and macroscopic modeling of the diffusion of hydrogen, carbon monoxide and water in heavy n-alkane mixtures.

    Science.gov (United States)

    Makrodimitri, Zoi A; Unruh, Dominik J M; Economou, Ioannis G

    2012-03-28

    The self-diffusion coefficient of hydrogen (H(2)), carbon monoxide (CO) and water (H(2)O) in n-alkanes was studied by molecular dynamics simulation. Diffusion in a few pure n-alkanes (namely n-C(8), n-C(20), n-C(64) and n-C(96)) was examined. In addition, binary n-C(12)-n-C(96) mixtures with various compositions as well as more realistic five- and six-n-alkane component mixtures were simulated. In all cases, the TraPPE united atom force field was used for the n-alkane molecules. The force field for the mixture of n-alkanes was initially validated against experimental density values and was shown to be accurate. Moreover, macroscopic correlations for predicting diffusion coefficient of H(2), CO and H(2)O in n-alkanes and mixtures of n-alkanes were developed. The functional form of the correlation was based on the rough hard sphere theory (RHS). The correlation was applied to simulation data and an absolute average deviation (AAD) of 5.8% for pure n-alkanes and 3.4% for n-alkane mixtures was obtained. Correlation parameters vary in a systematic way with carbon number and so they can be used to provide predictions in the absence of any experimental or molecular simulation data. Finally, in order to reduce the number of adjustable parameters, for the n-alkane mixtures the "pseudo-carbon number" approach was used. This approach resulted in relatively higher deviation from MD simulation data (AAD of 18.2%); however, it provides a convenient and fast method to predict diffusion coefficients. The correlations developed here are expected to be useful for engineering calculations related to the design of the Gas-to-Liquid process.

  20. Changes in iso- and n-alkane distribution during biodegradation of crude oil under nitrate and sulphate reducing conditions.

    Science.gov (United States)

    Hasinger, Marion; Scherr, Kerstin E; Lundaa, Tserennyam; Bräuer, Leopold; Zach, Clemens; Loibner, Andreas Paul

    2012-02-20

    Crude oil consists of a large number of hydrocarbons with different susceptibility to microbial degradation. The influence of hydrocarbon structure and molecular weight on hydrocarbon biodegradation under anaerobic conditions is not fully explored. In this study oxygen, nitrate and sulphate served as terminal electron acceptors (TEAs) for the microbial degradation of a paraffin-rich crude oil in a freshly contaminated soil. During 185 days of incubation, alkanes from n-C11 to n-C39, three n- to iso-alkane ratios commonly used as weathering indicators and the unresolved complex mixture (UCM) were quantified and statistically analyzed. The use of different TEAs for hydrocarbon degradation resulted in dissimilar degradative patterns for n- and iso-alkanes. While n-alkane biodegradation followed well-established patterns under aerobic conditions, lower molecular weight alkanes were found to be more recalcitrant than mid- to high-molecular weight alkanes under nitrate-reducing conditions. Biodegradation with sulphate as the TEA was most pronounced for long-chain (n-C32 to n-C39) alkanes. The observation of increasing ratios of n-C17 to pristane and of n-C18 to phytane provides first evidence of the preferential degradation of branched over normal alkanes under sulphate reducing conditions. The formation of distinctly different n- and iso-alkane biodegradation fingerprints under different electron accepting conditions may be used to assess the occurrence of specific degradation processes at a contaminated site. The use of n- to iso-alkane ratios for this purpose may require adjustment if applied for anaerobic sites.

  1. Molecular Arrangement in Self-Assembled Azobenzene-Containing Thiol Monolayers at the Individual Domain Level Studied through Polarized Near-Field Raman Spectroscopy

    Directory of Open Access Journals (Sweden)

    Razvigor Ossikovski

    2011-02-01

    Full Text Available 6-[4-(phenylazophenoxy]hexane-1-thiol self-assembled monolayers deposited on a gold surface form domain-like structures possessing a high degree of order with virtually all the molecules being identically oriented with respect to the surface plane. We show that, by using polarized near-field Raman spectroscopy, it is possible to derive the Raman scattering tensor of the ordered layer and consequently, the in-plane molecular orientation at the individual domain level. More generally, this study extends the application domain of the near-field Raman scattering selection rules from crystals to ordered organic structures.

  2. The most stable mono-layers of (111)-Pt (fcc) on Graphene: A first-principles GGA study

    Science.gov (United States)

    Otalora-Acevedo, J.; Rodríguez Martínez, J. A.; Moreno-Armenta, G.; Vera, E.; Takeuchi Tan, N.

    2016-08-01

    We investigate monolayers of planes (111) of Pt in the FCC structure located on graphene. The energy of formation showed that the most stable structure is √3×√3 — Pt on 2 × 2 — graphene. This system has a mismatch in the lattice constant of 0.45. The layers are completely flat, and its band structure shows that the new structure is metallic and the Dirac's cones are displaced 0.6eV above of the Fermi level. In this work we present the dependence of the enthalpy of formation of these structures and we calculated all structural parameters of their relaxation.

  3. Use of enzyme label for quantitative evaluation of liposome adhesion on cell surface: studies with J774 macrophage monolayers.

    Science.gov (United States)

    Trubetskoy, V S; Dormeneva, E V; Tsibulsky, V P; Repin, V S; Torchilin, V P

    1988-07-01

    A method for quantitation of cell surface-bound liposomes utilizing J774 macrophage monolayers is developed. Surface-bound biotinyl-containing and 125I-labeled liposomes were quantified with avidin-peroxidase in an ELISA-like assay. Peroxidase substrate absorbance values were recalculated into the absolute amount of liposomal lipid using a special calibration plot. Total liposome uptake by macrophages was determined following the binding of 125I radioactivity. The approach suggested allows quantitative evaluation of the changes in the content of surface-adhered liposomes during their interaction with cells in vitro.

  4. Enzymes and Genes Involved in Aerobic Alkane Degradation

    Directory of Open Access Journals (Sweden)

    Zongze eShao

    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.

  5. Self assembled monolayers on silicon for molecular electronics.

    Science.gov (United States)

    Aswal, D K; Lenfant, S; Guerin, D; Yakhmi, J V; Vuillaume, D

    2006-05-24

    We present an overview of various aspects of the self-assembly of organic monolayers on silicon substrates for molecular electronics applications. Different chemical strategies employed for grafting the self-assembled monolayers (SAMs) of alkanes having different chain lengths on native oxide of Si or on bare Si have been reviewed. The utility of different characterization techniques in determination of the thickness, molecular ordering and orientation, surface coverage, growth kinetics and chemical composition of the SAMs has been discussed by choosing appropriate examples. The metal counterelectrodes are an integral part of SAMs for measuring their electrical properties as well as using them for molecular electronic devices. A brief discussion on the variety of options available for the deposition of metal counterelectrodes, that is, soft metal contacts, vapor deposition and soft lithography, has been presented. Various theoretical models, namely, tunneling (direct and Fowler-Nordheim), thermionic emission, Poole-Frenkel emission and hopping conduction, used for explaining the electronic transport in dielectric SAMs have been outlined and, some experimental data on alkane SAMs have been analyzed using these models. It has been found that short alkyl chains show excellent agreement with tunneling models; while more experimental data on long alkyl chains are required to understand their transport mechanism(s). Finally, the concepts and realization of various molecular electronic components, that is, diodes, resonant tunnel diodes, memories and transistors, based on appropriate architecture of SAMs comprising of alkyl chains (sigma- molecule) and conjugated molecules (pi-molecule) have been presented.

  6. Conversion of alkanes to organoseleniums and organotelluriums

    Energy Technology Data Exchange (ETDEWEB)

    Periana, Roy A.; Konnick, Michael M.; Hashiguchi, Brian G.

    2016-11-29

    The invention provides processes and materials for the efficient and costeffective functionalization of alkanes and heteroalkanes, comprising contacting the alkane or heteroalkane and a soft oxidizing electrophile comprising Se(VI) or Te(VI), in an acidic medium, optionally further comprising an aprotic medium, which can be carried out at a temperature of less than 300 C. Isolation of the alkylselenium or alkyltellurium intermediate allows the subsequent conversion to products not necessarily compatible with the initial reaction conditions, such as amines, stannanes, organosulfur compounds, acyls, halocarbons, and olefins.

  7. Effect of Cd(2+) and Cd(2+)/auxin mixtures on lipid monolayers - Model membrane studies on the role of auxins in phytoremediation of metal ions from contaminated environment.

    Science.gov (United States)

    Hąc-Wydro, Katarzyna; Mach, Marzena; Węder, Karolina; Pająk, Katarzyna; Wydro, Paweł

    2017-03-23

    In this work Langmuir monolayer experiments were performed to analyze the effect of Cd(2+) ions and their mixtures with synthetic auxin (1-naphthaleneacetic acid - NAA) on lipid films. These investigations were motivated by the fact that auxins act effectively as the agents improving the removal of metal ions from contaminated water and soil by plants (phytoextraction), and although their mechanism of action in this area is still unclear, it was suggested that it can be membrane-related. The experiments were done for one component (1,2-dipalmitoyl-sn-glycero-3-phosphocholine - DPPC; 1,2-dioleoyl-sn-glycero-3-phosphocholine - DOPC; 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) - DPPG) monolayers and mixed (DPPG/DOPC and DPPG/DPPC) films treated as model of plant leaves membranes. The monolayer properties were analyzed based on the surface pressure-area isotherms obtained during film compression, stability measurements and Brewster angle microcopy studies. The collected results together with the data presented in literature evidenced that both metal ions and auxins modify lipid system properties and by using them in a combination it is possible to weaken the influence of sole metal ions on membrane organization. This seems to be in agreement with the hypothesis that the role of plant growth regulators in increasing phytoextraction effectiveness may be membrane-related. However, further experiments are required to find possible correlations between the type and concentration of metal ion, composition of membrane or structural elements in auxin molecule and observed alterations in membrane properties.

  8. 40 CFR 721.535 - Halogenated alkane (generic).

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Halogenated alkane (generic). 721.535... Substances § 721.535 Halogenated alkane (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halogenated alkane (PMN P-01-433) is...

  9. 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)...

  10. 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...

  11. Improving the dielectric properties of ethylene-glycol alkanethiol self-assembled monolayers.

    Science.gov (United States)

    Zaccari, Irene; Catchpole, Benjamin G; Laurenson, Sophie X; Davies, A Giles; Wälti, Christoph

    2014-02-11

    Self-assembled monolayers (SAMs) can be formed at the interface between solids and fluids, and are often used to modify the surface properties of the solid. One of the most widely employed SAM systems is exploiting thiol-gold chemistry, which, together with alkane-chain-based molecules, provides a reliable way of SAM formation to modify the surface properties of electrodes. Oligo ethylene-glycol (OEG) terminated alkanethiol monolayers have shown excellent antifouling properties and have been used extensively for the coating of biosensor electrodes to minimize nonspecific binding. Here, we report the investigation of the dielectric properties of COOH-capped OEG monolayers and demonstrate a strategy to improve the dielectric properties significantly by mixing the OEG SAM with small concentrations of 11-mercaptoundecanol (MUD). The monolayer properties and composition were characterized by means of impedance spectroscopy, water contact angle, ellipsometry and X-ray photoelectron spectroscopy. An equivalent circuit model is proposed to interpret the EIS data and to determine the conductivity of the monolayer. We find that for increasing MUD concentrations up to about 5% the resistivity of the SAM steadily increases, which together with a considerable decrease of the phase of the impedance, demonstrates significantly improved dielectric properties of the monolayer. Such monolayers will find widespread use in applications which depend critically on good dielectric properties such as capacitive biosensor.

  12. Squeeze-Out of Branched Alkanes on Graphite

    Science.gov (United States)

    Gosvami, N. N.; Sinha, S. K.; O'Shea, S. J.

    2008-02-01

    We study squalane and heptamethylnonane (HMN) confined between a conducting atomic force microscope tip and a graphite surface. Solvation layering occurs for both liquids but marked differences in the squeeze out mechanics are observed for ordered or disordered monolayers. The squalane monolayer at 25°C is an ordered solid, as verified by direct imaging, and the squeeze out can be modeled using elastic continuum mechanics. HMN is in a disordered state at 25°C and cannot be modeled as a single elastic asperity even in solid-solid contact because HMN liquid is trapped in the contact zone.

  13. Nitrated metalloporphyrins as catalysts for alkane oxidation

    Science.gov (United States)

    Ellis, Jr., Paul E.; Lyons, James E.

    1992-01-01

    Alkanes are oxidized by contact with oxygen-containing gas in the presence as catalyst of a metalloporphyrin in which hydrogen atoms in the porphyrin ring have been replaced with one or more nitro groups. Hydrogen atoms in the porphyrin ring may also be substituted with halogen atoms.

  14. 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})

  15. Structural, electronic and magnetic properties of 3d metal trioxide clusters-doped monolayer graphene: A first-principles study

    Science.gov (United States)

    Rafique, Muhammad; Shuai, Yong; Tan, He-Ping; Hassan, Muhammad

    2017-03-01

    We present first-principles density-functional calculations for the structural, electronic and magnetic properties of monolayer graphene doped with 3d (Ti, V, Cr, Fe, Co, Mn and Ni) metal trioxide TMO3 halogen clusters. In this paper we used two approaches for 3d metal trioxide clusters (i) TMO3 halogen cluster was embedded in monolayer graphene substituting four carbon (C) atoms (ii) three C atoms were substituted by three oxygen (O) atoms in one graphene ring and TM atom was adsorbed at the hollow site of O atoms substituted graphene ring. All the impurities were tightly bonded in the graphene ring. In first case of TMO3 doped graphene layer, the bond length between Csbnd O atom was reduced and bond length between TM-O atom was increased. In case of Cr, Fe, Co and Ni atoms substitution in between the O atoms, leads to Fermi level shifting to conduction band thereby causing the Dirac cone to move into valence band, however a band gap appears at high symmetric K-point. In case of TiO3 and VO3 substitution, system exhibits semiconductor properties. Interestingly, TiO3-substituted system shows dilute magnetic semiconductor behavior with 2.00 μB magnetic moment. On the other hand, the substitution of CoO3, CrO3, FeO3 and MnO3 induced 1.015 μB, 2.347 μB, 2.084 μB and 3.584 μB magnetic moment, respectively. In second case of O atoms doped in graphene and TM atoms adsorbed at the hollow site, the O atom bulges out of graphene plane and bond length between TM-O atom is increased. After TM atoms adsorption at the O substituted graphene ring the Fermi level (EF) shifts into conduction band. In case of Cr and Ni adsorption, system displays indirect band gap semiconductor properties with 0.0 μB magnetic moment. Co adsorption exhibits dilute magnetic semiconductor behavior producing 0.916 μB magnetic moment. Fe, Mn, Ti and V adsorption introduces band gap at high symmetric K-point also inducing 1.54 μB, 0.9909 μB, 1.912 μB, and 0.98 μB magnetic moments, respectively

  16. Characterization of n-alkanes in PM{sub 2.5} of the Taipei aerosol

    Energy Technology Data Exchange (ETDEWEB)

    Young, Li Hao [National Taiwan Univ., Taipei (Taiwan). Graduate Inst. of Environmental Health; Wang, Chiu Sen [National Taiwan Univ., Taipei (Taiwan). Dept. of Public Health

    2002-07-01

    Ambient concentrations of n-alkanes with carbon number ranging from 17 to 36 were determined for PM{sub 2.5} collected in Taipei city during September 1997-February 1998. The measured concentrations of particulate n-alkanes were in the range of 69-702ngm{sup -3} considerably higher than the concentration levels observed in Los Angeles and Hong Kong. The concentration distributions of n-alkanes homologues obtained in this study exhibited peaks at C{sub 19}, C{sub 24} or C{sub 25}. This suggests that fossil fuel utilization, such as vehicular exhaust and lubricant residues, was an important contributor to the Taipei aerosol. Source apportionment of PM{sub 2.5} was conducted using carbon preference index (CPI, defined as the ratio of the total concentration of particulate n-alkanes with odd carbon number to that with even carbon number) and U:R ratio (the concentration ratio of unresolved components to resolved components obtained from chromatograms). The low CPI value (0.9-1.9) and high U:R ratio (2.6-6.4) for each sample further confirmed that fossil fuel utilization was the major source of n-alkanes in ambient PM{sub 2.5} of Taipei city. Estimates from these results showed that 69-93% of the n-alkanes in PM{sub 2.5} of the Taipei aerosol originated from vehicular exhaust. The higher concentration level of particulate n-alkanes in the Taipei aerosol was mainly a result of vehicular emissions. (author)

  17. Regulation of the Alkane Hydroxylase CYP153 Gene in a Gram-Positive Alkane-Degrading Bacterium, Dietzia sp. Strain DQ12-45-1b.

    Science.gov (United States)

    Liang, Jie-Liang; JiangYang, Jing-Hong; Nie, Yong; Wu, Xiao-Lei

    2015-11-13

    CYP153, one of the most common medium-chain n-alkane hydroxylases belonging to the cytochrome P450 superfamily, is widely expressed in n-alkane-degrading bacteria. CYP153 is also thought to cooperate with AlkB in degrading various n-alkanes. However, the mechanisms regulating the expression of the protein remain largely unknown. In this paper, we studied CYP153 gene transcription regulation by the potential AraC family regulator (CypR) located upstream of the CYP153 gene cluster in a broad-spectrum n-alkane-degrading Gram-positive bacterium, Dietzia sp. strain DQ12-45-1b. We first identified the transcriptional start site and the promoter of the CYP153 gene cluster. Sequence alignment of upstream regions of CYP153 gene clusters revealed high conservation in the -10 and -35 regions in Actinobacteria. Further analysis of the β-galactosidase activity in the CYP153 gene promoter-lacZ fusion cell indicated that the CYP153 gene promoter was induced by n-alkanes comprised of 8 to 14 carbon atoms, but not by derived decanol and decanic acid. Moreover, we constructed a cypR mutant strain and found that the CYP153 gene promoter activities and CYP153 gene transcriptional levels in the mutant strain were depressed compared with those in the wild-type strain in the presence of n-alkanes, suggesting that CypR served as an activator for the CYP153 gene promoter. By comparing CYP153 gene arrangements in Actinobacteria and Proteobacteria, we found that the AraC family regulator is ubiquitously located upstream of the CYP153 gene, suggesting its universal regulatory role in CYP153 gene transcription. We further hypothesize that the observed mode of CYP153 gene regulation is shared by many Actinobacteria.

  18. A study on oxygen reduction inhibition at pyridine-terminated self assembled monolayer modified Au(111) electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Muglali, Mutlu Iskender; Bashir, Asif; Rohwerder, Michael [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany)

    2010-04-15

    The electroreduction of oxygen on self-assembled monolayers (SAMs) of various pyridinedisulfides and pyridinethiols on Au(111) surfaces has been investigated in alkaline solutions. Electrochemical experiments that were carried out in three-electrode cell reveal a good correlation between the chain-length of thiol molecules and the oxygen reduction inhibition of the resulting adlayer films. The effect of retarded diffusion of oxygen through the protective film has been investigated by forming additional layer of immobilized cytochrome c (cyt.c) metalloprotein on pyridine moiety during linear sweep voltammetry (LSV) scans. At sufficiently negative cathodic potentials the electrochemical reaction rate has been observed to increase together with the density of defects. Morphological changes at different levels of cathodic polarization were investigated by ex situ scanning tunneling microscopy (STM), indicating oxygen reduction reaction (ORR) induced structural defects at the metallorganic interface. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  19. Magnetism and magnetocrystalline anisotropy of 3dtransition metal monolayers on Pt(001): a density-functional study.

    Science.gov (United States)

    Taivansaikhan, P; Odkhuu, D; Kwon, O R; Tsogbadrakh, N; Hong, S C

    2014-12-01

    We systematically investigate the effects of having Pt as a substrate and/or capping layer on the magnetism and magnetocrystalline anisotropy (MCA) of 3d transition metal (TMs; Cr, Mn, Fe, and Co) monolayers (MLs) by using a first-principles calculationl method. We found that Fe and Co MLs are ferromagnetic (FM) on a Pt(001) surface, but Mn and Cr MLs are antiferromagnetic (AFM). The magnetic moments are quite robust with additional Pt-capping. Furthermore, Pt-capping enhances the small perpendicular MCA (meV) of Fe/Pt(001) significantly to 4.44 meV. Our electronic structure analyses indicate that strong hybridization between Pt-5d and TM-3d orbitals plays a crucial role in determining magnetic ordering and MCA. For comparison we also calculated magnetism and MCA of 3d TM MLs on Ta(001) with and without Ta-capping.

  20. Photoelectron spectroscopic study on monolayer pentacene thin-film/polar ZnO single-crystal hybrid interface

    Science.gov (United States)

    Nagata, Takahiro; Nakamura, Tatsuru; Hayakawa, Ryoma; Yoshimura, Takeshi; Oh, Seungjun; Hiroshiba, Nobuya; Chikyow, Toyohiro; Fujimura, Norifumi; Wakayama, Yutaka

    2017-02-01

    The polarity effects of ZnO on the electronic state of a monolayer pentacene/ZnO interface were investigated by X-ray photoelectron spectroscopy (XPS). XPS revealed that the Zn-polar ZnO (Zn-ZnO) strongly depleted electrons in pentacene at the interface. The O-polar ZnO showed greater electron transfer from ZnO to pentacene than Zn-ZnO. The surface potential of pentacene on ZnO was larger than that of bulk pentacene regardless of the ZnO polarity. These findings indicate that the polarity of ZnO has the potential to control the electronic state of the organic/inorganic semiconductor interface.

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

    Energy Technology Data Exchange (ETDEWEB)

    Shao, Bin; Shi, Wu-Jun [Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Feng, Min [School of Physics, Nankai University, Tianjin 300071 (China); Zuo, Xu, E-mail: xzuo@nankai.edu.cn [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China)

    2015-05-07

    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.

  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

    Energy Technology Data Exchange (ETDEWEB)

    Firment, L.E.

    1977-01-01

    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 (C/sub 3/ to C/sub 8/), 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/sup -4/ A sec cm/sup -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. Hydrogen isotopic compositions and their environmental significance for individual n-alkanes in typical plants from land in China

    Institute of Scientific and Technical Information of China (English)

    DUAN Yi; WU BaoXiang

    2009-01-01

    Hydrogen isotopes of n-alkanes in grasses, tree leaves and reeds from six regions with latitudes of 20° to 39°N in China are measured by GC-TC-IRMS analytical technique in order to understand their hy-drogen isotopic compositions and environmental significance. The results show that a difference in δD values (from -42.1‰ to -66.6‰) of n-alkanes exists among the same kinds of plants from various re-gions. Hydrogen isotopic compositions of most even carbon numbered n-alkanes in every plant are slightly heavier than that of the odd homologues. A trend toward D-enrichment with increasing chain length of n-alkanes in most plant samples is observed. Mean δD values of n-alkanes in the studied plants range from -202.6‰ to -130.7‰ and the reed from a salt marsh has the largest value. The mean δD values of individual n-alkanes among the same kinds of plants from various regions have the characteristics of leaf > reed > grass. The hydrogen isotopic compositions of n-alkanes are apparently distinct among various kinds of plants from the same region and the mean δD values exhibit a distri-bution of tree leaf > reed > grass. It is observed that the mean δD values of n-alkanes and δD values of C27 and C29 n-alkanes in the grasses and tree leaves from these studied regions correlate clearly nega-tively with latitude and positively with temperature, indicating that these values can be used as excel-lent indicators of environment and climate. These results provide important basic data for under-standing the distributional law of hydrogen isotopes of individual n-aikanes and their applied research.

  4. The long-chain alkane metabolism network of Alcanivorax dieselolei.

    Science.gov (United States)

    Wang, Wanpeng; Shao, Zongze

    2014-12-12

    Alkane-degrading bacteria are ubiquitous in marine environments, but little is known about how alkane degradation is regulated. Here we investigate alkane sensing, chemotaxis, signal transduction, uptake and pathway regulation in Alcanivorax dieselolei. The outer membrane protein OmpS detects the presence of alkanes and triggers the expression of an alkane chemotaxis complex. The coupling protein CheW2 of the chemotaxis complex, which is induced only by long-chain (LC) alkanes, sends signals to trigger the expression of Cyo, which participates in modulating the expression of the negative regulator protein AlmR. This change in turn leads to the expression of ompT1 and almA, which drive the selective uptake and hydroxylation of LC alkanes, respectively. AlmA is confirmed as a hydroxylase of LC alkanes. Additional factors responsible for the metabolism of medium-chain-length alkanes are also identified, including CheW1, OmpT1 and OmpT2. These results provide new insights into alkane metabolism pathways from alkane sensing to degradation.

  5. 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.

  6. Assembly of organic monolayers on polydicyclopentadiene.

    Science.gov (United States)

    Perring, Mathew; Bowden, Ned B

    2008-09-16

    The first well-defined organic monolayers assembled on polydicyclopentadiene is reported. Commercial grade dicyclopentadiene was polymerized with the Grubbs' second-generation catalyst in a fume hood under ambient conditions at very low monomer to catalyst loadings of 20 000 to 1. This simple method resulted in a polymer that was a hard solid and appeared slightly yellow. Brief exposures of a few seconds of this polymer to Br 2 lead to a surface with approximately half of the olefins brominated as shown by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection-infrared (ATR-IR) spectroscopy. The ATR-IR spectroscopy was carried out with the polymer in contact with a Ge hemisphere housed in a GATR accessory from Harrick. This brominated polydicyclopentadiene was immersed in DMF with 4-(trifluoromethyl)benzylamine to assemble a monolayer. The amines displaced Br on the surface to form a monolayer that exposed a CF 3 group on the surface. The surface was extensively studied by XPS using the method described by Tougaard to find the distribution of F within the surface layer. The ratio for the peak area, Ap, to the background height, B, measured 30 eV below the peak maximum was 109.8 eV. This value clearly indicated that F was found only at the surface and was not found within the polymer. A surface coverage of 1.37 amines per nm (2) was estimated and indicated that the monolayer was 28% as dense as a similar monolayer assembled from thiols on gold. Finally, a simple method to pattern these monolayers using soft lithography is described. This work is critically important because it reports the first monolayers on a relatively new and emerging polymer that has many desirable physical characteristics such as high hardness, chemical stability, and ease of forming different shapes.

  7. Leaf wax n-alkane distributions in and across modern plants: Implications for paleoecology and chemotaxonomy

    Science.gov (United States)

    Bush, Rosemary T.; McInerney, Francesca A.

    2013-09-01

    Long chain (C21 to C37) n-alkanes are among the most long-lived and widely utilized terrestrial plant biomarkers. Dozens of studies have examined the range and variation of n-alkane chain-length abundances in modern plants from around the world, and n-alkane distributions have been used for a variety of purposes in paleoclimatology and paleoecology as well as chemotaxonomy. However, most of the paleoecological applications of n-alkane distributions have been based on a narrow set of modern data that cannot address intra- and inter-plant variability. Here, we present the results of a study using trees from near Chicago, IL, USA, as well as a meta-analysis of published data on modern plant n-alkane distributions. First, we test the conformity of n-alkane distributions in mature leaves across the canopy of 38 individual plants from 24 species as well as across a single growing season and find no significant differences for either canopy position or time of leaf collection. Second, we compile 2093 observations from 86 sources, including the new data here, to examine the generalities of n-alkane parameters such as carbon preference index (CPI), average chain length (ACL), and chain-length ratios for different plant groups. We show that angiosperms generally produce more n-alkanes than do gymnosperms, supporting previous observations, and furthermore that CPI values show such variation in modern plants that it is prudent to discard the use of CPI as a quantitative indicator of n-alkane degradation in sediments. We also test the hypotheses that certain n-alkane chain lengths predominate in and therefore can be representative of particular plant groups, namely, C23 and C25 in Sphagnum mosses, C27 and C29 in woody plants, and C31 in graminoids (grasses). We find that chain-length distributions are highly variable within plant groups, such that chemotaxonomic distinctions between grasses and woody plants are difficult to make based on n-alkane abundances. In contrast

  8. Ubiquitous Presence and Novel Diversity of Anaerobic Alkane Degraders in Cold Marine Sediments.

    Science.gov (United States)

    Gittel, Antje; Donhauser, Johanna; Røy, Hans; Girguis, Peter R; Jørgensen, Bo B; Kjeldsen, Kasper U

    2015-01-01

    Alkanes are major constituents of crude oil and are released to the marine environment by natural seepage and from anthropogenic sources. Due to their chemical inertness, their removal from anoxic marine sediments is primarily controlled by the activity of anaerobic alkane-degrading microorganisms. To facilitate comprehensive cultivation-independent surveys of the diversity and distribution of anaerobic alkane degraders, we designed novel PCR primers that cover all known diversity of the 1-methylalkyl succinate synthase gene (masD/assA), which catalyzes the initial activation of alkanes. We studied masD/assA gene diversity in pristine and seepage-impacted Danish coastal sediments, as well as in sediments and alkane-degrading enrichment cultures from the Middle Valley (MV) hydrothermal vent system in the Pacific Northwest. MasD/assA genes were ubiquitously present, and the primers captured the diversity of both known and previously undiscovered masD/assA gene diversity. Seepage sediments were dominated by a single masD/assA gene cluster, which is presumably indicative of a substrate-adapted community, while pristine sediments harbored a diverse range of masD/assA phylotypes including those present in seepage sediments. This rare biosphere of anaerobic alkane degraders will likely increase in abundance in the event of seepage or accidental oil spillage. Nanomolar concentrations of short-chain alkanes (SCA) were detected in pristine and seepage sediments. Interestingly, anaerobic alkane degraders closely related to strain BuS5, the only SCA degrader in pure culture, were found in mesophilic MV enrichments, but not in cold sediments from Danish waters. We propose that the new masD/assA gene lineages in these sediments represent novel phylotypes that are either fueled by naturally occurring low levels of SCA or that metabolize medium- to long-chain alkanes. Our study highlights that masD/assA genes are a relevant diagnostic marker to identify seepage and microseepage, e

  9. Toward aldehyde and alkane production by removing aldehyde reductase activity in Escherichia coli.

    Science.gov (United States)

    Rodriguez, Gabriel M; Atsumi, Shota

    2014-09-01

    Advances in synthetic biology and metabolic engineering have enabled the construction of novel biological routes to valuable chemicals using suitable microbial hosts. Aldehydes serve as chemical feedstocks in the synthesis of rubbers, plastics, and other larger molecules. Microbial production of alkanes is dependent on the formation of a fatty aldehyde intermediate which is converted to an alkane by an aldehyde deformylating oxygenase (ADO). However, microbial hosts such as Escherichia coli are plagued by many highly active endogenous aldehyde reductases (ALRs) that convert aldehydes to alcohols, which greatly complicates strain engineering for aldehyde and alkane production. It has been shown that the endogenous ALR activity outcompetes the ADO enzyme for fatty aldehyde substrate. The large degree of ALR redundancy coupled with an incomplete database of ALRs represents a significant obstacle in engineering E. coli for either aldehyde or alkane production. In this study, we identified 44 ALR candidates encoded in the E. coli genome using bioinformatics tools, and undertook a comprehensive screening by measuring the ability of these enzymes to produce isobutanol. From the pool of 44 candidates, we found five new ALRs using this screening method (YahK, DkgA, GldA, YbbO, and YghA). Combined deletions of all 13 known ALRs resulted in a 90-99% reduction in endogenous ALR activity for a wide range of aldehyde substrates (C2-C12). Elucidation of the ALRs found in E. coli could guide one in reducing competing alcohol formation during alkane or aldehyde production.

