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Sample records for bilayer structure determination

  1. Fluid bilayer structure determination: Joint refinement in composition space using X-ray and neutron diffraction data

    Energy Technology Data Exchange (ETDEWEB)

    White, S.H. [Univ. of California, Irvine, CA (United States); Wiener, M.C. [Univ. of California, San Francisco, CA (United States)

    1994-12-31

    Experimentally-determined structural models of fluid lipid bilayers are essential for verifying molecular dynamics simulations of bilayers and for understanding the structural consequences of peptide interactions. The extreme thermal motion of bilayers precludes the possibility of atomic-level structural models. Defining {open_quote}the structure{close_quote} of a bilayer as the time-averaged transbilayer distribution of the water and the principal lipid structural groups such as the carbonyls and double-bonds (quasimolecular fragments), one can represent the bilayer structure as a sum of Gaussian functions referred to collectively as the quasimolecular structure. One method of determining the structure is by neutron diffraction combined with exhaustive specific deuteration. This method is impractical because of the expense of the chemical syntheses and the limited amount of neutron beam time currently available. We have therefore developed the composition space refinement method for combining X-ray and minimal neutron diffraction data to arrive at remarkably detailed and accurate structures of fluid bilayers. The composition space representation of the bilayer describes the probability of occupancy per unit length across the width of the bilayer of each quasimolecular component and permits the joint refinement of X-ray and neutron lamellar diffraction data by means of a single quasimolecular structure that is fitted simultaneously to both data sets. Scaling of each component by the appropriate neutron or X-ray scattering length maps the composition-space profile to the appropriate scattering length space for comparison to experimental data. The difficulty with the method is that fluid bilayer structures are generally only marginally determined by the experimental data. This means that the space of possible solutions must be extensively explored in conjunction with a thorough analysis of errors.

  2. X-ray structure determination of fully hydrated L alpha phase dipalmitoylphosphatidylcholine bilayers.

    OpenAIRE

    Nagle, J F; Zhang, R.; Tristram-Nagle, S; Sun, W.; Petrache, H I; Suter, R M

    1996-01-01

    Bilayer form factors obtained from x-ray scattering data taken with high instrumental resolution are reported for multilamellar vesicles of L alpha phase lipid bilayers of dipalmitoylphosphatidylcholine at 50 degrees C under varying osmotic pressure. Artifacts in the magnitudes of the form factors due to liquid crystalline fluctuations have been eliminated by using modified Caillé theory. The Caillé fluctuation parameter eta 1 increases systematically with increasing lamellar D spacing and th...

  3. Determination of structural topology of a membrane protein in lipid bilayers using polarization optimized experiments (POE) for static and MAS solid state NMR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Mote, Kaustubh R. [University of Minnesota, Department of Chemistry (United States); Gopinath, T. [University of Minnesota, Department of Biochemistry, Molecular Biology and Biophysics (United States); Veglia, Gianluigi, E-mail: vegli001@umn.edu [University of Minnesota, Department of Chemistry (United States)

    2013-10-15

    The low sensitivity inherent to both the static and magic angle spinning techniques of solid-state NMR (ssNMR) spectroscopy has thus far limited the routine application of multidimensional experiments to determine the structure of membrane proteins in lipid bilayers. Here, we demonstrate the advantage of using a recently developed class of experiments, polarization optimized experiments, for both static and MAS spectroscopy to achieve higher sensitivity and substantial time-savings for 2D and 3D experiments. We used sarcolipin, a single pass membrane protein, reconstituted in oriented bicelles (for oriented ssNMR) and multilamellar vesicles (for MAS ssNMR) as a benchmark. The restraints derived by these experiments are then combined into a hybrid energy function to allow simultaneous determination of structure and topology. The resulting structural ensemble converged to a helical conformation with a backbone RMSD {approx}0.44 A, a tilt angle of 24 Degree-Sign {+-} 1 Degree-Sign , and an azimuthal angle of 55 Degree-Sign {+-} 6 Degree-Sign . This work represents a crucial first step toward obtaining high-resolution structures of large membrane proteins using combined multidimensional oriented solid-state NMR and magic angle spinning solid-state NMR.

