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Sample records for adsorbed molecular monolayers

  1. Surface-enhanced nonlinear optical effects and detection of adsorbed molecular monolayers

    SciTech Connect

    Shen, Y.R.; Chen, C.K.; Heinz, T.F.; Ricard, D.

    1981-01-01

    The observation of a number of surface-enhanced nonlinear optical effects is discussed. The feasibility of using second-harmonic generation to detect the adsorption of molecular monolayers on a metal surface in an electrolytic solution is shown.

  2. Molecular dynamics simulations of SDS, DTAB, and C12E8 monolayers adsorbed at the air/water surface in the presence of DSEP.

    PubMed

    Pang, Jinyu; Wang, Yajing; Xu, Guiying; Han, Tingting; Lv, Xin; Zhang, Jian

    2011-03-24

    The properties of adsorbed monolayers of three hydrocarbon surfactants with the same hydrophobic tail, sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB) and octaethylene glycol dodecyl ether (C(12)E(8)) at the air/water surface in the absence and presence of a dimethylsiloxane ethoxylate-propoxylate (DSEP) were studied via molecular dynamics simulations to compare the effect of the headgroups on the aggregation behaviors of surfactant mixtures. The structures and dynamical properties of the monolayers were greatly affected after adding DSEP. In the presence of DSEP, SDS monolayer was better ordered and more compact, whereas C(12)E(8) monolayer was relatively disordered. Some DTAB molecules immerged into water, and the others adsorbed at the surface were in less compact but well-ordered arrangement. The reason for the appearance of different types of monolayers was also discussed, with the goal of providing a theoretical approach for their further applications.

  3. Molecular Adsorber Coating

    NASA Technical Reports Server (NTRS)

    Straka, Sharon; Peters, Wanda; Hasegawa, Mark; Hedgeland, Randy; Petro, John; Novo-Gradac, Kevin; Wong, Alfred; Triolo, Jack; Miller, Cory

    2011-01-01

    A document discusses a zeolite-based sprayable molecular adsorber coating that has been developed to alleviate the size and weight issues of current ceramic puck-based technology, while providing a configuration that more projects can use to protect against degradation from outgassed materials within a spacecraft, particularly contamination-sensitive instruments. This coating system demonstrates five times the adsorption capacity of previously developed adsorber coating slurries. The molecular adsorber formulation was developed and refined, and a procedure for spray application was developed. Samples were spray-coated and tested for capacity, thermal optical/radiative properties, coating adhesion, and thermal cycling. Work performed during this study indicates that the molecular adsorber formulation can be applied to aluminum, stainless steel, or other metal substrates that can accept silicate-based coatings. The coating can also function as a thermal- control coating. This adsorber will dramatically reduce the mass and volume restrictions, and is less expensive than the currently used molecular adsorber puck design.

  4. Mysterious Lattice Rotations in Adsorbed Monolayers

    NASA Astrophysics Data System (ADS)

    Diehl, Renee D.

    1997-03-01

    Lattice rotations due to a mismatch in structure have been observed in film growth for many years, probably beginning in the 1930's with the Nishiyama-Wasserman and Kurdjumov-Sachs orientations observed when fcc(111) films grow on bcc(110) surfaces, or vice versa. Early analysis of this problem was carried out with the aid of Moiré patterns and the observation that the preferred lattice orientations are those which maximize the Moiré fringe spacing. Later energy calculations indicated that the structures which were predicted by the the Moiré technique actually do correspond to energy minima. Epitaxial rotation in adsorbed monolayers is a conceptually simpler problem since in principle it involves only two planes of atoms, and it was first observed in 1977 for Ar on a graphite surface(C. G. Shaw, M. D. Chinn, S. C. Fain, Jr. Phys. Rev. Lett. 41 (1978) 955.). This observation came only a few months after a new theory, based on the expected elastic behavior of an overlayer, was developed by A. D. Novaco and J. P. McTague(A. D. Novaco and J. P. McTague, Phys. Rev. Lett. 38 (1977) 1286.), and the agreement with the experimental results was remarkable. It was later shown that a few symmetry principles similar to those used for the film growth studies sometimes can also predict the observed structures. However, the situation for incommensurate layers physisorbed on metal surfaces currently looks bleak. None of the existing theories or models appears to describe the experimental results. New data for physisorbed gases on metal surfaces will be presented, along with some half-baked (and probably wrong) ideas for what might be happening. This work was supported by NSF.

  5. Detection of Molecular Monolayers by Optical Second-Harmonic Generation

    SciTech Connect

    Chen, C. K.; Heinz, T. F.; Ricard, D.; Shen, Y. R.

    1980-12-22

    Second harmonic generation is shown to be sensitive enough to detect molecular monolayers adsorbed on a silver surface. Adsorption of AgCl and pyridine on silver during and after an electrolytic cycle can be easily observed,

  6. Observation of the dynamical change in a water monolayer adsorbed on a ZnO surface.

    PubMed

    Dulub, Olga; Meyer, Bernd; Diebold, Ulrike

    2005-09-23

    A combined scanning tunneling microscopy and density-functional theory (DFT) study shows a rich structure of water monolayers adsorbed on ZnO(1010) at room temperature. Most of the water is in a lowest-energy configuration where every second molecule is dissociated. It coexists with an energetically almost degenerate configuration consisting of a fully molecular water monolayer. Parts of the layer continuously switch back and forth between these two states. DFT calculations reveal that water molecules repeatedly associate and dissociate in this sustained dynamical process. PMID:16197151

  7. Volumetric Interpretation of Protein Adsorption: Capacity Scaling with Adsorbate Molecular Weight and Adsorbent Surface Energy

    PubMed Central

    Parhi, Purnendu; Golas, Avantika; Barnthip, Naris; Noh, Hyeran; Vogler, Erwin A.

    2009-01-01

    Silanized-glass-particle adsorbent capacities are extracted from adsorption isotherms of human serum albumin (HSA, 66 kDa), immunoglobulin G (IgG, 160 kDa), fibrinogen (Fib, 341 kDa), and immunoglobulin M (IgM, 1000 kDa) for adsorbent surface energies sampling the observable range of water wettability. Adsorbent capacity expressed as either mass-or-moles per-unit-adsorbent-area increases with protein molecular weight (MW) in a manner that is quantitatively inconsistent with the idea that proteins adsorb as a monolayer at the solution-material interface in any physically-realizable configuration or state of denaturation. Capacity decreases monotonically with increasing adsorbent hydrophilicity to the limit-of-detection (LOD) near τo = 30 dyne/cm (θ~65o) for all protein/surface combinations studied (where τo≡γlvocosθ is the water adhesion tension, γlvo is the interfacial tension of pure-buffer solution, and θ is the buffer advancing contact angle). Experimental evidence thus shows that adsorbent capacity depends on both adsorbent surface energy and adsorbate size. Comparison of theory to experiment implies that proteins do not adsorb onto a two-dimensional (2D) interfacial plane as frequently depicted in the literature but rather partition from solution into a three-dimensional (3D) interphase region that separates the physical surface from bulk solution. This interphase has a finite volume related to the dimensions of hydrated protein in the adsorbed state (defining “layer” thickness). The interphase can be comprised of a number of adsorbed-protein layers depending on the solution concentration in which adsorbent is immersed, molecular volume of the adsorbing protein (proportional to MW), and adsorbent hydrophilicity. Multilayer adsorption accounts for adsorbent capacity over-and-above monolayer and is inconsistent with the idea that protein adsorbs to surfaces primarily through protein/surface interactions because proteins within second (or higher

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

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

    2007-03-14

    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 91 K above its value in bulk. Therefore, squalane, like tetracosane, will be a poor lubricant in those nanoscale devices that require a fluid lubricant at room 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.

  12. Icelike water monolayer adsorbed on mica at room temperature

    SciTech Connect

    Miranda, P.B.; Xu, L.; Shen, Y.R.; Salmeron, M.

    1998-10-01

    The structure of a water film formed on mica at room temperature, in equilibrium with water vapor at various relative humidities (RH), was studied using sum-frequency-generation (SFG) vibrational spectroscopy and scanning polarization force microscopy (SPFM). Analysis of the O-D stretch modes in the SFG spectra of D{sub 2}O on mica indicates that as RH increases, the submonolayer water structure evolves into a more ordered hydrogen-bonding network. At full monolayer coverage ({approximately} 90% RH), the SFG spectrum suggests an icelike film with no dangling O-D groups, in agreement with a recent molecular dynamics simulation.

  13. Multiscale simulations of protein G B1 adsorbed on charged self-assembled monolayers.

    PubMed

    Liu, Jie; Liao, Chenyi; Zhou, Jian

    2013-09-10

    The orientation of an antibody plays an important role in the development of immunosensors. Protein G is an antibody binding protein, which specifically targets the Fc fragment of an antibody. In this work, the orientation of prototypical and mutated protein G B1 adsorbed on positively and negatively charged self-assembled monolayers was studied by parallel tempering Monte Carlo and all-atom molecular dynamics simulations. Both methods present generally similar orientation distributions of protein G B1 for each kind of surface. The root-mean-square deviation, DSSP, gyration radius, eccentricity, dipole moment, and superimposed structures of protein G B1 were analyzed. Moreover, the orientation of binding antibody was also predicted in this work. Simulation results show that with the same orientation trends, the mutant exhibits narrower orientation distributions than does the prototype, which was mainly caused by the stronger dipole of the mutant. Both kinds of proteins adsorbed on charged surfaces were induced by the competition of electrostatic interaction and vdW interaction; the electrostatic interaction energy dominated the adsorption behavior. The protein adsorption was also largely affected by the distribution of charged residues within the proteins. Thus, the prototype could adsorb on a negatively charged surface, although it keeps a net charge of -4 e. The mutant has imperfect opposite orientation when it adsorbed on oppositely charged surfaces. For the mutant on a carboxyl-functionalized self-assembled monolayer (COOH-SAM), the orientation was the same as that inferred by experiments. While for the mutant on amine-functionalized self-assembled monolayer (NH2-SAM), the orientation was induced by the competition between attractive interactions (led by ASP40 and GLU56) and repulsive interactions (led by LYS10); thus, the perfect opposite orientation could not be obtained. On both surfaces, the adsorbed protein could retain its native conformation. The desired

  14. Icelike Water Monolayer Adsorbed on Mica at Room Temperature

    SciTech Connect

    Miranda, P.B.; Xu, L.; Shen, Y.R.; Salmeron, M.

    1998-12-01

    The structure of a water film formed on mica at room temperature, in equilibrium with water vapor at various relative humidities (RH), was studied using sum-frequency-generation (SFG) vibrational spectroscopy and scanning polarization force microscopy (SPFM). Analysis of the O-D stretch modes in the SFG spectra of D{sub 2}O on mica indicates that as RH increases, the submonolayer water structure evolves into a more ordered hydrogen-bonding network. At full monolayer coverage ({approximately} 90{percent} RH) , the SFG spectrum suggests an icelike film with no dangling O-D groups, in agreement with a recent molecular dynamics simulation. {copyright} {ital 1998} {ital The American Physical Society}

  15. Mechanism of charge transfer and its impacts on Fermi-level pinning for gas molecules adsorbed on monolayer WS{sub 2}

    SciTech Connect

    Zhou, Changjie; Zhu, Huili; Yang, Weihuang

    2015-06-07

    Density functional theory calculations were performed to assess changes in the geometric and electronic structures of monolayer WS{sub 2} upon adsorption of various gas molecules (H{sub 2}, O{sub 2}, H{sub 2}O, NH{sub 3}, NO, NO{sub 2}, and CO). The most stable configuration of the adsorbed molecules, the adsorption energy, and the degree of charge transfer between adsorbate and substrate were determined. All evaluated molecules were physisorbed on monolayer WS{sub 2} with a low degree of charge transfer and accept charge from the monolayer, except for NH{sub 3}, which is a charge donor. Band structure calculations showed that the valence and conduction bands of monolayer WS{sub 2} are not significantly altered upon adsorption of H{sub 2}, H{sub 2}O, NH{sub 3}, and CO, whereas the lowest unoccupied molecular orbitals of O{sub 2}, NO, and NO{sub 2} are pinned around the Fermi-level when these molecules are adsorbed on monolayer WS{sub 2}. The phenomenon of Fermi-level pinning was discussed in light of the traditional and orbital mixing charge transfer theories. The impacts of the charge transfer mechanism on Fermi-level pinning were confirmed for the gas molecules adsorbed on monolayer WS{sub 2}. The proposed mechanism governing Fermi-level pinning is applicable to the systems of adsorbates on recently developed two-dimensional materials, such as graphene and transition metal dichalcogenides.

  16. Electronic and magnetic properties of nonmetal atoms adsorbed ReS{sub 2} monolayers

    SciTech Connect

    Zhang, Xiaoou; Li, Qingfang

    2015-08-14

    The stable configurations and electronic and magnetic properties of nonmetal atoms (H, N, P, O, S, F, and Cl) adsorbed ReS{sub 2} monolayers have been investigated by first-principles calculations. It is found that H, O, S, F, and Cl prefer to occupy the peak sites of S atoms, while both N and P atoms favor the valley sites of S atoms. The ReS{sub 2} sheet exhibits a good adsorption capability to nonmetal atoms. The reconstruction of the surface is pronounced in N- and P-adsorbed ReS{sub 2} monolayers. In H-adsorbed case, the Fermi level is pulled into the conduction band, which results in the semiconductor-metal transition. The same magnetic moment of 1μ{sub B} is found in the N-, P-, F-, and Cl-adsorbed ReS{sub 2} monolayers, while the mechanisms of forming magnetic moment for N (P)- and F (Cl)-adsorbed cases are different. In addition, the spatial extensions of spin density in P-, F-, and Cl-adsorbed cases are larger than that in N-adsorbed case, which is more suitable to achieve long-range magnetic coupling interaction at low defect concentrations. Our results provide insight for achieving metal-free magnetism and a tunable band gap for various electronic and spintronic devices based on ReS{sub 2}.

  17. Black Molecular Adsorber Coatings for Spaceflight Applications

    NASA Technical Reports Server (NTRS)

    Abraham, Nithin Susan; Hasegawa, Mark Makoto; Straka, Sharon A.

    2014-01-01

    The molecular adsorber coating is a new technology that was developed to mitigate the risk of on-orbit molecular contamination on spaceflight missions. The application of this coating would be ideal near highly sensitive, interior surfaces and instruments that are negatively impacted by outgassed molecules from materials, such as plastics, adhesives, lubricants, epoxies, and other similar compounds. This current, sprayable paint technology is comprised of inorganic white materials made from highly porous zeolite. In addition to good adhesion performance, thermal stability, and adsorptive capability, the molecular adsorber coating offers favorable thermal control characteristics. However, low reflectivity properties, which are typically offered by black thermal control coatings, are desired for some spaceflight applications. For example, black coatings are used on interior surfaces, in particular, on instrument baffles for optical stray light control. Similarly, they are also used within light paths between optical systems, such as telescopes, to absorb light. Recent efforts have been made to transform the white molecular adsorber coating into a black coating with similar adsorptive properties. This result is achieved by optimizing the current formulation with black pigments, while still maintaining its adsorption capability for outgassing control. Different binder to pigment ratios, coating thicknesses, and spray application techniques were explored to develop a black version of the molecular adsorber coating. During the development process, coating performance and adsorption characteristics were studied. The preliminary work performed on black molecular adsorber coatings thus far is very promising. Continued development and testing is necessary for its use on future contamination sensitive spaceflight missions.

  18. Black molecular adsorber coatings for spaceflight applications

    NASA Astrophysics Data System (ADS)

    Abraham, Nithin S.; Hasegawa, Mark M.; Straka, Sharon A.

    2014-09-01

    The molecular adsorber coating is a new technology that was developed to mitigate the risk of on-orbit molecular contamination on spaceflight missions. The application of this coating would be ideal near highly sensitive, interior surfaces and instruments that are negatively impacted by outgassed molecules from materials, such as plastics, adhesives, lubricants, epoxies, and other similar compounds. This current, sprayable paint technology is comprised of inorganic white materials made from highly porous zeolite. In addition to good adhesion performance, thermal stability, and adsorptive capability, the molecular adsorber coating offers favorable thermal control characteristics. However, low reflectivity properties, which are typically offered by black thermal control coatings, are desired for some spaceflight applications. For example, black coatings are used on interior surfaces, in particular, on instrument baffles for optical stray light control. Similarly, they are also used within light paths between optical systems, such as telescopes, to absorb light. Recent efforts have been made to transform the white molecular adsorber coating into a black coating with similar adsorptive properties. This result is achieved by optimizing the current formulation with black pigments, while still maintaining its adsorption capability for outgassing control. Different binder to pigment ratios, coating thicknesses, and spray application techniques were explored to develop a black version of the molecular adsorber coating. During the development process, coating performance and adsorption characteristics were studied. The preliminary work performed on black molecular adsorber coatings thus far is very promising. Continued development and testing is necessary for its use on future contamination sensitive spaceflight missions.

  19. Development and Testing of Molecular Adsorber Coatings

    NASA Technical Reports Server (NTRS)

    Abraham, Nithin; Hasegawa, Mark; Straka, Sharon

    2012-01-01

    The effect of on-orbit molecular contamination has the potential to degrade the performance of spaceflight hardware and diminish the lifetime of the spacecraft. For example, sensitive surfaces, such as optical surfaces, electronics, detectors, and thermal control surfaces, are vulnerable to the damaging effects of contamination from outgassed materials. The current solution to protect these surfaces is through the use of zeolite coated ceramic adsorber pucks. However, these pucks and its additional complex mounting hardware requirements result in several disadvantages, such as size, weight, and cost related concerns, that impact the spacecraft design and the integration and test schedule. As a result, a new innovative molecular adsorber coating was developed as a sprayable alternative to mitigate the risk of on-orbit molecular contamination. In this study, the formulation for molecular adsorber coatings was optimized using various binders, pigment treatment methods, binder to pigment ratios, thicknesses, and spray application techniques. The formulations that passed coating adhesion and vacuum thermal cycling tests were further tested for its adsorptive capacity. Accelerated molecular capacitance tests were performed in an innovatively designed multi-unit system containing idealized contaminant sources. This novel system significantly increased the productivity of the testing phase for the various formulations that were developed. Work performed during the development and testing phases has demonstrated successful application of molecular adsorber coatings onto metallic substrates, as well as, very promising results for the adhesion performance and the molecular capacitance of the coating. Continued testing will assist in the qualification of molecular adsorber coatings for use on future contamination sensitive spaceflight missions.

  20. Effect of colloidal particle size on adsorbed monodisperse and bidisperse monolayers.

    PubMed

    Rosenberg, Rachel T; Dan, Nily

    2011-07-19

    Coating hydrogel films or microspheres by an adsorbed colloidal shell is one synthesis method for forming colloidosomes. The colloidal shell allows control of the release rate of encapsulated materials, as well as selective transport. Previous studies found that the packing density of self-assembled, adsorbed colloidal monolayers is independent of the colloidal particle size. In this paper we develop an equilibrium model that correlates the packing density of charged colloidal particles in an adsorbed shell to the particle dimensions in monodisperse and bidisperse systems. In systems where the molar concentration in solution is fixed, the increase in adsorption energy with increasing particle size leads to a monotonic increase in the monolayer packing density with particle radius. However, in systems where the mass fraction of the particles in the adsorbing solutions is fixed, increasing particle size also reduces the molar concentration of particles in solution, thereby reducing the probability of adsorption. The result is a nonmonotonic dependence of the packing density in the adsorbed layer on the particle radius. In bidisperse monolayers composed of two particle sizes, the packing density in the layer increases significantly with size asymmetry. These results may be utilized to design the properties of colloidal shells and coatings to achieve specific properties such as transport rate and selectivity.

  1. Molecular Dynamics in Self-Assembled Monolayers

    NASA Astrophysics Data System (ADS)

    Bochinski, Jason; Stevens, Derrick; Scott, Mary; Guy, Laura; Dedeugd, Casey; Clarke, Laura

    2007-03-01

    Silane self-assembled monolayers (SAMs) are an important tool for both scientific research and technological applications. Despite their widespread use, few experimental investigations have addressed molecular motion within these films, which offer a unique and useful physical system for fundamental scientific studies, such as observing dipolar and other glass transitions in two-dimensions. In addition, relaxations such as ``rotator'' phases where molecular groups rotate in a plane parallel to the surface have been correlated with film conductivity, adhesive, and wetting properties. We utilize surface-sensitive, dielectric relaxation spectroscopy to probe molecular motion as a function of temperature within silane chemistry-based monolayers formed upon interdigitated electrodes. Our latest results exploring a previously published motion as well as comparisons to linear polymer films will be discussed.

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Structural and topographical characteristics of adsorbed WPI and monoglyceride mixed monolayers at the air-water interface.

    PubMed

    Patino, Juan M Rodríguez; Fernández, Marta Cejudo

    2004-05-25

    In this work we have analyzed the structural and topographical characteristics of mixed monolayers formed by an adsorbed whey protein isolate (WPI) and a spread monoglyceride monolayer (monopalmitin or monoolein) on the previously adsorbed protein film. Measurements of the surface pressure (pi)-area (A) isotherm were obtained at 20 degrees C and at pH 7 for protein-adsorbed films from water in a Wilhelmy-type film balance. Since the surface concentration (1/A) is actually unknown for the adsorbed monolayer, the values were derived by assuming that the A values for adsorbed and spread monolayers were equal at the collapse point of the mixed film. The pi-A isotherm deduced for adsorbed WPI monolayer in this work is practically the same as that obtained directly by spreading. For WPI-monoglyceride mixed films, the pi-A isotherms for adsorbed and spread monolayers at pi higher than the equilibrium surface pressure of WPI are practically coincident, a phenomenon which may be attributed to the protein displacement by the monoglyceride from the interface. At lower surface pressures, WPI and monoglyceride coexist at the interface and the adsorbed and spread pi-A isotherms (i.e., the monolayer structure of the mixed films) are different. Monopalmitin has a higher capacity than monoolein for the displacement of protein from the air-water interface. However, some degree of interactions exists between proteins and monoglycerides and these interactions are higher for adsorbed than for spread films. The topography of the monolayer corroborates these conclusions.

  4. Sputtering and secondary ion emission properties of alkali metal films and adsorbed monolayers

    SciTech Connect

    Krauss, A R; Gruen, D M

    1980-01-01

    The secondary ion emission of alkali metal adsorbed monlayer and multilayer films has been studied. Profiling with sub-monolayer resolution has been performed by Auger, x-ray photoemission and secondary ion mass spectroscopy. Characteristic differences in the sputtering yields, and ion fraction have been observed which are associated with both the surface bonding properties and the mechanism leading to the formation of secondary ions. By sputtering with a negative bias applied to the sample, positive secondary ions are returned to the surface, resulting in a reduced sputter-induced erosion rate. Comparison with the results obtained with K and Li overlayers sputtered without sample bias provides an experimental value of both the total and secondary ion sputtering yields. The first and second monolayers can be readily identified and the first monolayer exhibits a lower sputtering yield and higher secondary ion fraction. This result is related to adsorption theory and measured values are compared with those obtained by thermal desorption measurements.

  5. Electrochemical and scanning probe microscopic characterization of spontaneously adsorbed organothiolate monolayers at gold

    SciTech Connect

    Wong, Sze-Shun Season

    1999-12-10

    This dissertation presented several results which add to the general knowledge base regarding organothiolates monolayer spontaneously adsorbed at gold films. Common to the body of this work is the use of voltammetric reductive resorption and variants of scanning probe microscopy to gain insight into the nature of the monolayer formation process as well as the resulting interface. The most significant result from this work is the success of using friction force microscopy to discriminate the end group orientation of monolayer chemisorbed at smooth gold surfaces with micrometer resolution (Chapter 4). The ability to detect the differences in the orientational disposition is demonstrated by the use PDMS polymer stamp to microcontact print an adlayer of n-alkanethiolate of length n in a predefine pattern onto a gold surface, followed by the solution deposition of a n-alkanethiol of n {+-} 1 to fill in the areas on the gold surface intentionally not coated by the stamping process. These two-component monolayers can be discriminated by using friction force microscopy which detects differences in friction contributed by the differences in the orientation of the terminal groups at surfaces. This success has recently led to the detection of the orientation differences at nanometer scale. Although the substrates examined in this work consisted entirely of smooth gold films, the same test can be performed on other smooth substrates and monolayer materials.

  6. Effect of phosphonate monolayer adsorbate on the microwave photoresponse of TiO2 nanotube membranes mounted on a planar double ring resonator.

    PubMed

    Zarifi, Mohammad H; Farsinezhad, Samira; Wiltshire, Benjamin D; Abdorrazaghi, Mohammad; Najia Mahdi; Kar, Piyush; Daneshmand, Mojgan; Shankar, Karthik

    2016-09-16

    In this study, the effects of a phosphonate molecular monolayer adsorbed on the surface of a free-standing self-organized TiO2 nanotube membrane, on the microwave photoresponse of the membrane are presented. This phenomenon is monitored using planar microwave sensors. A double ring resonator is utilized to monitor the permittivity and conductivity variation on the monolayer coated membrane and the sensor environment separately. It is shown that the rise time and subsequent decay of the amplitude (A), resonance frequency (f 0) and quality factor (Q) of the resonator depend on the existence and the type of the monolayer coating the membrane. Three different monolayers of n-decylphosphonic acid (DPA), 1H, 1H', 2H, 2H'-perfluorodecyl phosphonic acid (PFDPA) and 16-phosphonohexadecanoic acid adsorbed on the titania nanotube membrane are investigated while monitoring their microwave properties during the illumination time period and in the relaxation period, which demonstrate different behavior in comparison to each other and to the bare nanotube membrane layer. The effect of humidity on the TiO2 nanotube membrane with and without different monolayers is also studied and the results demonstrate distinguishable microwave responses. While each of the monolayer-coated membranes exhibited an attenuation of the photo-induced change in A, f 0 and Q with respect to the bare membrane, PFDPA-coated membranes showed the smallest relative change in the monitored microwave parameters upon ultraviolet illumination and upon the introduction of different levels of humidity. These effects are explained on the basis of surface trap passivation by the monolayers as well as the hydrophobicity of the monolayers. Our work also shows how the interactions of self-assembled monolayers with charge carriers and surface states on metal oxides may be used to indirectly sense their presence through measurement of the microwave response.

  7. Effect of phosphonate monolayer adsorbate on the microwave photoresponse of TiO2 nanotube membranes mounted on a planar double ring resonator

    NASA Astrophysics Data System (ADS)

    Zarifi, Mohammad H.; Farsinezhad, Samira; Wiltshire, Benjamin D.; Abdorrazaghi, Mohammad; Mahdi, Najia; Kar, Piyush; Daneshmand, Mojgan; Shankar, Karthik

    2016-09-01

    In this study, the effects of a phosphonate molecular monolayer adsorbed on the surface of a free-standing self-organized TiO2 nanotube membrane, on the microwave photoresponse of the membrane are presented. This phenomenon is monitored using planar microwave sensors. A double ring resonator is utilized to monitor the permittivity and conductivity variation on the monolayer coated membrane and the sensor environment separately. It is shown that the rise time and subsequent decay of the amplitude (A), resonance frequency (f 0) and quality factor (Q) of the resonator depend on the existence and the type of the monolayer coating the membrane. Three different monolayers of n-decylphosphonic acid (DPA), 1H, 1H‧, 2H, 2H‧-perfluorodecyl phosphonic acid (PFDPA) and 16-phosphonohexadecanoic acid adsorbed on the titania nanotube membrane are investigated while monitoring their microwave properties during the illumination time period and in the relaxation period, which demonstrate different behavior in comparison to each other and to the bare nanotube membrane layer. The effect of humidity on the TiO2 nanotube membrane with and without different monolayers is also studied and the results demonstrate distinguishable microwave responses. While each of the monolayer-coated membranes exhibited an attenuation of the photo-induced change in A, f 0 and Q with respect to the bare membrane, PFDPA-coated membranes showed the smallest relative change in the monitored microwave parameters upon ultraviolet illumination and upon the introduction of different levels of humidity. These effects are explained on the basis of surface trap passivation by the monolayers as well as the hydrophobicity of the monolayers. Our work also shows how the interactions of self-assembled monolayers with charge carriers and surface states on metal oxides may be used to indirectly sense their presence through measurement of the microwave response.

  8. Effect of phosphonate monolayer adsorbate on the microwave photoresponse of TiO2 nanotube membranes mounted on a planar double ring resonator.

    PubMed

    Zarifi, Mohammad H; Farsinezhad, Samira; Wiltshire, Benjamin D; Abdorrazaghi, Mohammad; Najia Mahdi; Kar, Piyush; Daneshmand, Mojgan; Shankar, Karthik

    2016-09-16

    In this study, the effects of a phosphonate molecular monolayer adsorbed on the surface of a free-standing self-organized TiO2 nanotube membrane, on the microwave photoresponse of the membrane are presented. This phenomenon is monitored using planar microwave sensors. A double ring resonator is utilized to monitor the permittivity and conductivity variation on the monolayer coated membrane and the sensor environment separately. It is shown that the rise time and subsequent decay of the amplitude (A), resonance frequency (f 0) and quality factor (Q) of the resonator depend on the existence and the type of the monolayer coating the membrane. Three different monolayers of n-decylphosphonic acid (DPA), 1H, 1H', 2H, 2H'-perfluorodecyl phosphonic acid (PFDPA) and 16-phosphonohexadecanoic acid adsorbed on the titania nanotube membrane are investigated while monitoring their microwave properties during the illumination time period and in the relaxation period, which demonstrate different behavior in comparison to each other and to the bare nanotube membrane layer. The effect of humidity on the TiO2 nanotube membrane with and without different monolayers is also studied and the results demonstrate distinguishable microwave responses. While each of the monolayer-coated membranes exhibited an attenuation of the photo-induced change in A, f 0 and Q with respect to the bare membrane, PFDPA-coated membranes showed the smallest relative change in the monitored microwave parameters upon ultraviolet illumination and upon the introduction of different levels of humidity. These effects are explained on the basis of surface trap passivation by the monolayers as well as the hydrophobicity of the monolayers. Our work also shows how the interactions of self-assembled monolayers with charge carriers and surface states on metal oxides may be used to indirectly sense their presence through measurement of the microwave response. PMID:27487465

  9. Low-density phases of 3He monolayers adsorbed on graphite

    NASA Astrophysics Data System (ADS)

    Ruggeri, Michele; Vitali, Ettore; Galli, Davide Emilio; Boninsegni, Massimo; Moroni, Saverio

    2016-03-01

    Quantum Monte Carlo simulations at zero temperature of a 3He monolayer adsorbed on graphite, either clean or preplated with 4He, unexpectedly point to a gas-liquid phase transition at a very low areal density of the order of 0.01 Å-2 . This result stems from an essentially unbiased calculation of the ground-state energy for an infinite, defect-free substrate, which interacts with He atoms via a realistic potential, whereas the interaction between two He atoms includes two- and three-body terms. The sensitivity of the gas-liquid coexistence region on the model Hamiltonian employed is discussed.

  10. Transverse thermal depinning and nonlinear sliding friction of an adsorbed monolayer.

    PubMed

    Granato, E; Ying, S C

    2000-12-18

    We study the response of an adsorbed monolayer under a driving force as a model of sliding friction phenomena between two crystalline surfaces with a boundary lubrication layer. Using Langevin-dynamics simulation, we determine the nonlinear response in the direction transverse to a high symmetry direction along which the layer is already sliding. We find that below a finite transition temperature there exist a critical depinning force and hysteresis effects in the transverse response in the dynamical state when the adlayer is sliding smoothly along the longitudinal direction. PMID:11135998

  11. Transverse thermal depinning and nonlinear sliding friction of an adsorbed monolayer.

    PubMed

    Granato, E; Ying, S C

    2000-12-18

    We study the response of an adsorbed monolayer under a driving force as a model of sliding friction phenomena between two crystalline surfaces with a boundary lubrication layer. Using Langevin-dynamics simulation, we determine the nonlinear response in the direction transverse to a high symmetry direction along which the layer is already sliding. We find that below a finite transition temperature there exist a critical depinning force and hysteresis effects in the transverse response in the dynamical state when the adlayer is sliding smoothly along the longitudinal direction.

  12. Neutron Reflection Study of Bovine β-Casein Adsorbed on OTS Self- Assembled Monolayers

    NASA Astrophysics Data System (ADS)

    Fragneto, Giovanna; Thomas, Robert K.; Rennie, Adrian R.; Penfold, Jeffrey

    1995-02-01

    Specular neutron reflection has been used to determine the structure and composition of bovine β-casein adsorbed on a solid surface from an aqueous phosphate-buffered solution at pH 7. The protein was adsorbed on a hydrophobic monolayer self-assembled from deuterated octadecyltrichlorosilane solution on a silicon (111) surface. A two-layer structure formed consisting of one dense layer of thickness 23 ± 1 angstroms and a surface coverage of 1.9 milligrams per square meter adjacent to the surface and an external layer protruding into the solution of thickness 35 ± 1 angstroms and 12 percent protein volume fraction. The structure of the (β-casein) layer is explained in terms of the charge distribution in the protein.

  13. Intermixed adatom and surface-bound adsorbates in regular self-assembled monolayers of racemic 2-butanethiol on Au(111).

    PubMed

    Ouyang, Runhai; Yan, Jiawei; Jensen, Palle S; Ascic, Erhad; Gan, Shiyu; Tanner, David; Mao, Bingwei; Niu, Li; Zhang, Jingdong; Tang, Chunguang; Hush, Noel S; Reimers, Jeffrey R; Ulstrup, Jens

    2015-04-01

    In situ scanning tunneling microscopy combined with density functional theory molecular dynamics simulations reveal a complex structure for the self-assembled monolayer (SAM) of racemic 2-butanethiol on Au(111) in aqueous solution. Six adsorbate molecules occupy a (10×√3)R30° cell organized as two RSAuSR adatom-bound motifs plus two RS species bound directly to face-centered-cubic and hexagonally close-packed sites. This is the first time that these competing head-group arrangements have been observed in the same ordered SAM. Such unusual packing is favored as it facilitates SAMs with anomalously high coverage (30%), much larger than that for enantiomerically resolved 2-butanethiol or secondary-branched butanethiol (25%) and near that for linear-chain 1-butanethiol (33%).

  14. NASA Applications of Molecular Adsorber Coatings

    NASA Technical Reports Server (NTRS)

    Abraham, Nithin S.

    2015-01-01

    The Molecular Adsorber Coating (MAC) is a new, innovative technology that was developed to reduce the risk of molecular contamination on spaceflight applications. Outgassing from materials, such as plastics, adhesives, lubricants, silicones, epoxies, and potting compounds, pose a significant threat to the spacecraft and the lifetime of missions. As a coating made of highly porous inorganic materials, MAC offers impressive adsorptive capabilities that help capture and trap contaminants. Past research efforts have demonstrated the coating's promising adhesion performance, optical properties, acoustic durability, and thermal stability. These results advocate its use near or on surfaces that are targeted by outgassed materials, such as internal optics, electronics, detectors, baffles, sensitive instruments, thermal control coatings, and vacuum chamber test environments. The MAC technology has significantly progressed in development over the recent years. This presentation summarizes the many NASA spaceflight applications of MAC and how the coatings technology has been integrated as a mitigation tool for outgassed contaminants. For example, this sprayable paint technology has been beneficial for use in various vacuum chambers for contamination control and hardware bake-outs. The coating has also been used in small instrument cavities within spaceflight instrument for NASA missions.

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Stilling Waves with Ordered Molecular Monolayers

    ERIC Educational Resources Information Center

    Vitz, Ed

    2008-01-01

    A demonstration of the damping effect of an oil monolayer on water waves is described. The history of this remarkable demonstration--with a 2000 (or more) year span--and a brief explanation in terms of the properties of water and the monolayer are presented. If a layer of olive oil, one molecule thick (about one-ten millionth of a centimeter), is…

  17. Inelastic neutron scattering (INS) observations of rotational tunneling within partially deuterated methane monolayers adsorbed on MgO(1 0 0) surfaces

    NASA Astrophysics Data System (ADS)

    Hicks, Andy S.; Larese, J. Z.

    2013-12-01

    High resolution inelastic neutron scattering (INS) measurements of the low temperature (T ∼ 2.0 K) rotational dynamics of isotopically substituted methane monolayers adsorbed on MgO(1 0 0) are presented. These spectra, obtained using BASIS at SNS, represent the most detailed measurements available for surface-adsorbed monolayer films of methane. Distinct excitations are readily observed at 15, 31, 45 and 127 μeV for the CH2D2 on MgO monolayer and at 40, 51, 95 and 138 μeV for CH3D/MgO. These features are attributed to tunneling transitions between sublevels within the ground librational state and are interpreted using the pocket state (PS) formalism first proposed by Hüller. This theoretical analysis employs the findings of earlier studies of CH4 on MgO(1 0 0) which suggest that molecules adsorb with their C2v axes normal to the surface plane. The comparison between theory and experiment provides direct insight into the impact of molecular versus surface symmetry on the observed tunneling spectra.

  18. Accurate Molecular Dimensions from Stearic Acid Monolayers.

    ERIC Educational Resources Information Center

    Lane, Charles A.; And Others

    1984-01-01

    Discusses modifications in the fatty acid monolayer experiment to reduce the inaccurate moleculary data students usually obtain. Copies of the experimental procedure used and a Pascal computer program to work up the data are available from the authors. (JN)

  19. Surface Charge Transfer Doping of Monolayer Phosphorene via Molecular Adsorption.

    PubMed

    He, Yuanyuan; Xia, Feifei; Shao, Zhibin; Zhao, Jianwei; Jie, Jiansheng

    2015-12-01

    Monolayer phosphorene has attracted much attention owing to its extraordinary electronic, optical, and structural properties. Rationally tuning the electrical transport characteristics of monolayer phosphorene is essential to its applications in electronic and optoelectronic devices. Herein, we study the electronic transport behaviors of monolayer phosphorene with surface charge transfer doping of electrophilic molecules, including 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), NO2, and MoO3, using density functional theory combined with the nonequilibrium Green's function formalism. F4TCNQ shows optimal performance in enhancing the p-type conductance of monolayer phosphorene. Static electronic properties indicate that the enhancement is originated from the charge transfer between adsorbed molecule and phosphorene layer. Dynamic transport behaviors demonstrate that additional channels for hole transport in host monolayer phosphorene were generated upon the adsorption of molecule. Our work unveils the great potential of surface charge transfer doping in tuning the electronic properties of monolayer phosphorene and is of significance to its application in high-performance devices.

  20. Molecular beam epitaxy growth of monolayer niobium diselenide flakes

    NASA Astrophysics Data System (ADS)

    Hotta, Takato; Tokuda, Takuto; Zhao, Sihan; Watanabe, Kenji; Taniguchi, Takashi; Shinohara, Hisanori; Kitaura, Ryo

    2016-09-01

    Monolayer niobium diselenide (NbSe2) is prepared through molecular beam epitaxy with hexagonal boron nitride (hBN) as substrates. Atomic force microscopy and the Raman spectroscopy have shown that the monolayer NbSe2 grown on the hBN possesses triangular or truncated triangular shape whose lateral size amounts up to several hundreds of nanometers. We have found that the precisely controlled supply rate and ultraflat surface of hBN plays an important role in the growth of the monolayer NbSe2.

  1. Shock compression and flash-heating of molecular adsorbates on the picosecond time scale

    NASA Astrophysics Data System (ADS)

    Berg, Christopher Michael

    An ultrafast nonlinear coherent laser spectroscopy termed broadband multiplex vibrational sum-frequency generation (SFG) with nonresonant suppression was employed to monitor vibrational transitions of molecular adsorbates on metallic substrates during laser-driven shock compression and flash-heating. Adsorbates were in the form of well-ordered self-assembled monolayers (SAMs) and included molecular explosive simulants, such as nitroaromatics, and long chain-length alkanethiols. Based on reflectance measurements of the metallic substrates, femtosecond flash-heating pulses were capable of producing large-amplitude temperature jumps with DeltaT = 500 K. Laser-driven shock compression of SAMs produced pressures up to 2 GPa, where 1 GPa ≈ 1 x 104 atm. Shock pressures were estimated via comparison with frequency shifts observed in the monolayer vibrational transitions during hydrostatic pressure measurements in a SiC anvil cell. Molecular dynamics during flash-heating and shock loading were probed with vibrational SFG spectroscopy with picosecond temporal resolution and sub-nanometer spatial resolution. Flash-heating studies of 4-nitrobenzenethiolate (NBT) on Au provided insight into effects from hot-electron excitation of the molecular adsorbates at early pump-probe delay times. At longer delay times, effects from the excitation of SAM lattice modes and lower-energy NBT vibrations were shown. In addition, flash-heating studies of alkanethiolates demonstrated chain disordering behaviors as well as interface thermal conductances across the Au-SAM junction, which was of specific interest within the context of molecular electronics. Shock compression studies of molecular explosive simulants, such as 4-nitrobenzoate (NBA), demonstrated the proficiency of this technique to observe shock-induced molecular dynamics, in this case orientational dynamics, on the picosecond time scale. Results validated the utilization of these refined shock loading techniques to probe the shock

  2. Photoelectric response of purple membrane fragments adsorbed on a lipid monolayer supported by mercury and characterization of the resulting interphase.

    PubMed

    Dolfi, Andrea; Aloisi, Giovanni; Guidelli, Rolando

    2002-09-01

    Purple membrane (PM) fragments were adsorbed on a dioleoylphosphatidylcholine (DOPC) monolayer supported by mercury to investigate the kinetics of light-driven proton transport by bacteriorhodopsin (bR). PM fragments were also adsorbed on a mercury-supported triethyleneoxythiol (TET) monolayer. On both monolayers, the light-on current exhibits a finite, potential dependent stationary component that decreases linearly with a positive shift in the applied potential. The light-on and light-off capacitive photocurrents were interpreted on the basis of a simple equivalent circuit, which accounts for the potential dependence of the stationary light-on current. The potential of zero stationary current is about equal to +0.010 V vs. saturated calomel electrode (SCE) on DOPC-coated mercury. The absolute potential difference across the PM fragments adsorbed at this applied potential was estimated on the basis of extrathermodynamic considerations and amounts to about +260 mV; it compares favorably with the value, +250 mV, of the transmembrane potential of zero stationary current across an oocyte plasma membrane incorporating bR [Biophys. J. 74 (1998) 403.]. The effect of the proton pumping activity of photoexcited PM fragments on the electroreduction kinetics of ubiquinone-10 incorporated in the DOPC monolayer underlying the PM fragments was investigated.

  3. Molecular motion in alkylsilane self-assembled monolayers

    NASA Astrophysics Data System (ADS)

    Stevens, Derrick; Scott, Mary; Guy, Laura; Bochinski, Jason; Clarke, Laura

    2008-03-01

    We have investigated intra-molecular rotation within polar-substituted alkylsilane self-assembled monolayers (SAMs) on fused silica, utilizing surface-sensitive dielectric spectroscopy. Both trichlorosilanes (which allow crosslinking within the SAM) and monochlorosilanes (attached only to the surface) are utilized to grow monolayer and submonolayer films. Dielectric loss spectra as a function of temperature have been obtained for SAMs with varying carbon chain length, surface coverage, and alkyl terminal group. As shown by ellipsometry, contact angle measurements, and AFM, monochlorosilanes form a more disordered monolayer than trichlorosilanes. This more disordered film may result in additional degrees of freedom within the monolayer, or in the language of phase transitions, a rotator phase. Issues such as uncontrolled vertical polymerization and film growth by island formation and their effect on rotational dynamics will be discussed.

  4. Photoinduced Reconfiguration Cycle in a Molecular Adsorbate Layer Studied by Femtosecond Inner-Shell Photoelectron Spectroscopy

    SciTech Connect

    Dachraoui, H.; Michelswirth, M.; Bartz, P.; Pfeiffer, W.; Heinzmann, U.; Siffalovic, P.; Schaefer, C.; Schnatwinkel, B.; Mattay, J.; Drescher, M.

    2011-03-11

    A time-resolved study of core-level chemical shifts in a monolayer of aromatic molecules reveals complex photoinduced reaction dynamics. The combination of electron spectroscopy for chemical analysis and ultrashort pulse excitation in the extreme ultraviolet allows performing time-correlated 4d-core-level spectroscopy of iodine atoms that probe the local chemical environment in the adsorbate molecule. The selectivity of the method unveils metastable molecular configurations that appear about 50 ps after the excitation and are efficiently quenched back to the ground state.

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

    NASA Astrophysics Data System (ADS)

    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.

  6. Synthesis and CO₂ adsorption properties of molecularly imprinted adsorbents.

    PubMed

    Zhao, Yi; Shen, Yanmei; Bai, Lu; Hao, Rongjie; Dong, Liyan

    2012-02-01

    A series of molecularly imprinted adsorbents of CO(2) were developed by molecular self-assembly procedures, using ethanedioic acid, acrylamide, and ethylene glycol dimethacrylate as template, functional monomer, and cross-linker, respectively. Textural properties of these adsorbents were characterized by N(2) adsorption experiment, thermo-gravimetric analysis, and Fourier transform infrared spectroscopy. CO(2) adsorption capacities of adsorbents were investigated by thermo-gravimetric balance under 15% CO(2)/85% Ar atmosphere. Adsorption selectivity of CO(2) was studied by fixed-bed adsorption/desorption experiments. All the adsorbents displayed good thermal stability at 200 °C. Among them, MIP1b, with the higher amine content, exhibited the largest CO(2) capacity, which maintained steady after 50 adsorption-desorption cycles. Although MIP3 showed the highest specific surface, the CO(2) capacity was lower than that of MIP1b. CO(2) adsorption mechanism of molecularly imprinted adsorbents was determined to be physical sorption according to the adsorption enthalpies integrated from the DSC heatflow profiles. The calculated separation factors of CO(2) under 15% CO(2)/85% N(2) atmosphere were above 100 for all adsorbents.

  7. Equilibrium molecular theory of two-dimensional adsorbate drops on surfaces of heterogeneous adsorbents

    NASA Astrophysics Data System (ADS)

    Tovbin, Yu. K.

    2016-08-01

    A molecular statistical theory for calculating the linear tension of small multicomponent droplets in two-dimensional adsorption systems is developed. The theory describes discrete distributions of molecules in space (on a scale comparable to molecular size) and continuous distributions of molecules (at short distances inside cells) in their translational and vibrational motions. Pair intermolecular interaction potentials (the Mie type potential) in several coordination spheres are considered. For simplicity, it is assumed that distinctions in the sizes of mixture components are slight and comparable to the sizes of adsorbent adsorption centers. Expressions for the pressure tensor components inside small droplets on the heterogeneous surface of an adsorbent are obtained, allowing calculations of the thermodynamic characteristics of a vapor-fluid interface, including linear tension. Problems in refining the molecular theory are discussed: describing the properties of small droplets using a coordination model of their structure, considering the effect an adsorbate has on the state of a near-surface adsorbent region, and the surface heterogeneity factor in the conditions for the formation of droplets.

  8. From adsorption to condensation: the role of adsorbed molecular clusters.

    PubMed

    Yaghoubian, Sima; Zandavi, Seyed Hadi; Ward, C A

    2016-08-01

    The adsorption of heptane vapour on a smooth silicon substrate with a lower temperature than the vapour is examined analytically and experimentally. An expression for the amount adsorbed under steady state conditions is derived from the molecular cluster model of the adsorbate that is similar to the one used to derive the equilibrium Zeta adsorption isotherm. The amount adsorbed in each of a series of steady experiments is measured using a UV-vis interferometer, and gives strong support to the amount predicted to be adsorbed. The cluster distribution is used to predict the subcooling temperature required for the adsorbed vapour to make a disorder-order phase transition to become an adsorbed liquid, and the subcooling temperature is found to be 2.7 ± 0.4 K. The continuum approach for predicting the thickness of the adsorbed liquid film originally developed by Nusselt is compared with that measured and is found to over-predict the thickness by three-orders of magnitude. PMID:27426944

  9. Lotus Dust Mitigation Coating and Molecular Adsorber Coating

    NASA Technical Reports Server (NTRS)

    O'Connor, Kenneth M.; Abraham, Nithin S.

    2015-01-01

    NASA Goddard Space Flight Center has developed two unique coating formulations that will keep surfaces clean and sanitary and contain contaminants.The Lotus Dust Mitigation Coating, modeled after the self-cleaning, water-repellant lotus leaf, disallows buildup of dust, dirt, water, and more on surfaces. This coating, has been successfully tested on painted, aluminum, glass, silica, and some composite surfaces, could aid in keeping medical assets clean.The Molecular Adsorber Coating is a zeolite-based, sprayable molecular adsorber coating, designed to prevent outgassing in materials in vacuums. The coating works well to adsorb volatiles and contaminates in manufacturing and processing, such as in pharmaceutical production. The addition of a biocide would also aid in controlling bacteria levels.

  10. Method of recovering adsorbed liquid compounds from molecular sieve columns

    DOEpatents

    Burkholder, Harvey R.; Fanslow, Glenn E.

    1983-01-01

    Molecularly adsorbed volatile liquid compounds are recovered from molecular sieve adsorbent columns by directionally applying microwave energy to the bed of the adsorbent to produce a mixed liquid-gas effluent. The gas portion of the effluent generates pressure within the bed to promote the discharge of the effluent from the column bottoms. Preferably the discharged liquid-gas effluent is collected in two to three separate fractions, the second or intermediate fraction having a substantially higher concentration of the desorbed compound than the first or third fractions. The desorption does not need to be assisted by passing a carrier gas through the bed or by applying reduced pressure to the outlet from the bed.

  11. Method of recovering adsorbed liquid compounds from molecular sieve columns

    DOEpatents

    Burkholder, H.R.; Fanslow, G.E.

    1983-12-20

    Molecularly adsorbed volatile liquid compounds are recovered from molecular sieve adsorbent columns by directionally applying microwave energy to the bed of the adsorbent to produce a mixed liquid-gas effluent. The gas portion of the effluent generates pressure within the bed to promote the discharge of the effluent from the column bottoms. Preferably the discharged liquid-gas effluent is collected in two to three separate fractions, the second or intermediate fraction having a substantially higher concentration of the desorbed compound than the first or third fractions. The desorption does not need to be assisted by passing a carrier gas through the bed or by applying reduced pressure to the outlet from the bed. 8 figs.

  12. Molecular recognition on acoustic wave devices: Sorption in chemically anchored zeolite monolayers

    SciTech Connect

    Yan, Yongan; Bein, T.

    1992-11-12

    Zeolite crystals were attached to the gold electrodes of quartz crystal microbalances (QCM). Monolayers of thiol-alkoxysilanes on the gold surface served as interfacial layers for the subsequent adhesion of the zeolite crystals to the QCM. The process of anchoring the zeolite crystals via the thiol-silane monolayers was studied by reflection adsorption infrared (IR) spectroscopy, contact angle, and scanning electron microscopy (SEM). The siloxane linkages between the microporous zeolite crystals and the terminal cross-linked polysiloxane groups of the interfacial monolayer play an important role in enhancing the packing density of microporous crystals and the thermal stability (up to at least 350 {degrees}C) of the film on the gold surface. Dynamic sorption isotherms of organic vapors and nitrogen as well as the transient sorption behavior of organic vapor pulses were studied to characterize the zeolite-coated QCMs. The resonance frequency response of zeolite-coated QCMs to vapor pulses could be increased up to 500-fold compared to the bare sensor. The regular micropores (0.3-0.75 nm) of the QCM-attached zeolite crystals were found to efficiently control molecular access into the coating. Selectivity of the frequency response in excess of 100:1 toward molecules of different size and/or shape could be demonstrated. The kinetics of vapor desorption from the zeolite layers are strongly dependent on the adsorbate/zeolite combination, thus providing an additional capability for molecular recognition. 33 refs., 11 figs., 2 tabs.

  13. Thermodynamics of the adsorption of organic compounds from the gas phase over a monolayer of liquid crystal formed on the surface of a carbon adsorbent

    NASA Astrophysics Data System (ADS)

    Kopytin, K. A.; Bykov, E. S.; Onuchak, L. A.; Kudryashov, S. Yu.; Kuvshinova, S. A.; Burmistrov, V. A.

    2015-04-01

    Inverse gas-solid chromatography is used to study the adsorption of vapors of organic compounds with different structures and polarities on a carbon adsorbent modified with a monolayer of 4-(3-hydroxypropyloxy)-4'-formylazobenzene (HPOFAB) polar LIQUID crystal. The resulting thermodynamic characteristics of adsorption on the original and modified adsorbents are compared. The effect the nature and structure of adsorbate molecules and the liquid crystal modifier have on the thermodynamic characteristics of adsorption is considered.

  14. Stability and electronic properties of SiC nanowire adsorbed on MoS2 monolayer

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Structural stability and electronic properties of silicon carbide (SiC) nano-wire on MoS2 monolayer are investigated within the framework of density functional theory (DFT). The preferred binding site for the SiC nano-wire is predicted to be hollow site of monolayer. In the electronic band structure the states in valence band near Fermi level are mainly due to nano-wire leading to reduction of band gap relative to monolayer. These results provide a platform for their applications in optoelectronic devices.

  15. Chemically Transformable Configurations of Mercaptohexadecanoic Acid Self-Assembled Monolayers Adsorbed on Au(111)

    SciTech Connect

    van Buuren, T; Bostedt, C; Nelson, A J; Terminello, L J; Vance, A L; Fadley, C S; Willey, T M

    2003-10-21

    Carboxyl terminated Self-Assembled Monolayers (SAMs) are commonly used in a variety of applications, with the assumption that the molecules form well ordered monolayers. In this work, NEXAFS verifies well ordered monolayers can be formed using acetic acid in the solvent. Disordered monolayers with unbound molecules present in the result using only ethanol. A stark reorientation occurs upon deprotonation of the endgroup by rinsing in a KOH solution. This reorientation of the endgroup is reversible with tilted over, hydrogen bound carboxyl groups while carboxylate-ion endgroups are upright. C1s photoemission shows that SAMs formed and rinsed with acetic acid in ethanol, the endgroups are protonated, while without, a large fraction of the molecules on the surface are carboxylate terminated.

  16. Mechanochromism, Shear Force Anisotropy, and Molecular Mechanics in Polydiacetylene Monolayers

    SciTech Connect

    BURNS,ALAN R.; CARPICK,R.W.; SASAKI,DARRYL Y.; SHELNUTT,JOHN A.; HADDAD,R.

    2000-08-14

    The authors use scanning probe microscopy to actuate and characterize the nanoscale mechanochromism of polydiacetylene monolayer on atomically-flat silicon oxide substrates. They find explicit evidence that the irreversible blue-to-red transformation is caused by shear forces exerted normal to the polydiacetylene polymer backbone. The anisotropic probe-induced transformation is characterized by a significant change in the tilt orientation of the side chains with respect to the surface normal. They also describe a new technique, based on shear force microscopy, that allows them to image friction anisotropy of polydiacetylene monolayer independent of scan direction. Finally, they discuss preliminary molecular mechanics modeling and electronic structure calculations that allow them to understand the correlation of mechanochromism with bond-angle changes in the conjugated polymer backbone.

  17. Development of the Molecular Adsorber Coating for Spacecraft and Instrument Interiors

    NASA Technical Reports Server (NTRS)

    Abraham, Nithin

    2011-01-01

    On-orbit Molecular Contamination occurs when materials outgas and deposit onto very sensitive interior surfaces of the spacecraft and instruments. The current solution, Molecular Adsorber Pucks, has disadvantages, which are reviewed. A new innovative solution, Molecular Adsorber Coating (MAC), is currently being formulated, optimized, and tested. It is a sprayable alternative composed of Zeolite-based coating with adsorbing properties.

  18. Incorporation of molecular adsorbers into future Hubble Space Telescope instruments

    NASA Astrophysics Data System (ADS)

    Thomson, Shaun R.; Hansen, Patricia A.; Chen, Philip T.; Triolo, Jack J.; Carosso, Nancy P.

    1996-11-01

    The Hubble Space Telescope (HST) has been designed to accommodate changeout and/or repair of many of the primary instruments and subsystem components, in an effort to prolong the useful life of this orbiting observatory. In order to achieve the science goals established for this observatory, many HST instruments must operate in regimes that are greatly influenced by the presence of on-orbit propagated contaminants. To insure that the required performance of each instrument is not compromised due to these contaminant effects, great efforts have been made to minimize the level of on-orbit contamination. These efforts include careful material selection, performing extensive pre-flight vacuum bakeouts of parts and assemblies, assuring instrument assembly is carried out in strict cleanroom environments, performing precision cleaning of various parts, and most recently, the incorporation of a relatively new technology -- molecular adsorbers -- into the basic design of future replacement instruments. Molecular adsorbers were included as part of the wide field/planetary camera 2 (WFPC-2) instrument, which was integrated into the HST during the servicing mission 1 (SM1) in 1993. It is generally recognized that these adsorbers aided in the reductio of on-orbit contamination levels for the WFPC-2 instrument. This technology is now being implemented as part of the basic design for several new instruments being readied for the servicing mission 2 (SM2), scheduled for early 1997. An overview of the concept, design, applications, and to-date testing and predicted benefits associated with the molecular adsorbers within these new HST instruments are presented and discussed in this paper.

  19. Effective elastic properties of a van der Waals molecular monolayer at a metal surface

    NASA Astrophysics Data System (ADS)

    Sun, Dezheng; Kim, Dae-Ho; Le, Duy; Borck, Øyvind; Berland, Kristian; Kim, Kwangmoo; Lu, Wenhao; Zhu, Yeming; Luo, Miaomiao; Wyrick, Jonathan; Cheng, Zhihai; Einstein, T. L.; Rahman, Talat S.; Hyldgaard, Per; Bartels, Ludwig

    2010-11-01

    Adsorbing anthracene on a Cu(111) surface results in a wide range of complex and intriguing superstructures spanning a coverage range from 1 per 17 to 1 per 15 substrate atoms. In accompanying first-principles density-functional theory calculations we show the essential role of van der Waals interactions in estimating the variation in anthracene adsorption energy and height across the sample. We can thereby evaluate the compression of the anthracene film in terms of continuum elastic properties, which results in an effective Young’s modulus of 1.5 GPa and a Poisson ratio ≈0.1 . These values suggest interpretation of the molecular monolayer as a porous material—in marked congruence with our microscopic observations.

  20. Behavior of lysozyme adsorbed onto biological liquid crystal lipid monolayer at the air/water interface

    NASA Astrophysics Data System (ADS)

    Lu, Xiaolong; Shi, Ruixin; Hao, Changchun; Chen, Huan; Zhang, Lei; Li, Junhua; Xu, Guoqing; Sun, Runguang

    2016-09-01

    The interaction between proteins and lipids is one of the basic problems of modern biochemistry and biophysics. The purpose of this study is to compare the penetration degree of lysozyme into 1,2-diapalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethano-lamine (DPPE) by analyzing the data of surface pressure-area (π-A) isotherms and surface pressure-time (π-T) curves. Lysozyme can penetrate into both DPPC and DPPE monolayers because of the increase of surface pressure at an initial pressure of 15 mN/m. However, the changes of DPPE are larger than DPPC, indicating stronger interaction of lysozyme with DPPE than DPPC. The reason may be due to the different head groups and phase state of DPPC and DPPE monolayers at the surface pressure of 15 mN/m. Atomic force microscopy reveals that lysozyme was absorbed by DPPC and DPPE monolayers, which leads to self-aggregation and self-assembly, forming irregular multimers and conical multimeric. Through analysis, we think that the process of polymer formation is similar to the aggregation mechanism of amyloid fibers. Project supported by the National Natural Science Foundation of China (Grant Nos. 21402114 and 11544009), the Natural Science Basic Research Plan in Shaanxi Province of China (Grant No. 2016JM2010), the Fundamental Research Funds for the Central Universities of China (Grant No. GK201603026), and the National University Science and Technology Innovation Project of China (Grant No. 201610718013).

  1. Graphene symmetry-breaking with molecular adsorbates: modeling and experiment

    NASA Astrophysics Data System (ADS)

    Groce, M. A.; Hawkins, M. K.; Wang, Y. L.; Cullen, W. G.; Einstein, T. L.

    2012-02-01

    Graphene's structure and electronic properties provide a framework for understanding molecule-substrate interactions and developing techniques for band gap engineering. Controlled deposition of molecular adsorbates can create superlattices which break the degeneracy of graphene's two-atom unit cell, opening a band gap. We simulate scanning tunneling microscopy and spectroscopy measurements for a variety of organic molecule/graphene systems, including pyridine, trimesic acid, and isonicotinic acid, based on density functional theory calculations using VASP. We also compare our simulations to ultra-high vacuum STM and STS results.

  2. Molecular switches from benzene derivatives adsorbed on metal surfaces

    PubMed Central

    Liu, Wei; Filimonov, Sergey N.; Carrasco, Javier; Tkatchenko, Alexandre

    2013-01-01

    Transient precursor states are often experimentally observed for molecules adsorbing on surfaces. However, such precursor states are typically rather short-lived, quickly yielding to more stable adsorption configurations. Here we employ first-principles calculations to systematically explore the interaction mechanism for benzene derivatives on metal surfaces, enabling us to selectively tune the stability and the barrier between two metastable adsorption states. In particular, in the case of the tetrachloropyrazine molecule, two equally stable adsorption states are identified with a moderate and conceivably reversible barrier between them. We address the feasibility of experimentally detecting the predicted bistable behaviour and discuss its potential usefulness in a molecular switch. PMID:24157660

  3. pH-dependent conformational changes of diphtheria toxin adsorbed to lipid monolayers by neutron and X-ray reflection

    NASA Astrophysics Data System (ADS)

    Kent, Michael; Yim, Hyun; Satija, Sushil; Kuzmenko, Ivan

    2006-03-01

    Several important bacterial toxins, such as diphtheria, tetanus, and botulinum, invade cells through a process of high affinity binding, internalization via endosome formation, and subsequent membrane penetration of the catalytic domain activated by a pH drop in the endosome. These toxins are composed of three domains: a binding domain, a translocation domain, and an enzyme. The translocation process is not well understood with regard to the detailed conformational changes that occur at each step, To address this, we performed neutron reflectivity measurements for diphtheria toxin bound to lipid monolayers as a function of pH. While the final membrane inserted conformation will not be reproduced with the present monolayer system, important insights can still be gained into several intermediate stages. In particular, we show that no adsorption occurs at pH = 7.6, but strong adsorption occurs over at a pH range from 6.5 to 6.0. Following binding, at least two stages of conformational change occur, as the thickness increases from pH 6.3 to 5.3 and then decreases from pH 5.3 to 4.5. In addition, the dimension of the adsorbed layer substantially exceeds that of the largest dimension in the crystal structure of monomeric diphtheria, suggesting that the toxin may be present as multimers.

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

    SciTech Connect

    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.

  5. Behavior of lysozyme adsorbed onto biological liquid crystal lipid monolayer at the air/water interface

    NASA Astrophysics Data System (ADS)

    Lu, Xiaolong; Shi, Ruixin; Hao, Changchun; Chen, Huan; Zhang, Lei; Li, Junhua; Xu, Guoqing; Sun, Runguang

    2016-09-01

    The interaction between proteins and lipids is one of the basic problems of modern biochemistry and biophysics. The purpose of this study is to compare the penetration degree of lysozyme into 1,2-diapalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethano-lamine (DPPE) by analyzing the data of surface pressure–area (π–A) isotherms and surface pressure–time (π–T) curves. Lysozyme can penetrate into both DPPC and DPPE monolayers because of the increase of surface pressure at an initial pressure of 15 mN/m. However, the changes of DPPE are larger than DPPC, indicating stronger interaction of lysozyme with DPPE than DPPC. The reason may be due to the different head groups and phase state of DPPC and DPPE monolayers at the surface pressure of 15 mN/m. Atomic force microscopy reveals that lysozyme was absorbed by DPPC and DPPE monolayers, which leads to self-aggregation and self-assembly, forming irregular multimers and conical multimeric. Through analysis, we think that the process of polymer formation is similar to the aggregation mechanism of amyloid fibers. Project supported by the National Natural Science Foundation of China (Grant Nos. 21402114 and 11544009), the Natural Science Basic Research Plan in Shaanxi Province of China (Grant No. 2016JM2010), the Fundamental Research Funds for the Central Universities of China (Grant No. GK201603026), and the National University Science and Technology Innovation Project of China (Grant No. 201610718013).

  6. Nonequilibrium Molecular Dynamics Simulations of Organic Friction Modifiers Adsorbed on Iron Oxide Surfaces.

    PubMed

    Ewen, James P; Gattinoni, Chiara; Morgan, Neal; Spikes, Hugh A; Dini, Daniele

    2016-05-10

    For the successful development and application of lubricants, a full understanding of the nanoscale behavior of complex tribological systems is required, but this is difficult to obtain experimentally. In this study, we use nonequilibrium molecular dynamics (NEMD) simulations to examine the atomistic structure and friction properties of commercially relevant organic friction modifier (OFM) monolayers adsorbed on iron oxide surfaces and lubricated by a thin, separating layer of hexadecane. Specifically, acid, amide, and glyceride OFMs, with saturated and Z-unsaturated hydrocarbon tail groups, are simulated at various surface coverages and sliding velocities. At low and medium coverage, the OFMs form liquidlike and amorphous monolayers, respectively, which are significantly interdigitated with the hexadecane lubricant, resulting in relatively high friction coefficients. At high coverage, solidlike monolayers are formed for all of the OFMs, which, during sliding, results in slip planes between well-defined OFM and hexadecane layers, yielding a marked reduction in the friction coefficient. When present at equal surface coverage, OFMs with saturated and Z-unsaturated tail groups are found to yield similar structure and friction behavior. OFMs with glyceride head groups yield significantly lower friction coefficients than amide and particularly carboxylic acid head groups. For all of the OFMs and coverages simulated, the friction coefficient is found to increase linearly with the logarithm of sliding velocity; however, the gradient of this increase depends on the coverage. The structure and friction details obtained from these simulations agree well with experimental results and also shed light on the relative tribological performance of these OFMs through nanoscale structural variations. This has important implications in terms of the applicability of NEMD to aid the development of new formulations to control friction.

  7. Dynamic mechanical properties of a polyelectrolyte adsorbed insoluble lipid monolayer at the air-water interface.

    PubMed

    Park, Chang Young; Kim, Mahn Won

    2015-04-23

    Polymers have been used to stabilize interfaces or to tune the mechanical properties of interfaces in various contexts, such as in oil emulsions or biological membranes. Although the structural properties of these systems are relatively well-studied, instrumental limitations continue to make it difficult to understand how the addition of polymer affects the dynamic mechanical properties of thin and soft films. We have solved this challenge by developing a new instrument, an optical-tweezer-based interface shear microrheometer (ISMR). With this technique, we observed that the interface shear modulus, G*, of a dioctadecyldimethylammonium chloride (DODAC) monolayer at the air-water interface significantly increased with adsorption of polystyrenesulfonate (PSS). In addition, the viscous film (DODAC monolayer) became a viscoelastic film with PSS adsorption. At a low salt concentration, 10 mM of NaCl in the subphase, the viscoelasticity of the DODAC/PSS composite was predominantly determined by a particular property of PSS, that is, it behaves as a Gaussian chain in a θ-solvent. At a high salt concentration, 316 mM of NaCl, the thin film behaved as a polymer melt excluding water molecules. PMID:25826703

  8. Drug-Membrane Interactions Studied in Phospholipid Monolayers Adsorbed on Non-porous Alkylated Microspheres

    PubMed Central

    LUKACOVA, VIERA; PENG, MING; FANUCCI, GAIL; TANDLICH, ROMAN; HINDERLITER, ANNE; MAITY, BIKASH; MANIVANNAN, ETHIRAJAN; COOK, GREGORY R.; BALAZ, STEFAN

    2008-01-01

    Characterization of interactions with phospholipids is an integral part of the in vitro profiling of drug candidates because of the roles the interactions play in tissue accumulation and passive diffusion. Currently used test systems may inadequately emulate the bilayer core solvation properties (immobilized artificial membranes - IAM), suffer from potentially slow transport of some chemicals (liposomes in free or immobilized forms), and require a tedious separation (if used for free liposomes). Here we introduce a well-defined system overcoming these drawbacks: nonporous octadecylsilica particles coated with a self-assembled phospholipid monolayer. The coating mimics the structure of the headgroup region, as well as the thickness and properties of the hydrocarbon core more closely than IAM. The monolayer has a similar transition temperature pattern as the corresponding bilayer. The particles can be separated by filtration or a mild centrifugation. The partitioning equilibria of 81 tested chemicals were dissected into the headgroup and core contributions, the latter using the alkane/water partition coefficients. The deconvolution allowed a successful prediction of the bilayer/water partition coefficients with the standard deviation of 0.26 log units. The plate-friendly assay is suitable for high-throughput profiling of drug candidates without sacrificing the quality of analysis or details of the drug-phospholipid interactions. PMID:17218665

  9. Elastic response of a protein monolayer adsorbed at decorated water surface

    NASA Astrophysics Data System (ADS)

    Singh, Amarjeet; Konovalov, Oleg

    2015-05-01

    Under the in-plane isothermal compression the self-assembled protein monolayer expand in the direction perpendicular to the applied force as a function of applied compression. The structure finally buckle beyond a critical compression, which finally returns to the initial structure when the compression force was removed, behaving like an elastic body. We modelled the layer as homogeneous elastic medium and calculated elastic constants. Young's modulus of the protein layer is 2 orders of magnitude smaller than the bulk lysozyme crystals. It is of fundamental significance to be able to predict the elastic properties of the proteins at air-water interface since protein remains in their natural environment unlike protein crystals.

  10. Oligoethylene-bridged diferrocene on Ag(110): Monolayer structures and adsorbate-induced faceting

    SciTech Connect

    Zhong, D. Y.; Fuchs, H.; Wang, W. C.; Dou, R. F.; Chi, L. F.; Wedeking, K.; Erker, G.

    2007-11-15

    The self-assembly of a ferrocene (Fc) derivative, oligoethylene-bridged diferrocene (diFc), Fc(CH{sub 2}){sub 14}Fc, on Ag(110) surface has been investigated by scanning tunneling microscopy (STM) under ultrahigh vacuum. Three ordered structures, the majority {beta} and the minorities {alpha} and {gamma}, are formed at monolayer coverage. In {alpha} and {gamma}, a unit cell contains one molecule and the molecules are parallel to each other so that the distances between Fc groups and between oligoethylene chains are reduced. A unit cell contains five molecules in {beta}: four of them are parallel to each other but not parallel to the fifth. The interaction between diFc and Ag(110), which is relatively strong in comparison to the intermolecular interaction, is dominant for the assembly of the ordered structures. The adsorption of diFc molecules induces the reorganization of substrate steps, which prefer to follow the directions of the superstructure lattice vectors, i.e. ({+-}1,2) and ({+-}3,2) of the Ag(110) surface. The (12 13-1) facet is formed due to step bunching at regions with high step density. By using in situ STM, the process of step reorganization and faceting has been observed in real time. It is concluded that the Ag adatoms play a key role on the substrate reorganization.

  11. Adsorption of metal adatoms on FeO(111) and MgO(111) monolayers: Effects of charge state of adsorbate on rumpling of supported oxide film

    NASA Astrophysics Data System (ADS)

    Goniakowski, Jacek; Noguera, Claudine; Giordano, Livia; Pacchioni, Gianfranco

    2009-09-01

    We present a theoretical density-functional theory study on the deposition of metal atoms (Ir, Pd, Pt, Ag, and Au) on FeO(111) and MgO(111) monolayers supported on Pt(111). We show the existence of a strong coupling between the charge state of the adsorbed adatom and the local polaroniclike distortion of the oxide film, and we identify two qualitatively different adsorption modes in which the distortion either reinforces the rumpling of the supported oxide film (positively charged adsorbates) or reduces or even reverses the cation-anion stacking (negatively charged adsorbates). Thus, the adsorption mode is a response to the charge state of the adsorbate and is driven mainly by the capacity of adatoms to exchange electrons with the support.

  12. Interlayer correlation between two 4He monolayers adsorbed on both sides of α -graphyne

    NASA Astrophysics Data System (ADS)

    Ahn, Jeonghwan; Park, Sungjin; Lee, Hoonkyung; Kwon, Yongkyung

    2015-07-01

    Path-integral Monte Carlo calculations have been performed to study the 4He adsorption on both sides of a single α -graphyne sheet. For investigation of the interlayer correlation between the upper and the lower monolayers of 4He adatoms, the 4He-substrate interaction is described by the sum of the 4He-C interatomic pair potentials for which we use both Lennard-Jones and Yukawa-6 anisotropic potentials. When the lower 4He layer is a C4 /3 commensurate solid, the upper-layer 4He atoms are found to form a kagome lattice structure at a Mott-insulating density of 0.0706 Å-2 and a commensurate solid at an areal density of 0.0941 Å-2 for both substrate potentials. The correlation between upper- and lower-layer pseudospins, which were introduced in Kwon et al. [Phys. Rev. B 88, 201403(R) (2013)], 10.1103/PhysRevB.88.201403 for two degenerate configurations of three 4He atoms in a hexagonal cell, depends on the substrate potential used; with the substrate potential based on the anisotropic Yukawa-6 pair potentials, the Ising pseudospins of both 4He layers are found to be antiparallel to each other whereas the parallel and antiparallel pseudospin alignments between the two 4He layers are nearly degenerate with the Lennard-Jones potentials. This is attributed to the difference in the interlayer distance, which is ˜4 Å with the Yukawa-6 substrate potential but as large as ˜4.8 Å with the Lennard-Jones potential.

  13. Epitaxial Templating of C60 with a Molecular Monolayer.

    PubMed

    Rochford, L A; Jones, T S; Nielsen, C B

    2016-09-01

    Commensurate epitaxial monolayers of truxenone on Cu (111) were employed to template the growth of monolayer and bilayer C60. Through the combination of STM imaging and LEED analysis we have demonstrated that C60 forms a commensurate 8 × 8 overlayer on truxenone/Cu (111). Bilayers of C60 retain the 8 × 8 periodicity of templated monolayers and although Kagome lattice arrangements are observed these are explained with combinations of 8 × 8 symmetry. PMID:27540868

  14. Gold atom and dimer adsorbed on perfect and defective graphene and boron nitride monolayer: A first-principles study

    NASA Astrophysics Data System (ADS)

    Li, Guihua; Li, Feng; Wang, Xiaopeng; Zhao, Mingwen; Liu, Xiangdong

    2014-05-01

    Energetic and structural properties of gold atom (Au) and gold dimer (Au dimer) adsorbed on pristine and defective graphene (Gra) and boron nitride monolayer (BN) are investigated using density functional theory. Substitutional doping models in the neutral charge state are considered by replacing the C site in graphene with B or N atom impurities (Gra-CB and Gra-CN) or by doping the B or N sites in the BN sheet by a C atom (BN-BC and BN-NC). It is shown that while the binding of Au/Au-dimer to a pristine support is weak, stronger binding could be achieved by introducing a defect in the surface indicating that defects can trap metal atoms. It is found that Gra-CB and BN-NC support Au/Au-dimer well and BN-NC is more preferable from aspect of adsorption energy. Interaction between Au/Au-dimer and the BN-NC substrates is explained by assigning appropriate partial charge densities of the valence band maximum (VBM) and conduction band minimum (CBM) at the Г point and projected densities of states (PDOS). The results demonstrate that both pristine and defective BN surfaces can no longer be treated as inert supports for Au/Au-dimer.