  10. 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.

  11. Molecular Diffusive Motion in a Monolayer of a Model Lubricant

    Science.gov (United States)

    Diama, A.; Criswell, L.; Mo, H.; Taub, H.; Herwig, K. W.; Hansen, F. Y.; Volkmann, U. G.; Dimeo, R.; Neumann, D.

    2003-03-01

    Squalane (C_30H_62), a branched alkane of intermediate length consisting of a tetracosane backbone (n-C_24H_50 or C24) and six symmetrically placed methyl sidegroups, is frequently taken as a model lubricant. We have conducted quasielastic neutron scattering (QNS) experiments to investigate the diffusive motion on different time scales in a squalane monolayer adsorbed on the (0001) surfaces of an exfoliated graphite substrate. Unlike tetracosane, high-energy resolution spectra (time scale ˜0.1 - 4 ns) at temperatures of 215 K and 230 K show the energy width of the QNS to have a maximum near Q = 1.2 ÅThis nonmonotonic Q dependence suggests a more complicated diffusive motion than the simple rotation about the long molecular axis believed to occur in a C24 monolayer at this temperature. Lower-energy-resolution spectra (time scale ˜4 - 40 ps) show evidence of two types of diffusive motion whose rates have opposite temperature dependences. The rate of the faster motion decreases as the monolayer is heated, and we speculate that it is due to hindered rotation of the methyl groups. The rate of the slower motion increases with temperature and may involve both uniaxial rotation and translational diffusion. Our experimental results will be compared with molecular dynamics simulations.

  12. A density functional theory study of electronic and magnetic properties of rare earth doped monolayered molybdenum disulphide

    Science.gov (United States)

    Majid, Abdul; Imtiaz, Anum; Yoshiya, Masato

    2016-10-01

    The effects of Rare Earth (RE) atoms Sm, Eu, Gd, Tb, and Dy doping on structural, electronic, and magnetic properties of single layer MoS2 were investigated using first principles calculations. The analysis of electronic properties pointed out the appearance of host-impurity hybrid states on the edges of principal bands of the material, which appeared to cause narrowing of its bandgap. The values of total magnetic moment were calculated as 3.3 μB, 8.1 μB, 8.5 μB, 6.8 μB, and 6.4 μB for Sm-, Eu-, Gd-, Tb-, and Dy-doped MoS2, respectively. The underestimation of magnetic moment in the case of Sm doping is found which is assigned to shielding of 4f moments and quenching of angular momentum caused by Sm 4f-S 3p hybridization. On the other hand, the observed overestimation of magnetic moments for Eu and Gd cases is likely to be due to increase in angular momentum due to indirect exchange interaction of highly localized 4f states via 5d or 6s conduction electrons. The findings of this work point out the possibilities of tuning the band gap and magnetic properties of monolayer MoS2 upon RE doping for realization of p-type ferromagnetic semiconductors.

  13. Metal dependent motif transition in a self-assembled monolayer of bipyridine derivatives via coordination: An STM study

    Science.gov (United States)

    Wang, Yi; Yuan, Qunhui; Xu, Hongbo; Zhu, Xuefeng; Gan, Wei

    2016-07-01

    Low-dimensional molecular motifs with diversity developed via the on-surface chemistry are attracting growing interest for their potential in advanced nanofabrication. In this work, scanning tunneling microscopy was employed to investigate the in situ and ex situ metal coordinations between 4,4'-ditetradecyl-2,2'-bipyridine (bpy) and Zn(ii) or Cu(ii) ions at a highly oriented pyrolytic graphite (HOPG)/1-phenyloctane interface under ambient conditions. The results demonstrate that the bpy adopts a flat-lying orientation with its substituted alkyl chains in a tail-to-tail arrangement in a bpy monolayer. For the in situ coordination, the bpy/Zn(ii) and bpy/Cu(ii) complexes are aligned in edge-on fashions, wherein the bpy stands vertically on the HOPG surface and interdigitates at the alkyl chains. In the two-dimensional arrays of ex situ coordinated complexes, metal dependent motifs have been observed with Zn(ii) and Cu(ii), wherein the bipyridine moieties are parallel to the graphite surface. These results suggest that the desired on-surface coordination architectures may be achieved by the intentional selection of the metal centers.

  14. Hybrid graphene-BC2N monolayers and nanoribbons with extended line defects: An ab initio study

    Science.gov (United States)

    Guerra, T.; Azevedo, S.; Machado, M.

    2017-02-01

    Opening a bandgap in graphene is probably one of the most important and urgent topics in the graphene research currently, since most of the proposed applications for graphene in nanoelectronic devices require the ability to adjust its bandgap. In this work we perform first-principles calculations to investigate the alterations at the structural, energetic, electronic and magnetic properties of hybrid graphene-BC2N monolayers (GBMLs) and zigzag graphene-BC2N nanoribbons (ZGBNRs) with different types of extended line defects (ELDs) at the grain boundary. Different reconstruction processes are observed forming different types of ELDs depending on the nature of the atoms into the grain boundary as well as the structures type, arrangement, position/size of domains, and inserted atoms. The inclusion of these ELDs creates edge type effects in the ELD at GBNMLs, inducing spin polarization and localization of states at the Fermi level. GBNMLs show a wide range of electronic structures going from semimetallic to semiconducting and metallic, which can have magnetic ground states with ferromagnetic and antiferromagnetic. ZGBNRs are always metallic with ferromagnetic coupling between carbon atoms at the structures edges.

  15. 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.

  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. Homology modeling and protein engineering of alkane monooxygenase in Burkholderia thailandensis MSMB121: in silico insights.

    Science.gov (United States)

    Jain, Chakresh Kumar; Gupta, Money; Prasad, Yamuna; Wadhwa, Gulshan; Sharma, Sanjeev Kumar

    2014-07-01

    The degradation of hydrocarbons plays an important role in the eco-balancing of petroleum products, pesticides and other toxic products in the environment. The degradation of hydrocarbons by microbes such as Geobacillus thermodenitrificans, Burkhulderia, Gordonia sp. and Acinetobacter sp. has been studied intensively in the literature. The present study focused on the in silico protein engineering of alkane monooxygenase (ladA)-a protein involved in the alkane degradation pathway. We demonstrated the improvement in substrate binding energy with engineered ladA in Burkholderia thailandensis MSMB121. We identified an ortholog of ladA monooxygenase found in B. thailandensis MSMB121, and showed it to be an enzyme involved in an alkane degradation pathway studied extensively in Geobacillus thermodenitrificans. Homology modeling of the three-dimensional structure of ladA was performed with a crystal structure (protein databank ID: 3B9N) as a template in MODELLER 9v11, and further validated using PROCHECK, VERIFY-3D and WHATIF tools. Specific amino acids were substituted in the region corresponding to amino acids 305-370 of ladA protein, resulting in an enhancement of binding energy in different alkane chain molecules as compared to wild protein structures in the docking experiments. The substrate binding energy with the protein was calculated using Vina (Implemented in VEGAZZ). Molecular dynamics simulations were performed to study the dynamics of different alkane chain molecules inside the binding pockets of wild and mutated ladA. Here, we hypothesize an improvement in binding energies and accessibility of substrates towards engineered ladA enzyme, which could be further facilitated for wet laboratory-based experiments for validation of the alkane degradation pathway in this organism.

  18. Evolution of chemical bonding and electron density rearrangements during D(3h) → D(3d) reaction in monolayered TiS2: a QTAIM and ELF study.

    Science.gov (United States)

    Ryzhikov, Maxim R; Slepkov, Vladimir A; Kozlova, Svetlana G; Gabuda, Svyatoslav P

    2014-08-15

    Monolayered titanium disulfide TiS2, a prospective nanoelectronic material, was previously shown to be subject to an exothermic solid-state D3h -D3d reaction that proceeds via a newly discovered transition state. Here, we study the reaction in detail using topological methods of quantum chemistry (quantum theory of atoms in molecules and electron localization function analysis) and show how electron density and chemical bonding between the atoms change in the course of the reaction. The reaction is shown to undergo a series of topological catastrophes, associated with elementary chemical events such as break and formation of bonds (including the unexpected formation of S-S bonding between sulfur layers), and rearrangement of electron density of outer valence and core shells.

  19. Mie potentials for phase equilibria calculations: application to alkanes and perfluoroalkanes.

    Science.gov (United States)

    Potoff, Jeffrey J; Bernard-Brunel, Damien A

    2009-11-05

    Transferable united-atom force fields, based on n - 6 Lennard-Jones potentials, are presented for normal alkanes and perfluorocarbons. It is shown that by varying the repulsive exponent the range of the potential can be altered, leading to improved predictions of vapor pressures while also reproducing saturated liquid densities to high accuracy. Histogram-reweighting Monte Carlo simulations in the grand canonical ensemble are used to determine the vapor liquid coexistence curves, vapor pressures, heats of vaporization, and critical points for normal alkanes methane through tetradecane, and perfluorocarbons perfluoromethane through perfluorooctane. For all molecules studied, saturated liquid densities are reproduced to within 1% of experiment. Vapor pressures for normal alkanes and perfluorocarbons were predicted to within 3% and 6% of experiment, respectively. Calculations performed for binary mixture vapor-liquid equilibria for propane + pentane show excellent agreement with experiment, while slight deviations are observed for the ethane + perfluoroethane mixture.

  20. 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...

  1. Optically detected ESR and low magnetic field signals from spin triads: 2-imidazoline-1-oxyl derivatives in X-irradiated alkane liquids as a method to study three-spin systems.

    Science.gov (United States)

    Sviridenko, Fyodor B; Stass, Dmitri V; Kobzeva, Tatyana V; Tretyakov, Evgeny V; Klyatskaya, Svetlana V; Mshvidobadze, Elena V; Vasilevsky, Sergey F; Molin, Yuri N

    2004-03-10

    This contribution reports the design and synthesis of a series of spin-labeled charge acceptors to produce three-spin systems of "radical ion/biradical ion" type in X-irradiated alkane liquids. This opens the way to study spin triads in experimental conditions, in which short-lived radical ion pairs are conventionally studied, thus offering optically detected techniques such as magneto-resonance OD ESR and level-crossing MARY spectroscopy. The structure of the synthesized 2-imidazoline-1-oxyl derivatives is A-Sp-R, where A is a positive or negative charge acceptor, R is a stable radical, and Sp is a hydrocarbon bridge. The set of 20+ compounds represent a convenient tool to construct experimental three-spin systems with various properties, e.g. with the "third" spin introduced into one or the other partner of the radical ion pair. The degree of exchange coupling between the two paramagnetic fragments in the biradical ion has been demonstrated to strongly depend on the type of the radical fragment R and the structure of the bridge Sp. As a result, a series of acceptors with systematically reduced exchange interaction has been synthesized, and optimal systems for the observation of low magnetic field effect have been found. In the most favorable case, an OD ESR signal from a spin triad living as short as ca. 100 ns has been registered as a single unresolved line. The exchange integral for this biradical anion (9) was estimated from OD ESR and ESR experiments to be ca. 10(3) G by the order of magnitude, which is much greater than the hyperfine couplings in the biradical ion but much smaller than the thermal energy kT.

  2. Stiffness of lipid monolayers with phase coexistence.

    Science.gov (United States)

    Caruso, Benjamín; Mangiarotti, Agustín; Wilke, Natalia

    2013-08-27

    The surface dilational modulus--or compressibility modulus--has been previously studied for monolayers composed of pure materials, where a jump in this modulus was related with the onset of percolation as a result of the establishment of a connected structure at the molecular level. In this work, we focused on monolayers composed of two components of low lateral miscibility. Our aim was to investigate the compressibility of mixed monolayers at pressures and compositions in the two-phase region of the phase diagram, in order to analyze the effect of the mechanical properties of each phase on the stiffness of the composite. In nine different systems with distinct molecular dipoles and charges, the stiffness of each phase and the texture at the plane of the monolayer were studied. In this way, we were able to analyze the general compressibility of two-phase lipid monolayers, regardless of the properties of their constituent parts. The results are discussed in the light of the following two hypotheses: first, the stiffness of the composite could be dominated by the stiffness of each phase as a weighted sum according to the percentage of each phase area, regardless of the distribution of the phases in the plane of the monolayer. Alternatively, the stiffness of the composite could be dominated by the mechanical properties of the continuous phase. Our results were better explained by this latter proposal, as in all the analyzed mixtures it was found that the mechanical properties of the percolating phase were the determining factors. The value of the compression modulus was closer to the value of the connected phase than to that of the dispersed phase, indicating that the bidimensional composites displayed mechanical properties that were related to the properties of each phases in a rather complex manner.

  3. Adsorption and dissociation of H2S on monometallic and monolayer bimetallic Ni/Pd(111) surfaces: A first-principles study

    Science.gov (United States)

    Li, Yi; Huang, Pan; Tao, Dandan; Wu, Juan; Qiu, Mei; Huang, Xin; Ding, Kaining; Chen, Wenkai; Su, Wenyue; Zhang, Yongfan

    2016-11-01

    Periodic density functional theory calculations have been performed to investigate the adsorption structures and dissociative reaction pathways for H2S molecule on Ni(111), Pd(111) and Ni/Pd(111) monolayer bimetallic surfaces with surface monolayer and subsurface monolayer structures. Our results indicate that, for the molecular adsorption mode, the introducing Pd atoms on Ni(111) can enhance the binding strength between H2S and the surface, while an opposite effect is achieved when the Ni monolayer is formed on Pd(111) surface. The decompositions of H2S molecule on all Ni/Pd(111) surfaces are exothermic, especially for the surfaces that the top layer is composed of Ni atoms. According to the predicted minimum energy paths that connect the molecular and dissociative states, two elementary steps are found for all Ni/Pd(111) metal surfaces, and the breaking of the first Hsbnd S bond is the rate-determining step for the H2S dissociation. Our results reveal that in most cases, the decomposition of H2S molecule on the monometallic and Ni/Pd(111) monolayer bimetallic surfaces is easy to happen. However, on the monolayer Ni-Pd(111) surface, there is a competition between the trapping-desorption channel and activated dissociation channel, which implies that depositing one monolayer Ni on a Pd(111) surface may help reducing sulfur poisoning by hindering the dissociation of H2S molecule.

  4. Revisiting Mt. Kilimanjaro: Do n-alkane biomarkers in soils reflect the δ2H isotopic composition of precipitation?

    Directory of Open Access Journals (Sweden)

    M. Zech

    2014-06-01

    Full Text Available During the last decade compound-specific deuterium (δ2H analysis of plant leaf wax-derived n-alkanes has become a promising and popular tool in paleoclimate research. This is based on the widely accepted assumption that n-alkanes in soils and sediments generally reflect δ2H of precipitation (δ2Hprec. Recently, several authors suggested that δ2H of n-alkanes (δ2H,sub>n-alkanes can also be used as proxy in paleoaltimetry studies. Here we present results from a δ2H transect study (~1500 to 4000 m a.s.l. carried out on precipitation and soil samples taken from the humid southern slopes of Mt. Kilimanjaro. Contrary to earlier suggestions, a distinct altitude effect in δ2Hprec is present above ~2000 m a.s.l., i.e. δ2Hprec values become more negative with increasing altitude. The compound-specific δ2H values of nC27 and nC29 do not confirm this altitudinal trend, but rather become more positive both in the O-layers (organic layers and the Ah-horizons (mineral topsoils. Although our δ2Hn-alkane results are in agreement with previously published results from the southern slopes of Mt. Kilimanjaro (Peterse et al., 2009, BG, 6, 2799–2807, a major re-interpretation is required given that the δ2Hn-alkane results do not reflect the δ2Hprec results. The theoretical framework for this re-interpretation is based on the evaporative isotopic enrichment of leaf water associated with transpiration process. Modelling results show that relative humidity, decreasing considerably along the southern slopes of Mt. Kilimanjaro (from 78% at ~ 2000 m a.s.l. to 51% at 4000 m a.s.l., strongly controls δ2Hleaf water. The modelled δ2H leaf water enrichment along the altitudinal transect matches well the measured 2H leaf water enrichment as assessed by using the δ2Hprec and δ2Hn-alkane results and biosynthetic fractionation during n-alkane biosynthesis in leaves. Given that our results clearly demonstrate that n-alkanes in soils do not simply reflect δ2Hprec

  5. Thermal non-oxidative aromatization of light alkanes catalyzed by gallium nitride.

    Science.gov (United States)

    Li, Lu; Mu, Xiaoyue; Liu, Wenbo; Kong, Xianghua; Fan, Shizhao; Mi, Zetian; Li, Chao-Jun

    2014-12-15

    The thermal catalytic activity of GaN in non-oxidative alkane dehydroaromatization has been discovered for the first time. The origin of the catalytic activity was studied experimentally and theoretically. Commercially available GaN powders with a wurtzite crystal structure showed superior stability and reactivity for converting light alkanes, including methane, propane, n-butane, n-hexane and cyclohexane into benzene at an elevated temperature with high selectivity. The catalyst is highly robust and can be used repeatedly without noticeable deactivation.

  6. Homolytic Bond Dissociation Enthalpies of C C and C-H Bonds in Highly Crowded Alkanes

    Institute of Scientific and Technical Information of China (English)

    ZHU Chen; RUI Lei; FU Yao

    2008-01-01

    The homolytic C-C and C--H bond dissociation enthalpyies (BDE) of highly crowded alkanes were calcu- lated by using an ONIOM-G3B3 method. Geometric parameters such as bond length, bond angle and molecular volume were carefully investigated, as most of the acyclic alkanes in this study were not yet synthesized. These pa-rameters reflect the influence of steric effect on BDE. Good correlations were found between the rapid decrease of BDE and the increase of molecular volumes. The correlations can be applied to the prediction of the possible exis-tence of many highly strained compounds.

  7. Measurement and modelling of hydrogen bonding in 1-alkanol plus n-alkane binary mixtures

    DEFF Research Database (Denmark)

    von Solms, Nicolas; Jensen, Lars; Kofod, Jonas L.;

    2007-01-01

    Two equations of state (simplified PC-SAFT and CPA) are used to predict the monomer fraction of 1-alkanols in binary mixtures with n-alkanes. It is found that the choice of parameters and association schemes significantly affects the ability of a model to predict hydrogen bonding in mixtures, even...... studies, which is clarified in the present work. New hydrogen bonding data based on infrared spectroscopy are reported for seven binary mixtures of alcohols and alkanes. (C) 2007 Elsevier B.V. All rights reserved....

  8. In situ detection of anaerobic alkane metabolites in subsurface environments

    OpenAIRE

    Lisa eGieg; Akhil eAgrawal

    2013-01-01

    Alkanes comprise a substantial fraction of crude oil and refined fuels. As such, they are prevalent within deep subsurface fossil fuel deposits and in shallow subsurface environments such as aquifers that are contaminated with hydrocarbons. These environments are typically anaerobic, and host diverse microbial communities that can potentially use alkanes as substrates. Anaerobic alkane biodegradation has been reported to occur under nitrate-reducing, sulfate-reducing, and methanogenic cond...

  9. In situ detection of anaerobic alkane metabolites in subsurface environments

    OpenAIRE

    Agrawal, Akhil; Gieg, Lisa M.

    2013-01-01

    Alkanes comprise a substantial fraction of crude oil and refined fuels. As such, they are prevalent within deep subsurface fossil fuel deposits and in shallow subsurface environments such as aquifers that are contaminated with hydrocarbons. These environments are typically anaerobic, and host diverse microbial communities that can potentially use alkanes as substrates. Anaerobic alkane biodegradation has been reported to occur under nitrate-reducing, sulfate-reducing, and methanogenic conditi...

  10. 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.

  11. 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

    NARCIS (Netherlands)

    Schutte, M.E.; Freidig, A.P.; Sandt, J.J.M. van de; Alink, G.M.; Rietjens, I.M.C.M.; Groten, J.P.

    2006-01-01

    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 th

  12. 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

    NARCIS (Netherlands)

    Schutte, M.E.; Freidig, A.P.; Sandt, van de J.J.M.; Alink, G.M.; Rietjens, I.M.C.M.; Groten, J.P.

    2006-01-01

    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 th

  13. Study on the Selection and Degradation Characteristics of Long-chain Alkanes Degrading Bacteria%降解长链烷烃菌株的选育及性能研究

    Institute of Scientific and Technical Information of China (English)

    吕立君; 王光华; 李文兵; 卢露露; 刘念汝; 陈彪; 刘贝

    2016-01-01

    以正十六烷无机盐培养基为选择培养基,从武汉石化输油管附近土壤中筛选出1株高效降解长链烷烃的菌株,命名C3,对其进行生理生化、16S rDNA鉴定,C3为不动杆菌属。在正十六烷浓度为1000 mg/L的无机盐培养基中接入4%的种子液,放入35℃、125 r/min摇床中震荡60 h ,C3对正十六烷的降解率可达100%,其降解动力学拟合结果符合Monod模型。将C3应用到柴蜡的降解,96 h后,1000 mg/L的柴蜡混合溶液的降解率能达到91%。C3产生的生物表面活性剂经鉴定为磷脂类活性剂,排油圈直径为80 mm ,CMC约为35 mg/L ,能将水的表面张力降低到20.79 mN/m。该菌株对长链烷烃的降解提供了良好的菌源。%With the mineral salt medium with the n -hexadecane as the selecting medium ,a strain that can effectively de-grade the long-chain alkane is screened out from the soil near the pipeline of Wuhan Petrochemical Works ,named as C3 , conducted for physiological and biochemical identification and 16S rDNA comparison and the strain C3 is identified as Acine-tobacter sp .The n-hexadecane degradation is 100% after 4% seed liquid of the strain is inoculated on the mineral salt medi-um with 1 000 mg/L of n-hexadecane and cultured at 35 ℃ 、125 r/min for 60 h ,in accordance with Monod equation .The degradation of diesel and paraffin mixture can reach 91% after 96 h .The biosurfactants produced by strain C3 ,is identified as phospholipids ,whose oil spreading size is 80 mm ,the CMC of purified product is 35 mg/L ,and the lowest surface tension is 20 .79 mN/m .The study has provided the good resources of the microbial strain for degrading long -chain alkane .

  14. Phase Equilibria of Water/CO2 and Water/n-Alkane Mixtures from Polarizable Models.

    Science.gov (United States)

    Jiang, Hao; Economou, Ioannis G; Panagiotopoulos, Athanassios Z

    2017-02-16

    Phase equilibria of water/CO2 and water/n-alkane mixtures over a range of temperatures and pressures were obtained from Monte Carlo simulations in the Gibbs ensemble. Three sets of Drude-type polarizable models for water, namely the BK3, GCP, and HBP models, were combined with a polarizable Gaussian charge CO2 (PGC) model to represent the water/CO2 mixture. The HBP water model describes hydrogen bonds between water and CO2 explicitly. All models underestimate CO2 solubility in water if standard combining rules are used for the dispersion interactions between water and CO2. With the dispersion parameters optimized to phase compositions, the BK3 and GCP models were able to represent the CO2 solubility in water, however, the water composition in CO2-rich phase is systematically underestimated. Accurate representation of compositions for both water- and CO2-rich phases cannot be achieved even after optimizing the cross interaction parameters. By contrast, accurate compositions for both water- and CO2-rich phases were obtained with hydrogen bonding parameters determined from the second virial coefficient for water/CO2. Phase equilibria of water/n-alkane mixtures were also studied using the HBP water and an exponenial-6 united-atom n-alkanes model. The dispersion interactions between water and n-alkanes were optimized to Henry's constants of methane and ethane in water. The HBP water and united-atom n-alkane models underestimate water content in the n-alkane-rich phase; this underestimation is likely due to the neglect of electrostatic and induction energies in the united-atom model.

  15. Anaerobic biodegradation of longer-chain n-alkanes coupled to methane production in oil sands tailings.

    Science.gov (United States)

    Siddique, Tariq; Penner, Tara; Semple, Kathleen; Foght, Julia M

    2011-07-01

    Extraction of bitumen from mined oil sands ores produces enormous volumes of tailings that are stored in settling basins (current inventory ≥ 840 million m(3)). Our previous studies revealed that certain hydrocarbons (short-chain n-alkanes [C(6)-C(10)] and monoaromatics [toluene, o-xylene, m-xylene]) in residual naphtha entrained in the tailings are biodegraded to CH(4) by a consortium of microorganisms. Here we show that higher molecular weight n-alkanes (C(14), C(16), and C(18)) are also degraded under methanogenic conditions in oil sands tailings, albeit after a lengthy lag (~180 d) before the onset of methanogenesis. Gas chromatographic analyses showed that the longer-chain n-alkanes each added at ~400 mg L(-1) were completely degraded by the resident microorganisms within ~440 d at ~20 °C. 16S rRNA gene sequence analysis of clone libraries implied that the predominant pathway of longer-chain n-alkane metabolism in tailings is through syntrophic oxidation of n-alkanes coupled with CO(2) reduction to CH(4). These studies demonstrating methanogenic biodegradation of longer-chain n-alkanes by microbes native to oil sands tailings may be important for effective management of tailings and greenhouse gas emissions from tailings ponds.

  16. Expanding the alkane oxygenase toolbox: new enzymes and applications.

    Science.gov (United States)

    van Beilen, Jan B; Funhoff, Enrico G

    2005-06-01

    As highly reduced hydrocarbons are abundant in the environment, enzymes that catalyze the terminal or subterminal oxygenation of alkanes are relatively easy to find. A number of these enzymes have been biochemically characterized in detail, because the potential of alkane hydroxylases to catalyze high added-value reactions is widely recognized. Nevertheless, the industrial application of these enzymes is restricted owing to the complex biochemistry, challenging process requirements, and the limited number of cloned and expressed enzymes. Rational and evolutionary engineering approaches have started to yield more robust and versatile enzyme systems, broadening the alkane oxygenase portfolio. In addition, metagenomic approaches provide access to many novel alkane oxygenase sequences.

  17. Selective activation of lower alkanes

    OpenAIRE

    Tope, Balkrishna

    2008-01-01

    This goal of the present work is study highly industrially important reaction i) Oxy chlorination of methane (OCM) and ii) Ethane oxidative dehydrogenation (ODH). Oxy chlorination of methane is studied over four LaOCl precursor. Different analytical techniques including BET, XRD, SEM, TPD, Raman and IR spectroscopy, were used to characterize commercial samples. The temperature programmed chlorination experiments were carried out to study the conversion of the LaOCl precursor to the LaCl3 cata...

  18. The effect of environmental factors on stable isotopic composition of n-alkanes in Mediterranean olive oils

    Science.gov (United States)

    Pedentchouk, Nikolai; Mihailova, Alina; Abbado, Dimitri

    2014-05-01

    Traceability of the geographic origin of olive oils is an important issue from both commercial and health perspectives. This study evaluates the impact of environmental factors on stable C and H isotope compositions of n-alkanes in extra virgin olive oils from Croatia, France, Greece, Italy, Morocco, Portugal, Slovenia, and Spain. The data are used to investigate the applicability of stable isotope methodology for olive oil regional classification in the Mediterranean region. Analysis of stable C isotope composition of n-C29 alkane showed that extra virgin olive oils from Portugal and Spain have the most positive n-C29 alkane delta13C values. Conversely, olive oils from Slovenia, northern and central Italy are characterized by the most negative values. Overall, the n-C29 alkane delta13C values show a positive correlation with the mean air temperature during August-December and a negative correlation with the mean relative humidity during these months. Analysis of stable H isotope composition of n-C29 alkane revealed that the deltaD values are the most positive in olive oils from Greece and Morocco and the most negative in oils from northern Italy. The deltaD values of oils show significant correlation with all the analyses geographical parameters: the mean air temperature and relative humidity during August-December, the total amount of rainfall (the same months) and the annual deltaD values of precipitation. As predictor variables in the Categorical Data Analysis, the n-C29 alkane deltaD values show the most significant discriminative power, followed by the n-C29 alkane delta13C values. Overall, 93.4% of olive oil samples have been classified correctly into one of the production regions. Our findings suggest that an integrated analysis of C and H isotope compositions of n-alkanes extracted from extra virgin olive oil could become a useful tool for geographical provenancing of this highly popular food commodity.