  4. Determination of structural topology of a membrane protein in lipid bilayers using polarization optimized experiments (POE) for static and MAS solid state NMR spectroscopy

    International Nuclear Information System (INIS)

    The low sensitivity inherent to both the static and magic angle spinning techniques of solid-state NMR (ssNMR) spectroscopy has thus far limited the routine application of multidimensional experiments to determine the structure of membrane proteins in lipid bilayers. Here, we demonstrate the advantage of using a recently developed class of experiments, polarization optimized experiments, for both static and MAS spectroscopy to achieve higher sensitivity and substantial time-savings for 2D and 3D experiments. We used sarcolipin, a single pass membrane protein, reconstituted in oriented bicelles (for oriented ssNMR) and multilamellar vesicles (for MAS ssNMR) as a benchmark. The restraints derived by these experiments are then combined into a hybrid energy function to allow simultaneous determination of structure and topology. The resulting structural ensemble converged to a helical conformation with a backbone RMSD ∼0.44 Å, a tilt angle of 24° ± 1°, and an azimuthal angle of 55° ± 6°. This work represents a crucial first step toward obtaining high-resolution structures of large membrane proteins using combined multidimensional oriented solid-state NMR and magic angle spinning solid-state NMR

  5. Polymer bilayer structure via inkjet printing

    Science.gov (United States)

    Xia, Yajun; Friend, Richard H.

    2006-04-01

    We report the formation of a polymer bilayer structure by inkjet printing poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) from p-xylene solution onto a poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine (TFB) thin film. Despite the compatibility of both polymers with the same organic solvent, a TFB layer under the later-deposited F8BT was directly observed through fluorescence microscopy. Micro-Raman spectroscopy reveals that this bottom layer is ˜10nm thick for a film made by inkjet printing F8BT onto a TFB film of ˜20nm thickness. The bilayer structure leads to enhanced efficiency for light-emitting diodes in comparison with devices made from spin-coated TFB:F8BT blend films.

  6. Macroscopic and Nanoscopic Heterogeneous Structures in a Three-Component Lipid Bilayer Mixtures Determined by Atomic Force Microscopy.

    Science.gov (United States)

    Khadka, Nawal K; Ho, Chian Sing; Pan, Jianjun

    2015-11-17

    Much of lipid raft properties can be inferred from phase behavior of multicomponent lipid membranes. We use liquid compatible atomic force microscopy (AFM) to study a three-component system composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), egg sphingomyelin (eSM), and cholesterol. Specifically, we obtain macroscopic and nanoscopic heterogeneous structures in a broad compositional space of DOPC/eSM/cholesterol (23 °C). In the macroscopic liquid coexisting region, we quantify area fraction of the coexisting phases and determine a set of thermodynamic tie-lines. When lipid compositions are near the critical point, we obtain fluctuation-like nanoscopic structures. We also use AFM height images to explore the hypothetical three-phase coexisting region. Finally, we use fluorescence microscopy to compare the phase behavior from our AFM measurements to that in free-floating giant unilamellar vesicles (GUVs). Our results highlight the role of lipid composition in mediating lipid domain formation and stability. PMID:26506226

  7. Electronic structure theory of weakly interacting bilayers

    Science.gov (United States)

    Fang, Shiang; Kaxiras, Efthimios

    2016-06-01

    We derive electronic structure models for weakly interacting bilayers such as graphene-graphene and graphene-hexagonal boron nitride, based on density functional theory calculations followed by Wannier transformation of electronic states. These transferable interlayer coupling models can be applied to investigate the physics of bilayers with arbitrary translations and twists. The functional form, in addition to the dependence on the distance, includes the angular dependence that results from higher angular momentum components in the Wannier pz orbitals. We demonstrate the capabilities of the method by applying it to a rotated graphene bilayer, which produces the analytically predicted renormalization of the Fermi velocity, Van Hove singularities in the density of states, and moiré pattern of the electronic localization at small twist angles. We further extend the theory to obtain the effective couplings by integrating out neighboring layers. This approach is instrumental for the design of van der Walls heterostructures with desirable electronic features and transport properties and for the derivation of low-energy theories for graphene stacks, including proximity effects from other layers.

  8. Real-Time Structural Investigation of a Lipid Bilayer during Its Interaction with Melittin Using Sum Frequency Generation Vibrational Spectroscopy

    OpenAIRE

    Chen, Xiaoyun; Wang, Jie; Kristalyn, Cornelius B.; Chen, Zhan

    2007-01-01

    Interactions between membrane bilayers and peptides/proteins are ubiquitous throughout a cell. To determine the structure of membrane bilayers and the associated peptides/proteins, model systems such as supported lipid bilayers are often used. It has been difficult to directly investigate the interactions between a single membrane bilayer and peptides/proteins without exogenous labeling. In this work we demonstrate that sum frequency generation vibrational spectroscopy can be employed to stud...