  15. Molecular Factors in Dendritic Cell Responses to Adsorbed Glycoconjugates

    PubMed Central

    Hotaling, Nathan A.; Cummings, Richard D.; Ratner, Daniel M.; Babensee, Julia E.

    2014-01-01

    Carbohydrates and glycoconjugates have been shown to exert pro-inflammatory effects on the dendritic cell (DC), supporting pathogen-induced innate immunity and antigen processing, as well as immunosuppressive effects in the tolerance to self-proteins. Additionally, the innate inflammatory response to implanted biomaterials has been hypothesized to be mediated by inflammatory cells interacting with adsorbed proteins, many of which are glycosylated. However, the molecular factors relevant for surface displayed glycoconjugate modulation of DC phenotype are unknown. Thus, in this study, a model system was developed to establish the role of glycan composition, density, and carrier cationization state on DC response. Thiol modified glycans were covalently bound to a model protein carrier, maleimide functionalized bovine serum albumin (BSA), and the number of glycans per BSA modulated. Additionally, the carrier isoelectric point was scaled from a pI of ~4.0 to ~10.0 using ethylenediamine (EDA). The DC response to the neoglycoconjugates adsorbed to wells of a 384 well plate was determined via a high throughput assay. The underlying trends in DC phenotype in relation to conjugate properties were elucidated via multivariate general linear models. It was found that glycoconjugates with more than 20 glycans per carrier had the greatest impact on the pro-inflammatory response from DCs, followed by conjugates having an isoelectric point above 9.5. Surfaces displaying terminal α1–2 linked mannose structures were able to increase the inflammatory DC response to a greater extent than did any other terminal glycan structure. The results herein can be applied to inform the design of the next generation of combination products and biomaterials for use in future vaccines and implanted materials. PMID:24746228

  16. Modulation of the molecular spintronic properties of adsorbed copper corroles

    PubMed Central

    Wu, Fan; Liu, Jie; Mishra, Puneet; Komeda, Tadahiro; Mack, John; Chang, Yi; Kobayashi, Nagao; Shen, Zhen

    2015-01-01

    The ability to modulate the spin states of adsorbed molecules is in high demand for molecular spintronics applications. Here, we demonstrate that the spin state of a corrole complex can be tuned by expanding its fused ring as a result of the modification to the d–π interaction between the metal and ligand. A bicyclo[2.2.2]octadiene-fused copper corrole can readily be converted into a tetrabenzocorrole radical on an Au(111) substrate during the sublimation process. In the scanning tunnelling spectroscopy spectrum, a sharp Kondo resonance appears near the Fermi level on the corrole ligand of the tetrabenzocorrole molecule. In contrast, a non-fused-ring-expanded copper corrole molecule, copper 5,10,15-triphenylcorrole, shows no such Kondo feature. Mapping of the Kondo resonance demonstrates that the spin distribution of the tetrabenzocorrole molecule can be further modified by the rotation of the meso-aryl groups, in a manner that could lead to applications in molecular spintronics. PMID:26112968

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

    PubMed Central

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

    2012-01-01

    A study of the surface energetics of the thinnest substrate-free liquid films, fluid molecular monolayer and multilayer smectic liquid crystal films suspended in air, is reported. In films having monolayer and multilayer domains, the monolayer areas contract, contrary to predictions from the van der Waals disjoining pressure of thin uniform slabs. This discrepancy is accounted for by modeling the environmental asymmetry of the surface layers in multilayer films, leading to the possibility that preferential end-for-end polar ordering of the rod shaped molecules can reduce the surface energy of multilayers relative to that of the monolayer, which is inherently symmetric. PMID:22826264

  18. Molecular organization of phospholipid monolayers on the water surface by Maxwell displacement current measurement

    NASA Astrophysics Data System (ADS)

    Sulaiman, Khaulah; Majid, Wan Haliza Abdul; Muhamad, Muhamad Rasat

    2006-02-01

    The monolayer of organic molecules at the air-water interface has been studied using the Maxwell displacement current (MDC) technique. The materials used in this study were the biological materials of phosphatidyl ethanolamine (PE) and phosphatidic acids (PA). The configuration of the experimental set-up consists of the metal/air-gap/monolayer/metal coupled with the Langmuir method. This measurement enables the detection of current without destroying the monolayer. The phase transition and molecular orientation of the phospholipid monolayers were investigated using MDC measurement without mechanical contact between electrodes and the materials. Direct evidence of phase transition from gaseous to the polar ordering phase can be obtained across phospholipid monolayers even though at very low surface pressure. Relaxation process of the phospholipid monolayers was investigated by using the step compression on the MDC signals.

  19. Early molecular adsorbents recirculating system treatment of Amanita mushroom poisoning.

    PubMed

    Kantola, Taru; Kantola, Teemu; Koivusalo, Anna-Maria; Höckerstedt, Krister; Isoniemi, Helena

    2009-10-01

    Acute poisoning due to ingestion of hepatotoxic Amanita sp. mushrooms can result in a spectrum of symptoms, from mild gastrointestinal discomfort to life-threatening acute liver failure. With conventional treatment, Amanita phalloides mushroom poisoning carries a substantial risk of mortality and many patients require liver transplantation. The molecular adsorbent recirculating system (MARS) is an artificial liver support system that can partly compensate for the detoxifying function of the liver by removing albumin-bound and water-soluble toxins from blood. This treatment has been used in acute liver failure to enable native liver recovery and as a bridging treatment to liver transplantation. The aim of the study is to evaluate the outcome of 10 patients with Amanita mushroom poisoning who were treated with MARS. The study was a retrospectively analyzed case series. Ten adult patients with accidental Amanita poisoning of varying severity were treated in a liver disease specialized intensive care unit from 2001 to 2007. All patients received MARS treatment and standard medical therapy for mushroom poisoning. The demographic, laboratory, and clinical data from each patient were recorded upon admission. The one-year survival and need for liver transplantation were documented. The median times from mushroom ingestion to first-aid at a local hospital and to MARS treatment were 18 h (range 14-36 h) and 48 h (range 26-78 h), respectively. All 10 patients survived longer than one year. One patient underwent a successful liver transplantation. No serious adverse side-effects were observed with the MARS treatment. In conclusion, MARS treatment seems to offer a safe and effective treatment option in Amanita mushroom poisoning.

  20. Phase behavior of Langmuir monolayers with ionic molecular heads: Molecular simulations

    NASA Astrophysics Data System (ADS)

    González-Castro, Carlos A.; Ramírez-Santiago, Guillermo

    2015-03-01

    We carried out Monte Carlo simulations in the N ,Π,T ensemble of a Langmuir monolayer coarse-grained molecular model. Considering that the hydrophilic groups can be ionized by modulating acid-base interactions, here we study the phase behavior of a model that incorporates the short-range steric and long-range ionic interactions. The simulations were carried out in the reduced temperature range 0.1 ≤T*<4.0 , where there is a competition of these interactions. Different order parameters were calculated and analyzed for several values of the reduced surface pressure in the interval, 1 ≤Π*≤40. For most of the surface pressures two directions of molecular tilt were found: (i) towards the nearest neighbor (NN) at low temperatures, T*<0.7, and most of the values of Π* and (ii) towards next-nearest neighbors (NNN) in the temperature interval 0.7 ≤T*<1.1 for Π*<25. We also found the coexistence of the NN and NNN at intermediate temperatures and Π*>25 . A low-temperature reentrant disorder-order-disorder transition in the positions of the molecular heads and in the collective tilt of the tails was found for all the surface pressure values. It was also found that the molecular tails arranged forming "rotating patterns" in the temperature interval, 0.5 monolayer's surface pressure versus temperature and the temperature versus area per molecule phase diagrams. It was found that the LE ↔LC phase transition shifts to smaller temperatures when the molecular heads carry an ion in qualitative agreement with experimental observations of fatty acid monolayers with ionic head groups. Two surface pressure versus area per molecule isotherms were also calculated. At low temperatures near the LC-NN ↔ LC-NNN transitions and at higher temperatures close to the LE ↔ LC transitions. From these isotherms the monolayer's area compression modulus was obtained and its variation ranges in the LE and LC phases were

  1. Identification of a Novel Parallel β‐Strand Conformation within Molecular Monolayer of Amyloid Peptide

    PubMed Central

    Liu, Lei; Li, Qiang; Zhang, Shuai; Wang, Xiaofeng; Hoffmann, Søren Vrønning; Li, Jingyuan; Liu, Zheng

    2016-01-01

    The differentiation of protein properties and biological functions arises from the variation in the primary and secondary structure. Specifically, in abnormal assemblies of protein, such as amyloid peptide, the secondary structure is closely correlated with the stable ensemble and the cytotoxicity. In this work, the early Aβ33‐42 aggregates forming the molecular monolayer at hydrophobic interface are investigated. The molecular monolayer of amyloid peptide Aβ33‐42 consisting of novel parallel β‐strand‐like structure is further revealed by means of a quantitative nanomechanical spectroscopy technique with force controlled in pico‐Newton range, combining with molecular dynamic simulation. The identified parallel β‐strand‐like structure of molecular monolayer is distinct from the antiparallel β‐strand structure of Aβ33‐42 amyloid fibril. This finding enriches the molecular structures of amyloid peptide aggregation, which could be closely related to the pathogenesis of amyloid disease.

  2. Well-ordered monolayers of alkali-doped coronene and picene: Molecular arrangements and electronic structures

    SciTech Connect

    Yano, M.; Endo, M.; Hasegawa, Y.; Okada, R.; Yamada, Y. Sasaki, M.

    2014-07-21

    Adsorptions of alkali metals (such as K and Li) on monolayers of coronene and picene realize the formation of ordered phases, which serve as well-defined model systems for metal-intercalated aromatic superconductors. Upon alkali-doping of the monolayers of coronene and picene, scanning tunneling microscopy and X-ray absorption spectroscopy revealed the rearrangement of the entire molecular layer. The K-induced reconstruction of both monolayers resulted in the formation of a structure with a herringbone-like arrangement of molecules, suggesting the intercalation of alkali metals between molecular planes. Upon reconstruction, a shift in both the vacuum level and core levels of coronene was observed as a result of a charge transfer from alkali metals to coronene. In addition, a new density of states near the Fermi level was formed in both the doped coronene and the doped picene monolayers. This characteristic electronic feature of the ordered monolayer has been also reported in the multilayer picene films, ensuring that the present monolayer can model the properties of the metal-intercalated aromatic hydrocarbons. It is suggested that the electronic structure near the Fermi level is sensitive to the molecular arrangement, and that both the strict control and determinations of the molecular structure in the doped phase should be important for the determination of the electronic structure of these materials.

  3. Sum-frequency generation from molecular monolayers using 14 {mu}m radiation from the FELIX free-electron laser

    SciTech Connect

    Van der Ham, E.W.M.; Vrehen, Q.H.F.; Eliel, E.R.

    1995-12-31

    Sum-frequency generation (SFG) has developed into a widely applied tool for study of surfaces and interfaces where molecules are present. It combines the surface specificity of a second-order nonlinear optical technique with the power of a spectroscopic method, and it can be used under widely varying experimental conditions ranging from UHV to electrochemical cells. The important characteristic of SFG is that it allows one to study the average spatial orientation of a molecular bond in a monolayer of molecules at an interface. Until recently SFG measurements were confined to the frequency interval Y {mu} > 1700 cm{sup -1} because of a lack of suitable laser sources at wave-lengths {lambda} > 6 {mu}m. So for most molecules only a few vibrational modes and thus intramolecular bonds can be studied. We have developed a universal sum-frequency spectrometer around the FELIX free-electron law that covers the complete molecular fingerprint since we can generate any IR wavelength between 2.75 and 110 f{mu} at the FELIX facility. We have used this setup for a series of exploratory SFG experiments in a frequency range that was hitherto unexplored in the study of molecular monolayers. We have studied thiol monolayers chemisorbed on a variety of noble metals (Au, Ag, Pt) where we focussed on the C-S stretch vibration at {nu} = 702 cm{sup -1} ({lambda} = 14.3 {mu}m). We have found spectroscopic features revealing the presence of both the trane and gauche conformers of the adsorbed molecules. The present measurements open a whole new wavelength range for nonlinear optical studies of interfaces.

  4. Self assembled molecular monolayers on high surface area materials as molecular getters

    DOEpatents

    King, D.E.; Herdt, G.C.; Czanderna, A.W.

    1997-01-07

    The present invention relates to a gettering material that may be used as a filtration medium to remove pollutants from the environment. The gettering material comprises a high surface area material having a metal surface that chemically bonds n-alkanethiols in an organized manner thereby forming a molecular monolayer over the metal surface. The n-alkanethiols have a free functional group that interacts with the environment thereby binding specific pollutants that may be present. The gettering material may be exposed to streams of air in heating, ventilation, and air conditioning systems or streams of water to remove specific pollutants from either medium. 9 figs.

  5. Self assembled molecular monolayers on high surface area materials as molecular getters

    DOEpatents

    King, David E.; Herdt, Gregory C.; Czanderna, Alvin W.

    1997-01-01

    The present invention relates to a gettering material that may be used as a filtration medium to remove pollutants from the environment. The gettering material comprises a high surface area material having a metal surface that chemically bonds n-alkanethiols in an organized manner thereby forming a molecular monolayer over the metal surface. The n-alkanethiols have a free functional group that interacts with the environment thereby binding specific pollutants that may be present. The gettering material may be exposed to streams of air in heating, ventilation, and air conditioning systems or streams of water to remove specific pollutants from either medium.

  6. Electronic and magnetic properties of perfect, vacancy-doped, and nonmetal adsorbed MoSe2, MoTe2 and WS2 monolayers.

    PubMed

    Ma, Yandong; Dai, Ying; Guo, Meng; Niu, Chengwang; Lu, Jibao; Huang, Baibiao

    2011-09-14

    Very recently, two-dimensional nanosheets of MoSe(2), MoTe(2) and WS(2) were successfully synthesized experimentally [Science, 2011, 331, 568]. In the present work, the electronic and magnetic properties of perfect, vacancy-doped, and nonmetal element (H, B, C, N, O, and F) adsorbed MoSe(2), MoTe(2) and WS(2) monolayers are systematically investigated by means of first-principles calculations to give a detailed understanding of these materials. It is found that: (1) MoSe(2), MoTe(2) and WS(2) exhibit surprising confinement-induced indirect-direct-gap crossover; (2) among all the neutral native vacancies of MoSe(2), MoTe(2) and WS(2) monolayers, only the Mo vacancy in MoSe(2) can induce spin-polarization and long-range antiferromagnetic coupling; (3) adsorption of nonmetal elements on the surface of MoSe(2), MoTe(2) and WS(2) nanosheets can induce a local magnetic moment; H-absorbed WS(2), MoSe(2), and MoTe(2) monolayers and F-adsorbed WS(2) and MoSe(2) monolayers show long-range antiferromagnetic coupling between local moments even when their distance is as long as ∼12 Å. These findings are a useful addition to the experimental studies of these new synthesized two-dimensional nanosheets, and suggest a new route to facilitate the design of spintronic devices for complementing graphene. Further experimental studies are expected to confirm the attractive predictions. PMID:21808797

  7. Electronic and magnetic properties of perfect, vacancy-doped, and nonmetal adsorbed MoSe2, MoTe2 and WS2 monolayers.

    PubMed

    Ma, Yandong; Dai, Ying; Guo, Meng; Niu, Chengwang; Lu, Jibao; Huang, Baibiao

    2011-09-14

    Very recently, two-dimensional nanosheets of MoSe(2), MoTe(2) and WS(2) were successfully synthesized experimentally [Science, 2011, 331, 568]. In the present work, the electronic and magnetic properties of perfect, vacancy-doped, and nonmetal element (H, B, C, N, O, and F) adsorbed MoSe(2), MoTe(2) and WS(2) monolayers are systematically investigated by means of first-principles calculations to give a detailed understanding of these materials. It is found that: (1) MoSe(2), MoTe(2) and WS(2) exhibit surprising confinement-induced indirect-direct-gap crossover; (2) among all the neutral native vacancies of MoSe(2), MoTe(2) and WS(2) monolayers, only the Mo vacancy in MoSe(2) can induce spin-polarization and long-range antiferromagnetic coupling; (3) adsorption of nonmetal elements on the surface of MoSe(2), MoTe(2) and WS(2) nanosheets can induce a local magnetic moment; H-absorbed WS(2), MoSe(2), and MoTe(2) monolayers and F-adsorbed WS(2) and MoSe(2) monolayers show long-range antiferromagnetic coupling between local moments even when their distance is as long as ∼12 Å. These findings are a useful addition to the experimental studies of these new synthesized two-dimensional nanosheets, and suggest a new route to facilitate the design of spintronic devices for complementing graphene. Further experimental studies are expected to confirm the attractive predictions.

  8. Stability and electronic properties of SiC nanowire adsorbed on MoS{sub 2} monolayer

    SciTech Connect

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

    2015-06-24

    Structural stability and electronic properties of silicon carbide (SiC) nano-wire on MoS{sub 2} monolayer are investigated within the framework of density functional theory (DFT). The preferred binding site for the SiC nano-wire is predicted to be hollow site of monolayer. In the electronic band structure the states in valence band near Fermi level are mainly due to nano-wire leading to reduction of band gap relative to monolayer. These results provide a platform for their applications in optoelectronic devices.

  9. The Wide Field/Planetary Camera 2 (WFPC-2) molecular adsorber

    NASA Technical Reports Server (NTRS)

    Barengoltz, Jack; Moore, Sonya; Soules, David; Voecks, Gerald

    1995-01-01

    A device has been developed at the Jet Propulsion Laboratory, California Institute of Technology, for the adsorption of contaminants inside a space instrument during flight. The molecular adsorber was developed for use on the Wide Field Planetary Camera 2, and it has been shown to perform at its design specifications in the WFPC-2. The basic principle of the molecular adsorber is a zeolite-coated ceramic honeycomb. The arrangement is efficient for adsorption and also provides the needed rigidity to retain the special zeolite coating during the launch vibrational environment. The adsorber, on other forms, is expected to be useful for all flight instruments sensitive to internal sources of contamination. Typically, some internal contamination is unavoidable. A common design solution is to increase the venting to the exterior. However, for truly sensitive instruments, the external contamination environment is more severe. The molecular adsorber acts as a one-way vent to solve this problem. Continued development is planned for this device.

  10. Molecular Packing of Functionalized Fluorinated Lipids in Langmuir Monolayers

    SciTech Connect

    Landsberg, Michael J.; Ruggles, Jeremy L.; Hussein, Waleed M.; McGeary, Ross P.; Gentle, Ian R.; Hankamer, Ben

    2012-01-20

    Fluorinated amphipaths are a fascinating class of compounds, which, despite significant challenges associated with their syntheses, have found use across a number of areas of biotechnology. Applications range from the in vitro stabilization of membrane proteins to the development of enhanced stability intravenous drug and gene delivery systems. More recently, monolayer-forming fluorinated lipids have found use in the 2D crystallization of detergent-solubilized hydrophobic or partially hydrophobic proteins at the air-water interface. In this study, we investigate the surface properties of a novel suite of monolayer forming, partially fluorinated lipids. These modular lipid structures contain a densely fluorinated insertion in the hydrocarbon tail and a synthetically modifiable headgroup. Analyses of surface-pressure area isotherms and X-ray reflectometry profiles reveal that the lipids spread into fluid monolayers and are more compressible than their non-fluorinated counterparts. Furthermore, the data support a model whereby the partially fluorinated chains of the lipid tails form a film which is fundamentally incompatible with detergents and other destabilizing amphipaths.

  11. Electronic and transport properties of azobenzene monolayer junctions as molecular switches

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Cheng, Hai-Ping

    2012-07-01

    We investigate from first principles the change in transport properties of a two-dimensional azobenzene monolayer sandwiched between two Au electrodes that undergoes molecular switching. We focus on transport differences between a chemisorbed and physisorbed top monolayer-electrode contact. The conductance of the monolayer junction with a chemisorbed top contact is higher in the trans configuration, in agreement with the previous theoretical predictions of one-dimensional single-molecule junctions. However, with a physisorbed top contact, the ON state, with larger conductance, is associated with the cis configuration due to a reduced effective tunneling pathway, which successfully explains recent experimental measurements on azobenzene monolayer junctions. A simple model is developed to explain electron transmission across subsystems in the molecular junction. We also discuss the effects of monolayer packing density, molecule tilt angle, and contact geometry on the calculated transmission functions. In particular, we find that a tip-like contact with chemisorption significantly affects the electric current through the cis monolayer, leading to highly asymmetric current-voltage characteristics as well as large negative differential resistance behavior.

  12. A molecular dynamics study of the packing structures in monolayers of partially fluorinated amphiphiles

    NASA Astrophysics Data System (ADS)

    Shin, Seokmin; Collazo, Nancy; Rice, Stuart A.

    1992-01-01

    We report the results of molecular dynamics simulations of liquid-supported monolayers of three partially fluorinated amphiphile molecules, namely CF3(CF2)9CH2COOH, CF3(CF2)6CH2(CF2)3COOH, and CF3(CF2)6(CH2)4COOH. These studies were undertaken to provide information on the interplay between molecular flexibility and the packing structure in a monolayer so as to better interpret the results of recent experiments. The qualitative aspects of the predictions of the simulations are consistent with the recent experimental data for monolayers of CF3(CF2)9CH2COOH [S. W. Barton, A. Goudot, O. Boulassa, F. Rondelez, B. Lin, F. Novak, A. Acero, and S. A. Rice, J. Chem. Phys. 96, xxx (1992)]. In particular, the observed breakup of the homogeneous ordered monolayer into ordered islands with the same collective tilt of the molecules is correctly predicted, and the fact that the collective tilt angle is small is correctly predicted. However, the experimental and theoretical values of the tilt angles are not in quantitative agreement, which we attribute to the inadequacy of the atom-atom potentials used in the simulations. In general, for monolayers of CF3(CF2)9CH2COOH we find that the collective tilt angle predicted is a sensitive function of the area per molecule and is smaller than in monolayers of alkane alcohols and alkane acids. The results of the simulations of monolayers of other partially fluorinated species suggest that the difference in size between the fluorocarbon segments and the smaller head groups or flexible ``spacer'' CH2 segments can generate subtle changes in the packing structure of a monolayer and the relative stabilities of the untilted and tilted structures.

  13. Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers.

    PubMed

    Giner-Casares, Juan J; Pérez-Morales, Marta; Bolink, Henk J; Muñoz, Eulogia; de Miguel, Gustavo; Martín-Romero, María T; Camacho, Luis

    2007-11-01

    In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)(2)(tmphen)]PF(6), (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air-water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as pi-A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. BAM images reveal a whole homogeneous monolayer, with gradually increasing reflectivity along the compression process up to reaching the collapse of this equimolecular monolayer at pi approximately equal to 37 mNm(-1). Increasing the molar ratio of DMPA in the mixture, the excess of lipid molecules organizes themselves forming dark flower-like domains of pure DMPA at high surface pressures, coexisting with the mixed Ir-dye/DMPA = 1:1 monolayer. On the other hand, unstable mixed monolayers are obtained by using an initial dye surface concentration higher than the equimolecular one. These mixed Langmuir monolayers have been successfully transferred onto solid substrates by the LB (Langmuir-Blodgett) technique. PMID:17618641

  14. Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers.

    PubMed

    Giner-Casares, Juan J; Pérez-Morales, Marta; Bolink, Henk J; Muñoz, Eulogia; de Miguel, Gustavo; Martín-Romero, María T; Camacho, Luis

    2007-11-01

    In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)(2)(tmphen)]PF(6), (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air-water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as pi-A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. BAM images reveal a whole homogeneous monolayer, with gradually increasing reflectivity along the compression process up to reaching the collapse of this equimolecular monolayer at pi approximately equal to 37 mNm(-1). Increasing the molar ratio of DMPA in the mixture, the excess of lipid molecules organizes themselves forming dark flower-like domains of pure DMPA at high surface pressures, coexisting with the mixed Ir-dye/DMPA = 1:1 monolayer. On the other hand, unstable mixed monolayers are obtained by using an initial dye surface concentration higher than the equimolecular one. These mixed Langmuir monolayers have been successfully transferred onto solid substrates by the LB (Langmuir-Blodgett) technique.

  15. Smart Adsorbents with Photoregulated Molecular Gates for Both Selective Adsorption and Efficient Regeneration.

    PubMed

    Cheng, Lei; Jiang, Yao; Yan, Ni; Shan, Shu-Feng; Liu, Xiao-Qin; Sun, Lin-Bing

    2016-09-01

    Selective adsorption and efficient regeneration are two crucial issues for adsorption processes; unfortunately, only one of them instead of both is favored by traditional adsorbents with fixed pore orifices. Herein, we fabricated a new generation of smart adsorbents through grafting photoresponsive molecules, namely, 4-(3-triethoxysilylpropyl-ureido)azobenzene (AB-TPI), onto pore orifices of the support mesoporous silica. The azobenzene (AB) derivatives serve as the molecular gates of mesopores and are reversibly opened and closed upon light irradiation. Irradiation with visible light (450 nm) causes AB molecules to isomerize from cis to trans configuration, and the molecular gates are closed. It is easy for smaller adsorbates to enter while difficult for the larger ones, and the selective adsorption is consequently facilitated. Upon irradiation with UV light (365 nm), the AB molecules are transformed from trans to cis isomers, promoting the desorption of adsorbates due to the opened molecular gates. The present smart adsorbents can consequently benefit not only selective adsorption but also efficient desorption, which are exceedingly desirable for adsorptive separation but impossible for traditional adsorbents with fixed pore orifices. PMID:27559985

  16. Thermal stability and molecular ordering of organic semiconductor monolayers: effect of an anchor group.

    PubMed

    Jones, Andrew O F; Knauer, Philipp; Resel, Roland; Ringk, Andreas; Strohriegl, Peter; Werzer, Oliver; Sferrazza, Michele

    2015-06-01

    The thermal stability and molecular order in monolayers of two organic semiconductors, PBI-PA and PBI-alkyl, based on perylene derivatives with an identical molecular structure except for an anchor group for attachment to the substrate in PBI-PA, are reported. In situ X-ray reflectivity measurements are used to follow the stability of these monolayers in terms of order and thickness as temperature is increased. Films have thicknesses corresponding approximately to the length of one molecule; molecules stand upright on the substrate with a defined structure. PBI-PA monolayers have a high degree of order at room temperature and a stable film exists up to 250 °C, but decomposes rapidly above 300 °C. In contrast, stable physisorbed PBI-alkyl monolayers only exist up to 100 °C. Above the bulk melting point at 200 °C no more order exists. The results encourage using anchor groups in monolayers for various applications as it allows enhanced stability at the interface with the substrate.

  17. Molecular Dynamics Simulation Study of Two-Dimensional Diffusion Behavior in Smectic Liquid Crystalline Monolayers

    NASA Astrophysics Data System (ADS)

    Watanabe, Go; Saito, Jun-ichi; Fujita, Yusuke; Tabe, Yuka

    2013-08-01

    We have carried out molecular dynamics (MD) simulations for monolayers of smectic A and C liquid crystal (LC) phases in order to investigate the in-plane molecular diffusion from the microscopic point of view. In contrast to similar complex two-dimensional systems (e.g., biomembranes) whose molecular diffusion is anomalous, in-plane mean square displacements (MSDs) for both phases increase linearly with passing time similar to typical fluids on the nanosecond time scale. By following the relation between the diffusion and the viscosity in the fluids, we estimated the viscosity coefficients for both LC monolayers, and the obtained values indicate that the smectic A monolayer has a higher viscosity than the smectic C one. Moreover, we investigate the in-plane self-diffusion anisotropy D\\|/D\\bot for smectic C and found that the diffusion parallel to the molecular tilt is 1.5 times larger than that in the perpendicular direction. This anisotropic diffusion property in the smectic C monolayer has not been clearly confirmed thus far.

  18. Molecular organization in phospholipid monolayer domains by correlative fluorescence microscopy and electron diffraction.

    PubMed

    Hui, S W; Yu, H

    1994-04-01

    Lipid monolayer is a half leaflet model for lipid bilayer, which forms the basis of biological membranes. Within a certain range of surface area per molecular of phospholipid monolayers at the air-water interface, where the compressibility was nearly infinite, two phases with different molecular packings were observable by fluorescence microscopy. Mixed-phase monolayers of L-1,2-dipalmitoyl-N-monomethyl-3-phosphatidylethanolamine [DP(Me)PE] or L-1,2-dipalmitoyl-N-dimethyl-3-phosphatidyl-ethanolamine [DP(Me)2PE] were deposited on marker grids coated with Formvar films. The molecular organization in the dark and bright fluorescent areas on the grids was investigated by low dose, selected area electron diffraction. Sharp reflection arcs, at a spacing of 4.2A and arranged in a hexagon pattern, were detected from dark domains of both lipids. A diffuse reflection ring at a spacing of 4.6A was derived from the bright background areas. Diffraction patterns were obtained from neighboring areas along selected dark domains of both lipids. The orientations of diffraction patterns from areas along smooth and curving boundaries of DP(Me)2PE domains were found to turn with the boundaries. In the branching domains of DP(Me)PE, the orientations of diffraction patterns indicated that the branches were formed by twinning. Electron diffraction thus provides an unique way to sample the local molecular packing order and orientation within individual domains in phospholipid monolayers.

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

    SciTech Connect

    Taub, H.; Hansen, F.Y.; Diama, Amand; Matthies, Blake; Criswell, Leah; Mo, Haiding; Bai, M; Herwig, Kenneth 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-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.

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

    PubMed

    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.

  1. Facile preparation of surface-exchangeable core@shell iron oxide@gold nanoparticles for magnetic solid-phase extraction: use of gold shell as the intermediate platform for versatile adsorbents with varying self-assembled monolayers.

    PubMed

    Li, Yaping; Qi, Li; Shen, Ying; Ma, Huimin

    2014-02-01

    The core@shell Fe3O4@Au nanoparticles (NPs) functionalized with exchangeable self-assembled monolayers have been developed for mode switching magnetic solid-phase extraction (MSPE) using high performance liquid chromatography with ultraviolet detection. The adsorbents were synthesized by chemical coprecipitation to prepare magnetic cores followed by sonolysis to produce gold shells. Functionalization of Fe3O4@Au NPs surface was realized through self-assembly of commercially available low molecular weight thiol-containing ligands using gold shells as intermediate platform and the dynamic nature of Au-S chemistry allowed substituent of one thiol-containing ligand with another simply by thiol exchange process. The resultant adsorbents were characterized by transmission electronic microscopy, Fourier transform infrared spectroscopy, elemental analysis, contact angle measurement, and vibrating sample magnetometry. To evaluate the versatile performance of the developed MSPE adsorbents, they were applied for normal-phase SPE followed by reversed-phase SPE. A few kinds of diphenols and polycyclic aromatic hydrocarbons (PAHs) were employed as model analytes, respectively. The predominant parameters affecting extraction efficiency were investigated and optimized. Under the optimum experimental conditions, wide dynamic linear range (6.25-1600 μg L(-1) for diphenols and 1.56-100 μg L(-1) for PAHs) with good linearity (r(2)≥0.989) and low detection limits (0.34-16.67 μg L(-1) for diphenols and 0.26-0.52 μg L(-1) for PAHs) were achieved. The advantage of the developed method is that the Fe3O4@Au NPs could be reutilized for preconcentrating diverse target analytes in different SPE modes sequentially simply through treatment with desired thiol-containing ligands.

  2. Water and Molecular Transport across Nanopores in Monolayer Graphene Membranes

    NASA Astrophysics Data System (ADS)

    Jang, Doojoon; O'Hern, Sean; Kidambi, Piran; Boutilier, Michael; Song, Yi; Idrobo, Juan-Carlos; Kong, Jing; Laoui, Tahar; Karnik, Rohit

    2015-11-01

    Graphene's atomic thickness and high tensile strength allow it to outstand as backbone material for next-generation high flux separation membrane. Molecular dynamics simulations predicted that a single-layer graphene membrane could exhibit high permeability and selectivity for water over ions/molecules, qualifying as novel water desalination membranes. However, experimental investigation of water and molecular transport across graphene nanopores had remained barely explored due to the presence of intrinsic defects and tears in graphene. We introduce two-step methods to seal leakage across centimeter scale single-layer graphene membranes create sub-nanometer pores using ion irradiation and oxidative etching. Pore creation parameters were varied to explore the effects of created pore structures on water and molecular transport driven by forward osmosis. The results demonstrate the potential of nanoporous graphene as a reliable platform for high flux nanofiltration membranes.

  3. Molecular recognition using nanotube-adsorbed polymer phases: nanotube antibodies

    PubMed Central

    Zhang, Jingqing; Landry, Markita P.; Barone, Paul W.; Kim, Jong-Ho; Lin, Shangchao; Ulissi, Zachary W.; Lin, Dahua; Mu, Bin; Heller, Daniel A.; Boghossian, Ardemis A.; Hilmer, Andrew J.; Rwei, Alina; Hinckley, Allison C.; Kruss, Sebastian; Shandell, Mia A.; Nair, Nitish; Blake, Steven; Sen, Fatih; Sen, Selda; Croy, Robert G.; Li, Deyu; Yum, Kyungsuk; Ahn, Jin-Ho; Jin, Hong; Essigmann, John M.; Blankschtein, Daniel; Strano, Michael S.

    2016-01-01

    Molecular recognition is central to the design of therapeutics, chemical catalysis and sensors. Motifs for doing so most commonly involve biological structures such as antibodies and aptamers. The key to such biological recognition consists of a folded and constrained heteropolymer that, via intra-molecular forces, forms a unique three dimensional structure that creates a binding pocket or an interface able to recognize a specific molecule. In this work, we demonstrate that synthetic heteropolymers can be alternatively constrained by adsorption around a nanoparticle, and specifically a single walled carbon nanotube (SWNT), forming a corona phase and resulting in a new form of molecular recognition of specific molecules. The phenomenon is shown to be generic, with new heteropolymer recognition complexes demonstrated for three distinct examples: Riboflavin, l-thyroxine, and estradiol, each predicted using a 2D thermodynamic model of surface interactions. The dissociation constants are continuously tunable by perturbing the chemical structure of the heteropolymer. Moreover, these complexes can be used as new types of spatial-temporal sensors based on modulation of SWNT photoemission in the near-infrared, as we show by tracking riboflavin diffusion in murine macrophages. PMID:24270641

  4. Unveiling self-assembled monolayers' potential for molecular spintronics: spin transport at high voltage.

    PubMed

    Galbiati, Marta; Barraud, Clément; Tatay, Sergio; Bouzehouane, Karim; Deranlot, Cyrile; Jacquet, Eric; Fert, Albert; Seneor, Pierre; Mattana, Richard; Petroff, Frédéric

    2012-12-18

    Molecular magnetic tunnel junctions using self-assembled monolayers (SAMs) as tunnel barriers show stable and efficient spin transport properties. Large tunnel magnetoresistance with a flat bias voltage dependence of the magnetoresistance is observed in La(2/3) Sr(1/3) MnO(3) /dodecylphosphonic acid SAM/Co nanocontacts. This opens the door to spintronic tailoring though SAM engineering and could also lead to new venues for spin injection in organic devices.

  5. Enzymatic degradation of monolayer for poly(lactide) revealed by real-time atomic force microscopy: effects of stereochemical structure, molecular weight, and molecular branches on hydrolysis rates.

    PubMed

    Numata, Keiji; Finne-Wistrand, Anna; Albertsson, Ann-Christine; Doi, Yoshiharu; Abe, Hideki

    2008-08-01

    The influences of the stereochemical structure, the molecular weight, and the number of molecular branches for poly(lactide) (PLA) on enzymatic hydrolysis rates of PLA monolayers were studied by atomic force microscopy (AFM) and the Langmuir-Blodgett (LB) technique. Monolayers of six kinds of PLA with different molecular weights, stereochemical structure, and numbers of molecular branches were prepared by LB techniques and then characterized by AFM in air. The PLA molecules covered homogeneously with a silicon substrate and did not form lamellar crystals in the monolayer. We determined the initial hydrolysis rate of PLA monolayers in presence of proteinase K by volumetric analysis from the continuous AFM height images. The presence of D-lactyl unit reduced the hydrolysis rate of the monolayer. The hydrolysis rate for the linear PLLA samples increased with a decrease in the molecular weight. In contrast, the rates of erosion for branched PLLA monolayers were independent of the molecular weight of samples. The erosion rate of branched PLLA monolayers was found to be dependent on the average molecular weight of PLLA segment in branched molecules, not on the overall molecular weight of samples. From these results, furthermore, the hydrolysis mode of PLAs by proteinase K is discussed.

  6. Scanning Tunneling Microscopy and Spectroscopy of Air Exposure Effects on Molecular Beam Epitaxy Grown WSe2 Monolayers and Bilayers.

    PubMed

    Park, Jun Hong; Vishwanath, Suresh; Liu, Xinyu; Zhou, Huawei; Eichfeld, Sarah M; Fullerton-Shirey, Susan K; Robinson, Joshua A; Feenstra, Randall M; Furdyna, Jacek; Jena, Debdeep; Xing, Huili Grace; Kummel, Andrew C

    2016-04-26

    The effect of air exposure on 2H-WSe2/HOPG is determined via scanning tunneling microscopy (STM). WSe2 was grown by molecular beam epitaxy on highly oriented pyrolytic graphite (HOPG), and afterward, a Se adlayer was deposited in situ on WSe2/HOPG to prevent unintentional oxidation during transferring from the growth chamber to the STM chamber. After annealing at 773 K to remove the Se adlayer, STM images show that WSe2 layers nucleate at both step edges and terraces of the HOPG. Exposure to air for 1 week and 9 weeks caused air-induced adsorbates to be deposited on the WSe2 surface; however, the band gap of the terraces remained unaffected and nearly identical to those on decapped WSe2. The air-induced adsorbates can be removed by annealing at 523 K. In contrast to WSe2 terraces, air exposure caused the edges of the WSe2 to oxidize and form protrusions, resulting in a larger band gap in the scanning tunneling spectra compared to the terraces of air-exposed WSe2 monolayers. The preferential oxidation at the WSe2 edges compared to the terraces is likely the result of dangling edge bonds. In the absence of air exposure, the dangling edge bonds had a smaller band gap compared to the terraces and a shift of about 0.73 eV in the Fermi level toward the valence band. However, after air exposure, the band gap of the oxidized WSe2 edges became about 1.08 eV larger than that of the WSe2 terraces, resulting in the electronic passivation of the WSe2.

  7. David Adler Lectureship Award Talk: Friction and energy dissipation mechanisms in adsorbed molecules and molecularly thin films

    NASA Astrophysics Data System (ADS)

    Krim, Jacqueline

    2015-03-01

    Studies of the fundamental origins of friction have undergone rapid progress in recent years, with the development of new experimental and computational techniques for measuring and simulating friction at atomic length and time scales. The increased interest has sparked a variety of discussions and debates concerning the nature of the atomic-scale and quantum mechanisms that dominate the dissipative process by which mechanical energy is transformed into heat. Measurements of the sliding friction of physisorbed monolayers and bilayers can provide information on the relative contributions of these various dissipative mechanisms. Adsorbed films, whether intentionally applied or present as trace levels of physisorbed contaminants, moreover are ubiquitous at virtually all surfaces. As such, they impact a wide range of applications whose progress depends on precise control and/or knowledge of surface diffusion processes. Examples include nanoscale assembly, directed transport of Brownian particles, material flow through restricted geometries such as graphene membranes and molecular sieves, passivation and edge effects in carbon-based lubricants, and the stability of granular materials associated with frictional and frictionless contacts. Work supported by NSFDMR1310456.

  8. Molecular scale energy dissipation in oligothiophene monolayers measured by dynamic force microscopy.

    PubMed

    Martínez, Nicolas F; Kamiński, Wojciech; Gómez, Carlos J; Albonetti, Cristiano; Biscarini, Fabio; Pérez, Rubén; García, Ricardo

    2009-10-28

    We perform a combined experimental and theoretical approach to establish the atomistic origin of energy dissipation occurring while imaging a molecular surface with an amplitude modulation atomic force microscope. We show that the energy transferred by a single nano-asperity to a sexithiophene monolayer is about 0.15 eV/cycle. The configuration space sampled by the tip depends on whether it approaches or withdraws from the surface. The asymmetry arises because of the presence of energy barriers among different deformations of the molecular geometry. This is the source of the material contrast provided by the phase-shift images. PMID:19801766

  9. Molecular scale energy dissipation in oligothiophene monolayers measured by dynamic force microscopy.

    PubMed

    Martínez, Nicolas F; Kamiński, Wojciech; Gómez, Carlos J; Albonetti, Cristiano; Biscarini, Fabio; Pérez, Rubén; García, Ricardo

    2009-10-28

    We perform a combined experimental and theoretical approach to establish the atomistic origin of energy dissipation occurring while imaging a molecular surface with an amplitude modulation atomic force microscope. We show that the energy transferred by a single nano-asperity to a sexithiophene monolayer is about 0.15 eV/cycle. The configuration space sampled by the tip depends on whether it approaches or withdraws from the surface. The asymmetry arises because of the presence of energy barriers among different deformations of the molecular geometry. This is the source of the material contrast provided by the phase-shift images.

  10. Molecular dynamics study of C-C bond ordering in diacylglycerolipid monolayers

    NASA Astrophysics Data System (ADS)

    Rabinovich, Alexander L.; Ripatti, Pauli O.; Balabaev, Nikolay K.

    2000-02-01

    Molecular dynamics investigation of diacyldlycerolipid (DG) monolayers was carried out. Each lipid molecule contained stearic fatty acid chain (C18:0) in position 3-D and one of the fatty acid chains C18:0, C18:1(omega 9), C18:2(omega 6), C18:3(omega 3), C20:4(omega 6) or C22:6(omega 3) in position 2-D [for the nomenclature see M. Sundaralingam, Ann. N.Y. Acad. Sci. U.S.A., 195, 324 - 355 (1972)]. A polar head group of the lipid molecules was treated as an effective sphere. 1.5 nanosecond simulations were performed at temperature 303 K for monolayers 18:0/18:1(omega) 9cis DG, 18:0/18:2(omega) 6cis DG, 18:0/18:3(omega) 3cis DG, 18:0/20:4(omega) 6cis DG, 18:0/22:6(omega) 3cis DG and at T equals 326 K for 18:0/18:0 DG monolayer. The monolayers consisted of 48 glycerolipids of the same type arranged in a rectangular simulation cell. The average areas per lipid molecule over the simulations were 65.6 Angstrom2 in 18:0/18:0 DG monolayer, 66.2 Angstrom2 in 18:0/18:1(omega) 9cis DG, 66.1 angstrom2 in 18:0/18:2(omega) 6cis DG, 67.4 angstrom2 in 18:0/18:3(omega) 3cis DG, 70.6 angstrom2 in 18:0/20:4(omega) 6cis DG and 71.4 Angstrom2 in 18:0/22:6(omega) 3cis DG monolayer. The C-C bond orientation distributions and C-C bond order parameter profiles about the monolayer normals were calculated. The C-C bond orientation distribution function widths turned out to be depended on both bond location in the chain and chemical structure of the segment.

  11. Molecular dynamics study of C-C bond ordering in diacylglycerolipid monolayers

    NASA Astrophysics Data System (ADS)

    Rabinovich, Alexander L.; Ripatti, Pauli O.; Balabaev, Nikolay K.

    2001-02-01

    Molecular dynamics investigation of diacyldlycerolipid (DG) monolayers was carried out. Each lipid molecule contained stearic fatty acid chain (C18:0) in position 3-D and one of the fatty acid chains C18:0, C18:1(omega 9), C18:2(omega 6), C18:3(omega 3), C20:4(omega 6) or C22:6(omega 3) in position 2-D [for the nomenclature see M. Sundaralingam, Ann. N.Y. Acad. Sci. U.S.A., 195, 324 - 355 (1972)]. A polar head group of the lipid molecules was treated as an effective sphere. 1.5 nanosecond simulations were performed at temperature 303 K for monolayers 18:0/18:1(omega) 9cis DG, 18:0/18:2(omega) 6cis DG, 18:0/18:3(omega) 3cis DG, 18:0/20:4(omega) 6cis DG, 18:0/22:6(omega) 3cis DG and at T equals 326 K for 18:0/18:0 DG monolayer. The monolayers consisted of 48 glycerolipids of the same type arranged in a rectangular simulation cell. The average areas per lipid molecule over the simulations were 65.6 Angstrom2 in 18:0/18:0 DG monolayer, 66.2 Angstrom2 in 18:0/18:1(omega) 9cis DG, 66.1 angstrom2 in 18:0/18:2(omega) 6cis DG, 67.4 angstrom2 in 18:0/18:3(omega) 3cis DG, 70.6 angstrom2 in 18:0/20:4(omega) 6cis DG and 71.4 Angstrom2 in 18:0/22:6(omega) 3cis DG monolayer. The C-C bond orientation distributions and C-C bond order parameter profiles about the monolayer normals were calculated. The C-C bond orientation distribution function widths turned out to be depended on both bond location in the chain and chemical structure of the segment.

  12. Characterization and control of molecular ordering on adsorbate-induced reconstructed surfaces

    NASA Astrophysics Data System (ADS)

    Pai, Woei Wu; Hsu, C. L.; Lin, K. C.; Sin, L. Y.; Tang, Tong B.

    2005-02-01

    Understanding molecular ordering is a critical step in achieving molecular self-assembly for the fabrication of nanomaterials, and molecular ordering in the adsorption of large molecules on atomically flat surfaces can be characterized with precision by scanning tunneling microscopy (STM). Complications arise therein from the expanded possibility of various adsorption structures, conformations and surface reconstructions. Here we present two cases of C 60 adsorbed on Ag(1 0 0) and Cu(1 1 1) that illustrate the importance of competitive interactions in the presence of adsorbate-induced reconstruction. In both studies, strong STM contrasts derive from topographic features arising from reconstructed substrates. C 60/Ag(1 0 0) presents a unique uniaxially incommensurate molecular packing. We have also found that one can control molecular ordering with a stepped surface to produce a single-domain film. In C 60/Cu(1 1 1), we are able to obtain metastable, yet well-defined, molecular ordering with precise annealing procedures. These metastable states exhibit a clear correlation between molecular contrast patterns and the adlayer rotation angle, as a consequence of competitive interactions between optimizing C 60 bonding at preferred reconstructive sites and C 60-C 60 repulsion. Finer control of selective preparation of these metastable structures offers a plausible way of fabricating nanostructures by design.

  13. Helfrich's concept of intrinsic force and its molecular origin in bilayers and monolayers.

    PubMed

    Nandi, Nilashis; Vollhardt, Dieter

    2014-06-01

    Bilayers and monolayers are excellent models of biological membranes. The constituents of the biological membranes such as lipids, cholesterols and proteins are chiral. Chiral molecules are abundant in nature (protein, nucleic acid and lipid). It is obvious that relationship between chirality and morphology (as well as function) of biological membrane is of interest for its fundamental importance and has technological implication regarding various membrane functions. The recent years have witnessed that a number of experimental studies in biomimetic systems have shown fascinating morphologies where chirality of the constituent molecule has decisive influence. Significant progress is made towards the understanding of these systems from the theoretical and computational studies. Helfrich's concept of intrinsic force arising from chirality is a milestone in understanding the biomimetic system such as bilayer and the related concepts, further progresses in molecular understanding made in recent years and experimental studies revealing the influence of chirality on morphology are the focus of the present review. Helfrich's concept of intrinsic force arising due to chirality is useful in understanding two-dimensional bilayers and one-dimensional monolayers and related mimetic systems. Various experimental techniques are used, which can probe the molecular architecture of these mimetic systems at different length scales and both macroscopic (thermodynamic) as well as microscopic (molecular) theories are developed. These studies are aimed to understand the role of chirality in the molecular interaction when the corresponding molecule is present in an aggregate. When one looks into the variety of morphologies exhibited by three-dimensional bilayer and two-dimensional monolayer, the later types of systems are more exotic in the sense that they show more diversity and interesting chiral discrimination. Helfrich's concept of intrinsic force may be considered useful in both

  14. Application of the Molecular Adsorber Coating Technology on the Ionospheric Connection Explorer Program

    NASA Technical Reports Server (NTRS)

    Abraham, Nithin S.; Hasegawa, Mark M.; Secunda, Mark S.

    2016-01-01

    The Molecular Adsorber Coating (MAC) is a zeolite based highly porous coating technology that was developed by NASA Goddard Space Flight Center (GSFC) to capture outgassed contaminants, such as plastics, adhesives, lubricants, silicones, epoxies, potting compounds, and other similar materials. This paper describes the use of the MAC technology to address molecular contamination concerns on NASAs Ionospheric Connection Explorer (ICON) program led by the University of California (UC) Berkeleys Space Sciences Laboratory. The sprayable paint technology was applied onto plates that were installed within the instrument cavity of ICONs Far Ultraviolet Imaging Spectrograph (FUV). However, due to the instruments particulate sensitivity, the coating surface was vibrationally cleaned through simulated acoustics to reduce the risk of particle fall-out contamination. This paper summarizes the coating application efforts on the FUV adsorber plates, the simulated laboratory acoustic level cleaning test methods, particulation characteristics, and future plans for the MAC technology.

  15. Molecular arrangements in polymorphous monolayer structures of carbocyanine dye J-aggregates

    NASA Astrophysics Data System (ADS)

    Prokhorov, Valery V.; Pozin, Sergey I.; Lypenko, Dmitry A.; Perelygina, Olga M.; Mal'tsev, Eugene I.; Vannikov, Anatoly V.

    2012-05-01

    Subangstrom accuracy AFM height measurements and high-resolution visualization of crystallographic habits enabled us to give an insight into how stacked dye molecules are arranged in J-aggregate monolayers of 3,3'-di(γ-sulfopropyl)-4,4',5,5'-dibenzo-9-ethylthiacarbocyanine betaine pyridinium. Ladder and staircase molecular arrangements were self-consistently proposed for the explanation of the stripe-like and leaf-like J-aggregate polymorphism correspondingly. It is inferred that a J-aggregate building unit constitutes a symmetric monolayer of ˜1.35 nm in a height that consists of all-trans monomers with anti-parallel up-down orientation and a slip angle of ˜15°. As it follows from AFM images of folded/overlapped J-aggregates, these species manifest themselves as mechanically very flexible structures.

  16. Molecular adsorbates as probes of the local properties of doped graphene

    PubMed Central

    Pham, Van Dong; Joucken, Frédéric; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Rousset, Sylvie; Sporken, Robert; Santos, Maria Cristina dos; Lagoute, Jérôme

    2016-01-01

    Graphene-based sensors are among the most promising of graphene’s applications. The ability to signal the presence of molecular species adsorbed on this atomically thin substrate has been explored from electric measurements to light scattering. Here we show that the adsorbed molecules can be used to sense graphene properties. The interaction of porphyrin molecules with nitrogen-doped graphene has been investigated using scanning tunneling microscopy and ab initio calculations. Molecular manipulation was used to reveal the surface below the adsorbed molecules allowing to achieve an atomic-scale measure of the interaction of molecules with doped graphene. The adsorbate’s frontier electronic states are downshifted in energy as the molecule approaches the doping site, with largest effect when the molecule sits over the nitrogen dopant. Theoretical calculations showed that, due to graphene’s high polarizability, the adsorption of porphyrin induces a charge rearrangement on the substrate similar to the image charges on a metal. This charge polarization is enhanced around nitrogen site, leading to an increased interaction of molecules with their image charges on graphene. Consequently, the molecular states are stabilized and shift to lower energies. These findings reveal the local variation of polarizability induced by nitrogen dopant opening new routes towards the electronic tuning of graphene. PMID:27097555

  17. Measurement of molecular length of self-assembled monolayer probed by localized surface plasmon resonance

    NASA Astrophysics Data System (ADS)

    Ito, Juri; Kajikawa, Kotaro

    2016-02-01

    We propose a method to measure the variation of the molecular length of self-assembled monolayers (SAMs) when it is exposed to solutions at different pH conditions. The surface immobilized gold nanospheres (SIGNs) shows strong absorption peak at the wavelengths of 600-800 nm when p-polarized light is illuminated. The peak wavelength depends on the length of the gap distance between the SIGNs and the substrate. The gap is supported by the SAM molecules. According to the analytical calculation based on multiple expansion, the relation between the peak wavelength of the SIGN structures and the gap distance is calculated, to evaluate the molecular length of the SAM through the optical absorption spectroscopy for the SIGN structures. The molecular length of the SIGN structure was measured in air, water, acidic, and basic solutions. It was found that the molecular lengths are longer in acidic solutions.

  18. Selective adsorption of modified nucleoside cancer biomarkers by hybrid molecularly imprinted adsorbents.

    PubMed

    Iwanowska, Agnieszka; Yusa, Shin-Ichi; Nowakowska, Maria; Szczubiałka, Krzysztof

    2016-08-01

    Modified adenosine nucleosides have been proposed to be potential DNA-based biomarkers for early diagnosis of tumor and a promising tool for the development of noninvasive prediction systems. However, the low concentration of modified adenosine nucleosides in physiological fluids makes them challenging for both quantitative and qualitative determination. Therefore, materials, which are potentially useful for selective adsorption of nucleobase-containing compounds, were obtained. To obtain the adsorbents, the silica gel particles were coated layer-by-layer with films of the polymers with different combinations of polymers containing thymine groups. Next, the microspheres were irradiated with UV light in the presence of 2'-deoxyadenosine or 5'-deoxy-5'-(methylthio)adenosine, as template molecules, which resulted in the photodimerization of thymine moieties and molecular imprinting of adsorbed modified adenosine compounds. The selectivity of the adsorption was significantly enhanced by the photoimprinting process. Eventually, the imprinted particles have shown an improved ability to recognize mainly 2'-deoxyadenosine and 5'-deoxy-5'-(methylthio)adenosine molecules. The best performing adsorbent was obtained using modified natural polysaccharides. The studied materials could serve as promising adsorbents of biomarkers for tumor diagnostics. PMID:27296785

  19. Amino-terminated biphenylthiol self-assembled monolayers as highly reactive molecular templates

    SciTech Connect

    Meyerbroeker, N.; Waske, P.; Zharnikov, M.

    2015-03-14

    Self-assembled monolayers (SAMs) with amino tail groups are of interest due to their ability of coupling further compounds. Such groups can be, in particular, created by electron irradiation of nitro- or nitrile-substituted aromatic SAMs, which provide a basis for chemical nanolithography and the fabrication of functionalized nanomembranes. An estimate of reactivity of the created amino groups requires a reference system of homogeneous, amino-terminated aromatic SAMs, which can also be used as a highly reactive molecular template. Here, we describe the synthesis of 4′-aminobiphenyl-4-thiol (ABPT) and SAMs prepared from this precursor on Au(111). The monolayers were characterized by X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy, which revealed that they are well defined, chemically uniform, densely packed, and highly ordered. To examine the influence of electron irradiation on the reactivity of the terminal amino groups, ABPT SAMs were exposed to low energy (50 eV) electrons up to a dose of 40 mC/cm{sup 2} and, subsequently, immersed in either trifluoroacetic, pentafluoropropionic, or heptafluorobutyric anhydride. Analysing the amount of the attached anhydride species made it possible to determine the percentage of reactive amino groups as well as the effect of steric hindrance upon the coupling reaction. The above results are compared with those obtained for the well-established nitro-substituted biphenylthiol monolayers.

  20. Structure of Cholesterol/Ceramide Monolayer Mixtures: Implications to the Molecular Organization of Lipid Rafts

    PubMed Central

    Scheffer, Luana; Solomonov, Inna; Weygand, Markus Jan; Kjaer, Kristian; Leiserowitz, Leslie; Addadi, Lia

    2005-01-01

    The structure of monolayers of cholesterol/ceramide mixtures was investigated using grazing incidence x-ray diffraction, immunofluorescence, and atomic force microscopy techniques. Grazing incidence x-ray diffraction measurements showed the existence of a crystalline mixed phase of the two components within a range of compositions of cholesterol/ceramide between 100:0 and 67:33. The mixed phase coexists with the ceramide crystalline phase in the range of compositions between 50:50 and 30:70; between 30:70 and 0:100 only the highly crystalline phase of ceramide was detected. The latter was determined and modeled. Immunolabeling was performed with an antibody specific to the cholesterol monohydrate crystalline arrangement. The antibody recognizes crystalline cholesterol monolayers, but does not interact with crystalline ceramide. Immunofluorescence and atomic force microscopy data show that in uncompressed ceramide monolayers, the highly crystalline phase coexists with a disordered loosely packed phase. In contrast, no disordered phase coexists with the new crystalline mixed phase. We conclude that the new mixed phase represents a stable homogeneous arrangement of cholesterol with ceramide. As ceramide incorporates the lipid backbone common to all sphingolipids, this arrangement may be relevant to the understanding of the molecular organization of lipid rafts. PMID:15722431

  1. Amino-terminated biphenylthiol self-assembled monolayers as highly reactive molecular templates

    NASA Astrophysics Data System (ADS)

    Meyerbroeker, N.; Waske, P.; Zharnikov, M.

    2015-03-01

    Self-assembled monolayers (SAMs) with amino tail groups are of interest due to their ability of coupling further compounds. Such groups can be, in particular, created by electron irradiation of nitro- or nitrile-substituted aromatic SAMs, which provide a basis for chemical nanolithography and the fabrication of functionalized nanomembranes. An estimate of reactivity of the created amino groups requires a reference system of homogeneous, amino-terminated aromatic SAMs, which can also be used as a highly reactive molecular template. Here, we describe the synthesis of 4'-aminobiphenyl-4-thiol (ABPT) and SAMs prepared from this precursor on Au(111). The monolayers were characterized by X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy, which revealed that they are well defined, chemically uniform, densely packed, and highly ordered. To examine the influence of electron irradiation on the reactivity of the terminal amino groups, ABPT SAMs were exposed to low energy (50 eV) electrons up to a dose of 40 mC/cm2 and, subsequently, immersed in either trifluoroacetic, pentafluoropropionic, or heptafluorobutyric anhydride. Analysing the amount of the attached anhydride species made it possible to determine the percentage of reactive amino groups as well as the effect of steric hindrance upon the coupling reaction. The above results are compared with those obtained for the well-established nitro-substituted biphenylthiol monolayers.

  2. Amino-terminated biphenylthiol self-assembled monolayers as highly reactive molecular templates.

    PubMed

    Meyerbroeker, N; Waske, P; Zharnikov, M

    2015-03-14

    Self-assembled monolayers (SAMs) with amino tail groups are of interest due to their ability of coupling further compounds. Such groups can be, in particular, created by electron irradiation of nitro- or nitrile-substituted aromatic SAMs, which provide a basis for chemical nanolithography and the fabrication of functionalized nanomembranes. An estimate of reactivity of the created amino groups requires a reference system of homogeneous, amino-terminated aromatic SAMs, which can also be used as a highly reactive molecular template. Here, we describe the synthesis of 4'-aminobiphenyl-4-thiol (ABPT) and SAMs prepared from this precursor on Au(111). The monolayers were characterized by X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy, which revealed that they are well defined, chemically uniform, densely packed, and highly ordered. To examine the influence of electron irradiation on the reactivity of the terminal amino groups, ABPT SAMs were exposed to low energy (50 eV) electrons up to a dose of 40 mC/cm(2) and, subsequently, immersed in either trifluoroacetic, pentafluoropropionic, or heptafluorobutyric anhydride. Analysing the amount of the attached anhydride species made it possible to determine the percentage of reactive amino groups as well as the effect of steric hindrance upon the coupling reaction. The above results are compared with those obtained for the well-established nitro-substituted biphenylthiol monolayers. PMID:25770508

  3. One-Nanometer Thin Monolayers Remove the Deleterious Effect of Substrate Defects in Molecular Tunnel Junctions.

    PubMed

    Jiang, Li; Sangeeth, C S Suchand; Yuan, Li; Thompson, Damien; Nijhuis, Christian A

    2015-10-14

    Defects in self-assembled monolayer (SAMs) based junctions cause the largest deviation between predicted and measured values of the tunnelling current. We report the remarkable, seemingly counterintuitive finding that shorter, less-ordered SAMs provide, unlike taller crystalline-like SAMs, higher quality tunnelling barriers on defective substrates, which points to self-repair of liquid-like SAMs on defects. The molecular dynamics show that short-chain molecules can more easily rotate into low-density boundary regions and smoothen out defects than thick solid-like SAMs. Our findings point to an attractive means of removing their deleterious effects simply by using flexible molecules.

  4. An Electrically Driven and Readable Molecular Monolayer Switch Based on a Solid Electrolyte.

    PubMed

    Marchante, Elena; Crivillers, Núria; Buhl, Moritz; Veciana, Jaume; Mas-Torrent, Marta

    2016-01-01

    The potential application of molecular switches as active elements in information storage has been demonstrated through numerous works. Importantly, such switching capabilities have also been reported for self-assembled monolayers (SAMs). SAMs of electroactive molecules have recently been exploited as electrochemical switches. Typically, the state of these switches could be read out through their optical and/or magnetic response. These output reading processes are difficult to integrate into devices, and furthermore, there is a need to use liquid environments for switching the redox-active molecular systems. In this work, both of these challenges were overcome by using an ionic gel as the electrolyte medium, which led to an unprecedented solid-state device based on a single molecular layer. Moreover, electrochemical impedance has been successfully exploited as the output of the system.

  5. Multilayer graphene nanostructure separate CO2/CH4 mixture: Combining molecular simulations with ideal adsorbed solution theory

    NASA Astrophysics Data System (ADS)

    Cheng, Huiyuan; Lei, Guangping

    2016-09-01

    The molecular simulations (Grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations) combined with ideal adsorbed solution theory (IAST) are adopted to investigate the adsorption of CO2, CH4 and their mixture in multilayer graphene nanostructure. The effects of pressure, temperature and pre-adsorbed water on the separation behaviors are examined. The IAST accurately predict the loading of two species, but it has a slight deviation for the selectivity predictions. It is beneficial to the CO2/CH4 mixture separation by reducing temperature or pre-adsorbing some water. Due to additional adsorbate-H2O interactions, the diffusivities of two species drop down as the pre-adsorbed water content increases.

  6. Contributions of the substrate electric field to the molecular adsorbate optical nonlinearities

    SciTech Connect

    Zouari, M.; Villaeys, A.A.

    2005-10-15

    The nonlinear optical response of an adsorbate, whose structure is altered by the inhomogeneous electrostatic field of the substrate, has been evaluated with a particular emphasis on the sum-frequency generation process. In the limiting case of an homogeneous electrostatic field, besides the contributions associated with the induced dipole moments, we have additional contributions which only exist if the adsorbed molecule has permanent dipole moments. Also, the Franck-Condon factors of the unperturbed molecule weight the internal couplings induced by the electrostatic field. For the more general inhomogeneous electrostatic field case, while the main observations remain valid, the Franck-Condon factors are modified by the molecular structure changes induced by the electrostatic field. In addition, we have a strong redistribution of the vibronic couplings resulting from the analytical Q dependence of the partial charge distribution which is a signature of the field inhomogeneities.

  7. Effect of molecular orientation on monolayer and multilayer formations of fluorocarbon alcohol and fluorocarbon-α,ω-diol mixture at the hexane/water interface.

    PubMed

    Fukuhara, Ryushi; Tanida, Hajime; Nitta, Kiyofumi; Ina, Toshiaki; Uruga, Tomoya; Matsubara, Hiroki; Aratono, Makoto; Takiue, Takanori

    2014-10-30

    The effect of molecular orientation on the miscibility and structure of the adsorbed film of the 1H,1H,10H,10H-perfluorodecane-1,10-diol (FC10diol)-1H,1H,2H,2H-perfluorodecanol (FC10OH) mixture at the hexane/water interface were examined by interfacial tension and X-ray reflectivity measurements. The interfacial tension and X-ray reflectivity at the hexane solution/water interface were measured as a function of total molality m and composition of FC10OH in the mixture X2 under atmospheric pressure at 298.15 K. The interfacial pressure vs mean area per molecule curves showed that two kinds of condensed monolayers (C1 and C2) and multilayer (M) states appeared depending on m and X2. In the pure component systems, it was found that FC10OH forms condensed monolayer in which the molecules orient almost normally to the interface, and FC10diol orients parallel and is densely packed in the condensed monolayer and then piles spontaneously to form multilayer. In the mixed system, the phase diagram of adsorption indicated that FC10OH molecules are richer in C2 than in C1 state. The X-ray reflectivity measurements manifest that the condensed monolayer below X2 = 0.985 is heterogeneous in which the normal- and parallel-oriented domains coexist at the interface (C1 state), and that above X2 = 0.985 seems to be homogeneous with normal molecular orientation (C2 state). The structure of M state depends on those of condensed monolayers, on which the molecules pile spontaneously. The heterogeneous structure in C1 state is compared to that previously observed in the mixed system of FC10diol-FC12OH (1H,1H,2H,2H-perfluorododecanol), where FC12OH has longer fluorocarbon chain length than FC10OH and is discussed in terms of domain line tension.

  8. Metamaterial Absorbers for Infrared Detection of Molecular Self-Assembled Monolayers

    PubMed Central

    Ishikawa, Atsushi; Tanaka, Takuo

    2015-01-01

    The emerging field of plasmonic metamaterials has introduced new degree of freedom to manipulate optical field from nano to macroscopic scale, offering an attractive platform for sensing applications. So far, metamaterial sensor concepts, however, have focused on hot-spot engineering to improve the near-field enhancement, rather than fully exploiting tailored material properties. Here, we present a novel spectroscopic technique based on the metamaterial infrared (IR) absorber allowing for a low-background detection scheme as well as significant plasmonic enhancement. Specifically, we experimentally demonstrate the resonant coupling of plasmonic modes of a metamaterial absorber and IR vibrational modes of a molecular self-assembled monolayer. The metamaterial consisting of an array of Au/MgF2/Au structures exhibits an anomalous absorption at ~3000 cm−1, which spectrally overlaps with C-H stretching vibrational modes. Symmetric/asymmetric C-H stretching modes of a 16-Mercaptohexadecanoic acid monolayer are clearly observed as Fano-like anti-resonance peaks within a broad plasmonic absorption of the metamaterial. Spectral analysis using Fano line-shape fitting reveals the underlying resonant interference in plasmon-molecular coupled systems. Our metamaterial approach achieves the attomole sensitivity with a large signal-to-noise ratio in the far-field measurement, thus may open up new avenues for realizing ultrasensitive IR inspection technologies. PMID:26229011

  9. Self-assembled monolayer-functionalized half-metallic manganite for molecular spintronics.

    PubMed

    Tatay, Sergio; Barraud, Clément; Galbiati, Marta; Seneor, Pierre; Mattana, Richard; Bouzehouane, Karim; Deranlot, Cyrile; Jacquet, Eric; Forment-Aliaga, Alicia; Jegou, Pascale; Fert, Albert; Petroff, Frédéric

    2012-10-23

    (La,Sr)MnO(3) manganite (LSMO) has emerged as the standard ferromagnetic electrode in organic spintronic devices due to its highly spin-polarized character and air stability. Whereas organic semiconductors and polymers have been mainly envisaged to propagate spin information, self-assembled monolayers (SAMs) have been overlooked and should be considered as promising materials for molecular engineering of spintronic devices. Surprisingly, up to now the first key step of SAM grafting protocols over LSMO surface thin films is still missing. We report the grafting of dodecyl (C12P) and octadecyl (C18P) phosphonic acids over the LSMO half-metallic oxide. Alkylphosphonic acids form ordered self-assembled monolayers, with the phosphonic group coordinated to the surface and alkyl chains tilted from the surface vertical by 43° (C12P) and 27° (C18P). We have electrically characterized these SAMs in nanodevices and found that they act as tunnel barriers, opening the door toward the integration of alkylphosphonic acid//LSMO SAMs into future molecular/organic spintronic devices such as spin OLEDs.

  10. Atomic and molecular oxygen adsorbed on (111) transition metal surfaces: Cu and Ni

    SciTech Connect

    López-Moreno, S.; Romero, A. H.

    2015-04-21

    Density functional theory is used to investigate the reaction of oxygen with clean copper and nickel [111]-surfaces. We study several alternative adsorption sites for atomic and molecular oxygen on both surfaces. The minimal energy geometries and adsorption energies are in good agreement with previous theoretical studies and experimental data. From all considered adsorption sites, we found a new O{sub 2} molecular precursor with two possible dissociation paths on the Cu(111) surface. Cross barrier energies for the molecular oxygen dissociation have been calculated by using the climbing image nudge elastic band method, and direct comparison with experimental results is performed. Finally, the structural changes and adsorption energies of oxygen adsorbed on surface when there is a vacancy nearby the adsorption site are also considered.

  11. Nonlinear optical techniques for surface studies. [Monolayers

    SciTech Connect

    Shen, Y.R.

    1981-09-01

    Recent effort in developing nonlinear optical techniques for surface studies is reviewed. Emphasis is on monolayer detection of adsorbed molecules on surfaces. It is shown that surface coherent antiStokes Raman scattering (CARS) with picosecond pulses has the sensitivity of detecting submonolayer of molecules. On the other hand, second harmonic or sum-frequency generation is also sensitive enough to detect molecular monolayers. Surface-enhanced nonlinear optical effects on some rough metal surfaces have been observed. This facilitates the detection of molecular monolayers on such surfaces, and makes the study of molecular adsorption at a liquid-metal interface feasible. Advantages and disadvantages of the nonlinear optical techniques for surface studies are discussed.

  12. The structure, energetics, and nature of the chemical bonding of phenylthiol adsorbed on the Au(111) surface: implications for density-functional calculations of molecular-electronic conduction.

    PubMed

    Bilić, Ante; Reimers, Jeffrey R; Hush, Noel S

    2005-03-01

    The adsorption of phenylthiol on the Au(111) surface is modeled using Perdew and Wang density-functional calculations. Both direct molecular physisorption and dissociative chemisorption via S-H bond cleavage are considered as well as dimerization to form disulfides. For the major observed product, the chemisorbed thiol, an extensive potential-energy surface is produced as a function of both the azimuthal orientation of the adsorbate and the linear translation of the adsorbate through the key fcc, hcp, bridge, and top binding sites. Key structures are characterized, the lowest-energy one being a broad minimum of tilted orientation ranging from the bridge structure halfway towards the fcc one. The vertically oriented threefold binding sites, often assumed to dominate molecular electronics measurements, are identified as transition states at low coverage but become favored in dense monolayers. A similar surface is also produced for chemisorption of phenylthiol on Ag(111); this displays significant qualitative differences, consistent with the qualitatively different observed structures for thiol chemisorption on Ag and Au. Full contours of the minimum potential energy as a function of sulfur translation over the crystal face are described, from which the barrier to diffusion is deduced to be 5.8 kcal mol(-1), indicating that the potential-energy surface has low corrugation. The calculated bond lengths, adsorbate charge and spin density, and the density of electronic states all indicate that, at all sulfur locations, the adsorbate can be regarded as a thiyl species that forms a net single covalent bond to the surface of strength 31 kcal mol(-1). No detectable thiolate character is predicted, however, contrary to experimental results for alkyl thiols that indicate up to 20%-30% thiolate involvement. This effect is attributed to the asymptotic-potential error of all modern density functionals that becomes manifest through a 3-4 eV error in the lineup of the adsorbate and

  13. Molecular adsorbent recirculating system as artificial support therapy for liver failure: a meta-analysis.

    PubMed

    Vaid, Arjun; Chweich, Haval; Balk, Ethan M; Jaber, Bertrand L

    2012-01-01

    Molecular Adsorbent Recirculating System (MARS) is an artificial liver support system that has been developed for patients with liver failure until the liver regains function or as a bridge to transplantation. We conducted a meta-analysis to examine the efficacy of this promising therapy. We searched MEDLINE, EMBASE, and the Cochrane Registry of Controlled Trials databases, and abstracts from the proceedings of several scientific meetings. Patients with acute, acute on chronic, and hyperacute liver failure were included and we compared MARS with standard medical therapy. Randomized and nonrandomized controlled trials were included and Molecular Adsorbent Recirculating System was the intervention used. We evaluated net change in total bilirubin levels, improvement in hepatic encephalopathy and mortality. Nine randomized controlled trials and one nonrandomized controlled study met criteria and were included. By meta-analysis, MARS resulted in a significant decrease in total bilirubin levels (net change -7.0 mg/dl; 95% CI -10.4, -3.7; p < 0.001) and in an improvement in the West-Haven grade of hepatic encephalopathy (odds ratio [OR] 3.0; 95% CI 1.9, 5.0; p < 0.001). There was no beneficial effect on mortality (OR 0.91; 95% CI 0.64, 1.31; p = 0.62). The limitations of this study include a small sample size, an inability to blind with significant heterogeneity among studies, and variable definitions of liver failure. The Molecular Adsorbent Recirculating System is associated with a significant improvement in total bilirubin levels and hepatic encephalopathy but has no impact on survival. Large studies are required to assess the merit of this promising therapy on patient-centered outcomes. PMID:22210651

  14. Adsorbate shape selectivity: Separation of the HF/134a azeotrope over carbogenic molecular sieve

    SciTech Connect

    Hong, A.; Mariwala, R.K.; Kane, M.S.; Foley, H.C.

    1995-03-01

    Experimental evidence is provided for adsorptive shape selectivity in the separation of the azeotrope between HF and 1,1,1,2-tetrafluoroethane (134a) over pyrolyzed poly(furfuryl alcohol)-derived carbogenic molecular sieve (PPFA-CMS). The separation can be accomplished over coconut charcoal or Carbosieve G on the basis of the differences in the extent of equilibrium adsorption of HF and 134a. On these adsorbents 134a is more strongly bound than HF, thus it elutes much more slowly from the bed. The heat of adsorption for 134a in the vicinity of 200 C on Carbosieve G is {approximately}8.8 kcal/mol. In contrast, when the same azeotropic mixture is separated over PPFA-CMS prepared at 500 C, 134a is not adsorbed. As a result 134a elutes from the bed first, followed by HF. The reversal is brought about by the narrower pore size and pore size distribution of the PPFA-CMS versus that for Carbosieve G. Thus the separation over PPFA-CMS is an example of adsorbate shape selectivity and represents a limiting case of kinetic separation.

  15. Charged and metallic molecular monolayers through surface-induced aromatic stabilization

    NASA Astrophysics Data System (ADS)

    Heimel, G.; Duhm, S.; Salzmann, I.; Gerlach, A.; Strozecka, A.; Niederhausen, J.; Bürker, C.; Hosokai, T.; Fernandez-Torrente, I.; Schulze, G.; Winkler, S.; Wilke, A.; Schlesinger, R.; Frisch, J.; Bröker, B.; Vollmer, A.; Detlefs, B.; Pflaum, J.; Kera, S.; Franke, K. J.; Ueno, N.; Pascual, J. I.; Schreiber, F.; Koch, N.