  19. Alkane distribution and carbon isotope composition in fossil leaves: An interpretation of plant physiology in the geologic past

    Science.gov (United States)

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

    2014-12-01

    The relative chain-length distribution and carbon-isotope composition of n-alkanes extracted from sedimentary rocks are important geochemical tools for investigating past terrestrial ecosystems. Alkanes preserved in ancient sediments are assumed to be contemporaneous, derived from the same ecosystem, and integrated from the biomass present on the landscape at the time of deposition. Further, there is an underlying assumption that ancient plants exhibited the same metabolic and physiological responses to climate conditions that are observed for modern plants. Interpretations of alkane abundances and isotopic signatures are complicated by the strong influence of phylogenetic affiliation and ecological factors, such as canopy structure. A better understanding of how ecosystem and taxa influence alkane properties, including homologue abundance patterns and leaf-lipid carbon isotope fractionation would help strengthen paleoecological interpretations based on these widely employed plant biomarkers. In this study, we analyze the alkane chain-length distribution and carbon-isotope composition of phytoleim and alkanes (d13Cleaf and d13Clipid) extracted from a selection of Cretaceous and Paleocene fossil leaves from the Guaduas and Cerrejon Formations of Colombia. These data were compared with data for the same families in a modern analogue biome. Photosynthetic and biosynthetic fractionation (∆leaf and elipid) values determined from the fossil material indicate carbon metabolism patterns were similar to modern plants. Fossil data were incorporated in a biomass-weighted mixing model to represent the expected lipid complement of sediment arising from this ecosystem and compared with alkane measurements from the rock matrix. Modeled and observed isotopic and abundance patterns match well for alkane homologs most abundant in plants (i.e., n-C27 to n-C33). The model illustrates the importance of understanding biases in litter flux and taphonomic pressures inherent in the

  20. Electrochemical and structural characterization of self-assembled thiol monolayers on gold.

    NARCIS (Netherlands)

    Sondag-Huethorst, J.A.M.

    1994-01-01

    Self-assembled alkanethiol monolayers on gold are used as model systems in a fundamental study of the potential-dependent wetting and of the galvanic metal deposition. For using such monolayers as model systems, well-defined and ordered monolayers are required. In order to control the quality of the

  1. Geologic seepage of methane and light alkanes in Los Angeles

    Science.gov (United States)

    Doezema, L. A.; Chang, K.; Baril, R.; Nwachuku, I.; Contreras, P.; Marquez, A.; Howard, D.

    2013-12-01

    Natural geologic seepage of methane from underground oil and natural gas reservoirs has been suggested to be an underreported part of the global methane budget. Other light alkanes are also given off in combination with the methane seepage, making it possible that geologic seepage is also a potentially significant global source of these light alkanes. This study reports C1-C5 findings from geologic seepage made in the Los Angeles region. Microseepage, invisible escape of gases, was measured primarily at Kenneth Hahn Regional Park, while macroseepage, the visible release of gases, was measured at the La Brea Tar Pits. Samples were collected using stainless steel canisters and flux chambers and were analyzed using gas chromatography with flame ionization detectors (GC-FID). Average microseepage flux rates of 0.95 μg m-2 h-1 for ethane and 0.51 μg m-2 h-1 were found for propane, while average macroseepage rates for methane, ethane, and propane were 664, 19.8, and 18.1 mg m-2 h-1 respectively. Relationships between microseepage flux rate and location of underground oil and natural deposit and earthquake fault lines are presented. Additionally, the relative importance of findings in context with global budgets and local air quality is discussed.

  2. Optimized reaction mechanism rate rules for ignition of normal alkanes

    KAUST Repository

    Cai, Liming

    2016-08-11

    The increasing demand for cleaner combustion and reduced greenhouse gas emissions motivates research on the combustion of hydrocarbon fuels and their surrogates. Accurate detailed chemical kinetic models are an important prerequisite for high fidelity reacting flow simulations capable of improving combustor design and operation. The development of such models for many new fuel components and/or surrogate molecules is greatly facilitated by the application of reaction classes and rate rules. Accurate and versatile rate rules are desirable to improve the predictive accuracy of kinetic models. A major contribution in the literature is the recent work by Bugler et al. (2015), which has significantly improved rate rules and thermochemical parameters used in kinetic modeling of alkanes. In the present study, it is demonstrated that rate rules can be used and consistently optimized for a set of normal alkanes including n-heptane, n-octane, n-nonane, n-decane, and n-undecane, thereby improving the predictive accuracy for all the considered fuels. A Bayesian framework is applied in the calibration of the rate rules. The optimized rate rules are subsequently applied to generate a mechanism for n-dodecane, which was not part of the training set for the optimized rate rules. The developed mechanism shows accurate predictions compared with published well-validated mechanisms for a wide range of conditions.

  3. Non-rotator phases in phospholipid monolayers?

    DEFF Research Database (Denmark)

    Kenn, R.M.; Kjær, K.; Möhwald, H.

    1996-01-01

    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...

  4. 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.

  5. 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 of n-alkanes in anaerobic ecosystems plays a pivotal role in biogeochemical carbon cycling and bioremediation, but the requisite genetic machinery is not well elucidated.Desulfatibacillum alkenivorans AK-01 utilizes n-alkanes (C13 to 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 investigate ass-gene expression across AK-01's known substrate range, and microarray-based transcriptomic analysis served to investigate whole-cell responses to growth on n-hexadecane versus hexadecanoate. RT-qPCR revealed induction of ass gene cluster 1 during growth on all tested alkane substrates, and the transcriptional start sites in cluster 1 were determined via 5'RACE. Induction of ass gene 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.

  6. 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.

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

    Science.gov (United States)

    Huang, Xianyu; Xue, Jiantao; Guo, Shouyu

    2012-03-01

    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 C21 and 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 δ 13C 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.

  8. Molecular simulations of mixed self-assembled monolayer coated gold nanoparticles in water.

    Science.gov (United States)

    J, Meena Devi

    2015-06-01

    Molecular dynamics simulations have been employed to study the hydration of a series of nanoparticles, each of which was coated with a mixed self-assembled monolayer (SAM) comprising methyl- and hydroxy-terminated alkane thiol chains. The mixing ratio of those chains are different for each nanoparticle. The simulations focused on the wetting behavior of the SAM-coated gold nanoparticles and the distribution and structure of their interfacial water molecules. The interactions of the mixed SAM-coated gold nanoparticles with water were analyzed by evaluating the radial distribution function, hydrogen bonds, the dipole orientations of the water molecules, and the water residence time in the interfacial region. The wettability of the mixed SAM-coated gold nanoparticles improved as the concentration of terminal hydroxy moieties was increased. The distribution and dynamics of the interfacial water molecules were found to be influenced by the mixing ratio of the terminal moieties of the SAM chains. The results of our simulations suggest that the surface interactions of the mixed SAM-coated gold nanoparticles with the aqueous medium can be modulated by systematically altering the mixing ratio of the terminal methyl and hydroxy moieties. This work may lead to new biological and technological applications and inspire the development of novel biomimetic materials. Graphical Abstract Mixed SAM-coated gold nanoparticles.

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

    Science.gov (United States)

    Lee, Chang Woo; Yu, Sang-Cheol; Lee, Joo-Ho; Park, Sun-Ha; Park, Hyun; Oh, Tae-Jin; Lee, Jun Hyuck

    2016-01-01

    Enzymatic alkane hydroxylation reactions are useful for producing pharmaceutical and agricultural chemical intermediates from hydrocarbons. Several cytochrome P450 enzymes catalyze the regio- and stereo-specific hydroxylation of alkanes. We evaluated the substrate binding of a putative CYP alkane hydroxylase (CYP153D17) from the bacterium Sphingomonas sp. PAMC 26605. Substrate affinities to C10–C12 n-alkanes and C10–C14 fatty acids with Kd values varied from 0.42 to 0.59 μM. A longer alkane (C12) bound more strongly than a shorter alkane (C10), while shorter fatty acids (C10, capric acid; C12, lauric acid) bound more strongly than a longer fatty acid (C14, myristic acid). These data displayed a broad substrate specificity of CYP153D17, hence it was named as a putative CYP alkane hydroxylase. Moreover, the crystal structure of CYP153D17 was determined at 3.1 Å resolution. This is the first study to provide structural information for the CYP153D family. Structural analysis showed that a co-purified alkane-like compound bound near the active-site heme group. The alkane-like substrate is in the hydrophobic pocket containing Thr74, Met90, Ala175, Ile240, Leu241, Val244, Leu292, Met295, and Phe393. Comparison with other CYP structures suggested that conformational changes in the β1–β2, α3–α4, and α6–α7 connecting loop are important for incorporating the long hydrophobic alkane-like substrate. These results improve the understanding of the catalytic mechanism of CYP153D17 and provide valuable information for future protein engineering studies. PMID:27941697

  10. 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...

  11. Chain Length Effects of Linear Alkanes in Zeolite Ferrierite. 1. Sorption and 13C NMR Experiments

    NARCIS (Netherlands)

    Well, van Willy J.M.; Cottin, Xavier; Haan, vde Jan W.; Smit, Berend; Nivarthy, Gautam; Lercher, Johannes A.; Hooff, van Jan H.C.; Santen, van Rutger A.

    1998-01-01

    Temperature-programmed desorption, heat of adsorption, adsorption isotherm, and 13C NMR measurements are used to study the sorption properties of linear alkanes in ferrierite. Some remarkable chain length effects are found in these properties. While propane, n-butane, and n-pentane fill the ferrieri

  12. 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

  13. 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

  14. 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

  15. 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...

  16. Cool-flame Extinction During N-Alkane Droplet Combustion in Microgravity

    Science.gov (United States)

    Nayagam, Vedha; Dietrich, Daniel L.; Hicks, Michael C.; Williams, Forman A.

    2014-01-01

    Recent droplet combustion experiments onboard the International Space Station (ISS) have revealed that large n-alkane droplets can continue to burn quasi-steadily following radiative extinction in a low-temperature regime, characterized by negative-temperaturecoefficient (NTC) chemistry. In this study we report experimental observations of n-heptane, n-octane, and n-decane droplets of varying initial sizes burning in oxygen/nitrogen/carbon dioxide and oxygen/helium/nitrogen environments at 1.0, 0.7, and 0.5 atmospheric pressures. The oxygen concentration in these tests varied in the range of 14% to 25% by volume. Large n-alkane droplets exhibited quasi-steady low-temperature burning and extinction following radiative extinction of the visible flame while smaller droplets burned to completion or disruptively extinguished. A vapor-cloud formed in most cases slightly prior to or following the "cool flame" extinction. Results for droplet burning rates in both the hot-flame and cool-flame regimes as well as droplet extinction diameters at the end of each stage are presented. Time histories of radiant emission from the droplet captured using broadband radiometers are also presented. Remarkably the "cool flame" extinction diameters for all the three n-alkanes follow a trend reminiscent of the ignition delay times observed in previous studies. The similarities and differences among the n-alkanes during "cool flame" combustion are discussed using simplified theoretical models of the phenomenon

  17. Adhesive and conformational behaviour of mycolic acid monolayers.

    Science.gov (United States)

    Zhang, Zhenyu; Pen, Yu; Edyvean, Robert G; Banwart, Steven A; Dalgliesh, Robert M; Geoghegan, Mark

    2010-09-01

    We have studied the pH-dependent interaction between mycolic acid (MA) monolayers and hydrophobic and hydrophilic surfaces using molecular (colloidal probe) force spectroscopy. In both cases, hydrophobic and hydrophilic monolayers (prepared by Langmuir-Blodgett and Langmuir-Schaefer deposition on silicon or hydrophobized silicon substrates, respectively) were studied. The force spectroscopy data, fitted with classical DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory to examine the contribution of electrostatic and van der Waals forces, revealed that electrostatic forces are the dominant contribution to the repulsive force between the approaching colloidal probe and MA monolayers. The good agreement between data and the DLVO model suggest that beyond a few nm away from the surface, hydrophobic, hydration, and specific chemical bonding are unlikely to contribute to any significant extent to the interaction energy between the probe and the surface. The pH-dependent conformation of MA molecules in the monolayer at the solid-liquid interface was studied by ellipsometry, neutron reflectometry, and with a quartz crystal microbalance. Monolayers prepared by the Langmuir-Blodgett method demonstrated a distinct pH-responsive behaviour, while monolayers prepared by the Langmuir-Schaefer method were less sensitive to pH variation. It was found that the attachment of water molecules plays a vital role in determining the conformation of the MA monolayers.

  18. C3降解长链烷烃的条件优化及其机理研究%Conditions Optimization and Mechanism Study of Long -Chain Alkane Degradation by C3

    Institute of Scientific and Technical Information of China (English)

    吕立君; 王光华; 李文兵; 卢露露; 刘念汝; 陈彪; 刘贝

    2016-01-01

    以正十六烷无机盐培养基为选择培养基,从武汉石化输油管附近土壤中筛选出了1株高效降解长链烷烃的菌株C3。采用摇瓶实验,研究了菌株C3降解正十六烷的降解条件、降解动力学及降解机理。菌株C3降解正十六烷的最适宜条件为温度35℃、初始pH=7、摇床转速150 r/min。动力学研究显示,在底物质量浓度为1000 mg/L时,其降解动力学拟合结果符合Monod方程,半饱和常数 Ks=609.8 mg/L ,最大降解速率vmax=62.1mg/(L・h)。对C3降解正十六烷产物进行红外光谱及GC/MS分析,推测该降解方式为末端氧化。%Regarding the mineral salt medium with the n-hexadecane as the selecting medium ,strain C3 that can effec-tively degrade the long -chain alkane is screened out from the soil near the pipeline of Wuhan Petrochemical Company .The conditions of degrading n-hexadecane ,growth kinetics and mechanism of degradation are studied by shaking flask tests .It is found that the optimum conditions for the growth of strain C 3 are under 35℃ ,pH=7 and 150 r/min of table speed .The growth kinetics research shows that when the concentration of n-hexadecane is 1 000 mg/L under optimum conditions ,the n-hexadecane degradation is in accordance with Monod equation ,with Ks being 609 .8 mg/L and vmax being 62 .1 mg/(L・h) . The products from the degradation are analyzed by infrared spectrometer and GC/MS and it is forecast that the degradation is terminal oxidation .

  19. Monolayer to interdigitated partial bilayer smectic C transition in thiophene-based spacer mesogens: X-ray diffraction and (13)C nuclear magnetic resonance studies.

    Science.gov (United States)

    Kesava Reddy, M; Varathan, E; Lobo, Nitin P; Roy, Arun; Narasimhaswamy, T; Ramanathan, K V

    2015-10-06

    Mesophase organization of molecules built with thiophene at the center and linked via flexible spacers to rigid side arm core units and terminal alkoxy chains has been investigated. Thirty homologues realized by varying the span of the spacers as well as the length of the terminal chains have been studied. In addition to the enantiotropic nematic phase observed for all the mesogens, the increase of the spacer as well as the terminal chain lengths resulted in the smectic C phase. The molecular organization in the smectic phase as investigated by temperature dependent X-ray diffraction measurements revealed an interesting behavior that depended on the length of the spacer vis-a-vis the length of the terminal chain. Thus, a tilted interdigitated partial bilayer organization was observed for molecules with a shorter spacer length, while a tilted monolayer arrangement was observed for those with a longer spacer length. High-resolution solid state (13)C NMR studies carried out for representative mesogens indicated a U-shape for all the molecules, indicating that intermolecular interactions and molecular dynamics rather than molecular shape are responsible for the observed behavior. Models for the mesophase organization have been considered and the results understood in terms of segregation of incompatible parts of the mesogens combined with steric frustration leading to the observed lamellar order.

  20. Study of the Biotransformation of Tongmai Formula by Human Intestinal Flora and Its Intestinal Permeability across the Caco-2 Cell Monolayer

    Directory of Open Access Journals (Sweden)

    Shuai Wu

    2015-10-01

    Full Text Available Tongmai formula (TMF is a well-known Chinese medicinal preparation that contains isoflavones as its major bioactive constituents. As traditional Chinese medicines (TCMs are usually used by oral administration, their fate inside the intestinal lumen, including their biotransformation by human intestinal flora (HIF and intestinal absorption deserves study. In this work TMF extract was incubated with human intestinal bacteria under anaerobic conditions and the changes in the twelve main constituents of TMF were then investigated. Their intestinal permeabilities, i.e., the transport capability across the intestinal brush border were investigated with a human colon carcinoma cell line (Caco­2 cell monolayer model to predict the absorption mechanism. Meanwhile, rapid HPLC-DAD methods were established for the assay. According to the biotransformation curves of the twelve constituents and the permeability coefficients, the intestinal absorption capacity of the typical compounds was elevated from the levels of 10−7 cm/s to 10−5 cm/s from those of the original compounds in TMF. Among them the main isoflavone glycosides puerarin (4, mirificin (6 and daidzin (7 were transformed into the same aglycone, daidzein (10. Therefore it was predicted that the aglycone compounds might be the real active ingredients in TMF. The models used can represent a novel path for the TCM studies.

  1. Study of the Biotransformation of Tongmai Formula by Human Intestinal Flora and Its Intestinal Permeability across the Caco-2 Cell Monolayer.

    Science.gov (United States)

    Wu, Shuai; Xu, Wei; Wang, Fu-Rong; Yang, Xiu-Wei

    2015-10-15

    Tongmai formula (TMF) is a well-known Chinese medicinal preparation that contains isoflavones as its major bioactive constituents. As traditional Chinese medicines (TCMs) are usually used by oral administration, their fate inside the intestinal lumen, including their biotransformation by human intestinal flora (HIF) and intestinal absorption deserves study. In this work TMF extract was incubated with human intestinal bacteria under anaerobic conditions and the changes in the twelve main constituents of TMF were then investigated. Their intestinal permeabilities, i.e., the transport capability across the intestinal brush border were investigated with a human colon carcinoma cell line (Caco-2) cell monolayer model to predict the absorption mechanism. Meanwhile, rapid HPLC-DAD methods were established for the assay. According to the biotransformation curves of the twelve constituents and the permeability coefficients, the intestinal absorption capacity of the typical compounds was elevated from the levels of 10(-7) cm/s to 10(-5) cm/s from those of the original compounds in TMF. Among them the main isoflavone glycosides puerarin (4), mirificin (6) and daidzin (7) were transformed into the same aglycone, daidzein (10). Therefore it was predicted that the aglycone compounds might be the real active ingredients in TMF. The models used can represent a novel path for the TCM studies.

  2. Cuticular and internal n-alkane composition of Lucilia sericata larvae, pupae, male and female imagines: application of HPLC-LLSD and GC/MS-SIM.

    Science.gov (United States)

    Gołębiowski, M; Paszkiewicz, M; Grubba, A; Gąsiewska, D; Boguś, M I; Włóka, E; Wieloch, W; Stepnowski, P

    2012-08-01

    The composition of cuticular and internal n-alkanes in Lucilia sericata larvae, pupae, and male and female imagines were studied. The cuticular and internal lipid extracts were separated by HPLC-LLSD, after which the hydrocarbon fraction was identified by GC/MS in selected ion monitoring (SIM) and total ion current (TIC) modes. The cuticular lipids of the larvae contained seven n-alkanes from C23 to C31. The major n-alkane in L. sericata larvae was C29 (42.1%). The total cuticular n-alkane content in the cuticular lipids was 31.46 μg g-1 of the insect body. The internal lipids of L. sericata larvae contained five n-alkanes ranged from C25 to C31. The most abundant compound was C27 (61.71 μg g-1 of the insect body). Eighteen n-alkanes from C14 to C31 were identified in the cuticular lipids of the pupae. The most abundant n-alkanes ranged from C25 to C31; those with odd-numbered carbon chains were particularly abundant, the major one being C29:0 (59.5%). Traces of eight cuticular n-alkanes were present. The internal lipids of L. sericata pupae contained five n-alkanes, ranging from C25 to C31. The cuticular lipids of female imagines contained 17 n-alkanes from C12 to C30. Among the cuticular n-alkanes of females, C27 (47.5%) was the most abundant compound. Four n-alkanes, with only odd-numbered carbon chains, were identified in the internal lipids of females. The lipids from both sexes of L. sericata had similar n-alkane profiles. The cuticular lipids of adult males contained 16 n-alkanes ranging from C13 to C31. C27 (47.9%) was the most abundant cuticular n-alkanes in males. The same n-alkanes only with odd-numbered carbon chains and in smaller quantities of C27 (0.1%) were also identified in the internal lipids of males. The highest amounts of total cuticular n-alkanes were detected in males and females of L. sericata (330.4 and 158.93 μg g-1 of the insect body, respectively). The quantities of total cuticular alcohols in larvae and pupae were smaller (31.46

  3. Interrogation of Chesapeake Bay sediment microbial communities for intrinsic alkane-utilizing potential under anaerobic conditions.

    Science.gov (United States)

    Johnson, Jamie M; Wawrik, Boris; Isom, Catherine; Boling, Wilford B; Callaghan, Amy V

    2015-02-01

    Based on the transient exposure of Chesapeake Bay sediments to hydrocarbons and the metabolic versatility of known anaerobic alkane-degrading microorganisms, it was hypothesized that distinct Bay sediment communities, governed by geochemical gradients, would have intrinsic alkane-utilizing potential under sulfate-reducing and/or methanogenic conditions. Sediment cores were collected along a transect of the Bay. Community DNA was interrogated via pyrosequencing of 16S rRNA genes, PCR of anaerobic hydrocarbon activation genes, and qPCR of 16S rRNA genes and genes involved in sulfate reduction/methanogenesis. Site sediments were used to establish microcosms amended with n-hexadecane under sulfate-reducing and methanogenic conditions. Sequencing of 16S rRNA genes indicated that sediments associated with hypoxic water columns contained significantly greater proportions of Bacteria and Archaea consistent with syntrophic degradation of organic matter and methanogenesis compared to less reduced sediments. Microbial taxa frequently associated with hydrocarbon-degrading communities were found throughout the Bay, and the genetic potential for hydrocarbon metabolism was demonstrated via the detection of benzyl-(bssA) and alkylsuccinate synthase (assA) genes. Although microcosm studies did not indicate sulfidogenic alkane degradation, the data suggested that methanogenic conversion of alkanes was occurring. These findings highlight the potential role that anaerobic microorganisms could play in the bioremediation of hydrocarbons in the Bay.

  4. Solvent isotope effects on alkane formation by cyanobacterial aldehyde deformylating oxygenase and their mechanistic implications.

    Science.gov (United States)

    Waugh, Matthew W; Marsh, E Neil G

    2014-09-02

    The reaction catalyzed by cyanobacterial aldehyde deformylating oxygenase is of interest both because of its potential application to the production of biofuels and because of the highly unusual nature of the deformylation reaction it catalyzes. Whereas the proton in the product alkane derives ultimately from the solvent, the identity of the proton donor in the active site remains unclear. To investigate the proton transfer step, solvent isotope effect (SIE) studies were undertaken. The rate of alkane formation was found to be maximal at pH 6.8 and to be the same in D2O or H2O within experimental error, implying that proton transfer is not a kinetically significant step. However, when the ratio of protium to deuterium in the product alkane was measured as a function of the mole fraction of D2O, a (D2O)SIEobs of 2.19 ± 0.02 was observed. The SIE was invariant with the mole fraction of D2O, indicating the involvement of a single protic site in the reaction. We interpret this SIE as most likely arising from a reactant state equilibrium isotope effect on a proton donor with an inverse fractionation factor, for which Φ = 0.45. These observations are consistent with an iron-bound water molecule being the proton donor to the alkane in the reaction.

  5. Characteristics of Carbon Isotopes of Alkane Components and Identification Marks of Biogenic Gases in China

    Institute of Scientific and Technical Information of China (English)

    戴金星; 陈英

    1994-01-01

    The carbon isotope composition of alkane component in biogenic gases of China has the following characteristics:with the increase of carbon number of the alkane molecules in biogenic gases, (i) the distribution range of the δ13C values and their main frequency sections become narrower, and both the heaviest and the lightest δ13C boundary values shift to their heavier end; (ii) the δ13C values of ethane and propane in biogenic gases present a positive linear relationship and (iii) the values of δ13C1, δ13C2 and δ13C3 tend to become heavier with the increase of heavy alkane component (C2+3) in biogenic gases. The authors studied the relationship between the δ13C values and the amount of heavy alkane components in biogenic gases (δ13C1 -C2+3(%). δ13C2 -C2+3(%) ,δ13C3-C2+3(%) for the first time and set up the interrelated regression equations between δ13C and C2+3 content (C2+3%), and advance that δ13C1< -55‰ and C2+3<0. 5% are two fine marks for identification of biogenic gases of China. δ13C

  6. Determination of the shear modulus in self-assembled monolayers using quartz resonators

    Energy Technology Data Exchange (ETDEWEB)

    Schneider, T.W.; Martin, S.J.; Frye, G.C.

    1994-06-01

    This work examined self-assembled monolayers (SAMs) of n-alkane thiols using quartz resonators to determine the shear storage and loss moduli. Network analyzer measurements of electrical admittance at fundamental and corresponding harmonic values are fit to an equivalent circuit model. Shear modulus depends on frequency; the modulus values are three orders of magnitude lower than expected for a liquid or elastomeric polymer, more like those of a dense gas or supercritical fluid. A density of around 0.45 g/cm{sup 3} is calculated for a dodecane thiol SAM; this is roughly half of the bulk density. In conclusion, quartz resonators can be used to inertially deform SAMs.

  7. Molecular dynamics study of the effect of calcium ions on the monolayer of SDC and SDSn surfactants at the vapor/liquid interface.

    Science.gov (United States)

    Yan, Hui; Guo, Xin-Li; Yuan, Shi-Ling; Liu, Cheng-Bu

    2011-05-17

    The effect of Ca(2+) ions on the hydration shell of sodium dodecyl carboxylate (SDC) and sodium dodecyl sulfonate (SDSn) monolayer at vapor/liquid interfaces was studied using molecular dynamics simulations. For each surfactant, two different surface concentrations were used to perform the simulations, and the aggregation morphologies and structural details have been reported. The results showed that the aggregation structures relate to both the surface coverage and the calcium ions. The divalent ions can screen the interaction between the polar head and Na(+) ions. Thus, Ca(2+) ions locate near the vapor/liquid interface to bind to the headgroup, making the aggregations much more compact via the salt bridge. The potential of mean force (PMF) between Ca(2+) and the headgroups shows that the interaction is decided by a stabilizing solvent-separated minimum in the PMF. To bind to the headgroup, Ca(2+) should overcome the energy barrier. Among contributions to the PMF, the major repulsive interaction was due to the rearrangement of the hydration shell after the calcium ions entered into the hydration shell of the headgroup. The PMFs between the headgroup and Ca(2+) in the SDSn systems showed higher energy barriers than those in the SDC systems. This result indicated that SDSn binds the divalent ions with more difficulty compared with SDC, so the ions have a strong effect on the hydration shell of SDC. That is why sulfonate surfactants have better efficiency in salt solutions with Ca(2+) ions for enhanced oil recovery.

  8. Binding structure and kinetics of surfactin monolayer formed at the air/water interface to counterions: A molecular dynamics simulation study.

    Science.gov (United States)

    Gang, Hongze; Liu, Jinfeng; Mu, Bozhong

    2015-10-01

    The binding structure and kinetics of ionized surfactin monolayer formed at the air/water interface to five counterions, Li+, Na+, K+, Ca2+, and Ba2+ (molar ratios of surfactin to monovalent and divalent counterions are 1:2 and 1:1 respectively), have been studied using molecular dynamics simulation. The results show that surfactin exhibits higher binding affinity to divalent counterions, Ca2+, and Ba2+, and smaller monovalent counterion, Li+, than Na+ and K+. Both carboxyl groups in surfactin are accessible for counterions, but the carboxyl group in Glu1 is easier to access by counterions than Asp5. Salt bridges are widely built between carboxyl groups by counterions, and the probability of the formation of intermolecular salt bridge is markedly larger than that of intramolecular salt bridge. Divalent counterions perform well in forming salt bridges between carboxyl groups. The salt bridges mediated by Ca2+ are so rigid that the lifetimes are about 0.13 ns, and the break rates of these salt bridges are 1-2 orders of magnitude smaller than those mediated by K+ which is about 5 ps in duration. The positions of the hydration layer of carboxyl groups are independent of counterions, but the bound counterions induce the dehydration of carboxyl groups and disturb the hydrogen bonds built between carboxyl group and hydration water.