  9. Hydration-optimized oriented phospholipid bilayer samples for solid-state NMR structural studies of membrane proteins

    OpenAIRE

    Marassi, Francesca M.; Crowell, Kevin J.

    2003-01-01

    The preparation of oriented, hydration-optimized lipid bilayer samples, for NMR structure determination of membrane proteins, is described. The samples consist of planar phospholipid bilayers, containing membrane proteins, that are oriented on single pairs of glass slides, and are placed in the coil of the NMR probe with the bilayer plane perpendicular to the direction of the magnetic field. Lipid bilayers provide a medium that closely resembles the biological membrane, and sample orientation...

  10. Structure and properties of mixed-chain phosphatidylcholine bilayers.

    Science.gov (United States)

    Shah, J; Sripada, P K; Shipley, G G

    1990-05-01

    The structural and thermotropic properties of the hydrated mixed-chain phosphatidylcholines (PCs), C(8):C(18)-PC and C(10):C(18)-PC, have been studied by X-ray diffraction and differential scanning calorimetry. For fully hydrated C(8):C(18)-PC, the reversible chain melting transition is observed at 9.9 degrees C (delta H = 7.3 kcal/mol). X-ray diffraction at 0 degrees C (below the chain melting transition) shows a small bilayer repeat distance, d = 51.0 A, and a sharp, symmetric wide-angle reflection at 4.1 A, characteristic of a mixed interdigitated bilayer gel phase [see McIntosh, T. J., Simon, S. A., Ellington, J. C., Jr., & Porter, N. A. (1984) Biochemistry 23, 4038-4044; Hui, S. W., Mason, J. T., & Huang, C. (1984) Biochemistry 23, 5570-5577]. At 30 degrees C (above the chain melting transition), a diffuse band is observed at 4.5 A characteristic of an L alpha phase but with an increased bilayer periodicity, d = 61 A. Both the calculated lipid bilayer thickness (d1) and that determined directly from electron density profiles (dp-p) show unusual increases as a consequence of chain melting. In contrast, fully hydrated C(10):C(18)-PC shows an asymmetric endothermic transition at 11.8 degrees C. Below the chain melting transition, two lamellar phases are present, corresponding to coexisting interdigitated (d = 52.3 A) and noninterdigitated (d = 62.5 A) bilayer gel phases. The relative amounts of these phases depend upon the low-temperature incubation and/or hydration conditions, suggesting conversions, albeit kinetically complex, between metastable, and stable phases. The different behavior of C(8):C(18)-PC and C(10):C(18)-PC, as well as their positional isomers, is rationalized in terms of the molecular conformation of PC. PMID:2361142

  11. Nuclear Magnetic Resonance Structural Studies of Membrane Proteins in Micelles and Bilayers

    OpenAIRE

    Gong, Xiao-Min; Franzin, Carla M.; Thai, Khang; Yu, Jinghua; Marassi, Francesca M.

    2007-01-01

    Nuclear magnetic resonance (NMR) spectroscopy enables determination of membrane protein structures in lipid environments, such as micelles and bilayers. This chapter outlines the steps for membrane-protein structure determination using solution NMR with micelle samples, and solid-state NMR with oriented lipid-bilayer samples. The methods for protein expression and purification, sample preparation, and NMR experiments are described and illustrated with examples from γ and CHIF, two membrane pr...

  12. Inter- and intramolecular distance measurements by solid-state MAS NMR: Determination of gramicidin A channel dimer structure in hydrated phospholipid bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Fu Riqiang; Cotten, Myriam; Cross, Timothy A. [Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory (United States)