    2013-03-01

    Large π-conjugated molecules, when in contact with a metal surface, usually retain a finite electronic gap and, in this sense, stay semiconducting. In some cases, however, the metallic character of the underlying substrate is seen to extend onto the first molecular layer. Here, we develop a chemical rationale for this intriguing phenomenon. In many reported instances, we find that the conjugation length of the organic semiconductors increases significantly through the bonding of specific substituents to the metal surface and through the concomitant rehybridization of the entire backbone structure. The molecules at the interface are thus converted into different chemical species with a strongly reduced electronic gap. This mechanism of surface-induced aromatic stabilization helps molecules to overcome competing phenomena that tend to keep the metal Fermi level between their frontier orbitals. Our findings aid in the design of stable precursors for metallic molecular monolayers, and thus enable new routes for the chemical engineering of metal surfaces.

  16. Zwitterionic lipid assemblies: Molecular dynamics studies of monolayers, bilayers, and vesicles using a new coarse grain force field

    PubMed Central

    Shinoda, Wataru; DeVane, Russell; Klein, Michael L.

    2010-01-01

    A new coarse-grained (CG) intermolecular force field is presented for a series of zwitterionic lipids. The model is an extension of our previous work on nonionic surfactants and is designed to reproduce experimental surface/interfacial properties as well as distribution functions from all-atom molecular dynamics (MD) simulations. Using simple functional forms, the force field parameters are optimized for multiple lipid molecules, simultaneously. The resulting CG lipid bilayers have reasonable molecular areas, chain order parameters, and elastic properties. The computed surface pressure vs. area (π-A) curve for a DPPC monolayer demonstrates a significant improvement over the previous CG models. The DPPC monolayer has a longer persistence length than a PEG lipid monolayer, exhibiting a long-lived curved monolayer surface under negative tension. The bud ejected from an oversaturated DPPC monolayer has a large bicelle-like structure, which is different from the micellar bud formed from an oversaturated PEG lipid monolayer. We have successfully observed vesicle formation during CG-MD simulations, starting from an aggregate of DMPC molecules. Depending on the aggregate size, the lipid assembly spontaneously transforms into a closed vesicle or a bicelle. None of the various intermediate structures between these extremes seem to be stable. An attempt to observe fusion of two vesicles through the application of an external adhesion force was not successful. The present CG force field also supports stable multi-lamellar DMPC vesicles. PMID:20438090

  17. Electronic Friction-Based Vibrational Lifetimes of Molecular Adsorbates: Beyond the Independent-Atom Approximation.

    PubMed

    Rittmeyer, Simon P; Meyer, Jörg; Juaristi, J Iñaki; Reuter, Karsten

    2015-07-24

    We assess the accuracy of vibrational damping rates of diatomic adsorbates on metal surfaces as calculated within the local-density friction approximation (LDFA). An atoms-in-molecules (AIM) type charge partitioning scheme accounts for intramolecular contributions and overcomes the systematic underestimation of the nonadiabatic losses obtained within the prevalent independent-atom approximation. The quantitative agreement obtained with theoretical and experimental benchmark data suggests the LDFA-AIM scheme as an efficient and reliable approach to account for electronic dissipation in ab initio molecular dynamics simulations of surface chemical reactions. PMID:26252696

  18. Adsorption separation of carbon dioxide from flue gas by a molecularly imprinted adsorbent.

    PubMed

    Zhao, Yi; Shen, Yanmei; Ma, Guoyi; Hao, Rongjie

    2014-01-01

    CO2 separation by molecularly imprinted adsorbent from coal-fired flue gas after desulfurization system has been studied. The adsorbent was synthesized by molecular imprinted technique, using ethanedioic acid, acrylamide, and ethylene glycol dimethacrylate as the template, functional monomer, and cross-linker, respectively. According to the conditions of coal-fired flue gas, the influencing factors, including adsorption temperature, desorption temperature, gas flow rate, and concentrations of CO2, H2O, O2, SO2, and NO, were studied by fixed bed breakthrough experiments. The experimental conditions were optimized to gain the best adsorption performance and reduce unnecessary energy consumption in future practical use. The optimized adsorption temperature, desorption temperature, concentrations of CO2, and gas flow rate are 60 °C, 80 °C, 13%, and 170 mL/min, respectively, which correspond to conditions of practical flue gases to the most extent. The CO2 adsorption performance was nearly unaffected by H2O, O2, and NO in the flue gas, and was promoted by SO2 within the emission limit stipulated in the Chinese emission standards of air pollutants for a thermal power plant. The maximum CO2 adsorption capacity, 0.57 mmol/g, was obtained under the optimized experimental conditions, and the SO2 concentration was 150 mg/m(3). The influence mechanisms of H2O, O2, SO2, and NO on CO2 adsorption capacity were investigated by infrared spectroscopic analysis. PMID:24410306

  19. Two antibacterial nalidixate calixarene derivatives in cholesterol monolayers: Molecular dynamics and physicochemical effects.

    PubMed

    Korchowiec, Beata; Korchowiec, Jacek; Orlof-Naturalna, Monika; de Vains, Jean-Bernard Regnouf; Rogalska, Ewa

    2016-09-01

    The interaction of two antibacterial calixarene derivatives with cholesterol, a eukaryotic cell membrane lipid, was investigated with the aim to get more insight in the potential advers effects on our cells. The derivatives used had one or two nalidixic acid arms grafted on the lower rim of the calixarene aromatic crown. Monomolecular films spread at the air-water interface were used as model lipid membranes. Pure cholesterol and pure calixarene derivatives, as well as binary cholesterol - calixarene derivative mixtures were studied using surface pressure measurements, polarization-modulation infrared reflection absorption spectroscopy and molecular dynamics simulations. The properties of the mixed monolayers were described quantitatively using thermodynamic models. The analysis of surface pressure-area isotherms of mixed monolayers shows that cholesterol may form homogenous but metastable domains with both nalidixate derivatives. This phenomenon is more clearly observed with mono-substituted calixarene. A detailed modeling analysis indicates that cholesterol favors dehydration of the calixarene polar headgroups and transfer of the derivatives from the aqueous to the gas phase. This effect, more pronounced in the case of the monosubstituted calixarene, can be linked to the hydrophobic interaction with cholesterol. This observation may be useful for developing new calixarene derivatives allowing us to control disease-causing bacteria without harming our own cells. PMID:27295494

  20. Effect of Na+ and Ca2+ ions on a lipid Langmuir monolayer: an atomistic description by molecular dynamics simulations.

    PubMed

    Giner Casares, Juan José; Camacho, Luis; Martín-Romero, Maria Teresa; López Cascales, José Javier

    2008-12-01

    Studying the effect of alkali and alkaline-earth metal cations on Langmuir monolayers is relevant from biophysical and nanotechnological points of view. In this work, the effect of Na(+) and Ca(2+) on a model of an anionic Langmuir lipid monolayer of dimyristoylphosphatidate (DMPA(-)) is studied by molecular dynamics simulations. The influence of the type of cation on lipid structure, lipid-lipid interactions, and lipid ordering is analyzed in terms of electrostatic interactions. It is found that for a lipid monolayer in its solid phase, the effect of the cations on the properties of the lipid monolayer can be neglected. The influence of the cations is enhanced for the lipid monolayer in its gas phase, where sodium ions show a high degree of dehydration compared with calcium ions. This loss of hydration shell is partly compensated by the formation of lipid-ion-lipid bridges. This difference is ascribed to the higher charge-to-radius ratio q/r for Ca(2+), which makes ion dehydration less favorable compared to Na(+). Owing to the different dehydration behavior of sodium and calcium ions, diminished lipid-lipid coordination, lipid-ion coordination, and lipid ordering are observed for Ca(2+) compared to Na(+). Furthermore, for both gas and solid phases of the lipid Langmuir monolayers, lipid conformation and ion dehydration across the lipid/water interface are studied. PMID:19012310

  1. Effect of Na+ and Ca2+ ions on a lipid Langmuir monolayer: an atomistic description by molecular dynamics simulations.

    PubMed

    Giner Casares, Juan José; Camacho, Luis; Martín-Romero, Maria Teresa; López Cascales, José Javier

    2008-12-01

    Studying the effect of alkali and alkaline-earth metal cations on Langmuir monolayers is relevant from biophysical and nanotechnological points of view. In this work, the effect of Na(+) and Ca(2+) on a model of an anionic Langmuir lipid monolayer of dimyristoylphosphatidate (DMPA(-)) is studied by molecular dynamics simulations. The influence of the type of cation on lipid structure, lipid-lipid interactions, and lipid ordering is analyzed in terms of electrostatic interactions. It is found that for a lipid monolayer in its solid phase, the effect of the cations on the properties of the lipid monolayer can be neglected. The influence of the cations is enhanced for the lipid monolayer in its gas phase, where sodium ions show a high degree of dehydration compared with calcium ions. This loss of hydration shell is partly compensated by the formation of lipid-ion-lipid bridges. This difference is ascribed to the higher charge-to-radius ratio q/r for Ca(2+), which makes ion dehydration less favorable compared to Na(+). Owing to the different dehydration behavior of sodium and calcium ions, diminished lipid-lipid coordination, lipid-ion coordination, and lipid ordering are observed for Ca(2+) compared to Na(+). Furthermore, for both gas and solid phases of the lipid Langmuir monolayers, lipid conformation and ion dehydration across the lipid/water interface are studied.

  2. The fracture behaviors of monolayer phosphorene with grain boundaries under tension: a molecular dynamics study.

    PubMed

    Guo, Yangyang; Qiao, Chong; Wang, Aihua; Zhang, Jinping; Wang, Songyou; Su, Wan-Sheng; Jia, Yu

    2016-07-27

    The fracture behaviors of monolayer phosphorene (MP) with and without a grain boundary (GB) have been explored by molecular dynamics (MD) simulations. Firstly, in the case of perfect MP, fracture mostly happens on the bond in the zigzag direction when suffering random loading. With the existence of a GB, the crack propagates perpendicular to the GB in different ways under parallel tension to the GB, whereas it propagates along the GB under perpendicular tension to the GB. Then, we found that both the fracture strength and strain decrease with increasing temperature making fracture more likely at relatively high temperatures. Finally, we also found that, similar to graphene, the effect of strain rate on both the fracture strength and strain is not significant, demonstrating that MP is a typical brittle 2D material. Overall, our findings present a useful insight into utilizing phosphorene for mechanical design in electronic devices.

  3. Molecular-like hierarchical self-assembly of monolayers of mixtures of particles

    PubMed Central

    Singh, P.; Hossain, M.; Gurupatham, S. K.; Shah, K.; Amah, E.; Ju, D.; Janjua, M.; Nudurupati, S.; Fischer, I.

    2014-01-01

    We present a technique that uses an externally applied electric field to self-assemble monolayers of mixtures of particles into molecular-like hierarchical arrangements on fluid-liquid interfaces. The arrangements consist of composite particles (analogous to molecules) which are arranged in a pattern. The structure of a composite particle depends on factors such as the relative sizes of the particles and their polarizabilities, and the electric field intensity. If the particles sizes differ by a factor of two or more, the composite particle has a larger particle at its core and several smaller particles form a ring around it. The number of particles in the ring and the spacing between the composite particles depend on their polarizabilities and the electric field intensity. Approximately same sized particles form chains (analogous to polymeric molecules) in which positively and negatively polarized particles alternate. PMID:25510331

  4. The fracture behaviors of monolayer phosphorene with grain boundaries under tension: a molecular dynamics study.

    PubMed

    Guo, Yangyang; Qiao, Chong; Wang, Aihua; Zhang, Jinping; Wang, Songyou; Su, Wan-Sheng; Jia, Yu

    2016-07-27

    The fracture behaviors of monolayer phosphorene (MP) with and without a grain boundary (GB) have been explored by molecular dynamics (MD) simulations. Firstly, in the case of perfect MP, fracture mostly happens on the bond in the zigzag direction when suffering random loading. With the existence of a GB, the crack propagates perpendicular to the GB in different ways under parallel tension to the GB, whereas it propagates along the GB under perpendicular tension to the GB. Then, we found that both the fracture strength and strain decrease with increasing temperature making fracture more likely at relatively high temperatures. Finally, we also found that, similar to graphene, the effect of strain rate on both the fracture strength and strain is not significant, demonstrating that MP is a typical brittle 2D material. Overall, our findings present a useful insight into utilizing phosphorene for mechanical design in electronic devices. PMID:27405397

  5. Trapping dynamics of diindenoperylene (DIP) in self-assembled monolayers using molecular simulation

    NASA Astrophysics Data System (ADS)

    Kaushik, Ananth P.; Clancy, Paulette

    2011-07-01

    All-atom Molecular Dynamics simulation methods employing a well-tested intermolecular potential model, MM3 (Molecular Mechanics 3), demonstrate the propensity for diindenoperylene (DIP) molecules to insert between molecules of a self-assembled monolayer (SAM) during a deposition process intended to grow a thin film of this organic semiconductor molecule onto the surface of self-assembled monolayers. The tendency to insert between SAM molecules is fairly prevalent at normal growth temperatures and conditions, but is most strongly dependent on the density and the nature of the SAM. We posit the existence of an optimal density to favor surface adsorption over insertion for this system. DIP is less likely to insert in fluorinated SAMs, like FOTS (fluorooctatrichlorosilane), than its unfluorinated analog, OTS (octatrichlorosilane). It is also less likely to insert between shorter SAMs (e.g., less insertion in OTS than ODTS (octadecyltrichlorosilane)). Very short length, surface-coating molecules, like HDMS (hexamethyldisilazane), are more likely to scatter energetic incoming DIP molecules with little insertion on first impact (depending on the incident energy of the DIP molecule). Grazing angles of incidence of the depositing molecules generally favor surface adsorption, at least in the limit of low coverage, but are shown to be dependent on the nature of the SAM. The validity of these predictions is confirmed by comparison of the predicted sticking coefficients of DIP at a variety of incident energies on OTS, ODTS, and FOTS SAMs with results obtained experimentally by Desai et al. (2010) [23]. The simulation predictions of the tendency of DIP to insert can be explained, in large part, in terms of binding energies between SAM and DIP molecules. However, we note that entropic and stochastic events play a role in the deposition outcomes. Preliminary studies of multiple deposition events, emulating growth, show an unexpected diffusion of DIP molecules inserted within the

  6. Electron diffraction studies of molecular ordering and orientation in phospholipid monolayer domains.

    PubMed

    Hui, S W; Yu, H

    1993-01-01

    The molecular order and orientation of phase separated domains in monolayers of DP(Me)PE and DP(Me)2PE were determined by electron diffraction. Dark and bright fluorescent domains at the air-water interface were observed by fluorescence microscopy. The monolayers were transferred to Formvar coated electron microscope grids for electron diffraction studies. The positions of domains on the marker grids were recorded in fluorescence micrographs, which were used as guide maps to locate these domains in the electron microscope. Selected area electron diffraction patterns were obtained from predetermined areas within and outside the dark domains. Sharp hexagonal diffraction patterns were recorded from dark domains, and diffuse diffraction rings from bright areas in between dark domains. The diffraction results indicated that the dark domains and bright areas were comprised of lipid molecules in solid and fluid states, respectively. The orientation of diffraction patterns from adjacent locations within a dark domains changed gradually, indicating a continuous bending of the molecular packing lattice vector within these domains. Orientation directors in U-shaped DP(Me)2PE domains followed the turn of the arm; no vortex nor branching was indicated by electron diffraction. Directors branching from the "stem" of highly invaginated DP(Me)PE domains usually occurred at twinning angles of n pi/3 from the stem director, which would minimize packing defects in the development of thinner branches. Electron diffraction from local areas of individual domains proved that dark fluorescent domains were solid ones, and that pseudo-long range order existed in these solid domains.

  7. A DMPA Langmuir monolayer study: from gas to solid phase. An atomistic description by molecular dynamics Simulation.

    PubMed

    Giner-Casares, J J; Camacho, L; Martín-Romero, M T; Cascales, J J López

    2008-03-01

    In this work, a DMPA Langmuir monolayer at the air/water interface was studied by molecular dynamics simulations. Thus, an atomistic picture of a Langmuir monolayer was drawn from its expanded gas phase to its final solid condensed one. In this sense, some properties of monolayers that were traditionally poorly or even not reproduced in computer simulations, such as lipid domain formation or pressure-area per lipid isotherm, were properly reproduced in this work. Thus, the physical laws that control the lipid domain formation in the gas phase and the structure of lipid monolayers from the gas to solid condensed phase were studied. Thanks to the atomistic information provided by the molecular dynamics simulations, we were able to add valuable information to the experimental description of these processes and to access experimental data related to the lipid monolayers in their expanded phase, which is difficult or inaccessible to study by experimental techniques. In this sense, properties such as lipids head hydration and lipid structure were studied.

  8. A DMPA Langmuir monolayer study: from gas to solid phase. An atomistic description by molecular dynamics Simulation.

    PubMed

    Giner-Casares, J J; Camacho, L; Martín-Romero, M T; Cascales, J J López

    2008-03-01

    In this work, a DMPA Langmuir monolayer at the air/water interface was studied by molecular dynamics simulations. Thus, an atomistic picture of a Langmuir monolayer was drawn from its expanded gas phase to its final solid condensed one. In this sense, some properties of monolayers that were traditionally poorly or even not reproduced in computer simulations, such as lipid domain formation or pressure-area per lipid isotherm, were properly reproduced in this work. Thus, the physical laws that control the lipid domain formation in the gas phase and the structure of lipid monolayers from the gas to solid condensed phase were studied. Thanks to the atomistic information provided by the molecular dynamics simulations, we were able to add valuable information to the experimental description of these processes and to access experimental data related to the lipid monolayers in their expanded phase, which is difficult or inaccessible to study by experimental techniques. In this sense, properties such as lipids head hydration and lipid structure were studied. PMID:18225932

  9. Scanning tunneling microscopy studies of mixed self-assembled monolayers

    NASA Astrophysics Data System (ADS)

    Raigoza, Annette Fernandez

    This thesis examines the formation of multicomponent self-assembled mono-layers (SAMs) on the Au(111) surface using scanning tunneling microscopy. Two methods, sequential adsorption and coadsorption, are used to create these mixed SAMs. In the sequential adsorption experiments, a clean Au(111)-on-mica sub-strate is exposed to the first molecular species and then this adsorbate-covered sample is exposed to the second molecular species. Alternately, in the coadsorption experiments, a gold surface is exposed to both adsorbates simultaneously. Exposing a coronene- or dithiocarbamate-covered surface to excess thiol in the vapor phase results in a drastic restructuring of the initial surface. This is primarily driven by the kinetics of the octanethiol monolayer formation process, but the extent to which this happens is dependent on the molecule-molecule and molecule-surface interactions of the adsorbate due to the initial coverage and order of the monolayer. An octanethiolate monolayer is also substantially modified when immersed in a solution containing dithiocarbamate (DTC). Defects in the octanethiol monolayer are prime sites for molecular exchange. A surplus of DTC in the solution drives substitution that can lead to the complete removal of thiol from the surface. When a Au(111) surface is exposed to solutions containing both octanethiol and dithiocarbamate (DTC), both molecular species compete for available ad- sorption sites. At equal octanethiol-to-DTC ratios, molecular exchange hinders octanethiol monolayer formation. Higher octanethiol concentration in solution results in the incorporation of thiol into the resulting monolayer, with a strong dependence on the chain length of the DTC molecules.

  10. Custom-tailored adsorbers: A molecular dynamics study on optimal design of ion exchange chromatography material.

    PubMed

    Lang, Katharina M H; Kittelmann, Jörg; Pilgram, Florian; Osberghaus, Anna; Hubbuch, Jürgen

    2015-09-25

    The performance of functionalized materials, e.g., ion exchange resins, depends on multiple resin characteristics, such as type of ligand, ligand density, the pore accessibility for a molecule, and backbone characteristics. Therefore, the screening and identification process for optimal resin characteristics for separation is very time and material consuming. Previous studies on the influence of resin characteristics have focused on an experimental approach and to a lesser extent on the mechanistic understanding of the adsorption mechanism. In this in silico study, a previously developed molecular dynamics (MD) tool is used, which simulates any given biomolecule on resins with varying ligand densities. We describe a set of simulations and experiments with four proteins and six resins varying in ligand density, and show that simulations and experiments correlate well in a wide range of ligand density. With this new approach simulations can be used as pre-experimental screening for optimal adsorber characteristics, reducing the actual number of screening experiments, which results in a faster and more knowledge-based development of custom-tailored adsorbers.

  11. Molecular Insights into the pH-Dependent Adsorption and Removal of Ionizable Antibiotic Oxytetracycline by Adsorbent Cyclodextrin Polymers

    PubMed Central

    Zhang, Yu; Cai, Xiyun; Xiong, Weina; Jiang, Hao; Zhao, Haitong; Yang, Xianhai; Li, Chao; Fu, Zhiqiang; Chen, Jingwen

    2014-01-01

    Effects of pH on adsorption and removal efficiency of ionizable organic compounds (IOCs) by environmental adsorbents are an area of debate, because of its dual mediation towards adsorbents and adsorbate. Here, we probe the pH-dependent adsorption of ionizable antibiotic oxytetracycline (comprising OTCH2+, OTCH±, OTC−, and OTC2−) onto cyclodextrin polymers (CDPs) with the nature of molecular recognition and pH inertness. OTCH± commonly has high adsorption affinity, OTC− exhibits moderate affinity, and the other two species have negligible affinity. These species are evidenced to selectively interact with structural units (e.g., CD cavity, pore channel, and network) of the polymers and thus immobilized onto the adsorbents to different extents. The differences in adsorption affinity and mechanisms of the species account for the pH-dependent adsorption of OTC. The mathematical equations are derived from the multiple linear regression (MLR) analysis of quantitatively relating adsorption affinity of OTC at varying pH to adsorbent properties. A combination of the MLR analysis for OTC and molecular recognition of adsorption of the species illustrates the nature of the pH-dependent adsorption of OTC. Based on this finding, γ-HP-CDP is chosen to adsorb and remove OTC at pH 5.0 and 7.0, showing high removal efficiency and strong resistance to the interference of coexisting components. PMID:24465975

  12. Review article: the molecular adsorbents recirculating system (MARS) in liver failure.

    PubMed

    Sen, S; Mookerjee, R P; Davies, N A; Williams, R; Jalan, R

    2002-12-01

    In recent years different artificial liver support systems are being developed for use in patients with acute decompensation of chronic liver disease or acute liver failure. The molecular adsorbents recirculating system (MARS), a device in which patient's blood is dialysed across an albumin-impregnated membrane against a recirculated albumin-containing solution, seems to be effective in removing albumin-bound toxins, such as fatty acids, bile acids and bilirubin. Although the clinical experience with MARS is scarce, some pilot studies have reported its effectiveness at improving liver function and hepatic encephalopathy in patients with acute decompensation of chronic liver disease, and renal function in patients with hepatorenal syndrome type I. Data regarding MARS experience in acute liver failure and in primary graft dysfunction are encouraging but limited. Its real usefulness in these settings is, at present, under evaluation in randomized controlled clinical trials.

  13. Dynamics of Functionalized Surface Molecular Monolayers Studied with Ultrafast Infrared Vibrational Spectroscopy

    PubMed Central

    Rosenfeld, Daniel E.; Nishida, Jun; Yan, Chang; Gengeliczki, Zsolt; Smith, Brian J.; Fayer, Michael D.

    2012-01-01

    The structural dynamics of thin films consisting of tricarbonyl (1,10-phenanthroline)rhenium chloride (RePhen(CO)3Cl) linked to an alkyl silane monolayer through a triazole linker synthesized on silica-on-calcium-fluoride substrates are investigated using ultrafast infrared (IR) techniques. Ultrafast 2D IR vibrational echo experiments and polarization selective heterodyne detected transient grating (HDTG) measurements, as well as polarization dependent FT-IR and AFM experiments are employed to study the samples. The vibrational echo experiments measure spectral diffusion, while the HDTG experiments measure the vibrational excited state population relaxation and investigate the vibrational transition dipole orientational anisotropy decay. To investigate the anticipated impact of vibrational excitation transfer, which can be caused by the high concentration of RePhen(CO)3Cl in the monolayer, a concentration dependence of the spectral diffusion is measured. To generate a range of concentrations, mixed monolayers consisting of both hydrogen terminated and triazole/RePhen(CO)3Cl terminated alkyl silanes are synthesized. It is found that the measured rate of spectral diffusion is independent of concentration, with all samples showing spectral diffusion of 37 ± 6 ps. To definitively test for vibrational excitation transfer, polarization selective HDTG experiments are conducted. Excitation transfer will cause anisotropy decay. Polarization resolved heterodyne detected transient grating spectroscopy is sensitive to anisotropy decay (depolarization) caused by excitation transfer and molecular reorientation. The HDTG experiments show no evidence of anisotropy decay on the appropriate time scale, demonstrating the absence of excitation transfer the RePhen(CO)3Cl. Therefore the influence of excitation transfer on spectral diffusion is inconsequential in these samples, and the vibrational echo measurements of spectral diffusion report solely on structural dynamics. A small

  14. A Comprehensive Study of Hydrogen Adsorbing to Amorphous Water ice: Defining Adsorption in Classical Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Dupuy, John L.; Lewis, Steven P.; Stancil, P. C.

    2016-11-01

    Gas–grain and gas–phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas–grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H2) in the ISM is the prototypical example of a gas–grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking probabilities and coefficients. Here, using our new definition of a sticking event, we report sticking probabilities and sticking coefficients for nine different incident kinetic energies of hydrogen atoms [5–400 K] across seven different temperatures of dust grains [10–70 K]. We find that probabilities and coefficients vary both as a function of grain temperature and incident kinetic energy over the range of 0.99–0.22.

  15. OZONE REACTION WITH N-ALDEHYDES (N=4-10), BENZALDEHYDE, ETHANOL, ISOPROPANOL, AND N-PROPANOL ADSORBED ON A DUAL-BED GRAPHITIZED CARBON/CARBON MOLECULAR SIEVE ADSORBENT CARTRIDGE

    EPA Science Inventory

    Ozone reacts with n-aldehydes (n = 4 - 10), benzaldehyde, ethanol, isopropanol, and n-propanol adsorbed on a dual-bed graphitized carbon/carbon molecular sieve adsorbent cartridge. Destruction of n-aldehydes increases with n number and with ozone concentration. In some samp...

  16. Ligand Replacement Approach to Raman-Responded Molecularly Imprinted Monolayer for Rapid Determination of Penicilloic Acid in Penicillin.

    PubMed

    Zhang, Liying; Jin, Yang; Huang, Xiaoyan; Zhou, Yujie; Du, Shuhu; Zhang, Zhongping

    2015-12-01

    Penicilloic acid (PA) is a degraded byproduct of penicillin and often causes fatal allergies to humans, but its rapid detection in penicillin drugs remains a challenge due to its similarity to the mother structure of penicillin. Here, we reported a ligand-replaced molecularly imprinted monolayer strategy on a surface-enhanced Raman scattering (SERS) substrate for the specific recognition and rapid detection of Raman-inactive PA in penicillin. The bis(phenylenediamine)-Cu(2+)-PA complex was first synthesized and stabilized onto the surface of silver nanoparticle film that was fabricated by a bromide ion-added silver mirror reaction. A molecularly imprinted monolayer was formed by the further modification of alkanethiol around the stabilized complex on the Ag film substrate, and the imprinted recognition site was then created by the replacement of the complex template with Raman-active probe molecule p-aminothiophenol. When PA rebound into the imprinted site in the alkanethiol monolayer, the SERS signal of p-aminothiophenol exhibited remarkable enhancement with a detection limit of 0.10 nM. The imprinted monolayer can efficiently exclude the interference of penicillin and thus provides a selective determination of 0.10‰ (w/w) PA in penicillin, which is about 1 order of magnitude lower than the prescribed residual amount of 1.0‰. The strategy reported here is simple, rapid and inexpensive compared to the traditional chromatography-based methods. PMID:26545037

  17. Ligand Replacement Approach to Raman-Responded Molecularly Imprinted Monolayer for Rapid Determination of Penicilloic Acid in Penicillin.

    PubMed

    Zhang, Liying; Jin, Yang; Huang, Xiaoyan; Zhou, Yujie; Du, Shuhu; Zhang, Zhongping

    2015-12-01

    Penicilloic acid (PA) is a degraded byproduct of penicillin and often causes fatal allergies to humans, but its rapid detection in penicillin drugs remains a challenge due to its similarity to the mother structure of penicillin. Here, we reported a ligand-replaced molecularly imprinted monolayer strategy on a surface-enhanced Raman scattering (SERS) substrate for the specific recognition and rapid detection of Raman-inactive PA in penicillin. The bis(phenylenediamine)-Cu(2+)-PA complex was first synthesized and stabilized onto the surface of silver nanoparticle film that was fabricated by a bromide ion-added silver mirror reaction. A molecularly imprinted monolayer was formed by the further modification of alkanethiol around the stabilized complex on the Ag film substrate, and the imprinted recognition site was then created by the replacement of the complex template with Raman-active probe molecule p-aminothiophenol. When PA rebound into the imprinted site in the alkanethiol monolayer, the SERS signal of p-aminothiophenol exhibited remarkable enhancement with a detection limit of 0.10 nM. The imprinted monolayer can efficiently exclude the interference of penicillin and thus provides a selective determination of 0.10‰ (w/w) PA in penicillin, which is about 1 order of magnitude lower than the prescribed residual amount of 1.0‰. The strategy reported here is simple, rapid and inexpensive compared to the traditional chromatography-based methods.

  18. Molecular resonant dissociation of surface-adsorbed molecules by plasmonic nanoscissors

    NASA Astrophysics Data System (ADS)

    Zhang, Zhenglong; Sheng, Shaoxiang; Zheng, Hairong; Xu, Hongxing; Sun, Mengtao

    2014-04-01

    The ability to break individual bonds or specific modes in chemical reactions is an ardently sought goal by chemists and physicists. While photochemistry based methodologies are very successful in controlling e.g. photocatalysis, photosynthesis and the degradation of plastic, it is hard to break individual molecular bonds for those molecules adsorbed on the surface because of the weak light-absorption in molecules and the redistribution of the resulting vibrational energy both inside the molecule and to its surrounding environment. Here we show how to overcome these obstacles with a plasmonic hot-electron mediated process and demonstrate a new method that allows the sensitive control of resonant dissociation of surface-adsorbed molecules by `plasmonic' scissors. To that end, we used a high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) setup to dissociate resonantly excited NC2H6 fragments from Malachite green. The surface plasmons (SPs) excited at the sharp metal tip not only enhance the local electric field to harvest the light incident from the laser, but crucially supply `hot electrons' whose energy can be transferred to individual bonds. These processes are resonant Raman, which result in some active chemical bonds and then weaken these bonds, followed by dumping in lots of indiscriminant energy and breaking the weakest bond. The method allows for sensitive control of both the rate and probability of dissociation through their dependence on the density of hot electrons, which can be manipulated by tuning the laser intensity or tunneling current/bias voltage in the HV-TERS setup, respectively. The concepts of plasmonic scissors open up new versatile avenues for the deep understanding of in situ surface-catalyzed chemistry.The ability to break individual bonds or specific modes in chemical reactions is an ardently sought goal by chemists and physicists. While photochemistry based methodologies are very successful in controlling e.g. photocatalysis

  19. Self-assembled monolayer of o-aminothiophenol on Fe(1 1 0) surface: a combined study by electrochemistry, in situ STM, and molecular simulations

    NASA Astrophysics Data System (ADS)

    Kong, De-Sheng; Yuan, Shi-Ling; Sun, Yu-Xi; Yu, Zhang-Yu

    2004-12-01

    Electrochemical measurements, in situ scanning tunneling microscopy (STM) observation, and molecular mechanics (MM) simulations were performed to study the physiochemical properties such as the corrosion-inhibition effect and the optimal packing structure of o-aminothiophenol (OATP) self-assembled monolayer (SAM) formed on Fe(1 1 0) surface in 0.1 M NaClO 4 solution. The formation of OATP SAMs drastically depressed the Faradaic processes at the Fe(1 1 0) surface and reduced the electrical double-layer capacitance at the electrode/electrolyte interface, revealing the anticorrosion property and the blocking behavior of OATP adlayers. Two-dimensional ordered molecular arrays of OATP on Fe(1 1 0) surface with a p(2 × 2) commensurate structure were observed by STM measurements. MM calculations showed that the p(2 × 2) packing pattern is indeed the preferable structure for OATP molecules adsorbed on Fe(1 1 0), in accordance with STM experiments. The OATP SAM on Fe(1 1 0) is ≈0.50 nm in thickness and with a dielectric constant of ˜7.0.

  20. On the valve nature of a monolayer of aligned molecular magnets in tunneling spin-polarized electrons: Towards organic molecular spintronics

    SciTech Connect

    Chakrabarti, Sudipto; Pal, Amlan J.

    2014-01-06

    We form a monolayer of magnetic organic molecules and immobilize their moments pointing either upwards or downwards with respect to the substrate through an electrostatic-binding process. Such a monolayer is probed with a scanning tunneling microscope tip, which is also magnetized with the magnetization vector pointing towards (or away from) apex of the tip. From spin-polarized tunneling current, we show that the current was higher when magnetization vectors of the tip and molecules were parallel as compared to that when they were anti-parallel. We show that for tunneling of spin-polarized electrons, aligned organic molecular magnets can act as a valve.

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

    PubMed

    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.

  2. Fragmentation of molecular adsorbates by electron and ion bombardment: methoxy chemistry on Al(111)

    SciTech Connect

    Basu, P.; Chen, J.G.; Ng, L.; Colaianni, M.L.; Yates, J.T.

    1988-08-15

    High-resolution electron-energy-loss spectroscopy (HR)EELS has been used successfully to provide direct spectroscopic evidence regarding details of the molecular fragmentation of methoxy (CH3O) on Al(lll) caused by energetic electron and ion beams. Chemisorbed methoxy on Al(lll) is produced by heating of absorbed CH3OH. Irradiation of CH3O(a) by either energetic (approx 300 eV) electrons or Ar+ ions results in C-O and C-H bond scission with simultaneous formation of Al-O and Al-C bonds. During electron stimulated desorption the CH3O(a) species undergo sequential fragmentation first to CHx groups that are captured by the surface and in the final decay process to adsorbed carbon. C-O bonds in CH3O9a) are depleted preferentially compared to C-H bonds in CHx(a) species. The electron-induced sequential fragmentation of the patent CH3 group (from methoxy) to resultant CHx(a) occurs with an efficiency approx. 3 orders of magnitude greater than the subsequent process of CHx(a)=C(a). Cross sections for various bond scission processes in electron and ion bombardment have been estimated.

  3. Molecular simulations of intermediate and long alkanes adsorbed on graphite: tuning of non-bond interactions.

    PubMed

    Firlej, Lucyna; Kuchta, Bogdan; Roth, Michael W; Wexler, Carlos

    2011-04-01

    The interplay between the torsional potential energy and the scaling of the 1-4 van der Waals and Coulomb interactions determines the stiffness of flexible molecules. In this paper we demonstrate for the first time that the precise value of the nonbond scaling factor (SF)--often a value assumed without justification--has a significant effect on the critical properties and mechanisms of systems undergoing a phase transition, and that, for accurate simulations, this scaling factor is highly dependent on the system under consideration. In particular, by analyzing the melting of n-alkanes (hexane C6, dodecane C12, tetracosane C24) on graphite, we show that the SF is not constant over varying alkane chain lengths when the structural correlated transformations are concerned. Instead, monotonic decrease of SF with the molecular length drives a cross-over between two distinct mechanisms for melting in such systems. In a broad sense we show that the choice for SF in any simulation containing adsorbed or correlated long molecules needs to be carefully considered.

  4. Meta-analysis of survival with the molecular adsorbent recirculating system for liver failure

    PubMed Central

    He, Guo-Lin; Feng, Lei; Duan, Chong-Yang; Hu, Xiang; Zhou, Chen-Jie; Cheng, Yuan; Pan, Ming-Xin; Gao, Yi

    2015-01-01

    This study aims to assess the treatment effects of the molecular adsorbent recirculating system (MARS) in patients with acute and acute-on-chronic liver failure. We searched MEDLINE, EMBASE, and the Cochrane Controlled Trials Registry database between January 1966 and January 2014. We included randomized controlled trials, which compared the treatment effects of MARS with standard medical treatment. Study quality assessed according to Consolidated Standards of Reporting Trials (CONSORT) criteria. The risk ratio was used as the effect-size measure according to a fixed-effects model. The search strategy revealed 72 clinical studies, 10 of which were randomized controlled trials that met the criteria and were included. Four addressed ALF (93 patients) and six addressed AOCLF (453 patients). The mean CONSORT score was 15 (range 10-20). By meta-analysis, MARS significantly improved survival in ALF (risk ratio 0.61; 95% CI 0.38, 0.97; P = 0.04). There was no significant survival benefit in AOCLF (risk ratio 0.88; 95% CI 0.74, 1.06; P = 0.16). MARS significantly improved survival in patients with acute liver failure, however, there is no evidence that it improved survival in patients with acute-on-chronic liver failure. In conclusion, the present meta-analysis indicates that MARS therapy can improve survival in patients with ALF. It is necessary to develop MARS treatment because of the increasing demand for liver transplantation and the risk of liver failure. PMID:26770295

  5. Extracorporeal Elimination of Piperacillin/Tazobactam during Molecular Adsorbent Recirculating System Therapy.

    PubMed

    Personett, Heather A; Larson, Scott L; Frazee, Erin N; Nyberg, Scott L; El-Zoghby, Ziad M

    2015-08-01

    Use of the Molecular Adsorbent Recirculating System (MARS) as a liver support device continues to grow worldwide. Various components of the MARS circuit remove both protein-bound and water-soluble molecules. Little is known about the extent of the enhanced clearance mechanisms used in MARS therapy on drug elimination. Of particular interest to acute care practitioners is the impact of MARS on antibiotic clearance, as suboptimal concentrations of such drugs can negatively impact patient outcomes. The properties of piperacillin/tazobactam suggest that elimination may be enhanced in the setting of MARS therapy. We describe two cases in which this was studied. Piperacillin concentrations were determined at various points within the MARS circuit, and patient serum concentrations were reported throughout the dosing interval while receiving MARS therapy. Piperacillin concentrations in both cases were in excess of the desired goal minimum inhibitory concentrations for treatment of gram-negative infections. Use of an extended-infusion strategy of piperacillin/tazobactam 3.375 or 4.5 g given every 8 hours maintained desired serum levels throughout the dosing interval. To our knowledge, this is the second published report on the use of piperacillin/tazobactam during MARS therapy. These case reports reveal successful dosing strategies for patients requiring piperacillin/tazobactam while receiving MARS therapy, as well as quantify the influence of individual MARS elements on drug extraction. PMID:26289310

  6. Molecular dynamics simulations of Palmitic acid adsorbed on NaCl

    NASA Astrophysics Data System (ADS)

    Lovrić, Josip; Brizquez, Stéphane; Duflot, Denis; Monnerville, Maurice; Pouilly, Brigitte; Toubin, Céline

    2015-04-01

    The aerosol and gases effects in the atmosphere play an important role on health, air quality and climate, affecting both political decisions and economic activities around the world [1]. Among the several approaches of studying the origin of these effects, computational modeling is of fundamental importance, providing insights on the elementary chemical processes. Sea salts are the most important aerosol in the troposphere (109T/year) [2]. Our theoretical work consists in modeling a (100) NaCl surface coated with palmitic acid (PA) molecules. Molecular dynamics simulations are carried out with the GROMACS package [3], in the NPT ensemble at different temperatures, different PA coverages and various humidity. We focus on two aspects of the PA organization at the salt surface: the first one is related to transition in molecular orientation of the adsorbate as a function of PA coverage. The second one implies the effect of humidity, by adding water molecules, on the organization of the fatty acid at the salt surface, and especially on the occurrence of PA isolated islands as observed in the experiments [4]. For high humidity conditions, PA are removed from the salt surface and form islands on top of the water. This effect is enhanced when temperature increases. Acknowledgments: this research has been supported by the CaPPA project (Chemical and Physical Properties of the Atmosphere), funded by the French National Research Agency (ANR) through the PIA (Programme d'Investissement d'Avenir) under contract ANR-10-LABX-005. [1] O. Boucher et al, 5th Assessment Report IPCC, (2013) [2] B. J. Finlayson-Pitts, Chem. Rev.103, 4801-4822 (2003) [3] http://www.gromacs.org/ [4] S. Sobanska et al, private communication

  7. Molecular mobility in the monolayers of foam films stabilized by porcine lung surfactant.

    PubMed Central

    Lalchev, Z I; Todorov, R K; Christova, Y T; Wilde, P J; Mackie, A R; Clark, D C

    1996-01-01

    Certain physical properties of a range of foam film types that are believed to exist in vivo in the lung have been investigated. The contribution of different lung surfactant components found in porcine lung surfactant to molecular surface diffusion in the plane of foam films has been investigated for the first time. The influence of the type and thickness of black foam films, temperature, electrolyte concentration, and extract composition on surface diffusion has been studied using the fluorescence recovery after photobleaching technique. Fluorescent phospholipid probe molecules in foam films stabilized by porcine lung surfactant samples or their hydrophobic extracts consisting of surfactant lipids and hydrophobic lung surfactant proteins, SP-B and SP-C, exhibited more rapid diffusion than observed in films of its principal lipid component alone, L-alpha-phosphatidylcholine dipalmitoyl. This effect appears to be due to contributions from minor lipid components present in the total surfactant lipid extracts. The minor lipid components influence the surface diffusion in foam films both by their negative charge and by lowering the phase transition temperature of lung surfactant samples. In contrast, the presence of high concentrations of the hydrophillic surfactant protein A (SP-A) and non-lung-surfactant proteins in the sample reduced the diffusion coefficient (D) of the lipid analog in the adsorbed layer of the films. Hysteresis behavior of D was observed during temperature cycling, with the cooling curve lying above the heating curve. However, in cases where some surface molecular aggregation and surface heterogeneity were observed during cooling, the films became more rigid and molecules at the interfaces became immobilized. The thickness, size, capillary pressure, configuration, and composition of foam films of lung surfactant prepared in vitro support their investigation as realistic structural analogs of the surface films that exist in vivo in the lung

  8. Molecular separations with breathing metal-organic frameworks: modelling packed bed adsorbers.

    PubMed

    Van Assche, Tom R C; Baron, Gino V; Denayer, Joeri F M

    2016-03-14

    Various metal-organic framework (MOFs) adsorbents show peculiar adsorption behaviour as they can adopt different crystal phases, each phase with its own adsorption characteristics. Besides external stimuli such as temperature or light, different species of guest adsorbate can trigger a transition (breathing) of the host structure at a different pressure. Such phase transitions also occur during dynamic separations on a packed bed of adsorbent, where the concentrations of the adsorbates vary throughout axial column distance and time. This work presents a general strategy to model the adsorption behavior of such phase changing adsorbents during column separations and focuses on remarkable model predictions for pure components and binary mixtures in diluted and non-diluted conditions. During binary breakthrough experiments, the behaviour of flexible adsorbents is quite complex. A succession of complete or even partial phase transformations (resulting in phase coexistence) can occur during the adsorption process. A variety of unusual breakthrough profiles is observed for diluted binary mixtures. Simulations reveal at least five types of breakthrough profiles to emerge. The occurrence of these cases can be rationalized by the hodograph technique, combined with the phase diagram of the adsorbent. The remarkable experimental breakthrough profiles observed for ortho-xylene/ethylbenzene (diluted) and CO2/CH4 (non-diluted) separation on the flexible MIL-53 framework can be rationalized by application of the proposed model strategy. PMID:26885972

  9. Polymer composite adsorbents using particles of molecularly imprinted polymers or aluminium oxide nanoparticles for treatment of arsenic contaminated waters.

    PubMed

    Önnby, L; Pakade, V; Mattiasson, B; Kirsebom, H

    2012-09-01

    Removal of As(V) by adsorption from water solutions was studied using three different synthetic adsorbents. The adsorbents, (a) aluminium nanoparticles (Alu-NPs, <50 nm) incorporated in amine rich cryogels (Alu-cryo), (b) molecular imprinted polymers (<38 μm) in polyacrylamide cryogels (MIP-cryo) and (c) thiol functionalised cryogels (SH-cryo) were evaluated regarding material characteristics and arsenic removal in batch test and continuous mode. Results revealed that a composite design with particles incorporated in cryogels was a successful means for applying small particles (nano- and micro- scale) in water solutions with maintained adsorption capacity and kinetics. Low capacity was obtained from SH-cryo and this adsorbent was hence excluded from the study. The adsorption capacities for the composites were 20.3 ± 0.8 mg/g adsorbent (Alu-cryo) and 7.9 ± 0.7 mg/g adsorbent (MIP-cryo) respectively. From SEM images it was seen that particles were homogeneously distributed in Alu-cryo and heterogeneously distributed in MIP-cryo. The particle incorporation increased the mechanical stability and the polymer backbones of pure polyacrylamide (MIP-cryo) were of better stability than the amine containing polymer backbone (Alu-cryo). Both composites worked well in the studied pH range of pH 2-8. Adsorption tested in real wastewater spiked with arsenic showed that co-ions (nitrate, sulphate and phosphate) affected arsenic removal for Alu-cryo more than for MIP-cryo. Both composites still adsorbed well in the presence of counter-ions (copper and zinc) present at low concentrations (μg/l). The unchanged and selective adsorption in realistic water observed for MIP-cryo was concluded to be due to a successful imprinting, here controlled using a non-imprinted polymer (NIP). A development of MIP-cryo is needed, considering its low adsorption capacity.

  10. Lubrication and load-bearing properties of human salivary pellicles adsorbed ex vivo on molecularly smooth substrata.

    PubMed

    Harvey, Neale M; Yakubov, Gleb E; Stokes, Jason R; Klein, Jacob

    2012-01-01

    In a series of Surface Force Balance experiments, material from human whole saliva was adsorbed to molecularly smooth mica substrata (to form an 'adsorbed salivary film'). Measurements were taken of normal (load bearing, F (n)) and shear (frictional, F (s)*) forces between two interacting surfaces. One investigation involved a salivary film formed by overnight adsorption from undiluted, centrifuged saliva, with the adsorbed film rinsed with pure water before measurement. Measurements were taken under pure water and 70 mM NaNO(3). In a second investigation, a film was formed from and measured under a solution of 7% filtered saliva in 10 mM NaNO(3). F (n) results for both systems showed purely repulsive layers, with an uncompressed thickness of 35-70 nm for the diluted saliva investigation and, prior to the application of shear, 11 nm for the rinsed system. F (s)* was essentially proportional to F (n) for all systems and independent of shear speed (in the range 100-2000 nm s(-1)), with coefficients of friction μ ≈ 0.24 and μ ≈ 0.46 for the unrinsed and rinsed systems, respectively. All properties of the rinsed system remained similar when the pure water measurement environment was changed to 70 mM NaNO(3). For all systems studied, shear gave rise to an approximately threefold increase in the range of normal forces, attributed to the ploughing up of adsorbed material during shear to form debris that stood proud of the adsorbed layer. The results provide a microscopic demonstration of the wear process for a salivary film under shear and may be of particular interest for understanding the implications for in vivo oral lubrication under conditions such as rinsing of the mouth cavity. The work is interpreted in light of earlier studies that showed a structural collapse and increase in friction for an adsorbed salivary film in an environment of low ionic strength.

  11. Perforated monolayers

    SciTech Connect

    Regen, S.L.

    1989-12-01

    The goals of this DOE-sponsored program are to create novel organic thin films that possess well-defined and adjustable molecular pores; i.e. perforated monolayers,'' and to use such film for fabricating composite membranes that have unique permeation characteristics. The specific strategy that has been adopted involves (1) the synthesis of surfactant molecules bearing internal pores, i.e., porous surfactants,'' (2) the assembly of such molecules at an air--water interface, and (3) the stabilization of the resulting assembly via polymerization, before or after transfer to a macroporous support. Research that has been carried out to date has demonstrated the feasibility of using suitably designed calix(n)arene molecules as a basis for constructing perforated monolayers. Specifically, a broad range of calix(n)arenes have been mercurated with mercury trifluoracetate, and used to form polymerized and porous monolayers at the air--water interface. In related studies, p-tert- butylcalix(6)arene has been shown to produce stable monolayers at the air--water interface; removal of the p-tert-butyl groups afford a unique vesicle-forming surfactant, calix(6)arene.

  12. Molecular dynamics study of n-alcohols adsorbed on an aqueous electrolyte solution

    NASA Astrophysics Data System (ADS)

    Daiguji, Hirofumi

    2001-07-01

    The distribution of normal alcohol (n-alcohol) on water and the effect of salt on the structural and dynamical properties of n-alcohol on aqueous electrolyte solutions were investigated using molecular dynamics simulation. The stability of the alcohol distribution was studied for three types of n-alcohol (n-propanol, C3H7OH; n-heptanol, C7H15OH; and n-undecanol, C11H23OH), four or five concentrations of alcohol, and three concentrations of salt. The simulation results reveal the following. The distribution of n-propanol on water is homogeneous at all n-alcohol concentrations studied here and the distribution of n-heptanol and n-undecanol on water is heterogeneous. The n-alcohol concentration at which fluctuations in the alcohol distribution begin to increase depends on the length of the hydrocarbon chain of the n-alcohol. Salt concentration affects the surface excess concentration of n-alcohol and the stability of the adsorbed layer of n-alcohol. The degree of each effect depends on the length of the hydrocarbon chain of the n-alcohol. For n-undecanol, the surface structure of n-alcohol is independent of salt concentration because interaction between the hydrocarbon chains is sufficiently strong. In absorption refrigeration technology, to enhance the absorption rate of water vapor into a highly concentrated aqueous electrolyte solution, a small amount of alcohols is added to the aqueous electrolyte solution, which induces cellular convection referred to as Marangoni instability. Among the three types of n-alcohol studied here, only n-heptanol induces strong cellular convection. The simulations reveal two required conditions for Marangoni instability: generation of fluctuations in the alcohol distribution on water, and strong correlation between the structural and dynamical properties and salt concentration. Among the three types of n-alcohol studied here, based on the simulations, only n-heptanol satisfies both conditions.

  13. Organic transistor memory with a charge storage molecular double-floating-gate monolayer.

    PubMed

    Tseng, Chiao-Wei; Huang, Ding-Chi; Tao, Yu-Tai

    2015-05-13

    A flexible, low-voltage, and nonvolatile memory device was fabricated by implanting a functional monolayer on an aluminum oxide dielectric surface in a pentacene-based organic transistor. The monolayer-forming molecule contains a phosphonic acid group as the anchoring moiety and a charge-trapping core group flanked between two alkyl chain spacers as the charge trapping site. The memory characteristics strongly depend on the monolayer used due to the localized charge-trapping capability for different core groups, including the diacetylenic (DA) unit as the hole carrier trap, the naphthalenetetracarboxyldiimide (ND) unit as the electron carrier trap, and the one with both DA and ND units present, respectively. The device with the monolayer carrying both DA and ND groups has a larger memory window than that for the one containing DA only and a longer retention time than that for the one containing DA or ND only, giving a memory window of 1.4 V and a retention time around 10(9) s. This device with hybrid organic monolayer/inorganic dielectrics also exhibited rather stable device characteristics upon bending of the polymeric substrate.

  14. Effects of cholesterol component on molecular interactions between paclitaxel and phospholipid within the lipid monolayer at the air-water interface.

    PubMed

    Zhao, Lingyun; Feng, Si-Shen

    2006-08-01

    Cholesterol is a main component of the cell membrane and could have significant effects on drug-cell membrane interactions and thus the therapeutic efficacy of the drug. It also plays an important role in liposomal formulation of drugs for controlled and targeted delivery. In this research, Langmuir film technique, atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) are employed for a systematic investigation on the effects of cholesterol component on the molecular interactions between a prototype antineoplastic drug (paclitaxel) and 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) within the cell membrane by using the lipid monolayer at the air-water interface as a model of the lipid bilayer membrane and the biological cell membrane. Analysis of the measured surface pressure (pi) versus molecular area (a) isotherms of the mixed DPPC/paclitaxel/cholesterol monolayers at various molar ratios shows that DPPC, paclitaxel and cholesterol can form a non-ideal miscible system at the air-water interface. Cholesterol enhances the intermolecular forces between paclitaxel and DPPC, produces an area-condensing effect and thus makes the mixed monolayer more stable. Investigation of paclitaxel penetration into the mixed DPPC/cholesterol monolayer shows that the existence of cholesterol in the DPPC monolayer can considerably restrict the drug penetration into the monolayer, which may have clinical significance for diseases of high cholesterol. FTIR and AFM investigation on the mixed monolayer deposited on solid surface confirmed the obtained results.

  15. Mechanical and charge transport properties of alkanethiol self-assembled monolayers on Au (111) surface: The Role of Molecular Tilt

    SciTech Connect

    Mulleregan, Alice; Qi, Yabing; Ratera, Imma; Park, Jeong Y.; Ashby, Paul D.; Quek, Su Ying; Neaton, J. B.; Salmeron, Miquel

    2007-11-12

    The relationship between charge transport and mechanical properties of alkanethiol self-assembled monolayers (SAM) on Au(111) films has been investigated using an atomic force microscope with a conductive tip. Molecular tilts induced by the pressure applied by the tip cause stepwise increases in film conductivity. A decay constant {beta} = 0.57 {+-} 0.03 {angstrom}{sup -1} was found for the current passing through the film as a function of tip-substrate separation due to this molecular tilt. This is significantly smaller than the value of {approx} 1 {angstrom}{sup -1} found when the separation is changed by changing the length of the alkanethiol molecules. Calculations indicate that for isolated dithiol molecules S-bonded to hollow sites, the junction conductance does not vary significantly as a function of molecular tilt. The impact of S-Au bonding on SAM conductance is discussed.

  16. Molecular self-assembly at bare semiconductor surfaces: preparation and characterization of highly organized octadecanethiolate monolayers on GaAs(001).

    PubMed

    McGuiness, Christine L; Shaporenko, Andrey; Mars, Carole K; Uppili, Sundararajan; Zharnikov, Michael; Allara, David L

    2006-04-19

    Through rigorous control of preparation conditions, organized monolayers with a highly reproducible structure can be formed by solution self-assembly of octadecanethiol on GaAs (001) at ambient temperature. A combination of characterization probes reveal a structure with conformationally ordered alkyl chains tilted on average at 14 +/- 1 degrees from the surface normal with a 43 +/- 5 degrees twist, a highly oleophobic and hydrophobic ambient surface, and direct S-GaAs attachment. Analysis of the tilt angle and film thickness data shows a significant mismatch of the average adsorbate molecule spacings with the spacings of an intrinsic GaAs(001) surface lattice. The monolayers are stable up to approximately 100 degrees C and exhibit an overall thermal stability which is lower than that of the same monolayers on Au[111] surfaces. A two-step solution assembly process is observed: rapid adsorption of molecules over the first several hours to form disordered structures with molecules lying close to the substrate surface, followed by a slow densification and asymptotic approach to final ordering. This process, while similar to the assembly of alkanethiols on Au[111], is nearly 2 orders of magnitude slower. Finally, despite differences in assembly rates and the thermal stability, exchange experiments with isotopically tagged molecules show that the octadecanethiol on GaAs(001) monolayers undergo exchange with solute thiol molecules at roughly the same rate as the corresponding exchanges of the same monolayers on Au[111]. PMID:16608359

  17. Molecular self-assembly at bare semiconductor surfaces: preparation and characterization of highly organized octadecanethiolate monolayers on GaAs(001).

    PubMed

    McGuiness, Christine L; Shaporenko, Andrey; Mars, Carole K; Uppili, Sundararajan; Zharnikov, Michael; Allara, David L

    2006-04-19

    Through rigorous control of preparation conditions, organized monolayers with a highly reproducible structure can be formed by solution self-assembly of octadecanethiol on GaAs (001) at ambient temperature. A combination of characterization probes reveal a structure with conformationally ordered alkyl chains tilted on average at 14 +/- 1 degrees from the surface normal with a 43 +/- 5 degrees twist, a highly oleophobic and hydrophobic ambient surface, and direct S-GaAs attachment. Analysis of the tilt angle and film thickness data shows a significant mismatch of the average adsorbate molecule spacings with the spacings of an intrinsic GaAs(001) surface lattice. The monolayers are stable up to approximately 100 degrees C and exhibit an overall thermal stability which is lower than that of the same monolayers on Au[111] surfaces. A two-step solution assembly process is observed: rapid adsorption of molecules over the first several hours to form disordered structures with molecules lying close to the substrate surface, followed by a slow densification and asymptotic approach to final ordering. This process, while similar to the assembly of alkanethiols on Au[111], is nearly 2 orders of magnitude slower. Finally, despite differences in assembly rates and the thermal stability, exchange experiments with isotopically tagged molecules show that the octadecanethiol on GaAs(001) monolayers undergo exchange with solute thiol molecules at roughly the same rate as the corresponding exchanges of the same monolayers on Au[111].

  18. Adsorbed Proteins Influence the Biological Activity and Molecular Targeting of Nanomaterials

    SciTech Connect

    Dutta, Debamitra; Sundaram, S. K.; Teeguarden, Justin G.; Riley, Brian J.; Fifield, Leonard S.; Jacobs, Jon M.; Addleman, Raymond S.; Kaysen, George A.; Moudgil, Brij M.; Weber, Thomas J.

    2007-11-01

    The possible combination of unique physicochemical properties operating at unique sites of action within cells and tissues has led to considerable uncertainty surrounding nanomaterial toxic potential. Here we have investigated the relative importance of proteins adsorbed onto nanomaterial surfaces in guiding uptake and toxicity to determine whether a priori identification of adsorbed proteins will contribute to nanomaterial toxicity assessment. Albumin was identified as the major protein adsorbed onto single walled carbon nanotubes (SWCNTs) following incubation with fetal bovine or human serum/plasma, but not when plasma from the Nagase Analbuminemic Rat (NAR) was used, and precoating SWCNTs with a non-ionic surfactant (Pluronic F127) inhibited albumin adsorption. Damaged or structurally altered albumin is rapidly cleared by scavenger receptors. In the RAW 264.7 macrophage-like model, we observed that SWCNTs inhibited the induction of cyclooxygenase-2 (Cox-2) by lipopolysaccharide (LPS; 1 ng/ml, 6 hr) and this anti-inflammatory response was inhibited by fucoidan (scavenger receptor antagonist) and by precoating SWCNTs with Pluronic F127. Fucoidan also reduced the uptake of fluorescent SWCNTs (Alexa647) in RAW 264.7 cells. Albumin-coated SWCNTs reduced LPS-mediated Cox-2 induction. SWCNTs did not appear to reduce binding of a fluorescent LPS (Alexa488) to RAW 264.7 cells. The profile of proteins adsorbed onto amorphous silica (50 – 1000 nm) was qualitatively different, relative to SWCNTs, and coating amorphous silica with Pluronic F127 dramatically reduced protein binding and toxicity. Collectively, these observations are consistent with an important role for adsorbed proteins in guiding nanomaterial disposition and toxicity.

  19. Molecular Structure and Equilibrium Forces of Bovine Submaxillary Mucin Adsorbed at a Solid-Liquid Interface.

    PubMed

    Zappone, Bruno; Patil, Navinkumar J; Madsen, Jan B; Pakkanen, Kirsi I; Lee, Seunghwan

    2015-04-21

    By combining dynamic light scattering, circular dichroism spectroscopy, atomic force microscopy, and surface force apparatus, the conformation of bovine submaxillary mucin in dilute solution and nanomechanical properties of mucin layers adsorbed on mica have been investigated. The samples were prepared by additional chromatographic purification of commercially available products. The mucin molecule was found to have a z-average hydrodynamic diameter of ca. 35 nm in phosphate buffered solution, without any particular secondary or tertiary structure. The contour length of the mucin is larger than, yet of the same order of magnitude as the diameter, indicating that the molecule can be modeled as a relatively rigid polymeric chain due to the large persistence length of the central glycosylated domain. Mucin molecules adsorbed abundantly onto mica from saline buffer, generating polymer-like, long-ranged, repulsive, and nonhysteretic forces upon compression of the adsorbed layers. Detailed analysis of such forces suggests that adsorbed mucins had an elongated conformation favored by the stiffness of the central domain. Acidification of aqueous media was chosen as means to reduce mucin-mucin and mucin-substrate electrostatic interactions. The hydrodynamic diameter in solution did not significantly change when the pH was lowered, showing that the large persistence length of the mucin molecule is due to steric hindrance between sugar chains, rather than electrostatic interactions. Remarkably, the force generated by an adsorbed layer with a fixed surface coverage also remained unaltered upon acidification. This observation can be linked to the surface-protective, pH-resistant role of bovine submaxillary mucin in the variable environmental conditions of the oral cavity. PMID:25806669

  20. Conformation, orientation and interaction in molecular monolayers: A surface second harmonic and sum frequency generation study

    SciTech Connect

    Superfine, R.; Huang, J.Y.; Shen, Y.R.

    1988-12-01

    We have used sum frequency generation (SFG) to study the order in a silane monolayer before and after the deposition of a coadsorbed liquid crystal monolayer. We observe an increase in the order of the chain of the silane molecule induced by the interpenetration of the liquid crystal molecules. By using second harmonic generation (SHG) and SFG, we have studied the orientation and conformation of the liquid crystal molecule on clean and silane coated glass surfaces. On both surfaces, the biphenyl group is tilted by 70{degree} with the alkyl chain end pointing away from the surface. The shift in the C-H stretch frequencies in the coadsorbed system indicates a significant interaction between molecules. 9 refs., 3 figs.

  1. Molecular junctions of self-assembled monolayers with conducting polymer contacts.

    PubMed

    Neuhausen, Alexander B; Hosseini, Ali; Sulpizio, Joseph A; Chidsey, Christopher E D; Goldhaber-Gordon, David

    2012-11-27

    We present a method to fabricate individually addressable junctions of self-assembled monolayers (SAMs) that builds on previous studies which have shown that soft conductive polymer top contacts virtually eliminate shorts through the SAMs. We demonstrate devices with nanoscale lateral dimensions, representing an order of magnitude reduction in device area, with high yield and relatively low device-to-device variation, improving several features of previous soft contact devices. The devices are formed in pores in an inorganic dielectric layer with features defined by e-beam lithography and dry etching. We replace the aqueous PEDOT:PSS conductive polymer used in prior devices with Aedotron P, a low-viscosity, amphiphilic polymer, allowing incorporation of self-assembled monolayers with either hydrophobic or hydrophilic termination with the same junction geometry and materials. We demonstrate the adaptability of this new design by presenting transport measurements on SAMs composed of alkanethiols with methyl, thiol, carboxyl, and azide terminations. We establish that the observed room-temperature tunnel barrier is primarily a function of monolayer thickness, independent of the terminal group's hydrophilicity. Finally, we investigate the temperature dependence of transport and show that the low-temperature behavior is based on the energy distribution of sites from which carriers can tunnel between the polymer and gold contacts, as described by a model of variable-range hopping transport in a disordered conductor.

  2. Molecular junctions of self-assembled monolayers with conducting polymer contacts.

    PubMed

    Neuhausen, Alexander B; Hosseini, Ali; Sulpizio, Joseph A; Chidsey, Christopher E D; Goldhaber-Gordon, David

    2012-11-27

    We present a method to fabricate individually addressable junctions of self-assembled monolayers (SAMs) that builds on previous studies which have shown that soft conductive polymer top contacts virtually eliminate shorts through the SAMs. We demonstrate devices with nanoscale lateral dimensions, representing an order of magnitude reduction in device area, with high yield and relatively low device-to-device variation, improving several features of previous soft contact devices. The devices are formed in pores in an inorganic dielectric layer with features defined by e-beam lithography and dry etching. We replace the aqueous PEDOT:PSS conductive polymer used in prior devices with Aedotron P, a low-viscosity, amphiphilic polymer, allowing incorporation of self-assembled monolayers with either hydrophobic or hydrophilic termination with the same junction geometry and materials. We demonstrate the adaptability of this new design by presenting transport measurements on SAMs composed of alkanethiols with methyl, thiol, carboxyl, and azide terminations. We establish that the observed room-temperature tunnel barrier is primarily a function of monolayer thickness, independent of the terminal group's hydrophilicity. Finally, we investigate the temperature dependence of transport and show that the low-temperature behavior is based on the energy distribution of sites from which carriers can tunnel between the polymer and gold contacts, as described by a model of variable-range hopping transport in a disordered conductor. PMID:23035989

  3. MARS (Molecular Adsorbent Recirculating System): experience in 34 cases of acute liver failure.

    PubMed

    Novelli, Gilnardo; Rossi, Massimo; Pretagostini, Renzo; Poli, Luca; Novelli, Luigi; Berloco, Pasquale; Ferretti, Giancarlo; Iappelli, Massimo; Cortesini, Raffaello

    2002-01-01

    As reported in the literature, the mortality rates for patients with Acute Hepatic Failure (AHF) approaches 80% in cases in which liver transplantation is not possible. Post-transplant mortality mostly depends on the severity of the neurological condition at the time of the operation (20% in I-II degree coma patients and 44% in III degree coma patients). The primary indications for liver transplantation in AHF are Fulminant Hepatitis (FH)(93%), Subfulminant Hepatitis (5%) and other indications (2%). Other causes of AHF are Primary Non-Function (PNF) and Delayed Function (DF), which occur in 7-10%. Therefore it becomes necessary to monitor the patients with a Liver Support Device to be able to improve the clinical condition of the patients before liver transplantation (LT). In our experience we used the Molecular Adsorbent Recirculating System (MARS) (MARS Monitor; Teraklin AG, Rostock Germany), which enables the selective removal of albumin-bound substances accumulating in liver failure by the use of albumin-enriched dialysate. The system is used as a bridging device to orthotopic liver transplantation (OLT) of patients with FHF. We studied 34 patients, including 16 males and 18 females: 9 were affected by Primary-Non-Function (PNF), nine by Fulminant Hepatitis (FH), six by Delayed-Non-Function (DNF), and ten by Acute on Chronic Hepatic Failure (AOCHF). The average age of the patients was 41.8 years and the average number of applications was 6.4; the median length of application was about eight hours. The parameters that we monitored, before and after each treatment, were neurological status (EEG, cerebral CT, Glasgow Coma Score), haemodynamic parameters, acid base equilibrium, and blood gas analysis. We also monitored hepatic and renal function. In addition, the clinical conditions of the patients were monitored using kidney and liver ultrasound/ultrasonography (US). Inclusion criteria were bilirubin > 15 mg/dL, ammonia > 160 micro g/dL and a Glasgow Coma Score

  4. Removal of molecular adsorbates on gold nanoparticles using sodium borohydride in water.

    PubMed

    Ansar, Siyam M; Ameer, Fathima S; Hu, Wenfang; Zou, Shengli; Pittman, Charles U; Zhang, Dongmao

    2013-03-13

    The mechanism of sodium borohydride removal of organothiols from gold nanoparticles (AuNPs) was studied using an experimental investigation and computational modeling. Organothiols and other AuNP surface adsorbates such as thiophene, adenine, rhodamine, small anions (Br(-) and I(-)), and a polymer (PVP, poly(N-vinylpyrrolidone)) can all be rapidly and completely removed from the AuNP surfaces. A computational study showed that hydride derived from sodium borohydride has a higher binding affinity to AuNPs than organothiols. Thus, it can displace organothiols and all the other adsorbates tested from AuNPs. Sodium borohydride may be used as a hazard-free, general-purpose detergent that should find utility in a variety of AuNP applications including catalysis, biosensing, surface enhanced Raman spectroscopy, and AuNP recycle and reuse.

  5. Effect of molecular structure and packing density of an azo self-assembled monolayer on liquid crystal alignment.

    PubMed

    Vengatesan, M R; Lee, Seung-Ho; Son, Jong-Ho; Lim, Jeong-Ku; Song, Jang Kun

    2013-10-01

    We studied the alignment of liquid crystals (LCs) on a photo-switchable azo-containing self-assembled monolayer (azo-SAM) with different packing densities and molecular structures. The packing density of the azo-SAM substrates was varied by changing the dipping time of the substrate in azosilane monomers solution (2mM in toluene). The thickness of the monolayer on the silicon substrate increased as the dipping time was increased. The relative surface packing density on the glass substrates was estimated from the surface energies of the azo-SAM. The photo-induced dynamics of liquid crystal alignment on the azo-SAM significantly varied according to the packing density of the azo-SAM and the structure of the azo-SAM molecules. The azo-SAM from long octyloxy chain-terminated azosilane (azo-S1) possessed stable homeotropic alignment even after photobuffing, while the azo-SAM from short methyl group-terminated azosilane monomer (azo-S2) showed photo-switchable homeotropic and planar alignments. However, when the packing density was increased to an excessive degree, even the azo-SAM from azo-S2 exhibited stable homeotropic alignment regardless of photobuffing.

  6. Effect of molecular structure and packing density of an azo self-assembled monolayer on liquid crystal alignment.

    PubMed

    Vengatesan, M R; Lee, Seung-Ho; Son, Jong-Ho; Lim, Jeong-Ku; Song, Jang Kun

    2013-10-01

    We studied the alignment of liquid crystals (LCs) on a photo-switchable azo-containing self-assembled monolayer (azo-SAM) with different packing densities and molecular structures. The packing density of the azo-SAM substrates was varied by changing the dipping time of the substrate in azosilane monomers solution (2mM in toluene). The thickness of the monolayer on the silicon substrate increased as the dipping time was increased. The relative surface packing density on the glass substrates was estimated from the surface energies of the azo-SAM. The photo-induced dynamics of liquid crystal alignment on the azo-SAM significantly varied according to the packing density of the azo-SAM and the structure of the azo-SAM molecules. The azo-SAM from long octyloxy chain-terminated azosilane (azo-S1) possessed stable homeotropic alignment even after photobuffing, while the azo-SAM from short methyl group-terminated azosilane monomer (azo-S2) showed photo-switchable homeotropic and planar alignments. However, when the packing density was increased to an excessive degree, even the azo-SAM from azo-S2 exhibited stable homeotropic alignment regardless of photobuffing. PMID:23871311

  7. Structural characterization of self-assembled monolayers within molecular junctions: Effects of metallization and of substrate lateral confinement

    NASA Astrophysics Data System (ADS)

    Colavita, Paula Elena

    The structure of the molecules within metal-organic-metal junctions (MOMs) fabricated via evaporation of a metal on a self-assembled monolayer (SAM), as well as the nature of the interface between the molecule and the metallic leads, can determine the electronic properties measured using these junctions. The effects that vapor deposition of a copper overlayer has on the conformation, degree of order and defect density of SAMs of both test molecules (alkanethiols) and of a prospective molecular wire (an oligo(phenylene-ethynylene), OPE) were investigated. A combination of electrochemistry, FTIR, XPS and Ion Scattering Spectroscopy was used. Results indicate that molecular conformation, orientation and monolayer order, change upon metal evaporation. Therefore, probing the conductivity of SAMs within MOMS is not necessarily equivalent to probing their conductivity prior to the formation of the second metallic contact. The nature of the SAM/Cu interface was also investigated, determining that copper tends to diffuse throughout the thickness of the monolayer over time, and that chemical interactions can take place between copper atoms and the terminal groups of molecular wires. We also report on the fabrication of gold nanowell electrode ensembles that were used to determine the density of defects found in SAMs assembled on substrates whose lateral dimensions are confined to the few hundred nanometer range. SAMs of dodecanethiol (DT) and OPE were characterized via metal decoration on polished gold macro- and nanoelectrodes (200 nm diameter). It was found that whereas OPE SAMs display a comparable number of defects on both macro- and nanoelectrodes, DT SAMs are more defective on nanoelectrodes. The second part of this thesis describes results obtained for two additional research projects. First, an investigation toward the development of an enzymatic assay for detection of native DNA nucleotides is reported. Second, the design of an aerosol deposition system for calcium

  8. Modeling adsorption: Investigating adsorbate and adsorbent properties

    NASA Astrophysics Data System (ADS)

    Webster, Charles Edwin

    1999-12-01

    Surface catalyzed reactions play a major role in current chemical production technology. Currently, 90% of all chemicals are produced by heterogeneously catalyzed reactions. Most of these catalyzed reactions involve adsorption, concentrating the substrate(s) (the adsorbate) on the surface of the solid (the adsorbent). Pore volumes, accessible surface areas, and the thermodynamics of adsorption are essential in the understanding of solid surface characteristics fundamental to catalyst and adsorbent screening and selection. Molecular properties such as molecular volumes and projected molecular areas are needed in order to convert moles adsorbed to surface volumes and areas. Generally, these molecular properties have been estimated from bulk properties, but many assumptions are required. As a result, different literature values are employed for these essential molecular properties. Calculated molar volumes and excluded molecular areas are determined and tabulated for a variety of molecules. Molecular dimensions of molecules are important in the understanding of molecular exclusion as well as size and shape selectivity, diffusion, and adsorbent selection. Molecular dimensions can also be used in the determination of the effective catalytic pore size of a catalyst. Adsorption isotherms, on zeolites, (crystalline mineral oxides) and amorphous solids, can be analyzed with the Multiple Equilibrium Analysis (MEA) description of adsorption. The MEA produces equilibrium constants (Ki), capacities (ni), and thermodynamic parameters (enthalpies, ΔHi, and entropies, ΔSi) of adsorption for each process. Pore volumes and accessible surface areas are calculated from the process capacities. Adsorption isotherms can also be predicted for existing and new adsorbate-adsorbent systems with the MEA. The results show that MEA has the potential of becoming a standard characterization method for microporous solids that will lead to an increased understanding of their behavior in gas

  9. Isocyanide ligands adsorbed on metal surfaces: applications in catalysis, nanochemistry, and molecular electronics.

    PubMed

    Angelici, Robert J; Lazar, Mihaela

    2008-10-20

    Knowledge of the coordination chemistry and reactivity of isocyanide ligands in transition-metal complexes forms the basis for understanding the adsorption and reactions of isocyanides on metal surfaces. In this overview, we explore reactions (often catalytic) of isocyanides adsorbed on metal surfaces that reflect their patterns of reactivity in metal complexes. We also examine applications of isocyanide adsorption to the stabilization of metal nanoparticles, the functionalization of metal electrodes, and the creation of conducting organic-metal junctions in molecule-scale electronic devices.