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

    Science.gov (United States)

    Trippe, Kristin M; Wolpert, Thomas J; Hyman, Michael R; Ciuffetti, Lynda M

    2014-02-01

    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 identified, cloned and functionally characterized as an alkane-oxidizing cytochrome P450 (GSPALK1). Analysis of CYP52L1 suggests that it is a member of the CYP52 cytochrome P450 family, which is comprised of medium- and long-chain alkane-oxidizing enzymes found in yeasts. However, phylogenetic analysis of GSPALK1 with other CYP52 members suggests they are not closely related. Post-transcriptional ds-RNA-mediated gene silencing of CYP52L1 severely reduced the ability of this fungus to oxidize alkanes and ethers, however, downstream metabolic steps in these pathways were unaffected. Collectively, the results of this study suggest that GSPALK1 is the enzyme that catalyzes the initial oxidation of alkanes and ethers but is not involved in the later steps of alkane or ether metabolism.

  10. The Modeling of Pulmonary Particulate Matter Transport Using Langmuir Monolayers

    Science.gov (United States)

    Eaton, Jeremy M.

    The effects of a barrier in proximity to the air-water interface on the dynamics of a Langmuir monolayer system are observed. A monolayer of Survanta, bovine lung surfactant, is deposited onto the interface of an aqueous buffer solution. Polystyrene particles one micron in diameter and tagged with fluorescent carboxylate groups are distributed evenly throughout the monolayer surface. The bead-monolayer system is compressed and expanded to induce folding. A polydimethylsiloxane (PDMS) substrate is placed below the monolayer in the buffer solution to study interactions between the folding monolayer and a barrier. The presence of the substrate is shown to shift surface pressure-area isotherms toward regions of lower area by an average of 8.9 mN/m. The surface of the PDMS substrate can be imaged using fluorescence microscopy to detect the presence of particles or surfactant that may have been transported there from the air-water interface during folding. Images show the transferral of particles and monolayer together suggesting the pinch-off of a fold or the direct interaction of a fold with the barrier.

  11. First principles study on molecule doping in MoS2 monolayer%单层MoS2分子掺杂的第一性原理研究

    Institute of Scientific and Technical Information of China (English)

    刘俊; 梁培; 舒海波; 沈涛; 邢凇; 吴琼

    2014-01-01

    基于密度泛函理论的第一性原理平面波赝势方法的计算,研究了通过吸附不同有机分子对单层MoS2进行化学掺杂。计算结果表明有机分子与MoS2单层衬底间的相互作用主要是范德瓦尔斯作用力。吸附不同有机分子的单层MoS2结构均表现出间接带隙的特征,还表明吸附TTF分子的单层MoS2结构表现出n型半导体的特质,而吸附TCNQ, TCNE两种分子的单层MoS2结构均表现出p型半导体的性质,这些结果表明可以通过改变吸附的分子来实现对单层MoS2的掺杂类型的调控。本文的研究结果将对单层MoS2在晶体管中的应用提供理论基础和指导。%The chemical doping of organic molecules adsorbed on MoS2 monolayers are systematically studied by using plane-wave pseudo-potential method based on the density functional theory. Our results indicate that the interaction between organic molecules and the MoS2 monolayer substrate is of van der Waals’ type of force. Structure of monolayer MoS2 which adsorbs different organic molecules, exhibits indirect bandgap characteristics, and the energy band structure of monolayer MoS2 which adsorbs TTF molecules exhibits n-type conducting characteristics. However, the structures of monolayer MoS2 which adsorbs TCNQ or TCNE molecules would exhibit p-type conductivity characteristics. Thus, the results indicate that the doping type of molecules in monolayer MoS2 can be regulated by adsorbing different molecules. Results of this study may provide a theoretical basis for single-layer MoS2 transistor and guidance for it in the application.

  12. Expanding the product profile of a microbial alkane biosynthetic pathway.

    Science.gov (United States)

    Harger, Matthew; Zheng, Lei; Moon, Austin; Ager, Casey; An, Ju Hye; Choe, Chris; Lai, Yi-Ling; Mo, Benjamin; Zong, David; Smith, Matthew D; Egbert, Robert G; Mills, Jeremy H; Baker, David; Pultz, Ingrid Swanson; Siegel, Justin B

    2013-01-18

    Microbially produced alkanes are a new class of biofuels that closely match the chemical composition of petroleum-based fuels. Alkanes can be generated from the fatty acid biosynthetic pathway by the reduction of acyl-ACPs followed by decarbonylation of the resulting aldehydes. A current limitation of this pathway is the restricted product profile, which consists of n-alkanes of 13, 15, and 17 carbons in length. To expand the product profile, we incorporated a new part, FabH2 from Bacillus subtilis , an enzyme known to have a broader specificity profile for fatty acid initiation than the native FabH of Escherichia coli . When provided with the appropriate substrate, the addition of FabH2 resulted in an altered alkane product profile in which significant levels of n-alkanes of 14 and 16 carbons in length are produced. The production of even chain length alkanes represents initial steps toward the expansion of this recently discovered microbial alkane production pathway to synthesize complex fuels. This work was conceived and performed as part of the 2011 University of Washington international Genetically Engineered Machines (iGEM) project.

  13. The vapor-particle partitioning of n-alkanes

    Energy Technology Data Exchange (ETDEWEB)

    Doskey, P.V.

    1994-04-01

    A mixed-phase partitioning model has been proposed to predict the distribution of n-alkanes between the vapor and particle phases in the atmosphere. n-Alkanes having terrestrial plant wax and petroleum origins are assumed to be associated with atmospheric particles as microcrystalline solids and subcooled liquids, respectively. The fraction of n-alkanes on atmospheric particles having plant wax and petroleum origins is estimated with carbon preference indices. Hypothetical terrestrial plant wax and petroleum mixtures are used to estimate the mole fractions of the n-alkanes in each phase and the molecular weights of the phases. Solid and subcooled liquid phase n-alkane vapor pressures are used in the model to predict the fraction of n-alkanes associated with particles in the atmosphere. Trends in the prediction of vapor-particle partitioning using these assumptions agree well with field observations. However, the fraction of particle phase n-alkanes predicted by the model was significantly different from the field observations.

  14. Adhesive and conformational behaviour of mycolic acid monolayers

    OpenAIRE

    2010-01-01

    We have studied the pH-dependent interaction between mycolic acid (MA) monolayers and hydrophobic and hydrophilic surfaces using molecular (colloidal probe) force spectroscopy. In both cases, hydrophobic and hydrophilic monolayers (prepared by Langmuir-Blodgett and Langmuir-Schaefer deposition on silicon or hydrophobized silicon substrates, respectively) were studied. The force spectroscopy data, fitted with classical DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory to examine the contri...

  15. Leaf wax n-alkane δD values are determined early in the ontogeny of Populus trichocarpa leaves when grown under controlled environmental conditions.

    Science.gov (United States)

    Kahmen, Ansgar; Dawson, Todd E; Vieth, Andrea; Sachse, Dirk

    2011-10-01

    The stable hydrogen isotope ratios (δD) of leaf wax n-alkanes record valuable information on plant and ecosystem water relations. It remains, however, unknown if leaf wax n-alkane δD values record only environmental variation during the brief period of time of leaf growth or if leaf wax n-alkane δD values are affected by environmental variability throughout the entire lifespan of a leaf. To resolve these uncertainties, we irrigated Populus trichocarpa trees with a pulse of deuterium-enriched water and used compound-specific stable hydrogen isotope analyses to test if the applied tracer could be recovered from leaf wax n-alkanes of leaves that were at different stages of their development during the tracer application. Our experiment revealed that only leaf wax n-alkanes from leaves that had developed during the time of the tracer application were affected, while leaves that were already fully matured at the time of the tracer application were not. We conclude from our study that under controlled environmental conditions, leaf wax n-alkanes are synthesized only early in the ontogeny of a leaf. Our experiment has implications for the interpretation of leaf wax n-alkane δD values in an environmental context, as it suggests that these compounds record only a brief period of the environmental variability that a leaf experiences throughout its life.

  16. Enhanced biodegradation of alkane hydrocarbons and crude oil by mixed strains and bacterial community analysis.

    Science.gov (United States)

    Chen, Yu; Li, Chen; Zhou, Zhengxi; Wen, Jianping; You, Xueyi; Mao, Youzhi; Lu, Chunzhe; Huo, Guangxin; Jia, Xiaoqiang

    2014-04-01

    In this study, two strains, Acinetobacter sp. XM-02 and Pseudomonas sp. XM-01, were isolated from soil samples polluted by crude oil at Bohai offshore. The former one could degrade alkane hydrocarbons (crude oil and diesel, 1:4 (v/v)) and crude oil efficiently; the latter one failed to grow on alkane hydrocarbons but could produce rhamnolipid (a biosurfactant) with glycerol as sole carbon source. Compared with pure culture, mixed culture of the two strains showed higher capability in degrading alkane hydrocarbons and crude oil of which degradation rate were increased from 89.35 and 74.32 ± 4.09 to 97.41 and 87.29 ± 2.41 %, respectively. In the mixed culture, Acinetobacter sp. XM-02 grew fast with sufficient carbon source and produced intermediates which were subsequently utilized for the growth of Pseudomonas sp. XM-01 and then, rhamnolipid was produced by Pseudomonas sp. XM-01. Till the end of the process, Acinetobacter sp. XM-02 was inhibited by the rapid growth of Pseudomonas sp. XM-01. In addition, alkane hydrocarbon degradation rate of the mixed culture increased by 8.06 to 97.41 % compared with 87.29 % of the pure culture. The surface tension of medium dropping from 73.2 × 10(-3) to 28.6 × 10(-3) N/m. Based on newly found cooperation between the degrader and the coworking strain, rational investigations and optimal strategies to alkane hydrocarbons biodegradation were utilized for enhancing crude oil biodegradation.

  17. Phenomenological Modeling for Langmuir Monolayers

    Science.gov (United States)

    Baptiste, Dimitri; Kelly, David; Safford, Twymun; Prayaga, Chandra; Varney, Christopher N.; Wade, Aaron

    Experimentally, Langmuir monolayers have applications in molecular optical, electronic, and sensor devices. Traditionally, Langmuir monolayers are described by a rigid rod model where the rods interact via a Leonard-Jones potential. Here, we propose effective phenomenological models and utilize Monte Carlo simulations to analyze the phase behavior and compare with experimental isotherms. Research reported in this abstract was supported by UWF NIH MARC U-STAR 1T34GM110517-01.

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

    DEFF Research Database (Denmark)

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

    1996-01-01

    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...

  19. The use of alkanethiol self-assembled monolayers on 316L stainless steel for coronary artery stent nanomedicine applications: an oxidative and in vitro stability study.

    Science.gov (United States)

    Mahapatro, Anil; Johnson, Dave M; Patel, Devang N; Feldman, Marc D; Ayon, Arturo A; Agrawal, C Mauli

    2006-09-01

    The use of self-assembled monolayers (SAMs) on medical devices offers a methodology for the incorporation of nanotechnology into medicine. SAMs are highly ordered nanosized molecular coatings, adding 1 to 10 nm thickness to a surface. This work is part of an overall goal to deliver therapeutic drugs from the surface of metal coronary stents using SAMs. In this study the oxidative and in vitro stability of functional alkylthiol SAMs on 316L stainless steel (SS) has been demonstrated. SAMs of 11-mercaptoundecanoic acid (-COOH SAM) and 11-mercapto-1-undecanol (-OH SAM) were formed on 316L SS. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and contact angle (CA) measurements collectively confirmed the formation of functional alkylthiol SAMs on 316L SS. Well-formed SAMs (CA: 82 deg +/- 9 deg) were achieved within 48 hours of immersion in ethanolic solutions, after which no significant improvement in CA was observed. The ratio of the thiolate peak (163.5 eV) to the oxidized sulfur (sulfonates) peak (166.5 eV) gives us an indication of the percentage SAMs that would bind to the metal and serve as a drug reservoir in vivo; which in turn represents the stability and viability of these SAMs, keeping in mind the cardiovascular application under consideration. Oxidative and in vitro stability studies showed that alkanethiol SAMs oxidized completely within 14 days. The SAMs tend to desorb and leave the metal surface after longer time periods (21 days) in phosphate-buffered saline (PBS) immersion, whereas for oxidative exposure the SAMs continue to remain on the metal surface in the form of sulfonates. Although the chemistry of bonding of alkylthiol with the 316L SS is not well understood, the nanosized alkylthiol SAMs demonstrate sufficient stability to justify further study on these systems for potential in vivo drug delivery in the chosen coronary artery stent applications.

  20. Assessment and modulation of acamprosate intestinal absorption: comparative studies using in situ, in vitro (CACO-2 cell monolayers) and in vivo models.

    Science.gov (United States)

    Zornoza, Teodoro; Cano-Cebrián, María José; Nalda-Molina, Ricardo; Guerri, Consuelo; Granero, Luis; Polache, Ana

    2004-08-01

    The purpose of this study was to explore the intestinal absorption mechanism of acamprosate and to attempt to improve the bioavailability (BA) of the drug through modulation of its intestinal absorption using two enhancers (polysorbate 80 and sodium caprate) based on in situ, in vitro and in vivo models and comparing the results obtained. Intestinal transport of the drug, in the absence and in presence of polysorbate 80 (0.06, 0.28 and 9.6 mM) or sodium caprate (13 and 16 mM) was measured by using an in situ rat gut technique and Caco-2 cell monolayers. Additionally, the effect of sodium caprate on drug oral bioavailability, measured as urinary recovery, was quantified by performing in vivo experiments with the rat as animal model. Only sodium caprate was able to increase the absorption rate constant (ka) of acamprosate in the mid-intestine of the rats from 0.29 +/- 0.07 h-1 in the absence of the promoter to 0.51 +/- 0.19 h-1 in the presence of C10 16 mM, along with the apparent permeability (Papp) obtained in Caco-2 cells (around two-fold). However, the drug bioavailability in rats (around 20%) did not improve in the presence of any of the concentrations tested (13, 16 and 50 mM). It is concluded that acamprosate absorption likely occurs via paracellular pathway and can be enhanced by sodium caprate in situ and in vitro but not in vivo-thus suggesting that although in situ and in vitro studies could be useful in early screening to select a potential promoter, in vivo studies in animal models are necessary to confirm the utility of the enhancer and to determine the influence of physiological variables.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Involvement of an alkane hydroxylase system of Gordonia sp. strain SoCg in degradation of solid n-alkanes.

    Science.gov (United States)

    Lo Piccolo, Luca; De Pasquale, Claudio; Fodale, Roberta; Puglia, Anna Maria; Quatrini, Paola

    2011-02-01

    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 (C(12)) to hexatriacontane (C(36)) 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)-encoding systems of other alkane-degrading actinobacteria. Quantitative reverse transcription-PCR showed that the genes encoding AlkB (alkane 1-monooxygenase), RubA3 (rubredoxin), RubA4 (rubredoxin), and RubB (rubredoxin reductase) were induced by both n-hexadecane and n-triacontane, which were chosen as representative long-chain liquid and solid n-alkane molecules, respectively. Biotransformation of n-hexadecane into the corresponding 1-hexadecanol was detected by solid-phase microextraction coupled with gas chromatography-mass spectrometry (SPME/GC-MS) analysis. The Gordonia SoCg alkB was heterologously expressed in Escherichia coli BL21 and in Streptomyces coelicolor M145, and both hosts acquired the ability to transform n-hexadecane into 1-hexadecanol, but the corresponding long-chain alcohol was never detected on n-triacontane. However, the recombinant S. coelicolor M145-AH, expressing the Gordonia alkB gene, was able to grow on n-triacontane as the sole C source. A SoCg alkB disruption mutant that is completely unable to grow on n-triacontane was obtained, demonstrating the role of an AlkB-type AH system in degradation of solid n-alkanes.

  8. Diversity of alkane degrading bacteria associated with plants in a petroleum oil-contaminated environment and expression of alkane monooxygenase (alkB) genes

    Science.gov (United States)

    Andria, V.; Yousaf, S.; Reichenauer, T. G.; Smalla, K.; Sessitsch, A.

    2009-04-01

    Among twenty-six different plant species, Italian ryegrass (Lolium multiflorum var. Taurus), Birdsfoot trefoil (Lotus corniculatus var. Leo), and the combination of both plants performed well in a petroleum oil contaminated soil. Hydrocarbon degrading bacteria were isolated from the rhizosphere, root interior and shoot interior and subjected to the analysis of 16S rRNA, the 16S and 23S rRNA intergenic spacer region and alkane hydroxylase genes. Higher numbers of culturable, degrading bacteria were associated with Italian ryegrass, which were also characterized by a higher diversity, particularly in the plant interior. Only half of the isolated bacteria hosted known alkane hydroxylase genes (alkB and cytochrome P153-like). Our results indicated that alkB genes have spread through horizontal gene transfer, particularly in the Italian ryegrass rhizosphere, and suggested mobility of catabolic genes between Gram-negative and Gram-positive bacteria. We furthermore studied the colonization behaviour of selected hydrocarbon-degrading strains (comprising an endopyhte and a rhizosphere strain) as well as the expression of their alkane monooxygenase genes in association with Italian ryegrass. Results showed that the endophyte strain better colonized the plant, particularly the plant interior, and also showed higher expression of alkB genes suggesting a more efficient degradation of the pollutant. Furthermore, plants inoculated with the endophyte were better able to grow in the presence of diesel. The rhizosphere strain colonized primarily the rhizosphere and showed low alkB gene expression in the plant interior.

  9. Nisin Z, mutant nisin Z and lacticin 481 interactions with anionic lipids correlate with antimicrobial activity. A monolayer study

    NARCIS (Netherlands)

    Demel, Rudolf A.; Peelen, Tamara; Siezen, Roland J.; Kruijff, Ben de; Kuipers, Oscar P.

    1996-01-01

    Monomolecular layers of lipids at the air/water interface have been used as a model membrane to study membrane interactions of the lantibiotic nisin. The natural lantibiotics nisin A and nisin Z proved to have a high affinity for the anionic lipids phosphatidylglycerol and bis(phosphatidyl)glycerol

  10. Study of pharmacological properties of new drugs for external use by the method of cell monolayer bioindication.

    Science.gov (United States)

    Seregina, M V; Mikhailova, L P

    2002-04-01

    The effects of new plant extracts on phagocytosis-stimulating, antioxidant, antiinflammatory, and mitotic activities were studied by the method of bioindication on cultures of normal human leukocytes, RH cells, and blood neutrophils. The preparations showed dose-dependent antiinflammatory activity and produced wound-healing, antioxidant, and moderate phagocytosis-stimulating effects.

  11. 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.

  12. High molecular weight (C35+)n-alkanes of Neogene heavily biodegraded oil in the Qianmiqiao region, North China

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    With wax content of 1.62%, heavy oil has been produced from the sandstone reservoirs of Neogene Guantao Formation (Ng1Ⅲ). In the GC and GC-MS RIC profiles of its aliphatic fraction, n-alkanes are totally lost, which shows the result of heavy biodegradedation. However, the remaining trace C13-C36 n-alkanes can be still seen from its m/z 85 mass chromatogram. In addition, a complete series of C35-C73 high molecular weight (HMW) n-alkanes was detected by high-temperature gas chromatography (HTGC). The HMW n-alkane series shows a normal distribution pattern, a major peak at nC43, obvious odd-carbon-number predominance, CPI37-55 and OEP45-49 values up to 1.17 and 1.16-1.20 respectively. The present study not only has conformed the strong resistibility of HMW n-alkanes to biodegradation in crude oils as concluded by previous researchers, but also has provided some significant information on source input and maturity for the heavily biodegraded oil in the Qianmiqiao region.

  13. Metabolism of hydrophobic carbon sources and regulation of it in n-alkane-assimilating yeast Yarrowia lipolytica.

    Science.gov (United States)

    Fukuda, Ryouichi

    2013-01-01

    A potent ability to assimilate hydrophobic compounds, including n-alkanes and fatty acids as carbon sources, is one of important characteristics of the yeast Yarrowia lipolytica, and has been studied for both basic microbiological interest and biotechnological applications. This review summarizes recent progress on the metabolism of n-alkanes and its transcriptional control in response to n-alkanes and to fatty acids in Y. lipolytica. In the metabolism of n-alkanes, cytochromes P450ALK catalyze their initial hydroxylation to fatty alcohols, which are subsequently converted to fatty acids and utilized. The transcription of ALK1, encoding a predominant cytochrome P450ALK, is regulated in response to n-alkanes by two basic helix-loop-helix transcription activators, Yas1p and Yas2p, and Opi1-family transcription repressor Yas3p. Transcription of the genes involved in fatty acid utilization and peroxisome biogenesis is controlled by Ctf1-family Zn2Cys6 type transcription factor Por1p in response to fatty acids in Y. lipolytica.

  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. Unsupported single-atom-thick copper oxide monolayers

    Science.gov (United States)

    Yin, Kuibo; Zhang, Yu-Yang; Zhou, Yilong; Sun, Litao; Chisholm, Matthew F.; Pantelides, Sokrates T.; Zhou, Wu

    2017-03-01

    Oxide monolayers may present unique opportunities because of the great diversity of properties of these materials in bulk form. However, reports on oxide monolayers are still limited. Here we report the formation of single-atom-thick copper oxide layers with a square lattice both in graphene pores and on graphene substrates using aberration-corrected scanning transmission electron microscopy. First-principles calculations find that CuO is energetically stable and its calculated lattice spacing matches well with the measured value. Furthermore, free-standing copper oxide monolayers are predicted to be semiconductors with band gaps ∼3 eV. The new wide-bandgap single-atom-thick copper oxide monolayers usher a new frontier to study the highly diverse family of two-dimensional oxides and explore their properties and their potential for new applications.

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

    Energy Technology Data Exchange (ETDEWEB)

    Uedono, Akira, E-mail: uedono.akira.gb@u.tsukuba.ac.jp [Division of Applied Physics, Faculty of Pure and Applied Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Armini, Silvia; Zhang, Yu [IMEC, Kapeldreef 75, B-3001 Heverlee, Leuven (Belgium); Kakizaki, Takeaki [Division of Applied Physics, Faculty of Pure and Applied Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Krause-Rehberg, Reinhard [Department of Physics, Martin Luther University Halle, 06099 Halle (Germany); Anwand, Wolfgang; Wagner, Andreas [Institute for Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, 01314 Dresden (Germany)

    2016-04-15

    Graphical abstract: - Highlights: • Pores with cubic pore side lengths of 1.1 and 3.1 nm coexisted in the low-k film. • For the sample without the SAM sealing process, metal atoms diffused from the top Cu/MnN layer into the OSG film and were trapped by the pores. Almost all pore interiors were covered by those metals. • For the sample damaged by a plasma etch treatment before the SAM sealing process, self-assembled molecules diffused into the OSG film, and they were preferentially trapped by larger pores. - Abstract: 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, C{sub 4}F{sub 8} 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/C{sub 4}F{sub 8} 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.

  17. In vitro and in vivo characterization of antibacterial activity and biocompatibility: a study on silver-containing phosphonate monolayers on titanium.

    Science.gov (United States)

    Tîlmaciu, Carmen-Mihaela; Mathieu, Marc; Lavigne, Jean-Philippe; Toupet, Karine; Guerrero, Gilles; Ponche, Arnaud; Amalric, Julien; Noël, Danièle; Mutin, P Hubert

    2015-03-01

    Infections associated with implanted medical devices are a major cause of nosocomial infections, with serious medical and economic repercussions. A variety of silver-containing coatings have been proposed to decrease the risk of infection by hindering bacterial adhesion and biofilm formation. However, the therapeutic range of silver is relatively narrow and it is important to minimize the amount of silver in the coatings, in order to keep sufficient antibacterial activity without inducing cytotoxicity. In this study, the antibacterial efficiency and biocompatibility of nanocoatings with minimal silver loading (∼0.65 nmol cm(-2)) was evaluated in vitro and in vivo. Titanium substrates were coated by grafting mercaptododecylphosphonic acid (MDPA) monolayers followed by post-reaction with AgNO3. The MDPA/AgNO3 nanocoatings significantly inhibited Escherichia coli and Staphylococcus epidermidis adhesion and biofilm formation in vitro, while allowing attachment and proliferation of MC3T3-E1 preosteoblasts. Moreover, osteogenic differentiation of MC3T3 cells and murine mesenchymal stem cells was not affected by the nanocoatings. Sterilization by ethylene oxide did not alter the antibacterial activity and biocompatibility of the nanocoatings. After subcutaneous implantation of the materials in mice, we demonstrated that MDPA/AgNO3 nanocoatings exhibit significant antibacterial activity and excellent biocompatibility, both in vitro and in vivo, after postoperative seeding with S. epidermidis. These results confirm the interest of coating strategies involving subnanomolar amounts of silver exposed at the extreme surface for preventing bacterial adhesion and biofilm formation on metallic or ceramic medical devices without compromising their biocompatibility.

  18. AFM Study of Surface Nanobubbles on Binary Self-Assembled Monolayers on Ultraflat Gold with Identical Macroscopic Static Water Contact Angles and Different Terminal Functional Groups.

    Science.gov (United States)

    Song, Bo; Chen, Kun; Schmittel, Michael; Schönherr, Holger

    2016-11-01

    All experimental findings related to surface nanobubbles, such as their pronounced stability and the striking differences of macroscopic and apparent nanoscopic contact angles, need to be addressed in any theory or model of surface nanobubbles. In this work we critically test a recent explanation of surface nanobubble stability and their consequences and contrast this with previously proposed models. In particular, we elucidated the effect of surface chemical composition of well-controlled solid-aqueous interfaces of identical roughness and defect density on the apparent nanoscopic contact angles. Expanding on a previous atomic force microscopy (AFM) study on the systematic variation of the macroscopic wettability using binary self-assembled monolayers (SAMs) on ultraflat template stripped gold (TSG), we assessed here the effect of different surface chemical composition for macroscopically identical static water contact angles. SAMs on TSG with a constant macroscopic water contact angle of 81 ± 2° were obtained by coadsorption of a methyl-terminated thiol and a second thiol with different terminal functional groups, including hydroxy, amino, and carboxylic acid groups. In addition, surface nanobubbles formed by entrainment of air on SAMs of a bromoisobutyrate-terminated thiol were analyzed by AFM. Despite the widely differing surface potentials and different functionality, such as hydrogen bond acceptor or donor, and different dipole moments and polarizability, the nanoscopic contact angles (measured through the condensed phase and corrected for AFM tip broadening effects) were found to be 145 ± 10° for all surfaces. Hence, different chemical functionalities at identical macroscopic static water contact angle do not noticeably influence the apparent nanoscopic contact angle of surface nanobubbles. This universal contact angle is in agreement with recent models that rely on contact line pinning and the equilibrium of gas outflux due to the Laplace pressure and

  19. 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.

  20. 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...

  1. QSPR between Physical- Chemical Properties and Molecule Parameters of Alkanes

    Institute of Scientific and Technical Information of China (English)

    XU Qing-qing; LI Liang-chao; HU Li-ya

    2005-01-01

    A set of molecule parameters, namely, N, N′, p, q,n, were used to express the structures of alkanes. A correlative model was established between certain physical-chemical properties and molecular parameters of alkanes by regression method. Eightphysical-chemical properties, such as evaporation heat (△vH20m ),density(D20 ), capacity(C20 ), surface tension(σ20 ), boiling point ( Tb ), critical temperature ( Tc ), critical pressure (Pc) and critical volume(Vc), of fifty-six C3-C16 alkanes were calculated directly from the model in this paper. The calculated values are in good accordance with the literature ones reported for alkanes, and the correlation coefficients (R) equal or exceed 0.99. The research results indicate that the principle of the method is simple and clear, the method is practical, the correlativity is excellent, and the predicted data are credible.

  2. Alkane oxidation by Pseudomonas oleovorans: genes and proteins

    OpenAIRE

    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.

  3. 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.

  4. Stability and properties of the two-dimensional hexagonal boron nitride monolayer functionalized by hydroxyl (OH) radicals: a theoretical study.

    Science.gov (United States)

    Wang, Hong-mei; Liu, Yue-jie; Wang, Hong-xia; Zhao, Jing-xiang; Cai, Qing-hai; Wang, Xuan-zhang

    2013-12-01

    Motivated by the great advance in graphene hydroxide--a versatile material with various applications--we performed density functional theory (DFT) calculations to study the functionalization of the two-dimensional hexagonal boron nitride (h-BN) sheet with hydroxyl (OH) radicals, which has been achieved experimentally recently. Particular attention was paid to searching for the most favorable site(s) for the adsorbed OH radicals on a h-BN sheet and addressing the roles of OH radical coverage on the stability and properties of functionalized h-BN sheet. The results indicate that, for an individual OH radica, the most stable configuration is that it is adsorbed on the B site of the h-BN surface with an adsorption energy of -0.88 eV and a magnetic moment of 1.00 μ(B). Upon adsorption of more than one OH radical on a h-BN sheet, however, these adsorbates prefer to adsorb in pairs on the B and its nearest N atoms from both sides of h-BN sheet without magnetic moment. An energy diagram of the average adsorption energy of OH radicals on h-BN sheet as a function of its coverage indicates that when the OH radical coverage reaches to 60 %, the functionalized h-BN sheet is the most stable among all studied configurations. More importantly, this configuration exhibits good thermal and dynamical stability at room temperature. Owing to the introduction of certain impurity levels, the band gap of h-BN sheet gradually decreases with increasing OH coverage, thereby enhancing its electrical conductivity.