    2000-03-15

    Distance constraints are an important complement to orientational constraints. While a high-resolution monomer structure of the ion channel forming polypeptide, gramicidin A, has been solved with 120 orientational constraints, the precise geometry of the dimer interface has not been characterized. Here, using both {sup 13}C and {sup 15}N labeled gramicidin A samples in hydrated phospholipid bilayers, both inter- and intramolecular distances have been measured with a recently developed simultaneous frequency and amplitude modulation (SFAM) solid-state NMR scheme. Using this approach {sup 15}N-{sup 13}C{sub 1} residual dipolar couplings across a hydrogen bond as small as 20 {+-} 2 Hz have been characterized. While such distances are on the order of 4.2 {+-} 0.2 A, the spectroscopy is complicated by rapid global motion of the molecular structure about the bilayer normal and channel axis. Consequently, the nominal 40 Hz dipolar coupling is averaged depending on the orientation of the internuclear vector with respect to the motional axis. The intermolecular distance confirmed the previously described monomeric structure, while the intramolecular distance across the monomer-monomer interface defined this junction and confirmed the previous model of this interface.

  13. Stress Transfer and Structural Failure of Bilayered Material Systems

    Science.gov (United States)

    Prieto-Munoz, Pablo Arthur

    Bilayered material systems are common in naturally formed or artificially engineered structures. Understanding how loads transfer within these structural systems is necessary to predict failure and develop effective designs. Existing methods for evaluating the stress transfer in bilayered materials are limited to overly simplified models or require experimental calibration. As a result, these methods have failed to accurately account for such structural failures as the creep induced roofing panel collapse of Boston's I-90 connector tunnel, which was supported by adhesive anchors. The one-dimensional stress analyses currently used for adhesive anchor design cannot account for viscoelastic creep failure, and consequently results in dangerously under-designed structural systems. In this dissertation, a method for determining the two-dimensional stress and displacement fields for a generalized bilayered material system is developed, and proposes a closed-form analytical solution. A general linear-elastic solution is first proposed by decoupling the elastic governing equations from one another through the so-called plane assumption. Based on this general solution, an axisymmetric problem and a plane strain problem are formulated. These are applied to common bilayered material systems such as: (1) concrete adhesive anchors, (2) material coatings, (3) asphalt pavements, and (4) layered sedimentary rocks. The stress and displacement fields determined by this analytical analysis are validated through the use of finite element models. Through the correspondence principle, the linear-elastic solution is extended to consider time-dependent viscoelastic material properties, thus facilitating the analysis of adhesive anchors and asphalt pavements while incorporating their viscoelastic material behavior. Furthermore, the elastic stress analysis can explain the fracturing phenomenon of material coatings, pavements, and layered rocks, successfully predicting their fracture

  14. Molecular Simulation Study on the Influence of Dimethylsulfoxide on the Structure of Phospholipid Bilayers

    OpenAIRE

    Sum, Amadeu K.; de Pablo, Juan J.

    2003-01-01

    Molecular dynamics simulations of dipalmitoylphosphatidylcholine (DPPC) lipid bilayer/water systems were performed in the presence of dimethylsulfoxide (DMSO) at 2, 5, 10, and 100 mol % DMSO (lipid-free basis). The equilibrium structure and several dynamic properties were determined for these systems. Results show that DMSO penetrates much deeper into the bilayer than water does. It is also found that DMSO molecules do not interact with the polar groups of the lipid headgroup, but exhibit a p...

  15. The effect of temperature on supported dipalmitoylphosphatidylcholine (DPPC) bilayers: structure and lubrication performance.

    Science.gov (United States)

    Wang, Min; Zander, Thomas; Liu, Xiaoyan; Liu, Chao; Raj, Akanksha; Wieland, D C Florian; Garamus, Vasil M; Willumeit-Römer, Regine; Claesson, Per Martin; Dėdinaitė, Andra

    2015-05-01

    Phospholipids fulfill an important role in joint lubrication. They, together with hyaluronan and glycoproteins, are the biolubricants that sustain low friction between cartilage surfaces bathed in synovial fluid. In this work we have investigated how the friction force and load bearing capacity of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers on silica surfaces are affected by temperature, covering the temperature range 25-52°C. Friction forces have been determined utilizing the AFM colloidal probe technique, which showed that DPPC bilayers are able to provide low friction forces over the whole temperature interval. However, the load bearing capacity is improved at higher temperatures. We interpret this finding as being a consequence of lower rigidity and higher self-healing capacity of the DPPC bilayer in the liquid disordered state compared to the gel state. The corresponding structure of solid supported DPPC bilayers at the silica-liquid interface has been followed using X-ray reflectivity measurements, which suggests that the DPPC bilayer is in the gel phase at 25°C and 39°C and in the liquid disordered state at 55°C. Well-defined bilayer structures were observed for both phases. The deposited DPPC bilayers were also imaged using AFM PeakForce Tapping mode, and these measurements indicated a less homogeneous layer at temperatures below 37°C. PMID:25596372