  10. Molecular orientation of copper phthalocyanine thin films on different monolayers of fullerene on SiO{sub 2} or highly oriented pyrolytic graphite

    SciTech Connect

    Wang, Chenggong; Wang, Congcong; Liu, Xiaoliang; Xu, Xumei; Li, Youzhen; Xie, Fangyan; Gao, Yongli

    2015-03-23

    The interface electronic structures of copper phthalocyanine (CuPc) have been studied using ultraviolet photoemission spectroscopy as different monolayers of C{sub 60} were inserted between CuPc and a SiO{sub 2} or highly ordered pyrolytic graphite (HOPG) substrate. The results show that CuPc has standing up configuration with one monolayer of C{sub 60} insertion on SiO{sub 2} while lying down on HOPG, indicating that the insertion layer propagates the CuPc-substrate interaction. Meanwhile, CuPc on more than one monolayers of C{sub 60} on different substrates show that the substrate orientation effect quickly vanished. Our study elucidates intriguing molecular interactions that manipulate molecular orientation and donor-acceptor energy level alignment.

  11. Molecular orientation of copper phthalocyanine thin films on different monolayers of fullerene on SiO2 or highly oriented pyrolytic graphite

    NASA Astrophysics Data System (ADS)

    Wang, Chenggong; Liu, Xiaoliang; Wang, Congcong; Xu, Xumei; Li, Youzhen; Xie, Fangyan; Gao, Yongli

    2015-03-01

    The interface electronic structures of copper phthalocyanine (CuPc) have been studied using ultraviolet photoemission spectroscopy as different monolayers of C60 were inserted between CuPc and a SiO2 or highly ordered pyrolytic graphite (HOPG) substrate. The results show that CuPc has standing up configuration with one monolayer of C60 insertion on SiO2 while lying down on HOPG, indicating that the insertion layer propagates the CuPc-substrate interaction. Meanwhile, CuPc on more than one monolayers of C60 on different substrates show that the substrate orientation effect quickly vanished. Our study elucidates intriguing molecular interactions that manipulate molecular orientation and donor-acceptor energy level alignment.

  12. Perforated monolayers

    SciTech Connect

    Regen, S.L.

    1992-12-01

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

  13. Frictional transition from superlubric islands to pinned monolayers

    NASA Astrophysics Data System (ADS)

    Pierno, Matteo; Bruschi, Lorenzo; Mistura, Giampaolo; Paolicelli, Guido; di Bona, Alessandro; Valeri, Sergio; Guerra, Roberto; Vanossi, Andrea; Tosatti, Erio

    2015-08-01

    The inertial sliding of physisorbed submonolayer islands on crystal surfaces contains unexpected information on the exceptionally smooth sliding state associated with incommensurate superlubricity and on the mechanisms of its disappearance. Here, in a joint quartz crystal microbalance and molecular dynamics simulation case study of Xe on Cu(111), we show how superlubricity emerges in the large size limit of naturally incommensurate Xe islands. As coverage approaches a full monolayer, theory also predicts an abrupt adhesion-driven two-dimensional density compression on the order of several per cent, implying a hysteretic jump from superlubric free islands to a pressurized commensurate immobile monolayer. This scenario is fully supported by the quartz crystal microbalance data, which show remarkably large slip times with increasing submonolayer coverage, signalling superlubricity, followed by a dramatic drop to zero for the dense commensurate monolayer. Careful analysis of this variety of island sliding phenomena will be essential in future applications of friction at crystal/adsorbate interfaces.

  14. Method for Controlling Electrical Properties of Single-Layer Graphene Nanoribbons via Adsorbed Planar Molecular Nanoparticles

    NASA Astrophysics Data System (ADS)

    Tanaka, Hirofumi; Arima, Ryo; Fukumori, Minoru; Tanaka, Daisuke; Negishi, Ryota; Kobayashi, Yoshihiro; Kasai, Seiya; Yamada, Toyo Kazu; Ogawa, Takuji

    2015-07-01

    A simple method for fabricating single-layer graphene nanoribbons (sGNRs) from double-walled carbon nanotubes (DWNTs) was developed. A sonication treatment was employed to unzip the DWNTs by inducing defects in them through annealing at 500 °C. The unzipped DWNTs yielded double-layered GNRs (dGNRs). Further sonication allowed each dGNR to be unpeeled into two sGNRs. Purification performed using a high-speed centrifuge ensured that more than 99% of the formed GNRs were sGNRs. The changes induced in the electrical properties of the obtained sGNR by the absorption of nanoparticles of planar molecule, naphthalenediimide (NDI), were investigated. The shape of the I-V curve of the sGNRs varied with the number of NDI nanoparticles adsorbed. This was suggestive of the existence of a band gap at the narrow-necked part near the NDI-adsorbing area of the sGNRs.

  15. Method for Controlling Electrical Properties of Single-Layer Graphene Nanoribbons via Adsorbed Planar Molecular Nanoparticles

    PubMed Central

    Tanaka, Hirofumi; Arima, Ryo; Fukumori, Minoru; Tanaka, Daisuke; Negishi, Ryota; Kobayashi, Yoshihiro; Kasai, Seiya; Yamada, Toyo Kazu; Ogawa, Takuji

    2015-01-01

    A simple method for fabricating single-layer graphene nanoribbons (sGNRs) from double-walled carbon nanotubes (DWNTs) was developed. A sonication treatment was employed to unzip the DWNTs by inducing defects in them through annealing at 500 °C. The unzipped DWNTs yielded double-layered GNRs (dGNRs). Further sonication allowed each dGNR to be unpeeled into two sGNRs. Purification performed using a high-speed centrifuge ensured that more than 99% of the formed GNRs were sGNRs. The changes induced in the electrical properties of the obtained sGNR by the absorption of nanoparticles of planar molecule, naphthalenediimide (NDI), were investigated. The shape of the I-V curve of the sGNRs varied with the number of NDI nanoparticles adsorbed. This was suggestive of the existence of a band gap at the narrow-necked part near the NDI-adsorbing area of the sGNRs. PMID:26205209

  16. Method for Controlling Electrical Properties of Single-Layer Graphene Nanoribbons via Adsorbed Planar Molecular Nanoparticles.

    PubMed

    Tanaka, Hirofumi; Arima, Ryo; Fukumori, Minoru; Tanaka, Daisuke; Negishi, Ryota; Kobayashi, Yoshihiro; Kasai, Seiya; Yamada, Toyo Kazu; Ogawa, Takuji

    2015-01-01

    A simple method for fabricating single-layer graphene nanoribbons (sGNRs) from double-walled carbon nanotubes (DWNTs) was developed. A sonication treatment was employed to unzip the DWNTs by inducing defects in them through annealing at 500 °C. The unzipped DWNTs yielded double-layered GNRs (dGNRs). Further sonication allowed each dGNR to be unpeeled into two sGNRs. Purification performed using a high-speed centrifuge ensured that more than 99% of the formed GNRs were sGNRs. The changes induced in the electrical properties of the obtained sGNR by the absorption of nanoparticles of planar molecule, naphthalenediimide (NDI), were investigated. The shape of the I-V curve of the sGNRs varied with the number of NDI nanoparticles adsorbed. This was suggestive of the existence of a band gap at the narrow-necked part near the NDI-adsorbing area of the sGNRs. PMID:26205209

  17. Variation in anisotropic dispersion relations of self-assembled monolayer on Cu(001) induced by modulation of molecular structures

    NASA Astrophysics Data System (ADS)

    Kanazawa, Ken; Nakamura, Miki; Huang, Hui; Taninaka, Atsushi; Shigekawa, Hidemi

    2015-02-01

    The two-dimensional electron gas (2DEG) states formed by self-assembled monolayers (SAM) of β-alanine molecules on a Cu(001) surface showed anisotropic dispersion relations different from those formed by glycine SAM. β-Alanine has a structure with an additional methylene group compared with glycine, and enantiomeric isomers were formed through adsorption, similarly to glycine. The anisotropic ratio of the effective masses was changed from 10 for glycine to 3.6 for β-alanine, suggesting the possibility of manipulating electronic structures by modification of the molecular structures. Although the growth modes were different for β-alanine and glycine, 2DEG states with standing waves were observed only for the p(2 × 4) phase in both cases, suggesting a key role of the interactions in the arrangement of this phase, together with the importance of the enantiomeric isomers formed through adsorption, which is also a characteristic of both molecules.

  18. Mechanical Properties of a vdW molecular monolayer at a metal surface: Structural Polymorphism leading to facile compression

    NASA Astrophysics Data System (ADS)

    Sun, Dezheng; Kim, Daeho; Le, Duy; Borck, Øyvind; Berland, Kristian; Kim, Kwangmoo; Lu, Wenhao; Zhu, Yeming; Luo, Miaomiao; Wyrick, Jon; Cheng, Zhihai; Einstein, T. L.; Rahman, Talat; Hyldgaard, Per; Bartels, Ludwig

    2011-03-01

    Intermolecular force plays an important role in self-assembly and surface pattern formation. Anthracene and similar unsubstituted arenes attach to a metallic substrate predominantly through van der Waals interaction leading. In this contribution we present images how anthracene on Cu(111) forms a large number of highly ordered patterns that feature a broad array of structural motifs. Density functional theory modeling including vdW interactions allows us to model the energetic of the pattern formation at high fidelity. Moreover, it allows us to deduce the strain energy associated with films of varying coverage. From this work, we obtain the Young's modulus and Poisson Ratio of a molecular monolayer, which resemble properties conventionally found for porous materials. These patterns are in marked contrast to those found after introduction of functional groups in the molecules, such as carbonyls or thiols.

  19. Nanoscale transport of surface excitons at the interface between ZnO and a molecular monolayer

    NASA Astrophysics Data System (ADS)

    Friede, Sebastian; Kuehn, Sergei; Sadofev, Sergey; Blumstengel, Sylke; Henneberger, Fritz; Elsaesser, Thomas

    2015-03-01

    Excitons play a key role for the optoelectronic properties of hybrid systems. We apply steady-state and time-resolved near-field scanning optical microscopy with a 100-nm spatial resolution to study the photoluminescence (PL) of surface excitons (SX) in a 20-nm-thick ZnO film capped with a monolayer of stearic acid molecules. The PL spectra exhibit emission from SX, donor-bound (DX), and—at sample temperatures T >20 K —free (FX) excitons. The 4 meV broad smooth envelope of SX emission at T <10 K points to an inhomogeneous distribution of SX transition energies and spectral diffusion caused by diffusive SX transport on a 50-nm scale with a diffusion coefficient of DSX(T <10 K ) =0.30 cm 2/s .

  20. Large-area optoelastic manipulation of colloidal particles in liquid crystals using photoresponsive molecular surface monolayers

    PubMed Central

    Martinez, Angel; Mireles, Hector C.; Smalyukh, Ivan I.

    2011-01-01

    Noncontact optical trapping and manipulation of micrometer- and nanometer-sized particles are typically achieved by use of forces and torques exerted by tightly focused high-intensity laser beams. Although they were instrumental for many scientific breakthroughs, these approaches find few technological applications mainly because of the small-area manipulation capabilities, the need for using high laser powers, limited application to anisotropic fluids and low-refractive-index particles, as well as complexity of implementation. To overcome these limitations, recent research efforts have been directed toward extending the scope of noncontact optical control through the use of optically-guided electrokinetic forces, vortex laser beams, plasmonics, and optofluidics. Here we demonstrate manipulation of colloidal particles and self-assembled structures in nematic liquid crystals by means of single-molecule-thick, light-controlled surface monolayers. Using polarized light of intensity from 1,000 to 100,000 times smaller than that in conventional optical tweezers, we rotate, translate, localize, and assemble spherical and complex-shaped particles of various sizes and compositions. By controlling boundary conditions through the monolayer, we manipulate the liquid crystal director field and the landscape of ensuing elastic forces exerted on colloids by the host medium. This permits the centimeter-scale, massively parallel manipulation of particles and complex colloidal structures that can be dynamically controlled by changing illumination or assembled into stationary stable configurations dictated by the “memorized” optoelastic potential landscape due to the last illumination pattern. We characterize the strength of optically guided elastic forces and discuss the potential uses of this noncontact manipulation in fabrication of novel optically- and electrically-tunable composites from liquid crystals and colloids. PMID:22160673

  1. Influence of molecular structure and adsorbent properties on sorption of organic compounds to a temperature series of wood chars.

    PubMed

    Lattao, Charisma; Cao, Xiaoyan; Mao, Jingdong; Schmidt-Rohr, Klaus; Pignatello, Joseph J

    2014-05-01

    Chars from wildfires and soil amendments (biochars) are strong adsorbents that can impact the fate of organic compounds in soil, yet the effects of solute and adsorbent properties on sorption are poorly understood. We studied sorption of benzene, naphthalene, and 1,4-dinitrobenzene from water to a series of wood chars made anaerobically at different heat treatment temperatures (HTT) from 300 to 700 °C, and to graphite as a nonporous, unfunctionalized reference adsorbent. Peak suppression in the NMR spectrum by sorption of the paramagnetic relaxation probe TEMPO indicated that only a small fraction of char C atoms lie near sorption sites. Sorption intensity for all solutes maximized with the 500 °C char, but failed to trend regularly with N2 or CO2 surface area, micropore volume, mesopore volume, H/C ratio, O/C ratio, aromatic fused ring size, or HTT. A model relating sorption intensity to a weighted sum of microporosity and mesoporosity was more successful. Sorption isotherm linearity declined progressively with carbonization of the char. Application of a thermodynamic model incorporating solvent-water and char-graphite partition coefficients permitted for the first time quantification of steric (size exclusion in pores) and π-π electron donor-acceptor (EDA) free energy contributions, relative to benzene. Steric hindrance for naphthalene increases exponentially from 9 to 16 kJ/mol (∼ 1.6-2.9 log units of sorption coefficient) with the fraction of porosity in small micropores. π-π EDA interactions of dinitrobenzene contribute -17 to -19 kJ/mol (3-3.4 log units of sorption coefficient) to sorption on graphite, but less on chars. π-π EDA interaction of naphthalene on graphite is small (-2 to 2 kJ/mol). The results show that sorption is a complex function of char properties and solute molecular structure, and not very predictable on the basis of readily determined char properties.

  2. Influence of molecular structure and adsorbent properties on sorption of organic compounds to a temperature series of wood chars.

    PubMed

    Lattao, Charisma; Cao, Xiaoyan; Mao, Jingdong; Schmidt-Rohr, Klaus; Pignatello, Joseph J

    2014-05-01

    Chars from wildfires and soil amendments (biochars) are strong adsorbents that can impact the fate of organic compounds in soil, yet the effects of solute and adsorbent properties on sorption are poorly understood. We studied sorption of benzene, naphthalene, and 1,4-dinitrobenzene from water to a series of wood chars made anaerobically at different heat treatment temperatures (HTT) from 300 to 700 °C, and to graphite as a nonporous, unfunctionalized reference adsorbent. Peak suppression in the NMR spectrum by sorption of the paramagnetic relaxation probe TEMPO indicated that only a small fraction of char C atoms lie near sorption sites. Sorption intensity for all solutes maximized with the 500 °C char, but failed to trend regularly with N2 or CO2 surface area, micropore volume, mesopore volume, H/C ratio, O/C ratio, aromatic fused ring size, or HTT. A model relating sorption intensity to a weighted sum of microporosity and mesoporosity was more successful. Sorption isotherm linearity declined progressively with carbonization of the char. Application of a thermodynamic model incorporating solvent-water and char-graphite partition coefficients permitted for the first time quantification of steric (size exclusion in pores) and π-π electron donor-acceptor (EDA) free energy contributions, relative to benzene. Steric hindrance for naphthalene increases exponentially from 9 to 16 kJ/mol (∼ 1.6-2.9 log units of sorption coefficient) with the fraction of porosity in small micropores. π-π EDA interactions of dinitrobenzene contribute -17 to -19 kJ/mol (3-3.4 log units of sorption coefficient) to sorption on graphite, but less on chars. π-π EDA interaction of naphthalene on graphite is small (-2 to 2 kJ/mol). The results show that sorption is a complex function of char properties and solute molecular structure, and not very predictable on the basis of readily determined char properties. PMID:24758543

  3. Formation of Molecular Networks: Tailored Quantum Boxes and Behavior of Adsorbed CO in Them

    NASA Astrophysics Data System (ADS)

    Wyrick, Jon; Sun, Dezheng; Kim, Dae-Ho; Cheng, Zhihai; Lu, Wenhao; Zhu, Yeming; Luo, Miaomiao; Kim, Yong Su; Rotenberg, Eli; Kim, Kwangmoo; Einstein, T. L.; Bartels, Ludwig

    2011-03-01

    We show that the behavior of CO adsorbed into the pores of large regular networks on Cu(111) is significantly affected by their nano-scale lateral confinement and that formation of the networks themselves is directed by the Shockley surface state. Saturation coverages of CO are found to exhibit persistent dislocation lines; at lower coverages their mobility increases. Individual CO within the pores titrate the surface state, providing crucial information for understanding formation of the network as a result of optimization of the number N of electrons bound within each pore. Determination of N is based on quinone-coverage-dependent UPS data and an analysis of states of particles in a pore-shaped box (verified by CO's titration); a wide range of possible pore shapes and sizes has been considered. Work at UCR supported by NSF CHE 07-49949; at UMD by NSF CHE 07-50334 & UMD NSF-MRSEC DMR 05-20471.

  4. Molecular sieve adsorbents and membranes for applications in the production of renewable fuels and chemicals

    NASA Astrophysics Data System (ADS)

    Ranjan, Rajiv

    Metal organic frameworks (MOF), a new class of porous materials, have emerged as promising candidate for gas storage, separation membrane and chemical sensors. We used secondary growth method to grow microporous metal organic framework (MMOF) films on porous alumina supports. Examination of the film using SEM and XRD showed that the crystals were well inter-grown and preferentially oriented. Gas permeation study showed that membranes were defect free and moderate selectivity was achieved for H2/N2 gas pairs. The next project had to do with ethanol production from lignocellulosic biomass as an alternate energy source. However, toxic inhibitors produced from the hydrolysis of biomass decrease ethanol yield during the fermentation process. We demonstrated the use of zeolites for the pretreatment of hydrolyzate in order to remove inhibitors like 5-Hydroxymethylfurfuraldehyde (HMF) and furfural from aqueous solution. Zeolites exhibit preferential adsorption of the inhibitors and in effect improve the ethanol yield during fermentation. Ideal Adsorbed Solution Theory (IAST) was also used to predict adsorption isotherms for HMF-furfural mixtures using single component adsorption data. We also studied production of HMF, a potential substitute as a building block for plastic and chemical production, from renewable biomass resources. Catalytic dehydration of fructose for HMF production faces problems like low conversion and yield. Dimethyl sulfoxide (DMSO) can be used as the solvent as well as the catalyst resulting in high HMF yield. We studied a reaction-separation system for this dehydration reaction where the product (HMF) could be recovered by selective adsorption on solid adsorbents from the reaction mixture.

  5. Albumin dialysis with molecular adsorbent recirculating system (MARS) for the treatment of hepatic encephalopathy in liver failure.

    PubMed

    Kobashi-Margáin, Ramón A; Gavilanes-Espinar, Juan G; Gutiérrez-Grobe, Ylse; Gutiérrez-Jiménez, Angel A; Chávez-Tapia, Norberto; Ponciano-Rodríguez, Guadalupe; Uribe, Misael; Méndez Sánchez, Nahum

    2011-06-01

    Acute, acute-on-chronic and chronic liver diseases are major health issues worldwide, and most cases end with the need for liver transplantation. Up to 90% of the patients die waiting for an organ to be transplanted. Hepatic encephalopathy is a common neuropsychiatric syndrome that usually accompanies liver failure and impacts greatly on the quality of life. The molecular adsorbent recirculating system (MARS) is a recently developed form of artificial liver support that functions on a base of albumin dialysis. It facilitates the dialysis of albumin-bound and water-soluble toxins, allowing the patient to survive and even improving some clinical features of liver failure. The following manuscript reviews the technical features of MARS operation and some of the clinical trials that analyze the efficacy of the system in the therapy of liver diseases.

  6. Controlling Leakage Currents in Organic Field-Effect Transistors using Molecular Dipole Monolayers on Nanoscale Oxides

    NASA Astrophysics Data System (ADS)

    Martinez Hardigree, Josue F.; Dawidczyk, Thomas; Ireland, Robert; Johns, Gary; Jung, Byung-Jun; Markovic, Nina; Katz, Howard

    2013-03-01

    Self-assembled monolayers (SAM) have been explored as easily-processed, ultrathin interfacial layers in organic field-effect transistors (OFETs) for tuning the threshold voltage (Vt). We investigated the influence of Fermi-level pinning of the gate electrode by SAMs on leakage currents in OFETs fabricated on highly-doped n- and p-type Si gates with an intentionally marginal-quality, high leakage 8 nm SiO2 dielectric. Two dipolar alkyl SAMs, octyltriethoxysilane (OTS) and its fluorinated analogue (FOTS), were employed under a 40 nm active layer of a naphthalenetetracarboxylic diimide (NTCDI) derivative. Transistors on nSi displayed more positive Vt for OTS (+0.23 V) and FOTS (+1.09 V) than bare oxide (-0.56 V), while OFETs on pSi showed a lower Vt for OTS (+0.26 V) and a higher Vt for FOTS (+1.25 V) devices relative to bare oxide (+1.15 V). Differences in gate and subthreshold leakage between bare and SAM-treated oxides match the trends in Vt. Scanning Kelvin-probe measurements were consistent with this trend, indicating FOTS made both nSi and pSi oxide surfaces more negative relative to bare oxide, while OTS treatment resulted in more positive surface potentials on pSi and more negative surface potentials on nSi. Now at University of Seoul

  7. In-plane Van der Waals interactions of molecular self-assembly monolayer

    NASA Astrophysics Data System (ADS)

    Gao, Hong-Ying; Wagner, Hendrik; Held, Philipp Alexander; Du, Shixuan; Gao, Hong-Jun; Studer, Armido; Fuchs, Harald

    2015-02-01

    We demonstrate that the Van der Waals interactions in plane are important to control molecular self-assembly structure as well their phase transition. Using precise chemical modification to mediate such in-plane cohesive interactions, we observed the spontaneous formations of 2D order or disorder molecular self-assembly structures, as well their order-disorder phase transitions by annealing. Interestingly, we identified that the side alkyl chains stand up at surfaces and form the `locked' pairs/windmill structures. Moreover, we realized the covalent coupling based on ethynyl functionality before molecular desorption from metal surfaces, by enhancing the in-plane interactions.

  8. Effect of lipid composition and packing on the adsorption of apolipoproteins to lipid monolayers

    SciTech Connect

    Ibdah, J.A.; Lund-Katz, S.; Phillips, M.C.

    1987-05-01

    The monolayer system has been used to study the effects of lipoprotein surface lipid composition and packing on the affinities of apolipoproteins for the surfaces of lipoprotein particles. The adsorption of apolipoproteins injected beneath lipid monolayers prepared with pure lipids or lipoprotein surface lipids is evaluated by monitoring the surface pressure of the film and the surface concentration (Gamma) of /sup 14/C-labelled apolipoprotein. At a given initial film pressure (..pi../sub i/) there is a higher adsorption of human apo A-I to unsaturated phosphatidylcholine (PC) monolayers compared to saturated PC monolayers (e.g., at ..pi../sub i/ = 10 mN/m, Gamma = 0.35 and 0.06 mg/m/sup 2/ for egg PC and distearoyl PC, respectively, with 3 x 10/sup -4/ mg/ml apo A-I in the subphase). In addition, adsorption of apo A-I is less to an egg sphingomyelin monolayer than to an egg PC monolayer. The adsorption of apo A-I to PC monolayers is decreased by addition of cholesterol. Generally, apo A-I adsorption diminishes as the lipid molecular area decreases. Apo A-I adsorbs more to monolayers prepared with HDL/sub 3/ surface lipids than with LDL surface lipids. These studies suggest that lipoprotein surface lipid composition and packing are crucial factors influencing the transfer and exchange of apolipoproteins among various lipoprotein classes during metabolism of lipoprotein particles.

  9. Anisotropic orientational motion of molecular adsorbates at the air-water interface

    SciTech Connect

    Zimdars, D.; Dadap, J.I.; Eisenthal, K.B.; Heinz, T.F.

    1999-04-29

    The ultrafast orientational motions of coumarin 314 (C314) adsorbed at the air/water interface were investigated by time-resolved surface second harmonic generation (TRSHG). The theory and method of using TRSHG to detect both out-of-plane and in-plane orientational motions are discussed. The interfacial solute motions were found to be anisotropic, with differing out-of-plane and in-plane reorientation time constants. This report presents the first direct observation of in-plane orientational motion of a molecule (C314) at the air/water interface using TRSHG. The in-plane reorientation time constant is 600 {+-} 40 ps. The out-of-plane reorientation time constant is 350 {+-} 20 ps. The out-of-plane orientational motion of C314 is similar to the previous results on rhodamine 6G at the air/water interface which indicated increased interfacial friction compared with bulk aqueous solution. The surface reorientation times are 2--3 times slower than the bulk isotropic orientational diffusion time.

  10. Gradients of Rectification: Tuning Molecular Electronic Devices by the Controlled Use of Different-Sized Diluents in Heterogeneous Self-Assembled Monolayers.

    PubMed

    Kong, Gyu Don; Kim, Miso; Cho, Soo Jin; Yoon, Hyo Jae

    2016-08-22

    Molecular electronics has received significant attention in the last decades. To hone performance of devices, eliminating structural defects in molecular components inside devices is usually needed. We herein demonstrate this problem can be turned into a strength for modulating the performance of devices. We show the systematic dilution of a monolayer of an organic rectifier (2,2'-bipyridine-terminated n-undecanethiolate) with electronically inactive diluents (n-alkanethiolates of different lengths), gives remarkable gradients of rectification. Rectification is finely tunable in a range of approximately two orders of magnitude, retaining its polarity. Trends of rectification against the length of the diluent indicate the gradient of rectification is extremely sensitive to the molecular structure of the diluent. Further studies reveal that noncovalent intermolecular interactions within monolayers likely leads to gradients of structural defect and rectification.

  11. Gradients of Rectification: Tuning Molecular Electronic Devices by the Controlled Use of Different-Sized Diluents in Heterogeneous Self-Assembled Monolayers.

    PubMed

    Kong, Gyu Don; Kim, Miso; Cho, Soo Jin; Yoon, Hyo Jae

    2016-08-22

    Molecular electronics has received significant attention in the last decades. To hone performance of devices, eliminating structural defects in molecular components inside devices is usually needed. We herein demonstrate this problem can be turned into a strength for modulating the performance of devices. We show the systematic dilution of a monolayer of an organic rectifier (2,2'-bipyridine-terminated n-undecanethiolate) with electronically inactive diluents (n-alkanethiolates of different lengths), gives remarkable gradients of rectification. Rectification is finely tunable in a range of approximately two orders of magnitude, retaining its polarity. Trends of rectification against the length of the diluent indicate the gradient of rectification is extremely sensitive to the molecular structure of the diluent. Further studies reveal that noncovalent intermolecular interactions within monolayers likely leads to gradients of structural defect and rectification. PMID:27443577

  12. Ultrafast shock compression of self-assembled monolayers: a molecular picture.

    PubMed

    Patterson, James E; Dlott, Dana D

    2005-03-24

    Simulations of self-assembled monolayers (SAMs) are performed to interpret experimental measurements of ultrafast approximately 1 GPa (volume compression deltaV approximately 0.1) planar shock compression dynamics probed by vibrational sum-frequency generation (SFG) spectroscopy (Lagutchev, A. S.; Patterson, J. E.; Huang, W.; Dlott, D. D. J. Phys. Chem. B 2005, 109, XXXX). The SAMs investigated are octadecanethiol (ODT) and pentadecanethiol (PDT) on Au(111) and Ag(111) substrates, and benzyl mercaptan (BMT) on Au(111). In the alkane SAMs, SFG is sensitive to the instantaneous orientation of the terminal methyl; in BMT it is sensitive to the phenyl orientation. Computed structures of alkane SAMs are in good agreement with experiment. In alkanes, the energies of gauche defects increase with increasing number and depth below the methyl plane, with the exception of ODT/Au where both single and double gauche defects at the two uppermost dihedrals have similar energies. Simulations of isothermal uniaxial compression of SAM lattices show that chain and methyl tilting is predominant in PDT/Au, ODT/Ag and PDT/Ag, whereas single and double gauche defect formation is predominant in ODT/Au. Time-resolved shock data showing transient SFG signal loss of ODT/Au and PDT/Au are fit by calculations of the terminal group orientations as a function of deltaV and their contributions to the SFG hyperpolarizability. The highly elastic response of PDT/Au results from shock-generated methyl and chain tilting. The viscoelastic response of ODT/Au results from shock generation of single and double gauche defects. Isothermal compression simulations help explain and fit the time dependence of shock spectra but generally underestimate the magnitude of SFG signal loss because they do not include effects of high-strain-rate dynamics and shock front and surface irregularities. PMID:16863164

  13. Self-assembly, characterization, and chemical stability of isocyanide-bound molecular wire monolayers on gold and palladium surfaces.

    PubMed

    Stapleton, Joshua J; Daniel, Thomas A; Uppili, Sundarajan; Cabarcos, Orlando M; Naciri, Jawad; Shashidhar, Ranganathan; Allara, David L

    2005-11-22

    Self-assembled monolayers (SAMs) of the isocyano derivative of 4,4'-di(phenylene-ethynylene)benzene (1), a member of the "OPE" family of "molecular wires" of current interest in molecular electronics, have been prepared on smooth, {111} textured films of Au and Pd. For assembly in oxygen-free environments with freshly deposited metal surfaces, infrared reflection spectroscopy (IRS) indicates the molecules assume a tilted structure with average tilt angles of 18-24 degrees from the surface normal. The combination of IRS, X-ray photoelectron spectroscopy, and density functional theory calculations all support a single sigma-type bond of the -NC group to the Au surface and a sigma/pi-type of bond to the Pd surface. Both SAMs show significant chemical instability when exposed to typical ambient conditions. In the case of the Au SAM, even a few hours storage in air results in significant oxidation of the -NC moieties to -NCO (isocyanate) with an accompanying decrease in surface chemical bonding, as evidenced by a significant increase in instability toward dissolution in solvent. In the case of the Pd SAM, similar air exposure does not result in incorporation of oxygen or loss of solvent resistance but rather results in a chemically altered interface which is attributed to polymerization of the -NC moieties to quasi-2D poly(imine) structures. Conductance probe atomic force microscope measurements show the conductance of the degraded Pd SAMs can diminish by approximately 2 orders of magnitude, an indication that the SAM-Pd electrical contact has severely degraded. These results underscore the importance of careful control of the assembly procedures for aromatic isocyanide SAMs, particularly for applications in molecular electronics where the molecule-electrode junction is critical to the operational characteristics of the device.

  14. Mechanism of iron inhibition by stearic acid Langmuir-Blodgett monolayers

    SciTech Connect

    Xing, W.; Shan, Y.; Guo, D.; Lu, T.; Xi, S.

    1995-01-01

    Many organic compounds can be adsorbed onto the interface of a metal and solution to form a thin film that inhibits the corrosion process according to a blocking and/or negative catalytic effect. Using the Langmuir-Blodgett (LB) technique, stearic acid (SA) monolayers were deposited onto the surface of an iron (Fe) electrode to study the inhibition effect and the mechanism of SA in a neutral medium. Molecular orientation and the number of deposited monolayers of SA were shown to have marked effects on inhibition of Fe corrosion. The inhibition mechanism depended mainly on blocking.

  15. Mechanism of Action of Thymol on Cell Membranes Investigated through Lipid Langmuir Monolayers at the Air-Water Interface and Molecular Simulation.

    PubMed

    Ferreira, João Victor N; Capello, Tabata M; Siqueira, Leonardo J A; Lago, João Henrique G; Caseli, Luciano

    2016-04-01

    A major challenge in the design of biocidal drugs is to identify compounds with potential action on microorganisms and to understand at the molecular level their mechanism of action. In this study, thymol, a monoterpenoid found in the oil of leaves of Lippia sidoides with possible action in biological surfaces, was incorporated in lipid monolayers at the air-water interface that represented cell membrane models. The interaction of thymol with dipalmitoylphosphatidylcholine (DPPC) at the air-water interface was investigated by means of surface pressure-area isotherms, Brewster angle microscopy (BAM), polarization-modulation reflection-absorption spectroscopy (PM-IRRAS), and molecular dynamics simulation. Thymol expands DPPC monolayers, decreases their surface elasticity, and changes the morphology of the lipid monolayer, which evidence the incorporation of this compound in the lipid Langmuir film. Such incorporation could be corroborated by PM-IRRAS since some specific bands for DPPC were changed upon thymol incorporation. Furthermore, potential of mean force obtained by molecular dynamics simulations indicates that the most stable position of the drug along the lipid film is near the hydrophobic regions of DPPC. These results may be useful to understand the interaction between thymol and cell membranes during biochemical phenomena, which may be associated with its pharmaceutical properties at the molecular level.

  16. In situ studies of metal coordinations and molecular orientations in monolayers of amino-acid-derived Schiff bases at the air-water interface.

    PubMed

    Liu, Huijin; Zheng, Haifu; Miao, Wangen; Du, Xuezhong

    2009-03-01

    The surface behaviors of monolayers of amino-acid-derived Schiff bases, namely, 4-(4-(hexadecyloxy)benzylideneamino)benzoic acid (HBA), at the air-water interface on pure water and ion-containing subphases (Cu2+, Ca2+, and Ba2+) have been clarified by a combination of surface pressure-area isotherms and surface plasmon resonance (SPR) technique, and the metal coordinations and molecular orientations in the monolayers have been investigated using in situ infrared reflection absorption spectroscopy (IRRAS). The presence of metal ions gives rise to condensation of the monolayers (Cu2+, pH 6.1; Ca2+, pH 11; Ba2+, pH 10), even leading to the formation of three-dimensional structures of the compressed monolayer in the case of Ba2+ (pH 12). The metal coordinations with the carboxyl groups at the interface depend on the type of metal ions and pH of the aqueous subphase. The orientations of the aromatic Schiff base segments with surface pressure are elaborately described. The spectral behaviors of the Schiff base segments with incidence angle in the case of Ba2+ (pH 12) have so far presented an excellent example for the selection rule of IRRAS at the air-water interface for p-polarization with vibrational transition moments perpendicular to the water surface. The chain orientations in the monolayers are quantitatively determined on the assumption that the thicknesses of the HBA monolayers at the air-water interface are composed of the sublayers of alkyl chains and Schiff base segments. PMID:19437705

  17. Molecular dynamics simulations of water confined between matched pairs of hydrophobic and hydrophilic self-assembled monolayers.

    SciTech Connect

    Chandross, Michael Evan; Grest, Gary Stephen; Lane, J. Matthew D.; Lorenz, Christian Douglas; Stevens, Mark Jackson

    2008-12-01

    We have conducted a molecular dynamics (MD) simulation study of water confined between methyl-terminated and carboxyl-terminated alkylsilane self-assembled monolayers (SAMs) on amorphous silica substrates. In doing so, we have investigated the dynamic and structural behavior of the water molecules when compressed to loads ranging from 20 to 950 MPa for two different amounts of water (27 and 58 water molecules/nm{sup 2}). Within the studied range of loads, we observe that no water molecules penetrate the hydrophobic region of the carboxyl-terminated SAMs. However, we observe that at loads larger than 150 MPa water molecules penetrate the methyl-terminated SAMs and form hydrogen-bonded chains that connect to the bulk water. The diffusion coefficient of the water molecules decreases as the water film becomes thinner and pressure increases. When compared to bulk diffusion coefficients of water molecules at the various loads, we found that the diffusion coefficients for the systems with 27 water molecules/nm{sup 2} are reduced by a factor of 20 at low loads and by a factor of 40 at high loads, while the diffusion coefficients for the systems with 58 water molecules/nm{sup 2} are reduced by a factor of 25 at all loads.

  18. An Effective Approach to Improving Cadmium Telluride (111)A Surface by Molecular-Beam-Epitaxy Growth of Tellurium Monolayer.

    PubMed

    Ren, Jie; Fu, Li; Bian, Guang; Su, Jie; Zhang, Hao; Velury, Saavanth; Yukawa, Ryu; Zhang, Longxiang; Wang, Tao; Zha, Gangqiang; Guo, Rongrong; Miller, Tom; Hasan, M Zahid; Chiang, Tai-Chang

    2016-01-13

    The surface cleansing treatment of non-natural cleavage planes of semiconductors is usually performed in vacuum using ion sputtering and subsequent annealing. In this Research Article, we report on the evolution of surface atomic structure caused by different ways of surface treatment as monitored by in situ core-level photoemission measurements of Cd-4d and Te-4d atomic levels and reflection high-energy electron diffraction (RHEED). Sputtering of surface increases the density of the dangling bonds by 50%. This feature and the less than ideal ordering can be detrimental to device applications. An effective approach is employed to improve the quality of this surface. One monolayer (ML) of Te grown by the method of molecular beam epitaxy (MBE) on the target surface with heating at 300 °C effectively improves the surface quality as evidenced by the improved sharpness of RHEED pattern and a reduced diffuse background in the spectra measured by high-resolution ultraviolet photoemission spectroscopy (HRUPS). Calculations have been performed for various atomic geometries by employing first-principles geometry optimization. In conjunction with an analysis of the core level component intensities in terms the layer-attenuation model, we propose a "vacancy site" model of the modified 1 ML-Te/CdTe(111)A (2 × 2) surface.

  19. An Effective Approach to Improving Cadmium Telluride (111)A Surface by Molecular-Beam-Epitaxy Growth of Tellurium Monolayer.

    PubMed

    Ren, Jie; Fu, Li; Bian, Guang; Su, Jie; Zhang, Hao; Velury, Saavanth; Yukawa, Ryu; Zhang, Longxiang; Wang, Tao; Zha, Gangqiang; Guo, Rongrong; Miller, Tom; Hasan, M Zahid; Chiang, Tai-Chang

    2016-01-13

    The surface cleansing treatment of non-natural cleavage planes of semiconductors is usually performed in vacuum using ion sputtering and subsequent annealing. In this Research Article, we report on the evolution of surface atomic structure caused by different ways of surface treatment as monitored by in situ core-level photoemission measurements of Cd-4d and Te-4d atomic levels and reflection high-energy electron diffraction (RHEED). Sputtering of surface increases the density of the dangling bonds by 50%. This feature and the less than ideal ordering can be detrimental to device applications. An effective approach is employed to improve the quality of this surface. One monolayer (ML) of Te grown by the method of molecular beam epitaxy (MBE) on the target surface with heating at 300 °C effectively improves the surface quality as evidenced by the improved sharpness of RHEED pattern and a reduced diffuse background in the spectra measured by high-resolution ultraviolet photoemission spectroscopy (HRUPS). Calculations have been performed for various atomic geometries by employing first-principles geometry optimization. In conjunction with an analysis of the core level component intensities in terms the layer-attenuation model, we propose a "vacancy site" model of the modified 1 ML-Te/CdTe(111)A (2 × 2) surface. PMID:26672795

  20. Molecular adsorbates on HOPG: Toward modulation of graphene density of states

    NASA Astrophysics Data System (ADS)

    Groce, Michelle; Einstein, Theodore; Cullen, William

    2013-03-01

    Ordered molecular superlattices, particularly those made of planar aromatics with their attendant pi orbitals, have the potential to break the graphene sublattice degeneracy and create a band gap. Trimesic acid (TMA) is a promising candidate due to its self-assembly into symmetry-breaking superlattices nearly commensurate with that of graphene. We have used the graphite (0001) surface as a model system to explore the impact of TMA thin films on band structure. By examining correlations between STM topography and STS maps of corresponding regions, we are able to investigate the effects of TMA on the local density of states. Work supported by the University of Maryland NSF-MRSEC, DMR 0520471 and Shared Experimental Facilities.

  1. PM-IRRAS Determination of Molecular Orientation of Phosphonic Acid Self-Assembled Monolayers on Indium Zinc Oxide.

    PubMed

    Sang, Lingzi; Mudalige, Anoma; Sigdel, Ajaya K; Giordano, Anthony J; Marder, Seth R; Berry, Joseph J; Pemberton, Jeanne E

    2015-05-26

    Self-assembled monolayers (SAMs) of phosphonic acids (PAs) on transparent conductive oxide (TCO) surfaces can facilitate improvement in TCO/organic semiconductor interface properties. When ordered PA SAMs are formed on oxide substrates, interface dipole and electronic structure are affected by the functional group properties, orientation, and binding modes of the modifiers. Choosing octylphosphonic acid (OPA), F13-octylphosphonic acid (F13OPA), pentafluorophenyl phosphonic acid (F5PPA), benzyl phosphonic acid (BnPA), and pentafluorobenzyl phosphonic acid (F5BnPA) as a representative group of modifiers, we report polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS) of binding and molecular orientation on indium-doped zinc oxide (IZO) substrates. Considerable variability in molecular orientation and binding type is observed with changes in PA functional group. OPA exhibits partially disordered alkyl chains but on average the chain axis is tilted ∼57° from the surface normal. F13OPA tilts 26° with mostly tridentate binding. The F5PPA ring is tilted 23° from the surface normal with a mixture of bidentate and tridentate binding; the BnPA ring tilts 31° from normal with a mixture of bidentate and tridentate binding, and the F5BnPA ring tilts 58° from normal with a majority of bidentate with some tridenate binding. These trends are consistent with what has been observed previously for the effects of fluorination on orientation of phosphonic acid modifiers. These results from PM-IRRAS are correlated with recent results on similar systems from near-edge X-ray absorption fine structure (NEXAFS) and density functional theory (DFT) calculations. Overall, these results indicate that both surface binding geometry and intermolecular interactions play important roles in dictating the orientation of PA modifiers on TCO surfaces. This work also establishes PM-IRRAS as a routine method for SAM orientation determination on complex oxide substrates

  2. Molecular structure and vibrations of NTCDA monolayers on Ag(111) from density-functional theory and infrared absorption spectroscopy.

    PubMed

    Tonner, Ralf; Rosenow, Phil; Jakob, Peter

    2016-02-17

    The structure and vibrational properties of the metal-organic interface of 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) on Ag(111) were analysed using Fourier-transform infrared absorption spectroscopy in conjunction with density functional theory calculations including dispersion forces (PBE-D3). Mode assignments and polarizations as well as molecular distortions were determined for four adsorption geometries of NTCDA on top and bridge sites aligned either parallel or perpendicular to the Ag rows and compared to accurate calculations of the free molecule. This enables an in-depth understanding of surface effects on the computed and experimental vibrational spectra of the adsorbed NTCDA molecule. The molecule-substrate interaction comprises two major and equally important contributions: non-directional van der Waals forces between molecule and surface, and covalent bonding of the acyl oxygen atoms with underlying Ag atoms, which is quantified by charge-transfer analysis. Furthermore, adsorption energy calculations showed that the molecular axis of flat-lying NTCDA is oriented preferably in parallel to the Ag rows. The molecule is subject to particular distortions from the planar gas phase structure with covalent bonding leading to downward bending of the acyl oxygen atoms and Pauli repulsion to upward bending of the carbon core. In parallel, strong buckling of the silver surface was identified. As found in previous studies, the lowest unoccupied molecular orbital (LUMO) of the molecule slips below the Fermi level and becomes partially populated upon adsorption. Excitation of totally symmetric vibrational modes then leads to substantial interfacial dynamical charge transfer, which is convincingly reproduced in the calculated IR spectra.

  3. Molecular recognition using corona phase complexes made of synthetic polymers adsorbed on carbon nanotubes.

    PubMed

    Zhang, Jingqing; Landry, Markita P; Barone, Paul W; Kim, Jong-Ho; Lin, Shangchao; Ulissi, Zachary W; Lin, Dahua; Mu, Bin; Boghossian, Ardemis A; Hilmer, Andrew J; Rwei, Alina; Hinckley, Allison C; Kruss, Sebastian; Shandell, Mia A; Nair, Nitish; Blake, Steven; Şen, Fatih; Şen, Selda; Croy, Robert G; Li, Deyu; Yum, Kyungsuk; Ahn, Jin-Ho; Jin, Hong; Heller, Daniel A; Essigmann, John M; Blankschtein, Daniel; Strano, Michael S

    2013-12-01

    Understanding molecular recognition is of fundamental importance in applications such as therapeutics, chemical catalysis and sensor design. The most common recognition motifs involve biological macromolecules such as antibodies and aptamers. The key to biorecognition consists of a unique three-dimensional structure formed by a folded and constrained bioheteropolymer that creates a binding pocket, or an interface, able to recognize a specific molecule. Here, we show that synthetic heteropolymers, once constrained onto a single-walled carbon nanotube by chemical adsorption, also form a new corona phase that exhibits highly selective recognition for specific molecules. To prove the generality of this phenomenon, we report three examples of heteropolymer-nanotube recognition complexes for riboflavin, L-thyroxine and oestradiol. In each case, the recognition was predicted using a two-dimensional thermodynamic model of surface interactions in which the dissociation constants can be tuned by perturbing the chemical structure of the heteropolymer. Moreover, these complexes can be used as new types of spatiotemporal sensors based on modulation of the carbon nanotube photoemission in the near-infrared, as we show by tracking riboflavin diffusion in murine macrophages.

  4. Molecular recognition using corona phase complexes made of synthetic polymers adsorbed on carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Zhang, Jingqing; Landry, Markita P.; Barone, Paul W.; Kim, Jong-Ho; Lin, Shangchao; Ulissi, Zachary W.; Lin, Dahua; Mu, Bin; Boghossian, Ardemis A.; Hilmer, Andrew J.; Rwei, Alina; Hinckley, Allison C.; Kruss, Sebastian; Shandell, Mia A.; Nair, Nitish; Blake, Steven; Şen, Fatih; Şen, Selda; Croy, Robert G.; Li, Deyu; Yum, Kyungsuk; Ahn, Jin-Ho; Jin, Hong; Heller, Daniel A.; Essigmann, John M.; Blankschtein, Daniel; Strano, Michael S.

    2013-12-01

    Understanding molecular recognition is of fundamental importance in applications such as therapeutics, chemical catalysis and sensor design. The most common recognition motifs involve biological macromolecules such as antibodies and aptamers. The key to biorecognition consists of a unique three-dimensional structure formed by a folded and constrained bioheteropolymer that creates a binding pocket, or an interface, able to recognize a specific molecule. Here, we show that synthetic heteropolymers, once constrained onto a single-walled carbon nanotube by chemical adsorption, also form a new corona phase that exhibits highly selective recognition for specific molecules. To prove the generality of this phenomenon, we report three examples of heteropolymer-nanotube recognition complexes for riboflavin, L-thyroxine and oestradiol. In each case, the recognition was predicted using a two-dimensional thermodynamic model of surface interactions in which the dissociation constants can be tuned by perturbing the chemical structure of the heteropolymer. Moreover, these complexes can be used as new types of spatiotemporal sensors based on modulation of the carbon nanotube photoemission in the near-infrared, as we show by tracking riboflavin diffusion in murine macrophages.

  5. A molecular dynamics study on the transport of a charged biomolecule in a polymeric adsorbent medium and its adsorption onto a charged ligand.

    PubMed

    Riccardi, E; Wang, J-C; Liapis, A I

    2010-08-28

    The transport of a charged adsorbate biomolecule in a porous polymeric adsorbent medium and its adsorption onto the covalently immobilized ligands have been modeled and investigated using molecular dynamics modeling and simulations as the third part of a novel fundamental methodology developed for studying ion-exchange chromatography based bioseparations. To overcome computational challenges, a novel simulation approach is devised where appropriate atomistic and coarse grain models are employed simultaneously and the transport of the adsorbate is characterized through a number of locations representative of the progress of the transport process. The adsorbate biomolecule for the system studied in this work changes shape, orientation, and lateral position in order to proceed toward the site where adsorption occurs and exhibits decreased mass transport coefficients as it approaches closer to the immobilized ligand. Furthermore, because the ligands are surrounded by counterions carrying the same type of charge as the adsorbate biomolecule, it takes the biomolecule repeated attempts to approach toward a ligand in order to displace the counterions in the proximity of the ligand and to finally become adsorbed. The formed adsorbate-ligand complex interacts with the counterions and polymeric molecules and is found to evolve slowly and continuously from one-site (monovalent) interaction to multisite (multivalent) interactions. Such a transition of the nature of adsorption reduces the overall adsorption capacity of the ligands in the adsorbent medium and results in a type of surface exclusion effect. Also, the adsorption of the biomolecule also presents certain volume exclusion effects by not only directly reducing the pore volume and the availability of the ligands in the adjacent regions, but also causing the polymeric molecules to change to more compact structures that could further shield certain ligands from being accessible to subsequent adsorbate molecules. These

  6. A molecular dynamics study on the transport of a charged biomolecule in a polymeric adsorbent medium and its adsorption onto a charged ligand

    NASA Astrophysics Data System (ADS)

    Riccardi, E.; Wang, J.-C.; Liapis, A. I.

    2010-08-01

    The transport of a charged adsorbate biomolecule in a porous polymeric adsorbent medium and its adsorption onto the covalently immobilized ligands have been modeled and investigated using molecular dynamics modeling and simulations as the third part of a novel fundamental methodology developed for studying ion-exchange chromatography based bioseparations. To overcome computational challenges, a novel simulation approach is devised where appropriate atomistic and coarse grain models are employed simultaneously and the transport of the adsorbate is characterized through a number of locations representative of the progress of the transport process. The adsorbate biomolecule for the system studied in this work changes shape, orientation, and lateral position in order to proceed toward the site where adsorption occurs and exhibits decreased mass transport coefficients as it approaches closer to the immobilized ligand. Furthermore, because the ligands are surrounded by counterions carrying the same type of charge as the adsorbate biomolecule, it takes the biomolecule repeated attempts to approach toward a ligand in order to displace the counterions in the proximity of the ligand and to finally become adsorbed. The formed adsorbate-ligand complex interacts with the counterions and polymeric molecules and is found to evolve slowly and continuously from one-site (monovalent) interaction to multisite (multivalent) interactions. Such a transition of the nature of adsorption reduces the overall adsorption capacity of the ligands in the adsorbent medium and results in a type of surface exclusion effect. Also, the adsorption of the biomolecule also presents certain volume exclusion effects by not only directly reducing the pore volume and the availability of the ligands in the adjacent regions, but also causing the polymeric molecules to change to more compact structures that could further shield certain ligands from being accessible to subsequent adsorbate molecules. These

  7. Turning things downside up: Adsorbate induced water flipping on Pt(111)

    SciTech Connect

    Kimmel, Gregory A.; Zubkov, Tykhon; Smith, R. Scott; Petrik, Nikolay G.; Kay, Bruce D.

    2014-11-14

    We have examined the adsorption of the weakly bound species N2, O2, CO and Kr on the water monolayer on Pt(111) using a combination of molecular beam dosing, infrared reflection absorption spectroscopy (IRAS), and temperature programmed desorption (TPD). In contrast to multilayer crystalline ice, the adsorbate-free water monolayer is characterized by a lack of dangling OH bonds protruding into the vacuum (H-up). Instead, the non-hydrogen-bonded OH groups are oriented downward (H-down) to maximize their interaction with the underlying Pt(111) substrate. Adsorption of Kr and O2 have little effect on the structure and vibrational spectrum of the “ ” water monolayer while adsorption of both N2, and CO are effective in “flipping” H-down water molecules into an H-up configuration. This “flipping” occurs readily upon adsorption at temperatures as low as 20 K and the water monolayer transforms back to the H-down, “ ” structure upon adsorbate desorption above 35 K, indicating small energy differences and barriers between the H-down and H-up configurations. The results suggest that converting water in the first layer from H-down to H-up is mediated by the electrostatic interactions between the water and the adsorbates.

  8. Turning things downside up: Adsorbate induced water flipping on Pt(111)

    SciTech Connect

    Kimmel, Greg A. E-mail: bruce.kay@pnnl.gov; Zubkov, Tykhon; Smith, R. Scott; Petrik, Nikolay G.; Kay, Bruce D. E-mail: bruce.kay@pnnl.gov

    2014-11-14

    We have examined the adsorption of the weakly bound species N{sub 2}, O{sub 2}, CO, and Kr on the (√(37)×√(37))R25.3{sup ∘} water monolayer on Pt(111) using a combination of molecular beam dosing, infrared reflection absorption spectroscopy, and temperature programmed desorption. In contrast to multilayer crystalline ice, the adsorbate-free water monolayer is characterized by a lack of dangling OH bonds protruding into the vacuum (H-up). Instead, the non-hydrogen-bonded OH groups are oriented downward (H-down) to maximize their interaction with the underlying Pt(111) substrate. Adsorption of Kr and O{sub 2} have little effect on the structure and vibrational spectrum of the “√(37)” water monolayer while adsorption of both N{sub 2}, and CO are effective in “flipping” H-down water molecules into an H-up configuration. This “flipping” occurs readily upon adsorption at temperatures as low as 20 K and the water monolayer transforms back to the H-down, “√(37)” structure upon adsorbate desorption above 35 K, indicating small energy differences and barriers between the H-down and H-up configurations. The results suggest that converting water in the first layer from H-down to H-up is mediated by the electrostatic interactions between the water and the adsorbates.

  9. Chemical Potential of Triethylene Glycol Adsorbed on Surfaces Relevant to Gas Transport and Processing - Studies Using Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Kvamme, B.; Olsen, R.; Sjöblom, S.; Leirvik, K. N.; Kuznetsova, T.

    2014-12-01

    Natural gas will inevitably contain trace amounts of water and other impurities during different stages of processing and transport. Glycols, such as triethylene glycol (TEG), will in many cases follow the water. The glycol contents of the gas can originate from preceding glycol-drying units or it can be a residue from the direct injection of glycols used to prevent hydrate formation. Thus, it is important to know how glycol contents will affect the different paths leading to hydrate formation. Glycols may in some cases dominate the condensed water phase. If this occurs, it will lead to the well-documented shift in the hydrate stability curve, due to the altered activity of the water. A great deal of information on the molecular path of a glycol through the system can be obtained from calculating the chemical potential. Due to difficulties in measuring interfacial chemical potentials, these often need to be estimated using theoretical tools. We used molecular dynamics (MD) to study how TEG behaves in the vicinity of mineral surfaces such as calcite and hematite. Many methods exist for estimating chemical potentials based on MD trajectories. These include techniques such as free energy perturbation theory (FEP) and thermodynamic integration (TI). Such methods require sufficient sampling of configurations where free energy is to be estimated. Thus, it can be difficult to estimate chemical potentials on surfaces. There are several methods to circumvent this problem, such as blue moon sampling and umbrella sampling. These have been considered and the most important have been used to estimate chemical potentials of TEG adsorbed on the mineral surfaces. The resulting chemical potentials were compared to the chemical potential of TEG in bulk water, which was estimated using temperature thermodynamic integration.

  10. Adsorbent and adsorbent bed for materials capture and separation processes

    SciTech Connect

    Liu, Wei

    2011-01-25

    A method device and material for performing adsorption wherein a fluid mixture is passed through a channel in a structured adsorbent bed having a solid adsorbent comprised of adsorbent particles having a general diameter less than 100 um, loaded in a porous support matrix defining at least one straight flow channel. The adsorbent bed is configured to allow passage of a fluid through said channel and diffusion of a target material into said adsorbent under a pressure gradient driving force. The targeted molecular species in the fluid mixture diffuses across the porous support retaining layer, contacts the adsorbent, and adsorbs on the adsorbent, while the remaining species in the fluid mixture flows out of the channel.

  11. Orbital tomography for highly symmetric adsorbate systems

    NASA Astrophysics Data System (ADS)

    Stadtmüller, B.; Willenbockel, M.; Reinisch, E. M.; Ules, T.; Bocquet, F. C.; Soubatch, S.; Puschnig, P.; Koller, G.; Ramsey, M. G.; Tautz, F. S.; Kumpf, C.

    2012-10-01

    Orbital tomography is a new and very powerful tool to analyze the angular distribution of a photoemission spectroscopy experiment. It was successfully used for organic adsorbate systems to identify (and consequently deconvolute) the contributions of specific molecular orbitals to the photoemission data. The technique was so far limited to surfaces with low symmetry like fcc(110) oriented surfaces, owing to the small number of rotational domains that occur on such surfaces. In this letter we overcome this limitation and present an orbital tomography study of a 3,4,9,10-perylene-tetra-carboxylic-dianhydride (PTCDA) monolayer film adsorbed on Ag(111). Although this system exhibits twelve differently oriented molecules, the angular resolved photoemission data still allow a meaningful analysis of the different local density of states and reveal different electronic structures for symmetrically inequivalent molecules. We also discuss the precision of the orbital tomography technique in terms of counting statistics and linear regression fitting algorithm. Our results demonstrate that orbital tomography is not limited to low-symmetry surfaces, a finding which makes a broad field of complex adsorbate systems accessible to this powerful technique.

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

    PubMed

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

    2015-09-01

    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. PMID:26252422

  13. Dimensionality effect on the charge density wave and superconductivity of molecular beam epitaxy grown monolayer NbSe2

    NASA Astrophysics Data System (ADS)

    Ryu, Hyejin; Zhang, Yi; Hussain, Zahid; Mo, Sung-Kwan; Shen, Z.-X.; Ugeda, Miguel M.; Bradley, Aaron J.; Onishi, Seita; Chen, Yi; Ruan, Wei; Ojeda-Aristizabal, Claudia; Edmonds, Mark T.; Tsai, Hsin-Zon; Riss, Alexander; Lee, Dunghai; Zettl, Alex; Crommie, Michael F.

    Transition metal dichalcogenides are ideal compounds to investigate dimensionality effect since the weak coupling between layers enables to study single-layer material which removes interlayer interactions and introduces quantum confinement. We investigate dimensionality effect of NbSe2 in which the bulk phase shows charge density wave (CDW) (TCDW = 33 K) and superconductivity (Tc = 7.2 K). We report electronic band structure of MBE grown monolayer NbSe2 measured by Angel-resolved photoemission spectroscopy compared with bulk. We find the number of bands crossing the Fermi energy reduces from three (bulk) to one (monolayer). Based on the significant suppression of superconducting Tc = 0.65 K with robust CDW in monolayer NbSe2, our results imply the band remained at the Fermi level in monolayer NbSe2 may play a crucial role in CDW formation and the disappeared bands are possibly in charge of superconductivity.

  14. Non-linear optical studies of adsorbates: Spectroscopy and dynamics

    SciTech Connect

    Zhu, Xiangdong.

    1989-08-01

    In the first part of this thesis, we have established a systematic procedure to apply the surface optical second-harmonic generation (SHG) technique to study surface dynamics of adsorbates. In particular, we have developed a novel technique for studies of molecular surface diffusions. In this technique, the laser-induced desorption with two interfering laser beams is used to produce a monolayer grating of adsorbates. The monolayer grating is detected with diffractions of optical SHG. By monitoring the first-order second-harmonic diffraction, we can follow the time evolution of the grating modulation from which we are able to deduce the diffusion constant of the adsorbates on the surface. We have successfully applied this technique to investigate the surface diffusion of CO on Ni(111). The unique advantages of this novel technique will enable us to readily study anisotropy of a surface diffusion with variable grating orientation, and to investigate diffusion processes of a large dynamic range with variable grating spacings. In the second part of this work, we demonstrate that optical infrared-visible sum-frequency generation (SFG) from surfaces can be used as a viable surface vibrational spectroscopic technique. We have successfully recorded the first vibrational spectrum of a monolayer of adsorbates using optical infrared-visible SFG. The qualitative and quantitative correlation of optical SFG with infrared absorption and Raman scattering spectroscopies are examined and experimentally demonstrated. We have further investigated the possibility to use transient infrared-visible SFG to probe vibrational transients and ultrafast relaxations on surfaces. 146 refs.

  15. Voltage-controlled nonvolatile molecular memory of an azobenzene monolayer through solution-processed reduced graphene oxide contacts.

    PubMed

    Min, Misook; Seo, Sohyeon; Lee, Sae Mi; Lee, Hyoyoung

    2013-12-23

    The solution-processed fabrication of an azobenzene (ABC10) monolayer-based nonvolatile memory device on a reduced graphene oxide (rGO) electrode is successfully accomplished. Trans--cis isomerizations of ABC10 between two rGO electrodes in a crossbar device are controlled by applied voltage. An rGO soft-contact top electrode plays an important role in the conformational-change-dependent conductance switching process of an ABC10 monolayer.

  16. Detection of molecular oxygen adsorbate during room-temperature oxidation of Si(100)2 × 1 surface: In situ synchrotron radiation photoemission study

    NASA Astrophysics Data System (ADS)

    Yoshigoe, Akitaka; Yamada, Yoichi; Taga, Ryo; Ogawa, Shuichi; Takakuwa, Yuji

    2016-10-01

    Synchrotron radiation photoelectron spectroscopy during the oxidation of a Si(100)2 × 1 surface at room temperature revealed the existence of molecularly adsorbed oxygen, which was considered to be absent. The O 1s spectrum of such oxidation was found to be similar to that of Si(111)7 × 7 surface oxidation. Also, molecular oxygen appeared after the initial surface oxides were formed, indicating that it was not a precursor for dissociation oxygen adsorption on a clean surface. Considering this finding, we have proposed presumable structural models for atomic configurations, where molecular oxygen resided on the oxidized silicon with two oxygen atoms at the backbonds.

  17. Simulations of molecular self-assembled monolayers on surfaces: packing structures, formation processes and functions tuned by intermolecular and interfacial interactions.

    PubMed

    Wen, Jin; Li, Wei; Chen, Shuang; Ma, Jing

    2016-08-17

    Surfaces modified with a functional molecular monolayer are essential for the fabrication of nano-scale electronics or machines with novel physical, chemical, and/or biological properties. Theoretical simulation based on advanced quantum chemical and classical models is at present a necessary tool in the development, design, and understanding of the interfacial nanostructure. The nanoscale surface morphology, growth processes, and functions are controlled by not only the electronic structures (molecular energy levels, dipole moments, polarizabilities, and optical properties) of building units but also the subtle balance between intermolecular and interfacial interactions. The switchable surfaces are also constructed by introducing stimuli-responsive units like azobenzene derivatives. To bridge the gap between experiments and theoretical models, opportunities and challenges for future development of modelling of ferroelectricity, entropy, and chemical reactions of surface-supported monolayers are also addressed. Theoretical simulations will allow us to obtain important and detailed information about the structure and dynamics of monolayer modified interfaces, which will guide the rational design and optimization of dynamic interfaces to meet challenges of controlling optical, electrical, and biological functions. PMID:27138016

  18. Addition of Molecular Adsorbent Recirculating System (MARS®) Albumin Dialysis for the Preoperative Management of Jaundiced Patients with Hilar Cholangiocarcinoma

    PubMed Central

    Regimbeau, Jean-Marc; Fuks, David; Chapuis-Roux, Emilie; Yzet, Thierry; Cosse, Cyril; Bartoli, Eric; N'Guyen-Khac, Eric; Robert, Brice; Lobjoie, Eric

    2013-01-01

    The preoperative management of hilar cholangiocarcinoma (HC) with jaundice focuses on decreasing the total serum bilirubin level (SBL) by performing preoperative biliary drainage (PBD). However, it takes about 6–8 weeks for the SBL to fall at a sufficient extent. The objective of this preliminary study was to evaluate the impact of Molecular Adsorbent Recirculating System (MARS®) dialysis (in association with PBD) on SBL decrease. From January 2010 to January 2011, we prospectively selected all jaundiced patients admitted to our university hospital for resectable HC and requiring PBD prior to major hepatectomy. The PBD was followed by 3 sessions of MARS dialysis over a period of 72 h. A total of 10 patients with HC were screened and two of them were included (Bismuth-Corlette stage IIIa, gender ratio 1, median age 68 years). The initial SBL in the two patients was 328 and 242 μmol/l, respectively. After three MARS dialysis sessions, the SBL had fallen by 30 and 52%, respectively. After the end of each session, there was a SBL rebound of about 10 μmol/l. The MARS decreased the serum creatinine level, the platelet count and the prothrombin index, but did not modify the serum albumin level. Pruritus disappeared after one and two sessions, respectively. MARS-related morbidity included hypotension (n = 1), tachycardia (n = 1), thrombocytopenia (n = 2) and anaemia (n = 1). When combined with PBD, MARS dialysis appears to accelerate the decrease in SBL and thus may enable earlier surgery. This hypothesis must be validated in a larger study. PMID:24163652

  19. The Molecular Boat: A Hands-On Experiment to Demonstrate the Forces Applied to Self-Assembled Monolayers at Interfaces

    ERIC Educational Resources Information Center

    Chan, Charlene J.; Salaita, Khalid

    2012-01-01

    Demonstrating how surface chemistry and self-assembled monolayers (SAMs) control the macroscopic properties of materials is challenging as it often necessitates the use of specialized instrumentation. In this hands-on experiment, students directly measure a macroscopic property, the floatation of glass coverslips on water as a function of…

  20. Influence of molecular ordering on electrical and friction properties of omega-(trans-4-stilbene)alkylthiol self-assembled monolayers on Au (111)

    SciTech Connect

    Qi, Yabing; Liu, Xiaosong; Hendriksen, B.L.M.; Navarro, V.; Park, Jeong Y.; Ratera, Imma; Klopp, J.M.; Edder, C.; Himpsel, Franz J.; Frechet, J.M.J.; Haller, Eugene E.; Salmeron, Miquel

    2010-04-21

    The electrical and friction properties of omega-(trans-4-stilbene)alkylthiol self-assembled monolayers (SAMs) on Au(111) were investigated using atomic force microscopy (AFM) and near edge x-ray absorption fine structure spectroscopy (NEXAFS). The sample surface was uniformly covered with a molecular film consisting of very small grains. Well-ordered and flat monolayer islands were formed after the sample was heated in nitrogen at 120 oC for 1 h. While lattice resolved AFM images revealed a crystalline phase in the islands, the area between islands showed no order. The islands exhibit substantial reduction (50percent) in friction, supporting the existence of good ordering. NEXAFS measurements revealed an average upright molecular orientation in the film, both before and after heating, with a narrower tilt-angle distribution for the heated fim. Conductance-AFM measurements revealed a two orders of magnitude higher conductivity on the ordered islands than on the disordered phase. We propose that the conductance enhancement is a result of a better pi-pi stacking between the trans-stilbene molecular units as a result of improved ordering in islands.

  1. Formation of hydroxyl-functionalized stilbenoid molecular sieves at the liquid/solid interface on top of a 1-decanol monolayer

    NASA Astrophysics Data System (ADS)

    Bellec, Amandine; Arrigoni, Claire; Douillard, Ludovic; Fiorini-Debuisschert, Céline; Mathevet, Fabrice; Kreher, David; Attias, André-Jean; Charra, Fabrice

    2014-10-01

    Specific molecular tectons can be designed to form molecular sieves through self-assembly at the solid-liquid interface. After demonstrating a model tecton bearing apolar alkyl chains, we then focus on a modified structure involving asymmetric functionalization of some alkyl chains with polar hydroxyl groups in order to get chemical selectivity in the sieving. As the formation of supramolecular self-assembled networks strongly depends on molecule-molecule, molecule-substrate and molecule-solvent interactions, we compared the tectons’ self-assembly on graphite for two types of solvent. We demonstrate the possibility to create hydroxylated stilbenoid molecular sieves by using 1-decanol as a solvent. Interestingly, with this solvent, the porous network is developed on top of a 1-decanol monolayer.

  2. Adsorbent phosphates

    NASA Technical Reports Server (NTRS)

    Watanabe, S.

    1983-01-01

    An adsorbent which uses as its primary ingredient phosphoric acid salts of zirconium or titanium is presented. Production methods are discussed and several examples are detailed. Measurements of separating characteristics of some gases using the salts are given.

  3. Ammonia adsorption on iron phthalocyanine on Au(111): Influence on adsorbate-substrate coupling and molecular spin

    SciTech Connect

    Isvoranu, Cristina; Ataman, Evren; Knudsen, Jan; Andersen, Jesper N.; Schnadt, Joachim; Wang Bin; Bocquet, Marie-Laure; Schulte, Karina

    2011-03-21

    The adsorption of ammonia on Au(111)-supported monolayers of iron phthalocyanine has been investigated by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, and density functional theory calculations. The ammonia-induced changes of the x-ray photoemission lines show that a dative bond is formed between ammonia and the iron center of the phthalocyanine molecules, and that the local spin on the iron atom is quenched. This is confirmed by density functional theory, which also shows that the bond between the iron center of the metalorganic complex and the Au(111) substrate is weakened upon adsorption of ammonia. The experimental results further show that additional adsorption sites exist for ammonia on the iron phthalocyanine monolayer.

  4. Single-monolayer in situ modulus measurements using a SAW device: Photocrosslinking of a diacetylenic thiol-based monolayer

    SciTech Connect

    Ricco, A.J.; Staton, A.W.; Crooks, R.M.; Kim, Taisun

    1997-10-01

    We report direct measurement of the modulus change that accompanies the crosslinking of a single molecular monolayer. We measured a change in elastic modulus of 5 x 10{sup 10} dyn/cm{sup 2} as a result of ultraviolet-induced photocrosslinking of a single surface-confined monolayer of the conjugated diacetylenic thiol HS(CH{sub 2}){sub 10}C{triple_bond}CC{triple_bond}C(CH{sub 2}){sub 10}COOH, designated {open_quotes}DAT{close_quotes} hereafter. The modulus measurement was made on a monolayer of DAT chemisorbed upon a gold film on the surface of a 97-MHz ST-quartz surface acoustic wave delay line. The ratio of the changes recorded in SAW velocity and attenuation, approximately 4:1, suggests that the measured effect is mainly a change in the elastic (real) component of the complex shear modulus, viscous changes playing a lesser role. In relation to typical polymer modulus values, the change of 5 x 10{sup 10} dyn/cm{sup 2} is consistent with a change from a rubbery material (G{prime} {approximately} 10{sup 7} - 10{sup 8} dyn/cm{sup 2}) to a fairly rigid, glassy material (G{prime} {approximately} 10{sup 10} dyn/cm{sup 2}), reasonable for comparison of the monolayer in its as-adsorbed and crosslinked forms. This report of the direct SAW-based measurement of the modulus change associated with the crosslinking of a single molecular monolayer is complementary to and consistent with previous in-situ measurements of this process using thickness-shear mode resonators.

  5. Influence of the Hofmeister series of anions on the molecular organization of positively ionized monolayers of a viologen derivative.

    PubMed

    Giner, Ignacio; Pera, Gorka; Lafuente, Carlos; López, María Carmen; Cea, Pilar

    2007-11-15

    The effects of the Hofmeister series of ions are ubiquitous in chemistry and biology. In this paper specific ion effects on the surface behavior of a viologen dication, namely 1,1(')-dioctadecyl-4,4(')-bipyridilium, are shown. Surface pressure and surface potential vs area isotherms were obtained on aqueous subphases containing potassium salts with several representative counterions in the Hofmeister series (C6H5O3-7, SO2 -4, HPO2-4, Cl-, Br-, NO-3, I-, and ClO-4). The parameters obtained from the compression isotherms (area per molecule, phase transitions, Young modulus, initial surface potential, and variation of the surface potential upon compression) are dependent on the nature of the counterion, indicating ion specificity. Aqueous subphases containing C6H5O3-7, SO2-4, and HPO2-4 anions yield more expanded viologen monolayers and these anions do not effectively penetrate into the monolayer. Brewster angle microscopy was used to map the different phases of the viologen monolayers at the air-water interface. The Langmuir films were also characterized by UV-vis spectroscopy, with quantitative analysis of the reflection spectra supporting an organizational model in which the viologen chromophore undergoes a gradual transition to a more vertical position with respect to the water surface upon compression. A comparison of the tilt angles of the viologen on the different subphases indicates that anions that can more easily penetrate in the monolayer permit the viologen moieties to adopt a slightly more vertical position with respect to the water surface.

  6. Phenomenological Modeling for Langmuir Monolayers

    NASA Astrophysics Data System (ADS)

    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.

  7. Molecular Anchors for Self-Assembled Monolayers on ZnO: A Direct Comparison of the Thiol and Phosphic Acid Moieties

    SciTech Connect

    Perkins, C. L.

    2009-01-01

    Two of the most promising schemes for attaching organic molecules to metal oxides are based on the chemistry of the thiol and phosphonic acid moieties. We have made a direct comparison of the efficacy of these two molecular anchors on zinc oxide by comparing the chemical and physical properties of n-hexane derivatives of both. The surface properties of polycrystalline ZnO thin films and ZnO(000)-O crystals modified with 1-hexanethiol and 1-hexanephosphonic acid were examined with a novel quartz crystal microbalance (QCM)-based flow cell reactor, angle-resolved and temperature-dependent photoelectron spectroscopy, and contact angle measurements. A means of using ammonium chloride as a probe of molecule-ZnO interactions is introduced and used to ascertain the relative quality of self-assembled monolayers (SAMs) based on thiols and phosphonic acids. QCM data shows that a phosphonic acid-anchored alkyl chain only six carbons long can provide significant corrosion protection for ZnO against Bronsted acids, reducing the etch rate relative to the bare ZnO surface by a factor of more than nine. In contrast, we find that monolayers from the analogous molecule hexanethiol are more defective as revealed by their higher ionic permeability and lower hydrophobicity. Substrate attenuation X-ray photoelectron spectroscopy (XPS) experiments were used to determine the thickness of SAMs formed by the two hexane derivatives and it was found that SAMs from phosphonic acids were approximately twice as thick as those formed by hexanethiol. The thermal stability of the two linking groups was also explored and we find that previous claims of highly stable alkanethiolate monolayers on ZnO are suspect. Taken as a whole, our results indicate that the phosphonic acid moiety is preferred over thiols for the attachment of short alkyl groups to ZnO.

  8. Ground state degeneracy, energy barriers, and molecular dynamics evidence for two-dimensional disorder in black phosphorus and monochalcogenide monolayers at finite temperature

    NASA Astrophysics Data System (ADS)

    Mehboudi, Mehrshad; Barraza-Lopez, Salvador; Dorio, Alex M.; Zhu, Wenjuan; van der Zande, Arend; Churchill, Hugh O. H.; Pacheco-Sanjuan, Alejandro A.; Harriss, Edmund O.; Kumar, Pradeep

    Mono-layers of black phosphorus and other two dimensional materials such as mono-layers of SiSe, GeS, GeSe, GeTe, Sns, SnSe, and SnTe with a similar crystalline structure have a four-fold degenerate ground state that leads to two-dimensional disorder at finite temperature. Disorder happens when neighboring atoms gently re-accommodate bonds beyond a critical temperature. In this talk, the effect of atomic numbers on the transition temperature will be discussed. In addition Car-Parinello molecular dynamics calculations at temperatures 30, 300 and 1000 K were performed on supercells containing more than five hundred atoms and the results from these calculations confirm the transition onto a two-dimensional disordered structure past the critical temperature, which is close to room temperature for many of these compounds. References: M. Mehboudi, A.M. Dorio, W. Zhu, A. van der Zande, H.O.H. Churchill, A.A. Pacheco Sanjuan, E.O.H. Harris, P. Kumar, and S. Barraza-Lopez. arXiv:1510.09153.

  9. Glyoxal-Urea-Formaldehyde Molecularly Imprinted Resin as Pipette Tip Solid-Phase Extraction Adsorbent for Selective Screening of Organochlorine Pesticides in Spinach.