  5. X-ray reflectivity and grazing incidence diffraction studies of interaction between human adhesion/growth-regulatory galectin-1 and DPPE-GM1 lipid monolayer at an air/water interface.

    Science.gov (United States)

    Majewski, J; André, S; Jones, E; Chi, E; Gabius, H-J

    2015-07-01

    The specific interaction of ganglioside GM1 with the homodimeric (prototype) endogenous lectin galectin-1 triggers growth regulation in tumor and activated effector T cells. This proven biorelevance directed interest to studying association of the lectin to a model surface, i.e. a 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine/ganglioside GM1 (80 : 20 mol%) monolayer, at a bioeffective concentration. Surface expansion by the lectin insertion was detected at a surface pressure of 20 mN/m. On combining the methods of grazing incidence X-ray diffraction and X-ray reflectivity, a transient decrease in lipid-ordered phase of the monolayer was observed. The measured electron density distribution indicated that galectin-1 is oriented with its long axis in the surface plane, ideal for cis-crosslinking. The data reveal a conspicuous difference to the way the pentameric lectin part of the cholera toxin, another GM1-specific lectin, is bound to the monolayer. They also encourage further efforts to monitor effects of structurally different members of the galectin family such as the functionally antagonistic chimera-type galectin-3.

  6. 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.

  7. Contribution of cyanobacterial alkane production to the ocean hydrocarbon cycle.

    Science.gov (United States)

    Lea-Smith, David J; Biller, Steven J; Davey, Matthew P; Cotton, Charles A R; Perez Sepulveda, Blanca M; Turchyn, Alexandra V; Scanlan, David J; Smith, Alison G; Chisholm, Sallie W; Howe, Christopher J

    2015-11-03

    Hydrocarbons are ubiquitous in the ocean, where alkanes such as pentadecane and heptadecane can be found even in waters minimally polluted with crude oil. Populations of hydrocarbon-degrading bacteria, which are responsible for the turnover of these compounds, are also found throughout marine systems, including in unpolluted waters. These observations suggest the existence of an unknown and widespread source of hydrocarbons in the oceans. Here, we report that strains of the two most abundant marine cyanobacteria, Prochlorococcus and Synechococcus, produce and accumulate hydrocarbons, predominantly C15 and C17 alkanes, between 0.022 and 0.368% of dry cell weight. Based on global population sizes and turnover rates, we estimate that these species have the capacity to produce 2-540 pg alkanes per mL per day, which translates into a global ocean yield of ∼ 308-771 million tons of hydrocarbons annually. We also demonstrate that both obligate and facultative marine hydrocarbon-degrading bacteria can consume cyanobacterial alkanes, which likely prevents these hydrocarbons from accumulating in the environment. Our findings implicate cyanobacteria and hydrocarbon degraders as key players in a notable internal hydrocarbon cycle within the upper ocean, where alkanes are continually produced and subsequently consumed within days. Furthermore we show that cyanobacterial alkane production is likely sufficient to sustain populations of hydrocarbon-degrading bacteria, whose abundances can rapidly expand upon localized release of crude oil from natural seepage and human activities.

  8. 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.

  9. Alkane Biomarkers in Permian-Triassic Boundary Strata at Meishan Section, Changxing,Zhejiang Province

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Meishan Section D in Changxing County, Zhejiang Province, China has been selected as the global stratotype of the Permian-Triassic boundary and various studies have been done at the boundary, but the gas chromatographic-mass spectrographic analysis of alkane biomarkers has not been investigated. This paper presents the results of a study of the biomarkers analyzed in a series of samples across the Permian-Triassic boundary at both Meishan Section A and Section D. The results show that the overall concentration of alkane biomarkers in the Permian-Triassic boundary strata is high in Bed 26 while it is low in Bed 27. A variety of biomarker parameters demonstrate that the main sources of organic matter in the sediment are algae and bacteria and that the depositional environment varied from weakly oxidizing to reducing during the studied interval.

  10. 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

  11. Physiological hydrostatic pressure protects endothelial monolayer integrity.

    Science.gov (United States)

    Müller-Marschhausen, K; Waschke, J; Drenckhahn, D

    2008-01-01

    Endothelial monolayer integrity is required to maintain endothelial barrier functions and has found to be impaired in several disorders like inflammatory edema, allergic shock, or artherosclerosis. Under physiologic conditions in vivo, endothelial cells are exposed to mechanical forces such as hydrostatic pressure, shear stress, and cyclic stretch. However, insight into the effects of hydrostatic pressure on endothelial cell biology is very limited at present. Therefore, in this study, we tested the hypothesis that physiological hydrostatic pressure protects endothelial monolayer integrity in vitro. We investigated the protective efficacy of hydrostatic pressure in microvascular myocardial endothelial (MyEnd) cells and macrovascular pulmonary artery endothelial cells (PAECs) by the application of selected pharmacological agents known to alter monolayer integrity in the absence or presence of hydrostatic pressure. In both endothelial cell lines, extracellular Ca(2+) depletion by EGTA was followed by a loss of vascular-endothelial cadherin (VE-caherin) immunostaining at cell junctions. However, hydrostatic pressure (15 cmH(2)O) blocked this effect of EGTA. Similarly, cytochalasin D-induced actin depolymerization and intercellular gap formation and cell detachment in response to the Ca(2+)/calmodulin antagonist trifluperazine (TFP) as well as thrombin-induced cell dissociation were also reduced by hydrostatic pressure. Moreover, hydrostatic pressure significantly reduced the loss of VE-cadherin-mediated adhesion in response to EGTA, cytochalasin D, and TFP in MyEnd cells as determined by laser tweezer trapping using VE-cadherin-coated microbeads. In caveolin-1-deficient MyEnd cells, which lack caveolae, hydrostatic pressure did not protect monolayer integrity compromised by EGTA, indicating that caveolae-dependent mechanisms are involved in hydrostatic pressure sensing and signaling.

  12. Electrochemical Properties of Organosilane Self Assembled Monolayers on Aluminum 2024

    Science.gov (United States)

    Hintze, Paul E.; Calle, Luz Marina

    2004-01-01

    Self assembled monolayers are commonly used to modify surfaces. Within the last 15 years, self assembled monolayers have been investigated as a way to protect from corrosion[1,2] or biofouling.[3] In this study, self assembled monolayers of decitriethoxysilane (C10H21Si(OC2H5)3) and octadecyltriethoxysilane (C18H37Si(OC2H5)3) were formed on aluminum 2024-T3. The modified surfaces and bare Al 2024 were characterized by dynamic water contact angle measurements, x-ray photoelectron spectroscopy (XIPS) and infrared spectroscopy. Electrochemical impedance spectroscopy (EIS) in 0.5 M NaCl was used to characterize the monolayers and evaluate their corrosion protection properties. The advancing water contact angle and infrared measurements show that the mono layers form a surface where the hydrocarbon chains are packed and oriented away from the surface, consistent with what is found in similar systems. The contact angle hysteresis measured in these systems is relatively large, perhaps indicating that the hydrocarbon chains are not as well packed as monolayers formed on other substrates. The results of the EIS measurements were modeled using a Randle's circuit modified by changing the capacitor to a constant phase element. The constant phase element values were found to characterize the monolayer. The capacitance of the monolayer modified surface starts lower than the bare Al 2024, but approaches values similar to the bare Al 2024 within 24 hours as the monolayer is degraded. The n values found for bare Al 2024 quickly approach the value of a true capacitor and are greater than 0.9 within hours after the start of exposure. For the monolayer modified structure, n can stay lower than 0.9 for a longer period of time. In fact, n for the monolayer modified surfaces is different from the bare surface even after the capacitance values have converged. This indicates that the deviation from ideal capacitance is the most sensitive indicator of the presence of the monolayer.

  13. 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.

  14. CPI values of terrestrial higher plant-derived long-chain n-alkanes: a potential paleoclimatic proxy

    Institute of Scientific and Technical Information of China (English)

    Zhiguo RAO; Zhaoyu ZHU; Suping WANG; Guodong JIA; Mingrui QIANG; Yi WU

    2009-01-01

    Carbon Preference Index (CPI values) of higher plant-derived long-chain n-alkanes extracted from 62 surface soil samples in eastern China exhibited a specific pattern of variations, namely gradual increase with the increasing latitudes. Such regular variations existed in both forest soil and grassland soil. Our data implied that CPI values of higher plant-derived long-chain n-alkanes had a certain connection with climatic conditions, and such a connection was not influenced by vegetation types. Together with previous data from marine sediments, loess/ paleosol sequences, tertiary red clay and modern plants, our observation made us conclude that CPI values of higher plant-derived long-chain n-alkanes may be used as an excellent proxy for paleoclimatic studies.

  15. The true structural periodicities and superspace group descriptions of the prototypical incommensurate composite materials: Alkane/urea inclusion compounds

    Science.gov (United States)

    Couzi, Michel; Guillaume, François; Harris, Kenneth D. M.; Palmer, Benjamin A.; Christensen, Kirsten; Collins, Stephen P.

    2016-12-01

    The prototypical family of incommensurate composite materials are the n-alkane/urea inclusion compounds, in which n-alkane guest molecules are arranged in a periodic manner along one-dimensional tunnels in a urea host structure, with an incommensurate relationship between the periodicities of the host and guest substructures along the tunnel. We develop interpretations of the structural periodicities, superspace group descriptions and symmetry properties of the low-temperature phases of n-alkane/urea inclusion compounds, based in part on a high-resolution synchrotron single-crystal X-ray diffraction study of n-nonadecane/urea. Specifically, we prove that, on passing from phase I to phase II, the C-centering of the orthohexagonal unit cell is lost for both the host and guest substructures, and that the symmetries of all phases I, II and III are described completely by (3 + 1)-dimensional superspace groups.

  16. The Use of a Combination of alkB Primers to Better Characterize the Distribution of Alkane-Degrading Bacteria.

    Directory of Open Access Journals (Sweden)

    Diogo Jurelevicius

    Full Text Available The alkane monooxygenase AlkB, which is encoded by the alkB gene, is a key enzyme involved in bacterial alkane degradation. To study the alkB gene within bacterial communities, researchers need to be aware of the variations in alkB nucleotide sequences; a failure to consider the sequence variations results in the low representation of the diversity and richness of alkane-degrading bacteria. To minimize this shortcoming, the use of a combination of three alkB-targeting primers to enhance the detection of the alkB gene in previously isolated alkane-degrading bacteria was proposed. Using this approach, alkB-related PCR products were detected in 79% of the strains tested. Furthermore, the chosen set of primers was used to study alkB richness and diversity in different soils sampled in Carmópolis, Brazil and King George Island, Antarctica. The DNA extracted from the different soils was PCR amplified with each set of alkB-targeting primers, and clone libraries were constructed, sequenced and analyzed. A total of 255 alkB phylotypes were detected. Venn diagram analyses revealed that only low numbers of alkB phylotypes were shared among the different libraries derived from each primer pair. Therefore, the combination of three alkB-targeting primers enhanced the richness of alkB phylotypes detected in the different soils by 45% to 139%, when compared to the use of a single alkB-targeting primer. In addition, a dendrogram analysis and beta diversity comparison of the alkB composition showed that each of the sampling sites studied had a particular set of alkane-degrading bacteria. The use of a combination of alkB primers was an efficient strategy for enhancing the detection of the alkB gene in cultivable bacteria and for better characterizing the distribution of alkane-degrading bacteria in different soil environments.

  17. The Use of a Combination of alkB Primers to Better Characterize the Distribution of Alkane-Degrading Bacteria

    Science.gov (United States)

    Jurelevicius, Diogo; Alvarez, Vanessa Marques; Peixoto, Raquel; Rosado, Alexandre S.; Seldin, Lucy

    2013-01-01

    The alkane monooxygenase AlkB, which is encoded by the alkB gene, is a key enzyme involved in bacterial alkane degradation. To study the alkB gene within bacterial communities, researchers need to be aware of the variations in alkB nucleotide sequences; a failure to consider the sequence variations results in the low representation of the diversity and richness of alkane-degrading bacteria. To minimize this shortcoming, the use of a combination of three alkB-targeting primers to enhance the detection of the alkB gene in previously isolated alkane-degrading bacteria was proposed. Using this approach, alkB-related PCR products were detected in 79% of the strains tested. Furthermore, the chosen set of primers was used to study alkB richness and diversity in different soils sampled in Carmópolis, Brazil and King George Island, Antarctica. The DNA extracted from the different soils was PCR amplified with each set of alkB-targeting primers, and clone libraries were constructed, sequenced and analyzed. A total of 255 alkB phylotypes were detected. Venn diagram analyses revealed that only low numbers of alkB phylotypes were shared among the different libraries derived from each primer pair. Therefore, the combination of three alkB-targeting primers enhanced the richness of alkB phylotypes detected in the different soils by 45% to 139%, when compared to the use of a single alkB-targeting primer. In addition, a dendrogram analysis and beta diversity comparison of the alkB composition showed that each of the sampling sites studied had a particular set of alkane-degrading bacteria. The use of a combination of alkB primers was an efficient strategy for enhancing the detection of the alkB gene in cultivable bacteria and for better characterizing the distribution of alkane-degrading bacteria in different soil environments. PMID:23825163

  18. Density functional study on the mechanism for the highly active palladium monolayer supported on titanium carbide for the oxygen reduction reaction

    Science.gov (United States)

    Mao, Jianjun; Li, Shasha; Zhang, Yanxing; Chu, Xingli; Yang, Zongxian

    2016-05-01

    The adsorption, diffusion, and dissociation of O2 on the palladium monolayer supported on TiC(001) surface, MLPd/TiC(001), are investigated using ab initio density functional theory calculations. Strong adhesion of palladium monolayer to the TiC(001) support, accompanied by a modification of electronic structure of the supported palladium, is evidenced. Compared with Pt(111) surface, the MLPd/TiC(001) can enhance the adsorption of O2, leading to comparable dissociation barrier and a smaller diffusion barrier of O2. Whilst the adsorption strength of atomic O (the dissociation product of O2) on MLPd/TiC(001) is similar to that on the Pt(111) surface, possessing high mobility, our theoretical results indicate that MLPd/TiC(001) may serve as a good catalyst for the oxygen reduction reaction.

  19. Manipulation of electronic structure in WSe2 monolayer by strain

    Science.gov (United States)

    Yang, Cong-xia; Zhao, Xu; Wei, Shu-yi

    2016-11-01

    In this paper, we study the electronic properties of WSe2 monolayer with biaxial tensile strain and compressive strain by using first principles based on the density function theory. Under the biaxial tensile strain, WSe2 monolayer retains direct band gap with increasing strain and the band gap of WSe2 continuously decreases with increasing strain, eventually turn to metal when strain is equal to or more than 13%. Under the biaxial compressive strain, WSe2 monolayer turns to indirect gap and the band gap continuously decreases with increasing strain, finally turn to metal when strain is up to -7%. The strain can reduce the band gap of the WSe2 monolayer regardless of the strain direction. By comparison, we can see that the tensile strain appears to be more effective in reducing the band gap of pristine WSe2 monolayer than the compressive strain from -5% to 5%. But the band gap turns to zero quickly from -6% to -7% under compressive strain, however for tensile strain from 5% to 13%, the band gap decreases slowly. Based on the further analysis of the projected charge density for WSe2 monolayer, the fundamental reason of the change of band structure under biaxial tensile strain is revealed.

  20. Nonlinear optical characteristics of monolayer MoSe{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Le, Chinh Tam; Ullah, Farman; Senthilkumar, Velusamy; Kim, Yong Soo [Department of Physics and Energy Harvest Storage Research Center, University of Ulsan (Korea, Republic of); Clark, Daniel J.; Jang, Joon I. [Department of Physics, Applied Physics and Astronomy, Binghamton University, Binghamton, NY (United States); Sim, Yumin; Seong, Maeng-Je [Department of Physics, Chung-Ang University, Seoul (Korea, Republic of); Chung, Koo-Hyun [School of Mechanical Engineering, University of Ulsan (Korea, Republic of); Park, Hyoyeol [Electronics, Communication and Semiconductor Applications Department, Ulsan College (Korea, Republic of)

    2016-08-15

    In this study, we utilized picosecond pulses from an Nd:YAG laser to investigate the nonlinear optical characteristics of monolayer MoSe{sub 2}. Two-step growth involving the selenization of pulsed-laser-deposited MoO{sub 3} film was employed to yield the MoSe{sub 2} monolayer on a SiO{sub 2}/Si substrate. Raman scattering, photoluminescence (PL) spectroscopy, and atomic force microscopy verified the high optical quality of the monolayer. The second-order susceptibility χ{sup (2)} was calculated to be ∝50 pm V{sup -1} at the second harmonic wavelength λ{sub SHG} ∝810 nm, which is near the optical gap of the monolayer. Interestingly, our wavelength-dependent second harmonic scan can identify the bound excitonic states including negatively charged excitons much more efficiently, compared with the PL method at room temperature. Additionally, the MoSe{sub 2} monolayer exhibits a strong laser-induced damage threshold ∝16 GW cm{sup -2} under picosecond-pulse excitation{sub .} Our findings suggest that monolayer MoSe{sub 2} can be considered as a promising candidate for high-power, thin-film-based nonlinear optical devices and applications. (copyright 2016 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Thermoelectric properties of SnSe2 monolayer

    Science.gov (United States)

    Li, Guanpeng; Ding, Guangqian; Gao, Guoying

    2017-01-01

    The 2H (MoS2-type) phase of 2D transition metal dichalcogenides (TMDCs) has been extensively studied and exhibits excellent electronic and optoelectronic properties, but the high phonon thermal conductivity is detrimental to the thermoelectric performances. Here, we use first-principles methods combined with Boltzmann transport theory to calculate the electronic and phononic transport properties of 1T (CdI2-type) SnSe2 monolayer, a recently realized 2D metal dichalcogenide semiconductor. The calculated band gap is 0.85 eV, which is a little larger than the bulk value. Lower phonon thermal conductivity and higher power factor are obtained in 1T-SnSe2 monolayer compared to 2H-TMDCs monolayers. The low phonon thermal conductivity (3.27 W mK-1 at room temperature) is mainly due to the low phonon frequency of acoustic modes and the coupling of acoustic modes with optical modes. We also find that the p-type has better thermoelectric performance than the n-type, and the figure of merit within p-type can reach 0.94 at 600 K for 1T-SnSe2 monolayer, which is higher than those of most 2H-TMDCs monolayers, making 1T-SnSe2 monolayer a promising candidate for thermoelectric applications.

  2. (19)F Oximetry with semifluorinated alkanes.

    Science.gov (United States)

    Kegel, Stefan; Chacon-Caldera, Jorge; Tsagogiorgas, Charalambos; Theisinger, Bastian; Glatting, Gerhard; Schad, Lothar R

    2016-12-01

    This work examines the variation of longitudinal relaxation rate R1(= 1/T1) of the (19)F-CF3-resonance of semifluorinated alkanes (SFAs) with oxygen tension (pO2), temperature (T) and pH in vitro. Contrary to their related perfluorocarbons (PFCs), SFA are amphiphilic and facilitate stable emulsions, a prerequisite for clinical use. A linear relationship between R1 and pO2 was confirmed for the observed SFAs at different temperatures. Using a standard saturation recovery sequence, T1 has been successfully measured using fluorine (19)F-MRI with a self-constructed birdcage resonator at 9.4 T. A calibration curve to calculate pO2 depending on T and R1 was found for each SFA used. In contrast to the commonly used PFC, SFAs are less sensitive to changes in pO2, but more sensitive to changes in temperature. The influence of pH to R1 was found to be negligible.

  3. Study of translational, librational and intra-molecular motion of adsorbed liquid water monolayers at various TiO2 interfaces

    OpenAIRE

    Kavathekar, Ritwik S.; English, Niall J.; MacElroy, J. M. Don

    2011-01-01

    Equilibrium classical molecular dynamics (MD) simulations have been performed to investigate the vibrational motion of water in contact with rutile-(110), rutile-(100), rutile-(001), anatase-(101) and anatase-(001) surfaces at room temperature (300 K). The vibrational density of states (VDOS) of the first adsorbed monolayer of liquid water has been analysed for each surface. These have been compared with reported experimental INS values involving rutile and anatase polymorph surfaces, along w...

  4. 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......-octane (21μmol/min/gdcw); similar to the 5-fold difference observed between wild-type growth rates using the two respective alkanes as sole carbon source. Despite this, both total volumetric rate and final yield exceeded n-octane oxidation by 3.5-fold under the same conditions, due to the lower toxicity of n...

  5. Perspective: What is known, and not known, about the connections between alkane oxidation and metal uptake in alkanotrophs in the marine environment

    Science.gov (United States)

    Kenney, Grace E.; Rosenzweig, Amy C.

    2014-01-01

    Article Summary Should iron and copper be added to the environment to stimulate the natural bioremediation of marine oil spills? The key enzymes that catalyze the oxidation of alkanes require either iron or copper, and the concentration of these ions in seawater is vanishingly low. Nevertheless, the dependence of alkane oxidation activity on external metal concentrations remains unclear. This perspective will summarize what is known about the co-regulation of alkane oxidation and metal acquisition and pose a series of critical questions to which, for the most part, we do not yet have answers. The paucity of answers points to the need for additional studies to illuminate the cellular biology connecting microbial growth on alkanes to the acquisition of metal ions. PMID:24710692

  6. Molecular dynamics simulation of diffusion and structure of some n-alkanes in near critical and supercritical carbon dioxide at infinite dilution.

    Science.gov (United States)

    Feng, Huajie; Gao, Wei; Sun, Zhenfan; Lei, Bingxin; Li, Gaonan; Chen, Liuping

    2013-10-17

    The diffusion coefficients of n-alkanes (from CH4 to C14H30) in near critical and supercritical carbon dioxide at infinite dilution have been studied by molecular dynamics simulation. The simulation results agree well with experiment, which suggests that the simulation method is a powerful tool to obtain diffusion coefficients of solutes in fluids at high pressures. The local structures of such fluids are further investigated by calculating radial distribution functions and coordination numbers. Meanwhile, the dihedral, end-to-end distance and radius of gyration, which are calculated to characterize the flexibility of n-alkanes, are used to reasonably explain the abnormal trends on radial distribution functions and coordination numbers. Moreover, it is found that the flexibility effects on diffusion in pure n-alkanes and infinitely dilute n-alkane/CO2 system are different. The differences in MD simulation results of molecular diffusion in such systems could be qualitatively explained by the flexibility.

  7. Polymer Adsorption on Graphite and CVD Graphene Surfaces Studied by Surface-Specific Vibrational Spectroscopy.

    Science.gov (United States)

    Su, Yudan; Han, Hui-Ling; Cai, Qun; Wu, Qiong; Xie, Mingxiu; Chen, Daoyong; Geng, Baisong; Zhang, Yuanbo; Wang, Feng; Shen, Y R; Tian, Chuanshan

    2015-10-14

    Sum-frequency vibrational spectroscopy was employed to probe polymer contaminants on chemical vapor deposition (CVD) graphene and to study alkane and polyethylene (PE) adsorption on graphite. In comparing the spectra from the two surfaces, it was found that the contaminants on CVD graphene must be long-chain alkane or PE-like molecules. PE adsorption from solution on the honeycomb surface results in a self-assembled ordered monolayer with the C-C skeleton plane perpendicular to the surface and an adsorption free energy of ∼42 kJ/mol for PE(H(CH2CH2)nH) with n ≈ 60. Such large adsorption energy is responsible for the easy contamination of CVD graphene by impurity in the polymer during standard transfer processes. Contamination can be minimized with the use of purified polymers free of PE-like impurities.

  8. 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.

  9. 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 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...

  10. Quantification of chemotaxis-related alkane accumulation in Acinetobacter baylyi using Raman microspectroscopy.

    Science.gov (United States)

    Li, Hanbing; L Martin, Francis Luke; Zhang, Dayi

    2017-03-03

    Alkanes are one of the most widespread contaminants in the natural environment, primarily as a consequence of biological synthesis and oil spills. Many indigenous microbes metabolize alkanes, and the chemotaxis and accumulation in some strains has been identified. For the first time, we apply Raman microspectroscopy to identify such chemotaxis-related affinity, and quantify the alkane concentrations via spectral alterations. Raman spectral alterations were only found for the alkane chemo-attractant bacteria Acinetobacter baylyi ADP1, not for Pseudomonas fluorescence, which exhibits limited chemotaxis towards alkane. The significant alterations were attributed to the strong chemotactic ability of A. baylyi enhancing the affinity and accumulation of alkane molecules on cell membranes or cellular internalization. Spectral fingerprints of A. baylyi significantly altered after 1-h exposure to pure alkanes (dodecane or tetradecane) and alkane mixtures (mineral oil or crude oil), but not monocyclic aromatic hydrocarbons (MAHs) or polycyclic aromatic hydrocarbons (PAHs). A semi-log linear regression relationship between Raman spectral alterations and alkane concentrations showed its feasibility in quantifying alkane concentration in environmental samples. Pure alkanes or alkane mixtures exhibited different limits of detection and regression slopes, indicating that the chemotaxis-related alkane accumulation in A. baylyi is dependent on the carbon chain length. This work provides a novel biospectroscopy approach to characterize the chemotaxis-related alkane bioaccumulation, and has immense potential for fast and high-throughput screening bacterial chemotaxis.

  11. Inhibitory Potency of 4-Carbon Alkanes and Alkenes toward CYP2E1 Activity

    OpenAIRE

    2014-01-01

    CYP2E1 has been implicated in the bioactivation of many small molecules into reactive metabolites which form adducts with proteins and DNA, and thus a better understanding of the molecular determinants of its selectivity are critical for accurate toxicological predictions. In this study, we determined the potency of inhibition of human CYP2E1 for various 4-carbon alkanes, alkenes and alcohols. In addition, known CYP2E1 substrates and inhibitors including 4-methylpyrazole, aniline, and dimethy...

  12. A comparative study of structural and electronic properties of formaldehyde molecule on monolayer honeycomb structures based on vdW-DF prospective

    Energy Technology Data Exchange (ETDEWEB)

    Ganji, M.D., E-mail: ganji_md@yahoo.com [Department of Chemistry, Qaemshahr branch, Islamic Azad University, Qaemshahr (Iran, Islamic Republic of); Jameh-Bozorgi, S. [Department of Chemistry, Faculty of Science, Hamedan Branch, Islamic Azad University, Hamedan (Iran, Islamic Republic of); Rezvani, M. [Department of Chemistry, Faculty of Science, Arak branch, Islamic Azad university, Arak (Iran, Islamic Republic of)

    2016-10-30

    Graphical abstract: The adsorption of formaldehyde molecule on the monolayer honeycomb structure was investigated by using first-principles calculations with the vdW-DF method. Display Omitted - Highlights: • The meaningful enhancement in binding energy values and electrical conductivity of h-AlN nanosheet can be potential candidate for detection of formaldehydemolecule. • The adsorption of formaldehyde molecule changed the conductivity of monolayer honeycomb structure especially h-AlN nanosheet. • The favorable adsorption sites of formaldehyde molecule depend on binding energy, HOMO-LUMO gap, Mulliken, Hirshfeld and Voronoi population. - Abstract: In order to develop the potential applications of monolayer sheets as gas sensors, the adsorption of formaldehyde (H{sub 2}CO) molecule on graphene, hexagonal silicon carbide (h-SiC) as well as hexagonal aluminum nitride (h-AlN) monolayer sheets have been investigated. In this work we have used the so-called van der Waals density functional (vdW-DF) method. It was found that H{sub 2}CO molecule adsorption on h-AlN nanosheet had relatively higher adsorption energy and shorter binding distance and finally much more reactive in the adsorption of H{sub 2}CO compared with the h-SiC and graphene sheets. The density of states (DOS) was calculated and the results show that the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gap of h-AlN and h-SiC sheets is significantly reduced upon the H{sub 2}CO adsorption compared to the graphene which leads to an enhancement in the electrical conductivity of respective systems. We have evaluated these findings by well-known Mulliken as well as Hirshfeld and Voronoi charges analyses for aforementioned systems. The purpose of this work is to achieve deep insights into the influence of H{sub 2}CO molecule on the electronic properties of h-AlN and h-SiC monolayer sheets, and how these effects could be used to design more sensitive gas sensing

  13. 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 ...

  14. 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.

  15. 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.; Charles W Greer

    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...

  16. Fully atomistic molecular-mechanical model of liquid alkane oils: Computational validation.

    Science.gov (United States)

    Zahariev, Tsvetan K; Slavchov, Radomir I; Tadjer, Alia V; Ivanova, Anela N

    2014-04-15

    Fully atomistic molecular dynamics simulations were performed on liquid n-pentane, n-hexane, and n-heptane to derive an atomistic model for middle-chain-length alkanes. All simulations were based on existing molecular-mechanical parameters for alkanes. The computational protocol was optimized, for example, in terms of thermo- and barostat, to reproduce properly the properties of the liquids. The model was validated by comparison of thermal, structural, and dynamic properties of the normal alkane liquids to experimental data. Two different combinations of temperature and pressure coupling algorithms were tested. A simple differential approach was applied to evaluate fluctuation-related properties with sufficient accuracy. Analysis of the data reveals a satisfactory representation of the hydrophobic systems behavior. Thermodynamic parameters are close to the experimental values and exhibit correct temperature dependence. The observed intramolecular geometry corresponds to extended conformations domination, whereas the intermolecular structure demonstrates all characteristics of liquid systems. Cavity size distribution function was calculated from coordinates analysis and was applied to study the solubility of gases in hexane and heptane oils. This study provides a platform for further in-depth research on hydrophobic solutions and multicomponent systems.