  16. Tethered and Polymer Supported Bilayer Lipid Membranes: Structure and Function

    Directory of Open Access Journals (Sweden)

    Jakob Andersson

    2016-05-01

    Full Text Available Solid supported bilayer lipid membranes are model systems to mimic natural cell membranes in order to understand structural and functional properties of such systems. The use of a model system allows for the use of a wide variety of analytical tools including atomic force microscopy, impedance spectroscopy, neutron reflectometry, and surface plasmon resonance spectroscopy. Among the large number of different types of model membranes polymer-supported and tethered lipid bilayers have been shown to be versatile and useful systems. Both systems consist of a lipid bilayer, which is de-coupled from an underlying support by a spacer cushion. Both systems will be reviewed, with an emphasis on the effect that the spacer moiety has on the bilayer properties.

  17. The Water Permeability and Pore Entrance Structure of Aquaporin-4 Depend on Lipid Bilayer Thickness.

    Science.gov (United States)

    Tong, Jihong; Wu, Zhe; Briggs, Margaret M; Schulten, Klaus; McIntosh, Thomas J

    2016-07-12

    Aquaporin-4 (AQP4), the primary water channel in glial cells of the mammalian brain, plays a critical role in water transport in the central nervous system. Previous experiments have shown that the water permeability of AQP4 depends on the cholesterol content in the lipid bilayer, but it was not clear whether changes in permeability were due to direct cholesterol-AQP4 interactions or to indirect effects caused by cholesterol-induced changes in bilayer elasticity or bilayer thickness. To determine the effects resulting only from bilayer thickness, here we use a combination of experiments and simulations to analyze AQP4 in cholesterol-free phospholipid bilayers with similar elastic properties but different hydrocarbon core thicknesses previously determined by x-ray diffraction. The channel (unit) water permeabilities of AQP4 measured by osmotic-gradient experiments were 3.5 ± 0.2 × 10(-13) cm(3)/s (mean ± SE), 3.0 ± 0.3 × 10(-13) cm(3)/s, 2.5 ± 0.2 × 10(-13) cm(3)/s, and 0.9 ± 0.1 × 10(-13) cm(3)/s in bilayers containing (C22:1)(C22:1)PC, (C20:1)(C20:1)PC, (C16:0)(C18:1)PC, and (C13:0)(C13:0)PC, respectively. Channel permeabilities obtained by molecular dynamics (MD) simulations were 3.3 ± 0.1 × 10(-13) cm(3)/s and 2.5 ± 0.1 × 10(-13) cm(3)/s in (C22:1)(C22:1)PC and (C14:0)(C14:0)PC bilayers, respectively. Both the osmotic-gradient and MD-simulation results indicated that AQP4 channel permeability decreased with decreasing bilayer hydrocarbon thickness. The MD simulations also suggested structural modifications in AQP4 in response to changes in bilayer thickness. Although the simulations showed no appreciable changes to the radius of the pore located in the hydrocarbon region of the bilayers, the simulations indicated that there were changes in both pore length and α-helix organization near the cytoplasmic vestibule of the channel. These structural changes, caused by mismatch between the hydrophobic length of AQP4 and the bilayer hydrocarbon

  18. Determining bilayer hydrocarbon thickness from neutron diffraction measurements using strip-function models

    International Nuclear Information System (INIS)

    Neutron diffraction methods provide information about the distribution of matter in biological and model membrane systems. The information is derived from plots (profiles) of scattering length density along an axis normal to the membrane plane. Without the use of specific deuteration, the generally low resolution of the profiles limits their interpretation in terms of specific chemical constituents (e.g., lipid headgroup, lipid hydrocarbon, protein, and water). A fundamental and useful structural assignment to make is the boundary between the headgroup and hydrocarbon regions of bilayers. We demonstrate here that strip-function model representations of neutron scattering length density profiles of bilayers are sufficient to determine accurately the position of the headgroup-hydrocarbon boundary. The resulting hydrocarbon thickness of the bilayer is useful for determining the area per lipid molecule and consequently the molecular packing arrangements of the membrane constituents. We analyze data obtained from dioleoylphosphatidylcholine (DOPC) bilayers at 66% RH using standard Fourier profile analyses and from DOPC deuterated specifically at the C-2 carbon of the acyl chains using difference Fourier analysis. We demonstrate that strip-function models accurately define the positions of the C-2 carbons and thus the hydrocarbon thickness (dhc) of the bilayer. We then show, using quasi-molecular models, that the strip-model analysis probably provides an accurate measure of dhc because of the exceptionally high scattering length density difference between the carbonyl and methylene groups