    PubMed

    Yang, Chen; Lv, Tianwei; Yan, Hongyuan; Wu, Gaochan; Li, Haonan

    2015-11-01

    A new kind of glyoxal-urea-formaldehyde molecularly imprinted resin (GUF-MIR) was synthesized by a glyoxal-urea-formaldehyde (GUF) gel imprinting method with 4,4'-dichlorobenzhydrol as a dummy template. The obtained GUF-MIR was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) and applied as a selective adsorbent of miniaturized pipet tip solid-phase extraction (PT-SPE) for the separation and extraction of three organochlorine pesticides (dicofol (DCF), dichlorodiphenyl dichloroethane (DDD), and tetradifon) in spinach samples. The proposed pretreatment procedures of spinach samples involved only 5.0 mg of GUF-MIR, 0.7 mL of MeOH-H2O (1:1, v/v) (washing solvent), and 0.6 mL of cyclohexane-ethyl acetate (9:1, v/v) (elution solvent). In comparison with other adsorbents (such as silica gel, C18, NH2-silica gel, and neutral alumina (Al2O3-N)), GUF-MIR showed higher adsorption and purification capacity for DCF, DDD, and tetradifon in aqueous solution. The average recoveries at three spiked levels ranged from 89.1% to 101.9% with relative standard deviations (RSDs) ≤ 7.1% (n = 3). The presented GUF-MIR-PT-SPE method combines the advantages of molecularly imprinted polymers (MIPs), GUF, and PT-SPE and can be used in polar solutions with high affinity and selectivity to the analytes in complex samples.

  10. Perforated monolayers

    SciTech Connect

    Regen, S.L.

    1992-01-01

    Our research over this past grant period has focused on (1) developing methods for making in situ permeation measurements at the air-water interface, (2) defining the structural and conformational behavior of selected calix(4)arenes, (3) defining the metal complexation properties of certain upper-rim functionalized calix(4)arenes, and (4) synthesizing a broad series of polymerizable calixarenes, to be used for constructing perforated monolayers and multilayers.

  11. Solvent Dependence of the Molecular Order in Ion-Exchanged Self-Assembled dialkylammonium Monolayers on Mica Studied with Soft X-ray Absorption

    SciTech Connect

    Hahner,G.; Zwahlen, M.; Caseri, W.

    2005-01-01

    Dialkyldimethylammonium films on mica prepared via ion exchange from solution have been reported to be of high quality in terms of their density and molecular orientation. Different preparation procedures are described in the literature. The molecular order and the inclination of the alkyl chains, however, are often deduced from indirect experimental evidence such as the wettability and the film thickness. In the present study we employed near edge X-ray absorption fine structure spectroscopy (NEXAFS) to determine directly the order of the molecules adsorbed from different solvents (water, methanol, water/methanol 1:1, cyclohexanol, and chloroform). It was found that films prepared from different solvents are displaying large differences in the established surface coverage and orientation. In particular, NEXAFS disclosed that the orientation of the alkyl chains can differ significantly even when similar water contact angle values are observed.

  12. Spontaneous formation of interfacial lipid-protein monolayers during adsorption from vesicles.

    PubMed Central

    Nag, K; Perez-Gil, J; Cruz, A; Rich, N H; Keough, K M

    1996-01-01

    Spread and adsorbed monolayers of lipid-protein mixtures have served as models for biomembranes and pulmonary surfactant, but their similarity was unclear. Epifluorescence microscopy of monolayers spontaneously adsorbed from vesicles of dipalmitoylphosphatidylcholine or dipalmitoylphosphatidylcholine plus surfactant protein C (SP-C) showed gas, liquid expanded, and liquid condensed (LC) domains. The shapes and distribution of LC domains in the adsorbed and solvent-spread monolayers were quite similar. Labeled SP-C adsorbed into the air-water interface in the company of the lipids. In both forms of monolayers, SP-C occupied the fluid phase and reduced the size and amount of the LC domains. The properties suggest that these adsorbed and spread monolayers are analogous to one another. Images FIGURE 1 FIGURE 2 FIGURE 3 PMID:8874011

  13. Acid effect on excited Auramine-O molecular rotor relaxations in solution and adsorbed on insulin fibrils

    NASA Astrophysics Data System (ADS)

    Simkovitch, R.; Akulov, K.; Erez, Y.; Amdursky, N.; Gepshtein, R.; Schwartz, T.; Huppert, D.

    2015-09-01

    Steady-state and time-resolved UV-Vis spectroscopy techniques were employed to study the non-radiative process of Auramine-O (AuO). We focused our attention on the ultrafast nonradiative decay of Auramine-O in water and on the acid effect on Auramine-O spectroscopy. We found that weak acids like formic acid shorten the excited-state decay times of both the emission and the transient pump-probe spectra of Auramine-O. We found three time domains in the relaxation of the excited states back to the ground state. In mixtures of acetic and formic acids, the three decay times associated with the relaxation process are shorter in the presence of formic acid in Auramine-O solutions. We qualitatively explain the very large non-radiative rate in water and in formic-acetic acid mixtures by a protic nonradiative model proposed by Sobolewski and Domcke. The steady-state emission spectrum of AuO adsorbed on insulin fibrils consists of two bands assigned to protonated and deprotonated forms and the emission intensity increases by three orders of magnitude. We conclude that the nonradiative process prevails in the liquid state, whereas when AuO is adsorbed on fibrils the nonradiative rate is reduced by three orders of magnitude and thus enables a slow ESPT process to occur.

  14. The interaction between the outer layer of a mixed ion pair amphiphile/double-chained cationic surfactant vesicle and DNA: a Langmuir monolayer study.

    PubMed

    Lee, Jung; Chang, Chien-Hsiang

    2014-03-21

    The charge density of vesicular bilayers plays an important role in the structure characteristic of the vesicle-DNA complex for gene delivery. In this work, the charge density effect of catanionic vesicle surfaces on the association behavior of the vesicle with DNA was explored with the model Langmuir monolayer approach. The interaction of negatively charged DNA with positively charged Langmuir monolayers composed of catanionic vesicle-forming materials, hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS) and dihexadecyldimethylammonium bromide (DHDAB), was investigated with surface pressure-area isotherms, area-time relaxation curves and Brewster angle microscope images. The results showed that the adsorption of DNA molecules onto the monolayers was enhanced with an increased DHDAB molar fraction (XDHDAB), which was apparently related to the increased charge density of the monolayers. With XDHDAB being increased up to 0.5, the mixed monolayers with a higher XDHDAB, or higher charge density, possessed a more stable characteristic at high surface pressures, at which the molecular status was close to that in a corresponding vesicular bilayer, due to the DHDAB-improved molecular packing/interaction. It was found that the composition of the mixed HTMA-DS-DHDAB monolayers at high surface pressures would be affected by the adsorbed DNA with the extent depending on XDHDAB. For the formation of stable HTMA-DS-DHDAB monolayer-DNA complexes, a strong electrostatic interaction of DNA with a monolayer of high charge density and a high monolayer stability characteristic resulting from DHDAB-improved molecular packing/interaction were thus required. The finding has an implication for the formulation of catanionic vesicles composed of an ion pair amphiphile, HTMA-DS, with DHDAB in gene delivery applications.

  15. Molecular-Resolution Interrogation of a Porphyrin Monolayer by Ultrahigh Vacuum Tip-Enhanced Raman and Fluorescence Spectroscopy.

    PubMed

    Chiang, Naihao; Jiang, Nan; Chulhai, Dhabih V; Pozzi, Eric A; Hersam, Mark C; Jensen, Lasse; Seideman, Tamar; Van Duyne, Richard P

    2015-06-10

    Tip-enhanced Raman scattering (TERS) and optically excited tip-enhanced fluorescence (TEF) of a self-assembled porphyrin monolayer on Ag(111) are studied using an ultrahigh vacuum scanning tunneling microscope (UHV-STM). Through selectively exciting different Q-bands of meso-tetrakis- (3,5-ditertiarybutylphenyl)-porphyrin (H2TBPP), chemical information regarding different vibronic excited states is revealed by a combination of theory and experiment; namely, TERS and time-dependent density functional theory (TDDFT) simulations. The observed TEF spectra suggest a weak coupling of H2TBPP to the substrate due to the bulky t-butyl groups and a possible alternative excited state decay path. This work demonstrates the potential of combining TERS and TEF for studying surface-mounted porphyins on substrates, thus providing insight into porphyrin-sensitized solar cells and catalysis.

  16. A New Route to Nondestructive Top-Contacts for Molecular Electronics on Si: Pb Evaporated on Organic Monolayers.

    PubMed

    Lovrinčić, Robert; Kraynis, Olga; Har-Lavan, Rotem; Haj-Yahya, Abd-Elrazek; Li, Wenjie; Vilan, Ayelet; Cahen, David

    2013-02-01

    Thermally evaporated Pb preserves the electronic properties of an organic monolayer (ML) on Si and surface passivation of the Si surface itself. The obtained current-voltage characteristics of Pb/ML/Si junctions agree with results obtained with the well-established Hg contact and preserve both the molecule-induced dipole effect on, and length-attenuation of, the current. We rationalize our findings by the lack of interaction between the Pb and the Si substrate. This method is fast, scalable, and compatible with standard semiconductor processing, results in close to 100% yield, and can help the development of large-scale utilization of silicon-organic hybrid electronics. Our experimental data show a dependence of the transport across the molecules on the substrate orientation, expressed in the smaller distance decay parameter with Si(100) than that with Si(111).

  17. Reducing leakage currents in n-channel organic field-effect transistors using molecular dipole monolayers on nanoscale oxides.

    PubMed

    Martínez Hardigree, Josué F; Dawidczyk, Thomas J; Ireland, Robert M; Johns, Gary L; Jung, Byung-Jun; Nyman, Mathias; Osterbacka, Ronald; Marković, Nina; Katz, Howard E

    2013-08-14

    Leakage currents through the gate dielectric of thin film transistors remain a roadblock to the fabrication of organic field-effect transistors (OFETs) on ultrathin dielectrics. We report the first investigation of a self-assembled monolayer (SAM) dipole as an electrostatic barrier to reduce leakage currents in n-channel OFETs fabricated on a minimal, leaky ∼10 nm SiO2 dielectric on highly doped Si. The electric field associated with 1H,1H,2H,2H-perfluoro-octyltriethoxysilane (FOTS) and octyltriethoxysilane (OTS) dipolar chains affixed to the oxide surface of n-Si gave an order of magnitude decrease in gate leakage current and subthreshold leakage and a two order-of-magnitude increase in ON/OFF ratio for a naphthalenetetracarboxylic diimide (NTCDI) transistor. Identically fabricated devices on p-Si showed similarly reduced leakage and improved performance for oxides treated with the larger dipole FOTS monolayer, while OTS devices showed poorer transfer characteristics than those on bare oxide. Comparison of OFETs on both substrates revealed that relative device performance from OTS and FOTS treatments was dictated primarily by the organosilane chain and not the underlying siloxane-substrate bond. This conclusion is supported by the similar threshold voltages (VT) extrapolated for SAM-treated devices, which display positive relative VT shifts for FOTS on either substrate but opposite VT shifts for OTS treatment on n-Si and p-Si. Our results highlight the potential of dipolar SAMs as performance-enhancing layers for marginal quality dielectrics, broadening the material spectrum for low power, ultrathin organic electronics.

  18. Molecular orientation of molybdate ions adsorbed on goethite nanoparticles revealed by polarized in situ ATR-IR spectroscopy

    NASA Astrophysics Data System (ADS)

    Davantès, Athénaïs; Lefèvre, Grégory

    2016-11-01

    The speciation of species adsorbed on nanoparticles is a major concern for several fields, as environmental pollution and remediation, surface functionalization, or catalysis. Attenuated total reflectance infrared spectroscopy (ATR-IR) was amongst the rare methods able to give in situ information about the geometry of surface complexes on nanoparticles. A new possibility using this technique is illustrated here with the MoO42 -/goethite system. Using deuterated goethite to avoid spectral interferences, adsorption of molybdate ions on a spontaneous oriented film of nanoparticles has been followed using a polarized infrared beam. From the decomposition of spectra in the x, y and z directions, a monodentate surface complex on the {101} faces has been found as the most probable geometry. This result demonstrates that polarized ATR-IR allows to characterize in more details adsorption mode at the atomic scale, in comparison with usual ATR-IR spectroscopy.

  19. On the widths of Stokes lines in Raman scattering from molecules adsorbed at metal surfaces and in molecular conduction junctions

    NASA Astrophysics Data System (ADS)

    Gao, Yi; Galperin, Michael; Nitzan, Abraham

    2016-06-01

    Within a generic model we analyze the Stokes linewidth in surface enhanced Raman scattering (SERS) from molecules embedded as bridges in molecular junctions. We identify four main contributions to the off-resonant Stokes signal and show that under zero voltage bias (a situation pertaining also to standard SERS experiments) and at low bias junctions only one of these contributions is pronounced. The linewidth of this component is determined by the molecular vibrational relaxation rate, which is dominated by interactions with the essentially bosonic thermal environment when the relevant molecular electronic energy is far from the metal(s) Fermi energy(ies). It increases when the molecular electronic level is close to the metal Fermi level so that an additional vibrational relaxation channel due to electron-hole (eh) exciton in the molecule opens. Other contributions to the Raman signal, of considerably broader linewidths, can become important at larger junction bias.

  20. Natural gas cleanup: Evaluation of a molecular sieve carbon as a pressure swing adsorbent for the separation of methane/nitrogen mixtures

    SciTech Connect

    Grimes, R.W.

    1994-06-01

    This report describes the results of a preliminary evaluation to determine the technical feasibility of using a molecular sieve carbon manufactured by the Takeda Chemical Company of Japan in a pressure owing adsorption cycle for upgrading natural gas (methane) contaminated with nitrogen. Adsorption tests were conducted using this adsorbent in two, four, and five-step adsorption cycles. Separation performance was evaluated in terms of product purity, product recovery, and sorbent productivity for all tests. The tests were conducted in a small, single-column adsorption apparatus that held 120 grams of the adsorbent. Test variables included adsorption pressure, pressurization rate, purge rate and volume, feed rate, and flow direction in the steps from which the product was collected. Sorbent regeneration was accomplished by purging the column with the feed gas mixture for all but one test series where a pure methane purge was used. The ratio between the volumes of the pressurization gas and the purge gas streams was found to be an important factor in determining separation performance. Flow rates in the various cycle steps had no significant effect. Countercurrent flow in the blow-down and purge steps improved separation performance. Separation performance appears to improve with increasing adsorption pressure, but because there are a number of interrelated variables that are also effected by pressure, further testing will be needed to verify this. The work demonstrates that a molecular sieve carbon can be used to separate a mixture of methane and nitrogen when used in a pressure swing cycle with regeneration by purge. Further work is needed to increase product purity and product recovery.

  1. Ultra-high vacuum scanning tunneling microscopy and theoretical studies of 1-halohexane monolayers on graphite

    PubMed Central

    Müller, Thomas; Werblowsky, Tova L.; Florio, Gina M.; Berne, Bruce J.; Flynn, George W.

    2005-01-01

    A simple model system for the 2D self-assembly of functionalized organic molecules on surfaces was examined in a concerted experimental and theoretical effort. Monolayers of 1-halohexanes were formed through vapor deposition onto graphite surfaces in ultrahigh vacuum. Low-temperature scanning tunneling microscopy allowed the molecular conformation, orientation, and monolayer crystallographic parameters to be determined. Essentially identical noncommensurate monolayer structures were found for all 1-halohexanes, with differences in image contrast ascribed mainly to electronic factors. Energy minimizations and molecular dynamics simulations reproduced structural parameters of 1-bromohexane monolayers quantitatively. An analysis of interactions driving the self-assembly process revealed the crucial role played by small but anisotropic electrostatic forces associated with the halogen substituent. While alkyl chain dispersion interactions drive the formation of a close-packed adsorbate monolayer, electrostatic headgroup forces are found to compete successfully in the control of both the angle between lamella and backbone axes and the angle between surface and backbone planes. This competition is consistent with energetic tradeoffs apparent in adsorption energies measured in earlier temperature-programmed desorption studies. In accordance with the higher degree of disorder observed in scanning tunneling microscopy images of 1-fluorohexane, theoretical simulations show that electrostatic forces associated with the fluorine substituent are sufficiently strong to upset the delicate balance of interactions required for the formation of an ordered monolayer. The detailed dissection of the driving forces for self-assembly of these simple model systems is expected to aid in the understanding of the more complex self-assembly processes taking place in the presence of solvent. PMID:15758073

  2. Temperature-dependent dynamic response to flash heating of molecular monolayers on metal surfaces: vibrational energy exchange.

    PubMed

    Berg, Christopher M; Sun, Yuxiao; Dlott, Dana D

    2014-07-17

    An ultrafast nonlinear coherent laser spectroscopy termed vibrational sum-frequency generation (SFG) was used to monitor vibrational transitions of a self-assembled monolayer (SAM) of 4-nitrobenzenethiolate (NBT) on Au after Au flash heating. Ultrafast thermoreflectance measurements showed the surface temperature jumps ΔT were in the 35-250 K range. The NBT symmetric and antisymmetric nitro stretches νsNO2 and νasNO2 and a phenyl ring stretch νCC were probed. Flash heating caused these transitions to lose intensity, shift, and broaden. The time dependences all had overshoot-decay-plateau structures. In the long-lived plateau, the SAM was in thermal equilibrium with the hot Au surface. The SFG plateau intensity losses of νsNO2 and νCC, two vibrations with parallel transition moments, were identical, indicating that the SFG intensity loss was caused by thermally induced SAM orientational disorder. The T-jump-induced frequency shifts of νsNO2 and νasNO2 were identical and opposite in sign. The rise times of the shifts were identical and equal to the ∼3.5 ps time constant for the rise of Au surface temperature, which indicates that both shifts were caused by anharmonic coupling to the same lower-energy vibration. The temperature dependence of the νsNO2 shift and width indicated that this vibration was the ∼480 cm(-1) nitro bend. The νsNO2 temperature dependence was interpreted using a vibrational energy exchange mechanism between the nitro stretch and bend.

  3. Ti-decorated graphitic-C3N4 monolayer: A promising material for hydrogen storage

    NASA Astrophysics Data System (ADS)

    Zhang, Weibin; Zhang, Zhijun; Zhang, Fuchun; Yang, Woochul

    2016-11-01

    Ti-decorated graphitic carbon nitride (g-C3N4) monolayer as a promising material system for high-capacity hydrogen storage is proposed through density functional theory calculations. The stability and hydrogen adsorption of Ti-decorated g-C3N4 is analyzed by computing the adsorption energy, the charge population, and electronic density of states. The most stable decoration site of Ti atom is the triangular N hole in g-C3N4 with an adsorption energy of -7.58 eV. The large diffusion energy barrier of the adsorbed Ti atom of ∼6.00 eV prohibits the cluster formation of Ti atoms. The electric field induced by electron redistribution of Ti-adsorbed porous g-C3N4 significantly enhanced hydrogen adsorption up to five H2 molecules at each Ti atom with an average adsorption energy of -0.30 eV/H2. The corresponding hydrogen capacity reaches up to 9.70 wt% at 0 K. In addition, the hydrogen capacity is predicted to be 6.30 wt% at 233 K and all adsorbed H2 are released at 393 K according to molecular dynamics simulation. Thus, the Ti-decorated g-C3N4 monolayer is suggested to be a promising material for hydrogen storage suggested by the DOE for commercial applications.

  4. Analysis of structural changes in active site of luciferase adsorbed on nanofabricated hydrophilic Si surface by molecular-dynamics simulations

    SciTech Connect

    Nishiyama, Katsuhiko; Hoshino, Tadatsugu

    2007-05-21

    Interactions between luciferase and a nanofabricated hydrophilic Si surface were explored by molecular-dynamics simulations. The structural changes in the active-site residues, the residues affecting the luciferin binding, and the residues affecting the bioluminescence color were smaller on the nanofabricated hydrophilic Si surface than on both a hydrophobic Si surface and a hydrophilic Si surface. The nanofabrication and wet-treatment techniques are expected to prevent the decrease in activity of luciferase on the Si surface.

  5. Biomass-based palm shell activated carbon and palm shell carbon molecular sieve as gas separation adsorbents.

    PubMed

    Sethupathi, Sumathi; Bashir, Mohammed Jk; Akbar, Zinatizadeh Ali; Mohamed, Abdul Rahman

    2015-04-01

    Lignocellulosic biomass has been widely recognised as a potential low-cost source for the production of high added value materials and proved to be a good precursor for the production of activated carbons. One of such valuable biomasses used for the production of activated carbons is palm shell. Palm shell (endocarp) is an abundant by-product produced from the palm oil industries throughout tropical countries. Palm shell activated carbon and palm shell carbon molecular sieve has been widely applied in various environmental pollution control technologies, mainly owing to its high adsorption performance, well-developed porosity and low cost, leading to potential applications in gas-phase separation using adsorption processes. This mini-review represents a comprehensive overview of the palm shell activated carbon and palm shell carbon molecular sieve preparation method, physicochemical properties and feasibility of palm shell activated carbon and palm shell carbon molecular sieve in gas separation processes. Some of the limitations are outlined and suggestions for future improvements are pointed out.

  6. The Use of the Molecular Adsorber Coating Technology to Mitigate Vacuum Chamber Contamination During Pathfinder Testing for the James Webb Space Telescope

    NASA Technical Reports Server (NTRS)

    Abraham, Nithin S.; Hasegawa, Mark M.; Wooldridge, Eve M.; Henderson-Nelson, Kelly A.

    2016-01-01

    As a coating made of highly porous zeolite materials, the Molecular Adsorber Coating (MAC) was developed to capture outgassed molecular contaminants, such as hydrocarbons and silicones. For spaceflight applications, the adsorptive capabilities of the coating can alleviate on-orbit outgassing concerns on or near sensitive surfaces and instruments within the spacecraft. Similarly, this sprayable paint technology has proven to be significantly beneficial for ground based space applications, in particular, for vacuum chamber environments. This paper describes the recent use of the MAC technology during Pathfinder testing of the Optical Ground Support Equipment (OGSE) for the James Webb Space Telescope (JWST) at NASA Johnson Space Center (JSC). The coating was used as a mitigation tool to entrap persistent outgassed contaminants, specifically silicone based diffusion pump oil, from within JSC's cryogenic optical vacuum chamber test facility called Chamber A. This paper summarizes the sample fabrication, installation, laboratory testing, post-test chemical analysis results, and future plans for the MAC technology, which was effectively used to protect the JWST test equipment from vacuum chamber contamination.

  7. Molecular dynamics simulation of the interfacial structure of [C(n)mim][PF6] adsorbed on a graphite surface: effects of temperature and alkyl chain length.

    PubMed

    Dou, Q; Sha, M L; Fu, H Y; Wu, G Z

    2011-05-01

    The structures and diffusion behaviors of a series of ionic liquids [C(n)mim][PF(6)] (n = 1, 4, 8 and 12) on a graphite surface have been investigated by means of molecular dynamics simulation. It was found that three or four ordering layers of ionic liquids were formed near the graphite surface, and this layering structure was stable over the temperature range investigated. At the liquid/vacuum interface, the ionic liquid with a butyl chain had a monolayer ordering surface, while [C(8)mim][PF(6)] and [C(12)mim][PF(6)] exhibited a bilayer ordering with a polar domain sandwiched between two orientational nonpolar domains. More impressively, the simulated results showed that for the ionic liquids with alkyl chains longer than C(4), the adjacent alkyl chains in the whole film tended to be parallel to each other, with the imidazolium rings packed closely together. This indicated that the ionic liquids have a better regulated short-range structure than was previously expected. It was also found that both in the bottom layer and in the bulk region, the diffusion of the alkyl chains was much faster than that of the polar groups. However, as the alkyl chain length increased, the charge delocalization in the cation and the enhanced van der Waals interaction between the nonpolar groups contributed by reducing this difference in the diffusivity of major groups.

  8. Nonlinear optical studies of organic monolayers

    SciTech Connect

    Shen, Y.R.

    1988-02-01

    Second-order nonlinear optical effects are forbidden in a medium with inversion symmetry, but are necessarily allowed at a surface where the inversion summary is broken. They are often sufficiently strong so that a submonolayer perturbation of the surface can be readily detected. They can therefore be used as effective tools to study monolayers adsorbed at various interfaces. We discuss here a number of recent experiments in which optical second harmonic generation (SHG) and sum-frequency generation (SFG) are employed to probe and characterize organic monolayers. 15 refs., 5 figs.

  9. Electromelting of Confined Monolayer Ice

    NASA Astrophysics Data System (ADS)

    Qiu, Hu; Guo, Wanlin

    2013-05-01

    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 a perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to the field-induced disruption of the water-wall interaction induced well-ordered network of the hydrogen bond. This electromelting process should add an important new ingredient to the physics of water.

  10. Electromelting of confined monolayer ice.

    PubMed

    Qiu, Hu; Guo, Wanlin

    2013-05-10

    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 a perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to the field-induced disruption of the water-wall interaction induced well-ordered network of the hydrogen bond. This electromelting process should add an important new ingredient to the physics of water. PMID:23705718

  11. Self-Healing of Stone—Wales Defects in Boron Nitride Monolayer by Irradiation: Ab Initio Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Xue, Shu-Wen; Chen, Jian; Zhang, Jun

    2013-10-01

    We show an effective method of healing the Stone—Wales (SW) defects through low energy electron irradiation using ab initio molecular dynamics simulation. The SW defects can be healed by irradiation through bond rotation. Although the healing energy shows an anisotropic behavior, it is lower than the displacement threshold energy. The healing of the SW defect through electron irradiation can be effectively used in other sp2-bonded materials.

  12. Spontaneous waveguide Raman spectroscopy of self-assembled monolayers in silica micropores.

    PubMed

    Calkins, Jacob A; Peacock, Anna C; Sazio, Pier J A; Allara, David L; Badding, John V

    2011-01-18

    Advances in nanoscience are critically dependent on the ability to control and probe chemical and physical phenomena in confined geometries. A key challenge is to identify confinement structures with high surface area to volume ratios and controlled surface boundaries that can be probed quantitatively at the molecular level. Herein we report an approach for probing molecular structures within nano- to microscale pores by the application of spontaneous Raman spectroscopy. We demonstrate the method by characterization of the structural features of picomole quantities of well-organized octadecyltrichlorosilane (OTS) monolayers self-assembled on the interior pore surfaces of high aspect ratio (1 μm diameter × 1-10 cm length), near-atomically smooth silica microstructured optical fibers (MOFs). The simple Raman backscattering collection geometry employed is well suited for a wide variety of diagnostic applications as demonstrated by tracking the combustion of the hydrocarbon chains of the OTS self-assembled monolayer (SAM) and spectral confirmation of the formation of an adsorbed monolayer of human serum albumin (HSA) protein. Using this MOF Raman approach, molecular processes in precisely defined, highly confined geometries can be probed at high pressures and temperatures, with a wide range of excitation wavelengths from the visible to the near-IR, and under other external perturbations such as electric and magnetic fields.

  13. Drug induced `softening' in phospholipid monolayers

    NASA Astrophysics Data System (ADS)

    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.

  14. Molecular-beam epitaxy of monolayer and bilayer WSe2: a scanning tunneling microscopy/spectroscopy study and deduction of exciton binding energy

    NASA Astrophysics Data System (ADS)

    Liu, H. J.; Jiao, L.; Xie, L.; Yang, F.; Chen, J. L.; Ho, W. K.; Gao, C. L.; Jia, J. F.; Cui, X. D.; Xie, M. H.

    2015-09-01

    Interest in two-dimensional (2D) transition-metal dichalcogenides (TMDs) has prompted some recent efforts to grow ultrathin layers of these materials epitaxially using molecular-beam epitaxy (MBE). However, growths of monolayer (ML) and bilayer (BL) WSe2—an important member of the TMD family—by the MBE method remain uncharted, probably because of the difficulty in generating tungsten fluxes from the elemental source. In this work, we present a scanning tunneling microscopy and spectroscopy (STM/S) study of MBE-grown WSe2 ML and BL, showing atomically flat epifilm with no domain boundary (DB) defect. This contrasts epitaxial MoSe2 films grown by the same method, where a dense network of the DB defects is present. The STS measurements of ML and BL WSe2 domains of the same sample reveal not only the bandgap narrowing upon increasing the film thickness from ML to BL, but also a band-bending effect across the boundary (step) between ML and BL domains. This band-bending appears to be dictated by the edge states at steps of the BL islands. Finally, comparison is made between the STS-measured electronic bandgaps with the exciton emission energies measured by photoluminescence, and the exciton binding energies in ML and BL WSe2 (and MoSe2) are thus estimated.

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

    PubMed

    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.

  16. A molecular simulation study of methylated and hydroxyl sugar-based self-assembled monolayers: Surface hydration and resistance to protein adsorption

    NASA Astrophysics Data System (ADS)

    Hower, Jason C.; He, Yi; Jiang, Shaoyi

    2008-12-01

    In this work molecular simulations are performed to investigate protein interactions with hydroxylated and methylated mannitol and sorbitol terminated self-assembled monolayer (SAM) surfaces in the presence of explicit water molecules. The role of surface hydrogen bond donor versus acceptor groups is evaluated by comparing the hydration layer structure and resulting forces generated by the two classes of sugar SAM surfaces. Both hydroxyl and methyl-terminated sugar SAM surfaces interact with hydrating water molecules. Regardless of hydrogen bond donor or acceptor groups, both classes of sugar SAM surface groups interact strongly with hydrating water molecules to induce significant repulsive forces and resistance to protein adsorption. Our results indicate that the repulsive force generated on the probe protein is related to the ability of the surface to orient the hydration layer water. The repulsive force is also proportional to the number of hydrating water molecules interacting with the protein. The repulsive force and subsequent resistance to protein adsorption are dependent on the surface hydration, not the origin of that hydration.

  17. Substituent-Controlled Reversible Switching of Charge Injection Barrier Heights at Metal/Organic Semiconductor Contacts Modified with Disordered Molecular Monolayers.

    PubMed

    Nouchi, Ryo; Tanimoto, Takaaki

    2015-07-28

    Electrically stimulated switching of a charge injection barrier at the interface between an organic semiconductor and an electrode modified with a disordered monolayer (DM) is studied by using various benzenethiol derivatives as DM molecules. The switching behavior is induced by a structural change in the DM molecules and is manifested as a reversible inversion of the polarity of DM-modified Au electrode/rubrene/DM-modified Au electrode diodes. The switching direction is found to be dominantly determined by the push-back effect of the thiol bonding group, while the terminal group modulates the switching strength. A device with 1,2-benzenedithiol DMs exhibited the highest switching ratios of 20, 10(2), and 10(3) for the switching voltages of 3, 5, and 7 V, respectively. A variation in the tilt angle of benzenethiol DMs due to the application of 7 V is estimated to be smaller than 23.6° by model calculations. This study offers an understanding for obtaining highly stable operations of organic electronic devices, especially with molecular modification layers. PMID:26161447

  18. Surface Electrostatic Potential and Water Orientation in the presence of Sodium Octanoate Dilute Monolayers Studied by Means of Molecular Dynamics Simulations.

    PubMed

    Bernardino, Kalil; de Moura, André F

    2015-10-13

    A series of atomistic molecular dynamics simulations were performed in the present investigation to assess the spontaneous formation of surfactant monolayers of sodium octanoate at the water-vacuum interface. The surfactant surface coverage increased until a saturation threshold was achieved, after which any further surfactant addition led to the formation of micellar aggregates within the solution. The saturated films were not densely packed, as might be expected for short-chained surfactants, and all films regardless of the surface coverage presented surfactant molecules with the same ordering pattern, namely, with the ionic heads toward the aqueous solution and the tails lying nearly parallel to the interface. The major contributions to the electrostatic surface potential came from the charged heads and the counterion distribution, which nearly canceled out each other. The balance between the oppositely charged ions rendered the electrostatic contributions from water meaningful, amounting to ca. 10% of the contributions arising from the ionic species. And even the aliphatic tails, whose atoms bear relatively small partial atomic charges as compared to the polar molecules and molecular fragments, contributed with ca. 20% of the total electrostatic surface potential of the systems under investigation. Although the aliphatic tails were not so orderly arranged as in a compact film, the C-H bonds assumed a preferential orientation, leading to an increased contribution to the electrostatic properties of the interface. The most prominent feature arising from the partitioning of the electrostatic potential into individual contributions was the long-range ordering of the water molecules. This ordering of the water molecules produced a repulsive dipole-dipole interaction between the two interfaces, which increased with the surface coverage. Only for a water layer wider than 10 nm was true bulk behavior observed, and the repulsive dipole-dipole interaction faded away. PMID

  19. In silico modelling of permeation enhancement potency in Caco-2 monolayers based on molecular descriptors and random forest.

    PubMed

    Welling, Søren H; Clemmensen, Line K H; Buckley, Stephen T; Hovgaard, Lars; Brockhoff, Per B; Refsgaard, Hanne H F

    2015-08-01

    Structural traits of permeation enhancers are important determinants of their capacity to promote enhanced drug absorption. Therefore, in order to obtain a better understanding of structure-activity relationships for permeation enhancers, a Quantitative Structural Activity Relationship (QSAR) model has been developed. The random forest-QSAR model was based upon Caco-2 data for 41 surfactant-like permeation enhancers from Whitehead et al. (2008) and molecular descriptors calculated from their structure. The QSAR model was validated by two test-sets: (i) an eleven compound experimental set with Caco-2 data and (ii) nine compounds with Caco-2 data from literature. Feature contributions, a recent developed diagnostic tool, was applied to elucidate the contribution of individual molecular descriptors to the predicted potency. Feature contributions provided easy interpretable suggestions of important structural properties for potent permeation enhancers such as segregation of hydrophilic and lipophilic domains. Focusing on surfactant-like properties, it is possible to model the potency of the complex pharmaceutical excipients, permeation enhancers. For the first time, a QSAR model has been developed for permeation enhancement. The model is a valuable in silico approach for both screening of new permeation enhancers and physicochemical optimisation of surfactant enhancer systems.

  20. Characterization of organosulfur monolayer formation at gold electrodes

    SciTech Connect

    Tani Woods, N.

    1996-08-01

    Among the many types of organic films, covalently-attached organosulfur monolayers have attracted a great deal of attention. The authors have focused their interest on the fundamental characterization of spontaneously adsorbed organosulfur monolayers. An introductory chapter presents general aspects of monolayer preparation and characterization, followed by a few examples that illustrate the range of applications of these films. This thesis contains two papers. In the first paper, three analogous monolayer precursors are studied to determine their similarities and differences in the monolayer structure. A GC-MS analysis of products form the chemisorption process and open circuit potential measurements are used to derive possible mechanisms behind monolayer formation. The second paper focuses on monolayers formed from thioctic acid, including its characterization and application to cytochrome c electrochemistry. Although thiols and disulfides have been extensively studied as monolayer precursors, thioctic acid is particularly interesting because the disulfide functionality of this asymmetric molecule is contained in a strained five-membered ring. Given the ring strain, steric bulk and asymmetry of the molecule, the study of these monolayers lend insight into the factors important for the formation of organosulfur monolayers. This thesis concludes with a general summary and directions for future studies. 40 refs.

  1. Molecular Adsorbent Recirculating System (MARS(®)) removal of piperacillin/tazobactam in a patient with acetaminophen-induced acute liver failure.

    PubMed

    Ruggero, M A; Argento, A C; Heavner, M S; Topal, J E

    2013-04-01

    The objective of this study was to illustrate the pharmacokinetic removal of piperacillin/tazobactam in an anuric patient on Molecular Adsorbent Recirculating System (MARS(®)). The patient was a 32-year-old woman who presented to a medical intensive care unit with acute liver failure secondary to an acetaminophen overdose. While awaiting transplant, she was started on MARS therapy as a bridge to liver transplant and empirically started on piperacillin/tazobactam therapy. MARS is an extracorporeal hemofiltration device, which incorporates a continuous venovenous hemofiltration (CVVHD) machine linked to an albumin-enriched dialysate filter to normalize excess electrolytes, metabolic waste, and protein-bound toxins. In addition to protein-bound waste, MARS removes water-soluble, low molecular-weight molecules. The patient received piperacillin/tazobactam 4.5 g infused intravenously over 3 h. A steep decline in serum levels occurred between hours 4 and 6 while MARS continued and no antibiotic was infused. The elimination rate constant (k(e)) for the removal of piperacillin in this patent was 0.453 h(-1) and the half-life (λ) was 1.53 h. The k(e) was 2.9-fold higher than with CVVHD alone and the λ was 3.7-fold shorter. Low levels of piperacillin are achieved during MARS therapy, but in the treatment of more resistant organisms, such as Pseudomonas aeruginosa, these low levels may not be adequate to achieve bactericidal activity. Drug levels following a standard infusion of 30 min would likely be even lower. Formalized pharmacokinetic studies of piperacillin/tazobactam removal in patients on MARS therapy are necessary to make clear dosing recommendations.

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

    NASA Astrophysics Data System (ADS)

    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

  3. Molecular assembly at bare semiconductor surfaces

    NASA Astrophysics Data System (ADS)

    McGuiness, Christine L.

    The formation of well-organized monolayers with highly reproducible structures by solution self assembly of octadecanethiol (ODT) on GaAs (001) and (011) surfaces at ambient temperature through rigorous control of assembly conditions is demonstrated. Using TOF-SIMs and HRXPS measurements, it is shown that ODT molecules form a direct S-GaAs attachment with little to no substrate oxidation and exhibit an overall thermal stability up to ˜100°C, lower than the same monolayers on Au{111} surfaces. Detailed characterization using a combination of ellipsometry, liquid drop contact angles, atomic force microscopy, near edge x-ray absorption fine structure, infrared spectroscopy and x-ray photoemission spectroscopy probes reveal a structure with conformationally ordered alkyl chains tilted 14 +/-1° from the surface normal with a 43 +/-5° twist, a highly oleophobic and hydrophobic ambient surface. On GaAs (111A) surfaces, the ODT monolayers also form a direct S-GaAs attachment with little to no substrate oxidation but the final monolayer structure is more disordered, with the alkyl chains tilted 25 +/-5° from surface normal with a 45 +/-5° twist, resulting in a less oleophobic and hydrophobic ambient surface. Further, in contrast to previously reported results with Na2S9H2O treatments, Raman scattering measurements reveal that the ODT monolayers do not significantly modify the near-surface electronic structure of GaAs. Analysis of the tilt angle and film thickness data in conjunction with grazing incidence x-ray diffraction measurements show that the monolayers form structures with a significant mismatch of the average adsorbate molecule spacings with the spacings of intrinsic GaAs crystal lattices. For the square surface lattices of GaAs (001) and (011), ODT monolayers are observed to form pseudo-hcp structures. On the hcp surface lattice of GaAs (111A) however, the monolayers form a true hcp structure. This suggests that formation of the monolayers is driven

  4. Adsorption of Ions at Uncharged Insoluble Monolayers.

    PubMed

    Peshkova, Tatyana V; Minkov, Ivan L; Tsekov, Roumen; Slavchov, Radomir I

    2016-09-01

    A method is proposed for the experimental determination of the adsorption of inorganic electrolytes at a surface covered with insoluble surfactant monolayer. This task is complicated by the fact that the change of the salt concentration alters both chemical potentials of the electrolyte and the surfactant. Our method resolves the question by combining data for the surface pressure versus area of the monolayer at several salt concentrations with data for the equilibrium spreading pressure of crystals of the surfactant (used to fix a standard state). We applied the method to alcohols spread at the surface of concentrated halide solutions. The measured salt adsorption is positive and has nonmonotonic dependence on the area per surfactant molecule. For the liquid expanded film, depending on the concentration, there is one couple of ions adsorbed per each 3-30 surfactant molecules. We analyzed which ion, the positive or the negative, stands closer to the surface, by measuring the effect of NaCl on the Volta potential of the monolayer. The potentiometric data suggest that Na(+) is specifically adsorbed, while Cl(-) remains in the diffuse layer, i.e., the surface is positively charged. The observed reverse Hofmeister series of the adsorptions of NaF, NaCl, and NaBr suggests the same conclusion holds for all these salts. The force that causes the adsorption of Na(+) seems to be the interaction of the ion with the dipole moment of the monolayer. PMID:27529571

  5. Adsorption of Ions at Uncharged Insoluble Monolayers

    NASA Astrophysics Data System (ADS)

    Peshkova, T. V.; Minkov, I. L.; Tsekov, R.; Slavchov, R. I.

    2016-08-01

    A method is proposed for the experimental determination of the adsorption of inorganic electrolytes at a surface covered with insoluble surfactant monolayer. This task is complicated by the fact that the change of the salt concentration alters both chemical potentials of the electrolyte and the surfactant. Our method resolves the question by combining data for the surface pressure versus area of the monolayer at several salt concentrations with data for the equilibrium spreading pressure of crystals of the surfactant (used to fix a standard state). We applied the method to alcohols spread at the surface of concentrated halide solutions. The measured salt adsorption is positive and has nonmonotonic dependence on the area per surfactant molecule. For the liquid expanded film, depending on the concentration, there is one couple of ions adsorbed per each 3–30 surfactant molecules. We analyzed which ion, the positive or the negative, stands closer to the surface, by measuring the effect of NaCl on the Volta potential of the monolayer. The potentiometric data suggest that Na+ is specifically adsorbed, while Cl– remains in the diffuse layer, i.e., the surface is positively charged. The observed reverse Hofmeister series of the adsorptions of NaF, NaCl, and NaBr suggests the same conclusion holds for all these salts. The force that causes the adsorption of Na+ seems to be the interaction of the ion with the dipole moment of the monolayer.

  6. Thermodynamic investigations using molecular dynamics simulations with potential of mean force calculations for cardiotoxin protein adsorption on mixed self-assembled monolayers.

    PubMed

    Hung, Shih-Wei; Hsiao, Pai-Yi; Lu, Ming-Chang; Chieng, Ching-Chang

    2012-10-25

    Understanding protein adsorption onto solid surfaces is of critical importance in the field of bioengineering, especially for applications such as medical implants, diagnostic biosensors, drug delivery systems, and tissue engineering. This study proposed the use of molecular dynamics simulations with potential of mean force (PMF) calculations to identify and characterize the mechanisms of adsorption of a protein molecule on a designed surface. A set of model systems consisting of a cardiotoxin (CTX) protein and mixed self-assembled monolayer (SAM) surfaces were used as examples. The set of mixed SAM surfaces with varying topographies were created by mixing alkanethiol chains of different lengths. The results revealed that CTX proteins underwent similar conformal changes upon adsorption onto the various mixed SAMs but showed distinctive characteristics in free energy profiles. Enhancement of the adsorption affinity, i.e., the change in free energy of adsorption, for mixed SAMs was demonstrated by using atomic force microscopic measurements. A component analysis conducted to quantify the physical mechanisms that promoted CTX adsorption revealed contributions from both SAMs and the solvent. Further component analyses of thermodynamic properties, such as the free energy, enthalpy, and entropy, indicated that the contribution from SAMs was driven by enthalpy, and the contribution from the solvent was driven by entropy. The results indicated that CTX adsorption was an entropy-driven process, and the entropic component from the solvent, i.e., the hydrophobic interaction, was the major driving force for CTX adsorption onto SAMs. The study also concluded that the surfaces composed of mixtures of SAMs with different chain lengths promoted the adsorption of CTX protein.

  7. Forsterite Carbonation in Wet-scCO2: Dependence on Adsorbed Water Concentration

    NASA Astrophysics Data System (ADS)

    Loring, J.; Benezeth, P.; Qafoku, O.; Thompson, C.; Schaef, T.; Bonneville, A.; McGrail, P.; Felmy, A.; Rosso, K.

    2013-12-01

    showed no change with time, and the spectra indicated only the presence of a highly structured water and bicarbonate film. From our cumulative experiments, we conclude that the reactivity of forsterite with wet-scCO2 can be divided into three adsorbed water concentration threshold regimes: (1) Up to ~2 monolayers, only a highly structured and low mobility chemisorbed water and bicarbonate film is present. (2) Between ~2 to ~5 monolayers, limited carbonation occurs then nearly stops. (3) Above ~5 monolayers, continuous carbonation occurs, and magnesite is the dominant product. The results of these studies provide important insights into metal silicate carbonation mechanisms in low water scCO2 environments. They reinforced the concept of a water threshold for carbonation to occur, which has also been demonstrated for steel corrosion in the presence of wet scCO2. These results will also constrain thermodynamic models and molecular dynamic simulations used to predict mineral trapping extent in basaltic host rocks.

  8. Structural prediction for scandium carbide monolayer sheet

    NASA Astrophysics Data System (ADS)

    Ma, Hong-Man; Wang, Jing; Zhao, Hui-Yan; Zhang, Dong-Bo; Liu, Ying

    2016-09-01

    A two-dimensional tetragonal scandium carbide monolayer sheet has been constructed and studied using density functional theory. The results show that the scandium carbide sheet is stable and exhibits a novel tetracoordinated quasiplanar structure, as favored by the hybridization between Sc-3d orbitals and C-2p orbitals. Calculations of the phonon dispersion as well as molecular dynamics simulations also demonstrate the structural stability of this scandium carbide monolayer sheet. Electronic properties show that the scandium carbide monolayer sheet is metallic and non-magnetic.

  9. Understanding Chemical versus Electrostatic Shifts in X-ray Photoelectron Spectra of Organic Self-Assembled Monolayers

    PubMed Central

    2016-01-01

    The focus of the present article is on understanding the insight that X-ray photoelectron spectroscopy (XPS) measurements can provide when studying self-assembled monolayers. Comparing density functional theory calculations to experimental data on deliberately chosen model systems, we show that both the chemical environment and electrostatic effects arising from a superposition of molecular dipoles influence the measured core-level binding energies to a significant degree. The crucial role of the often overlooked electrostatic effects in polar self-assembled monolayers (SAMs) is unambiguously demonstrated by changing the dipole density through varying the SAM coverage. As a consequence of this effect, care has to be taken when extracting chemical information from the XP spectra of ordered organic adsorbate layers. Our results, furthermore, imply that XPS is a powerful tool for probing local variations in the electrostatic energy in nanoscopic systems, especially in SAMs. PMID:26937264

  10. Employing X-ray Photoelectron Spectroscopy for Determining Layer Homogeneity in Mixed Polar Self-Assembled Monolayers

    PubMed Central

    2016-01-01

    Self-assembled monolayers (SAMs) containing embedded dipolar groups offer the particular advantage of changing the electronic properties of a surface without affecting the SAM–ambient interface. Here we show that such systems can also be used for continuously tuning metal work functions by growing mixed monolayers consisting of molecules with different orientations of the embedded dipolar groups. To avoid injection hot-spots when using the SAM-modified electrodes in devices, a homogeneous mixing of the two components is crucial. We show that a combination of high-resolution X-ray photoelectron spectroscopy with state-of-the-art simulations is an ideal tool for probing the electrostatic homogeneity of the layers and thus for determining phase separation processes in polar adsorbate assemblies down to inhomogeneities at the molecular level. PMID:27429041

  11. Employing X-ray Photoelectron Spectroscopy for Determining Layer Homogeneity in Mixed Polar Self-Assembled Monolayers.

    PubMed

    Hehn, Iris; Schuster, Swen; Wächter, Tobias; Abu-Husein, Tarek; Terfort, Andreas; Zharnikov, Michael; Zojer, Egbert

    2016-08-01

    Self-assembled monolayers (SAMs) containing embedded dipolar groups offer the particular advantage of changing the electronic properties of a surface without affecting the SAM-ambient interface. Here we show that such systems can also be used for continuously tuning metal work functions by growing mixed monolayers consisting of molecules with different orientations of the embedded dipolar groups. To avoid injection hot-spots when using the SAM-modified electrodes in devices, a homogeneous mixing of the two components is crucial. We show that a combination of high-resolution X-ray photoelectron spectroscopy with state-of-the-art simulations is an ideal tool for probing the electrostatic homogeneity of the layers and thus for determining phase separation processes in polar adsorbate assemblies down to inhomogeneities at the molecular level. PMID:27429041

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

    PubMed

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

    2016-04-01

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

  13. Spectral and electrochemical properties of phenylazonaphthalene based on a self-assembled monolayer

    NASA Astrophysics Data System (ADS)

    Zhang, Aidong; Qin, Jingui; Gu, Jianhua; Lu, Zu-Hong

    1998-08-01

    A thiol-terminated phenylazonaphthalene derivative, namely 1-mercapto-6-[1-(4-phenylazonaphthoxy)]hexane 1, was synthesized by diazo coupling of aniline with 1-naphthol, etherification with 1,6-dibromohexane and thiol derivatization, subsequently. By self-assembly technology, the compound was spontaneously absorbed in thin, optically transparent gold film and formed stable self-assembled monolayer (SAM). The self-assembly course was monitored by UV-visible absorption spectra which gave direct evidence for the self-assembly mechanism of self-assembled monolayer, i.e., chemically adsorbed firstly, then came through a long- time orientation. Meanwhile, cyclic voltammogram was employed to study the electrochemical reduction and oxidation of the immobilized phenylazonaphthalene. The single molecular area obtained using the two methods was almost the same: ca. 0.9 nm2. The irreversibility of the electrode process, sluggish reaction and reduction peak splitting all were originated from the well molecular orientation, not the dense packing in the SAM. This implied the process of oxidation and reduction accompanied the molecular conformation change which needed more free space for the movement of the molecular chain during the electrode processes.

  14. Tracing the 4000 year history of organic thin films: From monolayers on liquids to multilayers on solidsa)

    NASA Astrophysics Data System (ADS)

    Greene, J. E.

    2015-03-01

    The recorded history of organic monolayer and multilayer thin films spans approximately 4000 years. Fatty-acid-based monolayers were deposited on water by the ancients for applications ranging from fortune telling in King Hammurabi's time (˜1800 BC, Mesopotamia) to stilling choppy waters for sailors and divers as reported by the Roman philosopher Pliny the Elder in ˜78 AD, and then much later (1774) by the peripatetic American statesman and natural philosopher Benjamin Franklin, to Japanese "floating-ink" art (suminagashi) developed ˜1000 years ago. The modern science of organic monolayers began in the late-1800s/early-1900s with experiments by Lord Rayleigh and the important development by Agnes Pockels, followed two decades later by Irving Langmuir, of the tools and technology to measure the surface tension of liquids, the surface pressure of organic monolayers deposited on water, interfacial properties, molecular conformation of the organic layers, and phase transitions which occur upon compressing the monolayers. In 1935, Katherine Blodgett published a landmark paper showing that multilayers can be synthesized on solid substrates, with controlled thickness and composition, using an apparatus now known as the Langmuir-Blodgett (L-B) trough. A disadvantage of LB films for some applications is that they form weak physisorbed bonds to the substrate. In 1946, Bigelow, Pickett, and Zisman demonstrated, in another seminal paper, the growth of organic self-assembled monolayers (SAMs) via spontaneous adsorption from solution, rather than from the water/air interface, onto SiO2 and metal substrates. SAMs are close-packed two-dimensional organic crystals which exhibit strong covalent bonding to the substrate. The first multicomponent adsorbed monolayers and multilayer SAMs were produced in the early 1980s. Langmuir monolayers, L-B multilayers, and self-assembled mono- and multilayers have found an extraordinarily broad range of applications including controlled wetting

  15. Tracing the 4000 year history of organic thin films: From monolayers on liquids to multilayers on solids

    SciTech Connect

    Greene, J. E.

    2015-03-15

    The recorded history of organic monolayer and multilayer thin films spans approximately 4000 years. Fatty-acid-based monolayers were deposited on water by the ancients for applications ranging from fortune telling in King Hammurabi's time (∼1800 BC, Mesopotamia) to stilling choppy waters for sailors and divers as reported by the Roman philosopher Pliny the Elder in ∼78 AD, and then much later (1774) by the peripatetic American statesman and natural philosopher Benjamin Franklin, to Japanese “floating-ink” art (suminagashi) developed ∼1000 years ago. The modern science of organic monolayers began in the late-1800s/early-1900s with experiments by Lord Rayleigh and the important development by Agnes Pockels, followed two decades later by Irving Langmuir, of the tools and technology to measure the surface tension of liquids, the surface pressure of organic monolayers deposited on water, interfacial properties, molecular conformation of the organic layers, and phase transitions which occur upon compressing the monolayers. In 1935, Katherine Blodgett published a landmark paper showing that multilayers can be synthesized on solid substrates, with controlled thickness and composition, using an apparatus now known as the Langmuir-Blodgett (L-B) trough. A disadvantage of LB films for some applications is that they form weak physisorbed bonds to the substrate. In 1946, Bigelow, Pickett, and Zisman demonstrated, in another seminal paper, the growth of organic self-assembled monolayers (SAMs) via spontaneous adsorption from solution, rather than from the water/air interface, onto SiO{sub 2} and metal substrates. SAMs are close-packed two-dimensional organic crystals which exhibit strong covalent bonding to the substrate. The first multicomponent adsorbed monolayers and multilayer SAMs were produced in the early 1980s. Langmuir monolayers, L-B multilayers, and self-assembled mono- and multilayers have found an extraordinarily broad range of applications including

  16. Asphaltene Adsorption onto Self-Assembled Monolayers of Mixed Aromatic

    SciTech Connect

    Turgman-Cohen, S.; Smith, M; Fischer, D; Kilpatrick, P; Genzer, J

    2009-01-01

    The adsorption of asphaltenes onto flat solid surfaces modified with mixed self-assembled monolayers (SAMs) of aliphatic and aromatic trichlorosilanes with varying wettabilities, aromaticities, and thicknesses is tested. The mixed SAMs are characterized by means of contact angle to assess hydrophobicity and molecular and chemical uniformity, spectroscopic ellipsometry to measure the thickness of the films, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy to assess chemical and molecular composition. The molecular characteristics of the adsorbed asphaltene layer and the extent of asphaltene adsorption are determined using NEXAFS and spectroscopic ellipsometry, respectively. The SAMs are formed by depositing phenyl-, phenethyl-, butyl-, and octadecyl- trichlorosilanes from toluene solutions onto silica-coated substrates; the chemical composition and the wettability of the SAM surface is tuned systematically by varying the trichlorosilane composition in the deposition solutions. The adsorption of asphaltenes on the substrates does not correlate strongly with the SAM chemical composition. Instead, the extent of asphaltene adsorption decreases with increasing SAM thickness. This observation suggests that the leading interaction governing the adsorption of asphaltenes is their interaction with the polar silica substrate and that the chemical composition of the SAM is of secondary importance.

  17. Structure and dynamics of water near the interface with oligo(ethylene oxide) self-assembled monolayers

    NASA Astrophysics Data System (ADS)

    Ismail, Ahmed E.; Grest, Gary S.; Stevens, Mark J.

    2007-03-01

    Oligo(ethylene oxide) self-assembled monolayers (OEO SAM's) deposited on Au are the prototypical materials used to study protein resistance. Recently, protein resistance has been shown to vary as a function of surface coverage and to be maximal at about two-thirds coverage, not complete coverage. We use molecular dynamics simulations to study the nature of the interface between water and the OEO SAM for a range of SAM coverages. As SAM coverage decreases, the amount of water within the OEO monolayer increases monotonically; however, the penetration depth of the water shows a maximum near the experimentally-found maximal coverage. As the water content increases, the SAM-water mixture becomes harder to distinguish from bulk water. Since the oxygen atoms of OEO are hydrogen bond acceptors, a hydrogen bond network forms within the SAM-water mixture. The water molecules diffuse freely within the monolayer and exchange with the bulk water. Because the monolayer becomes increasingly like bulk water as the coverage decreases, proteins stay in their bulk soluble conformation and do not adsorb. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract No. DE-AC04-94AL85000.

  18. The structures and dynamics of atomic and molecular adsorbates on metal surfaces by scanning tunneling microscopy and low energy electron diffraction

    SciTech Connect

    Yoon, Hyungsuk Alexander

    1996-12-01

    Studies of surface structure and dynamics of atoms and molecules on metal surfaces are presented. My research has focused on understanding the nature of adsorbate-adsorbate and adsorbate-substrate interactions through surface studies of coverage dependency and coadsorption using both scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The effect of adsorbate coverage on the surface structures of sulfur on Pt(111) and Rh(111) was examined. On Pt(111), sulfur forms p(2x2) at 0.25 ML of sulfur, which transforms into a more compressed ({radical}3x{radical}3)R30{degrees} at 0.33 ML. On both structures, it was found that sulfur adsorbs only in fcc sites. When the coverage of sulfur exceeds 0.33 ML, it formed more complex c({radical}3x7)rect structure with 3 sulfur atoms per unit cell. In this structure, two different adsorption sites for sulfur atoms were observed - two on fcc sites and one on hcp site within the unit cell.

  19. Tuning the structure of thermosensitive gold nanoparticle monolayers.

    PubMed

    Rezende, Camila A; Shan, Jun; Lee, Lay-Theng; Zalczer, Gilbert; Tenhu, Heikki

    2009-07-23

    Gold nanoparticles grafted with poly(N-isopropylacrylamide) (PNIPAM) are rendered amphiphilic and thermosensitive. When spread on the surface of water, they form stable Langmuir monolayers that exhibit surface plasmon resonance. Using Langmuir balance and contrast-matched neutron reflectivity, the detailed structural properties of these nanocomposite monolayers are revealed. At low surface coverage, the gold nanoparticles are anchored to the interface by an adsorbed PNIPAM layer that forms a thin and compact pancake structure. Upon isothermal compression (T=20 degrees C), the adsorbed layer thickens with partial desorption of polymer chains to form brush structures. Two distinct polymer conformations thus coexist: an adsorbed conformation that assures stability of the monolayer, and brush structures that dangle in the subphase. An increase in temperature to 30 degrees C results in contractions of both adsorbed and brush layers with a concomitant decrease in interparticle distance, indicating vertical as well as lateral contractions of the graft polymer layer. The reversibility of this thermal response is also shown by the contraction-expansion of the polymer layers in heating-cooling cycles. The structure of the monolayer can thus be tuned by compression and reversibly by temperature. These compression and thermally induced conformational changes are discussed in relation to optical properties. PMID:19569632

  20. Transition from superlubrically sliding islands to pinned monolayer, demonstrated in Xe/Cu(111)

    NASA Astrophysics Data System (ADS)

    Guerra, Roberto; Vanossi, Andrea; Tosatti, Erio; Trieste Nanofriction Team

    A molecular dynamics simulation case study of Xe on Cu(111) reveals unexpected information on the exceptionally smooth sliding state associated with incommensurate superlubricity which is argued to emerge in the large size limit of naturally incommensurate Xe islands. As coverage approaches a full monolayer, theory predicts an abrupt adhesion-driven two-dimensional density compression on the order of several per cent, implying a hysteretic jump from superlubric free islands to a pressurized sqrt()x sqrt()commensurate (and pinned, and therefore immobile) monolayer. These results match with recent quartz crystal microbalance data which show remarkably large slip times with increasing submonolayer coverage, signalling superlubricity, followed by a dramatic drop to zero for the dense commensurate monolayer. Careful analysis of this variety of island sliding phenomena should be essential in future applications of friction at crystal/adsorbate interfaces. Matching experimental work by M. Pierno, L. Bruschi, G. Mistura, G. Paolicelli, A. di Bona, S. Valeri. Supported by ERC Advanced Grant N. 320796 - MODPHYSFRICT.

  1. Understanding the biocide action of poly(hexamethylene biguanide) using Langmuir monolayers of dipalmitoyl phosphatidylglycerol.

    PubMed

    Souza, Adriano L; Ceridório, Lucinéia F; Paula, Gustavo F; Mattoso, Luiz H C; Oliveira, Osvaldo N

    2015-08-01

    The disinfectant activity of poly(hexamethylene biguanide) (PHMB) has been explored in industrial applications, in agriculture and in food manipulation, but this biocide action is not completely understood. It is believed to arise from electrostatic interactions between the polyhexanide group and phosphatidylglycerol, which is the main phospholipid on the bacterial membrane. In this study, we investigated the molecular-level interactions between PHMB and dipalmitoyl phosphatidylglycerol (DPPG) in Langmuir monolayers that served as cell membrane models. PHMB at a concentration of 2×10(-4) g L(-1) in a Theorell-Stenhagen at pH 3.0 and in a phosphate at pH 7.4 was used as a subphase to prepare the DPPG monolayers. Surface pressure-area isotherms showed that PHMB adsorbs and penetrates into the DPPG monolayers, expanding them and increasing their elasticity under both conditions examined. Results from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) indicated that PHMB induces disorder in the DPPG chains and dehydrates their C=O groups, especially for the physiological medium. Overall, these findings point to hydrophobic interactions and dehydration being as relevant as electrostatic interactions to explain changes in membrane fluidity and permeability, believed to be responsible for the biocide action of PHMB.

  2. Performance of mango seed adsorbents in the adsorption of anthraquinone and azo acid dyes in single and binary aqueous solutions.

    PubMed

    Dávila-Jiménez, Martín M; Elizalde-González, María P; Hernández-Montoya, Virginia

    2009-12-01

    In this study the husk of mango seed and two carbonaceous adsorbents prepared from it were used to study the adsorption behavior of eight acid dyes. The adsorbed amount in mmol m(-2) decayed asymptotically as the molecular volume and area increased. The interaction between the studied dyes and the mesoporous carbon was governed by the ionic species in solution and the acidic/basic groups on the surface. Less than 50% of the external surface of the microporous carbon became covered with the dyes molecules, though monolayer formation demonstrating specific interactions only with active sites on the surface and the adsorption magnitudes correlated with the shape parameter of the molecule within a particular dye group. The adsorption behavior in mixtures was determined by the molecular volume of the constituents; the greater the molecular volume difference, the greater the effect on the adsorbed amount. We also demonstrated that the raw husk of the mango seed can be used to remove up to 50% from model 50 mg l(-1) solutions of the studied acid dyes.

  3. Surface rheology of PEO-PPO-PEO triblock copolymers at the air-water interface: comparison of spread and adsorbed layers.

    PubMed

    Blomqvist, B Rippner; Wärnheim, T; Claesson, P M

    2005-07-01

    The dilatational rheological properties of monolayers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-type block copolymers at the air-water interface have been investigated by employing an oscillating ring trough method. The properties of adsorbed monolayers were compared to spread layers over a range of surface concentrations. The studied polymers were PEO26-PPO39-PEO26 (P85), PEO103-PPO40-PEO103 (F88), and PEO99-PPO65-PEO99 (F127). Thus, two of the polymers have similar PPO block size and two of them have similar PEO block size, which allows us to draw conclusions about the relationship between molecular structure and surface dilatational rheology. The dilatational properties of adsorbed monolayers were investigated as a function of time and bulk solution concentration. The time dependence was found to be rather complex, reflecting structural changes in the layer. When the dilatational modulus measured at different concentrations was replotted as a function of surface pressure, one unique master curve was obtained for each polymer. It was found that the dilatational behavior of spread (Langmuir) and adsorbed (Gibbs) monolayers of the same polymer is close to identical up to surface concentrations of approximately 0.7 mg/m2. At higher coverage, the properties are qualitatively alike with respect to dilatational modulus, although some differences are noticeable. Relaxation processes take place mainly within the interfacial layers by a redistribution of polymer segments. Several conformational transitions were shown to occur as the area per molecule decreased. PEO desorbs significantly from the interface at segmental areas below 20 A(2), while at higher surface coverage, we propose that segments of PPO are forced to leave the interface to form a mixed sublayer in the aqueous region. PMID:15982044

  4. Chain-length dependence of the dissociation dynamics of oriented molecular adsorbates: n-alkyl bromides on GaAs(110)

    SciTech Connect

    Khan, K.A.; Camillone, N. III; Osgood, R.M. Jr.

    1999-07-01

    Brominated hydrocarbons adsorbed on semiconductor surfaces serve as ideal model systems for investigating the photoinduced chemistry of oriented molecules in the condensed phase. Under UV irradiation these adsorbates dissociate via attachment of photoexcited substrate electrons giving rise to energetic alkyl and surface-bound bromine fragments. In this report the authors describe the effect on the fragmentation dynamics due to systematic variation of the complexity (alkyl chain length) of the adsorbate. Increasing the length of the alkyl chain leads to distinct changes in the alkyl fragment angular distributions. For methyl bromide, the angular distribution is dominated by a focused beam of directly ejected hyperthermal methyl radicals at 44{degree} (in the [0{bar 1}] direction) from the surface normal. While a similar direct beam is observed for ethyl and propyl bromide, inelastic scattering of these fragments is found to result in increased importance of a slower diffuse cos{sup n} {theta} desorption. In addition, significant retention of alkyl fragments is detected by postirradiation thermal desorption measurements for these longer-chain homologues. Increasing the number of degrees of freedom of the adsorbate is also observed to dramatically alter the energetics of the ejection of the photofragments from the surface. As the number of carbons in the fragment is increased from one to three, the average energy of the directly ejected radicals decreases from 1.48 to 1.1 to 0.69 eV (UV incident at {lambda} = 193 nm). Variations in the energy and angular distributions are discussed in terms of initial adsorbate orientation, energy partitioning into rovibrational modes, and influence of radical-surface interactions.

  5. Electron-Stimulated Oxidation of Thin Water Films Adsorbed on TiO2(110)

    SciTech Connect

    Lane, Christopher D.; Petrik, Nikolay G.; Orlando, Thomas M.; Kimmel, Greg A.

    2007-11-08

    Electron-stimulated reactions in thin (< 3 monolayer, ML) water films adsorbed on TiO2(110) are investigated. For electron fluences less than ~1×1016 e-/cm2, irradiation with 100 eV electrons results in electron-stimulated desorption (ESD) of atomic and molecular hydrogen, but no measurable O2. The ESD leaves adsorbed hydroxyls which oxidize the TiO2(110) surface and change the post-irradiation TPD spectra of the remaining water in characteristic ways. The species remaining on the TiO2(110) after irradiation of adsorbed water films are apparently similar to those produced without irradiation by co-dosing water and O2. Annealing above ~600 K reduces the oxidized surfaces, and water TPD spectra characteristic of ion sputtered and annealed TiO2(110) are recovered. The rate of electron-stimulated “oxidation” of the water films is proportional to the coverage of water in the first layer for coverages less than 1 ML. However, higher coverages suppress this reaction. When thin water films are irradiated, the rate of electron-stimulated oxidation is independent of the initial oxygen vacancy concentration, as is the final oxidized state achieved at high electron fluences. To explain the results, we propose that electron excitation of water molecules adsorbed on Ti4+ sites leads to desorption of hydrogen atoms and leaves an OH adsorbed at the site. If hydroxyls are present in the bridging oxygen rows, these react with the OH’s on the Ti4+ sites to reform water and heal the oxygen vacancy associated with the bridging OH. Once the bridge bonded hydroxyls have been eliminated, further irradiation increases the concentration of OH’s in the Ti4+ rows leading to the creation of species which block sites in the Ti4+ rows, perhaps H2O2 and/or HO2.

  6. Interactions of N-alcohols with self-assembled monolayer surfaces on nickel(111) studied by temperature-programmed desorption

    NASA Astrophysics Data System (ADS)

    Vogt, Andrew Dale

    1999-12-01

    The interactions of molecules with self-assembled monolayer (SAM) surfaces formed on nickel (111) as studied by temperature-programmed desorption (TPD) are discussed. First, the adsorption of 11-mercaptoundecanoic acid (HS(CH 2)10COOH), 11-mercaptoundecanol (HS(CH2) 11OH) and octadecyl mercaptan (HS(CH2)17CH 3) was characterized by X-ray photoelectron spectroscopy (XPS) and angle-dependent XPS (ADXPS). These long-chain functionalized n-alkanethiols adsorbed onto a clean nickel (111) single crystal via their sulfur atom and the alkyl chain and the carboxyl-, hydroxyl- and methyl-terminal groups were disposed away from the nickel surface. The basic concepts of XPS, AMPS and TPD are discussed. Second, TPD showed that the interactions of low-molecular-weight straight-chain alcohols (n- CxH2x+1 OH for x = 1 through 6) with the carboxyl-, hydroxyl- and methyl-terminated SAM surfaces exhibited an alcohol-coverage-dependent effect on the alcohol's desorption energy based on their respective sets of TPD spectra at different alcohol coverages and based on the desorption spectra's subsequent analysis for desorption energy. The threshold TPD method (TTPD) was used to determine the desorption energy as a function of coverage for all alcohol-substrate pairs. For these adsorbate-substrate systems the desorption energies (TTPD) were the lowest (10--25 kJ mol-1) for the lowest relative alcohol coverages and increased to a desorption energy of 40--60 kJ mol-1 that was invariant with relative coverage after reaching a monolayer. The constant desorption energy (TTPD) at high relative coverages suggests there might be a completely formed hydrogen bonding network between adsorbates on the surfaces at alcohol coverages near a monolayer. The Redhead method, the "complete analysis" and the TTPD method are discussed and compared.

  7. Adsorption and reaction of maleic anhydride on Mo(110), monolayer Pd(111)/Mo(110), and multilayer Pd(111)/Mo(110)

    SciTech Connect

    Xu, C.; Goodman, D.W.

    1996-04-03

    The adsorption and reaction of maleic anhydride and deuterated maleic anhydride on Mo(110), monolayer Pd/Mo(110), and multilayer Pd(111)/Mo(110) surfaces have been studied using temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). Maleic anhydride adsorbs irreversibly on the Mo(110) surface at 100 K. Heating to 1200 K yields adsorbed carbon (C{sub ads}) and gas-phase CO and H{sub 2}. In contrast, the adsorption of maleic anhydride on monolayer Pd(111)/Mo(110) and multilayer Pd(111)/Mo(110) surfaces is largely reversible with the chemisorbed maleic anhydride desorbing at 365 and 375 K, respectively. Approximately 15% of the chemisorbed maleic anhydride decomposes upon heating to 400K, forming CO, CO{sub 2} and C{sub 2}H{sub 2}; C{sub 2}H{sub 2} further dehydrogenates upon heating to C{sub ads} and gas-phase H{sub 2}. The HREELS measurements indicate that maleic anhydride is bonded to multilayer Pd(111)/Mo(110) through the olefin bond in a di-{sigma} configuration, while on monolayer Pd(111)/Mo(110), the maleic anhydride is bonded to the surface through the olefin via a {pi}-bond. On the Mo(110) surface, maleic anhydride is bonded to the surface through the ring oxygen with the molecular plane perpendicular to the surface. As a result of this modified adsorption geometry, the carbonyl stretching mode is red-shifted nearly 150 cm{sup -1} on the monolayer Pd(111)/Mo(110) surface, unshifted on the multilayer Pd(111)/Mo(110) surface, and blue-shifted by nearly 100 cm{sup -1} on the Mo(110) surface. 31 refs., 14 figs., 3 tabs.

  8. Growth and Dissolution of Calcite in the Presence of Adsorbed Stearic Acid.

    PubMed

    Ricci, Maria; Segura, Juan José; Erickson, Blake W; Fantner, Georg; Stellacci, Francesco; Voïtchovsky, Kislon

    2015-07-14

    The interaction of organic molecules with the surface of calcite plays a central role in many geochemical, petrochemical, and industrial processes and in biomineralization. Adsorbed organics, typically fatty acids, can interfere with the evolution of calcite when immersed in aqueous solutions. Here we use atomic force microscopy in liquid to explore in real-time the evolution of the (1014) surface of calcite covered with various densities of stearic acid and exposed to different saline solutions. Our results show that the stearic acid molecules tend to act as "pinning points" on the calcite's surface and slow down the crystal's restructuring kinetics. Depending on the amount of material adsorbed, the organic molecules can form monolayers or bilayer islands that become embedded into the growing crystal. The growth process can also displaces the organic molecules and actively concentrate them into stacked multilayers. Our results provide molecular-level insights into the interplay between the adsorbed fatty acid molecules and the evolving calcite crystal, highlighting mechanisms that could have important implications for several biochemical and geochemical processes and for the oil industry.

  9. First principle identification of SiC monolayer as an efficient catalyst for CO oxidation

    SciTech Connect

    Sinthika, S. E-mail: sinthika90@gmail.com; Thapa, Ranjit E-mail: sinthika90@gmail.com; Reddy, C. Prakash

    2015-06-24

    Using density functional theory, we investigated the electronic properties of SiC monolayer and tested its catalytic activity toward CO oxidation. The planar nature of a SiC monolayer is found to stable and is a high band gap semiconductor. CO interacts physically with SiC surface, whereas O{sub 2} is adsorbed with moderate binding. CO oxidation on SiC monolayer prefers the Eley Rideal mechanism over the Langmuir Hinshelwood mechanism, with an easily surmountable activation barrier during CO{sub 2} formation. Overall metal free SiC monolayer can be used as efficient catalyst for CO oxidation.

  10. Hydrophobic Porous Material Adsorbs Small Organic Molecules

    NASA Technical Reports Server (NTRS)

    Sharma, Pramod K.; Hickey, Gregory S.

    1994-01-01

    Composite molecular-sieve material has pore structure designed specifically for preferential adsorption of organic molecules for sizes ranging from 3 to 6 angstrom. Design based on principle that contaminant molecules become strongly bound to surface of adsorbent when size of contaminant molecules is nearly same as that of pores in adsorbent. Material used to remove small organic contaminant molecules from vacuum systems or from enclosed gaseous environments like closed-loop life-support systems.

  11. Surfactant Dynamics: Spreading and Wave Induced Dynamics of a Monolayer

    NASA Astrophysics Data System (ADS)

    Strickland, Stephen Lee

    Material adsorbed to the surface of a fluid - for instance crude oil in the ocean, biological surfactant on ocular or pulmonary mucous, or emulsions - can form a 2-dimensional mono-molecular layer. These materials, called surfactants, can behave like a compressible viscous 2-dimensional fluid, and can generate surface stresses that influence the sub-fluid's bulk flow. Additionally, the sub-fluid's flow can advect the surfactant and generate gradients in the surfactant distribution and thereby generate gradients in the interfacial properties. Due to the difficulty of non-invasive measurements of the spatial distribution of a molecular monolayer at the surface, little is known about the dynamics that couple the surface motion and the evolving density field. In this dissertation, I will present a novel method for measuring the spatiotemporal dynamics of the surfactant surface density through the fluorescence emission of NBD-tagged phosphatidylcholine, a lipid, and we will compare the surfactant dynamics to the dynamics of the surface morphology.With this method, we will consider the inward and outward spreading of a surfactant on a thin fluid film as well as the advection of a surfactant by linear and non-linear gravity-capillary waves. These two types of surfactant coupled fluid flows will allow us to probe well-accepted assumptions about the coupled fluid-surfactant dynamics. In chapter 1, we review the models used for understanding the spreading of a surfactant on a thin fluid film and the motion of surfactant on a linear gravity-capillary wave. In chapter 2, we will present the experimental methods used in this dissertation. In chapter 3, we will study the outward spreading of a localized region of surfactant and show that the spreading of a monolayer is considerably different from the spreading of thicker-layered surfactant. In chapter 4, we will investigate the inward spreading of a surfactant into a circular surfactant-free region and show that hole closure and

  12. Continuum elastic theory of adsorbate vibrational relaxation

    NASA Astrophysics Data System (ADS)

    Lewis, Steven P.; Pykhtin, M. V.; Mele, E. J.; Rappe, Andrew M.