  17. Molecular dynamics simulations of layers of linear and branched alkanes under shear

    Science.gov (United States)

    Soza, P.; Hansen, F. Y.; Taub, H.; Volkmann, U. G.

    2008-03-01

    We have previously studied the equilibrium structure and dynamical excitations in films of the linear alkane tetracosane (n-C24H50) and the branched alkane squalane (C30H62) in great detail^2. Here we report the results of nonequilibrium molecular dynamics simulations of these systems in order to compare the rheological properties of alkanes of the same length but with different architecture. The simulations were done in the NVT ensemble using the reverse nonequilibrium algorithm proposed by F. Müller-Plathe et al.^3. The viscosity was calculated for different shear rates and compared with experimental values. Different structural parameters such as the mean end-to-end distance, the radius of gyration, and the angle of alignment of the molecules with the flow were studied as a function of the shear rate. ^2A.D. Enevoldsen et al., J. Chem. Phys. 126, 104703-10 (2007); 126, 104704-17 (2007). ^3F. Müller-Plathe et al., Phys. Rev. E, 59, 4894 (1998)

  18. Gold nanoparticle self-assembly in two-component lipid Langmuir monolayers.

    Science.gov (United States)

    Mogilevsky, Alina; Jelinek, Raz

    2011-02-15

    Self-assembly processes are considered to be fundamental factors in supramolecular chemistry. Langmuir monolayers of surfactants or lipids have been shown to constitute effective 2D "templates" for self-assembled nanoparticles and colloids. Here we show that alkyl-coated gold nanoparticles (Au NPs) adopt distinct configurations when incorporated within Langmuir monolayers comprising two lipid components at different mole ratios. Thermodynamic and microscopy analyses reveal that the organization of the Au NP aggregates is governed by both lipid components. In particular, we show that the configurations of the NP assemblies were significantly affected by the extent of molecular interactions between the two lipid components within the monolayer and the monolayer phases formed by each individual lipid. This study demonstrates that multicomponent Langmuir monolayers significantly modulate the self-assembly properties of embedded Au NPs and that parameters such as the monolayer composition, surface pressure, and temperature significantly affect the 2D nanoparticle organization.

  19. 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

  20. Phosphatidic acid and phosphoinositides facilitate liposome association of Yas3p and potentiate derepression of ARE1 (alkane-responsive element one)-mediated transcription control.

    Science.gov (United States)

    Kobayashi, Satoshi; Hirakawa, Kiyoshi; Horiuchi, Hiroyuki; Fukuda, Ryouichi; Ohta, Akinori

    2013-12-01

    In the n-alkane assimilating yeast Yarrowia lipolytica, the expression of ALK1, encoding a cytochrome P450 that catalyzes terminal mono-oxygenation of n-alkanes, is induced by n-alkanes. The transcription of ALK1 is regulated by a heterocomplex that comprises the basic helix-loop-helix transcription activators, Yas1p and Yas2p, and binds to alkane-responsive element 1 (ARE1) in the ALK1 promoter. An Opi1 family transcription repressor, Yas3p, represses transcription by binding to Yas2p. Yas3p localizes in the nucleus when Y. lipolytica is grown on glucose but localizes to the endoplasmic reticulum (ER) upon the addition of n-alkanes. In this study, we showed that recombinant Yas3p binds to the acidic phospholipids, phosphatidic acid (PA) and phosphoinositides (PIPs), in vitro. The ARE1-mediated transcription was enhanced in vivo in mutants defective in an ortholog of the Saccharomyces cerevisiae gene PAH1, encoding PA phosphatase, and in an ortholog of SAC1, encoding PIP phosphatase in the ER. Truncation mutation analyses for Yas3p revealed two regions that bound to PA and PIPs. These results suggest that the interaction with acidic phospholipids is important for the n-alkane-induced association of Yas3p with the ER membrane.

  1. Chemodiversity of Epicuticular n-Alkanes and Morphological Traits of Natural Populations of Satureja subspicata Bartl. ex Vis. along Dinaric Alps - Ecological and Taxonomic Aspects.

    Science.gov (United States)

    Dodoš, Tanja; Rajčević, Nemanja; Tešević, Vele; Marin, Petar D

    2017-02-01

    Morphological characters and the composition of epicuticular leaf n-alkanes of two Satureja subspicata Bartl. ex Vis. subspecies (subsp. liburnica Šilić and subsp. subspicata) from nine natural populations along Dinaric Alps range were studied. Morphological characters were chosen based on Šilić's subspecies separation. Seventeen n-alkane homologues (C19 - C35 ) were identified using gas chromatography/mass spectrometry (GC/MS) and GC/flame ionisation detector (FID). The most abundant n-alkane in all populations was n-nonacosane (C29 ), followed by n-hentriacontane (C31 ), with the exception of Divača population where these two alkanes were co-dominant. Diversity and variability of n-alkane patterns and morphological characters and their relation to different geographic and bioclimatic parameters, including exposure, were analysed by several statistical multivariate methods (PCA, HCA, Discriminant Analysis, Mantel test). These tests showed clear separation of subsp. liburnica from subsp. subspicata, even though population Velebit showed separation from other subsp. liburnica populations based on phytochemical characters. Mantel test showed high correlation with geographical distribution in both investigated data sets. High correlation between morphological and phytochemical characters was also established. However, exposure can influence n-alkane profile, suggesting precaution while taking samples from natural habitats.

  2. 40 CFR 721.10145 - Modified reaction products of alkyl alcohol, halogenated alkane, substituted epoxide, and amino...

    Science.gov (United States)

    2010-07-01

    ... alcohol, halogenated alkane, substituted epoxide, and amino compound (generic). 721.10145 Section 721... Modified reaction products of alkyl alcohol, halogenated alkane, substituted epoxide, and amino compound... identified generically as modified reaction products of alkyl alcohol, halogenated alkane,...

  3. Determining and quantifying specific sources of light alkane

    Science.gov (United States)

    Bill, M.; Conrad, M. E.

    2015-12-01

    Determining and quantifying specific sources of emission of methane (an important greenhouse gas) and light alkanes from abandoned gas and oil wells, hydraulic fracturing or associated with CO2 sequestration are a challenge in determining their contribution to the atmospheric greenhouse gas budget or to identify source of groundwater contamination. Here, we review organic biogeochemistry proprieties and isotopic fingerprinting of C1-C5 alkanes to address this problem. For instance, the concentration ratios of CH4 to C2-C5 alkanes can be used to distinguish between thermogenic and microbial generated CH4. Together C and H isotopes of CH4 are used to differentiate bacterial generated sources and thermogenic CH4 and may also identify processes such as alteration and source mixing. Carbon isotope ratios pattern of C1-C5 alkanes highlight sources and oxidation processes in the gas reservoirs. Stable carbon isotope measurements are a viable tool for monitoring the degradation progress of methane and light hydrocarbons. The carbon isotope ratios of the reactants and products are independent of the concentration and only depend on the relative progress of the particular reaction. Oxidation/degradation of light alkanes are typically associated with increasing ð13C values. Isotopic mass balances offer the possibility to independently determine the fractions coming from microbial versus thermogenic and would also permit differentiation of the isotope fractionations associated with degradation. Unlike conventional concentration measurements, this approach is constrained by the different isotopic signatures of various sources and sinks.

  4. 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.

  5. A comparative study of structural and electronic properties of formaldehyde molecule on monolayer honeycomb structures based on vdW-DF prospective

    Science.gov (United States)

    Ganji, M. D.; Jameh-Bozorgi, S.; Rezvani, M.

    2016-10-01

    In order to develop the potential applications of monolayer sheets as gas sensors, the adsorption of formaldehyde (H2CO) molecule on graphene, hexagonal silicon carbide (h-SiC) as well as hexagonal aluminum nitride (h-AlN) monolayer sheets have been investigated. In this work we have used the so-called van der Waals density functional (vdW-DF) method. It was found that H2CO molecule adsorption on h-AlN nanosheet had relatively higher adsorption energy and shorter binding distance and finally much more reactive in the adsorption of H2CO compared with the h-SiC and graphene sheets. The density of states (DOS) was calculated and the results show that the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gap of h-AlN and h-SiC sheets is significantly reduced upon the H2CO adsorption compared to the graphene which leads to an enhancement in the electrical conductivity of respective systems. We have evaluated these findings by well-known Mulliken as well as Hirshfeld and Voronoi charges analyses for aforementioned systems. The purpose of this work is to achieve deep insights into the influence of H2CO molecule on the electronic properties of h-AlN and h-SiC monolayer sheets, and how these effects could be used to design more sensitive gas sensing devices. Based on the DFT calculation results, the h-AlN and also h-h-SiC sheets are anticipated to be potential novel sensor for detecting the presence of H2CO toxic gas.

  6. Supercooling Suppression of Microencapsulated n-Alkanes by Introducing an Organic Gelator

    Institute of Scientific and Technical Information of China (English)

    ZHU Kong-ying; WANG Shuang; QI Heng-zhi; LI Hui; ZHAO Yun-hui; YUAN Xiao-yan

    2012-01-01

    Supercooling of the microencapsulated phase change materials(PCMs) during cooling usually happens.This phenomenon can interfere with heat transfer and is necessary to further overcome.In this study,melamine-formaldehyde microcapsules containing two n-alkane PCMs,namely,n-dodecane(C12) or n-tetradecane(C14)were prepared by in situ polymerization.A small amount of n-hexatriacontane(C36) was introduced as an organic gelator into the core of microcapsules to cope with the supercooling problem.Analyses demonstrate that supcrcooling of the microencapsulated C12 or C14 was significantly suppressed by adding 3%(mass fraction) C36,without changing the spherical morphology and dispersibility.It could be also found that the enthalpy of microencapsulated C12 or C14 containing C36 was similar to that of microencapsulated n-alkanes without C36,whereas the difference between onsets of crystallization and melting(degree of supercooling) is similar to that of those of pure n-alkanes,suggesting the remarkable suppression ability of the organic gelator on supercooling.

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

    Energy Technology Data Exchange (ETDEWEB)

    Bredholt, H.; Eimhjellen, K. [Norwegian Univ. of Science and Technology, Dept. of Biotechnology, Trondheim, (Norway)

    1999-08-01

    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.

  8. Scanning tunneling microscopy study of the c(4x4) structure formation in the sub-monolayer Sb/Si(100) system

    Energy Technology Data Exchange (ETDEWEB)

    Saranin, A.A.; Zotov, A.V. [Osaka Univ., Suita (Japan). Faculty of Engineering; Kotlyar, V.G. [Institute of Automation and Control Processes, Vladivostok (RU)] (and others)

    2001-10-01

    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)

  9. Platinum monolayer electrocatalysts for oxygen reduction in fuel cells

    Science.gov (United States)

    Zhang, Junliang

    Fuel cells are expected to be one of the major clean energy sources in the near future. However, the slow kinetics of electrocatalytic oxygen reduction reaction (ORR) and the high loading of Pt for the cathode material are the urgent issues to be addressed since they determine the efficiency and the cost of this energy source. In this study, a new approach was developed for designing electrocatalysts for the ORR in fuel cells. These electrocatalysts consist of only one Pt monolayer, or mixed transition metal-Pt monolayer, on suitable carbon-supported metal, or alloy nanoparticles. The synthesis involved depositing a monolayer of Cu on a suitable transition metal or metal alloy surface at underpotentials, followed by galvanic displacement of the Cu monolayer with Pt or mixed metal-Pt. It was found that the electronic properties of Pt monolayer could be fine-tuned by the electronic and geometric effects introduced by the substrate metal (or alloy) and the lateral effects of the neighboring metal atoms. The role of substrates was found reflected in a "volcano" plot of the monolayer activity for the ORR as a function of their calculated d-band centers. The Pt mass-specific activity of the new Pt monolayer electrocatalysts was up to twenty times higher than the state-of-the-art commercial Pt/C catalysts. The enhancement of the activity is caused mainly by decreased formation of PtOH (the blocking species for ORR), and to a lesser degree by the electronic effects. Fuel cell tests showed a very good long term stability of the new electrocatalysts. Our results demonstrated a viable way to designing the electrocatalysts which could successfully alleviate two issues facing the commercialization of fuel cells---the costs of electrocatalysts and their efficiency.

  10. Sensitive detection of n-alkanes using a mixed ionization mode proton-transfer-reaction mass spectrometer

    Science.gov (United States)

    Amador-Muñoz, Omar; Misztal, Pawel K.; Weber, Robin; Worton, David R.; Zhang, Haofei; Drozd, Greg; Goldstein, Allen H.

    2016-11-01

    Proton-transfer-reaction mass spectrometry (PTR-MS) is a technique that is widely used to detect volatile organic compounds (VOCs) with proton affinities higher than water. However, n-alkanes generally have a lower proton affinity than water and therefore proton transfer (PT) by reaction with H3O+ is not an effective mechanism for their detection. In this study, we developed a method using a conventional PTR-MS to detect n-alkanes by optimizing ion source and drift tube conditions to vary the relative amounts of different primary ions (H3O+, O2+, NO+) in the reaction chamber (drift tube). There are very few studies on O2+ detection of alkanes and the mixed mode has never been proposed before. We determined the optimum conditions and the resulting reaction mechanisms, allowing detection of n-alkanes from n-pentane to n-tridecane. These compounds are mostly emitted by evaporative/combustion process from fossil fuel use. The charge transfer (CT) mechanism observed with O2+ was the main reaction channel for n-heptane and longer n-alkanes, while for n-pentane and n-hexane the main reaction channel was hydride abstraction (HA). Maximum sensitivities were obtained at low E / N ratios (83 Td), low water flow (2 sccm) and high O2+ / NO+ ratios (Uso = 180 V). Isotopic 13C contribution was taken into account by subtracting fractions of the preceding 12C ion signal based on the number of carbon atoms and the natural abundance of 13C (i.e., 5.6 % for n-pentane and 14.5 % for n-tridecane). After accounting for isotopic distributions, we found that PT cannot be observed for n-alkanes smaller than n-decane. Instead, protonated water clusters of n-alkanes (M ṡ H3O+) species were observed with higher abundance using lower O2+ and higher water cluster fractions. M ṡ H3O+ species are probably the source for the M + H+ species observed from n-decane to n-tridecane. Normalized sensitivities to O2+ or to the sum of O2++ NO+ were determined to be a good metric with which to

  11. 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.

  12. 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.

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

    DEFF Research Database (Denmark)

    Westh, Peter

    2006-01-01

    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......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...... 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 DMPC. First...

  14. Characterization of phospholipid+semifluorinated alkane vesicle system.

    Science.gov (United States)

    Sabín, Juan; Ruso, Juan M; González-Pérez, Alfredo; Prieto, Gerardo; Sarmiento, Félix

    2006-01-15

    The aim of this study is to characterize vesicles obtained by the incorporation of the semifluorinated alkane, (perfluoro-n-hexyl)ethane (diblock F6H2) to a standard lipid, egg yolk phosphatidylcholine (PC). Large unilamellar vesicles (LUVs), prepared by extrusion, were characterized by fluorescence spectroscopy, zeta potential (zeta-potential) and light scattering. By using the fluorescence spectroscopy technique, the anisotropy of l,6-diphenyl-l,3,5-hexatriene (DPH) probe at different temperatures was determined. It was demonstrated that F6H2 is placed inside of the lipid bilayer and that the hydrocarbon acyl chain in the bilayers has higher viscosity in the presence of fluoroalkane. The zeta-potential of the PC-F6H2 system is negative and increases (in absolute value) from -10 to -19 mV when the temperature rises from 10 to 25 degrees C, this last value keeping practically constant with a further increase of temperature. The adsorption of K+ ions on the liposome surface was measured by zeta-potential. This adsorption originates a sudden increase of the initial zeta-potential followed by a slight decrease with K+ concentration. The application of the DLVO theory of colloidal stability showed a growing dependence of the DLVO potential with K+ concentration and consequently a increasing stability.

  15. 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).

  16. Langmuir monolayers of non-ionic polymers: equilibrium or metastability? Case study of PEO and its PPO-PEO diblock copolymers.

    Science.gov (United States)

    Deschênes, Louise; Saint-Germain, François; Lyklema, Johannes

    2015-07-01

    Stability and reorganization in Langmuir films of PEO in PEO homopolymers and PPO-PEO block copolymers were investigated using film balance measurements. The apparent fractional losses of EO segments transferred into the subphase resulting from successive compression-expansion cycles have been estimated. The apparent loss is mainly Γ(max), M(n) and time-dependent. At surface concentrations Γ⩽0.32 mg/m(2), PEO films are in equilibrium. For 0.32⩽Γ⩽0.7 mg/m(2), the losses remain modest. Further compression leads to densification of the monolayer, requiring the interplay of thermodynamics and kinetic factors In the plateau regime, the loss is higher and constant for 1⩽Γ(max)⩽2 mg/m(2) upon maintaining the achieved surface area for 15 min. Similar losses were obtained for PEO homopolymers of high Mn and PPO353-PEO2295. It suggests that the PEO remains anchored in a metastable state at the air-water interface at surface concentration well above the onset of the plateau. Additional losses are incurred for PEO homopolymers for monolayers kept compressed in the plateau for 2 h. For the interpretation of these phenomena a combination of elements from self-consistent field theory and scaling is desirable with as a trend an increasing contribution of the latter with increasing surface concentration.

  17. Regioselective alkane hydroxylation with a mutant AlkB enzyme

    Science.gov (United States)

    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.

  18. 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...

  19. 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.

  20. Holocene vegetation cover in Qin'an area of western Chinese Loess Plateau revealed by n-alkane

    Institute of Scientific and Technical Information of China (English)

    ZHONG YanXia; CHEN FaHu; AN ChengBang; XIE ShuCheng; HUANG XianYu

    2007-01-01

    Previous studies have found that wetlands prevailed in western Chinese Loess Plateau and pine pollen could reach up to 80% in Qin'an area of the plateau during middle Holocene.It was then deduced that forest vegetation covered Qin'an area in a warm and wet climate during middle Holocene.The proxies of molecule biomarkers from two Holocene sections,a swamp-alluvial loess section and a typical loess-paleosol section are used to reconstruct regional vegetation history.It is found that the heavy-molecular-weight(HMW)homologues of the n-alkanes in all samples exhibit a pronounced odd-over-even predominance,maximizing at C31 and the abundance of the nC27-alkanes is the lowest in nC27,nC29,nC31,i.e.C27<C29<C31,a typical grass n-alkanes model.The results are the same as those of model surface soil samples under grass cover but different from both forest cover and modern pine leaves,which yield preferentially nC29-alkanes peak.It could be jnferred that the area was dominated by grass cover but not forest cover during whole Holocene epoch.The study shows that combining both molecule biomarkers and pollen analysis can avoid the disadvantage of pollen analysis in reconstruction of regional vegetation cover.

  1. 40 CFR 721.10148 - Acryloxy alkanoic alkane derivative with mixed metal oxides (generic).

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Acryloxy alkanoic alkane derivative... Significant New Uses for Specific Chemical Substances § 721.10148 Acryloxy alkanoic alkane derivative with...) The chemical substance identified generically as acryloxy alkanoic alkane derivative with mixed...

  2. 40 CFR 721.785 - Halogenated alkane aromatic compound (generic name).

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Halogenated alkane aromatic compound... Specific Chemical Substances § 721.785 Halogenated alkane aromatic compound (generic name). (a) Chemical... as a halogenated alkane aromatic compound (PMN P-94-1747) is subject to reporting under this...

  3. 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.

  4. 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 sp(3)-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.

  5. Paleoclimate and Asian monsoon variability inferred from n-alkanes and their stable isotopes at lake Donggi Cona, NE Tibetan Plateau

    Science.gov (United States)

    Saini, Jeetendra; Guenther, Franziska; Mäusbacher, Roland; Gleixner, Gerd

    2015-04-01

    The Tibetan Plateau is one of the most extensive and sensitive region of elevated topography affecting global climate. The interplay between the Asian summer monsoon and the westerlies greatly influences the lake systems at the Tibetan Plateau. Despite a considerable number of research efforts in last decade, possible environmental reactions to change in monsoon dynamics are still not well understood. Here we present results from a sediment core of lake Donggi Cona, which dates back to late glacial period. Distinct organic geochemical proxies and stable isotopes are used to study the paleoenvironmental and hydrological changes in late glacial and Holocene period. Sedimentary n-alkanes of lake Donggi Cona are used as a proxy for paleoclimatic and monsoonal reconstruction. The hydrogen (δD) and carbon (δ13C) isotopes of n-alkanes are used as proxy for hydrological and phytoplankton productivity, respectively . Qualitative and quantitative analysis were performed for n-alkanes over the sediment core. δD proxy for sedimentary n-alkanes is used to infer lake water and rainfall signal. δD of (n-alkane C23) records the signal of the lake water, whereas δD of (n-alkane C29) record the precipitation signal, hence act as an appropriate proxy to track Asian monsoon. Long chain n-alkanes dominate over the sediment core while unsaturated mid chain n-alkenes have high abundance in some samples. From 18.4-13.8 cal ka BP, sample shows low organic productivity due to cold and arid climate. After 13.8-11.8 cal ka BP, slight increase in phytoplankton productivity indicate onset of weaker monsoon. From 11.8-6.8 cal ka BP, high content of organic matter indicates rise in productivity and strong monsoon with high inflow. After 6.8 cal ka BP, decrease in phytoplankton productivity indicating cooler climate and show terrestrial signal. Our results provide new insight into the variability of east Asian monsoon and changes in phytoplankton productivity for last 18.4 ka. Keywords: n-alkanes

  6. 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

  7. 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...

  8. Use of the N-alkanes to Estimate Intake, Apparent Digestibility and Diet Composition in Sheep Grazing on Stipa brevilfora Desert Steppe

    Institute of Scientific and Technical Information of China (English)

    HU Hong-lian; LIU Yong-zhi; LI Ya-kui; LU De-xun; GAO Min

    2014-01-01

    The application of n-alkane as markers to estimate herbage intake, apparent digestibility and species composition of diet consumed by grazing sheep was studied. Six local Mongolian sheep were used to determine dry matter (DM) intake, apparent DM digestibility and species composition of diet during summer, autumn and winter. Animals were orally dosed twice daily with n-alkane gelatin capsules containing 60 mg C32-alkane as an external marker. Diet composition was estimated by comparing the odd-chain n-alkanes pattern profile (C27-C31) of the consumed plant species with the n-alkanes fecal concentrations of grazing animals, using a non-negative least squares algorithm called EATWHAT software package. The alkane pair C32:C33 and C33 alkane were used to estimate DM intake and diet apparent DM digestibility, respectively. The results showed that daily dry matter intake of the sheep were 1.77, 1.61 and 1.18 kg d-1 in summer, autumn and winter, respectively. Apparent DM digestibility, crude protein (CP), metabolizable energy (ME) and neutral detergent ifber (NDF) intake of diet consumed by sheep decreased signiifcantly (P<0.01) from summer to winter, with no evident changes in ADF and ADL intake. Diet composition indicated Artemisia frigida Willd was the most dominant diet component, contributed 79.68, 68.12 and 86.26% of sheep’s diets in summer, autumn and winter, respectively. Cleistogenes songorica Ohwi and Convolvulus ammannii Desr were the important components of the diet. Although Stipa brevilfora Griseb is one of the main plant species in the study area, the sheep rarely choosed it. The study indicated that CP and ME in diet consumed by sheep were deifcient in winter. Therefore, appropriate supplementation strategies should be indispensable during this period.

  9. Alkane production by the marine cyanobacterium Synechococcus sp. NKBG15041c possessing the α-olefin biosynthesis pathway.

    Science.gov (United States)

    Yoshino, Tomoko; Liang, Yue; Arai, Daichi; Maeda, Yoshiaki; Honda, Toru; Muto, Masaki; Kakunaka, Natsumi; Tanaka, Tsuyoshi

    2015-02-01

    The production of alkanes in a marine cyanobacterium possessing the α-olefin biosynthesis pathway was achieved by introducing an exogenous alkane biosynthesis pathway. Cyanobacterial hydrocarbons are synthesized via two separate pathways: the acyl-acyl carrier protein (ACP) reductase/aldehyde-deformylating oxygenase (AAR/ADO) pathway for the alkane biosynthesis and the α-olefin synthase (OLS) pathway for the α-olefin biosynthesis. Coexistence of these pathways has not yet been reported. In this study, the marine cyanobacterium Synechococcus sp. NKBG15041c was shown to produce α-olefins similar to those of Synechococcus sp. PCC7002 via the α-olefin biosynthesis pathway. The production of heptadecane in Synechococcus sp. NKBG15041c was achieved by expressing the AAR/ADO pathway genes from Synechococcus elongatus PCC 7942. The production yields of heptadecane in Synechococcus sp. NKBG15041c varied with the expression level of the aar and ado genes. The maximal yield of heptadecane was 4.2 ± 1.2 μg/g of dried cell weight in the transformant carrying a homologous promoter. Our results also suggested that the effective activation of ADO may be more important for the enhancement of alkane production by cyanobacteria.

  10. Isolation and characterization of alkane degrading bacteria from petroleum reservoir waste water in Iran (Kerman and Tehran provenances).

    Science.gov (United States)

    Hassanshahian, Mehdi; Ahmadinejad, Mohammad; Tebyanian, Hamid; Kariminik, Ashraf

    2013-08-15

    Petroleum products spill and leakage have become two major environmental challenges in Iran. Sampling was performed in the petroleum reservoir waste water of Tehran and Kerman Provinces of Iran. Alkane degrading bacteria were isolated by enrichment in a Bushnel-Hass medium, with hexadecane as sole source of carbon and energy. The isolated strains were identified by amplification of 16S rDNA gene and sequencing. Specific primers were used for identification of alkane hydroxylase gene. Fifteen alkane degrading bacteria were isolated and 8 strains were selected as powerful degradative bacteria. These 8 strains relate to Rhodococcus jostii, Stenotrophomonas maltophilia, Achromobacter piechaudii, Tsukamurella tyrosinosolvens, Pseudomonas fluorescens, Rhodococcus erythropolis, Stenotrophomonas maltophilia, Pseudomonas aeruginosa genera. The optimum concentration of hexadecane that allowed high growth was 2.5%. Gas chromatography results show that all strains can degrade approximately half of hexadecane in one week of incubation. All of the strains have alkane hydroxylase gene which are important for biodegradation. As a result, this study indicates that there is a high diversity of degradative bacteria in petroleum reservoir waste water in Iran.

  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. Evaluation of the organic matter sources using the δ13C composition of individual n-alkanes in sediments from Brazilian estuarine systems by GC/C/IRMS

    Science.gov (United States)

    Maioli, Otávio Luiz Gusso; de Oliveira, Cristiane Rossi; Dal Sasso, Marco Aurélio; Madureira, Luiz Augusto dos Santos; Azevedo, Débora de Almeida; de Aquino Neto, Francisco Radler

    2012-12-01

    The δ13C composition of individual n-alkanes (from C16 to C34) was measured from surface sediments of five Brazilian estuarine systems affected by different organic matter sources, such as harbor area, industries, urban centers and sugar cane crops, in order to determine the origins of the organic matter. The aliphatic hydrocarbon fraction was analyzed by gas chromatography-combustion-isotope ratio mass spectrometry (GC/C/IRMS). The levels of n-alkanes in the studied areas ranged from 0.34 to 18.14 μg kg-1, being relatively low in comparison to high polluted environments. The Carbon Preference Index (CPI) calculated in the C23-C34 range indicates that n-alkanes are mainly inherited from cuticular waxes of higher plants. The δ13C composition of all n-alkanes detected in the sediment samples ranged from -39.6 to -18.3‰ showing different sources for the studied estuarine systems. Through Principal Component Analysis (PCA) it was possible to verify the petrogenic influence in the n-alkane sources, especially in the Paraíba do Sul sediment samples. Differences up to 15‰ of the δ13C values between n-alkanes of odd and even carbon number (C26 and C27) also indicated mixture of petrogenic and biogenic sources in Paraíba do Sul River. High (less negative) δ13C n-alkane values of odd carbon number were obtained from two sampling sites located close to an ethanol plant, indicating residues discharge of sugar cane (C4 plant). Influence of C3 plants that are the main components of dense ombrophile forest was observed in the Itajaí-Açu sediments by the decrease of δ13C (about 10‰ compared to the Paraíba do Sul River δ13C).

  13. Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(0001¯) surfaces

    Science.gov (United States)

    Tochihara, Hiroshi; Shirasawa, Tetsuroh; Suzuki, Takayuki; Miyamachi, Toshio; Kajiwara, Takashi; Yagyu, Kazuma; Yoshizawa, Shunsuke; Takahashi, Toshio; Tanaka, Satoru; Komori, Fumio

    2014-02-01

    An epitaxial silicon-oxide monolayer of chemical composition of Si2O3 (the Si2O3 layer) formed on hexagonal SiC(0001¯) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si2O3 layer are found to be missing SiOn (n = 1, 2, 3) molecules. The band gap of the Si2O3 layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO2, 8.9 eV. It is proposed that the Si2O3 layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

  14. Hexadecadienyl monolayers on hydrogen-terminated Si(111): faster monolayer formation and improved surface coverage using the enyne moiety.