  19. Nuclear magnetic resonance structural studies of membrane proteins in micelles and bilayers.

    Science.gov (United States)

    Gong, Xiao-Min; Franzin, Carla M; Thai, Khang; Yu, Jinghua; Marassi, Francesca M

    2007-01-01

    Nuclear magnetic resonance (NMR) spectroscopy enables determination of membrane protein structures in lipid environments, such as micelles and bilayers. This chapter outlines the steps for membrane-protein structure determination using solution NMR with micelle samples, and solid-state NMR with oriented lipid-bilayer samples. The methods for protein expression and purification, sample preparation, and NMR experiments are described and illustrated with examples from gamma and CHIF, two membrane proteins that function as regulatory subunits of the Na+- and K+-ATPase. PMID:17951757

  20. Structure and metastability of N-lignocerylgalactosylsphingosine (cerebroside) bilayers.

    Science.gov (United States)

    Reed, R A; Shipley, G G

    1987-01-26

    Differential scanning calorimetry (DSC) and X-ray diffraction have been used to study hydrated N-lignocerylgalactosylsphingosine (NLGS) bilayers. DSC of fully hydrated NLGS shows an endothermic transition at 69-70 degrees C, immediately followed by an exothermic transition at 72-73 degrees C; further heating shows a high-temperature (Tc = 82 degrees C), high-enthalpy (delta H = 15.3 kcal/mol NLGS) transition. Heating to 75 degrees C, cooling to 20 degrees C and subsequent reheating shows no transitions at 69-73 degrees C; only the high-temperature (82 degrees C), high-enthalpy (15.3 kcal/mol) transition. Two exothermic transitions are observed on cooling; for the upper transition its temperature (about 65 degrees C) and enthalpy (about 6 kcal/mol NLGS) are essentially independent of cooling rate, whereas the lower transition exhibits marked changes in both temperature (30----60 degrees C) and enthalpy (2.2----9.5 kcal/mol NLGS) as the cooling rate decreases from 40 to 0.625 Cdeg/min. On reheating, the enthalpy of the 69-70 degrees C transition is dependent on the previous cooling rate. The DSC data provide clear evidence of conversions between metastable and stable forms. X-ray diffraction data recorded at 26, 75 and 93 degrees C show clearly that NLGS bilayer phases are present at all temperatures. The X-ray diffraction pattern at 75 degrees C shows a bilayer periodicity d = 65.4 A, and a number of sharp reflections in the wide-angle region indicative of a crystalline chain packing mode. This stable bilayer form converts to a liquid-crystal bilayer phase; at 93 degrees C, the bilayer periodicity d = 59.1 A, and a diffuse reflection at 1/4.6 A-1 is observed. The diffraction pattern at 22 degrees C represents a combination of the stable and metastable low-temperature bilayer forms. NLGS exhibits a complex pattern of thermotropic changes related to conversions between metastable (gel), stable (crystalline) and liquid-crystalline bilayer phases. The structure and

  1. Formation and finite element analysis of tethered bilayer lipid structures.

    Science.gov (United States)

    Kwak, Kwang Joo; Valincius, Gintaras; Liao, Wei-Ching; Hu, Xin; Wen, Xuejin; Lee, Andrew; Yu, Bo; Vanderah, David J; Lu, Wu; Lee, L James