    1998-01-01

    An analytical theory is presented for the damping of low-frequency adsorbate vibrations via resonant coupling to the substrate phonons. The system is treated classically, with the substrate modeled as a semi-infinite elastic continuum and the adsorbate overlayer modeled as an array of point masses connected to the surface by harmonic springs. The theory provides a simple expression for the relaxation rate in terms of fundamental parameters of the system: γ=mω¯02/AcρcT, where m is the adsorbate mass, ω¯0 is the measured frequency, Ac is the overlayer unit-cell area, and ρ and cT are the substrate mass density and transverse speed of sound, respectively. This expression is strongly coverage dependent, and predicts relaxation rates in excellent quantitative agreement with available experiments. For a half-monolayer of carbon monoxide on the copper (100) surface, the predicted damping rate of in-plane frustrated translations is 0.50×1012s-1, as compared to the experimental value of (0.43±0.07)×1012s-1. Furthermore it is shown that, for all coverages presently accessible to experiment, adsorbate motions exhibit collective effects which cannot be treated as stemming from isolated oscillators.

  13. Methods of making monolayers

    DOEpatents

    Alford, Kentin L.; Simmons, Kevin L.; Samuels, William D.; Zemanian, Thomas S.; Liu, Jun; Shin, Yongsoon; Fryxell, Glen E.

    2009-09-15

    The invention pertains to methods of forming monolayers on various surfaces. The surfaces can be selected from a wide array of materials, including, for example, aluminum dioxide, silicon dioxide, carbon and SiC. The substrates can be planar or porous. The monolayer is formed under enhanced pressure conditions. The monolayer contains functionalized molecules, and accordingly functionalizes a surface of the substrate. The properties of the functionalized substrate can enhance the substrate's applicability for numerous purposes including, for example, utilization in extracting contaminants, or incorporation into a polymeric matrix.

  14. Methods of making monolayers

    DOEpatents

    Alford, Kentin L.; Simmons, Kevin L.; Samuels, William D.; Zemanian, Thomas S.; Liu, Jun; Shin, Yongsoon; Fryxell, Glen E.

    2009-12-08

    The invention pertains to methods of forming monolayers on various surfaces. The surfaces can be selected from a wide array of materials, including, for example, aluminum dioxide, silicon dioxide, carbon and SiC. The substrates can be planar or porous. The monolayer is formed under enhanced pressure conditions. The monolayer contains functionalized molecules, and accordingly functionalizes a surface of the substrate. The properties of the functionalized substrate can enhance the substrate's applicability for numerous purposes including, for example, utilization in extracting contaminants, or incorporation into a polymeric matrix.

  15. Nanotubes based on monolayer blue phosphorus

    NASA Astrophysics Data System (ADS)

    Montes, E.; Schwingenschlögl, U.

    2016-07-01

    We demonstrate structural stability of monolayer zigzag and armchair blue phosphorus nanotubes by means of molecular dynamics simulations. The vibrational spectrum and electronic band structure are determined and analyzed as functions of the tube diameter and axial strain. The nanotubes are found to be semiconductors with a sensitive indirect band gap that allows flexible tuning.

  16. Controlling adsorbate interactions for advanced chemical patterning

    NASA Astrophysics Data System (ADS)

    Saavedra Garcia, Hector M.

    Molecules designed to have specific interactions were used to influence the structural, physical, and chemical properties of self-assembled monolayers. In the case of 1-adamantanethiolate monolayers, the molecular structure influences lability, enabling alkanethiol molecules in solution to displace the 1-adamantanethiolate monolayers, ultimately leading to complete molecular exchange. The similar Au-S bond environments measured for both n-alkanethiolate and 1-adamantanethiolate monolayers indicate that displacement is not a result of weakened Au-S bonds. Instead, it was hypothesized that the density differences in the two monolayers provide a substantial enthalpic driver, aided by differences in van der Waals forces, ultimately leading to complete displacement of the 1-adamantenthiol molecules. Additionally, it was discovered that displacement occurs via fast insertion of n-dodecanethiolate at the defects in the original 1-adamantanethiolate monolayer, which nucleates an island growth phase and is followed by slow ordering of the n-dodecanethiolate domains into a denser and more crystalline form. Langmuir-based kinetics, which describe alkanethiolate adsorption on bare Au{111}, fail to model this displacement reaction. Instead, a model of perimeter-dependent island growth yields good agreement with kinetic data over a 100-fold variation in n-dodecanethiol concentration. Rescaling the growth rate at each concentration collapses all the data onto a single universal curve, suggesting that displacement is a scale-free process. Exploiting the knowledge gained by studying 1-adamantethiolate monolayer displacement, a reversible molecular resist was developed, in which displacement is controlled via external stimuli. This methodology for the fabrication of controllably displaceable monolayers relies on carboxyl-functionalized self-assembled monolayers and in-situ Fischer esterification. Using an 11-mercaptoundecanoic acid monolayer as a model system, it was shown that in

  17. Growth of rare-earth monolayers on synthetic fluorine mica

    NASA Astrophysics Data System (ADS)

    Tsui, F.; Han, P. D.; Flynn, C. P.

    1993-05-01

    We have grown single-crystal rare-earth films on cleaved faces of synthetic fluorine mica fluorophlogopite by molecular-beam-epitaxy techniques. This has made it possible to measure material properties such as magnetism in monolayer structures.

  18. Diamondoid monolayers as electron emitters

    DOEpatents

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

    2013-10-29

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

  19. Diamondoid monolayers as electron emitters

    DOEpatents

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

    2012-04-10

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

  20. Active Tensile Modulus of an Epithelial Monolayer

    NASA Astrophysics Data System (ADS)

    Vincent, Romaric; Bazellières, Elsa; Pérez-González, Carlos; Uroz, Marina; Serra-Picamal, Xavier; Trepat, Xavier

    2015-12-01

    A general trait of cell monolayers is their ability to exert contractile stresses on their surroundings. The scaling laws that link such contractile stresses with the size and geometry of constituent cells remain largely unknown. In this Letter, we show that the active tension of an epithelial monolayer scales linearly with the size of the constituent cells, a surprisingly simple relationship. The slope of this relationship defines an active tensile modulus, which depends on the concentration of myosin and spans more than 2 orders of magnitude across cell types and molecular perturbations.

  1. Characterization of functionalized self-assembled monolayers and surface-attached interlocking molecules using near-edge X-ray absorption fine structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Willey, Trevor Michael

    Quantitative knowledge of the fundamental structure and substrate binding, as well as the direct measurement of conformational changes, are essential to the development of self-assembled monolayers (SAMs) and surface-attached interlocking molecules, catenanes and rotaxanes. These monolayers are vital to development of nano-mechanical, molecular electronic, and biological/chemical sensor applications. This dissertation investigates properties of functionalized SAMs in sulfur-gold based adsorbed molecular monolayers using quantitative spectroscopic techniques including near-edge x-ray absorption fine structure spectroscopy (NEXAFS) and x-ray photoelectron spectroscopy (XPS). The stability of the gold-thiolate interface is addressed. A simple model SAM consisting of dodecanethiol adsorbed on Au(111) degrades significantly in less than 24 hours under ambient laboratory air. S 2p and O 1s XPS show the gold-bound thiolates oxidize to sulfinates and sulfonates. A reduction of organic material on the surface and a decrease in order are observed as the layer degrades. The effect of the carboxyl vs. carboxylate functionalization on SAM structure is investigated. Carboxyl-terminated layers consisting of long alkyl-chain thiols vs. thioctic acid with short, sterically separated, alkyl groups are compared and contrasted. NEXAFS shows a conformational change, or chemical switchability, with carboxyl groups tilted over and carboxylate endgroups more upright. Surface-attached loops and simple surface-attached rotaxanes are quantitatively characterized, and preparation conditions that lead to desired films are outlined. A dithiol is often insufficient to form a molecular species bound at each end to the substrate, while a structurally related disulfide-containing polymer yields surface-attached loops. Similarly, spectroscopic techniques show the successful production of a simple, surface-attached rotaxane that requires a "molecular riveting" step to hold the mechanically attached

  2. Characterization of Functionalized Self-Assembled Monolayers and Surface-Attached Interlocking Molecules Using Near-Edge X-ray Absorption Fine Structure Spectroscopy

    SciTech Connect

    Willey, Trevor M.

    2004-04-01

    Quantitative knowledge of the fundamental structure and substrate binding, as well as the direct measurement of conformational changes, are essential to the development of self-assembled monolayers (SAMs) and surface-attached interlocking molecules, catenanes and rotaxanes. These monolayers are vital to development of nano-mechanical, molecular electronic, and biological/chemical sensor applications. This dissertation investigates properties of functionalized SAMs in sulfur-gold based adsorbed molecular monolayers using quantitative spectroscopic techniques including near-edge x-ray absorption fine structure spectroscopy (NEXAFS) and x-ray photoelectron spectroscopy (XPS). The stability of the gold-thiolate interface is addressed. A simple model SAM consisting of dodecanethiol adsorbed on Au(111) degrades significantly in less than 24 hours under ambient laboratory air. S 2p and O 1s XPS show the gold-bound thiolates oxidize to sulfinates and sulfonates. A reduction of organic material on the surface and a decrease in order are observed as the layer degrades. The effect of the carboxyl vs. carboxylate functionalization on SAM structure is investigated. Carboxyl-terminated layers consisting of long alkyl-chain thiols vs. thioctic acid with short, sterically separated, alkyl groups are compared and contrasted. NEXAFS shows a conformational change, or chemical switchability, with carboxyl groups tilted over and carboxylate endgroups more upright. Surface-attached loops and simple surface-attached rotaxanes are quantitatively characterized, and preparation conditions that lead to desired films are outlined. A dithiol is often insufficient to form a molecular species bound at each end to the substrate, while a structurally related disulfide-containing polymer yields surface-attached loops. Similarly, spectroscopic techniques show the successful production of a simple, surface-attached rotaxane that requires a ''molecular riveting'' step to hold the mechanically attached

  3. Crystallographic order and decomposition of [MnIII6CrIII]3+ single-molecule magnets deposited in submonolayers and monolayers on HOPG studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin probe force microscopy in UHV.

    PubMed

    Gryzia, Aaron; Volkmann, Timm; Brechling, Armin; Hoeke, Veronika; Schneider, Lilli; Kuepper, Karsten; Glaser, Thorsten; Heinzmann, Ulrich

    2014-01-01

    Monolayers and submonolayers of [MnIII6CrIII]3+ single-molecule magnets (SMMs) adsorbed on highly oriented pyrolytic graphite (HOPG) using the droplet technique characterized by non-contact atomic force microscopy (nc-AFM) as well as by Kelvin probe force microscopy (KPFM) show island-like structures with heights resembling the height of the molecule. Furthermore, islands were found which revealed ordered 1D as well as 2D structures with periods close to the width of the SMMs. Along this, islands which show half the heights of intact SMMs were observed which are evidences for a decomposing process of the molecules during the preparation. Finally, models for the structure of the ordered SMM adsorbates are proposed to explain the observations.

  4. Recombinant albumin monolayers on latex particles.

    PubMed

    Sofińska, Kamila; Adamczyk, Zbigniew; Kujda, Marta; Nattich-Rak, Małgorzata

    2014-01-14

    The adsorption of recombinant human serum albumin (rHSA) on negatively charged polystyrene latex micro-particles was studied at pH 3.5 and the NaCl concentration range of 10(-3) to 0.15 M. The electrophoretic mobility of latex monotonically increased with the albumin concentration in the suspension. The coverage of adsorbed albumin was quantitatively determined using the depletion method, where the residual protein concentration was determined by electrokinetic measurements and AFM imaging. It was shown that albumin adsorption was irreversible. Its maximum coverage on latex varied between 0.7 mg m(-2) for 10(-3) M NaCl to 1.3 mg m(-2) for 0.15 M NaCl. The latter value matches the maximum coverage previously determined for human serum albumin on mica using the streaming potential method. The increase in the maximum coverage was interpreted in terms of reduced electrostatic repulsion among adsorbed molecules. These facts confirm that albumin adsorption at pH 3.5 is governed by electrostatic interactions and proceeds analogously to colloid particle deposition. The stability of albumin monolayers was measured in additional experiments where changes in the latex electrophoretic mobility and the concentration of free albumin in solutions were monitored over prolonged time periods. Based on these experimental data, a robust procedure of preparing albumin monolayers on latex particles of well-controlled coverage and molecule distribution was proposed. PMID:24354916

  5. Controlling self assembled monolayers

    NASA Astrophysics Data System (ADS)

    Wei, Yanhu

    2007-12-01

    In this thesis, we demonstrate novel methods of controlling the morphology of self-assembled monolayers at the solution-graphite interface. Scanning tunneling microscopy is used to evaluate the capacity of chain length and weak dipolar interactions to direct packing and neighboring chain selection within monolayers. We designed and synthesized a series of 1,5-substituted anthracene derivatives and investigated the relationship between side chain structure and monolayer morphology. We report that the morphology of monolayers formed on HOPG from symmetrically substituted anthracene derivatives switches from a 2D racemate to a 2D conglomerate by the addition of a single methylene unit to each side chain, i.e., by changing the side chain lengths from even to odd. We introduced ether groups into the side chains of anthracene derivatives in an attempt to use dipolar interactions to alter monolayer morphology. We report that the insertion of electronegative oxygen atoms into the side chains of anthracene derivatives can disturb the odd - even effect of chain length and influence monolayer morphology. By introducing a proper number of ether groups at specific side chain locations, we designed two self-repelling and complementary chains: COC12OC and C2OC10OC 2. COC12OC (or C2OC10OC2) chains repel themselves but select the other C2OC10OC 2 (or COC12OC) chains as their neighbors in self-assembled monolayers. Taking into account chain length matching and dipolar complementary as mechanisms for adjacent side chain selection, we designed and synthesized two symmetrical anthracenes 12 (COC12OC-An-COC 12OC), 13 (C2OC10OC2-An-C 2OC10OC2) and two unsymmetrical anthracenes 15 (C11OC-An-COC12OC) and 16 (C 18OC2-An-C2OC10OC2). Using a mixture solution of these molecules, we prepared a highly ordered AABB monolayer pattern in which paired rows of 15 alternate with paired rows of 16, and a highly ordered AAB monolayer pattern in which rows consisting of 12 are sandwiched between paired

  6. Binding of methylene blue onto Langmuir monolayers representing cell membranes may explain its efficiency as photosensitizer in photodynamic therapy.

    PubMed

    Schmidt, Thaís F; Caseli, Luciano; Oliveira, Osvaldo N; Itri, Rosangela

    2015-04-14

    We provide evidence for the electrostatic interactions between the cationic photosensitizer methylene blue (MB) and cell membrane models represented by neat and mixed Langmuir monolayers of dioleylphosphatidylcholine (DOPC) and 1,1',2,2'-tetraoleoylcardiolipin (CL). From surface pressure measurements, MB was found to adsorb strongly and expand CL-containing monolayers, while it caused an apparent decreasing in molecular area on neat DOPC monolayer. The binding site of MB could be inferred from data with the surface-specific polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) technique, where changes induced by MB were observed in the vibrational modes of the phosphate groups of both CL and DOPC. The incorporation of MB also affected the carbonyl groups and the packing of the alkyl chains, thus indicating that MB binding site favors singlet oxygen generation close to the double bonds in the alkyl chains, an important requirement for photodynamic efficiency. Significantly, the data presented here demonstrate that MB may act in membranes composed by PCs, such as mammalian plasma membranes, and in those containing CL, as in bacterial and inner mitochondrial membranes.

  7. Fibrinogen monolayer characterization by colloid deposition.

    PubMed

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

    2013-09-24

    Colloid particle deposition was applied to characterize bovine and human fibrinogen (Fb) monolayers on mica produced by controlled adsorption under diffusion transport at pH 3.5. The surface concentration of Fb was determined by AFM enumeration of single molecules adsorbed over the substrate surface. The electrokinetic properties of Fb monolayers for various ionic strength were studied using the in situ streaming potential measurements. It was shown that Fb adsorbs irreversibly on mica for a broad range of ionic strength of 4 × 10(-4) to 0.15 M, NaCl. The overcharging of initially negative mica surface occurred for fibrinogen surface concentrations higher than 1400 μm(-2). The orientation of fibrinogen molecules in the monolayers was evaluated by the colloid deposition method involving negatively charged polystyrene latex microspheres, 820 nm in diameter. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential was observed, which contradicts the mean-field DLVO predictions. Measurable deposition was observed even at low ionic strength where the minimum approach distance of latex particles to the interface exceeds 70 nm (for 6 × 10(-4) M NaCl). This confirms that, at this pH, fibrinogen molecules adsorb end-on on mica assuming extended conformations with the positive charge located mostly in the end part of the αA chains. This agrees with previous experimental and theoretical results discussed in the literature (Santore, M. M.; Wertz Ch. F. Protein spreading kinetics at liquid-solid interfaces via an adsorption probe method. Langmuir 2005, 21, 10172-10178 (experimental); Adamczyk, Z.; Barbasz, J.; Cieśla, M.; Mechanisms of fibrinogen adsorption at solid substrates. Langmuir, 2011, 25, 6868-6878 (theoretical)). This unusual latex deposition on Fb monolayers was quantitatively interpreted in terms of the model developed in ref 55 (Jin, X.; Wang, N. H. L.; Tarjus, G.; Talbot, J. Irreversible adsorption on nonuniform

  8. Size selective hydrophobic adsorbent for organic molecules

    NASA Technical Reports Server (NTRS)

    Sharma, Pramod K. (Inventor); Hickey, Gregory S. (Inventor)

    1997-01-01

    The present invention relates to an adsorbent formed by the pyrolysis of a hydrophobic silica with a pore size greater than 5 .ANG., such as SILICALITE.TM., with a molecular sieving polymer precursor such as polyfurfuryl alcohol, polyacrylonitrile, polyvinylidene chloride, phenol-formaldehyde resin, polyvinylidene difluoride and mixtures thereof. Polyfurfuryl alcohol is the most preferred. The adsorbent produced by the pyrolysis has a silicon to carbon mole ratio of between about 10:1 and 1:3, and preferably about 2:1 to 1:2, most preferably 1:1. The pyrolysis is performed as a ramped temperature program between about 100.degree. and 800.degree. C., and preferably between about 100.degree. and 600.degree. C. The present invention also relates to a method for selectively adsorbing organic molecules having a molecular size (mean molecular diameter) of between about 3 and 6 .ANG. comprising contacting a vapor containing the small organic molecules to be adsorbed with the adsorbent composition of the present invention.

  9. Synthesis of mimic molecularly imprinted ordered mesoporous silica adsorbent by thermally reversible semicovalent approach for pipette-tip solid-phase extraction-liquid chromatography fluorescence determination of estradiol in milk.

    PubMed

    Wang, Lu; Yan, Hongyuan; Yang, Chunliu; Li, Zan; Qiao, Fengxia

    2016-07-22

    A mimic molecularly imprinted ordered mesoporous silica (MIOMS) adsorbent was prepared utilizing a thermally reversible semicovalent approach. The thermally reversible covalent template-monomer complex was firstly synthesized by employing 4,4'-sulfonyldiphenol (BPS) and (3-isocyanatopropyl) triethoxysilane (ICPTES) as template and monomer, respectively. The template-monomer complex was incorporated into ordered mesoporous silica via a simple self-assembly process. The adsorption experiment illustrated that the imprint-removed silica (MIOMS-ir) had higher special recognition ability (250μgg(-1)) for estradiol (E2) than the non-imprinted silica (NIOMS-ir) (25μgg(-1)). MIOMS-ir was applied as an adsorbent in pipette-tip solid-phase extraction (PT-SPE) coupled with liquid chromatography-fluorescence detector (LC-FLD) for determination of E2 in milk samples. Under the optimized conditions, only 3mg of the adsorbent, 0.3mL of water as washing solvent, and 0.5mL of acetonitrile-acetic acid (96:4, v/v) as elution solvent were used in the pretreatment procedure of milk samples. Good calibration linearity was obtained in a range of 25ngL(-1) to 1000ngL(-1), and the recoveries at three spiked levels were ranged from 95.4% to 107.0% with relative standard deviations (RSDs) ≤3.1% (n=3). The proposed MIOMS-ir-PT-SPE-LC-FLD method combined the advantages of PT-SPE and ordered mesoporous material such as ease assembly, low cost, high extraction efficiency and large specific surface area, so it is a potential pretreatment strategy for the extraction and determination of E2 in complex milk samples. PMID:27328886

  10. Quantum chemical investigation on the role of Li adsorbed on anatase (101) surface nano-materials on the storage of molecular hydrogen.

    PubMed

    Srinivasadesikan, V; Raghunath, P; Lin, M C

    2015-06-01

    Lithiation of TiO2 has been shown to enhance the storage of hydrogen up to 5.6 wt% (Hu et al. J Am Chem Soc 128:11740-11741, 2006). The mechanism for the process is still unknown. In this work we have carried out a study on the adsorption and diffusion of Li atoms on the surface and migration into subsurface layers of anatase (101) by periodic density functional theory calculations implementing on-site Coulomb interactions (DFT+U). The model consists of 24 [TiO2] units with 11.097 × 7.655 Å(2) surface area. Adsorption energies have been calculated for different Li atoms (1-14) on the surface. A maximum of 13 Li atoms can be accommodated on the surface at two bridged O, Ti-O, and Ti atom adsorption sites, with 83 kcal mol(-1) adsorption energy for a single Li atom adsorbed between two bridged O atoms from where it can migrate into the subsurface layer with 27 kcal mol(-1) energy barrier. The predicted adsorption energies for H2 on the lithiated TiO2 (101) surface with 1-10 Li atoms revealed that the highest adsorption energies occurred on 1-Li, 5-Li, and 9-Li surfaces with 3.5, 4.4, and 7.6 kcal mol(-1), respectively. The values decrease rapidly with additional H2 co-adsorbed on the lithiated surfaces; the maximum H2 adsorption on the 9Li-TiO2(a) surface was estimated to be only 0.32 wt% under 100 atm H2 pressure at 77 K. The result of Bader charge analysis indicated that the reduction of Ti occurred depending on the Li atoms covered on the TiO2 surface.

  11. FRET study of G-quadruplex forming fluorescent oligonucleotide probes at the lipid monolayer interface

    NASA Astrophysics Data System (ADS)

    Swiatkowska, Angelika; Kosman, Joanna; Juskowiak, Bernard

    2016-01-01

    Spectral properties and G-quadruplex folding ability of fluorescent oligonucleotide probes at the cationic dioctadecyldimethylammonium bromide (DODAB) monolayer interface are reported. Two oligonucleotides, a 19-mer bearing thrombin binding aptamer sequence and a 21-mer with human telomeric sequence, were end-labeled with fluorescent groups (FAM and TAMRA) to give FRET probes F19T and F21T, respectively. The probes exhibited abilities to fold into a quadruplex structure and to bind metal cations (Na+ and K+). Fluorescence spectra of G-quadruplex FRET probes at the monolayer interface are reported for the first time. Investigations included film balance measurements (π-A isotherms) and fluorescence spectra recording using a fiber optic accessory interfaced with a spectrofluorimeter. The effect of the presence of DODAB monolayer, metal cations and the surface pressure of monolayer on spectral behavior of FRET probes were examined. Adsorption of probe at the cationic monolayer interface resulted in the FRET signal enhancement even in the absence of metal cations. Variation in the monolayer surface pressure exerted rather modest effect on the spectral properties of probes. The fluorescence energy transfer efficiency of monolayer adsorbed probes increased significantly in the presence of sodium or potassium ion in subphase, which indicated that the probes retained their cation binding properties when adsorbed at the monolayer interface.

  12. Mercury adsorption properties of sulfur-impregnated adsorbents

    USGS Publications Warehouse

    Hsi, N.-C.; Rood, M.J.; Rostam-Abadi, M.; Chen, S.; Chang, R.

    2002-01-01

    Carbonaceous and noncarbonaceous adsorbents were impregnated with elemental sulfur to evaluate the chemical and physical properties of the adsorbents and their equilibrium mercury adsorption capacities. Simulated coal combustion flue gas conditions were used to determine the equilibrium adsorption capacities for Hg0 and HgCl2 gases to better understand how to remove mercury from gas streams generated by coal-fired utility power plants. Sulfur was deposited onto the adsorbents by monolayer surface deposition or volume pore filling. Sulfur impregnation increased the total sulfur content and decreased the total and micropore surface areas and pore volumes for all of the adsorbents tested. Adsorbents with sufficient amounts of active adsorption sites and sufficient microporous structure had mercury adsorption capacities up to 4,509 ??g Hg/g adsorbent. Elemental sulfur, organic sulfur, and sulfate were formed on the adsorbents during sulfur impregnation. Correlations were established with R2>0.92 between the equilibrium Hg0/HgCl2 adsorption capacities and the mass concentrations of elemental and organic sulfur. This result indicates that elemental and organic sulfur are important active adsorption sites for Hg0 and HgCl2.

  13. Effect of surface charge distribution on the adsorption orientation of proteins to lipid monolayers.

    PubMed

    Tiemeyer, Sebastian; Paulus, Michael; Tolan, Metin

    2010-09-01

    The adsorption orientation of the proteins lysozyme and ribonuclease A (RNase A) to a neutral 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a negatively charged stearic acid lipid film was investigated by means of X-ray reflectivity. Both proteins adsorbed to the negatively charged lipid monolayer, whereas at the neutral monolayer, no adsorption was observed. For acquiring comprehensive information on the proteins' adsorption, X-ray reflectivity data were combined with electron densities obtained from crystallographic data. With this method, it is possible to determine the orientation of adsorbed proteins in solution underneath lipid monolayers. While RNase A specifically coupled with its positively charged active site to the negatively charged lipid monolayer, lysozyme prefers an orientation with its long axis parallel to the Langmuir film. In comparison to the electrostatic maps of the proteins, our results can be explained by the discriminative surface charge distribution of lysozyme and RNase A.

  14. Effect of surface charge distribution on the adsorption orientation of proteins to lipid monolayers.

    PubMed

    Tiemeyer, Sebastian; Paulus, Michael; Tolan, Metin

    2010-09-01

    The adsorption orientation of the proteins lysozyme and ribonuclease A (RNase A) to a neutral 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a negatively charged stearic acid lipid film was investigated by means of X-ray reflectivity. Both proteins adsorbed to the negatively charged lipid monolayer, whereas at the neutral monolayer, no adsorption was observed. For acquiring comprehensive information on the proteins' adsorption, X-ray reflectivity data were combined with electron densities obtained from crystallographic data. With this method, it is possible to determine the orientation of adsorbed proteins in solution underneath lipid monolayers. While RNase A specifically coupled with its positively charged active site to the negatively charged lipid monolayer, lysozyme prefers an orientation with its long axis parallel to the Langmuir film. In comparison to the electrostatic maps of the proteins, our results can be explained by the discriminative surface charge distribution of lysozyme and RNase A. PMID:20707324

  15. Methylene blue adsorption on a DMPA lipid langmuir monolayer.

    PubMed

    Giner Casares, Juan José; Camacho, Luis; Martín-Romero, Maria Teresa; López Cascales, José Javier

    2010-07-12

    Adsorption of methylene blue (MB) onto a dimyristoylphosphatidic acid (DMPA) Langmuir air/water monolayer is studied by molecular dynamics (MD) simulations, UV reflection spectroscopy and surface potential measurements. The free-energy profile associated with MB transfer from water to the lipid monolayer shows two minima of -66 and -60 kJ mol(-1) for its solid and gas phase, respectively, corresponding to a spontaneous thermodynamic process. From the position of the free-energy minima, it is possible to predict the precise location of MB in the interior of the DMPA monolayer. Thus, MB is accommodated in the phosphoryl or carbonyl region of the DMPA Langmuir air/water interface, depending on the isomorphic state (solid or gas phase, respectively). Reorientation of MB, measured from the bulk solution to the interior of the lipid monolayer, passes from a random orientation in bulk solution to an orientation parallel to the surface of the lipid monolayer when MB is absorbed. PMID:20544777

  16. Methylene blue adsorption on a DMPA lipid langmuir monolayer.

    PubMed

    Giner Casares, Juan José; Camacho, Luis; Martín-Romero, Maria Teresa; López Cascales, José Javier

    2010-07-12

    Adsorption of methylene blue (MB) onto a dimyristoylphosphatidic acid (DMPA) Langmuir air/water monolayer is studied by molecular dynamics (MD) simulations, UV reflection spectroscopy and surface potential measurements. The free-energy profile associated with MB transfer from water to the lipid monolayer shows two minima of -66 and -60 kJ mol(-1) for its solid and gas phase, respectively, corresponding to a spontaneous thermodynamic process. From the position of the free-energy minima, it is possible to predict the precise location of MB in the interior of the DMPA monolayer. Thus, MB is accommodated in the phosphoryl or carbonyl region of the DMPA Langmuir air/water interface, depending on the isomorphic state (solid or gas phase, respectively). Reorientation of MB, measured from the bulk solution to the interior of the lipid monolayer, passes from a random orientation in bulk solution to an orientation parallel to the surface of the lipid monolayer when MB is absorbed.

  17. The wavelength dependence of photoinduced hot electron dissociative attachment to methyl bromide adsorbed on gallium arsenide (110)

    SciTech Connect

    Camillone, N. III; Khan, K.A.; Lasky, P.J.; Wu, L.; Moryl, J.E.; Osgood, R.M. Jr.

    1998-11-01

    The wavelength dependence of photoinduced dissociation of CH{sub 3}Br via dissociative electron attachment (DEA) of {open_quotes}hot{close_quotes} electrons for one monolayer CH{sub 3}Br adsorbed on GaAs(110) has been measured. The cross section for dissociation is found to decrease monotonically by two orders of magnitude as the incident wavelength is varied from 308 to 550 nm. There is an apparent threshold near 490 nm (2.5 eV), well below the gas phase photodissociation threshold near 250 nm (5.0 eV), but in good agreement with a simple estimate based on expected values for the decrease in the photoemission threshold and the lowering of the molecular affinity level upon adsorption of CH{sub 3}Br on a semiconductor surface. The observed threshold is found to move to higher energy as dissociation of the monolayer proceeds. Based on the work of Hasselbrink and co-workers [F. Weik, A. de Meijere, and E. Hasselbrink, J. Chem. Phys. {bold 99}, 682 (1993)], a simple theoretical model is developed which considers the tunneling of hot electrons through the interfacial barrier between the physisorbed CH{sub 3}Br and the GaAs. The results of our theoretical model in conjunction with those of earlier {ital ab initio} calculations [S. Black, R. Friesner, P. H. Lu, and R. M. Osgood, Jr., Surf. Sci. {bold 382}, 154 (1997)] suggest that the adsorbate affinity level is centered at {approximately}0.6 eV above the (adsorbate- modified) vacuum level of the substrate. This value corresponds to a {approximately}1.8 eV stabilization of the negative ion resonance upon adsorption. {copyright} {ital 1998 American Institute of Physics.}

  18. Using specialized adsorbents for remediation

    SciTech Connect

    Hochmuth, D.P.; Grant, A.

    1995-11-01

    This paper describes two remediation case studies in which specialized adsorbents were used. In one case, the adsorbents were used to treat effluent from a soil vapor extraction system. In the other case, the adsorbents were used to treat air from a groundwater air stripper. The specialized adsorbents effectively removed volatile organic compounds from each air stream.

  19. An amorphous monolayer: Infrared spectroscopic and theoretical studies of SO2 on NaCl (100)

    NASA Astrophysics Data System (ADS)

    Berg, Otto; Ewing, George E.; Meredith, Andrew W.; Stone, Anthony J.

    1996-05-01

    At temperatures between 100 and 110 K, exposing the (100) face of NaCl to unsaturated SO2 gas yields a stable adlayer. Infrared spectra of adsorbed SO2 contain complex resonances near the origins of the molecular symmetric and asymmetric stretching vibrations. On photometric grounds the absolute coverage of the surface is found to be one molecule per exposed Na+Cl- ion pair. The spectra of this monolayer consist of several sharp lines overlapping one broad feature for each molecular mode. By comparison to vibrational excitons in simpler systems, the coexistence of crystalline and amorphous adlayer structures is strongly indicated. This partial ordering is pressure dependent, and develops spontaneously on a time scale of minutes. The disordered component, in contrast, is never in equilibrium with the gas phase. Computational simulations have detailed the microscopic basis of this behavior. Accurate ab initio models of the SO2 molecule and NaCl(100) surface were used in a Monte Carlo simulation of the experimental conditions. At both half and full coverage, an amorphous two-dimensional condensate developed. This is minimally consistent with the polarized infrared photometry. Seemingly equilibrated Monte Carlo runs retained some memory of the initial molecular configuration, again consistent with hysteresis observed in the spectroscopic experiments. No structural order developed in the simulations, but the energetic state of affairs was clarified: the potential driving adsorption and condensation is deep in comparison to available thermal energy, but relatively insensitive to molecular orientation.

  20. Formation of self-assembled monolayers with homogeneously mixed, loosely packed alkyl groups using unsymmetrical dialkyldithiophosphinic acids.

    PubMed

    San Juan, Ronan R; Carmichael, Tricia Breen

    2012-12-21

    We report the formation and characterization of self-assembled monolayers (SAMs) formed from unsymmetrical dialkyldithiophosphinic acid (R(1)R(2)DTPA) adsorbates [CH(3)(CH(2))(n)][CH(3)(CH(2))(15)]P(S)SH (n = 5, 9) on gold substrates. These SAMs were characterized using X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, contact angle goniometry, electrochemical impedance spectroscopy, and atomic force microscopy. Unsymmetrical R(1)R(2)DTPA SAMs contain mixtures of bidentate and monodentate adsorbates, similar to SAMs formed from analogous symmetrical R(2)DTPAs. In unsymmetrical R(1)R(2)DTPA SAMs, however, the short alkyl substituent of the R(1)R(2)DTPA adsorbates enforces spacing between the long hexadecyl substituents, which disrupts van der Waals interactions and causes the hexadecyl groups to be loosely packed and disordered. The structure of the SAM depends on the length of the short alkyl substituent: The hexyl chains in the C(6)C(16)DTPA SAM are not long enough to stabilize the alkyl zone close to the substrate, leading to highly disordered SAMs with a low molecular packing density in which the hexadecyl chains lie down to fill the gaps between adjacent adsorbates. In contrast, the additional van der Waals interactions provided by the decyl chains of the C(10)C(16)DTPA SAM enable dense molecular packing in the alkyl zone close to the substrate. The structure of the SAM consists of a zone close to the substrate composed of a packed alkyl layer, with hexadecyl chains protruding above to form a loosely packed, disordered alkyl layer. Regardless of the structural differences between the C(6)C(16)DTPA and C(10)C(16)DTPA SAMs, both SAMs exhibit homogeneous mixing of the alkyl chains within the SAM, demonstrating that binding two different chains to a single headgroup is an effective method to prevent phase segregation.

  1. Simulations of calcite crystallization on self-assembled monolayers.

    PubMed

    Freeman, Colin L; Harding, John H; Duffy, Dorothy M

    2008-09-01

    This paper presents simulations of calcium carbonate ordering in contact with self-assembled monolayers. The calculations use potential-based molecular dynamics to model the crystallization of calcium carbonate to calcite expressing both the (00.1) and (01.2) surfaces. The effect of monolayer properties: ionization; epitaxial matching; charge density; and headgroup orientation on the crystallization process are examined in detail. The results demonstrate that highly charged surfaces are vital to stimulate ordering and crystallization. Template directed crystallization requires charge epitaxy between both the crystal surface and the monolayer. The orientation of the headgroup appears to make no contribution to the selection of the crystal surface.

  2. Redox Equilibria of Cytochrome C3 Immobilised on Self-Assembled Monolayers Coated Silver Electrodes

    NASA Astrophysics Data System (ADS)

    Di Paolo, R. E.; Rivas, L.; Murgida, D.; Hildebrandt, P.

    2005-01-01

    Cytochromes c3 are soluble electron transfer proteins in the periplasm of sulphate-reducing bacteria. They act as electron-proton couplers between hydrogenase and the electron transfer chain of sulphate respiration. In this work, cytochrome c3 (Cyt-c3) obtained from both Desulfovibrio vulgaris and Desulfovibrio gigas, is electrostatically adsorbed on Ag electrodes coated with self-assembled monolayers of 11-mercaptoundecanoic acid. The redox equilibria of the adsorbed tetraheme protein are studied by surface enhanced resonance Raman spectroscopy (SERRS). The quantitative analysis of the SERR spectra, which were measured as a function of the electrode potential, allows determining the redox potentials for the individual hemes of Cyt-c3. The values obtained of the redox potentials are compared with the data provided by NMR experiments and by molecular dynamics simulation studies of the electrostatically bound protein on a coated electrode. It is found that immobilisation causes substantial shifts of the redox potential, which would have an impact on the intramolecular electron flow.

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

    PubMed

    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.

  4. Regenerative adsorbent heat pump

    NASA Technical Reports Server (NTRS)

    Jones, Jack A. (Inventor)

    1991-01-01

    A regenerative adsorbent heat pump process and system is provided which can regenerate a high percentage of the sensible heat of the system and at least a portion of the heat of adsorption. A series of at least four compressors containing an adsorbent is provided. A large amount of heat is transferred from compressor to compressor so that heat is regenerated. The process and system are useful for air conditioning rooms, providing room heat in the winter or for hot water heating throughout the year, and, in general, for pumping heat from a lower temperature to a higher temperature.

  5. Water adsorption on hydrophilic and hydrophobic self-assembled monolayers as proxies for atmospheric surfaces. A grand canonical Monte Carlo simulation study.

    PubMed

    Szori, Milán; Jedlovszky, Pál; Roeselová, Martina

    2010-05-14

    Grand canonical Monte Carlo simulations are used to determine water adsorption on prototypical organic surfaces as a function of relative humidity at 300 K. Three model surfaces formed by well-ordered self-assembled monolayers (SAMs) of alkanethiolate chains on gold are investigated: (i) a smooth hydrophobic surface of methyl-terminated C(7)-CH(3) SAM; (ii) a rough hydrophobic surface of randomly mixed two-component SAM, composed of equal fractions of C(5)-CH(3) and C(7)-CH(3) chains (C(5)/C(7)-CH(3) SAM); and (iii) a smooth hydrophilic surface of carboxyl-terminated C(7)-COOH SAM. The all atom CHARMM22 force field is used for the SAM chains together with the SPC/E model for water. No noticeable water adsorption is observed on the smooth hydrophobic surface up to saturation. The mild surface roughness introduced by the uneven chain length of the two components constituting the C(5)/C(7)-CH(3) SAM has no significant effect on the surface hydrophobicity, and the rough hydrophobic surface also remains dry up to the point when water condensation occurs. In contrast, water readily adsorbs onto the hydrophilic surface by forming hydrogen bonds with the COOH groups of the substrate. In addition, hydrogen bonding with pre-adsorbed water molecules contributes to the mechanism of water uptake. Under low humidity conditions, water is present on the hydrophilic surface as individual molecules or small water clusters and, with increasing relative humidity, the surface coverage grows continuously beyond a monolayer formation. The adsorbed water film is observed to be rather inhomogeneous with patches of bare surface exposed. The amount of water constituting a stable adsorption layer prior to condensation is estimated to consist of about 2-5 molecular layers. Detailed analysis of the simulation results is used to obtain important insights into the structure and energetics of water adsorbed on highly oxidized organic surfaces exposed to ambient air of increasing relative humidity.

  6. Water adsorption on hydrophilic and hydrophobic self-assembled monolayers as proxies for atmospheric surfaces. A grand canonical Monte Carlo simulation study.

    PubMed

    Szori, Milán; Jedlovszky, Pál; Roeselová, Martina

    2010-05-14

    Grand canonical Monte Carlo simulations are used to determine water adsorption on prototypical organic surfaces as a function of relative humidity at 300 K. Three model surfaces formed by well-ordered self-assembled monolayers (SAMs) of alkanethiolate chains on gold are investigated: (i) a smooth hydrophobic surface of methyl-terminated C(7)-CH(3) SAM; (ii) a rough hydrophobic surface of randomly mixed two-component SAM, composed of equal fractions of C(5)-CH(3) and C(7)-CH(3) chains (C(5)/C(7)-CH(3) SAM); and (iii) a smooth hydrophilic surface of carboxyl-terminated C(7)-COOH SAM. The all atom CHARMM22 force field is used for the SAM chains together with the SPC/E model for water. No noticeable water adsorption is observed on the smooth hydrophobic surface up to saturation. The mild surface roughness introduced by the uneven chain length of the two components constituting the C(5)/C(7)-CH(3) SAM has no significant effect on the surface hydrophobicity, and the rough hydrophobic surface also remains dry up to the point when water condensation occurs. In contrast, water readily adsorbs onto the hydrophilic surface by forming hydrogen bonds with the COOH groups of the substrate. In addition, hydrogen bonding with pre-adsorbed water molecules contributes to the mechanism of water uptake. Under low humidity conditions, water is present on the hydrophilic surface as individual molecules or small water clusters and, with increasing relative humidity, the surface coverage grows continuously beyond a monolayer formation. The adsorbed water film is observed to be rather inhomogeneous with patches of bare surface exposed. The amount of water constituting a stable adsorption layer prior to condensation is estimated to consist of about 2-5 molecular layers. Detailed analysis of the simulation results is used to obtain important insights into the structure and energetics of water adsorbed on highly oxidized organic surfaces exposed to ambient air of increasing relative humidity

  7. Robust Maleimide-Functionalized Gold Surfaces and Nanoparticles Generated Using Custom-Designed Bidentate Adsorbates.

    PubMed

    Park, Chul Soon; Lee, Han Ju; Jamison, Andrew C; Lee, T Randall

    2016-07-26

    A series of custom-designed alkanethioacetate ligands were synthesized to provide a facile method of attaching maleimide-terminated adsorbates to gold nanostructures via thiolate bonds. Monolayers on flat gold substrates derived from both mono- and dithioacetates, with and without oligo(ethylene glycol) (OEG) moieties in their alkyl spacers, were characterized using X-ray photoelectron spectroscopy, polarization modulation infrared reflection-absorption spectroscopy, ellipsometry, and contact angle goniometry. For all adsorbates, the resulting monolayers revealed that a higher packing density and more homogeneous surface were generated when the film was formed in EtOH, but a higher percentage of bound thiolate was obtained in THF. A series of gold nanoparticles (AuNPs) capped with each adsorbate were prepared to explore how adsorbate structure influences aqueous colloidal stability under extreme conditions, as examined visually and spectroscopically. The AuNPs coated with adsorbates that include OEG moieties exhibited enhanced stability under high salt concentration, and AuNPs capped with dithioacetate adsorbates exhibited improved stability against ligand exchange in competition with dithiothreitol (DTT). Overall, the best results were obtained with a chelating dithioacetate adsorbate that included OEG moieties in its alkyl spacer, imparting improved stability via enhanced solubility in water and superior adsorbate attachment owing to the chelate effect. PMID:27385466

  8. Origins of viscoelastic dissipation in self-assembled organic monolayers

    SciTech Connect

    Shinn, N.D.; Michalske, T.A.

    1998-04-01

    Although self-assembled monolayers (SAMs) are promising candidates for interfacial lubricants in micro-electromechanical systems, the relationship between the monolayer structure and its viscoelastic properties is not understood. Using Acoustic Wave Damping (AWD), the authors have measured the complex shear modulus of linear alkane thiol monolayers, HS(CH{sub 2}){sub n{minus}1}CH{sub 3} denoted as C{sub n}, on Au(111)-textured substrates. The AWD technique measures the elastic energy storage and dissipative loss within a SAM adsorbed onto the electrodes of a quartz crystal microbalance. For C{sub 12}, C{sub 14} and C{sub 18} SAMs, the storage modulus increases with alkane chain length, but the loss modulus exhibits no systematic correlation. To investigate the origins of energy dissipation, the authors used a new, high-sensitivity oscillator circuit to simultaneously monitor the adsorption kinetics and acoustic damping during monolayer growth from the gas phase. For both C{sub 9} and C{sub 12} thiols, the dissipation in the growing monolayer can be correlated with distinct two-dimensional fluid phases and the nucleation and growth of condensed-phase islands.

  9. Determination of preferential molecular orientation in porphyrin-fullerene dyad ZnDHD6ee monolayers by the X-ray standing-wave method and X-ray reflectometry

    SciTech Connect

    Seregin, A. Yu. D'yakova, Yu. A.; Yakunin, S. N.; Makhotkin, I. A.; Alekseev, A. S.; Klechkovskaya, V. V.; Tereschenko, E. Yu.; Tkachenko, N. V.; Lemmetyinen, H.; Feigin, L. A.; Kovalchuk, M. V.

    2013-11-15

    Monolayers of porphyrin-fullerene dyad molecules with zinc atoms incorporated into the porphyrin ring (ZnDHD6ee) on the surface of aqueous subphase and on Si substrates have been investigated by the X-ray standing-wave method and X-ray reflectometry. The experiments have been performed under laboratory conditions and on synchrotron radiation sources (KMC-2 station of BESSY II (Berlin) and Langmuir station at the National Research Centre 'Kurchatov Institute'). Depth distributions of Zn atoms and electron density in the monolayer film are calculated. On the basis of the analysis of these distributions, it is concluded that ZnDHD6ee dyad molecules in monolayers have preferential orientation. The data obtained indicate that the molecules in monolayer film retain their orientation when the monolayer is transferred from a liquid subphase surface onto a solid substrate.

  10. Neutron Reflectometry Studies of the Adsorbed Structure of the Amelogenin, LRAP

    SciTech Connect

    Tarasevich, Barbara J.; Perez-Salas, Ursula; Masica, David L.; Philo, John; Krueger, Susan; Majkrzak, Charles F.; Gray, Jeffrey J.; Shaw, Wendy J.

    2013-03-21

    Amelogenins make up over 90 percent of the protein present during enamel formation and have been demonstrated to be critical in proper enamel development, but the mechanism governing this control is not well understood. Leucine-rich amelogenin peptide (LRAP) is a 59-residue splice variant of amelogenin and contains the charged regions from the full protein thought to control crystal regulation. In this work, we utilized neutron reflectivity (NR) to investigate the structure and orientation of LRAP adsorbed from solutions onto molecularly smooth COOH-terminated self-assembled monolayers (SAMs) surfaces. Sedimentation velocity experiments revealed that LRAP is primarily a monomer in saturated calcium phosphate (SCP) solutions (0.15 M NaCl) at pH 7.4. LRAP adsorbed as ~33 Å thick layers at ~70% coverage as determined by NR. Rosetta simulations of the dimensions of LRAP in solution (37 Å diameter) indicate that the NR determined z dimension is consistent with an LRAP monomer. Sedimentation velocity experiments and Rosetta simulation show that the LRAP monomer has an extended, asymmetric shape in solution. The NR data suggests that the protein is not completely extended on the surface, having some degree of structure away from the surface. A protein orientation with the C-terminal and inner N-terminal region (~8-24)) located near the surface is consistent with the higher scattering length density (SLD) and higher protein hydration found near the surface by NR. This work presents new information on the tertiary and quaternary structure of LRAP in solution and adsorbed onto surfaces. It also presents further evidence that the monomeric species may be an important functional form of amelogenin proteins.

  11. Toward control of the metal-organic interfacial electronic structure in molecular electronics: a first-principles study on self-assembled monolayers of pi-conjugated molecules on noble metals.

    PubMed

    Heimel, Georg; Romaner, Lorenz; Zojer, Egbert; Brédas, Jean-Luc

    2007-04-01

    Self-assembled monolayers (SAMs) of organic molecules provide an important tool to tune the work function of electrodes in plastic electronics and significantly improve device performance. Also, the energetic alignment of the frontier molecular orbitals in the SAM with the Fermi energy of a metal electrode dominates charge transport in single-molecule devices. On the basis of first-principles calculations on SAMs of pi-conjugated molecules on noble metals, we provide a detailed description of the mechanisms that give rise to and intrinsically link these interfacial phenomena at the atomic level. The docking chemistry on the metal side of the SAM determines the level alignment, while chemical modifications on the far side provide an additional, independent handle to modify the substrate work function; both aspects can be tuned over several eV. The comprehensive picture established in this work provides valuable guidelines for controlling charge-carrier injection in organic electronics and current-voltage characteristics in single-molecule devices.

  12. Self-Assembled Monolayers of Oligophenylenecarboxylic Acids on Silver Formed at the Liquid-Solid Interface.

    PubMed

    Aitchison, Hannah; Lu, Hao; Hogan, Simon W L; Früchtl, Herbert; Cebula, Izabela; Zharnikov, Michael; Buck, Manfred

    2016-09-20

    A series of para-oligophenylene mono- and dicarboxylic acids (R-(C6H4)nCOOH, n = 1-3, R = H,COOH) was studied. Adsorbed on Au(111)/mica modified by an underpotential deposited bilayer of Ag, the self-assembled monolayers (SAMs) were analyzed by near-edge X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and scanning tunneling microscopy. In all cases SAMs are formed with molecules adopting an upright orientation and anchored to the substrate by a carboxylate. Except benzoic acid, all SAMs could be imaged at molecular resolution, which revealed highly crystalline layers with a dense molecular packing. The structures of the SAMs are described by a rectangular (5 × √3) unit cell for the prevailing phase of the monocarboxylic acids and an oblique ([Formula: see text]) unit cell for the dicarboxylic acids, thus evidencing a pronounced influence of the second COOH moiety on the SAM structure. Density functional theory calculations suggest that hydrogen bonding between the SAM-terminating COOH moieties accounts for the difference. Contrasting other classes of SAMs, the systems studied here are determined by intermolecular interactions whereas molecule-substrate interactions play a secondary role. Thus, eliminating problems arising from the mismatch between the molecular and the substrate lattices, coordinatively bonded carboxylic acids on silver should provide considerable flexibility in the design of SAM structures. PMID:27588836

  13. Arsenic(III, V) adsorption on a goethite-based adsorbent in the presence of major co-existing ions: Modeling competitive adsorption consistent with spectroscopic and molecular evidence

    NASA Astrophysics Data System (ADS)

    Kanematsu, Masakazu; Young, Thomas M.; Fukushi, Keisuke; Green, Peter G.; Darby, Jeannie L.

    2013-04-01

    Adsorption of the two oxyanions, arsenate (As(V)) and arsenite (As(III)), on a common goethite-based granular porous adsorbent is studied in the presence of major co-existing ions in groundwater (i.e., phosphate, silicic acid, sulfate, carbonate, magnesium, and calcium) and predicted using the extended triple layer model (ETLM), a dipole modified single-site triple layer surface complexation model consistent with spectroscopic and molecular evidence. Surface species of all ions were selected according to the previous ETLM studies and published experimental spectroscopic/theoretical molecular information. The adsorption equilibrium constants for all ions were determined using adsorption data obtained in single-solute systems. The adsorption equilibrium constants referenced to the site-occupancy standard state (indicated by Kθ) were compared with those for goethite in the literature if available. The values of these constants for the goethite-based adsorbent are found to be close to the values for goethite previously studied. These "constrained" adsorption equilibrium constants determined in single-solute systems were used in the ETLM to predict the competitive interactions of As(III, V) with the co-existing ions in binary-solute systems. The ETLM is capable of predicting As(III, V) adsorption in the presence of oxyanions (phosphate, silicic acid, sulfate, and carbonate). This study presents the first successful and systematic prediction of the competitive interactions of As(III, V) with these oxyanions using the ETLM. The ETLM prediction of surface (and aqueous) speciation also provides insights into the distinct adsorption behavior of As(III, V) in the presence of the oxyanions. Magnesium and calcium significantly enhanced As(V) adsorption at higher pH values, while they had little effect on As(III) adsorption. The enhanced adsorption of As(V), however, could not be predicted by the ETLM using the surface species proposed in previous ETLM studies. Further studies

  14. Adhesive and conformational behaviour of mycolic acid monolayers.

    PubMed

    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.

  15. Preparation of High Purity, High Molecular-Weight Chitin from Ionic Liquids for Use as an Adsorbate for the Extraction of Uranium from Seawater

    SciTech Connect

    Rogers, Robin

    2013-12-21

    Ensuring a domestic supply of uranium is a key issue facing the wider implementation of nuclear power. Uranium is mostly mined in Kazakhstan, Australia, and Canada, and there are few high-grade uranium reserves left worldwide. Therefore, one of the most appealing potential sources of uranium is the vast quantity dissolved in the oceans (estimated to be 4.4 billion tons worldwide). There have been research efforts centered on finding a means to extract uranium from seawater for decades, but so far none have resulted in an economically viable product, due in part to the fact that the materials that have been successfully demonstrated to date are too costly (in terms of money and energy) to produce on the necessary scale. Ionic Liquids (salts which melt below 100{degrees}C) can completely dissolve raw crustacean shells, leading to recovery of a high purity, high molecular weight chitin powder and to fibers and films which can be spun directly from the extract solution suggesting that continuous processing might be feasible. The work proposed here will utilize the unprecedented control this makes possible over the chitin fiber a) to prepare electrospun nanofibers of very high surface area and in specific architectures, b) to modify the fiber surfaces chemically with selective extractant capacity, and c) to demonstrate their utility in the direct extraction and recovery of uranium from seawater. This approach will 1) provide direct extraction of chitin from shellfish waste thus saving energy over the current industrial process for obtaining chitin; 2) allow continuous processing of nanofibers for very high surface area fibers in an economical operation; 3) provide a unique high molecular weight chitin not available from the current industrial process, leading to stronger, more durable fibers; and 4) allow easy chemical modification of the large surface areas of the fibers for appending uranyl selective functionality providing selectivity and ease of stripping. The

  16. Removal of acutely hazardous pharmaceuticals from water using multi-template imprinted polymer adsorbent.

    PubMed

    Venkatesh, Avinash; Chopra, Nikita; Krupadam, Reddithota J

    2014-05-01

    Molecularly imprinted polymer adsorbent has been prepared to remove a group of recalcitrant and acutely hazardous (p-type) chemicals from water and wastewaters. The polymer adsorbent exhibited twofold higher adsorption capacity than the commercially used polystyrene divinylbenzene resin (XAD) and powdered activated carbon adsorbents. Higher adsorption capacity of the polymer adsorbent was explained on the basis of high specific surface area formed during molecular imprinting process. Freundlich isotherms drawn showed that the adsorption of p-type chemicals onto polymer adsorbent was kinetically faster than the other reference adsorbents. Matrix effect on adsorption of p-type chemicals was minimal, and also polymer adsorbent was amenable to regeneration by washing with water/methanol (3:1, v/v) solution. The polymer adsorbent was unaltered in its adsorption capacity up to 10 cycles of adsorption and desorption, which will be more desirable in cost reduction of treatment compared with single-time-use activated carbon. PMID:24499987

  17. C₆₀ fullerene promotes lung monolayer collapse.

    PubMed

    Barnoud, Jonathan; Urbini, Laura; Monticelli, Luca

    2015-03-01

    Airborne nanometre-sized pollutants are responsible for various respiratory diseases. Such pollutants can reach the gas-exchange surface in the alveoli, which is lined with a monolayer of lung surfactant. The relationship between physiological effects of pollutants and molecular-level interactions is largely unknown. Here, we determine the effects of carbon nanoparticles on the properties of a model of lung monolayer using molecular simulations. We simulate phase-separated lipid monolayers in the presence of a model pollutant nanoparticle, C₆₀ fullerene. In the absence of nanoparticles, the monolayers collapse only at very low surface tensions (around 0 mN m(-1)). In the presence of nanoparticles, instead, monolayer collapse is observed at significantly higher surface tensions (up to ca 10 mN m(-1)). Collapse at higher tensions is related to lower mechanical rigidity of the monolayer. It is possible that similar mechanisms operate on lung surfactant in vivo, which suggests that health effects of airborne carbon nanoparticles may be mediated by alterations of the mechanical properties of lung surfactant.

  18. Synthesis of metronidazole-imprinted molecularly imprinted polymers by distillation precipitation polymerization and their use as a solid-phase adsorbent and chromatographic filler.

    PubMed

    Liu, Jiang; Zhang, Lu; Li Han Song, Le; Liu, Yuan; Tang, Hui; Li, Yingchun

    2015-04-01

    Metronidazole-imprinted polymers with superior recognition properties were prepared by a novel strategy called distillation-precipitation polymerization. The as-obtained polymers were characterized by Fourier-transform infrared spectroscopy, laser particle size determination and scanning electron microscopy, and their binding performances were evaluated in detail by static, kinetic and dynamic rebinding tests, and Scatchard analysis. The results showed that when the fraction of the monomers was 5 vol% in the whole reaction system, the prepared polymers afforded good morphology, monodispersity, and high adsorption capacity and excellent selectivity to the target molecule, metronidazole. The optimal binding performance is 12.41 mg/g for metronidazole just before leakage occurred and 38.51 mg/g at saturation in dynamic rebinding tests. Metronidazole-imprinted polymers were further applied as packing agents in solid-phase extraction and as chromatographic filler, both of which served for the detection of metronidazole in fish tissue. The results illustrated the recoveries of spiked samples ranged from 82.97 to 87.83% by using molecularly imprinted solid-phase extraction combined with a C18 commercial column and 93.7 to 101.2% by directly using the polymer-packed chromatographic column. The relative standard deviation of both methods was less than 6%. PMID:25594306

  19. Fatty-acid monolayers at the nematic/water interface: phases and liquid-crystal alignment.

    PubMed

    Price, Andrew D; Schwartz, Daniel K

    2007-02-01

    The two-dimensional (2D) phases of fatty-acid monolayers (hexadecanoic, octadecanoic, eicosanoic, and docosanoic acids) have been studied at the interface of a nematic liquid crystal (LC) and water. When observed between crossed polarizers, the LC responds to monolayer structure owing to mesoscopic alignment of the LC by the adsorbed molecules. Similar to Langmuir monolayers at the air/water interface, the adsorbed monolayer at the nematic/water interface displays distinct thermodynamic phases. Observed are a 2D gas, isotropic liquid, and two condensed mesophases, each with a characteristic anchoring of the LC zenithal tilt and azimuth. By varying the monolayer temperature and surface concentration we observe reversible first-order phase transitions from vapor to liquid and from liquid to condensed. A temperature-dependent transition between two condensed phases appears to be a reversible swiveling transition in the tilt azimuth of the monolayer. Similar to monolayers at the air/water interface, the temperature of the gas/liquid/condensed triple-point temperature increased by about 10 degrees C for a two methylene group increase in chain length. However, the absolute value of the triple-point temperatures are depressed by about 40 degrees C compared to those of analogous monolayers at the air/water interface. We also observe a direct influence by the LC layer on the mesoscopic and macroscopic structure of the monolayer by analyzing the shapes and internal textures of gas domains in coexistence with a 2D liquid. An effective anisotropic line tension arises from elastic forces owing to deformation of the nematic director across phase boundaries. This results in the deformation of the domain from circular to elongated, with a distinct singularity. The LC elastic energy also gives rise to transition zones displaying mesoscopic realignment of the director tilt or azimuth between adjacent regions with a sudden change in anchoring.

  20. Structure and Reactivity of Adsorbed Fibronectin Films on Mica

    PubMed Central

    Hull, James R.; Tamura, Glen S.; Castner, David G.

    2007-01-01

    Understanding the interactions of adsorbed fibronectin (Fn) with other biomolecules is important for many biomedical applications. Fn is found in almost all body fluids, in the extracellular matrix, and plays a fundamental role in many biological processes. This study found that the structure (conformation, orientation) and reactivity of Fn adsorbed onto mica is dependent on the Fn surface concentration. Atomic force microscopy and x-ray photoelectron spectroscopy were used to determine the surface coverage of adsorbed Fn from isolated molecules at low surface coverage to full monolayers at high surface coverage. Both methods showed that the thickness of Fn film continued to increase after the mica surface was completely covered, consistent with Fn adsorbed in a more upright conformation at the highest surface-Fn concentrations. Time-of-flight secondary ion mass spectrometry showed that relative intensities of both sulfur-containing (cystine, methionine) and hydrophobic (glycine, leucine/isoleucine) amino acids varied with changing Fn surface coverage, indicating that the conformation of adsorbed Fn depended on surface coverage. Single-molecule force spectroscopy with collagen-related peptides immobilized onto the atomic force microscope tip showed that the specific interaction force between the peptide and Fn increases with increasing Fn surface coverage. PMID:17890402

  1. Controlling Assembly of Mixed Thiol Monolayers on Silver Nanoparticles to Tune Their Surface Properties

    PubMed Central

    2012-01-01

    Modifying the surfaces of metal nanoparticles with self-assembled monolayers of functionalized thiols provides a simple and direct method to alter their surface properties. Mixed self-assembled monolayers can extend this approach since, in principle, the surfaces can be tuned by altering the proportion of each modifier that is adsorbed. However, this works best if the composition and microstructure of the monolayers can be controlled. Here, we have modified preprepared silver colloids with binary mixtures of thiols at varying concentrations and modifier ratios. Surface-enhanced Raman spectroscopy was then used to determine the effect of altering these parameters on the composition of the resulting mixed monolayers. The data could be explained using a new model based on a modified competitive Langmuir approach. It was found that the composition of the mixed monolayer only reflected the ratio of modifiers in the feedstock when the total amount of modifier was sufficient for approximately one monolayer coverage. At higher modifier concentrations the thermodynamically favored modifier dominated, but working at near monolayer concentrations allowed the surface composition to be controlled by changing the ratios of modifiers. Finally, a positively charged porphyrin probe molecule was used to investigate the microstructure of the mixed monolayers, i.e., homogeneous versus domains. In this case the modifier domains were found to be <2 nm. PMID:22500816

  2. Orientational and Translational Properties of Hydrogen Films Adsorbed onto Boron Nitride

    NASA Astrophysics Data System (ADS)

    Evans, Morgan David

    As physics continues to expand its knowledge base, physicists seek new frontiers to investigate. Quantum -mechanical, two-dimensional systems have proven to be a subject that is not only rich in new discoveries (e.g., Kousterlitz-Thoules transitions and new phases of matter), but also filled with exciting predictions (e.g., new superfluids). The physisorption of a gas onto the surface of a homogenous, spacious (on a molecular scale) substrate with a low adsorption potential is one physical analogue to the much-analyzed theoretical two-dimensional system. Hydrogen in reduced dimensions has been found to have suppressed melting and freezing points, thus possibly permitting the onset of Bose condensation and a new superfluid phase. The use of boron nitride as an adsorption substrate allows for the study of physisorbed systems with a lower adsorption potential than previous studies using similar substrates (i.e., graphite and magnesium oxide). This dissertation has two parts. The first concerns the translational properties and adsorption energies of hydrogen adsorbed onto boron nitride. These properties are investigated through the use of volumetric adsorption isotherm techniques. The data suggest that the adsorption of hydrogen occurs in a step-wise manner at temperatures below 20 Kelvin. Changes in the translational phases (vapor -liquid-solid) occur between 10 to 20 Kelvin for the first four adsorbed monolayers. Isotopic effects are investigated through the use of the three common forms of hydrogen: molecular hydrogen (H_2), deuterium hydride (HD), and deuterium (D_2). The critical temperatures of the second, third, and fourth layers are determined, presented, and compared with the known phase diagrams of hydrogen isotopes adsorbed onto graphite and MgO. While the adsorption potential of the hydrogen-boron nitride system is found to be less than that of previously studied substrates, it does not translate into lower critical temperatures. The second part of this

  3. Origin of the instability of octadecylamine Langmuir monolayer at low pH

    SciTech Connect

    Avazbaeva, Zaure; Sung, Woongmo; Lee, Jonggwan; Phan, Minh Dinh; Shin, Kwanwoo; Vaknin, David; Kim, Doseok

    2015-11-30

    In this paper, it has been reported that an octadecylamine (ODA) Langmuir monolayer becomes unstable at low pH values with no measurable surface pressure at around pH 3.5, suggesting significant dissolution of the ODA molecule into the subphase solution (Albrecht, Colloids Surf. A 2006, 284–285, 166–174). However, by lowering the pH further, ODA molecules reoccupy the surface, and a full monolayer is recovered at pH 2.5. Using surface sum-frequency spectroscopy and pressure–area isotherms, it is found that the recovered monolayer at very low pH has a larger area per molecule with many gauche defects in the ODA molecules as compared to that at high pH values. This structural change suggests that the reappearance of the monolayer is due to the adsorbed Cl– counterions to the protonated amine groups, leading to partial charge neutralization. This proposition is confirmed by intentionally adding monovalent salts (i.e., NaCl, NaBr, or NaI) to the subphase to recover the monolayer at pH 3.5, in which the detailed structure of the monolayer is confirmed by sum frequency spectra and the adsorbed anions by X-ray reflectivity.

  4. Origin of the instability of octadecylamine Langmuir monolayer at low pH

    DOE PAGES

    Avazbaeva, Zaure; Sung, Woongmo; Lee, Jonggwan; Phan, Minh Dinh; Shin, Kwanwoo; Vaknin, David; Kim, Doseok

    2015-11-30

    In this paper, it has been reported that an octadecylamine (ODA) Langmuir monolayer becomes unstable at low pH values with no measurable surface pressure at around pH 3.5, suggesting significant dissolution of the ODA molecule into the subphase solution (Albrecht, Colloids Surf. A 2006, 284–285, 166–174). However, by lowering the pH further, ODA molecules reoccupy the surface, and a full monolayer is recovered at pH 2.5. Using surface sum-frequency spectroscopy and pressure–area isotherms, it is found that the recovered monolayer at very low pH has a larger area per molecule with many gauche defects in the ODA molecules as comparedmore » to that at high pH values. This structural change suggests that the reappearance of the monolayer is due to the adsorbed Cl– counterions to the protonated amine groups, leading to partial charge neutralization. This proposition is confirmed by intentionally adding monovalent salts (i.e., NaCl, NaBr, or NaI) to the subphase to recover the monolayer at pH 3.5, in which the detailed structure of the monolayer is confirmed by sum frequency spectra and the adsorbed anions by X-ray reflectivity.« less

  5. Revealing deposition mechanism of colloid particles on human serum albumin monolayers.

    PubMed

    Nattich-Rak, Małgorzata; Adamczyk, Zbigniew; Kujda, Marta

    2016-01-01

    Colloid particle deposition was applied in order to characterize human serum albumin (HSA) monolayers on mica adsorbed under diffusion transport at pH 3.5. The surface concentration of HSA was determined by a direct AFM imaging of single molecules. The electrokinetic characteristics of the monolayers for various ionic strength were done by in situ streaming potential measurements. In this way the mean-field zeta potential of monolayers was determined. It was shown that the initially negative potential changed its sign for HSA surface concentrations above 2800μm(-2) that was interpreted as overcharging effect. The monolayers were also characterized by the colloid deposition method where negatively charged polystyrene particles, 810nm in diameter were used. The kinetics of particle deposition and their maximum coverage were determined as a function of the HSA monolayer surface concentration. An anomalous deposition of particles on substrates exhibiting a negative zeta potential was observed, which contradicts the mean-field theoretical predictions. This effect was quantitatively interpreted in terms of the random site sequential adsorption model. It was shown that efficient immobilization of particles only occurs at adsorption sites formed by three and more closely adsorbed HSA molecules. These results can be exploited as useful reference data for the analysis of deposition phenomena of bioparticles at protein monolayers that has practical significance for the regulation of the bioadhesive properties of surfaces.

  6. Origin of the Instability of Octadecylamine Langmuir Monolayer at Low pH.

    PubMed

    Avazbaeva, Zaure; Sung, Woongmo; Lee, Jonggwan; Phan, Minh Dinh; Shin, Kwanwoo; Vaknin, David; Kim, Doseok

    2015-12-29

    It has been reported that an octadecylamine (ODA) Langmuir monolayer becomes unstable at low pH values with no measurable surface pressure at around pH 3.5, suggesting significant dissolution of the ODA molecule into the subphase solution (Albrecht, Colloids Surf. A 2006, 284-285, 166-174). However, by lowering the pH further, ODA molecules reoccupy the surface, and a full monolayer is recovered at pH 2.5. Using surface sum-frequency spectroscopy and pressure-area isotherms, it is found that the recovered monolayer at very low pH has a larger area per molecule with many gauche defects in the ODA molecules as compared to that at high pH values. This structural change suggests that the reappearance of the monolayer is due to the adsorbed Cl(-) counterions to the protonated amine groups, leading to partial charge neutralization. This proposition is confirmed by intentionally adding monovalent salts (i.e., NaCl, NaBr, or NaI) to the subphase to recover the monolayer at pH 3.5, in which the detailed structure of the monolayer is confirmed by sum frequency spectra and the adsorbed anions by X-ray reflectivity.

  7. A Theoretical Study of Single-Atom Catalysis of CO Oxidation Using Au Embedded 2D h-BN Monolayer: A CO-Promoted O2 Activation

    PubMed Central

    Mao, Keke; Li, Lei; Zhang, Wenhua; Pei, Yong; Zeng, Xiao Cheng; Wu, Xiaojun; Yang, Jinlong

    2014-01-01

    The CO oxidation behaviors on single Au atom embedded in two-dimensional h-BN monolayer are investigated on the basis of first-principles calculations, quantum Born-Oppenheim molecular dynamic simulations (BOMD) and micro-kinetic analysis. We show that CO oxidation on h-BN monolayer support single gold atom prefers an unreported tri-molecular Eley-Rideal (E-R) reaction, where O2 molecule is activated by two pre-adsorbed CO molecules. The formed OCOAuOCO intermediate dissociates into two CO2 molecules synchronously, which is the rate-limiting step with an energy barrier of 0.47 eV. By using the micro-kinetic analysis, the CO oxidation following the tri-molecular E-R reaction pathway entails much higher reaction rate (1.43 × 105 s−1) than that of bimolecular Langmuir-Hinshelwood (L-H) pathway (4.29 s−1). Further, the quantum BOMD simulation at the temperature of 300 K demonstrates the complete reaction process in real time. PMID:24962006

  8. A theoretical study of single-atom catalysis of CO oxidation using Au embedded 2D h-BN monolayer: a CO-promoted O₂ activation.

    PubMed

    Mao, Keke; Li, Lei; Zhang, Wenhua; Pei, Yong; Zeng, Xiao Cheng; Wu, Xiaojun; Yang, Jinlong

    2014-01-01

    The CO oxidation behaviors on single Au atom embedded in two-dimensional h-BN monolayer are investigated on the basis of first-principles calculations, quantum Born-Oppenheim molecular dynamic simulations (BOMD) and micro-kinetic analysis. We show that CO oxidation on h-BN monolayer support single gold atom prefers an unreported tri-molecular Eley-Rideal (E-R) reaction, where O2 molecule is activated by two pre-adsorbed CO molecules. The formed OCOAuOCO intermediate dissociates into two CO2 molecules synchronously, which is the rate-limiting step with an energy barrier of 0.47 eV. By using the micro-kinetic analysis, the CO oxidation following the tri-molecular E-R reaction pathway entails much higher reaction rate (1.43 × 10(5) s(-1)) than that of bimolecular Langmuir-Hinshelwood (L-H) pathway (4.29 s(-1)). Further, the quantum BOMD simulation at the temperature of 300 K demonstrates the complete reaction process in real time. PMID:24962006

  9. Nanofiltration across Defect-Sealed Nanoporous Monolayer Graphene.

    PubMed

    O'Hern, Sean C; Jang, Doojoon; Bose, Suman; Idrobo, Juan-Carlos; Song, Yi; Laoui, Tahar; Kong, Jing; Karnik, Rohit

    2015-05-13

    Monolayer nanoporous graphene represents an ideal membrane for molecular separations, but its practical realization is impeded by leakage through defects in the ultrathin graphene. Here, we report a multiscale leakage-sealing process that exploits the nonpolar nature and impermeability of pristine graphene to selectively block defects, resulting in a centimeter-scale membrane that can separate two fluid reservoirs by an atomically thin layer of graphene. After introducing subnanometer pores in graphene, the membrane exhibited rejection of multivalent ions and small molecules and water flux consistent with prior molecular dynamics simulations. The results indicate the feasibility of constructing defect-tolerant monolayer graphene membranes for nanofiltration, desalination, and other separation processes.

  10. Nanofiltration across Defect-Sealed Nanoporous Monolayer Graphene

    SciTech Connect

    O'Hern, Sean C.; Jang, Doojoon; Bose, Suman; Idrobo Tapia, Juan Carlos; Song, Yi; Laoui, Tahar; Kong, Jing; Karnik, Rohit

    2015-04-27

    Monolayer nanoporous graphene represents an ideal membrane for molecular separations, but its practical realization is impeded by leakage through defects in the ultrathin graphene. Here, we report a multiscale leakage-sealing process that exploits the nonpolar nature and impermeability of pristine graphene to selectively block defects, resulting in a centimeter-scale membrane that can separate two fluid reservoirs by an atomically thin layer of graphene. After introducing subnanometer pores in graphene, the membrane exhibited rejection of multivalent ions and small molecules and water flux consistent with prior molecular dynamics simulations. The results indicate the feasibility of constructing defect-tolerant monolayer graphene membranes for nanofiltration, desalination, and other separation processes.

  11. Alkanethiols on platinum: multicomponent self-assembled monolayers.

    PubMed

    Petrovykh, Dmitri Y; Kimura-Suda, Hiromi; Opdahl, Aric; Richter, Lee J; Tarlov, Michael J; Whitman, Lloyd J

    2006-03-14

    We have studied the formation of self-assembled monolayers (SAMs) of n-alkanethiols on platinum thin films using X-ray photoelectron spectroscopy (XPS), reflection-absorption infrared spectroscopy (RAIRS), spectroscopic ellipsometry (SE), and contact angle (CA) measurements. Specifically, SAMs of 1-hexanethiol, 1-dodecanethiol, and 1-octadecanethiol were grown on polycrystalline Pt films, and the effects of Pt surface preparation, deposition conditions, and solvent treatments on the initial quality and stability of the monolayer in air were investigated. The SAMs prepared under ambient conditions on piranha-cleaned and UV/ozone-cleaned substrates were compared to monolayers formed on template-stripped Pt in an inert atmosphere. We found that alkanethiols deposited from 1 mM ethanolic solutions on piranha-cleaned Pt formed densely packed monolayers in which alkyl chains were oriented close to the surface normal. Stored in the laboratory ambient, these monolayers were unchanged over about 1 week but were largely oxidized in about 1 month. No evidence was found of molecules being weakly bound within the monolayer or having undergone C-S bond scission; however, three distinct sulfur states were observed for all samples in the XPS of the S 2p region. The lowest- and highest-binding-energy components are assigned to alkylthiolate and partially oxidized alkylthiolate species, respectively. The remaining S 2p component (approximately one-third of the sulfur layer), intermediate in binding energy between the other two components, is attributed to a chemisorbed species with a S binding configuration distinct from the majority alkylthiolate: for example, S bound to Pt bound to O, S with a different Pt coordination number, or S in an adsorbed disulfide.