    Science.gov (United States)

    Rijksen, Bart; Pujari, Sidharam P; Scheres, Luc; van Rijn, Cees J M; Baio, J E; Weidner, Tobias; Zuilhof, Han

    2012-04-24

    To further improve the coverage of organic monolayers on hydrogen-terminated silicon (H-Si) surfaces with respect to the hitherto best agents (1-alkynes), it was hypothesized that enynes (H-C≡C-HC═CH-R) would be even better reagents for dense monolayer formation. To investigate whether the increased delocalization of β-carbon radicals by the enyne functionality indeed lowers the activation barrier, the kinetics of monolayer formation by hexadec-3-en-1-yne and 1-hexadecyne on H-Si(111) were followed by studying partially incomplete monolayers. Ellipsometry and static contact angle measurements indeed showed a faster increase of layer thickness and hydrophobicity for the hexadec-3-en-1-yne-derived monolayers. This more rapid monolayer formation was supported by IRRAS and XPS measurements that for the enyne show a faster increase of the CH2 stretching bands and the amount of carbon at the surface (C/Si ratio), respectively. Monolayer formation at room temperature yielded plateau values for hexadec-3-en-1-yne and 1-hexadecyne after 8 and 16 h, respectively. Additional experiments were performed for 16 h at 80° to ensure full completion of the layers, which allows comparison of the quality of both layers. Ellipsometry thicknesses (2.0 nm) and contact angles (111-112°) indicated a high quality of both layers. XPS, in combination with DFT calculations, revealed terminal attachment of hexadec-3-en-1-yne to the H-Si surface, leading to dienyl monolayers. Moreover, analysis of the Si2p region showed no surface oxidation. Quantitative XPS measurements, obtained via rotating Si samples, showed a higher surface coverage for C16 dienyl layers than for C16 alkenyl layers (63% vs 59%). The dense packing of the layers was confirmed by IRRAS and NEXAFS results. Molecular mechanics simulations were undertaken to understand the differences in reactivity and surface coverage. Alkenyl layers show more favorable packing energies for surface coverages up to 50-55%. At higher

  15. Magnetic measurements of monolayer-thickness films of Cr sandwiched by Au

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, M.B.; Sill, L.R.; Sowers, C.H.

    1985-06-01

    Calculations show ferromagnetic moments (3.1..mu../sub B/) in Au-Cr-Au sandwiches, for monolayers of Cr. The measured moment (0.41..mu../sub B/ at 2/sup 0/K) is larger in Cr monolayers than for thicker Cr samples. Results are discussed in terms of other studies of this system including those which showed superconductivity.

  16. Modulation of endothelial monolayer permeability induced by plasma obtained from lipopolysaccharide-stimulated whole blood.

    NARCIS (Netherlands)

    Nooteboom, A.; Bleichrodt, R.P.; Hendriks, T.

    2006-01-01

    The aim of this study was to elucidate the time course of the permeability response of endothelial monolayers after exposure to plasma obtained from lipopolysaccharide (LPS)-treated human whole blood; to investigate the role of apoptosis in monolayer permeability, and to inhibit the permeability inc

  17. Confined thin films of linear and branched alkanes

    NARCIS (Netherlands)

    Dijkstra, Marjolein

    1997-01-01

    We report computer simulations in the Grand canonical ensemble of a system of several alkanes between two solid surfaces. We computed the solvation force exerted by the fluid on the plates. The solvation force for linear decane oscillates with distance with a periodicity close to the width of the mo

  18. 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...

  19. Cyano- and polycyanometallo-porphyrins as catalysts for alkane oxidation

    Science.gov (United States)

    Ellis, Jr., Paul E.; Lyons, James E.

    1993-01-01

    New compositions of matter comprising cyano-substituted metal complexes of porphyrins are catalysts for the oxidation of alkanes. The metal is iron, chromium, manganese, ruthenium, copper or cobalt. The porphyrin ring has cyano groups attached thereto in meso and/or .beta.-pyrrolic positions.

  20. Improving alkane synthesis in Escherichia coli via metabolic engineering.

    Science.gov (United States)

    Song, Xuejiao; Yu, Haiying; Zhu, Kun

    2016-01-01

    Concerns about energy security and global petroleum supply have made the production of renewable biofuels an industrial imperative. The ideal biofuels are n-alkanes in that they are chemically and structurally identical to the fossil fuels and can "drop in" to the transportation infrastructure. In this work, an Escherichia coli strain that produces n-alkanes was constructed by heterologous expression of acyl-acyl carrier protein (ACP) reductase (AAR) and aldehyde deformylating oxygenase (ADO) from Synechococcus elongatus PCC7942. The accumulation of alkanes ranged from 3.1 to 24.0 mg/L using different expressing strategies. Deletion of yqhD, an inherent aldehyde reductase in E. coli, or overexpression of fadR, an activator for fatty acid biosynthesis, exhibited a nearly twofold increase in alkane titers, respectively. Combining yqhD deletion and fadR overexpression resulted in a production titer of 255.6 mg/L in E. coli, and heptadecene was the most abundant product.

  1. Cyano- and polycyanometalloporphyrins as catalysts for alkane oxidation

    Science.gov (United States)

    Ellis, Jr., Paul E.; Lyons, James E.

    1992-01-01

    Alkanes are oxidized by contact with oxygen-containing gas in the presence as catalyst of a metalloporphyrin in which hydrogen atoms in the porphyrin ring have been substituted with one or more cyano groups. Hydrogen atoms in the porphyrin ring may also be substituted with halogen atoms.

  2. Integrated process for preparing a carboxylic acid from an alkane

    Science.gov (United States)

    Benderly, Abraham; Chadda, Nitin; Sevon, Douglass

    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.

  3. Catalytic production of branched small alkanes from biohydrocarbons.

    Science.gov (United States)

    Oya, Shin-ichi; Kanno, Daisuke; Watanabe, Hideo; Tamura, Masazumi; Nakagawa, Yoshinao; Tomishige, Keiichi

    2015-08-10

    Squalane, C30 algae-derived branched hydrocarbon, was successfully converted to smaller hydrocarbons without skeletal isomerization and aromatization over ruthenium on ceria (Ru/CeO2 ). The internal CH2 CH2 bonds located between branches are preferably dissociated to give branched alkanes with very simple distribution as compared with conventional methods using metal-acid bifunctional catalysts.

  4. 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.

  5. Progressive degradation of crude oil n-alkanes coupled to methane production under mesophilic and thermophilic conditions.

    Science.gov (United States)

    Cheng, Lei; Shi, Shengbao; Li, Qiang; Chen, Jianfa; Zhang, Hui; Lu, Yahai

    2014-01-01

    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.

  6. Compositional characteristics of n-alkanes of the glaciers over the Tibetan Plateau and their environmental and climatic significances

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    We report on the concentration and compositional features of n-alkanes of natural and anthropogenic origins in the snow samples collected from the Qiyi glacier in the Qilian Mountains, the Yuzhufeng glacier in eastern Kunlun Mountains, the Xiaodongkemadi glacier in the Tanggula Mountains, and the Gurenhekou glacier in the Nyainqêntanglha Range. The results indicate a decrease in the total n-alkane concentration (T-HCs) from the northeast to the south over the Tibetan Plateau. The T-HCs in these studied areas were close to those in the Belukha and Sofiyskiy glacier, Russian Alati Mountains and the Dasuopu glacier in the Himalaya but were much higher than those in the Greenland ice sheet, suggesting that the mountain glaciers in the Asian continent may receive a higher loading of n-alkanes than the Greenland ice core. Moreover, the compositional characteristics of n-alkanes indicated that the n-alkanes in the studied areas were probably originated from the plant waxes as well as the fossil-fuel combustion exhaust, whereas the contribution from the lower organisms was small. In addition, the plant wax (Cn(wax)) and anthropogenic (non-Cn(wax)) contributions revealed that fast industrialization may have significant effects on the organic pollutant composition in glacier over the Tibetan Plateau and its circumference environment. Particularly, except for the Yuzhufeng glacier, the ΣnC21-/ΣnC22+ and (nC15+nC17+nC19)/(nC27+nC29+nC31) ratio decreased from the Qiyi glacier to the Gurenhekou glacier over the Tibetan Plateau, while the carbon preference index (CPI) values increased. These results indicate a decrease in terrigenous input while an increase in marine input from the northeast to the south over the Tibetan Plateau. These two ratios can be used as the climatic and environmental change indicators.

  7. Distributions and sources of n-alkanes in PM2.5 at urban,industrial and coastal sites in Tianjin,China

    Institute of Scientific and Technical Information of China (English)

    Weifang Li; Yue Peng; Zhipeng Bai

    2010-01-01

    Aliphatic hydrocarbons (n-alkanes) associated with fine particulate matter were determined in the ambient air of urban,industrial and coastal areas in Tianjin,China,where intensive coal burning for industrial and domestic purpose takes place,n-Alkane homologues from C12 to C35 were quantifiable in all samples with C20-C31 being the most abundant species.Average concentrations of the total n-alkanes were 148.7,250.1 and 842.0 ng/m3 in July,April and January,respectively.Seasonal variations were mainly attributed to ambient temperature changes and coal combustion for residential heating.Among the three studied areas,the highest levels of n-alkanes were observed in the industrial complex in winter and spring,but in summer the coastal alkane concentration moved up to the highest.A mono-modai distribution for n-alkanes was observed in spring and summer with odd carbon number predominance and a maximum centered at C27-C31,suggesting the release of plant wax into the atmosphere.The bimodal distribution with maxima at C22 and C26 observed in winter indicated a substantial influence of fossil fuel sources.All the CPIs (CPI1,CPI2,CPI3) values,varying between 0.64 and 1.97,indicated the influence of anthropogenic emissions on fine organic aerosols.The estimated contributions of plant wax to total n-alkanes were on average of 12.9%,19.1% and 26.1% for winter,spring and summer,respectively.

  8. Oxidation of methyl tert-butyl ether by alkane hydroxylase in dicyclopropylketone-induced and n-octane-grown Pseudomonas putida GPo1.

    Science.gov (United States)

    Smith, Christy A; Hyman, Michael R

    2004-08-01

    The alkane hydroxylase enzyme system in Pseudomonas putida GPo1 has previously been reported to be unreactive toward the gasoline oxygenate methyl tert-butyl ether (MTBE). We have reexamined this finding by using cells of strain GPo1 grown in rich medium containing dicyclopropylketone (DCPK), a potent gratuitous inducer of alkane hydroxylase activity. Cells grown with DCPK oxidized MTBE and generated stoichiometric quantities of tert-butyl alcohol (TBA). Cells grown in the presence of DCPK also oxidized tert-amyl methyl ether but did not appear to oxidize either TBA, ethyl tert-butyl ether, or tert-amyl alcohol. Evidence linking MTBE oxidation to alkane hydroxylase activity was obtained through several approaches. First, no TBA production from MTBE was observed with cells of strain GPo1 grown on rich medium without DCPK. Second, no TBA production from MTBE was observed in DCPK-treated cells of P. putida GPo12, a strain that lacks the alkane-hydroxylase-encoding OCT plasmid. Third, all n-alkanes that support the growth of strain GPo1 inhibited MTBE oxidation by DCPK-treated cells. Fourth, two non-growth-supporting n-alkanes (propane and n-butane) inhibited MTBE oxidation in a saturable, concentration-dependent process. Fifth, 1,7-octadiyne, a putative mechanism-based inactivator of alkane hydroxylase, fully inhibited TBA production from MTBE. Sixth, MTBE-oxidizing activity was also observed in n-octane-grown cells. Kinetic studies with strain GPo1 grown on n-octane or rich medium with DCPK suggest that MTBE-oxidizing activity may have previously gone undetected in n-octane-grown cells because of the unusually high K(s) value (20 to 40 mM) for MTBE.

  9. Role of ozone in SOA formation from alkane photooxidation

    Directory of Open Access Journals (Sweden)

    X. Zhang

    2013-09-01

    Full Text Available Long-chain alkanes, which can be categorized as intermediate volatile organic compounds (IVOCs, are an important source of secondary organic aerosol (SOA. Mechanisms for the gas-phase OH-initiated oxidation of long-chain alkanes have been well documented; particle-phase chemistry, however, has received less attention. The δ-hydroxycarbonyl, which is generated from the isomerization of alkoxy radicals, can undergo heterogeneous cyclization to form substituted dihydrofuran. Due to the presence of C=C bonds, the substituted dihydrofuran is predicted to be highly reactive with OH, and even more so with O3 and NO3, thus opening a reaction pathway that is not usually accessible to alkanes. This work focuses on the role of substituted dihydrofuran formation and its subsequent reaction with OH, and more importantly ozone, in SOA formation from the photooxidation of long-chain alkanes. Experiments were carried out in the Caltech Environmental Chamber using dodecane as a representative alkane to investigate the difference in aerosol composition generated from "OH-oxidation dominating" vs. "ozonolysis dominating" environments. A detailed mechanism incorporating the specific gas-phase photochemistry, together with the heterogeneous formation of substituted dihydrofuran and its subsequent gas-phase OH/O3 oxidation, is presented to evaluate the importance of this reaction channel in the dodecane SOA formation. We conclude that: (1 the formation of δ-hydroxycarbonyl and its subsequent heterogeneous conversion to substituted dihydrofuran is significant in the presence of NOx; (2 the ozonolysis of substituted dihydrofuran dominates over the OH-initiated oxidation under conditions prevalent in urban and rural air; and (3 a spectrum of highly-oxygenated products with carboxylic acid, ester, and ether functional groups are produced from the substituted dihydrofuran chemistry, thereby affecting the average oxidation state of the SOA.

  10. 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.

  11. Sequence-specific DNA interactions with calixarene-based langmuir monolayers.

    Science.gov (United States)

    Rullaud, Vanessa; Moridi, Negar; Shahgaldian, Patrick

    2014-07-29

    The interactions of an amphiphilic calixarene, namely p-guanidino-dodecyloxy-calix[4]arene, 1, self-assembled as Langmuir monolayers, with short double stranded DNA, were investigated by surface pressure-area (π-A) isotherms, surface ellipsometry and Brewster angle microscopy (BAM). Three DNA 30mers were used as models, poly(AT), poly(GC) and a random DNA sequence with 50% of G:C base pairs. The interactions of these model DNA duplexes with 1-based Langmuir monolayers were studied by measuring compression isotherms using increasing DNA concentrations (10(-6), 10(-5), 10(-4), and 5 × 10(-4) g L(-1)) in the aqueous subphase. The isotherms of 1 showed an expansion of the monolayer with, interestingly, significant differences depending on the duplex DNA sequence studied. Indeed, the interactions of 1-based monolayers with poly(AT) led to an expansion of the monolayer that was significantly more pronounced that for monolayers on subphases of poly(GC) and the random DNA sequence. The structure and thickness of 1-based Langmuir monolayers were investigated by BAM and surface ellipsometry that showed differences in thickness and structure between a monolayer formed on pure water or on a DNA subphase, with here again relevant dissimilarities depending on the DNA composition.

  12. 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.

  13. Polycyclic aromatic hydrocarbons (PAHs) and n-alkanes in beaked sea snake Enhydrina schistose (Daudin, 1803) from the Mandovi estuary, Goa.

    Science.gov (United States)

    Mote, Sambhaji; Kumar, Ranjeet; Naik, B G; Ingole, Baban S

    2015-02-01

    An ecotoxicological study were conducted to evaluate the concentrations of PAHs and n-alkanes, in gut, liver and kidney tissues of two individuals of Enhydrina schistose (Daudin, 1803), using gas chromatography/mass spectrometry. The concentrations of PAHs (0.10 µg/g) and n-alkanes (8.12 µg/g) were elevated in the gut, and liver (PAHs 0.05 µg/g tissue, n-alkanes 29.16 µg/g tissue). In kidney of both specimen-A and B the PAHs (0.01 and 0.1 µg/g) and n-alkanes (0.22 and 2.06 µg/g) concentration was detected. This was an initial survey (n = 2) and the main goal was to know accumulation and distribution of PAHs and n-alkanes in the sea snakes. This study indicates high accumulation of petroleum hydrocarbon in gut, liver and kidney of sea snake. Since, this species also act as pray for sea eagles and some predatory fishes such as tiger shark, there is high possibilities of PAHs being circulated in marine food chain.

  14. 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)

  15. 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.

  16. Tuning Oleophobicity of Silicon Oxide Surfaces with Mixed Monolayers of Aliphatic and Fluorinated Alcohols.

    Science.gov (United States)

    Lee, Austin W H; Gates, Byron D

    2016-12-13

    We demonstrate the formation of mixed monolayers derived from a microwave-assisted reaction of alcohols with silicon oxide surfaces in order to tune their surface oleophobicity. This simple, rapid method provides an opportunity to precisely tune the constituents of the monolayers. As a demonstration, we sought fluorinated alcohols and aliphatic alcohols as reagents to form monolayers from two distinct constituents for tuning the surface oleophobicity. The first aspect of this study sought to identify a fluorinated alcohol that formed monolayers with a relatively high surface coverage. It was determined that 1H,1H,2H,2H-perfluoro-1-octanol yielded high quality monolayers with a water contact angle (WCA) value of ∼110° and contact angle values of ∼80° with toluene and hexadecane exhibiting both an excellent hydrophobicity and oleophobicity. Tuning of the oleophobicity of the modified silicon oxide surfaces was achieved by controlling the molar ratio of 1H,1H,2H,2H-perfluoro-1-octanol within the reaction mixtures. Surface oleophobicity progressively decreased with a decrease in the fluorinated alcohol content while the monolayers maintained their hydrophobicity with WCA values of ∼110°. The simple and reliable approach to preparing monolayers of a tuned composition that is described in this article can be utilized to control the fluorocarbon content of the hydrophobic monolayers on silicon oxide surfaces.

  17. Fluorescent self-assembled monolayers as new sensing materials

    NARCIS (Netherlands)

    Basabe Desmonts, Lourdes

    2006-01-01

    Fluorescent self-assembled monolayers (SAMs) on glass surfaces have been studied as a new material for chemical sensing. The new sensing system presented in this thesis is a label-free sensing approach suitable for metal ion and inorganic anions sensing in both organic solvents and aqueous solution.

  18. STM visualisation of counterions and the effect of charges on self-assembled monolayers of macrocycles.

    Science.gov (United States)

    Kudernac, Tibor; Shabelina, Natalia; Mamdouh, Wael; Höger, Sigurd; De Feyter, Steven

    2011-01-01

    Despite their importance in self-assembly processes, the influence of charged counterions on the geometry of self-assembled organic monolayers and their direct localisation within the monolayers has been given little attention. Recently, various examples of self-assembled monolayers composed of charged molecules on surfaces have been reported, but no effort has been made to prove the presence of counterions within the monolayer. Here we show that visualisation and exact localisation of counterions within self-assembled monolayers can be achieved with scanning tunnelling microscopy (STM). The presence of charges on the studied shape-persistent macrocycles is shown to have a profound effect on the self-assembly process at the liquid-solid interface. Furthermore, preferential adsorption was observed for the uncharged analogue of the macrocycle on a surface.

  19. Nd-doped ZnO monolayer: High Curie temperature and large magnetic moment

    Science.gov (United States)

    Tan, Changlong; Sun, Dan; Zhou, Long; Tian, Xiaohua; Huang, Yuewu

    2016-10-01

    We performed first-principles calculations within density-functional theory to study the structural, electronic, and magnetic properties of Nd-doped ZnO monolayer. The calculated results reveal that Nd-doped ZnO monolayer exhibits stable room temperature ferromagnetism with a large saturation magnetic moment of 3.99 μB per unit in ZnO monolayer. The magnetic property is contributed to the localized f sates of Nd atoms. When two Zn atoms are substituted by two Nd dopants, they tend to form ferromagnetic (FM) coupling and the estimated Curie temperature is higher than room temperature. More interesting, the impurity bands appear within the band gap of ZnO monolayer due to the introduction of Nd dopant. Our results may provide a reference for modifying the material property of ZnO monolayer and are promising as nanoscale building block in spintronic devices.

  20. 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.

  1. Different response of bulk and n-alkane δ13C signatures to seasonal shifts in environmental conditions in a temperate coastal ecosystem

    Science.gov (United States)

    Eley, Yvette; Pedentchouk, Nikolai; Dawson, Lorna

    2014-05-01

    The carbon isotope signal recorded in land plants represents an important reservoir of information for reconstructing climatically driven shifts in plant ecophysiology and biochemistry. Analytical advances have led to widespread usage of compound-specific (CS) carbon isotope analysis of leaf wax biomarkers, such as n-alkanes, in addition to traditional bulk isotope methods, to identify shifts in the relative percentage of C3 and C4 vegetation contributing to the sedimentary record. Recent studies, however, have extended the application of leaf wax biomarkers, using bulk and n-alkane δ13C values interchangeably to derive information about plant-environment relations, both in modern ecosystems and throughout the geological past. Even though previous work on C3 plants has shown a clear link between climatically influenced plant physiology and bulk δ13C values, further research is needed to establish whether the same link can be seen in leaf wax biomarkers. To address this question, we collected bulk and n-alkane δ13C data from plants growing at Stiffkey marsh on the north Norfolk coast, UK over a period of 15 months. Maximum interspecies variation in weighted average (WA) n-alkane δ13C among C3 species was typically 2-3o greater than in bulk. We observed a close correlation in the bulk and WA n-alkane δ13C seasonal trends from C3 grasses and reeds (R2=0.9, P

  2. Phylogenetic and functional diversity of alkane degrading bacteria associated with Italian ryegrass (Lolium multiflorum) and Birdsfoot trefoil (Lotus corniculatus) in a petroleum oil-contaminated environment.

    Science.gov (United States)

    Yousaf, Sohail; Andria, Verania; Reichenauer, Thomas G; Smalla, Kornelia; Sessitsch, Angela

    2010-12-15

    Twenty-six different plant species were analyzed regarding their performance in soil contaminated with petroleum oil. Two well-performing species, Italian ryegrass (Lolium multiflorum var. Taurus), Birdsfoot trefoil (Lotus corniculatus var. Leo) and the combination of these two plants were selected to study the ecology of plant-associated, culturable alkane-degrading bacteria. Hydrocarbon degrading bacteria were isolated from the rhizosphere, root interior and shoot interior and subjected to the analysis of 16S rRNA gene, the 16S and 23S rRNA intergenic spacer region and alkane hydroxylase genes. Furthermore, we investigated whether alkane hydroxylase genes are plasmid located. Higher numbers of culturable, alkane-degrading bacteria were associated with Italian ryegrass, which were also characterized by a higher diversity, particularly in the plant interior. Only half of the isolated bacteria hosted known alkane hydroxylase genes (alkB and cytochrome P153-like). Degradation genes were found both on plasmids as well as in the chromosome. In regard to application of plants for rhizodegradation, where support of numerous degrading bacteria is essential for efficient break-down of pollutants, Italian ryegrass seems to be more appropriate than Birdsfoot trefoil.

  3. 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.

  4. Structural Order in Ultrathin Films of the Monolayer Protected Clusters Based Upon 4-nm Gold Nanocrystals: An Experimental and Theoretical Study

    Science.gov (United States)

    Bhattarai, Nabraj; Khanal, Subarna; Bahena, Daniel; Olmos-Asar, Jimena A.; Ponce, Arturo; Whetten, Robert L.; Mariscal, Marcelo M.; Jose-Yacaman, Miguel

    2014-01-01

    The structural order in ultrathin films of monolayer protected clusters (MPCs) is important in a number of application areas but can be difficult to demonstrate by conventional methods, particularly when the metallic core dimension, d, is in the intermediate size-range, 1.5 < d < 5.0 nm. Here, improved techniques for the synthesis of monodisperse thiolate-protected gold nanoparticles have made possible the production of dodecane-thiolate saturated ~ 4 ± 0.5 nm Au clusters with single-crystal core structure and morphology. An ultrathin ordered film or superlattice of these nanocrystal-core MPCs is prepared and investigated using aberration corrected scanning/transmission electron microscopy (STEM) which allowed imaging of long-range hexagonally ordered superlattices of the nanocrystals, separated by the thiolate groups. The lattice constants determined by direct imaging are in good agreement with those determined by small-angle electron diffraction. The STEM image revealed the characteristic grain boundary (GB) with sigma (Σ) 13 in the interface between two crystals. The formation and structures found are interpreted on the basis of theoretical calculations employing molecular dynamics (MD) simulations and coarse-grained (CG) approach. PMID:24875295

  5. 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.

  6. 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.

  7. Comparative electrochemical scanning tunneling microscopy study of nonionic fluorosurfactant zonyl FSN self-assembled monolayers on Au(111) and Au(100): a potential-induced structural transition.

    Science.gov (United States)

    Tang, Yongan; Yan, Jiawei; Zhu, Feng; Sun, Chunfeng; Mao, Bingwei

    2011-02-01

    We investigate the structure of nonionic fluorosurfactant zonyl FSN self-assembled monolayers on Au(111) and Au(100) in 0.05 M H(2)SO(4) as a function of the electrode potential by electrochemical scanning tunneling microscopy (ECSTM). On Au(111), a (3(1/2) × 3(1/2))R30° arrangement of the FSN SAMs is observed, which remains unchanged in the potential range where the redox reaction of FSN molecules does not occur. On Au(100), some parallel corrugations of the FSN SAMs are observed, which originate from the smaller distance and the repulsive interaction between FSN molecules to make the FSN molecules deviate from the bridging sites, and ECSTM reveals a potential-induced structural transition of the FSN SAMs. The experimental observations are rationalized by the effect of the intermolecular interaction. The smaller distance between molecules on Au(100) results in the repulsive force, which increases the probability of structural change induced by external factors (i.e., the electrode potential). The appropriate distance and interactions of FSN molecules account for the stable structure of FSN SAMs on Au(111). Surface crystallography may influence the intermolecular interaction through changing the molecular arrangements of the SAMs. The results benefit the molecular-scale understanding of the behavior of the FSN SAMs under electrochemical potential control.

  8. Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(0001{sup ¯}) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Tochihara, Hiroshi, E-mail: tochihara@fukuoka-u.ac.jp, E-mail: tochihara.hiroshi.146@m.kyushu-u.ac.jp; Suzuki, Takayuki; Yagyu, Kazuma [Department of Electronics Engineering and Computer Science, Fukuoka University, Fukuoka 814-0180 (Japan); Shirasawa, Tetsuroh; Takahashi, Toshio [Laser and Synchrotron Research Center, Institute for Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan); Miyamachi, Toshio; Yoshizawa, Shunsuke; Komori, Fumio [Nanoscale Science Division, Institute for Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan); Kajiwara, Takashi; Tanaka, Satoru [Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka 819-0395 (Japan)

    2014-02-03

    An epitaxial silicon-oxide monolayer of chemical composition of Si{sub 2}O{sub 3} (the Si{sub 2}O{sub 3} layer) formed on hexagonal SiC(0001{sup ¯}) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si{sub 2}O{sub 3} layer are found to be missing SiO{sub n} (n = 1, 2, 3) molecules. The band gap of the Si{sub 2}O{sub 3} layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO{sub 2}, 8.9 eV. It is proposed that the Si{sub 2}O{sub 3} layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

  9. Cation-induced monolayer collapse at lower surface pressure follows specific headgroup percolation

    Science.gov (United States)

    Das, Kaushik; Sah, Bijay Kumar; Kundu, Sarathi

    2017-02-01

    A Langmuir monolayer can be considered as a two-dimensional (2D) sheet at higher surface pressure which structurally deform with mechanical compression depending upon the elastic nature of the monolayer. The deformed structures formed after a certain elastic limit are called collapsed structures. To explore monolayer collapses at lower surface pressure and to see the effect of ions on such monolayer collapses, out-of-plane structures and in-plane morphologies of stearic acid Langmuir monolayers have been studied both at lower (≈6.8) and higher (≈9.5) subphase p H in the presence of M g2 +,C a2 +,Z n2 +,C d2 + , and B a2 + ions. At lower subphase p H and in the presence of all cations, the stearic acid monolayer remains as a monolayer before collapse, which generally takes place at higher surface pressure (πc>50 mN /m ). However, at higher subphase p H , structural changes of stearic acid monolayers occur at relatively lower surface pressure depending upon the specific dissolved ions. Among the same group elements of M g2 +,C a2 + , and B a2 + , only for B a2 + ions does monolayer to multilayer transition take place from a much lower surface pressure of the monolayer, remaining, however, as a monolayer for M g2 + and C a2 + ions. For another same group elements of Z n2 + and C d2 + ions, a less covered bilayer structure forms on top of the monolayer structure at lower surface pressure, which is evidenced from both x-ray reflectometry and atomic force microscopy. Fourier transform infrared spectroscopy confirms the presence of two coexisting conformations formed by the two different metal-headgroup coordinations and the monolayer to trilayer or multilayer transformation takes place when the coverage ratio of the two molecular conformations changes from the critical value (pc) of ≈0.66 . Such ion-specific monolayer collapses are correlated with the 2D lattice percolation model.