  12. Self-Organization of Polystyrene-b-polyacrylic Acid (PS-b-PAA) Monolayer at the Air/Water Interface: A Process Driven by the Release of the Solvent Spreading.

    PubMed

    Guennouni, Zineb; Cousin, Fabrice; Fauré, Marie-Claude; Perrin, Patrick; Limagne, Denis; Konovalov, Oleg; Goldmann, Michel

    2016-03-01

    We present an in situ structural study of the surface behavior of PS-b-PAA monolayers at the air/water interface at pH 2, for which the PAA blocks are neutral and using N,N-dimethyformamide (DMF) as spreading solvent. The surface pressure versus molecular area isotherm shows a perfectly reversible pseudoplateau over several cycles of compression/decompression. The width of such plateau enlarges when increasing temperature, conversely to what is classically observed in the case of an in-plane first order transition. We combined specular neutron reflectivity (SNR) experiments with contrast variation to solve the profile of each block perpendicular to the surface with grazing-incidence small-angle scattering (GISAXS) measurements to determine the in-plane structure of the layer. SNR experiments showed that both PS and PAA blocks remain adsorbed on the surface for all surface pressure probed. A correlation peak at Q(xy)* = 0.021 Å(-1) is evidenced by GISAXS at very low surface pressure which intensity first increases on the plateau. When compressing further, its intensity decays while Q(xy)* is shifted toward low Q(xy). The peak fully disappears at the end of the plateau. These results are interpreted by the formation of surface aggregates induced by DMF molecules at the surface. These DMF molecules remain adsorbed within the PS core of the aggregates. Upon compression, they are progressively expelled from the monolayer, which gives rise to the pseudoplateau on the isotherm. The intensity of the GISAXS correlation peak is set by the amount of DMF within the monolayer as it vanishes when all DMF molecules are expelled. This result emphizes the role of the solvent in Langmuir monolayer formed by amphiphilic copolymers which hydrophobic and hydrophilic parts are composed by long polymer chains.

  13. New insights into the pH-dependent interfacial adsorption of dog gastric lipase using the monolayer technique.

    PubMed

    Bénarouche, Anaïs; Point, Vanessa; Parsiegla, Goetz; Carrière, Frédéric; Cavalier, Jean-François

    2013-11-01

    The access to kinetic parameters of lipolytic enzyme adsorption onto lipids is essential for a better understanding of interfacial enzymology and lipase-lipid interactions. The interfacial adsorption of dog gastric lipase (DGL) was monitored as a function of pH and surface pressure (Π), independently from the catalytic activity, using non-hydrolysable 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) monomolecular films. The acid-stable DGL, which initiates fat digestion in the stomach, was then selected because its adsorption kinetics onto hydrophobic solid surfaces were already studied. This gastric lipase was therefore used as a model enzyme to validate both experimental and theoretical approaches. Results show that the adsorption process of DGL at the lipid/water interface depends on a pH-dependent adsorption equilibrium coefficient which is optimum at pH 5.0 (K(Ads) = 1.7 ± 0.05 × 10(8)M(-1)). KAds values further allowed an indirect estimation of the molar fraction (ΦE*(%), mol%) as well as the molecular area (AE*) of DGL adsorbed onto DLPC monolayer. Based on these data, a model for DGL adsorption onto DLPC monolayer at pH 5.0 is proposed for a surface pressure range of 15-25 mNm(-1).

  14. Unoccupied electronic states in adsorbate systems

    NASA Astrophysics Data System (ADS)

    Bertel, E.

    1991-11-01

    Experimental work on unoccupied electronic states in adsorbate systems on metallic substrates is reviewed with emphasis on recent developments. The first part is devoted to molecular adsorbates. Weakly chemisorbed hydrocarbons are briefly discussed. An exhaustive inverse photoemission (IPE) study of the CO bond to the transition metals Ni, Pb, and Pt is presented. Adsorbed NO is taken as an example to demonstrate the persisting discrepancies in the interpretation of IPE spectra. Atomic adsorbates are discussed in the second part. The quantum well state model is applied to interpret the surface states in reconstructing and non-reconstructing adsorption systems of alkali metals and hydrogen. A recent controversy on the unoccupied electronic states of the Cu(110)/O p(2×1) surface is critically reviewed. The quantum well state model is then compared to tight binding and local-density-functional calculations of the unoccupied bands and the deficiencies of the various approaches are pointed out. Finally, the relation between the surface state model and more chemically oriented models of surface bonding is briefly discussed.

  15. Direct observation of poloxamer 188 insertion into lipid monolayers.

    PubMed Central

    Maskarinec, Stacey A; Hannig, Jürgen; Lee, Raphael C; Lee, Ka Yee C

    2002-01-01

    P188, a triblock copolymer of the form poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) helps seal electroporated cell membranes, arresting the leakage of intracellular materials from the damaged cells. To explore the nature of the interaction between P188 and cell membranes, we have constructed a model system that assesses the ability of P188 to insert into lipid monolayers. Using concurrent Langmuir isotherm and fluorescence microscopy measurements, we find that P188 changes the phase behavior and morphology of the monolayers. P188 inserts into both dipalmitoylphosphatidlycholine and dipalmitoylphosphatidylglycerol monolayers at surface pressures equal to and lower than approximately 22 mN/m at 30 degrees C; this pressure corresponds to the maximal surface pressure attained by P188 on a pure water subphase. Similar results for the two phospholipids indicate that P188 insertion is not influenced by headgroup electrostatics. Because the equivalent surface pressure of a normal bilayer is on the order of 30 mN/m, the lack of P188 insertion above 22 mN/m further suggests the poloxamer selectively adsorbs into damaged portions of electroporated membranes, thereby localizing its effect. P188 is also found to be "squeezed out" of the monolayers at high surface pressures, suggesting a mechanism for the cell to be rid of the poloxamer when the membrane is restored. PMID:11867460

  16. Modified optical absorption of molecules on metallic nanoparticles at sub-monolayer coverage

    NASA Astrophysics Data System (ADS)

    Darby, Brendan L.; Auguié, Baptiste; Meyer, Matthias; Pantoja, Andres E.; Le Ru, Eric C.

    2016-01-01

    Enhanced optical absorption of molecules in the vicinity of metallic nanostructures is key to a number of surface-enhanced spectroscopies and of great general interest to the fields of plasmonics and nano-optics. However, experimental access to this absorbance has long proven elusive. Here, we present direct measurements of the surface absorbance of dye molecules adsorbed onto silver nanospheres and, crucially, at sub-monolayer concentrations where dye-dye interactions become negligible. With a large detuning from the plasmon resonance, distinct shifts and broadening of the molecular resonances reveal the intrinsic properties of the dye in contact with the metal colloid, in contrast to the often studied strong-coupling regime where the optical properties of the dye molecules cannot be isolated. The observation of these shifts together with the ability to routinely measure them has broad implications in the interpretation of experiments involving resonant molecules on metallic surfaces, such as surface-enhanced spectroscopies and many aspects of molecular plasmonics.

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

    NASA Astrophysics Data System (ADS)

    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.

  18. On the Interaction between Digitonin and Cholesterol in Langmuir Monolayers.

    PubMed

    Wojciechowski, Kamil; Orczyk, Marta; Gutberlet, Thomas; Brezesinski, Gerald; Geue, Thomas; Fontaine, Philippe

    2016-09-01

    In this article, we describe the effect of a highly hemolytic saponin, digitonin, on model lipids cholesterol and dipalmitoylphosphatidylcholine (DPPC) using a combination of tensiometric (surface pressure and dilatational surface elasticity), spectroscopic (infrared reflection absorption spectroscopy, IRRAS), microscopic (fluorescence microscopy), and scattering techniques (neutron reflectivity, NR, and grazing incidence X-ray diffraction, GIXD). The monolayers of individual lipids and their 10:9 (mol/mol) mixture were exposed to an aqueous solution of digitonin (10(-4) M) by subphase exchange using a setup developed recently in our laboratory. The results confirm that digitonin can adsorb onto both bare and lipid-covered water-air interfaces. In the case of DPPC, a relatively weak interaction can be observed, but the presence of cholesterol drastically enhances the effect of digitonin. The latter is shown to dissociate the weak cholesterol-DPPC complexes and to bind cholesterol in an additional layer attached to the original lipid monolayer.

  19. Growth of a collapsing Langmuir monolayer

    SciTech Connect

    Kundu, S.; Datta, A.; Hazra, S.

    2006-05-15

    Langmuir monolayers of stearic acid on Co ions in the aqueous subphase have been deposited at different stages of constant pressure collapse, on hydrophilic Si(001) using a modified version of the inverse Langmuir-Schaefer method of horizontal deposition. The electron density profiles (EDPs) along the depth of the deposited films, extracted from the x-ray reflectivity data, show that a monolayer to bi-molecular layer transformation takes place after collapse. The molecules in the lower monolayer have asymmetric configurations with head groups touching water and tails in air, whereas molecules in the upper layer are in symmetric configurations with tails on both sides of the heads. Atomic force microscopy images of the deposited films after collapse, however, show nearly circular islands of height more than that of the bimolecular layer observed in the EDP. As pressure increases, ridges are seen to coexist with these islands. Although the coverage of such islands and ridges is low, they play an important role in determining the growth mode. The growth of the wetting and island layers, taken together, has a striking similarity with the Stranski-Krastanow mode, observed usually for heteroepitaxial growth.

  20. Atomistic simulations of langmuir monolayer collapse.

    PubMed

    Lorenz, Christian D; Travesset, Alex

    2006-11-21

    Monolayers at the vapor/water interface collapse by exploring the third dimension at sufficient lateral compression, either by forming three-dimensional structures or by solubilization into the aqueous solution. In this paper, we provide an atomistic description of collapse from molecular dynamics (MD) simulations. More specifically, we investigate monolayers of arachidic acids spread on pure water and in an aqueous solution with Ca2+ ions in the subphase. In both cases, it is found that the collapsed systems generally lead to the formation of multilayer structures, which in the system with Ca2+ ions, proceeds by an intermediate regime where the monolayer exhibits significant roughness (of the order of 4 A). If no roughness is present, the system forms collapsed structures into the aqueous solution. The computational cost of atomic MD limits our simulations to relatively small system sizes, fast compression rates, and temporal scales on the order of a nanosecond. We discuss the issues caused by these limitations and present a detailed discussion of how the collapse regime proceeds at long time scales. We conclude with a summary of the implications of our results for further theoretical and experimental studies. PMID:17106994

  1. Investigation on gallium ions impacting monolayer graphene

    SciTech Connect

    Wu, Xin; Zhao, Haiyan Yan, Dong; Pei, Jiayun

    2015-06-15

    In this paper, the physical phenomena of gallium (Ga{sup +}) ion impacting monolayer graphene in the nanosculpting process are investigated experimentally, and the mechanisms are explained by using Monte Carlo (MC) and molecular dynamics (MD) simulations. Firstly, the MC method is employed to clarify the phenomena happened to the monolayer graphene target under Ga{sup +} ion irradiation. It is found that substrate has strong influence on the damage mode of graphene. The mean sputtering yield of graphene under 30 keV Ga{sup +} ion irradiation is 1.77 and the least ion dose to completely remove carbon atoms in graphene is 21.6 ion/nm{sup 2}. Afterwards, the focused ion beam over 21.6 ion/nm{sup 2} is used for the irradiation on a monolayer graphene supported by SiO2 experimentally, resulting in the nanostructures, i.e., nanodot and nanowire array on the graphene. The performances of the nanostructures are characterized by atomic force microscopy and Raman spectrum. A plasma plume shielding model is put forward to explain the nanosculpting results of graphene under different irradiation parameters. In addition, two damage mechanisms are found existing in the fabrication process of the nanostructures by using empirical MD simulations. The results can help us open the possibilities for better control of nanocarbon devices.

  2. Molecular structure and chiral separation in {alpha}-sexithiophene ultrathin films on Au(111): Low-energy electron diffraction and scanning tunneling microscopy

    SciTech Connect

    Kiel, Mario; Duncker, Klaus; Hagendorf, Christian; Widdra, Wolf

    2007-05-15

    The adsorption of the {pi}-conjugated organic molecule {alpha}-sexithiophene which is widely used in molecular electronics has been studied on Au(111) by low-energy electron diffraction and scanning tunneling microscopy. For monolayer adsorption at room temperature, large, well-ordered domains of flat-lying molecules which arrange in molecular rows are observed. A detailed structure analysis reveals an incommensurate, line-on-line oriented monolayer with one molecule per unit cell. In contrast to the behavior in the three-dimensional bulk structure, flat-lying adsorption introduces molecular chirality: Right- and left-handed molecules separate into domains of different orientations which are mirror symmetric with respect to the [112] substrate direction. Details of the adlayer structure and the chiral self-recognition can be rationalized based on the van der Waals contour of the adsorbed molecules.

  3. Calculation of monolayer structures of hydrocarbon chains on transition metal dichalcogenides: Dotriacontane on MoSe2

    NASA Astrophysics Data System (ADS)

    Cincotti, S.; Burda, J.; Hentschke, R.; Rabe, J. P.

    1995-03-01

    In situ scanning tunneling microscopy at the interface between atomically flat solid surfaces and solutions containing alkyl chains or alkyl derivatives show that the solute molecules often adsorb from solution to form dense crystalline monolayers at the liquid-solid interface. The structure of these layers depends on the nature of the substrate, and thus cannot be predicted from simple packing considerations alone. As an example of a theoretical approach to this problem on the atomic level, we present a calculation of the monolayer structure of dotriacontane on MoSe2. We carry out energy minimizations of periodic clusters of dotriacontane on MoSe2, where the potential energy is based on ab initio second-order Mo/ller-Plesset perturbation calculations of the adsorbate-substrate interactions combined with a phenomenological force field description of the intra-adsorbate interactions. The resulting adsorbate structure is in excellent agreement with the experimentally observed structure.

  4. Hollow-fiber-based adsorbers for gas separation by pressure-swing adsorption

    SciTech Connect

    Feng, X.; Pan, C.Y.; McMinis, C.W.; Ivory, J.; Ghosh, D.

    1998-07-01

    Hollow-fiber-based adsorbers for gas separation by pressure-swing adsorption (PSA) was studied experimentally. The high efficiency of hollow-fiber-based adsorbers for gas separation was illustrated by hydrogen separation using fine-powder-activated carbon and molecular sieve as adsorbents. The adsorption equilibrium and dynamics of the hollow-fiber adsorbers were determined. The pressure drop of the gas flowing through the adsorbers was also examined. The adsorbers were tested for hydrogen separation from nitrogen, carbon dioxide, and a multicomponent gas mixture simulating ammonia synthesis purge gas. The PSA systems using the hollow-fiber adsorbers were very effective for hydrogen purification. The high separation efficiency is derived from the fast mass-transfer rate and low pressure drop, two key features of hollow-fiber-based adsorbers.

  5. Topological features of engineered arrays of adsorbates in honeycomb lattices

    NASA Astrophysics Data System (ADS)

    Gonzalez-Arraga, Luis A.; Lado, J. L.; Guinea, Francisco

    2016-09-01

    Hydrogen adatoms are one of the most the promising proposals for the functionalization of graphene. The adatoms induce narrow resonances near the Dirac energy, which lead to the formation of magnetic moments. Furthermore, they also create local lattice distortions which enhance the spin-orbit coupling. The combination of magnetism and spin-orbit coupling allows for a rich variety of phases, some of which have non-trivial topological features. We analyze the interplay between magnetism and spin-orbit coupling in ordered arrays of adsorbates on honeycomb lattice monolayers, and classify the different phases that may arise. We extend our model to consider arrays of adsorbates in graphene-like crystals with stronger intrinsic spin-orbit couplings. We also consider a regime away from half-filling in which the Fermi level is at the bottom of the conduction band, we find a Berry curvature distribution corresponding to a Valley-Hall effect.

  6. Contact forces at the sliding interface: Mixed versus pure model alkane monolayers

    NASA Astrophysics Data System (ADS)

    Mikulski, Paul T.; Gao, Guangtu; Chateauneuf, Ginger M.; Harrison, Judith A.

    2005-01-01

    Classical molecular dynamics simulations of an amorphous carbon tip sliding against monolayers of n-alkane chains are presented. The tribological behavior of tightly packed, pure monolayers composed of chains containing 14 carbon atoms is compared to mixed monolayers that randomly combine equal amounts of 12- and 16-carbon-atom chains. When sliding in the direction of chain cant under repulsive (positive) loads, pure monolayers consistently show lower friction than mixed monolayers. The distribution of contact forces between individual monolayer chain groups and the tip shows pure and mixed monolayers resist tip motion similarly. In contrast, the contact forces "pushing" the tip along differ in the two monolayers. The pure monolayers exhibit a high level of symmetry between resisting and pushing forces which results in a lower net friction. Both systems exhibit a marked friction anisotropy. The contact force distribution changes dramatically as a result of the change in sliding direction, resulting in an increase in friction. Upon continued sliding in the direction perpendicular to chain cant, both types of monolayers are often capable of transitioning to a state where the chains are primarily oriented with the cant along the sliding direction. A large change in the distribution of contact forces and a reduction in friction accompany this transition.

  7. Processing of monolayer materials via interfacial reactions

    DOEpatents

    Sutter, Peter Werner; Sutter, Eli Anguelova

    2014-05-20

    A method of forming and processing of graphene is disclosed based on exposure and selective intercalation of the partially graphene-covered metal substrate with atomic or molecular intercalation species such as oxygen (O.sub.2) and nitrogen oxide (NO.sub.2). The process of intercalation lifts the strong metal-carbon coupling and restores the characteristic Dirac behavior of isolated monolayer graphene. The interface of graphene with metals or metal-decorated substrates also provides for controlled chemical reactions based on novel functionality of the confined space between a metal surface and a graphene sheet.

  8. Computer simulations of adsorbed liquid crystal films

    NASA Astrophysics Data System (ADS)

    Wall, Greg D.; Cleaver, Douglas J.

    2003-01-01

    The structures adopted by adsorbed thin films of Gay-Berne particles in the presence of a coexisting vapour phase are investigated by molecular dynamics simulation. The films are adsorbed at a flat substrate which favours planar anchoring, whereas the nematic-vapour interface favours normal alignment. On cooling, a system with a high molecule-substrate interaction strength exhibits substrate-induced planar orientational ordering and considerable stratification is observed in the density profiles. In contrast, a system with weak molecule-substrate coupling adopts a director orientation orthogonal to the substrate plane, owing to the increased influence of the nematic-vapour interface. There are significant differences between the structures adopted at the two interfaces, in contrast with the predictions of density functional treatments of such systems.

  9. Ozonation of isoproturon adsorbed on silica particles under atmospheric conditions

    NASA Astrophysics Data System (ADS)

    Pflieger, Maryline; Grgić, Irena; Kitanovski, Zoran

    2012-12-01

    The results on heterogeneous ozonation of a phenylurea pesticide, isoproturon, under atmospheric conditions are presented for the first time in the present study. The study was carried out using an experimental device previously adopted and validated for the heterogeneous reactivity of organics toward ozone (Pflieger et al., 2011). Isoproturon was adsorbed on silica particles via a liquid-to-solid equilibrium with a load far below a monolayer (0.02% by weight/surface coverage of 0.5%). The rate constants were estimated by measuring the consumption of the organic (dark, T = 26 °C, RH < 1%). The experimental data were fitted by both the modified Langmuir-Hinshelwood and the Eley-Rideal patterns, resulting in atmospheric lifetimes of heterogeneous ozonation of 4 and 6 days, respectively (for 40 ppb of O3). Parameters, such as the number and the quantity of pesticides adsorbed on the solid support, which can significantly influence the heterogeneous kinetics, were investigated as well. The results obtained suggest that the organic compound is adsorbed in multilayer aggregates on the aerosol even though submonolayer coverage is assumed. The presence of a second herbicide, trifluralin, together with isoproturon on the aerosol surface does not affect the kinetics of ozonation, indicating that both compounds are adsorbed on different surface sites of silica particles.

  10. Sorption of methylene blue on treated agricultural adsorbents: equilibrium and kinetic studies

    NASA Astrophysics Data System (ADS)

    Tiwari, D. P.; Singh, S. K.; Sharma, Neetu

    2015-03-01

    Agricultural adsorbents are reported to have a remarkable performance for adsorption of dyes. In the present study, formaldehyde and sulphuric acid treated two agricultural adsorbents; potato peel and neem bark are used to adsorb methylene blue. On the whole, the acid-treated adsorbents are investigated to have high sorption efficiency compared to HCHO treated adsorbents. The percentage removal efficiency of H2SO4 treated potato peel (APP) increases considerably high from 75 to 100 % with increase in adsorbent dose, whereas the removal efficiency of H2SO4 treated neem bark (ANB) is found to be 98 % after adding the first dose only. The monolayer sorption behaviour of HCHO treated potato peel (PP) and APP is well defined by Langmuir, whereas the chemisorptions behaviour of HCHO treated neem bark (NB) and ANB is suggested by Temkin's isotherm model. The maximum adsorption capacity measured is highest in ANB followed by NB, PP and APP with the values of 1000, 90, 47.62 and 40.0 mg/g, respectively. The pseudo-second-order kinetic model fitted well with the observed data of all the four adsorbents. The results obtained reveal that NB and ANB both are good adsorbents compared to PP and APP.

  11. Spectroscopy of the conformational disorder in molecular films: tetracosane and squalane on Pt(111).

    PubMed

    Fuhrmann, D; Graham, A P

    2004-02-01

    The spectroscopic investigation of the molecular vibrations of adsorbed branched and unbranched alkane molecules using helium atom scattering (HAS) provides evidence for the thermal formation of gauche defects in tetracosane (C24H50) monolayers above 200 K. HAS results for the vibration of tetracosane molecules perpendicular to the Pt(111) surface reveal a strong frequency decrease and peak broadening above the transition temperature which can be related to a reduction of the force holding the molecules to the surface. This reduction of the force is interpreted as being due to the thermal formation of gauche defects within the tetracosane molecules.

  12. Spectroscopy of the conformational disorder in molecular films: Tetracosane and squalane on Pt(111)

    NASA Astrophysics Data System (ADS)

    Fuhrmann, D.; Graham, A. P.

    2004-02-01

    The spectroscopic investigation of the molecular vibrations of adsorbed branched and unbranched alkane molecules using helium atom scattering (HAS) provides evidence for the thermal formation of gauche defects in tetracosane (C24H50) monolayers above 200 K. HAS results for the vibration of tetracosane molecules perpendicular to the Pt(111) surface reveal a strong frequency decrease and peak broadening above the transition temperature which can be related to a reduction of the force holding the molecules to the surface. This reduction of the force is interpreted as being due to the thermal formation of gauche defects within the tetracosane molecules.

  13. Ultraviolet and electron radiation induced fragmentation of adsorbed ferrocene

    SciTech Connect

    Welipitiya, D.; Green, A.; Woods, J.P.; Dowben, P.A.; Robertson, B.W.; Byun, D.; Zhang, J.

    1996-06-01

    From thermal desorption spectroscopy we find that ferrocene, Fe(C{sub 5}H{sub 5}){sub 2}, adsorbs and desorbs associatively on Ag(100). Photoemission results indicate that the initially adsorbed surface species closely resembles that of molecular ferrocene. The shift in photoemission binding energies relative to the gas phase is largely independent of the molecular orbital. We find that ultraviolet light does lead to partial fragmentation of the ferrocene and that the molecular fragments are much more strongly bound to the surface than the associatively adsorbed ferrocene. Since fragmentation occurs only in the presence of incident radiation, selective area deposition from this class of molecules is possible. Using a focused electron beam in a scanning transmission electron microscope, we show that selective area deposition of features with resolution of a few hundred angstroms is readily achieved. {copyright} {ital 1996 American Institute of Physics.}

  14. Patterning Self-Assembled Monolayers on Gold: Green Materials Chemistry in the Teaching Laboratory

    ERIC Educational Resources Information Center

    McFarland, Adam D.; Huffman, Lauren M.; Parent, Kathryn, E.; Hutchison, James E.; Thompson, John E.

    2004-01-01

    An experiment demonstrating self-assembled monolayer (SAM) chemistry, organic thin-film patterning and the use of molecular functionality to control macroscopic properties is described. Several important green chemistry principles are introduced.

  15. Phase Transitions in Dipalmitoylphosphatidylcholine Monolayers.

    PubMed

    Zuo, Yi Y; Chen, Rimei; Wang, Xianju; Yang, Jinlong; Policova, Zdenka; Neumann, A Wilhelm

    2016-08-23

    A self-assembled phospholipid monolayer at an air-water interface is a well-defined model system for studying surface thermodynamics, membrane biophysics, thin-film materials, and colloidal soft matter. Here we report a study of two-dimensional phase transitions in the dipalmitoylphosphatidylcholine (DPPC) monolayer at the air-water interface using a newly developed methodology called constrained drop surfactometry (CDS). CDS is superior to the classical Langmuir balance in its capacity for rigorous temperature control and leak-proof environments, thus making it an ideal alternative to the Langmuir balance for studying lipid polymorphism. In addition, we have developed a novel Langmuir-Blodgett (LB) transfer technique that allows the direct transfer of lipid monolayers from the droplet surface under well-controlled conditions. This LB transfer technique permits the direct visualization of phase coexistence in the DPPC monolayer. With these technological advances, we found that the two-dimensional phase behavior of the DPPC monolayer is analogous to the three-dimensional phase transition of a pure substance. This study has implications in the fundamental understanding of surface thermodynamics as well as applications such as self-assembled monolayers and pulmonary surfactant biophysics. PMID:27479299

  16. Methane Recovery from Gaseous Mixtures Using Carbonaceous Adsorbents

    NASA Astrophysics Data System (ADS)

    Buczek, Bronisław

    2016-06-01

    Methane recovery from gaseous mixtures has both economical and ecological aspect. Methane from different waste gases like mine gases, nitrogenated natural gases and biogases can be treated as local source for production electric and heat energy. Also occurs the problem of atmosphere pollution with methane that shows over 20 times more harmful environmental effect in comparison to carbon dioxide. One of the ways utilisation such gases is enrichment of methane in the PSA technique, which requires appropriate adsorbents. Active carbons and carbon molecular sieve produced by industry and obtained in laboratory scale were examined as adsorbent for methane recuperation. Porous structure of adsorbents was investigated using densimetry measurements and adsorption of argon at 77.5K. On the basis of adsorption data, the Dubinin-Radushkevich equation parameters, micropore volume (Wo) and characteristics of energy adsorption (Eo) as well as area micropores (Smi) and BET area (SBET) were determined. The usability of adsorbents in enrichment of the methane was evaluated in the test, which simulate the basic stages of PSA process: a) adsorbent degassing, b) pressure raise in column by feed gas, c) cocurrent desorption with analysis of out flowing gas. The composition of gas phase was accepted as the criterion of the suitability of adsorbent for methane separation from gaseous mixtures. The relationship between methane recovery from gas mixture and texture parameters of adsorbents was found.

  17. Properties of the gold-sulphur interface: from self-assembled monolayers to clusters

    NASA Astrophysics Data System (ADS)

    Bürgi, Thomas

    2015-09-01

    The gold-sulphur interface of self-assembled monolayers (SAMs) was extensively studied some time ago. More recently tremendous progress has been made in the preparation and characterization of thiolate-protected gold clusters. In this feature article we address different properties of the two systems such as their structure, the mobility of the thiolates on the surface and other dynamical aspects, the chirality of the structures and characteristics related to it and their vibrational properties. SAMs and clusters are in the focus of different communities that typically use different experimental approaches to study the respective systems. However, it seems that the nature of the Au-S interfaces in the two cases is quite similar. Recent single crystal X-ray structures of thiolate-protected gold clusters reveal staple motifs characterized by gold ad-atoms sandwiched between two sulphur atoms. This finding contradicts older work on SAMs. However, newer studies on SAMs also reveal ad-atoms. Whether this finding can be generalized remains to be shown. In any case, more and more studies highlight the dynamic nature of the Au-S interface, both on flat surfaces and in clusters. At temperatures slightly above ambient thiolates migrate on the gold surface and on clusters. Evidence for desorption of thiolates at room temperature, at least under certain conditions, has been demonstrated for both systems. The adsorbed thiolate can lead to chirality at different lengths scales, which has been shown both on surfaces and for clusters. Chirality emerges from the organization of the thiolates as well as locally at the molecular level. Chirality can also be transferred from a chiral surface to an adsorbate, as evidenced by vibrational spectroscopy.

  18. Electronic structure of benzene adsorbed on Ni and Cu surfaces

    SciTech Connect

    Weinelt, M.; Nilsson, A.; Wassdahl, N.

    1997-04-01

    Benzene has for a long time served as a prototype adsorption system of large molecules. It adsorbs with the molecular plane parallel to the surface. The bonding of benzene to a transition metal is typically viewed to involve the {pi} system. Benzene adsorbs weakly on Cu and strongly on Ni. It is interesting to study how the adsorption strength is reflected in the electronic structure of the adsorbate-substrate complex. The authors have used X-ray Emission (XE) and X-ray Absorption (XA) spectroscopies to selectively study the electronic states localized on the adsorbed benzene molecule. Using XES the occupied states can be studies and with XAS the unoccupied states. The authors have used beamline 8.0 and the Swedish endstation equipped with a grazing incidence x-ray spectrometer and a partial yield absorption detector. The resolution in the XES and XAS were 0.5 eV and 0.05 eV, respectively.

  19. Theory of Covalent Adsorbate Frontier Orbital Energies on Functionalized Light-Absorbing Semiconductor Surfaces.

    PubMed

    Yu, Min; Doak, Peter; Tamblyn, Isaac; Neaton, Jeffrey B

    2013-05-16

    Functional hybrid interfaces between organic molecules and semiconductors are central to many emerging information and solar energy conversion technologies. Here we demonstrate a general, empirical parameter-free approach for computing and understanding frontier orbital energies - or redox levels - of a broad class of covalently bonded organic-semiconductor surfaces. We develop this framework in the context of specific density functional theory (DFT) and many-body perturbation theory calculations, within the GW approximation, of an exemplar interface, thiophene-functionalized silicon (111). Through detailed calculations taking into account structural and binding energetics of mixed-monolayers consisting of both covalently attached thiophene and hydrogen, chlorine, methyl, and other passivating groups, we quantify the impact of coverage, nonlocal polarization, and interface dipole effects on the alignment of the thiophene frontier orbital energies with the silicon band edges. For thiophene adsorbate frontier orbital energies, we observe significant corrections to standard DFT (∼1 eV), including large nonlocal electrostatic polarization effects (∼1.6 eV). Importantly, both results can be rationalized from knowledge of the electronic structure of the isolated thiophene molecule and silicon substrate systems. Silicon band edge energies are predicted to vary by more than 2.5 eV, while molecular orbital energies stay similar, with the different functional groups studied, suggesting the prospect of tuning energy alignment over a wide range for photoelectrochemistry and other applications.

  20. Controlling molecular assemblies

    NASA Astrophysics Data System (ADS)

    Dameron, Arrelaine A.

    Using molecules designed to have only specific differences in their functionality, we have explored the influence of molecular conformation on the structural, electronic, and physical properties of self-assembled monolayers using both scanning probe and ensemble techniques. In the former case, we used two structurally similar molecules that differ in the degrees of freedom afforded to each. We found that this influenced the degree of order and conductance of self-assembled monolayers of each molecule, but had little influence of conductance switching of individual molecules inserted in alkanethiolate self-assembled monolayers. We further demonstrated how molecular structure influences phase separation, displace-ability, and molecular mobility of self-assembled monolayers by assembling 1-adamantanethiol on Au{111}. Molecular-resolution imaging of the self-assembled monolayers with the scanning tunneling microscopy confirmed a highly ordered hexagonally close-packed molecular lattice. We found that the 1-adamantanethiolate self-assembled monolayers were susceptible to replacement by the presence of another thiolated species, both from solution and vapor phases. Additionally, we determined that the displacement process is a nucleation and growth mechanism and the structure of the resulting self-assembled monolayers is dependent on the strength of the intermolecular interactions of the displacing molecules. It was hypothesized that 1-adamantanethiolate displacement was driven by a combination of energies gained from the exchange of one self-assembled monolayer for a denser self-assembled monolayer and from the increased stability due to intermolecular interaction forces. Exploiting the susceptibility of the 1-adamantanethiolate self-assembled monolayers to displacement, we have designed a novel patterning strategy, termed 'microdisplacement printing', by combining these sacrificial self-assembled monolayers with microcontact printing. During microdisplacement printing

  1. Modulating electronic, magnetic and chemical properties of MoS2 monolayer sheets by substitutional doping with transition metals

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    Based on first-principles calculations, the effects of substitutional doping with transition-metal (TM) atoms (Co, Ni, Ru, Rh, Pd, Ir, Pt and Au) were investigated on the electronic structure, magnetic property and chemical activity of the molybdenum disulfide (MoS2) monolayer sheet. It is found that all the considered TM atoms are strongly bonded to the sulfur defects. The magnetic properties of MoS2 monolayer sheets can be modulated by embedding TM atoms. The introduced spin magnetic moments are 1.00, 1.00, 1.00, 0.99, and 2.00μB, respectively, for Ir, Rh, Co, Au and Ru doping. The electronic properties of MoS2 monolayer sheets are also significantly changed due to the induced impurity states in the band gap. The chemical activity of the TM-doped MoS2 monolayer sheet (TM-MoS2) is significantly enhanced compared with the undoped sheet. Most TM-MoS2 can strongly adsorb and thus effectively activate the adsorbed O2. It is proposed that the partially occupied d orbitals of the doped TM atoms localized in the vicinity of the Fermi level play a crucial role in adsorbing and activating the adsorbed O2. The adsorption of O2 can in turn modify the electronic structures and magnetic properties of TM-MoS2.

  2. Transition metal decorated graphene-like zinc oxide monolayer: A first-principles investigation

    SciTech Connect

    Lei, Jie; Xu, Ming-Chun; Hu, Shu-Jun

    2015-09-14

    Transition metal (TM) atoms have been extensively employed to decorate the two-dimensional materials, endowing them with promising physical properties. Here, we have studied the adsorption of TM atoms (V, Cr, Mn, Fe, and Co) on graphene-like zinc oxide monolayer (g-ZnO) and the substitution of Zn by TM using first-principles calculations to search for the most likely configurations when TM atoms are deposited on g-ZnO. We found that when a V atom is initially placed on the top of Zn atom, V will squeeze out Zn from the two-dimensional plane then substitute it, which is a no barrier substitution process. For heavier elements (Cr to Co), although the substitution configurations are more stable than the adsorption ones, there is an energy barrier for the adsorption-substitution transition with the height of tens to hundreds meV. Therefore, Cr to Co prefers to be adsorbed on the hollow site or the top of oxygen, which is further verified by the molecular dynamics simulations. The decoration of TM is revealed to be a promising approach in terms of tuning the work function of g-ZnO in a large energy range.

  3. Comparative study of decyl thiocyanate and decanethiol self-assembled monolayers on gold substrates

    NASA Astrophysics Data System (ADS)

    Dreesen, L.; Volcke, C.; Sartenaer, Y.; Peremans, A.; Thiry, P. A.; Humbert, C.; Grugier, J.; Marchand-Brynaert, J.

    2006-09-01

    In a recent paper Ciszek et al. [J.W. Ciszek, M.P. Stewart, J.M. Tour, J. Am. Chem. Soc. 126 (2004) 13172] showed that organic thiocyanates may be an interesting alternative to the use of thiols for thiolate assemblies. We use scanning tunnelling microscopy (STM), infrared reflection absorption and sum-frequency generation spectroscopies (IRRAS and SFG) in order to study the adsorption properties of decyl thiocyanates (DTCN) and compare them to the decanethiol (DT) ones. Firstly, IRRAS measurements show that DTCN molecules form self-assembled monolayers (SAMs) on gold via a thiolate link with the metallic substrate. Secondly, the DTCN SAM on gold is less ordered than the DT one as highlighted by SFG spectroscopy. Indeed, the intensities of the methyl vibration modes vanish while the methylene ones increase when DTCN molecules are adsorbed on the substrate instead of DT. We explain the differences in SAMs quality on the basis of STM measurements which reveal differences in molecular order and packing.

  4. Rupture force of adsorbed self-assembled surfactant layers. Effect of the dielectric exchange force

    NASA Astrophysics Data System (ADS)

    Teschke, O.; Ceotto, G.; de Souza, E. F.

    2001-08-01

    The tip applied force necessary to obtain tip/substrate contact, i.e., rupture force between adsorbed layers of self-assembled surfactant films and atomic force microscope (AFM) tips in water has been measured. A substantial contribution of this rupture force is due to the dielectric exchange force (DEF). The DEF model is in agreement with the observation that the surfactant layer rupture forces are smaller in the thickest layers, where the compactness of the adsorbed film results in the smallest values of the dielectric permittivity. Within experimental accuracy a dielectric permittivity value of ˜4 for bilayers and of ˜36 for monolayers is found.

  5. The Dependence of the Oxidation Enhancement of InP(100) Surface on the Coverage of the Adsorbed Cs

    SciTech Connect

    Sun, Yun

    2010-06-07

    We report the oxidation of the InP(100) surface promoted by adsorbed Cs by synchrotron radiation photoemission. Oxygen exposure causes reduction of the charge transferred to the InP substrate from Cs and the growth of indium oxide and phosphorous oxide. The oxide growth displays a clear dependence on the Cs coverage. The oxidation of phosphorous is negligible up to 1000 L of O{sub 2} exposure when the Cs coverage is less than half a monolayer (ML), but the formation of the second half monolayer of Cs greatly accelerates the oxidation. This different enhancement of the InP oxidation by the first and the second half monolayer of Cs is due to the double layer structure of the adsorbed Cs atoms, and consequently the higher 6s electron density in the Cs atoms when Cs coverage is larger than 0.5 ML.

  6. Lipid monolayer states and their relationships to bilayers.

    PubMed Central

    MacDonald, R C; Simon, S A

    1987-01-01

    Uncommon methods of formation and analysis of lipid monolayers have enabled the recognition of several monolayer states and the identification of that in which molecular organization corresponds closely to that of the bilayer. Monolayers were formed by continuously adding a solution of phospholipid [dimyristoyl phosphatidylcholine in hexane/ethanol, 9:1 (vol/vol)] to the air/water interface of a constant-area trough. This procedure generates unconventional surface pressure (pi)-surface concentration (gamma) isotherms, which for liquid-crystalline monolayers consist of straight lines with three prominent intersections, two of which are not apparent in conventional pi-A isotherms. The regions of linear change of pi are explicable in terms of the area dependence of alkyl chain entropy. The two breaks at lower pi delimit states in which both chains lie parallel to the surface. The third occurs at collapse, which corresponds to a true equilibrium for unstressed liposomes. Mechanical and thermodynamic properties of bilayers, particularly phase-transition parameters, correspond closely to those of monolayers with which they are in equilibrium. Images PMID:3473494

  7. Structure and Function Evolution of Thiolate Monolayers on Gold

    SciTech Connect

    Grant Alvin Edwards

    2006-05-01

    The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (inbred reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.

  8. Diacetylene mixed Langmuir monolayers for interfacial polymerization.

    PubMed

    Ariza-Carmona, Luisa; Rubia-Payá, Carlos; García-Espejo, G; Martín-Romero, María T; Giner-Casares, Juan J; Camacho, Luis

    2015-05-19

    Polydiacetylene (PDA) and its derivatives are promising materials for applications in a vast number of fields, from organic electronics to biosensing. PDA is obtained through polymerization of diacetylene (DA) monomers, typically using UV irradiation. DA polymerization is a 1-4 addition reaction with both initiation and growth steps with topochemical control, leading to the "blue" polymer form as primary reaction product in bulk and at interfaces. Herein, the diacetylene monomer 10,12-pentacosadiynoic acid (DA) and the amphiphilic cationic N,N'-dioctadecylthiapentacarbocyanine (OTCC) have been used to build a mixed Langmuir monolayer. The presence of OTCC imposes a monolayer supramolecular structure instead of the typical trilayer of pure DA. Surface pressure, Brewster angle microscopy, and UV-vis reflection spectroscopy measurements, as well as computer simulations, have been used to assess in detail the supramolecular structure of the DA:OTCC Langmuir monolayer. Our experimental results indicate that the DA and OTCC molecules are sequentially arranged, with the two OTCC alkyl chains acting as spacing diacetylene units. Despite this configuration is expected to prevent photopolymerization of DA, the polymerization takes place without phase segregation, thus exclusively leading to the red polydiacetylene form. We propose a simple model for the initial formation of the "blue" or "red" PDA forms as a function of the relative orientation of the DA units. The structural insights and the proposed model concerning the supramolecular structure of the "blue" and "red" forms of the PDA are aimed at the understanding of the relation between the molecular and macroscopical features of PDAs.

  9. Monolayer coated aerogels and method of making

    DOEpatents

    Zemanian, Thomas Samuel; Fryxell, Glen; Ustyugov, Oleksiy A.

    2006-03-28

    Aerogels having a monolayer coating are described. The aerogel and a monolayer forming precursor are provided in a supercritical fluid, whereupon the aerogel and the monolayer forming precursor are reacted in said supercritical fluid to form a covalent bond between the aerogel and the monolayer forming precursor. Suitable aerogels are ceramic oxides such as silica, alumina, aluminosilicate, and combinations thereof. Suitable monolayer forming precursors include alkyl silanes, chlorosilanes, boranes, chloroboranes, germanes, and combinations thereof. The method may also include providing a surface preparation agent such as water, or hydroetching an aerogel to enhance the coating of the monolayer.

  10. FTIR Studies Of Molecular Assemblies On Solid Surfaces

    NASA Astrophysics Data System (ADS)

    Hallmark, V. M.; Shih, L. B.; Stroeve, P.; Rabolt, J. F.

    1989-12-01

    The first observation of spontaneous assembly from solution of a well-ordered polymer monolayer is reported for the system poly(1-octadecene-co-maleic anhydride) adsorbed from ethanol solution onto silver substrates. Analysis by grazing incidence reflection infrared spectroscopy suggests that these monolayers compare quite favorably in terms of orientational order with Langmuir-Blodgett films made from the same material. Thermal stability of these films is significantly enhanced compared to analogous monomeric monolayers of fatty acids.

  11. The entropies of adsorbed molecules.

    PubMed

    Campbell, Charles T; Sellers, Jason R V

    2012-10-31

    Adsorbed molecules are involved in many reactions on solid surface that are of great technological importance. As such, there has been tremendous effort worldwide to learn how to predict reaction rates and equilibrium constants for reactions involving adsorbed molecules. Theoretical calculation of both the rate and equilibrium constants for such reactions requires knowing the entropy and enthalpy of the adsorbed molecule. While much effort has been devoted to measuring and calculating the enthalpies of well-defined adsorbates, few measurements of the entropies of adsorbates have been reported. We present here a new way to determine the standard entropies of adsorbed molecules (S(ad)(0)) on single crystal surfaces from temperature programmed desorption data, prove its accuracy by comparison to entropies measured by equilibrium methods, and apply it to published data to extract new entropies. Most importantly, when combined with reported entropies, we find that at high coverage, they linearly track the entropy of the gas-phase molecule at the same temperature (T), such that S(ad)(0)(T) = 0.70 S(gas)(0)(T) - 3.3R (R = the gas constant), with a standard deviation of only 2R over a range of 50R. These entropies, which are ~2/3 of the gas, are huge compared to most theoretical predictions. This result can be extended to reliably predict prefactors in the Arrhenius rate constant for surface reactions involving such species, as proven here for desorption. PMID:23033909

  12. Concentrating materials covered by molecular imprinted nanofiltration layer with reconfigurability prepared by a surface sol-gel process for gas-selective detection.

    PubMed

    Imahashi, Masahiro; Hayashi, Kenshi

    2013-09-15

    Sensors that recognize molecules are acquired for the comprehensive detection of great many kinds of gases. Adsorbents with high molecular recognition and condensation ability were developed for selective gas sensing with a molecular imprinting technique. Developed adsorbents have multilayer structures consisted of a chemically modified polymer layer on the surface of a substrate covered by a TiO2 gel monolayer by the surface sol-gel process. Ellipsometry measurements showed that the 6-nm-thick layers deposited on the substrate. Cavities of molecular templates were imprinted on these layers, and thus, the film acts as a molecular gas filter without concentrating ability, which could form specific binding sites for various molecules that confirmed using solid-phase microextraction and gas chromatography-mass spectrometry. Gases were selectively absorbed into an accumulating adsorption layer and other gas molecules were blocked by the nanofiltration. These developed adsorbents enabled effective concentration ability and the filtration of gases or odors. In addition, these filters possess the flexibility to be easily configured with specific surface properties to interact with volatile molecules under appropriate conditions. A successful multiplex filter, imprinted simultaneously on an adsorbent with different sites, was demonstrated.

  13. Structural Properties and Phase Transition of Na Adsorption on Monolayer MoS2.

    PubMed

    He, Hai; Lu, Pengfei; Wu, Liyuan; Zhang, Chunfang; Song, Yuxin; Guan, Pengfei; Wang, Shumin

    2016-12-01

    First-principles calculations are performed to investigate the structural stability of Na adsorption on 1H and 1T phases of monolayer MoS2. Our results demonstrate that it is likely to make the stability of distorted 1T phase of MoS2 over the 1H phase through adsorption of Na atoms. The type of distortion depends on the concentration of adsorbed Na atoms and changes from zigzag-like to diamond-like with the increasing of adsorbed Na atom concentrations. Our calculations show that the phase transition from 1H-MoS2 to 1T-MoS2 can be obtained by Na adsorption. We also calculate the electrochemical properties of Na adsorption on MoS2 monolayer. These results indicate that MoS2 is one of potential negative electrodes for Na-ion batteries. PMID:27416903

  14. Structural Properties and Phase Transition of Na Adsorption on Monolayer MoS2

    NASA Astrophysics Data System (ADS)

    He, Hai; Lu, Pengfei; Wu, Liyuan; Zhang, Chunfang; Song, Yuxin; Guan, Pengfei; Wang, Shumin

    2016-07-01

    First-principles calculations are performed to investigate the structural stability of Na adsorption on 1H and 1T phases of monolayer MoS2. Our results demonstrate that it is likely to make the stability of distorted 1T phase of MoS2 over the 1H phase through adsorption of Na atoms. The type of distortion depends on the concentration of adsorbed Na atoms and changes from zigzag-like to diamond-like with the increasing of adsorbed Na atom concentrations. Our calculations show that the phase transition from 1H-MoS2 to 1T-MoS2 can be obtained by Na adsorption. We also calculate the electrochemical properties of Na adsorption on MoS2 monolayer. These results indicate that MoS2 is one of potential negative electrodes for Na-ion batteries.

  15. Structural Properties and Phase Transition of Na Adsorption on Monolayer MoS2.

    PubMed

    He, Hai; Lu, Pengfei; Wu, Liyuan; Zhang, Chunfang; Song, Yuxin; Guan, Pengfei; Wang, Shumin

    2016-12-01

    First-principles calculations are performed to investigate the structural stability of Na adsorption on 1H and 1T phases of monolayer MoS2. Our results demonstrate that it is likely to make the stability of distorted 1T phase of MoS2 over the 1H phase through adsorption of Na atoms. The type of distortion depends on the concentration of adsorbed Na atoms and changes from zigzag-like to diamond-like with the increasing of adsorbed Na atom concentrations. Our calculations show that the phase transition from 1H-MoS2 to 1T-MoS2 can be obtained by Na adsorption. We also calculate the electrochemical properties of Na adsorption on MoS2 monolayer. These results indicate that MoS2 is one of potential negative electrodes for Na-ion batteries.

  16. Electrochemical evaluation of the interfacial capacitance upon phosphorylation of amino acid analogue molecular films.

    PubMed

    Ekeroth, J; Björefors, F; Borgh, A; Lundström, I; Liedberg, B; Konradsson, P

    2001-09-15

    An approach based on electrochemistry to differentiate between phosphorylated and nonphosphorylated amino acid analogues adsorbed on gold is presented. Analogues of serine, threonine, and tyrosine, containing thiohexadecyl headgroups, were synthesized and assembled on gold, and the surface capacitance was evaluated using electrochemical impedance spectroscopy. A procedure for deprotection of tert-butyl phosphate protecting groups, on the monolayer, is also described. Characterizations of the assembled analogues by cyclic voltammetry, infrared spectroscopy, and ellipsometry are used to confirm the insulating properties of the monolayers and the outcome of surface modifications. The results from cyclic voltammetry show good insulating properties for the monolayers even after phosphate deprotection. The infrared measurements reveal well-ordered monolayers, and the thickness from ellipsometry is in good agreement with expectations from molecular modeling. The impedance experiments show a capacitance increase up to 0.6 microF/cm2 as phosphate groups are introduced. The results in this study indicate the possibility of using a surface chemical and impedance spectroscopy approach to detect the kinase/phosphatase activity and kinetics involved in phosphorylation reactions.

  17. A Brief Review of the Relationships Between Monolayer Viscosity, Phase Behavior, Surface Pressure and Temperature Using a Simple Monolayer Viscometer

    PubMed Central

    Alonso, Coralie

    2008-01-01

    The two-dimensional surface shear viscosity, η, of fatty acid monolayers of different chain lengths, measured using a simple magnetic needle viscometer, strongly correlates with the molecular organization in condensed phases and the absolute temperature. η can increase by orders of magnitude at phase boundaries associated with tilted to untilted molecular order, providing the underlying order is semi-crystalline. Hence, untilted, long-range ordered CS phases are the most viscous films. However, despite being untilted, the LS rotator phase is less viscous than certain laterally ordered tilted phases, suggesting a decrease of the Van der Waals interactions due to molecular rotation. In certain regions of the L2 phase, η reaches a maximum before the L2-LS transition, an anomalous behavior correlated with the change in the lattice symmetry of the head group. Surface shear viscosity, even when measured with a macroscopic probe, is particularly sensitive to the microscopic organization of monolayers. PMID:17078656

  18. Tip enhanced Raman spectroscopy, DFT and PED calculations of 4″-trimethylsilylethylsulfanyl-4,4‧-di(phenyleneethynylene)benzene thiol adsorbed on silver

    NASA Astrophysics Data System (ADS)

    Fletcher, Melissa C.; Alexson, Dimitri M.; Moore, Martin M.; Prokes, S. M.; Glembocki, Orest; Vivoni, Alberto; McCoy, Rhonda; Mishra, Soni; Tandon, Poonam; Hosten, Charles M.

    2015-11-01

    Monolayers of α,ω-dithiol oligo(phenyleneethynlene) molecules are critical to the field of molecular electronics because of their abilities to form bonds with many metallic surfaces and rectify current. In this study Fourier Transformation-Raman, surface-enhanced Raman scattering (SERS) spectroscopy and Tip-enhanced Raman Spectroscopy (TERS) were used to characterize a selectively oriented self-assembled monolayer of 4″-trimethylsilylethylsulfanyl-4,4‧-bis-(phenyleneethynylene)benzenethiol (OPE‧) on silver coated nanospheres. Selective orientation was achieved by synthesizing 4″-trimethylsilylethylsulfanyl-4,4‧-bis-(phenyleneethynylene)benzene disulfide, which undergoes oxidative dissociation and covalently bonds to the metal surface. The Ag coated nanosphere surfaces were characterized by scanning electron microscopy (SEM), which showed a large area of surface charging. The SERS and TERS spectra show similar results; however, a greater enhancement was achieved with the TERS relative to the SERS spectra. Assignments of vibrational bands were based on DFT calculations performed at the B3LYP level with good agreement between theoretical and experimental values. An average percent difference of 2.5 cm-1 was obtained for the non-CH stretching frequencies and a scaling factor was not applied to theoretically generated frequencies. A red shift of the ν(C-S) peak at 1087 cm-1 was observed when OPE‧ was adsorbed on a Ag surface. Vibrations specific to the trimethylsilylethyl (TMSE) group were visible in the TERS spectra, and disappear upon deprotection.

  19. Interaction of Egg-Sphingomyelin with DOPC in Langmuir Monolayers

    NASA Astrophysics Data System (ADS)

    Hao, Chang-chun; Sun, Run-guang; Zhang, Jing

    2012-12-01

    Lipid rafts are a dynamic microdomain structure found in recent years, enriched in sphingolipids, cholesterol and particular proteins. The change of structure and function of lipid rafts could result in many diseases. In this work, the monolayer miscibility behavior of mixed systems of Egg-Sphingomyelin (ESM) 1 with 2-dioleoyl-sn-glycero-3-phosphocholine was investigated in terms of mean surface area per molecule and excess molecular area ΔAex at certain surface pressure, surface pressure and excess surface pressure Δπex at certain mean molecular area. The stability and compressibility of the mixed monolayers was assessed by the parameters of surface excess Gibbs free energy ΔGex, excess Helmholtz energy ΔHex and elasticity. Thermodynamic analysis indicates ΔAex and Δπex in the binary systems with positive deviations from the ideal behavior, suggesting repulsive interaction. The maximum of ΔGex and ΔHex was at the molar fraction of ESM of 0.6, demonstrating the mixed monolayer was more unstable. The repulsive interaction induced phase separation in the monolayer.

  20. Adsorption isotherm of non-azeotropic solution onto porous adsorbents

    NASA Astrophysics Data System (ADS)

    Bono, A.; Ramlan, N. A.; Anisuzzaman, S. M.; Chu, C. M.; Farm, Y. Y.

    2016-06-01

    Adsorption isotherm is essential component in the understanding of the adsorption process. Several methods of the measurements, analysis and interpretation of adsorption from solution have been reported in the literature. Most of the measurements of adsorption isotherm from solution were involved the measurement of excess isotherm conducted at low region of sorbates concentration. Direct interpretation of excess adsorption isotherm as adsorption isotherm is always been practice. Therefore, in this work a study on the measurement of the adsorption isotherm from solution of non-azeotropic organic solvent mixture onto porous adsorbents for whole range of liquid concentration was conducted. The study included the measurement of excess adsorption isotherm using conventional technique. Theoretical analysis and interpretation of adsorption isotherm from the excess isotherm were conducted using Pseudo Ideal Adsorption, Gibbs Dividing Plane Model and Langmuir-Fruendlich binary isotherm model. For organic solvents, acetone and propanol were chosen as the adsorbates due to the non-azeotropic properties in the mixture. Activated carbon and silicalite were chosen as adsorbents due to the different in their porosity such as macro porous and micro porous structure. The result of the study has revealed that the adsorption isotherm of non-azeotropic mixture onto activated carbon and silicalite can be interpreted as monolayer type of adsorption.

  1. Fluctuations in the number of irreversibly adsorbed particles

    NASA Astrophysics Data System (ADS)

    Adamczyk, Zbigniew; Szyk-Warszyńska, Lilianna; Siwek, B.; Weroński, P.

    2000-12-01

    Fluctuations in the number of colloid particles adsorbed irreversibly under pure diffusion transport conditions were determined as a function of surface density and ionic strength of the suspension. The experiments were carried out for monodisperse polystyrene latex particles of micrometer size range adsorbing irreversibly at mica surface. The surface density of adsorbed particles at various areas was determined using the direct microscope observation method. A new experimental cell was used enabling in situ observations of particles adsorption under conditions of negligible gravity effects. It was found that the particle density fluctuations for high ionic strength were in a good agreement with the theoretical results derived from the random sequential adsorption (RSA) model. Also, the theoretical results stemming from the equilibrium scaled particle theory reflected the experimental data satisfactorily. For lower ionic strength a deviation from the hard sphere behavior was experimentally demonstrated. This effect due to the repulsive electrostatic interactions was interpreted in terms of the effective hard particle concept. The universal dependence of variance on particle density obtained in this way was found in a good agreement with the RSA model for all ionic strength. These results proved that fluctuations in particle density of monolayer formed under diffusional conditions differ fundamentally from these obtained under ballistic transport conditions.

  2. Mechanical Properties of Monolayers on the Surface of Water

    NASA Astrophysics Data System (ADS)

    Bohanon, Thomas Michael

    Heneicosanoic acid monolayers have many phases over a temperature range of 0 to 30^circ C. The structures of these phases have been well studied. All of these phases are ordered, and two of the phases appear to have long range order. However, little is known about the molecular interactions in these phases. In this work the shear modulus and viscosity of these phases are studied using a torsion pendulum. In order to study the mechanical properties in some phases of these monolayers, it was necessary to alter the accepted manner of compressing and measuring the surface pressure of these films. Generating capillary waves with an alternating electric field gradient is a non-contact way to measure the surface tension and study the mechanical properties of monolayers. The surface elasticity can be deduced and film inhomogeneity can be determined. A fiber optic detection system has been incorporated into a capillary wave apparatus. This instrument is also used to measure anomalous viscoelastic properties of valinomycin monolayers. Capillary wave measurements have been performed on uniaxially compressed Langmuir films both parallel and perpendicular to the direction of compression. A large change in surface tension anisotropy with a small change in pH was observed, signaling a phase transition. An apparatus that radially compresses monolayers on the surface of water was constructed. This mode of compression prevents the anisotropy that is observed in films that are compressed uniaxially. The area is changed using an elastic band stretched around twelve fingers which move synchronously. Isotherms obtained using this apparatus illustrate the difference between uniaxial compression and radial compression for a heneicosanoic acid monolayer. The shear response of heneicosanoic acid monolayers at different temperatures and pressures, has been studied using a torsion pendulum. The data fit well to a stretched exponential. This suggests that there is a continuous distribution of

  3. Isomerization reactions on single adsorbed molecules.

    PubMed

    Morgenstern, Karina

    2009-02-17

    Molecular switches occur throughout nature. In one prominent example, light induces the isomerization of retinal from the compact 11-cis form to the elongated all-trans form, a conversion that triggers the transformation of light into a neural impulse in the eye. Applying these natural principles to synthetic systems offers a promising way to construct smaller and faster nanoelectronic devices. In such systems, electronic switches are essential components for storage and logical operations. The development of molecular switches on the single-molecule level would represent a major step toward incorporating molecules as building units into nanoelectronic circuits. Molecular switches must be both reversible and bistable. To meet these requirements, a molecule must have at least two different thermally stable forms and a way to repeatedly interconvert between those forms based on changes in light, heat, pressure, magnetic or electric fields, pH, mechanical forces, or electric currents. The conversion should be connected to a measurable change in electronic, optical, magnetic, or mechanical properties. Because isomers can differ significantly in physical and chemical properties, isomerization could serve as a molecular switching mechanism. Integration of molecular switches into larger circuits will probably require arranging them on surfaces, which will require a better understanding of isomerization reactions in these environments. In this Account, we describe our scanning tunneling microscopy studies of the isomerization of individual molecules adsorbed on metal surfaces. Investigating chlorobenzene and azobenzene derivatives on the fcc(111) faces of Ag, Cu, and Au, we explored the influence of substituents and the substrate on the excitation mechanism of the isomerization reaction induced by inelastically tunneling electrons. We achieved an irreversible configurational (cis-trans) isomerization of individual 4-dimethyl-amino-azobenzene-4-sulfonic acid molecules on Au

  4. The influence of the structure of the Au(110) surface on the ordering of a monolayer of cytochrome P450 reductase at the Au(110)/phosphate buffer interface

    PubMed Central

    Smith, C. I.; Convery, J. H.; Khara, B.; Scrutton, N. S.; Weightman, P.

    2016-01-01

    The reflection anisotropy spectra (RAS) observed initially from Au(110)/phosphate buffer interfaces at applied potentials of −0.652 and 0.056 V are very similar to the spectra observed from ordered Au(110) (1 × 3) and anion induced (1 × 1) surface structures respectively. These RAS profiles transform to a common profile after cycling the potential between these two values over 72 h indicating the formation of a less ordered surface. The RAS of a monolayer of a P499C variant of the human flavoprotein cytochrome P450 reductase adsorbed at 0.056 V at an ordered Au(110)/phosphate buffer interface is shown to arise from an ordered layer in which the optical dipole transitions are in a plane that is orientated roughly normal to the surface and parallel to either the [11̄0] or [001] axes of the Au(110) surface. The same result was found previously for adsorption of P499C on an ordered interface at −0.652 V. The adsorption of P499C at the disordered surface does not result in the formation of an ordered monolayer confirming that the molecular ordering is strongly influenced by both the local structure and the long range macroscopic order of the Au(110) surface.

  5. The influence of the structure of the Au(110) surface on the ordering of a monolayer of cytochrome P450 reductase at the Au(110)/phosphate buffer interface

    PubMed Central

    Smith, C. I.; Convery, J. H.; Khara, B.; Scrutton, N. S.; Weightman, P.

    2016-01-01

    The reflection anisotropy spectra (RAS) observed initially from Au(110)/phosphate buffer interfaces at applied potentials of −0.652 and 0.056 V are very similar to the spectra observed from ordered Au(110) (1 × 3) and anion induced (1 × 1) surface structures respectively. These RAS profiles transform to a common profile after cycling the potential between these two values over 72 h indicating the formation of a less ordered surface. The RAS of a monolayer of a P499C variant of the human flavoprotein cytochrome P450 reductase adsorbed at 0.056 V at an ordered Au(110)/phosphate buffer interface is shown to arise from an ordered layer in which the optical dipole transitions are in a plane that is orientated roughly normal to the surface and parallel to either the [11̄0] or [001] axes of the Au(110) surface. The same result was found previously for adsorption of P499C on an ordered interface at −0.652 V. The adsorption of P499C at the disordered surface does not result in the formation of an ordered monolayer confirming that the molecular ordering is strongly influenced by both the local structure and the long range macroscopic order of the Au(110) surface. PMID:27630536

  6. Efficient Lateral Electron Transport inside a Monolayer of Aromatic Amines Anchored on Nanocrystalline Metal Oxide Films.

    PubMed

    Bonhôte, P; Gogniat, E; Tingry, S; Barbé, C; Vlachopoulos, N; Lenzmann, F; Comte, P; Grätzel, M

    1998-02-26

    A monolayer of a phosphonated triarylamine adsorbed on nanocrystalline TiO2, ZrO2, or Al2O3 film deposited on conducting glass displays reversible electrochemical and electrochromic behavior although the redox potential of the electroactive molecules (0.80 V vs NHE) lies in the forbidden band of the semiconducting or insulating oxides. The mechanism of charge transport was found to involve hole injection from the conducting support followed by lateral electron hopping within the monolayer. The apparent diffusion coefficient ranged from 2.8 × 10(-12) m(2) s(-1) in the neat 1-ethyl-2-methylimidazolium bis(trifluoromethylsulfonyl)imide (EtMeIm(+)Tf2N(-)) to 1.1 × 10(-11) m(2) s(-1) in acetonitrile + 2 M EtMeIm(+)Tf2N(-). A percolation threshold for electronic conductivity was found at a surface coverage corresponding to 50% of a full monolayer. PMID:27577008

  7. RADIOLYSIS OF ORGANIC COMPOUNDS IN THE ADSORBED STATE

    DOEpatents

    Sutherland, J.W.; Allen, A.O.

    1961-10-01

    >A method of forming branch chained hydrocarbons by means of energetic penetrating radiation is described. A solid zeolite substrate is admixed with a cobalt ion and is irradiated with a hydrocarbon adsorbed therein. Upon irradiation with gamma rays, there is an increased yield of branched and lower molecular straight chain compounds. (AEC)

  8. Inhibiting plasmon catalyzed conversion of para-nitrothiophenol on monolayer film of Au nanoparticles probed by surface enhanced Raman spectroscopy.

    PubMed

    Weng, Hua-Yi; Guo, Qing-Hua; Wang, Xing-Rong; Xu, Min-Min; Yuan, Ya-Xian; Gu, Ren-Ao; Yao, Jian-Lin

    2015-11-01

    The plasmon catalyzed surface reaction has been attracted considerable attention due to its promising application in heterogeneous catalysis. This kind of plasmon catalysis played bilateral roles in driving the unconventional reactions or destructing the surface molecule layer. The acceleration or inhibition on this catalysis is still remained significant challenge. In this paper, monolayer film of Au nanoparticles was fabricated at air/water interface as substrates both for surface enhanced Raman spectroscopy (SERS) and plasmon catalyzed surface reaction. The influence from several issues, involving surfactants, coadsorption species, the solvent and water, were systemically investigated to probe the acceleration and inhibition on the plasmon catalysis reaction. The concentration and molecular weight of surfactant polyvinylpyrrolidone (PVP) exhibited significant influence in the reactive activity for the plasmon catalyzed dimerization of para-nitrothiophenol (PNTP) to p,p'-dimercaptoazobenzene (DMAB). A suitable molecular weight of 10,000 and concentration of 10mg/mL were beneficial for improving the conversion efficiency of PNTP to DMAB. The higher molar ratio of coadsorbed 1-octanethiol and the aprotic solvents resulted in the inhibition of dimerization because 1-octanethiol occupied the surface sites to isolate the adsorbed PNTP molecules with a larger distance and lack of proton source. The plasmon catalysis occurred in ionic liquids suggested that water was essential for the dimerization of PNTP, in which it was used to accelerate the reaction rate and severed as the hydrogen source.

  9. Adsorption behavior of Fe atoms on a naphthalocyanine monolayer on Ag(111) surface

    NASA Astrophysics Data System (ADS)

    Yan, Ling-Hao; Wu, Rong-Ting; Bao, De-Liang; Ren, Jun-Hai; Zhang, Yan-Fang; Zhang, Hai-Gang; Huang, Li; Wang, Ye-Liang; Du, Shi-Xuan; Huan, Qing; Gao, Hong-Jun

    2015-07-01

    Adsorption behavior of Fe atoms on a metal-free naphthalocyanine (H2Nc) monolayer on Ag(111) surface at room temperature has been investigated using scanning tunneling microscopy combined with density functional theory (DFT) based calculations. We found that the Fe atoms were adsorbed on the centers of H2Nc molecules and formed Fe-H2Nc complexes at low coverage. DFT calculations show that Fe sited in the center of the molecule is the most stable configuration, in good agreement with the experimental observations. After an Fe-H2Nc complex monolayer was formed, the extra Fe atoms self-assembled to Fe clusters of uniform size and adsorbed dispersively at the interstitial positions of Fe-H2Nc complex monolayer. Therefore, the H2Nc monolayer grown on Ag(111) could be a good template to grow dispersed magnetic metal atoms and clusters at room temperature for further investigation of their magnetism-related properties. Project supported by the National Natural Science Foundation of China (Grant Nos. 61390501, 51325204, and 11204361), the National Basic Research Program of China (Grant Nos. 2011CB808401 and 2011CB921702), the National Key Scientific Instrument and Equipment Development Project of China (Grant No. 2013YQ1203451), the National Supercomputing Center in Tianjin, China, and the Chinese Academy of Sciences.

  10. Atomic and molecular adsorption on Au(111)

    SciTech Connect

    Santiago-Rodríguez, Yohaselly; Herron, Jeffrey A.; Curet-Arana, María C.; Mavrikakis, Manos

    2014-09-01

    Periodic self-consistent density functional theory (DFT-GGA) calculations were used to study the adsorption of several atomic species, molecular species and molecular fragments on the Au(111) surface with a coverage of 1/4 monolayer (ML). Binding geometries, binding energies, and diffusion barriers were calculated for 27 species. Furthermore, we calculated the surface deformation energy associated with the binding events. The binding strength for all the analyzed species can be ordered as follows: NH3 < NO < CO < CH3 < HCO < NH2 < COOH < OH < HCOO < CNH2 < H < N < NH < NOH < COH < Cl,< HCO3 < CH2 < CN b HNO < O < F < S < C < CH. Although the atomic species preferred to bind at the three-fold fcc site, no tendency was observed in site preference for the molecular species and fragments. The intramolecular and adsorbate-surface vibrational frequencies were calculated for all the adsorbates on their most energetically stable adsorption site. Most of the theoretical binding energies and frequencies agreed with experimental values reported in the literature. In general, the values obtained with the PW91 functional are more accurate than RPBE in reproducing these experimental binding energies. The energies of the adsorbed species were used to calculate the thermochemical potential energy surfaces for decomposition of CO, NO, N2, NH3 and CH4, oxidation of CO, and hydrogenation of CO, CO2 and NO, giving insight into the thermochemistry of these reactions on gold nanoparticles. These potential energy surfaces demonstrated that: the decomposition of species is not energetically favorable on Au(111); the desorption of NH3, NO and CO are more favorable than their decomposition; the oxidation of CO and hydrogenation of CO and NO on Au(111) to form HCO and HNO, respectively, are also thermodynamically favorable.

  11. 2D attenuated total reflectance infrared spectroscopy reveals ultrafast vibrational dynamics of organic monolayers at metal-liquid interfaces

    NASA Astrophysics Data System (ADS)

    Kraack, Jan Philip; Lotti, Davide; Hamm, Peter

    2015-06-01

    We present two-dimensional infrared (2D IR) spectra of organic monolayers immobilized on thin metallic films at the solid liquid interface. The experiments are acquired under Attenuated Total Reflectance (ATR) conditions which allow a surface-sensitive measurement of spectral diffusion, sample inhomogeneity, and vibrational relaxation of the monolayers. Terminal azide functional groups are used as local probes of the environment and structural dynamics of the samples. Specifically, we investigate the influence of different alkyl chain-lengths on the ultrafast dynamics of the monolayer, revealing a smaller initial inhomogeneity and faster spectral diffusion with increasing chain-length. Furthermore, by varying the environment (i.e., in different solvents or as bare sample), we conclude that the most significant contribution to spectral diffusion stems from intra- and intermolecular dynamics within the monolayer. The obtained results demonstrate that 2D ATR IR spectroscopy is a versatile tool for measuring interfacial dynamics of adsorbed molecules.

  12. 2D attenuated total reflectance infrared spectroscopy reveals ultrafast vibrational dynamics of organic monolayers at metal-liquid interfaces.

    PubMed

    Kraack, Jan Philip; Lotti, Davide; Hamm, Peter

    2015-06-01

    We present two-dimensional infrared (2D IR) spectra of organic monolayers immobilized on thin metallic films at the solid liquid interface. The experiments are acquired under Attenuated Total Reflectance (ATR) conditions which allow a surface-sensitive measurement of spectral diffusion, sample inhomogeneity, and vibrational relaxation of the monolayers. Terminal azide functional groups are used as local probes of the environment and structural dynamics of the samples. Specifically, we investigate the influence of different alkyl chain-lengths on the ultrafast dynamics of the monolayer, revealing a smaller initial inhomogeneity and faster spectral diffusion with increasing chain-length. Furthermore, by varying the environment (i.e., in different solvents or as bare sample), we conclude that the most significant contribution to spectral diffusion stems from intra- and intermolecular dynamics within the monolayer. The obtained results demonstrate that 2D ATR IR spectroscopy is a versatile tool for measuring interfacial dynamics of adsorbed molecules.

  13. Rotary adsorbers for continuous bulk separations

    DOEpatents

    Baker, Frederick S.

    2011-11-08

    A rotary adsorber for continuous bulk separations is disclosed. The rotary adsorber includes an adsorption zone in fluid communication with an influent adsorption fluid stream, and a desorption zone in fluid communication with a desorption fluid stream. The fluid streams may be gas streams or liquid streams. The rotary adsorber includes one or more adsorption blocks including adsorbent structure(s). The adsorbent structure adsorbs the target species that is to be separated from the influent fluid stream. The apparatus includes a rotary wheel for moving each adsorption block through the adsorption zone and the desorption zone. A desorption circuit passes an electrical current through the adsorbent structure in the desorption zone to desorb the species from the adsorbent structure. The adsorbent structure may include porous activated carbon fibers aligned with their longitudinal axis essentially parallel to the flow direction of the desorption fluid stream. The adsorbent structure may be an inherently electrically-conductive honeycomb structure.

  14. Binary functionalization of H:Si(111) surfaces by alkyl monolayers with different linker atoms enhances monolayer stability and packing.

    PubMed

    Arefi, Hadi H; Nolan, Michael; Fagas, Giorgos

    2016-05-14

    Alkyl monolayer modified Si forms a class of inorganic-organic hybrid materials with applications across many technologies such as thin-films, fuel/solar-cells and biosensors. Previous studies have shown that the linker atom, through which the monolayer binds to the Si substrate, and any tail group in the alkyl chain, can tune the monolayer stability and electronic properties. In this paper we study the H:Si(111) surface functionalized with binary SAMs: these are composed of alkyl chains that are linked to the surface by two different linker groups. Aiming to enhance SAM stability and increase coverage over singly functionalized Si, we examine with density functional theory simulations that incorporate vdW interactions, a range of linker groups which we denote as -X-(alkyl) with X = CH2, O(H), S(H) or NH(2) (alkyl = C6 and C12 chains). We show how the stability of the SAM can be enhanced by adsorbing alkyl chains with two different linkers, e.g. Si-[C, NH]-alkyl, through which the adsorption energy is increased compared to functionalization with the individual -X-alkyl chains. Our results show that it is possible to improve stability and optimum coverage of alkyl functionalized SAMs linked through a direct Si-C bond by incorporating alkyl chains linked to Si through a different linker group, while preserving the interface electronic structure that determines key electronic properties. This is important since any enhancement in stability and coverage to give more densely packed monolayers will result in fewer defects. We also show that the work function can be tuned within the interval of 3.65-4.94 eV (4.55 eV for bare H:Si(111)).

  15. Organic Monolayer Protected Topological Surface State.

    PubMed

    Yang, Hung-Hsiang; Chu, Yu-Hsun; Lu, Chun-I; Butler, Christopher John; Sankar, Raman; Chou, Fang-Cheng; Lin, Minn-Tsong

    2015-10-14

    Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)/Bi2Se3 and Fe/PTCDA/Bi2Se3 heterointerfaces are investigated using scanning tunneling microscopy and spectroscopy. The close-packed self-assembled PTCDA monolayer possesses big molecular band gap and weak molecule-substrate interactions, which leaves the Bi2Se3 topological surface state intact under PTCDA. Formation of Fe-PTCDA hybrids removes interactions between the Fe dopant and the Bi2Se3 surface, such as doping effects and Coulomb scattering. Our findings reveal the functionality of PTCDA to prevent dopant disturbances in the TSS and provide an effective alternative for interface designs of realistic TI devices.