  10. 湛江湾柱状沉积物 n-alkanes 和 PAHs 组合分子特征及其环境指示作用%The molecular characteristic of n-alkanes and PAHs in core sediments of Zhanjiang Bay and its environmental indication significance

    Institute of Scientific and Technical Information of China (English)

    陈志强; 赵利容; 刘贝贝; 孙省利

    2016-01-01

    本文对湛江湾湾内、湾口和湾外柱状沉积物 n-alkanes 和 PAHs 的空间分布、成分谱特征和排放源进行调查分析。结果表明:(1)n-alkanes 和 PAHs 的空间分布一致,浓度水平由高到低依次为:湾内、湾口、湾外,垂直变化不明显;(2)n-alkanes 和 PAHs 的成分谱和 L/H、CPI、Ant/(Ant+Phe)、Flu/(Flu+Pyr)、BaA/(BaA+Chry)、IP/(IP+BghiP)等特征参数比值以及主成分分析结果表明 C25~C35高碳数 n-alkanes 的高等植物贡献具有绝对优势,C14~C24中低碳数的 n-alkanes 和 PAHs 则有共同的石油、化石燃料燃烧和生物质燃烧等人为源;(3)C14~C24中低碳 n-alkanes 与 PAHs 的源解析结果相同,其线性相关系数在0.67以上,表明两者具有较好的相关性,但两者之间的定量关系还需进一步的研究。本研究表明 n-alkanes 和 PAHs 对人为源的指示具有一致性,两者具有良好的相关性,能够较好地反映城市的社会经济状况,在进一步的研究中可以建立两者之间的定量关系并形成新的参数,提高人为源解析结果的准确性,深入反映人类活动对海洋环境的影响。%Spatial distribution and components of n-alkanes and PAHs in the core sediments were investigated in Zhanjiang bay,and their different and common sources were discussed by methods of principal component analysis, correlation analysis and ratios of L/H,CPI,Ant/(Ant+Phe),Flu/(Flu+Pyr),BaA/(BaA+Chry)and IP/(IP+BghiP).This study aimed to found the different and common characteristics of n-alkane and PAHs from human ac-tivities,and future discussed their sources and effects of human activity on marine environment.Both of n-alkanes and PAHs had the same spatial distributions.Their levels were higher in bay and lower in out of bay but non-sig-nificant changes in vertical sediment samples.The CPI,results of principal component analysis,components spec-trum of n-alkane

  11. 单双层结构的石墨烯纳米带边界态的第一原理研究%First-principles studies on edge states of zigzag graphene nanoribbons with monolayer and bilayer structures

    Institute of Scientific and Technical Information of China (English)

    陆肖励; 张燕娜; 姚志东

    2011-01-01

    This paper studies the stable structure and electronic structure of monolayer and bilayer zigzag graphene nanoribbons based on the first-principle calculation of density functional theory. The result shows that the bilayer with a-alignment edge attracts e%利用基于密度泛函理论的第一性计算,对单双层结构的石墨烯纳米带的稳态结构和电子结构进行了研究。研究表明:α型的边界层的吸引使体系发生边界弯曲并存在非零能量边界态,届型的边界体系保持结构平整。它们都在单双层边界存在零能量的边界态。

  12. Hydrogen Isotope Analysis of Individual n-Alkanes in Crude Oils%原油正构烷单体的氢同位素分析

    Institute of Scientific and Technical Information of China (English)

    李钜源; 李祥臣; 曹智; 王宝山

    2005-01-01

    A hydrogen isotope analytical method on individual n-alkanes in crude oil was established, including the sample pretreatments and the instrumental tests. The error of δD was less than 5‰. The factors which influenced determination, such as the effective separation between individual hydrocarbons, the organic H in target components completely convert into H2 and the accurate measurement by mass spectrometry, were discussed. The hydrogen isotope compositions and the geochemical significance about the individual n-alkanes of two type crude oils in Dongying City depression were also studied. The results show that the hydrogen isotope of individual n-alkanes is a good index sign for studying the paleoenvironment and the oil source.

  13. 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

    , Keitaro Yoshimoto, Shuji Kojima and Keichiro Yamashita, Ichiro Yamanaka, Hidenori Otsuka, Kazunori Kataoka, Yukio Nagasaki, Biointerphases. 2007, 2, 4, 126. 2. L. Selan, F. Berluti, C. Passariello, M. R. Comodiballanti, M. C. Thaller, Antimicrobial agents and chemotherapy, 1993, 37, 12, 2618. 3. Susan J...

  14. Identification and use of an alkane transporter plug-in for application in biocatalysis and whole-cell biosensing of alkanes

    DEFF Research Database (Denmark)

    Grant, Chris; Deszcz, Dawid; Wei, Yu-Chia

    2014-01-01

    plug-in, specific yields improved by up to 100-fold for bioxidation of>C12 alkanes to fatty alcohols and acids. The alkL protein was shown to be toxic to the host when overexpressed but when expressed from a vector capable of controlled induction, yields of alkane oxidation were improved a further 10...

  15. Biomimetic Oxidation Studies. 11. Alkane Functionalization in Aqueous Solution Utilizing in Situ Formed [Fe(2)O(eta(1)-H(2)O)(eta(1)-OAc)(TPA)(2)](3+), as an MMO Model Precatalyst, Embedded in Surface-Derivatized Silica and Contained in Micelles.

    Science.gov (United States)

    Neimann, Karine; Neumann, Ronny; Rabion, Alain; Buchanan, Robert M.; Fish, Richard H.

    1999-07-26

    The biomimetic, methane monooxygenase enzyme (MMO) precatalyst, [Fe(2)O(eta(1)-H(2)O)(eta(1)-OAc)(TPA)(2)](3+) (TPA = tris[(2-pyridyl)methyl]amine), 1, formed in situ at pH 4.2 from [Fe(2)O(&mgr;-OAc)(TPA)(2)](3+), 2, was embedded in an amorphous silicate surface modified by a combination of hydrophilic poly(ethylene oxide) and hydrophobic poly(propylene oxide). The resulting catalytic assembly was found to be a biomimetic model for the MMO active site within a hydrophobic macroenvironment, allowing alkane functionalization with tert-butyl hydroperoxide (TBHP)/O(2) in an aqueous reaction medium (pH 4.2). For example, cyclohexane was oxidized to a mixture of cyclohexanone, cyclohexanol, and cyclohexyl-tert-butyl peroxide, in a ratio of approximately 3:1:2. The balance between poly(ethylene oxide) and poly(propylene oxide), tethered on the silica surface, was crucial for maximizing the catalytic activity. The silica-based catalytic assembly showed reactivity somewhat higher in comparison to an aqueous micelle system utilizing the surfactant, cetyltrimethylammonium hydrogen sulfate at its critical micelle concentration, in which functionalization of cyclohexane with TBHP/O(2) in the presence of 1 was also studied at pH 4.2 and was found to provide similar products: cyclohexanol, cyclohexanone, and cyclohexyl-tert-butyl peroxide, in a ratio of approximately 2:3:1. Moreover, the mechanism for both the silica-based catalytic assembly and the aqueous micelle system was found to occur via the Haber-Weiss process, in which redox chemistry between 1 and TBHP provides both the t-BuO(*)() and t-BuOO(*)()( )()radicals. The t-BuO(*)()( )()radical initiates the C-H functionalization reaction to form the carbon radical, followed by O(2) trapping, to provide cyclohexyl hydroperoxide, which produces the cyclohexanol and cyclohexanone in the presence of 1, whereas the coupling product emanates from t-BuOO(*)() and cyclohexyl radicals. A discussion concerning both approaches for

  16. Influence of compost amendments on the diversity of alkane degrading bacteria in hydrocarbon contaminated soils

    Directory of Open Access Journals (Sweden)

    Michael eSchloter

    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

  17. 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

  18. Metal-organic framework for the separation of alkane isomers

    Energy Technology Data Exchange (ETDEWEB)

    Long, Jeffrey R.; Herm, Zoey R.; Wiers, Brian M.; Krishna, Rajamani

    2017-01-10

    A metal organic framework Fe.sub.2(bdp).sub.3 (BDP.sup.2-=1,4-benzenedipyrazolate) with triangular channels is particularly suited for C5-C7 separations of alkanes according to the number of branches in the molecule rather than by carbon number. The metal-organic framework can offer pore geometries that is unavailable in zeolites or other porous media, facilitating distinct types of shape-based molecular separations.

  19. Alkane production from biomass: chemo-, bio- and integrated catalytic approaches.

    Science.gov (United States)

    Deneyer, Aron; Renders, Tom; Van Aelst, Joost; Van den Bosch, Sander; Gabriëls, Dries; Sels, Bert F

    2015-12-01

    Linear, branched and cyclic alkanes are important intermediates and end products of the chemical industry and are nowadays mainly obtained from fossil resources. In search for alternatives, biomass feedstocks are often presented as a renewable carbon source for the production of fuels, chemicals and materials. However, providing a complete market for all these applications seems unrealistic due to both financial and logistic issues. Despite the very large scale of current alkane-based fuel applications, biomass definitely has the potential to offer a partial solution to the fuel business. For the smaller market of chemicals and materials, a transition to biomass as main carbon source is more realistic and even probably unavoidable in the long term. The appropriate use and further development of integrated chemo- and biotechnological (catalytic) process strategies will be crucial to successfully accomplish this petro-to-bio feedstock transition. Furthermore, a selection of the most promising technologies from the available chemo- and biocatalytic tool box is presented. New opportunities will certainly arise when multidisciplinary approaches are further explored in the future. In an attempt to select the most appropriate biomass sources for each specific alkane-based application, a diagram inspired by van Krevelen is applied, taking into account both the C-number and the relative functionality of the product molecules.

  20. Quantitative comparison of cancer and normal cell adhesion using organosilane monolayer templates: an experimental study on the anti-adhesion effect of green-tea catechins.

    Science.gov (United States)

    Sakamoto, Rumi; Kakinuma, Eisuke; Masuda, Kentaro; Takeuchi, Yuko; Ito, Kosaku; Iketaki, Kentaro; Matsuzaki, Takahisa; Nakabayashi, Seiichiro; Yoshikawa, Hiroshi Y; Yamamoto, Hideaki; Sato, Yuko; Tanii, Takashi

    2016-09-01

    The main constituent of green tea, (-)-Epigallocatechin-3-O-gallate (EGCG), is known to have cancer-specific chemopreventive effects. In the present work, we investigated how EGCG suppresses cell adhesion by comparing the adhesion of human pancreatic cancer cells (AsPC-1 and BxPC-3) and their counterpart, normal human embryonic pancreas-derived cells (1C3D3), in catechin-containing media using organosilane monolayer templates (OMTs). The purpose of this work is (1) to evaluate the quantitativeness in the measurement of cell adhesion with the OMT and (2) to show how green-tea catechins suppress cell adhesion in a cancer-specific manner. For the first purpose, the adhesion of cancer and normal cells was compared using the OMT. The cell adhesion in different type of catechins such as EGCG, (-)-Epicatechin-3-O-gallate (ECG) and (-)-Epicatechin (EC) was also evaluated. The measurements revealed that the anti-adhesion effect of green-tea catechins is cancer-specific, and the order is EGCG≫ECG>EC. The results agree well with the data reported to date, showing the quantitativeness of the new method. For the second purpose, the contact area of cells on the OMT was measured by reflection interference contrast microscopy. The cell-OMT contact area of cancer cells decreases with increasing EGCG concentration, whereas that of normal cells remains constant. The results reveal a twofold action of EGCG on cancer cell adhesion-suppressing cell attachment to a candidate adhesion site and decreasing the contact area of the cells-and validates the use of OMT as a tool for screening cancer cell adhesion.

  1. 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...

  2. 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.

  3. Phase equilibria in model surfactants forming Langmuir monolayers.

    Science.gov (United States)

    Ramírez, E; Santana, A; Cruz, A; López, G E

    2007-12-14

    The study of Langmuir monolayers has generated the attention of researchers because of their unique properties and their not well understood phase equilibrium. These monolayers exhibit interesting phase diagrams where the unusual liquid-liquid equilibrium can be observed for a single component monolayer. Monte Carlo computer simulations in the virtual Gibbs ensemble were used to obtain the phase diagram of Langmuir monolayers. The liquid-vapor and liquid-liquid phase equilibria were considered by constructing the Cailletet-Mathias phase diagrams. By using the Ising model and the rectilinear approximations the identification of the critical properties for both equilibria was determined. These critical parameters were calculated as a function of the strength of the interaction between the surfactant molecules and the aqueous subphase. As a result, we have identified the coexistence between a liquid expanded state (LES)-vapor and the liquid condensed state-LES, in agreement with experimental and theoretical evidence in the literature. We obtained a clear separation of phases and a strong dependence on the strength of the solvent used. Namely, as the interaction between the solvent and the head of the surfactant increases, the critical properties also increase. Equilibrium states were characterized by computing thermodynamic quantities as a function of temperature and solvent strength.

  4. Multi-origin alkanes related to CO2-rich, mantle-derived fluid in Dongying Sag, Bohai Bay Basin

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    With the newly obtained carbon isotope data for the natural gas, a pilot study of multiple-sourced alkanes related to the mantled-derived fluid is presented. The carbon isotope values of alkanes in the Dongying Sag possess thefea tures indicating a general organic origin. However, there are two sub-populations in the isotopic data set, which reflect two specific types of origins. In gene ral, the sub-population with high δ13CCH4 values is related to the CO2-rich, mantle-derived fluid, and it is distributed in the belts where mantle-derived fluid flow and basic volcanic activities have occurred. Geological and geochemical studies demonstrate that this variation of methane carbon isotope values in the Dongying Sag is unrelated with the basin bury and thermal histories, types of source rocks, and reactions between basin fluid and rocks. Mixing of mantle-derived fluid and organic sourced hydrocarbons is probably the cause for the variation .

  5. Free exciton emission and vibrations in pentacene monolayers

    Science.gov (United States)

    He, Rui

    2011-03-01

    Pentacene is a benchmark organic semiconductor material because of its potential applications in electronic and optoelectronic devices. Recently we demonstrated that optical and vibrational characterizations of pentacene films can be carried out down to the sub-monolayer limit. These milestones were achieved in highly uniform pentacene films that were grown on a compliant polymeric substrate. Films with thickness ranging from sub- monolayer to tens of monolayers were studied at low temperatures. The intensity of the free exciton (FE) luminescence band increases quadratically with the number of layers N when N is small. This quadratic dependence is explained as arising from the linear dependence of the intensity of absorption and the probability of emission on the number of layers N. Large enhancements of Raman scattering intensities at the FE resonance enable the first observations of low-lying lattice modes in the monolayers. The measured low- lying modes (in the 20 to 100 cm-1 range) display characteristic changes when going from a single monolayer to two layers. The Raman intensities by high frequency intra-molecular vibrations display resonance enhancement double-peaks when incident or scattered photon energies overlap the FE optical emission. The double resonances are about the same strength which suggests that Franck-Condon overlap integrals for the respective vibronic transitions have the same magnitude. The interference between scattering amplitudes in the Raman resonance reveals quantum coherence of the symmetry-split states (Davydov doublet) of the lowest intrinsic singlet exciton. These results demonstrate novel venues for ultra-thin film characterization and studies of fundamental physics in organic semiconductor structures. In collaboration with Nancy G. Tassi (Dupont), Graciela B. Blanchet (Nanoterra, Cambridge, MA), and Aron Pinczuk (Columbia University).

  6. Chemical characterization of organosulfates in secondary organic aerosol derived from the photooxidation of alkanes

    Science.gov (United States)

    Riva, Matthieu; Da Silva Barbosa, Thais; Lin, Ying-Hsuan; Stone, Elizabeth A.; Gold, Avram; Surratt, Jason D.

    2016-09-01

    We report the formation of aliphatic organosulfates (OSs) in secondary organic aerosol (SOA) from the photooxidation of C10-C12 alkanes. The results complement those from our laboratories reporting the formation of OSs and sulfonates from gas-phase oxidation of polycyclic aromatic hydrocarbons (PAHs). Both studies strongly support the formation of OSs from the gas-phase oxidation of anthropogenic precursors, as hypothesized on the basis of recent field studies in which aromatic and aliphatic OSs were detected in fine aerosol collected from several major urban locations. In this study, dodecane, cyclodecane and decalin, considered to be important SOA precursors in urban areas, were photochemically oxidized in an outdoor smog chamber in the presence of either non-acidified or acidified ammonium sulfate seed aerosol. Effects of acidity and relative humidity on OS formation were examined. Aerosols collected from all experiments were characterized by ultra performance liquid chromatography coupled to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-QTOFMS). Most of the OSs identified could be explained by formation of gaseous epoxide precursors with subsequent acid-catalyzed reactive uptake onto sulfate aerosol and/or heterogeneous reactions of hydroperoxides. The OSs identified here were also observed and quantified in fine urban aerosol samples collected in Lahore, Pakistan, and Pasadena, CA, USA. Several OSs identified from the photooxidation of decalin and cyclodecane are isobars of known monoterpene organosulfates, and thus care must be taken in the analysis of alkane-derived organosulfates in urban aerosol.

  7. High frequency of Thermodesulfovibrio spp. and Anaerolineaceae in association with Methanoculleus spp. in a long-term incubation of n-alkanes-degrading methanogenic enrichment culture

    Directory of Open Access Journals (Sweden)

    Bo Liang

    2016-09-01

    Full Text Available In the present study, the microbial community and functional gene composition of a long-term active alkane-degrading methanogenic culture was established after two successive enrichment culture transfers and incubated for a total period of 1750 days. Molecular analysis was conducted after the second transfer (incubated for 750 days for both the active alkanes-degrading methanogenic enrichment cultures (T2-AE and the background control (T2-BC. A net increase of methane as the end product was detected in the headspace of the enrichment cultures amended with long-chain n-alkanes and intermediate metabolites, including octadecanoate, hexadecanoate, isocaprylate, butyrate, isobutyrate, propionate, acetate and formate were measured in the liquid cultures. The composition of microbial community shifted through the successive transfers over time of incubation. Sequences of bacterial and archaeal 16S rRNA gene (16S rDNA and mcrA functional gene indicated that bacterial sequences affiliated to Thermodesulfovibrio spp. and Anaerolineaceae and archaeal sequences falling within the genus Methanoculleus were the most frequently encountered and thus represented the dominant members performing the anaerobic degradation of long-chain n-alkanes and methanogenesis. In addition, the presence of assA functional genes encoding the alkylsuccinate synthase α subunit indicated that fumarate addition mechanism could be considered as a possible initial activation step of n-alkanes in the present study. The succession pattern of microbial communities indicates that Thermodesulfovibrio spp. could be a generalist participating in the metabolism of intermediates, while Anaerolineaceae plays a key role in the initial activation of long-chain n-alkane biodegradation.

  8. Electronic transport in disordered n-alkanes: From fluid methane to amorphous polyethylene

    Science.gov (United States)

    Cubero, David; Quirke, Nicholas; Coker, David F.

    2003-08-01

    We use a fast Fourier transform block Lanczos diagonalization algorithm to study the electronic states of excess electrons in fluid alkanes (methane, ethane, and propane) and in a molecular model of amorphous polyethylene (PE) relevant to studies of space charge in insulating polymers. We obtain a new pseudopotential for electron-PE interactions by fitting to the electronic properties of fluid alkanes and use this to obtain new results for electron transport in amorphous PE. From our simulations, while the electronic states in fluid methane are extended throughout the whole sample, in amorphous PE there is a transition between localized and delocalized states slightly above the vacuum level (˜+0.06 eV). The localized states in our amorphous PE model extend to -0.33 eV below this level. Using the Kubo-Greenwood equation we compute the zero-field electron mobility in pure amorphous PE to be μ≈2×10-3 cm2/V s. Our results highlight the importance of electron transport through extended states in amorphous regions to an understanding of electron transport in PE.

  9. Drug induced `softening' in phospholipid monolayers

    Science.gov (United States)

    Basak, Uttam Kumar; Datta, Alokmay; Bhattacharya, Dhananjay

    2015-06-01

    Compressibility measurements on Langmuir monolayers of the phospholipid Dimystoryl Phospatidylcholine (DMPC) in pristine form and in the presence of the Non-steroidal Anti-inflammatory Drug (NSAID) Piroxicam at 0.025 drug/lipid (D/L) molecular ratio at different temperatures, show that the monolayer exhibits large increase (and subsequent decrease) in compressibility due to the drug in the vicinity of the Liquid Expanded - Liquid Condensed (LE-LC) phase transition. Molecular dynamics simulations of the lipid monolayer in presence of drug molecules show a disordering of the tail tilt, which is consistent with the above result.

  10. Electrochemical Deposition Of Thiolate Monolayers On Metals

    Science.gov (United States)

    Porter, Marc D.; Weissharr, Duane E.

    1995-01-01

    Electrochemical method devised for coating metal (usually, gold) surfaces with adherent thiolate monolayers. Affords greater control over location and amount of material deposited and makes it easier to control chemical composition of deposits. One important potential use for this method lies in fabrication of chemically selective thin-film resonators for microwave oscillators used to detect pollutants: monolayer formulated to bind selectively pollutant chemical species of interest, causing increase in mass of monolayer and corresponding decrease in frequency of resonance. Another important potential use lies in selective chemical derivatization for purposes of improving adhesion, lubrication, protection against corrosion, electrocatalysis, and electroanalysis.

  11. Biosurfactant produced by novel Pseudomonas sp. WJ6 with biodegradation of n-alkanes and polycyclic aromatic hydrocarbons.

    Science.gov (United States)

    Xia, Wenjie; Du, Zhifeng; Cui, Qingfeng; Dong, Hao; Wang, Fuyi; He, Panqing; Tang, YongChun

    2014-07-15

    Alkanes and polycyclic aromatic hydrocarbons (PAHs) have threatened the environment due to toxicity and poor bioavailability. Interest in degradation of these hazardous materials by biosurfactant-producing bacteria has been steadily increasing in recent years. In this work, a novel biosurfactant-producing Pseudomonas sp. WJ6 was isolated to degrade a wide range of n-alkanes and polycyclic aromatic hydrocarbons. Production of lipopeptide biosurfactant was observed in all biodegradable studies. These lipopeptides were purified and identified by C18 RP-HPLC system and electrospray ionization-mass spectrometry. Results of structural analysis showed that these lipopeptides generated from different hydrocarbons were classified to be surfactin, fengycin and lichenysin. Heavy-oil sludge washing experiments demonstrated that lipopeptides produced by Pseudomonas sp. WJ6 have 92.46% of heavy-oil washing efficiency. The obtained results indicate that this novel bacterial strain and its lipopeptides have great potentials in the environmental remediation and petroleum recovery.

  12. Changes in atmospheric CO2 levels recorded by the isotopic signature of n-alkanes from plants

    Science.gov (United States)

    Machado, Karina Scurupa; Froehner, Sandro

    2017-01-01

    The isotopic signature of sedimentary organic matter acts as a tracer for past changes in the terrestrial and aquatic carbon cycles. The temporal variation in δ13C values of n-alkanes from plants was assigned as resulting from changes in atmospheric composition in the study area, due to both global and local influences. Two rises in atmospheric CO2 concentration were assigned from the variation in n-alkane δ13C values for the periods between 1600 and 1880 and from 1930 to the present. In the first period, the sources of excess CO2 were predominantly natural, mainly volcanism, while in the second period local anthropogenic emissions were the major reason.

  13. Biobased production of alkanes and alkenes through metabolic engineering of microorganisms

    DEFF Research Database (Denmark)

    Kang, Min Kyoung; Nielsen, Jens

    2016-01-01

    hydrocarbon biosynthesis, and in particular, alkanes and alkenes are important high-value chemicals as they can be utilized for a broad range of industrial purposes as well as ‘drop-in’ biofuels. Some microorganisms have the ability to biosynthesize alkanes and alkenes naturally, but their production level...... is extremely low. Therefore, there have been various attempts to recruit other microbial cell factories for production of alkanes and alkenes by applying metabolic engineering strategies. Here we review different pathways and involved enzymes for alkane and alkene production and discuss bottlenecks...

  14. Tools for characterizing the whole‐cell bio‐oxidation of alkanes at microscale

    DEFF Research Database (Denmark)

    Grant, Chris; da Silva Damas Pinto, Ana Catarina; Lui, Hai‐Po;

    2012-01-01

    ‐dodecanol after 48 h obtained in a stirred tank reactor. Using the microwell platform we present a rapid and systematic approach to identify the key bottlenecks in the bio‐oxidation of long‐chain alkanes using Escherichia coli expressing the alkane hydroxylase (alkB) complex. The results indicate that mass...... time, this in vivo rate difference is within the range reported for the purified enzyme. Finally, the results obtained also provide strong evidence that the mechanism of E. coli interaction with alkanes is mainly via uptake of alkanes dissolved in the aqueous phase rather than by direct cell...

  15. Surface viscoelastic properties of spread ferroelectric liquid crystal monolayer on air-water interface

    Science.gov (United States)

    Kaur, Ramneek; Bhullar, Gurpreet Kaur; Raina, K. K.

    2013-06-01

    Ferroelectric Liquid crystal having Smectic C* phase at room temperature was capable of forming Langmuir monolayer due to presence of both hydrophilic and hydrophobic groups in it. Surface viscoelasticity properties of FLC monolayer spread on water surface had been determined by dynamic oscillation method and discussed as a function of surface pressure. Dynamic viscoelastic properties such as G (Elastic modulus), G' (storage (elastic) modulus), G' (Loss (viscous) modulus) and phase change with sinusoidal oscillation had been measured at phase changing surface pressure values. As monolayer was becoming condensed, increasing trend was observed in G' values while G' was decreasing. At higher frequencies, viscous modulus G' had negative values. This relaxation phenomenon was probably caused by conformational rearrangements that acted to fluidize monolayer. Phase change tan θ was positive, response in surface pressure was ahead of the de-formation in area and the monolayer had positive dilatational viscosity. Phase change tan θ was negative, response in surface pressure was hysteretic to the deformation in area, and negative dilatational viscosity had been observed. Studies of monolayer in barrier oscillating mode provided us the surface pressure which was most suitable for Langmuir Blodgett monolayer deposition.

  16. Langmuir-Blodgett monolayers of InP quantum dots with short chain ligands.

    Science.gov (United States)

    Lambert, K; Wittebrood, L; Moreels, I; Deresmes, D; Grandidier, B; Hens, Z

    2006-08-15

    We demonstrate the organization of nearly monodisperse colloidal InP quantum dots at the air/water interface in Langmuir monolayers. The organization of the particles is monitored in situ by surface pressure-surface area measurements and ex situ by AFM measurements on films transferred to mica by Langmuir-Blodgett deposition. The influence of different ligands on the quality of the monolayer formed has been studied. We show that densely packed monolayers with little holes can be formed using short chain ligands like pyridine and pentamethylene sulfide. The advantage of using short chain ligands for electron tunneling to or from the quantum dots is demonstrated using scanning tunneling spectroscopy.

  17. 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.

  18. Features of the complexation of octadecane-2,4-dione and lanthanide ions in Langmuir monolayers

    Science.gov (United States)

    Sokolov, M. E.; Repina, I. N.; Raitman, O. A.; Kolokolov, F. A.; Panyushkin, V. T.

    2016-05-01

    Monolayers of octadecane-2,4-dione on the surfaces of EuCl3 and TbCl3 solutions in the concentration range of 1 × 10-4 to 5 × 10-3 M at pH 5.8 are studied. It is found that the limiting area of octadecane-2,4-dione molecule in a monolayer dependence on Eu3+ and Tb3+ concentration is of extreme nature. The formation of complex compounds in the ligand monolayer is postulated, and structures are proposed for these compounds at different concentrations of metal ions.

  19. Topological phase diagrams of bulk and monolayer TiS2-x Tex.

    Science.gov (United States)

    Zhu, Zhiyong; Cheng, Yingchun; Schwingenschlögl, Udo

    2013-02-15

    With the use of ab initio calculations, the topological phase diagrams of bulk and monolayer TiS(2-x) Te(x) are established. Whereas bulk TiS(2-x) Te(x) shows two strong topological phases [1;(000)] and [1;(001)] for 0.44monolayer is topologically nontrivial for 0.48monolayer, TiS(2-x) Te(x) is a unique system for studying topological phases in three and two dimensions simultaneously.

  20. Near-Edge X-ray Absorption Fine Structure Spectroscopy of Diamondoid Thiol Monolayers on Gold

    Energy Technology Data Exchange (ETDEWEB)

    Willey, T M; Fabbri, J; Lee, J I; Schreiner, P; Fokin, A A; Tkachenko, B A; Fokina, N A; Dahl, J; Carlson, B; Vance, A L; Yang, W; Terminello, L J; van Buuren, T; Melosh, N

    2007-11-27

    Diamondoids, hydrocarbon molecules with cubic-diamond-cage structures, have unique properties with potential value for nanotechnology. The availability and ability to selectively functionalize this special class of nanodiamond materials opens new possibilities for surface-modification, for high-efficiency field emitters in molecular electronics, as seed crystals for diamond growth, or as robust mechanical coatings. The properties of self-assembled monolayers (SAMs) of diamondoids are thus of fundamental interest for a variety of emerging applications. This paper presents the effects of thiol substitution position and polymantane order on diamondoid SAMs on gold using near-edge X-ray absorption fine structure spectroscopy (NEXAFS) and X-ray photoelectron spectroscopy (XPS). A framework to determine both molecular tilt and twist through NEXAFS is presented and reveals highly ordered diamondoid SAMs, with the molecular orientation controlled by the thiol location. C 1s and S 2p binding energies are lower in adamantane thiol than alkane thiols on gold by 0.67 {+-} 0.05 eV and 0.16 {+-} 0.04 eV respectively. These binding energies vary with diamondoid monolayer structure and thiol substitution position, consistent with different amounts of steric strain and electronic interaction with the substrate. This work demonstrates control over the assembly, in particular the orientational and electronic structure, providing a flexible design of surface properties with this exciting new class of diamond clusters.