  16. Nanofiltration across Defect-Sealed Nanoporous Monolayer Graphene

    DOE PAGES

    O'Hern, Sean C.; Jang, Doojoon; Bose, Suman; Idrobo Tapia, Juan Carlos; Song, Yi; Laoui, Tahar; Kong, Jing; Karnik, Rohit

    2015-04-27

    Monolayer nanoporous graphene represents an ideal membrane for molecular separations, but its practical realization is impeded by leakage through defects in the ultrathin graphene. Here, we report a multiscale leakage-sealing process that exploits the nonpolar nature and impermeability of pristine graphene to selectively block defects, resulting in a centimeter-scale membrane that can separate two fluid reservoirs by an atomically thin layer of graphene. After introducing subnanometer pores in graphene, the membrane exhibited rejection of multivalent ions and small molecules and water flux consistent with prior molecular dynamics simulations. The results indicate the feasibility of constructing defect-tolerant monolayer graphene membranes formore » nanofiltration, desalination, and other separation processes.« less

  17. Nanofiltration across Defect-Sealed Nanoporous Monolayer Graphene.

    PubMed

    O'Hern, Sean C; Jang, Doojoon; Bose, Suman; Idrobo, Juan-Carlos; Song, Yi; Laoui, Tahar; Kong, Jing; Karnik, Rohit

    2015-05-13

    Monolayer nanoporous graphene represents an ideal membrane for molecular separations, but its practical realization is impeded by leakage through defects in the ultrathin graphene. Here, we report a multiscale leakage-sealing process that exploits the nonpolar nature and impermeability of pristine graphene to selectively block defects, resulting in a centimeter-scale membrane that can separate two fluid reservoirs by an atomically thin layer of graphene. After introducing subnanometer pores in graphene, the membrane exhibited rejection of multivalent ions and small molecules and water flux consistent with prior molecular dynamics simulations. The results indicate the feasibility of constructing defect-tolerant monolayer graphene membranes for nanofiltration, desalination, and other separation processes. PMID:25915708

  18. Monolayer-induced band shifts at Si(100) and Si(111) surfaces

    SciTech Connect

    Mäkinen, A. J. Kim, Chul-Soo; Kushto, G. P.

    2014-01-27

    We report our study of the interfacial electronic structure of Si(100) and Si(111) surfaces that have been chemically modified with various organic monolayers, including octadecene and two para-substituted benzene derivatives. X-ray photoelectron spectroscopy reveals an upward band shift, associated with the assembly of these organic monolayers on the Si substrates, that does not correlate with either the dipole moment or the electron withdrawing/donating character of the molecular moieties. This suggests that the nature and quality of the self-assembled monolayer and the intrinsic electronic structure of the semiconductor material define the interfacial electronic structure of the functionalized Si(100) and Si(111) surfaces.

  19. Affinity Adsorbents Based on Carriers Activated by Epoxy-compounds

    NASA Astrophysics Data System (ADS)

    Klyashchitskii, B. A.; Kuznetsov, P. V.

    1984-10-01

    The review is devoted to the synthesis and applications of affinity adsorbents based on carriers activated by epoxy-compounds. The methods for the introduction of epoxy-groups into carriers of different chemical types are discussed and conditions for the immobilisation of three-dimensional spacers and low-molecular-weight and polymeric ligands on carriers containing epoxy-groups are considered. Data are presented on the properties and applications of adsorbents of this type in affinity chromatography. The bibliography includes 144 references.

  20. Hydrogen molecule on lithium adsorbed graphene: A DFT study

    NASA Astrophysics Data System (ADS)

    Kaur, Gagandeep; Gupta, Shuchi; Gaganpreet, Dharamvir, Keya

    2016-05-01

    Electronic structure calculations for the adsorption of molecular hydrogen on lithium (Li) decorated and pristine graphene have been studied systematically using SIESTA code [1] within the framework of the first-principle DFT under the Perdew-Burke-Ernzerhof (PBE) form of the generalized gradient approximation (GGA)[2], including spin polarization. The energy of adsorption of hydrogen molecule on graphene is always enhanced by the presence of co-adsorbed lithium. The most efficient adsorption configuration is when H2 is lying parallel to lithium adsorbed graphene which is in contrast to its adsorption on pristine graphene (PG) where it prefers perpendicular orientation.

  1. Large-Scale Synthesis and Systematic Photoluminescence Properties of Monolayer MoS2 on Fused Silica.

    PubMed

    Wan, Yi; Zhang, Hui; Zhang, Kun; Wang, Yilun; Sheng, Bowen; Wang, Xinqiang; Dai, Lun

    2016-07-20

    Monolayer MoS2, with fascinating mechanical, electrical, and optical properties, has generated enormous scientific curiosity and industrial interest. Controllable and scalable synthesis of monolayer MoS2 on various desired substrates has significant meaning in both basic scientific research and device application. Recent years have witnessed many advances in the direct synthesis of single-crystalline MoS2 flakes or their polycrystalline aggregates on numerous diverse substrates, such as SiO2-Si, mica, sapphire, h-BN, and SrTiO3, etc. In this work, we used the dual-temperature-zone atmospheric-pressure chemical vapor deposition method to directly synthesize large-scale monolayer MoS2 on fused silica, the most ordinary transparent insulating material in daily life. We systematically investigated the photoluminescence (PL) properties of monolayer MoS2 on fused silica and SiO2-Si substrates, which have different thermal conductivity coefficients and thermal expansion coefficients. We found that there exists a stronger strain on monolayer MoS2 grown on fused silica, and the strain becomes more obvious as temperature decreases. Moreover, the monolayer MoS2 grown on fused silica exhibits the unique trait of a fractal shape with tortuous edges and has stronger adsorbability. The monolayer MoS2 grown on fused silica may find application in sensing, energy storage, and transparent optoelectronics, etc. PMID:27338112

  2. Large-Scale Synthesis and Systematic Photoluminescence Properties of Monolayer MoS2 on Fused Silica.

    PubMed

    Wan, Yi; Zhang, Hui; Zhang, Kun; Wang, Yilun; Sheng, Bowen; Wang, Xinqiang; Dai, Lun

    2016-07-20

    Monolayer MoS2, with fascinating mechanical, electrical, and optical properties, has generated enormous scientific curiosity and industrial interest. Controllable and scalable synthesis of monolayer MoS2 on various desired substrates has significant meaning in both basic scientific research and device application. Recent years have witnessed many advances in the direct synthesis of single-crystalline MoS2 flakes or their polycrystalline aggregates on numerous diverse substrates, such as SiO2-Si, mica, sapphire, h-BN, and SrTiO3, etc. In this work, we used the dual-temperature-zone atmospheric-pressure chemical vapor deposition method to directly synthesize large-scale monolayer MoS2 on fused silica, the most ordinary transparent insulating material in daily life. We systematically investigated the photoluminescence (PL) properties of monolayer MoS2 on fused silica and SiO2-Si substrates, which have different thermal conductivity coefficients and thermal expansion coefficients. We found that there exists a stronger strain on monolayer MoS2 grown on fused silica, and the strain becomes more obvious as temperature decreases. Moreover, the monolayer MoS2 grown on fused silica exhibits the unique trait of a fractal shape with tortuous edges and has stronger adsorbability. The monolayer MoS2 grown on fused silica may find application in sensing, energy storage, and transparent optoelectronics, etc.

  3. Structural precursor to adsorbate-induced reconstruction: C on Ni(100)

    SciTech Connect

    Terborg, R.; Hoeft, J.T.; Polcik, M.; Lindsay, R.; Schaff, O.; Bradshaw, A.M.; Toomes, R.; Booth, N.A.; Woodruff, D.P.; Rotenberg, E.; Denlinger, J.

    1999-10-01

    The local structure around adsorbed carbon atoms on Ni(100) has been determined at low coverage as well as in the 0.5 monolayer (2{times}2)p4g {open_quotes}clock{close_quotes} reconstruction by scanned energy mode photoelectron diffraction. At low coverage, there is no radial strain of the Ni atoms surrounding the adsorbed carbon, contrary to previous suggestions. None of the C-Ni near-neighbor distances are changed by reconstruction, but the Ni-Ni nearest-neighbor distance in the top layer increases significantly, showing that the adsorbate-induced compressive stress is associated with Ni-Ni, rather than Ni-C, repulsion. {copyright} {ital 1999} {ital The American Physical Society}

  4. Low-cost magnetic adsorbent for As(III) removal from water: adsorption kinetics and isotherms.

    PubMed

    Kango, Sarita; Kumar, Rajesh

    2016-01-01

    Magnetite nanoparticles as adsorbent for arsenic (As) were coated on sand particles. The coated sand was used for the removal of highly toxic element 'As(III)' from drinking water. Here, batch experiments were performed with the variation of solution pH, adsorbent dose, contact time and initial arsenic concentration. The adsorbent showed significant removal efficiency around 99.6 % for As(III). Analysis of adsorption kinetics revealed that the adsorbent follows pseudo-second-order kinetics model showing R (2) = 0.999, whereas for pseudo-first-order kinetics model, the value of R (2) was 0.978. In the case of adsorption equilibrium, the data is well fitted with Langmuir adsorption isotherm model (R (2) > 0.99), indicating monolayer adsorption of As(III) on the surface of adsorbent. The existence of commonly present ions in water influences the removal efficiency of As(III) minutely in the following order PO4 (3-) > HCO3 (-) > Cl(-) > SO4 (2-). The obtained adsorbent can be used to overcome the problem of water filtration in rural areas. Moreover, as the nano-magnetite is coated on the sand, it avoids the problem of extraction of nanoparticles from treated water and can easily be removed by a simple filtration process. PMID:26711813

  5. Adsorbate modification of the structural, electronic, and magnetic properties of ferromagnetic fcc {110} surfaces

    NASA Astrophysics Data System (ADS)

    Gunn, D. S. D.; Jenkins, Stephen J.

    2011-03-01

    We identify trends in structural, electronic, and magnetic modifications that occur on ferromagnetic {110} surfaces upon varying either the substrate material or the adsorbate species. First, we have modeled the adsorption of several first-row p-block elements on the surface of fcc Co{110} at two coverages [0.5 and 1.0 monolayer (ML)]. All adsorbates were found to expand the distance between the first and second substrate layers and to contract the distance between the second and third layers. The energetic location of a characteristic trough in the density-of-d-states difference plot correlates with the direction of the adsorbate magnetic coupling to the surface, and a trend of antiferromagnetic to ferromagnetic coupling to the surface was observed across the elements from boron to fluorine. A high fluorine adatom coverage (1.0 ML) was found to enhance the surface spin magnetic moment by 11%. Second, we also calculate and contrast adsorption of 0.5 and 1.0 ML of carbon, nitrogen, and oxygen adatoms on fcc iron, cobalt, and nickel {110} surfaces and compare the structural, electronic, and magnetic properties of these systems. Carbon and nitrogen are found to couple antiferromagnetically, and oxygen ferromagnetically, to all surfaces. It was found that antiferromagnetically coupled adsorbates retained their largest spin moment values on iron, whereas ferromagnetically coupled adsorbates possessed their lowest moments on this surface. The strongly localized influence of these adsorbates is clearly illustrated in partial density-of-states plots for the surface atoms.

  6. Low-cost magnetic adsorbent for As(III) removal from water: adsorption kinetics and isotherms.

    PubMed

    Kango, Sarita; Kumar, Rajesh

    2016-01-01

    Magnetite nanoparticles as adsorbent for arsenic (As) were coated on sand particles. The coated sand was used for the removal of highly toxic element 'As(III)' from drinking water. Here, batch experiments were performed with the variation of solution pH, adsorbent dose, contact time and initial arsenic concentration. The adsorbent showed significant removal efficiency around 99.6 % for As(III). Analysis of adsorption kinetics revealed that the adsorbent follows pseudo-second-order kinetics model showing R (2) = 0.999, whereas for pseudo-first-order kinetics model, the value of R (2) was 0.978. In the case of adsorption equilibrium, the data is well fitted with Langmuir adsorption isotherm model (R (2) > 0.99), indicating monolayer adsorption of As(III) on the surface of adsorbent. The existence of commonly present ions in water influences the removal efficiency of As(III) minutely in the following order PO4 (3-) > HCO3 (-) > Cl(-) > SO4 (2-). The obtained adsorbent can be used to overcome the problem of water filtration in rural areas. Moreover, as the nano-magnetite is coated on the sand, it avoids the problem of extraction of nanoparticles from treated water and can easily be removed by a simple filtration process.

  7. The Impact of Enzyme Orientation and Electrode Topology on the Catalytic Activity of Adsorbed Redox Enzymes

    PubMed Central

    McMillan, Duncan G. G.; Marritt, Sophie J.; Kemp, Gemma L.; Gordon-Brown, Piers; Butt, Julea N.; Jeuken, Lars J. C.

    2014-01-01

    It is well established that the structural details of electrodes and their interaction with adsorbed enzyme influences the interfacial electron transfer rate. However, for nanostructured electrodes, it is likely that the structure also impacts on substrate flux near the adsorbed enzymes and thus catalytic activity. Furthermore, for enzymes converting macro-molecular substrates it is possible that the enzyme orientation determines the nature of interactions between the adsorbed enzyme and substrate and therefore catalytic rates. In essence the electrode may impede substrate access to the active site of the enzyme. We have tested these possibilities through studies of the catalytic performance of two enzymes adsorbed on topologically distinct electrode materials. Escherichia coli NrfA, a nitrite reductase, was adsorbed on mesoporous, nanocrystalline SnO2 electrodes. CymA from Shewanella oneidensis MR-1 reduces menaquinone-7 within 200 nm sized liposomes and this reaction was studied with the enzyme adsorbed on SAM modified ultra-flat gold electrodes. PMID:24634538

  8. The Impact of Enzyme Orientation and Electrode Topology on the Catalytic Activity of Adsorbed Redox Enzymes.

    PubMed

    McMillan, Duncan G G; Marritt, Sophie J; Kemp, Gemma L; Gordon-Brown, Piers; Butt, Julea N; Jeuken, Lars J C

    2013-11-01

    It is well established that the structural details of electrodes and their interaction with adsorbed enzyme influences the interfacial electron transfer rate. However, for nanostructured electrodes, it is likely that the structure also impacts on substrate flux near the adsorbed enzymes and thus catalytic activity. Furthermore, for enzymes converting macro-molecular substrates it is possible that the enzyme orientation determines the nature of interactions between the adsorbed enzyme and substrate and therefore catalytic rates. In essence the electrode may impede substrate access to the active site of the enzyme. We have tested these possibilities through studies of the catalytic performance of two enzymes adsorbed on topologically distinct electrode materials. Escherichia coli NrfA, a nitrite reductase, was adsorbed on mesoporous, nanocrystalline SnO2 electrodes. CymA from Shewanella oneidensis MR-1 reduces menaquinone-7 within 200 nm sized liposomes and this reaction was studied with the enzyme adsorbed on SAM modified ultra-flat gold electrodes.

  9. Surface coverage and structure of mixed DNA/alkylthiol monolayers on gold: characterization by XPS, NEXAFS, and fluorescence intensity measurements.

    PubMed

    Lee, Chi-Ying; Gong, Ping; Harbers, Gregory M; Grainger, David W; Castner, David G; Gamble, Lara J

    2006-05-15

    Self-assembly of thiol-terminated single-stranded DNA (HS-ssDNA) on gold has served as an important model system for DNA immobilization at surfaces. Here, we report a detailed study of the surface composition and structure of mixed self-assembled DNA monolayers containing a short alkylthiol surface diluent [11-mercapto-1-undecanol (MCU)] on gold supports. These mixed DNA monolayers were studied with X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and fluorescence intensity measurements. XPS results on sequentially adsorbed DNA/MCU monolayers on gold indicated that adsorbed MCU molecules first incorporate into the HS-ssDNA monolayer and, upon longer MCU exposures, displace adsorbed HS-ssDNA molecules from the surface. Thus, HS-ssDNA surface coverage steadily decreased with MCU exposure time. Polarization-dependent NEXAFS and fluorescence results both show changes in signals consistent with changes in DNA orientation after only 30 min of MCU exposure. NEXAFS polarization dependence (followed by monitoring the N 1s --> pi* transition) of the mixed DNA monolayers indicated that the DNA nucleotide base ring structures are oriented more parallel to the gold surface compared to DNA bases in pure HS-ssDNA monolayers. This indicates that HS-ssDNA oligomers reorient toward a more-upright position upon MCU incorporation. Fluorescence intensity results using end-labeled DNA probes on gold show little observable fluorescence on pure HS-ssDNA monolayers, likely due to substrate quenching effects between the fluorophore and the gold. MCU diluent incorporation into HS-ssDNA monolayers initially increases DNA fluorescence signal by densifying the chemisorbed monolayer, prompting an upright orientation of the DNA, and moving the terminal fluorophore away from the substrate. Immobilized DNA probe density and DNA target hybridization in these mixed DNA monolayers, as well as effects of MCU diluent on DNA hybridization in complex

  10. Adsorption and switching properties of a N-benzylideneaniline based molecular switch on a Au(111) surface

    SciTech Connect

    Ovari, Laszlo; Luo, Ying; Haag, Rainer; Leyssner, Felix; Tegeder, Petra; Wolf, Martin

    2010-07-28

    High resolution electron energy loss spectroscopy has been employed to analyze the adsorption geometry and the photoisomerization ability of the molecular switch carboxy-benzylideneaniline (CBA) adsorbed on Au(111). CBA on Au(111) adopts a planar (trans) configuration in the first monolayer (ML) as well as for higher coverages (up to 6 ML), in contrast to the strongly nonplanar geometry of the molecule in solution. Illumination with UV light of CBA in direct contact with the Au(111) surface ({<=}1 ML) caused no changes in the vibrational structure, whereas at higher coverages (>1 ML) pronounced modifications of vibrational features were observed, which we assign to a trans{yields}cis isomerization. Thermal activation induced the back reaction to trans-CBA. We propose that the photoisomerization is driven by a direct (intramolecular) electronic excitation of the adsorbed CBA molecules in the second ML (and above) analogous to CBA in the liquid phase.

  11. X-ray studies of self-assembled organic monolayers grown on hydrogen-terminated Si(111).

    PubMed

    Jin, Hua; Kinser, C Reagan; Bertin, Paul A; Kramer, Donald E; Libera, Joseph A; Hersam, Mark C; Nguyen, Sonbinh T; Bedzyk, Michael J

    2004-07-20

    The structure of self-assembled monolayers (SAMs) of undecylenic acid methyl ester (SAM-1) and undec-10-enoic acid 2-bromo-ethyl ester (SAM-2) grown on hydrogen-passivated Si(111) were studied by X-ray reflectivity (XRR), X-ray standing waves (XSW), X-ray fluorescence (XRF), atomic force microscopy, and X-ray photoelectron spectroscopy (XPS). The two different SAMs were grown by immersion of H-Si(111) substrates into the two different concentrated esters. UV irradiation during immersion was used to create Si dangling bond sites that act as initiators of the surface free-radical addition process that leads to film growth. The XRR structural analysis reveals that the molecules of SAM-1 and SAM-2 respectively have area densities corresponding to 50% and 57% of the density of Si(111) surface dangling bonds and produce films with less than 4 angstroms root-mean-square roughness that have layer thicknesses of 12.2 and 13.2 angstroms. Considering the molecular lengths, these thicknesses correspond to a 38 degrees and 23 degrees tilt angle for the respective molecules. For SAM-2/Si(111) samples, XRF analysis reveals a 0.58 monolayer (ML) Br total coverage. Single-crystal Bragg diffraction XSW analysis reveals (unexpectedly) that 0.48 ML of these Br atoms are at a Si(111) lattice position height that is identical to the T1 site that was previously found by XSW analysis for Br adsorbed onto Si(111) from a methanol solution and from ultrahigh vacuum. From the combined XPS, XRR, XRF, and XSW evidence, it is concluded that Br abstraction by reactive surface dangling bonds competes with olefin addition to the surface.

  12. Adsorbate-induced curvature and stiffening of graphene.

    PubMed

    Svatek, Simon A; Scott, Oliver R; Rivett, Jasmine P H; Wright, Katherine; Baldoni, Matteo; Bichoutskaia, Elena; Taniguchi, Takashi; Watanabe, Kenji; Marsden, Alexander J; Wilson, Neil R; Beton, Peter H

    2015-01-14

    The adsorption of the alkane tetratetracontane (TTC, C44H90) on graphene induces the formation of a curved surface stabilized by a gain in adsorption energy. This effect arises from a curvature-dependent variation of a moiré pattern due to the mismatch of the carbon-carbon separation in the adsorbed molecule and the period of graphene. The effect is observed when graphene is transferred onto a deformable substrate, which in our case is the interface between water layers adsorbed on mica and an organic solvent, but is not observed on more rigid substrates such as boron nitride. Our results show that molecular adsorption can be influenced by substrate curvature, provide an example of two-dimensional molecular self-assembly on a soft, responsive interface, and demonstrate that the mechanical properties of graphene may be modified by molecular adsorption, which is of relevance to nanomechanical systems, electronics, and membrane technology. PMID:25469625

  13. Adsorbate-Induced Curvature and Stiffening of Graphene

    PubMed Central

    2014-01-01

    The adsorption of the alkane tetratetracontane (TTC, C44H90) on graphene induces the formation of a curved surface stabilized by a gain in adsorption energy. This effect arises from a curvature-dependent variation of a moiré pattern due to the mismatch of the carbon–carbon separation in the adsorbed molecule and the period of graphene. The effect is observed when graphene is transferred onto a deformable substrate, which in our case is the interface between water layers adsorbed on mica and an organic solvent, but is not observed on more rigid substrates such as boron nitride. Our results show that molecular adsorption can be influenced by substrate curvature, provide an example of two-dimensional molecular self-assembly on a soft, responsive interface, and demonstrate that the mechanical properties of graphene may be modified by molecular adsorption, which is of relevance to nanomechanical systems, electronics, and membrane technology. PMID:25469625

  14. Cholesterol in condensed and fluid phosphatidylcholine monolayers studied by epifluorescence microscopy.

    PubMed Central

    Worthman, L A; Nag, K; Davis, P J; Keough, K M

    1997-01-01

    Epifluorescence microscopy was used to investigate the effect of cholesterol on monolayers of dipalmitoylphosphatidylcholine (DPPC) and 1 -palmitoyl-2-oleoyl phosphatidylcholine (POPC) at 21 +/- 2 degrees C using 1 mol% 1-palmitoyl-2-[12-[(7-nitro-2-1, 3-benzoxadizole-4-yl)amino]dodecanoyl]phosphatidylcholine (NBD-PC) as a fluorophore. Up to 30 mol% cholesterol in DPPC monolayers decreased the amounts of probe-excluded liquid-condensed (LC) phase at all surface pressures (pi), but did not effect the monolayers of POPC, which remained in the liquid-expanded (LE) phase at all pi. At low pi (2-5 mN/m), 10 mol% or more cholesterol in DPPC induced a lateral phase separation into dark probe-excluded and light probe-rich regions. In POPC monolayers, phase separation was observed at low pi when > or =40 mol% or more cholesterol was present. The lateral phase separation observed with increased cholesterol concentrations in these lipid monolayers may be a result of the segregation of cholesterol-rich domains in ordered fluid phases that preferentially exclude the fluorescent probe. With increasing pi, monolayers could be transformed from a heterogeneous dark and light appearance into a homogeneous fluorescent phase, in a manner that was dependent on pi and cholesterol content. The packing density of the acyl chains may be a determinant in the interaction of cholesterol with phosphatidylcholine (PC), because the transformations in monolayer surface texture were observed in phospholipid (PL)/sterol mixtures having similar molecular areas. At high pi (41 mN/m), elongated crystal-like structures were observed in monolayers containing 80-100 mol% cholesterol, and these structures grew in size when the monolayers were compressed after collapse. This observation could be associated with the segregation and crystallization of cholesterol after monolayer collapse. Images FIGURE 3 FIGURE 4 PMID:9168032

  15. Physical adsorption and charge transfer of molecular Br2 on graphene.

    PubMed

    Chen, Zheyuan; Darancet, Pierre; Wang, Lei; Crowther, Andrew C; Gao, Yuanda; Dean, Cory R; Taniguchi, Takashi; Watanabe, Kenji; Hone, James; Marianetti, Chris A; Brus, Louis E

    2014-03-25

    We present a detailed study of gaseous Br2 adsorption and charge transfer on graphene, combining in situ Raman spectroscopy and density functional theory (DFT). When graphene is encapsulated by hexagonal boron nitride (h-BN) layers on both sides, in a h-BN/graphene/h-BN sandwich structure, it is protected from doping by strongly oxidizing Br2. Graphene supported on only one side by h-BN shows strong hole doping by adsorbed Br2. Using Raman spectroscopy, we determine the graphene charge density as a function of pressure. DFT calculations reveal the variation in charge transfer per adsorbed molecule as a function of coverage. The molecular adsorption isotherm (coverage versus pressure) is obtained by combining Raman spectra with DFT calculations. The Fowler-Guggenheim isotherm fits better than the Langmuir isotherm. The fitting yields the adsorption equilibrium constant (∼0.31 Torr(-1)) and repulsive lateral interaction (∼20 meV) between adsorbed Br2 molecules. The Br2 molecule binding energy is ∼0.35 eV. We estimate that at monolayer coverage each Br2 molecule accepts 0.09 e- from single-layer graphene. If graphene is supported on SiO2 instead of h-BN, a threshold pressure is observed for diffusion of Br2 along the (somewhat rough) SiO2/graphene interface. At high pressure, graphene supported on SiO2 is doped by adsorbed Br2 on both sides. PMID:24528378

  16. Mixed-Metal Pt Monolayer Electrocatalysts with Improved CO Tolerance

    SciTech Connect

    Nilekar, Anand U.; Sasaki, Kotaro; Farberow, Carrie A.; Adzic, Radoslav R.; Mavrikakis, Manos

    2011-11-23

    Using a combination of periodic, self-consistent, density functional theory (DFT) calculations and COstripping voltammetry experiments, we have designed a new class of Pt-M bimetallic monolayer catalysts supported on a non-Pt metal, which exhibit improved stability against CO poisoning and might be suitable for proton-exchange membrane fuel cell anodes. These surfaces help in reducing the overpotential associated with anodic CO oxidation and minimize the amount of Pt used, thereby reducing materials cost. DFT calculations predict highly repulsive interactions between adsorbed CO molecules on these surfaces, leading to weaker binding and lower coverage of CO than on pure Pt, which in turn facilitates oxidative removal of CO from these catalytic surfaces.

  17. Mixed-Metal Pt Monolayer Electrocatalysts with Improved CO Tolerance

    SciTech Connect

    Sasaki K.; Nilekar A.U.; Farberow C.A.; Adzic R.R.; Mavrikakis M.

    2011-11-23

    Using a combination of periodic, self-consistent, density functional theory (DFT) calculations and CO-stripping voltammetry experiments, we have designed a new class of Pt-M bimetallic monolayer catalysts supported on a non-Pt metal, which exhibit improved stability against CO poisoning and might be suitable for proton-exchange membrane fuel cell anodes. These surfaces help in reducing the overpotential associated with anodic CO oxidation and minimize the amount of Pt used, thereby reducing materials cost. DFT calculations predict highly repulsive interactions between adsorbed CO molecules on these surfaces, leading to weaker binding and lower coverage of CO than on pure Pt, which in turn facilitates oxidative removal of CO from these catalytic surfaces.

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

    PubMed

    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.

  19. Trends in adsorbate induced core level shifts

    NASA Astrophysics Data System (ADS)

    Nilsson, Viktor; Van den Bossche, Maxime; Hellman, Anders; Grönbeck, Henrik

    2015-10-01

    Photoelectron core level spectroscopy is commonly used to monitor atomic and molecular adsorption on metal surfaces. As changes in the electron binding energies are convoluted measures with different origins, calculations are often used to facilitate the decoding of experimental signatures. The interpretation could in this sense benefit from knowledge on trends in surface core level shifts for different metals and adsorbates. Here, density functional theory calculations have been used to systematically evaluate core level shifts for (111) and (100) surfaces of 3d, 4d, and 5d transition metals upon CO, H, O and S adsorption. The results reveal trends and several non-intuitive cases. Moreover, the difficulties correlating core level shifts with charging and d-band shifts are underlined.

  20. Efficient C–C bond splitting on Pt monolayer and sub-monolayer catalysts during ethanol electro-oxidation: Pt layer strain and morphology effects

    SciTech Connect

    Loukrakpam, Rameshwori; Yuan, Qiuyi; Petkov, Valeri; Gan, Lin; Rudi, Stefan; Yang, Ruizhi; Huang, Yunhui; Brankovic, Stanko R.; Strasser, Peter

    2014-07-23

    Efficient catalytic C–C bond splitting coupled with complete 12-electron oxidation of the ethanol molecule to CO2 is reported on nanoscale electrocatalysts comprised of a Pt monolayer (ML) and sub-monolayer (sML) deposited on Au nanoparticles (Au@Pt ML/sML). The Au@Pt electrocatalysts were synthesized using surface limited redox replacement (SLRR) of an underpotentially deposited (UPD) Cu monolayer in an electrochemical cell reactor. Au@Pt ML showed improved catalytic activity for ethanol oxidation reaction (EOR) and, unlike their Pt bulk and Pt sML counterparts, was able to generate CO2 at very low electrode potentials owing to efficient C–C bond splitting. To explain this, we explore the hypothesis that competing strain effects due to the Pt layer coverage/morphology (compressive) and the Pt–Au lattice mismatch (tensile) control surface chemisorption and overall activity. Control experiments on well-defined model Pt monolayer systems are carried out involving a wide array of methods such as high-energy X-ray diffraction, pair-distribution function (PDF) analysis, in situ electrochemical FTIR spectroscopy, and in situ scanning tunneling microscopy. The vibrational fingerprints of adsorbed CO provide compelling evidence on the relation between surface bond strength, layer strain and morphology, and catalytic activity.

  1. Fullerene-derivative PC61BM forms three types of phase-pure monolayer on the surface of Au(111)

    NASA Astrophysics Data System (ADS)

    Li, Wen-Jie; Du, Ying-Ying; Zhang, Han-Jie; Chen, Guang-Hua; Sheng, Chun-Qi; Wu, Rui; Wang, Jia-Ou; Qian, Hai-Jie; Ibrahim, Kurash; He, Pi-Mo; Li, Hong-Nian

    2016-12-01

    We have studied the packing structures of C60-derivative PC61BM on the surface of Au(111) in ultrahigh vacuum using scanning tunneling microscopy. The Au(111) has a triangle-like reconstructed surface, which results in some packing structures different from those reported for low coverages. PC61BM can form three types of phase-pure monolayer, namely, the compact straight molecular double-row monolayer, the hexagonal-packing monolayer and the glassy monolayer. The different types of monolayer form for different molecular densities and different annealing temperatures. In addition to the already known inter-molecular interactions (Van de Waals interaction and hydrogen bond), the steric effect of the phenyl-butyric-acid-methyl-ester side tail plays conspicuous role in the molecular self-assembly at high coverages. The steric effect makes it difficult to prepare a hexagonal-packing monolayer at room temperature and decides the instability of the hexagonal-packing monolayer prepared by thermal annealing.

  2. Vectorially oriented monolayers of detergent-solubilized Ca(2+) -ATPase from sarcoplasmic reticulum.

    PubMed Central

    Prokop, L A; Stongin, R M; Smith, A B; Blasie, J K; Peticolas, L J; Bean, J C

    1996-01-01

    A method for tethering proteins to solid surfaces has been utilized to form vectorially oriented monolayers of the detergent-solubilized integral membrane protein Ca(2+) -ATPase from the sarcoplasmic reticulum (SR). Bifunctional, organic self-assembled monolayers (SAMs) possessing "headgroup" binding specificity for the substrate and "endgroup" binding specificity for the enzyme were utilized to tether the enzyme to the substrate. Specifically, an amine-terminated 11-siloxyundecaneamine SAM was found to bind the Ca(2+)-ATPase primarily electrostatically. The Ca(2+)-ATPase was labeled with the fluorescent probe 5-(2-[(iodoacetyl)amino]ethyl)aminonaphthalene-1-sulfonic acid before monolayer formation. Consequently, fluorescence measurements performed on amine-terminated SAM/enzyme monolayers formed on quartz substrates served to establish the nature of protein binding. Formation of the monolayers on inorganic multilayer substrates fabricated by molecular beam epitaxy made it possible to use x-ray interferometry to determine the profile structure for the system, which was proved correct by x-ray holography. The profile structures established the vectorial orientation of the Ca(2+)-ATPase within these monolayers, to a spatial resolution of approximately 12 A. Such vectorially oriented monolayers of detergent-solubilized Ca(2+)-ATPase from SR make possible a wide variety of correlative structure/function studies, which would serve to elucidate the mechanism of Ca(2+) transport by this enzyme. Images FIGURE 8 PMID:9172737

  3. Free exciton emission and vibrations in pentacene monolayers

    NASA Astrophysics Data System (ADS)

    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).

  4. Photocatalytic Nanolithography of Self-Assembled Monolayers and Proteins

    PubMed Central

    2013-01-01

    Self-assembled monolayers of alkylthiolates on gold and alkylsilanes on silicon dioxide have been patterned photocatalytically on sub-100 nm length-scales using both apertured near-field and apertureless methods. Apertured lithography was carried out by means of an argon ion laser (364 nm) coupled to cantilever-type near-field probes with a thin film of titania deposited over the aperture. Apertureless lithography was carried out with a helium–cadmium laser (325 nm) to excite titanium-coated, contact-mode atomic force microscope (AFM) probes. This latter approach is readily implementable on any commercial AFM system. Photodegradation occurred in both cases through the localized photocatalytic degradation of the monolayer. For alkanethiols, degradation of one thiol exposed the bare substrate, enabling refunctionalization of the bare gold by a second, contrasting thiol. For alkylsilanes, degradation of the adsorbate molecule provided a facile means for protein patterning. Lines were written in a protein-resistant film formed by the adsorption of oligo(ethylene glycol)-functionalized trichlorosilanes on glass, leading to the formation of sub-100 nm adhesive, aldehyde-functionalized regions. These were derivatized with aminobutylnitrilotriacetic acid, and complexed with Ni2+, enabling the binding of histidine-labeled green fluorescent protein, which yielded bright fluorescence from 70-nm-wide lines that could be imaged clearly in a confocal microscope. PMID:23971891

  5. Nonlinear spectroscopic studies of interfacial molecular ordering

    SciTech Connect

    Superfine, R.

    1991-07-01

    The second order nonlinear optical processes of second harmonic generation and sum frequency generation are powerful new probes of surfaces. They possess unusual surface sensitivity due to the symmetry properties of the nonlinear susceptibility. In particular, infrared-visible sum frequency generation (SFG) can obtain the vibrational spectrum of sub-monolayer coverages of molecules. In this thesis, we explore the unique information that can be obtained from SFG. We take advantage of the sensitivity of SFG to the conformation of alkane chains to study the interaction between adsorbed liquid crystal molecules and surfactant treated surfaces. The sign of the SFG susceptibility depends on the sign of the molecular polarizability and the orientation, up or down, of the molecule. We experimentally determine the sign of the susceptibility and use it to determine the absolute orientation to obtain the sign of the molecular polarizability and show that this quantity contains important information about the dynamics of molecular charge distributions. Finally, we study the vibrational spectra and the molecular orientation at the pure liquid/vapor interface of methanol and water and present the most detailed evidence yet obtained for the structure of the pure water surface. 32 refs., 4 figs., 2 tabs.

  6. Supercritical fluid regeneration of adsorbents

    NASA Astrophysics Data System (ADS)

    Defilippi, R. P.; Robey, R. J.

    1983-05-01

    The results of a program to perform studies supercritical (fluid) carbon dioxide (SCF CO2) regeneration of adsorbents, using samples of industrial wastewaters from manufacturing pesticides and synthetic solution, and to estimate the economics of the specific wastewater treatment regenerations, based on test data are given. Processing costs for regenerating granular activated carbon GAC) for treating industrial wastewaters depend on stream properties and regeneration throughput.

  7. Dip-pen nanolithography on (bio)reactive monolayer and block-copolymer platforms: deposition of lines of single macromolecules.

    PubMed

    Salazar, Ramon B; Shovsky, Alexander; Schönherr, Holger; Vancso, G Julius

    2006-11-01

    The application of atomic force microscopy (AFM) tip-mediated molecular transfer (dip-pen nanolithography or DPN) to fabricate nanopatterned (bio)reactive platforms based on dendrimers on reactive self-assembled monolayer (SAM) and polymer thin films is discussed. The transfer of high-molar-mass polyamidoamine (PAMAM) dendrimers (generation 5) and the rapid in situ covalent attachment of the deposited adsorbates onto reactive N-hydroxysuccinimide (NHS) terminated SAMs on gold and NHS-activated polystyrene-block-poly(tert-butyl acrylate) (PS(690)-b-PtBA(1210)) block copolymer thin films were investigated as strategies to suppress line broadening by surface diffusion in DPN. By exploiting carefully controlled environmental conditions (such as temperature and relative humidity), scan rates, and in particular the covalent attachment of the dendrimers to the reactive films, the observed line broadening and hence the lateral diffusion of dendrimers was substantially less pronounced compared to that observed with DPN of thiols on gold. By this method, high-definition patterns of dendrimers were conveniently fabricated down to 30-nm length scales. The presence of primary amino groups in the deposited dendrimers ultimately offers the possibility to anchor biochemically relevant molecules, such as proteins and polypeptides, to these nanostructured platforms for a wide range of possible applications in the life sciences and in particular for the investigation of controlled cell-surface interactions. PMID:17192974

  8. Adsorbed polyelectrolyte coatings decrease Fe(0) nanoparticle reactivity with TCE in water: conceptual model and mechanisms.

    PubMed

    Phenrat, Tanapon; Liu, Yueqiang; Tilton, Robert D; Lowry, Gregory V

    2009-03-01

    The surfaces of reactive nanoscale zerovalent iron (NZVI) particles used for in situ groundwater remediation are modified with polymers or polyelectrolytes to enhance colloidal stability and mobility in the subsurface. However, surface modification decreases NZVI reactivity. Here, the TCE dechlorination rate and reaction products are measured as a function of adsorbed polyelectrolyte mass for three commercially available polyelectrolytes used for NZVI surface modification including poly(styrene sulfonate) (PSS), carboxymethyl cellulose (CMC), and polyaspartate (PAP). The adsorbed mass, extended layer thickness, and TCE-polyelectrolyte partition coefficient are measured and used to explain the effect of adsorbed polyelectrolyte on NZVI reactivity. For all modifiers, the dechlorination rate constant decreased nonlinearly with increasing surface excess, with a maximum of a 24-fold decrease in reactivity. The TCE dechlorination pathways were not affected. Consistent with Scheutjens-Fleer theory for homopolymer adsorption, the nonlinear relationship between the dechlorination rate and the surface excess of adsorbed polyelectrolyte suggests that adsorbed polyelectrolyte decreases reactivity primarily by blocking reactive surface sites at low surface excess where they adsorb relatively flat onto the NZVI surface, and by a combination of site blocking and decreasing the aqueous TCE concentration at the NZVI surface due to partitioning of TCE to adsorbed polyelectrolytes. This explanation is also consistent with the effect of adsorbed polyelectrolyte on acetylene formation. This conceptual model should apply to other medium and high molecular weight polymeric surface modifiers on nanoparticles, and potentially to adsorbed natural organic matter.

  9. Dielectric exchange-force effect on the rupture force of adsorbed bilayers of self-assembled surfactant films

    NASA Astrophysics Data System (ADS)

    Teschke, O.; Ceotto, G.; de Souza, E. F.

    2001-05-01

    We measured and formulated dielectric exchange forces between adsorbed layers of self-assembled surfactant films and atomic-force microscope tips in water. The dielectric exchange-force model is in agreement with the observation that the surfactant-layer rupture forces (tip-applied force necessary to obtain tip/substrate contact) are smaller in the thickest layers, where the compactness of the adsorbed film results in the smallest values of the dielectric permittivity. Within experimental accuracy, a dielectric permittivity value of ˜4 for bilayers and of ˜36 for monolayers is found.

  10. Ordering and defects in self-assembled monolayers on nanoporous gold

    NASA Astrophysics Data System (ADS)

    Patel, Dipna A.; Weller, Andrew M.; Chevalier, Robert B.; Karos, Constantine A.; Landis, Elizabeth C.

    2016-11-01

    Self-assembled monolayers are commonly used to tailor nanoporous structures for applications, and they also provide a model system for determining the effects of nanoscale structure on self-assembly. We have investigated the ordering and defects in alkanethiol self-assembled monolayers on nanoporous gold, a high surface area mesoporous material. Infrared reflection absorption spectroscopy was used to characterize the effects of alkyl chain length and nanoporous gold pore size on molecular layer ordering. Cyclic voltammetry was used to characterize the monolayer density and ordering, with ferrocenylalkylthiolates used to quantify and characterize defect sites. We find that dense and well-ordered molecular layers form quickly with low defect levels. However, we do not observe differences in molecular layer ordering or defects with changes in pore size.

  11. Binding to the lipid monolayer induces conformational transition in Aβ monomer.

    PubMed

    Kim, Seongwon; Klimov, Dmitri K

    2013-02-01

    Using implicit solvent atomistic model and replica exchange molecular dynamics, we study binding of Aβ monomer to zwitterionic dimyristoylphosphatidylcholine (DMPC) lipid monolayer. Our results suggest that Aβ binding to the monolayer is governed primarily by positively charged and aromatic amino acids. Lysine residues tend to interact with surface choline and phosphorous lipid groups, whereas aromatic amino acids penetrate deeper into the monolayer, reaching its hydrophobic core. We show that binding to the DMPC monolayer causes a dramatic conformational transition in Aβ monomer, resulting in chain extension, loss of intrapeptide interactions, and formation of β-structure. This conformational transition is far more significant than that occurring during the initial stages of aggregation in water. We also found that Aβ binding perturbs surface ordering of lipids interacting with Aβ. PMID:23053007

  12. Actinide sequestration using self-assembled monolayers on mesoporous supports.

    PubMed

    Fryxell, Glen E; Lin, Yuehe; Fiskum, Sandy; Birnbaum, Jerome C; Wu, Hong; Kemner, Ken; Kelly, Shelley

    2005-03-01

    Surfactant templated synthesis of mesoporous ceramics provides a versatile foundation upon which to create high efficiency environmental sorbents. These nanoporous ceramic oxides condense a huge amount of surface area into a very small volume. The ceramic oxide interface is receptive to surface functionalization through molecular self-assembly. The marriage of mesoporous ceramics with self-assembled monolayer chemistry creates a powerful new class of environmental sorbent materials called self-assembled monolayers on mesoporous supports (SAMMS). These SAMMS materials are highly efficient sorbents whose interfacial chemistry can be fine-tuned to selectively sequester a specific target species, such as heavy metals, tetrahedral oxometalate anions, and radionuclides. Details addressing the design, synthesis, and characterization of SAMMS materials specifically designed to sequester actinides, of central importance to the environmental cleanup necessary after 40 years of weapons-grade plutonium production, as well as evaluation of their binding affinities and kinetics are presented.

  13. Actinide sequestration using self-assembled monolayers on mesoporous supports.

    PubMed

    Fryxell, Glen E; Lin, Yuehe; Fiskum, Sandy; Birnbaum, Jerome C; Wu, Hong; Kemner, Ken; Kelly, Shelley

    2005-03-01

    Surfactant templated synthesis of mesoporous ceramics provides a versatile foundation upon which to create high efficiency environmental sorbents. These nanoporous ceramic oxides condense a huge amount of surface area into a very small volume. The ceramic oxide interface is receptive to surface functionalization through molecular self-assembly. The marriage of mesoporous ceramics with self-assembled monolayer chemistry creates a powerful new class of environmental sorbent materials called self-assembled monolayers on mesoporous supports (SAMMS). These SAMMS materials are highly efficient sorbents whose interfacial chemistry can be fine-tuned to selectively sequester a specific target species, such as heavy metals, tetrahedral oxometalate anions, and radionuclides. Details addressing the design, synthesis, and characterization of SAMMS materials specifically designed to sequester actinides, of central importance to the environmental cleanup necessary after 40 years of weapons-grade plutonium production, as well as evaluation of their binding affinities and kinetics are presented. PMID:15787373

  14. Actinide Sequestration Using Self-Assembled Monolayers on Mesoporous Supports

    SciTech Connect

    Fryxell, Glen E.; Lin, Yuehe; Fiskum, Sandra K.; Birnbaum, Jerome C.; Wu, Hong; Kemner, K. M.; Kelly, Shelley

    2005-03-01

    Surfactant templated synthesis of mesoporous ceramics provides a versatile foundation upon which to create high efficiency environmental sorbents. These nanoporous ceramic oxides condense a huge amount of surface area into a very small volume. The ceramic oxide interface is receptive to surface functionalization through molecular self-assembly. The marriage of mesoporous ceramics with self-assembled monolayer chemistry creates a powerful new class of environmental sorbent materials called self-assembled monolayers on mesoporous supports (SAMMS). These SAMMS materials are highly efficient sorbents, whose interfacial chemistry can be fine-tuned to selectively sequester a specific target species, such as heavy metals, tetrahedral oxometallate anions and radionuclides. Details addressing the design, synthesis and characterization of SAMMS materials specifically designed to sequester actinides, of central importance to the environmental clean-up necessary after 40 years of weapons grade plutonium production, as well as evaluation of their binding affinities and kinetics are presented.

  15. Structure and shear response of lipid monolayers

    SciTech Connect

    Dutta, P.; Ketterson, J.B.

    1990-02-01

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

  16. Quantum resolved studies of electron-stimulated reactions on adsorbate covered Pt(111) surfaces

    NASA Astrophysics Data System (ADS)

    Orlando, T. M.; Burns, A. R.; Stechel, E. B.; Jennison, D. R.

    1991-06-01

    Using laser resonance-enhanced ionisation spectroscopy, we have studied electron (6-350 eV) stimulated dissociation of NO 2 coadsorbed with up to 0.75 monolayer of atomic O on Pt(111). Several dramatic effects on NO 2 dissociation occur due to the presence of O. There is a large ( × 26) enhancement in the specific dissociation yield, a narrowing of the NO translational energy distributions, and a distinct propensity ( > 4:1 at low J) for populating the upper Ω = {3}/{2} NO spin-orbit level over the Ω = {1}/{2} level. The spin-orbit state distribution of the O( 3PJ) dissociation fragment is (5.0): (2.5): (1.0) for J = 2, 1 and 0, which is within experimental error of the statistical ( T → ∞) 2 J + 1 limit. The enhanced yield probably results from an increased excited state lifetime due to a reduction in substrate charge-transfer screening. We have also detected O( 3PJ = 2,1,0) andNO X2 Π {3}/{2}, {1}/{2}(v = 5) above an electron (6-350 eV) beam irradiated Pt(111) surface containing coadsorbed O 2 and NO at 90 K. We conclude that both O( 3PJ) andNO(v = 5) are laser-induced photodissociation fragments of NO 2desorbates. The NO 2 is probably the reaction product of a collision between an O atom (created by electron-stimulated dissociation of adsorbed O 2) and an NO(a). We correlate the 10 eV NO 2 production threshold with the dissociative ionization of the 3σ g molecular bonding orbital of O 2(a).

  17. Characterization of production of free gluconic acid by Gluconobacter suboxydans adsorbed on ceramic honeycomb monolith.

    PubMed

    Shiraishi, F; Kawakami, K; Kono, S; Tamura, A; Tsuruta, S; Kusunoki, K

    1989-05-01

    Gluconobacter suboxydans IFO 3290 was immobilized by adsorption on ceramic honeycomb monolith and continuous production of free gluconic acid from glucose was performed in an aerated reactor. The effects of reactor residence time, aeration rate, and glucose concentration were investigated on the gluconic acid yield. Observation of SEM photographs revealed that the cells were adsorbed with a high density not only on the outer surface of the support but also on the inner surface of large pores. From measurement of the number of the adsorbed cells, it was elucidated that the biofilm comprised a monolayer or bilayer of the cells. Maximum specific rate of growth was estimated for the free and adsorbed cells, and the adsorbed cells were found to grow at a fast rate compared with the free cells. In the continuous fermentation performed for one month at the glucose concentration of 100 kg/m(3), reactor residence time of 3.5 h and aeration rate of 900 cm(3)/min, the activity of the adsorbed cells was appreciably stable. The high productivity of 26.3 kg/(m(3)-reactor . h) was attained with the gluconic acid yield of 84.6% and glucose conversion of 94%.

  18. Single stage batch adsorber design for efficient Eosin yellow removal by polyaniline coated ligno-cellulose.

    PubMed

    Debnath, Sushanta; Ballav, Niladri; Maity, Arjun; Pillay, Kriveshini

    2015-01-01

    Polyaniline-coated lignin-based adsorbent (PLC) was synthesized and used for uptake of reactive dye eosin yellow (EY) from aqueous solution. The adsorption capability of the adsorbent was found to be more effective than the unmodified adsorbent (LC). In particular, the adsorption capability of the PLC was effective over a wider pH range. This could be owing to its higher point of zero charge, which is more favorable for the uptake of the anionic dye. Adsorption isotherm models suggested a monolayer adsorption was predominant. The mean free energy of adsorption (E(DR)) was found to have values between 8 and 16 kJ mol(-1) which suggests that an electrostatic mechanism of adsorption predominated over other underlying mechanisms. The adsorption process was also found to be spontaneous, with increasing negative free energy values observed at higher temperatures. Chemisorption process was supported by the changes in enthalpy above 40 kJ mol(-1) and by the results of desorption studies. This new adsorbent was also reusable and regenerable over four successive adsorption-desorption cycles. The single stage adsorber design revealed that PLC can be applicable as an effective biosorbent for the treatment of industrial effluents containing EY dye.

  19. NMR Studies of Quantum Tunneling in Monolayers of Helium Three

    NASA Astrophysics Data System (ADS)

    Parks, Charles; Stachowiak, Piotr; Sullivan, Neil

    2002-03-01

    The results of NMR studies of the nuclear spin-spin relaxation are reported for commensurate monolayers of helium three adsorbed on hexagonal boron nitride. The measurements were made using pulsed NMR techniques for low temperatures, 0.01 < T < 5.0 K, and for moderately high magnetic fields (up to 6 T). The relaxation rate is independent of temperature at low temperatures, 0.12 < T < 0.85 K, and this behavior is interpreted in terms of particle-particle exchange motions of the adsorbed helium atoms. The effective exchange rates were observed to change significantly on replacing a fraction of the helium atoms with relatively immobile neon atoms. This is understood if there is a significant 3-particle exchange in addition to 2-particle exchange. The analyses of the experimental results indicate that the 3-spin exchange term in the exchange Hamiltonian is of opposite sign to that of the 2-spin exchange and also has a larger amplitude. At high temperatures, 0.8 < T < 5.0 K, an exponential temperature dependence of the rate is observed that is attributed to the thermal activation of vacancies.

  20. Kinetics of self-assembled monolayer formation on individual nanoparticles.

    PubMed

    Smith, Jeremy G; Jain, Prashant K

    2016-08-24

    Self-assembled monolayer (SAM) formation of alkanethiols on nanoparticle surfaces is an extensively studied surface reaction. But the nanoscale aspects of the rich microscopic kinetics of this reaction may remain hidden due to ensemble-averaging in colloidal samples, which is why we investigated in real-time how alkanethiol SAMs form on a single Ag nanoparticle. From single-nanoparticle trajectories obtained using in situ optical spectroscopy, the kinetics of SAM formation appears to be limited by the growth of the layer across the nanoparticle surface. A significant spread in the growth kinetics is seen between nanoparticles. The single-nanoparticle rate distributions suggest two distinct modes for SAM growth: spillover of adsorbed thiols from the initial binding sites on the nanoparticle and direct adsorption of thiol from solution. At low concentrations, wherein direct adsorption from solution is not prevalent and growth takes place primarily by adsorbate migration, the SAM formation rate was less variable from one nanoparticle to another. On the other hand, at higher thiol concentrations, when both modes of growth were operative, the population of nanoparticles with inherent variations in surface conditions and/or morphology exhibited a heterogeneous distribution of rates. These new insights into the complex dynamics of SAM formation may inform synthetic strategies for ligand passivation and functionalization of nanoparticles and models of reactive adsorption and catalysis on nanoparticles. PMID:27523488

  1. Adsorbed molecules in external fields: Effect of confining potential.

    PubMed

    Tyagi, Ashish; Silotia, Poonam; Maan, Anjali; Prasad, Vinod

    2016-12-01

    We study the rotational excitation of a molecule adsorbed on a surface. As is well known the interaction potential between the surface and the molecule can be modeled in number of ways, depending on the molecular structure and the geometry under which the molecule is being adsorbed by the surface. We explore the effect of change of confining potential on the excitation, which is largely controlled by the static electric fields and continuous wave laser fields. We focus on dipolar molecules and hence we restrict ourselves to the first order interaction in field-molecule interaction potential either through permanent dipole moment or/and the molecular polarizability parameter. It is shown that confining potential shapes, strength of the confinement, strongly affect the excitation. We compare our results for different confining potentials. PMID:27387127

  2. Dynamics in Adsorbed Homopolymer Layers: Entanglements and Osmotic Effects

    NASA Astrophysics Data System (ADS)

    Santore, Maria; Mubarekyan, Ervin

    2001-03-01

    This work seeks the dynamic mechanism for the exchange of homopolymer chains between a dilute solution and a layer adsorbed at the solid-liquid interface. With the model system of polyethylene oxide (PEO) adsorbed onto silica from aqueous solution, it is shown that the behavior of saturated interfaces compared to starved layers reveals an interesting trend: The characteristic self exchange time is dependent only on coverage, not molecular weight, for chains of 100K or less. Therefore, it is concluded that classical entanglements do not play a role below 100K. For all molecular weights, when the coverage of 0.2 mg/m2 is exceeded, the interfacial dynamics become slow. At lower coverages, chains lie flat in train, with no loops or tails, and no lateral interactions either. The onset of slow dynamics at higher coverages may be a result of both surface crowding and the resistance of loops and tails to new chains approaching the layer.

  3. Method And Apparatus For Regenerating Nox Adsorbers

    DOEpatents

    Driscoll, J. Joshua; Endicott, Dennis L.; Faulkner, Stephen A.; Verkiel, Maarten

    2006-03-28

    Methods and apparatuses for regenerating a NOx adsorber coupled with an exhaust of an engine. An actuator drives a throttle valve to a first position when regeneration of the NOx adsorber is desired. The first position is a position that causes the regeneration of the NOx adsorber. An actuator drives the throttle valve to a second position while regeneration of the NOx adsorber is still desired. The second position being a position that is more open than the first position and operable to regenerate a NOx adsorber.

  4. Removal of sulfamethazine by hypercrosslinked adsorbents in aquatic systems.

    PubMed

    Grimmett, Maria E

    2013-01-01

    Four hundred tons of sulfamethazine are fed to livestock annually in North America to prevent disease and promote growth, but most of the drug is excreted unmetabolized into the environment. Because of slow degradation and high mobility, sulfamethazine contaminates groundwater supplies and causes aquatic ecosystem damage. Current water treatment methods to remove pharmaceuticals are not universally effective and have considerable limitations, which necessitate newer remediation techniques. Hypercrosslinked adsorbents, polystyrene polymers 100% crosslinked with methylene bridges, show promise because of high surface areas, high mechanical strength, and regenerable properties. This study screened four Purolite hypercrosslinked adsorbents (MN152, MN250, PAD400, and PAD600) to remove sulfamethazine from contaminated water and then characterized the most efficient resin, MN250, with batch adsorption and desorption experiments to optimize its use. Sulfamethazine adsorption onto MN250 displayed an L-class isotherm shape consistent with monolayer adsorption, negligible solute-solute interactions at the adsorbent surface, and decreasing activation energies of desorption with increasing surface coverage. MN250 had a maximum experimental adsorption capacity of 111 mg g, showing high correlation to the Langmuir and Freundlich models. Adsorption kinetics revealed prolonged adsorption over 59 h and were best described by Ho's pseudo-second-order model. There was minimal desorption from MN250 in distilled water, indicating an irreversible adsorption process. MN250's high capacity for sulfamethazine adsorption, minimal desorption in water, and ability to be regenerated make it a practical solution for sulfamethazine removal in areas that have contaminated groundwater supplies (e.g., areas near concentrated livestock operations), especially as current treatment methods have significant drawbacks.

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

    SciTech Connect

    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.

  6. Coulomb bound states and resonances due to groups of Ca dimers adsorbed on suspended graphene

    NASA Astrophysics Data System (ADS)

    Saffarzadeh, Alireza; Kirczenow, George

    2014-10-01

    The electronic bound states and resonances in the vicinity of the Dirac point energy due to the adsorption of calcium dimers on a suspended graphene monolayer are explored theoretically using density functional theory (DFT) and an improved extended Hückel model that includes electrostatic potentials. The Mulliken atomic charges and the electrostatic potentials are obtained from DFT calculations and reveal charge transfer from the Ca dimers to the graphene which is responsible for the emergence of resonant states in the electronic spectrum. The number of resonant states increases as the number of adsorbed dimers is increased. We find a bound "atomic-collapse" state in the graphene local density of states, as has been observed experimentally [Wang et al., Science 340, 734 (2013), 10.1126/science.1234320]. We find the formation of the atomic-collapse state and its population with electrons to require fewer adsorbed Ca dimers than in the experiment, possibly due to the different spacing between dimers and the dielectric screening by a boron nitride substrate in the experiment. We also predict the onset of filling of a second atomic-collapse state with electrons when six Ca dimers are adsorbed on the suspended graphene monolayer. Experiments testing these predictions would be of interest.

  7. Rotational Tunneling of CH2D2 Monolayers on MgO(100)

    NASA Astrophysics Data System (ADS)

    Hicks, Andrew; Larese, John

    2013-03-01

    Understanding the detailed nature of the interactions governing physisorption is a central topic in surface science, with wide ranging energy applications in heterogeneous catalysis, gas separation, and hydrogen storage. For systems with a strong interaction potential relative to the rotational constant of the adsorbate, adsorbed molecules are constrained to minima in the rotational potential. Adsorbed molecules may then tunnel through the rotational barrier between potential minima. Rotational tunneling spectra (RTS) are extremely sensitive to changes in the symmetry and strength of the rotational potential and are unmatched in their ability to probe the electrostatic potentials associated with adsorption sites. Furthermore, RTS can be clearly observed using inelastic neutron scattering. Building upon previous work of CH4 on MgO (see J.Z. Larese, Physica B, 1998), RTS of CH3D and CH2D2 are interpreted using the pocket state (PS) formalism developed by Hüller et al. The ground librational state of the adsorbate is split into twelve ``pockets'', each localized around one of twelve minima in the rotational potential. We report recent RTS of single monolayers of CH3D and CH2D2 adsorbed on the MgO(100) surface using BASIS at the SNS at ORNL. These pioneering measurements represent the highest resolution investigation available for this (or any other) RTS. The discussion will include challenges in reconciling the transitions predicted by PS theory and the features observed in the experimental data.

  8. Distribution of cooperative unit size of amphiphilic molecules in the phase coexistence region in Langmuir monolayers.

    PubMed

    Hatta, E; Nishimura, T

    2013-02-01

    The dependence of the size of the cooperative unit (C.U.) of amphiphilic molecules on surface pressure (π) in the liquid expanded (LE)-liquid condensed (LC) phase coexistence region of Langmuir monolayers has been formulated and calculated using measured isotherm data. The C.U. size changes largely depending on the surface pressure in the coexistence region: these submicroscopic molecular aggregates are not static objects, but dynamic ones characterized by large fluctuations in size. It has been found that the C.U. size distribution can be a natural consequence of the significant change of monolayer compressibility, which reflects large molecular area density fluctuations, in the coexistence region.

  9. Cross linking molecular systems to form ultrathin dielectric layers

    NASA Astrophysics Data System (ADS)

    Feng, Danqin

    Dehydrogenation leads to cross linking of polymer or polymer like formation in very different systems: self-assembled monolayers and in closo -carboranes leading to the formation of semiconducting and dielectric boron carbide. We find evidence of intermolecular interactions for a self-assembled monolayer (SAM) formed from a large molecular adsorbate, [1,1';4',1"-terphenyl]-4,4"-dimethanethiol, from the dispersion of the molecular orbitals with changing the wave vector k and from the changes with temperature. With the formation self assembled molecular (SAM) layer, the molecular orbitals hybridize to electronic bands, with indications of significant band dispersion of the unoccupied molecular orbitals. Although organic adsorbates and thin films are generally regarded as "soft" materials, the effective Debye temperature, indicative of the dynamic motion of the lattice normal to the surface, can be very high, e.g. in the multilayer film formed from [1,1'-biphenyl]-4,4'-dimethanethiol (BPDMT). Depending on molecular orientation, the effective Debye temperature can be comparable to that of graphite due to the 'stiffness' of the benzene rings, but follows the expected Debye-Waller behavior for the core level photoemission intensities with temperature. This is not always the case. We find that a monomolecular film formed from [1,1';4',1"-terphenyl]-4,4"-dimethanethiol deviates from Debye-Waller temperature behavior and is likely caused by temperature dependent changes in molecular orientation. We also find evidence for the increase in dielectric character with polymerization (cross-linking) in spite of the decrease in the HOMO-LUMO gap upon irradiation of TPDMT. The changes in the HOMO-LUMO gap, with cross-linking, are roughly consistent with the band dispersion. The decomposition and cross-linking processes are also accompanied by changes in molecular orientation. The energetics of the three isomeric carborane cage compounds [ closo-1,2-orthocarborane, closo-1

  10. Multifunctional self-assembled monolayers

    SciTech Connect

    Zawodzinski, T.; Bar, G.; Rubin, S.; Uribe, F.; Ferrais, J.

    1996-06-01

    This is the final report of at three year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The specific goals of this research project were threefold: to develop multifunctional self-assembled monolayers, to understand the role of monolayer structure on the functioning of such systems, and to apply this knowledge to the development of electrochemical enzyme sensors. An array of molecules that can be used to attach electrochemically active biomolecules to gold surfaces has been synthesized. Several members of a class of electroactive compounds have been characterized and the factors controlling surface modification are beginning to be characterized. Enzymes have been attached to self-assembled molecules arranged on the gold surface, a critical step toward the ultimate goal of this project. Several alternative enzyme attachment strategies to achieve robust enzyme- modified surfaces have been explored. Several means of juxtaposing enzymes and mediators, electroactive compounds through which the enzyme can exchange electrons with the electrode surface, have also been investigated. Finally, the development of sensitive biosensors based on films loaded with nanoscale-supported gold particles that have surface modified with the self-assembled enzyme and mediator have been explored.

  11. Adsorption of tannic acid on polyelectrolyte monolayers determined in situ by streaming potential measurements.

    PubMed

    Oćwieja, M; Adamczyk, Z; Morga, M

    2015-01-15

    Physicochemical characteristics of tannic acid (tannin) suspensions comprising its stability for a wide range of ionic strength and pH were thoroughly investigated using UV-vis spectrophotometry, dynamic light scattering and microelectrophoretic measurements. These studies allowed to determine the hydrodynamic diameter of the tannic acid that was 1.63 nm for the pH range 3.5-5.5. For pH above 6.0 the hydrodynamic diameter significantly decreased as a result of the tannin hydrolysis. The electrophoretic mobility measurements confirmed that tannic acid is negatively charged for these values of pH and ionic strength 10(-4)-10(-2) M. Therefore, in order to promote adsorption of tannin molecules on negatively charged mica, the poly(allylamine hydrochloride) (PAH) supporting monolayers were first adsorbed under diffusion transport conditions. The coverage of polyelectrolyte monolayers was regulated by changing bulk concentration of PAH and the adsorption time. The electrokinetic characteristics of bare and PAH-covered mica were determined using the streaming potential measurements. The zeta potential of these PAH monolayers was highly positive, equal to 46 mV for ionic strength of 10(-2) M. The kinetics of tannin adsorption on these PAH supporting monolayers was evaluated by the in situ the streaming potential measurements. The zeta potential of PAH monolayers abruptly decreases with the adsorption of tannin molecules that was quantitatively interpreted in terms of the three-dimensional electrokinetic model. The acid-base characteristics of tannin monolayers were acquired via the streaming potential measurements for a broad range of pH. The obtained results indicate that it is possible to control adsorption of tannin on positively charged surfaces in order to designed new multilayer structures of desirable electrokinetic properties and stability.

  12. Intermolecular forces in spread phospholipid monolayers at oil/water interfaces.

    PubMed

    Mingins, James; Pethica, Brian A

    2004-08-31

    The lateral intermolecular forces between phospholipids are of particular relevance to the behavior of biomembranes, and have been approached via studies of monolayer isotherms at aqueous interfaces, mostly restricted to air/water (A/W) systems. For thermodynamic properties, the oil/water (O/W) interface has major advantages but is experimentally more difficult and less studied. A comprehensive reanalysis of the available thermodynamic data on spread monolayers of phosphatidyl cholines (PC) and phosphatidyl ethanolamines (PE) at O/W interfaces is conducted to identify the secure key features that will underpin further development of molecular models. Relevant recourse is made to isotherms of single-chain molecules and of mixed monolayers to identify the contributions of chain-chain interactions and interionic forces. The emphasis is on the properties of the phase transitions for a range of oil phases. Apparent published discrepancies in thermodynamic properties are resolved and substantial agreement emerges on the main features of these phospholipid monolayer systems. In compression to low areas, the forces between the zwitterions of like phospholipids are repulsive. The molecular model for phospholipid headgroup interactions developed by Stigter et al. accounts well for the virial coefficients in expanded phospholipid O/W monolayers. Inclusion of the changes in configuration and orientation of the zwitterion headgroups on compression, which are indicated by the surface potentials in the phase transition region, and inclusion of the energy of chain demixing from the oil phase will be required for molecular modeling of the phase transitions.

  13. Calixarene monolayers as quartz crystal microbalance sensing elements in aqueous solution.

    PubMed

    Cygan, M T; Collins, G E; Dunbar, T D; Allara, D L; Gibbs, C G; Gutsche, C D

    1999-01-01

    We have examined p-tert-butylcalix[4]arenetetrathiolate (BCAT) monolayers for their potential use as molecular recognition elements for in situ aqueous chemical sensors. Spectroscopic and wetting studies of BCAT monolayers on Au{111} reveal that the calixarene molecules exist in monolayers, preferentially oriented with their phenyl rings parallel to the surface normal axis. Using quartz crystal microbalance (QCM) sensors with gold-coated electrodes, the chemical specificity of monolayers and thin films to a variety of aromatic and aliphatic analytes in aqueous solution was examined. The response of BCAT sensors was compared to the responses of p-tert-butylcalix[4]arene (BCA)- and decanethiolate (DT)-coated QCM electrodes. BCAT is very selective for alkylbenzenes, much more so than either its spray-coated thin-film analogue, BCA, or the highly ordered DT monolayer. From these measurements, the factors behind molecular differentiation in each film are explored. Drawing upon these findings, the roles of cavitation and film order in molecular recognition for calixarene films are discussed. PMID:21662936

  14. Structural characterization of adsorbed helical and beta-sheet peptides

    NASA Astrophysics Data System (ADS)

    Samuel, Newton Thangadurai

    Adsorbed peptides on surfaces have potential applications in the fields of biomaterials, tissue engineering, peptide microarrays and nanobiotechnology. The surface region, the "biomolecular interface" between a material and the biological environment, plays a crucial role in these applications. As a result, characterization of adsorbed peptide structure, especially with respect to identity, concentration, spatial distribution, conformation and orientation, is important. The present research employs NEXAFS (near-edge X-ray absorption fine structure spectroscopy) and SFG (sum frequency generation spectroscopy) to provide information about the adsorbed peptide structure. Soft X-ray NEXAFS is a synchrotron-based technique which typically utilizes polarized X-rays to interrogate surfaces under ultra-high vacuum conditions. SFG is a non-linear optical technique which utilizes a combination of a fixed visible and a tunable infrared laser beams to generate a surface-vibrational spectrum of surface species. SFG has the added advantage of being able to directly analyze the surface-structure at the solid-liquid interface. The main goals of the present research were twofold: characterize the structure of adsorbed peptides (1) ex situ using soft X-ray NEXAFS, and (2) in situ using non-linear laser spectroscopy (SFG). Achieving the former goal involved first developing a comprehensive characterization of the carbon, nitrogen and oxygen k-edge NEXAFS spectra for amino acids, and then using a series of helical and beta-sheet peptides to demonstrate the sensitivity of polarization-dependent NEXAFS to secondary structure of adsorbed peptides. Characterizing the structure of adsorbed peptides in situ using SFG involved developing a model system to probe the solid-liquid interface in situ; demonstrating the ability to probe the molecular interactions and adsorbed secondary structure; following the time-dependent ordering of the adsorbed peptides; and establishing the ability to obtain

  15. Evaluation of gaseous fluorocarbon adsorption isotherms on porous adsorbents under high pressure

    SciTech Connect

    Kaliappan, S.; Furuya, E.G.; Noll, K.E.; Chang, H.T.; Wang, H.C.

    1996-11-01

    In this study data have been collected to aid in the design of a control system that will remove fluorocarbons by adsorbing onto porous adsorbents. A bench scale experimental adsorption system had been designed using high accuracy MKS pressure transducers of 10,000 torr (two nos.) and a 100 torr connected to digital readout units. Tetrafluoromethane (CF{sub 4}) one of the fluorinated carbon family has been selected to evaluate the adsorption characteristics on porous adsorbents. The CF{sub 4} was charged to a sample reservoir in the test system at 200 psig pressure and at 22 C was allowed into an adsorption chamber at small increment of pressure rise. The pressure drop, using a Valydine PS 309 differential pressure gauge from the sample reservoir and the pressure buildup in the adsorption chamber were measured and the amount of CF{sub 4} adsorbed onto the adsorbents was calculated using ideal gas law. Various adsorbents, molecular sieve 13X, Silicagel (14 x 20), Beads Activated Carbon, Granular Activated Carbons PCB 6 x 16, BPL 4 x 10, F300, and F400 had been studied. It has been found that GAC-PCB 6 x 16 has the highest adsorbing capacity of 0.51 gm/gm at the conditions established. GAC-F300 had the second highest adsorbing capacity of 0.413 gm/gm, among all the adsorbents tested. The isotherms were analyzed using several equations employing both two parameters and three parameters. The relationship between the constants and physical properties of adsorbent solids and adsorbate molecules is discussed. The result of this study will be utilized to design a pressure swing fluorocarbon adsorption system that can be economically (using recycle of the collected fluorocarbons) applied to fluorocarbon removal in the electronic industry.

  16. Revealing Defect-State Photoluminescence in Monolayer WS2 by Cryogenic Laser Processing.

    PubMed

    He, Zhengyu; Wang, Xiaochen; Xu, Wenshuo; Zhou, Yingqiu; Sheng, Yuewen; Rong, Youmin; Smith, Jason M; Warner, Jamie H

    2016-06-28

    Understanding the stability of monolayer transition metal dichalcogenides in atmospheric conditions has important consequences for their handling, life-span, and utilization in applications. We show that cryogenic photoluminescence spectroscopy (PL) is a highly sensitive technique to the detection of oxidation induced degradation of monolayer tungsten disulfide (WS2) caused by exposure to ambient conditions. Although long-term exposure to atmospheric conditions causes massive degradation from oxidation that is optically visible, short-term exposure produces no obvious changes to the PL or Raman spectra measured at either room temperature or even cryogenic environment. Laser processing was employed to remove the surface adsorbents, which enables the defect states to be detected via cryogenic PL spectroscopy. Thermal cycling to room temperature and back down to 77 K shows the process is reversible. We also monitor the degradation process of WS2 using this method, which shows that the defect related peak can be observed after one month aging in ambient conditions. PMID:27295362

  17. Electronic Transport of the Adsorbed Trigonal Graphene Flake: A First Principles Calculation

    NASA Astrophysics Data System (ADS)

    Tan, Xun-Qiong

    2014-12-01

    Based on the non-equilibrium Green's function method combined with the density functional theory, we investigate the transport properties of a zigzag trigonal graphene flake (zTGF) adsorbed by a single atom (F or H) or a single group (OH or CH3) at the central site and connected to two symmetric Au electrodes by Au-S bonds. The results show that the OH adsorption can enhance the conductance, followed by the negative differential resistance effects, while the conductance for the zTGF adsorbed by H and CH3 is lowered obviously, and rectifying characteristics can be observed for the H-adsorbed system. The adsorbing action alters the molecular level position and the spatial distribution of the molecular orbital, leading to different transport properties.

  18. Competition between Displacement and Dissociation of a Strong Acid Compared to a Weak Acid Adsorbed on Silica Particle Surfaces: The Role of Adsorbed Water.

    PubMed

    Fang, Yuan; Tang, Mingjin; Grassian, Vicki H

    2016-06-16

    The adsorption of nitric (HNO3) and formic (HCOOH) acids on silica particle surfaces and the effect of adsorbed water have been investigated at 296 K using transmission FTIR spectroscopy. Under dry conditions, both nitric and formic acids adsorb reversibly on silica. Additionally, the FTIR spectra show that both of these molecules remain in the protonated form. At elevated relative humidities (RH), adsorbed water competes both for surface adsorption sites with these acids as well as promotes their dissociation to hydronium ions and the corresponding anions. Compared to HNO3, the extent of dissociation is much smaller for HCOOH, very likely because it is a weaker acid. This study provides valuable insights into the interaction of HNO3 and HCOOH with silica surface on the molecular level and further reveals the complex roles of surface-adsorbed water in atmospheric heterogeneous chemistry of mineral dust particles-many of these containing silica.

  19. Competition between Displacement and Dissociation of a Strong Acid Compared to a Weak Acid Adsorbed on Silica Particle Surfaces: The Role of Adsorbed Water.

    PubMed

    Fang, Yuan; Tang, Mingjin; Grassian, Vicki H

    2016-06-16

    The adsorption of nitric (HNO3) and formic (HCOOH) acids on silica particle surfaces and the effect of adsorbed water have been investigated at 296 K using transmission FTIR spectroscopy. Under dry conditions, both nitric and formic acids adsorb reversibly on silica. Additionally, the FTIR spectra show that both of these molecules remain in the protonated form. At elevated relative humidities (RH), adsorbed water competes both for surface adsorption sites with these acids as well as promotes their dissociation to hydronium ions and the corresponding anions. Compared to HNO3, the extent of dissociation is much smaller for HCOOH, very likely because it is a weaker acid. This study provides valuable insights into the interaction of HNO3 and HCOOH with silica surface on the molecular level and further reveals the complex roles of surface-adsorbed water in atmospheric heterogeneous chemistry of mineral dust particles-many of these containing silica. PMID:27220375

  20. Optical modulation of nano-gap tunnelling junctions comprising self-assembled monolayers of hemicyanine dyes.

    PubMed

    Pourhossein, Parisa; Vijayaraghavan, Ratheesh K; Meskers, Stefan C J; Chiechi, Ryan C

    2016-01-01

    Light-driven conductance switching in molecular tunnelling junctions that relies on photoisomerization is constrained by the limitations of kinetic traps and either by the sterics of rearranging atoms in a densely packed monolayer or the small absorbance of individual molecules. Here we demonstrate light-driven conductance gating; devices comprising monolayers of hemicyanine dyes trapped between two metallic nanowires exhibit higher conductance under irradiation than in the dark. The modulation of the tunnelling current occurs faster than the timescale of the measurement (∼1 min). We propose a mechanism in which a fraction of molecules enters an excited state that brings the conjugated portion of the monolayer into resonance with the electrodes. This mechanism is supported by calculations showing the delocalization of molecular orbitals near the Fermi energy in the excited and cationic states, but not the ground state and a reasonable change in conductance with respect to the effective barrier width. PMID:27272394