    2010-12-01

    Rapid solvent exchange of an ethanolic solution of diphytanoyl phosphatidylcholine (DPhyPC) in the presence of a mixed self-assembled monolayer (SAM) [thiolipid/β-mercaptoethanol (βME) (3/7 mol/mol) on Au] shows a transition from densely packed tethered bilayer lipid membranes [(dp)tBLMs], to loosely packed tethered bilayer lipid membranes [(lp)tBLMs], and tethered bilayer liposome nanoparticles (tBLNs) with decreasing DPhyPC concentration. The tethered lipidic constructs in the aqueous medium were analyzed by atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). Finite element analysis (FEA) was applied to interpret spectral EIS features without referring to equivalent circuit modeling. Using structural data obtained earlier from neutron reflectometry and dielectric constants of lipid bilayers, we reproduced experimentally observed features of the electrochemical impedance (EI) spectra of complex surface constructs involving small pinhole defects, large membrane-free patches, and bound liposomes. We demonstrated by FEA that highly insulating (dp)tBLMs with low-defect density exhibit EI spectra in the shape of a perfect semicircle with or without low-frequency upward "tails" in the Cole-Cole representation. Such EI spectra were observed at DPhyPC concentrations of >5 × 10(-3) mol L(-1). While AFM was not able to visualize very small lateral defects in such films, EI spectra unambiguously signaled their presence by increased low frequency "tails". Using FEA we demonstrate that films with large diameter visible defects (>25 nm by AFM) produce EI spectral features consisting of two semicircles of comparable size. Such films were typically obtained at DPhyPC concentrations of FEA revealed that, to account for these EI features for bound liposome systems (50-500 nm diameter), one needs to assume much lower tBLM conductivities of the submembrane space, which separates the electrode surface and the phospholipid bilayer. Alternatively, FEA

  2. Phase Transition of MoS2 Bilayer Structures

    DEFF Research Database (Denmark)

    Pandey, Mohnish; Bothra, Pallavi; Pati, Swapan K.

    2016-01-01

    In the present study, using density functional calculations we have investigated a possible mechanism for the structural phase transition of the semiconducting bilayer 2H-MoS2 via lithiation. The results indicate that the addition of lithium to the bilayer 2H-MoS2 transforms the bilayer to a hete...

  3. Structural Effects of Small Molecules on Phospholipid Bilayers Investigated by Molecular Simulations

    CERN Document Server

    Lee, B W; Sum, A K; Vattulainen, I; Patra, M; Karttunen, M; Lee, Bryan W; Faller, Roland; Sum, Amadeu K; Vattulainen, Ilpo; Patra, Michael; Karttunen, Mikko

    2004-01-01

    We summarize and compare recent Molecular Dynamics simulations on the interactions of dipalmitoylphosphatidylcholine (DPPC) bilayers in the liquid crystalline phase with a number of small molecules including trehalose, a disaccharide of glucose, alcohols, and dimethylsulfoxide (DMSO). The sugar molecules tend to stabilize the structure of the bilayer as they bridge adjacent lipid headgroups. They do not strongly change the structure of the bilayer. Alcohols and DMSO destabilize the bilayer as they increase its area per molecule in the bilayer plane and decrease the order parameter. Alcohols have a stronger detrimental effect than DMSO. The observables which we compare are the area per molecule in the plane of the bilayer, the membrane thickness, and the NMR order parameter of DPPC hydrocarbon tails. The area per molecule and the order parameter are very well correlated whereas the bilayer thickness is not necessarily correlated with them.

  4. Neutron Diffraction Studies of Fluid Bilayers with Transmembrane Proteins: Structural Consequences of the Achondroplasia Mutation

    OpenAIRE

    Han, Xue; Mihailescu, Mihaela; Hristova, Kalina

    2006-01-01

    Achondroplasia, the most common form of human dwarfism, is due to a G380R mutation in the transmembrane domain of fibroblast growth factor receptor 3 (FGFR3) in >97% of the studied cases. While the molecular mechanism of pathology induction is under debate, the structural consequences of the mutation have not been studied. Here we use neutron diffraction to determine the disposition of FGFR3 transmembrane domain in fluid lipid bilayers, and investigate whether the G380R mutation affects the t...

  5. Assessment of pseudo-bilayer structures in the heterogate germanium electron-hole bilayer tunnel field-effect transistor

    Energy Technology Data Exchange (ETDEWEB)

    Padilla, J. L., E-mail: jose.padilladelatorre@epfl.ch; Alper, C.; Ionescu, A. M. [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Medina-Bailón, C.; Gámiz, F. [Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain)

    2015-06-29

    We investigate the effect of pseudo-bilayer configurations at low operating voltages (≤0.5 V) in the heterogate germanium electron-hole bilayer tunnel field-effect transistor (HG-EHBTFET) compared to the traditional bilayer structures of EHBTFETs arising from semiclassical simulations where the inversion layers for electrons and holes featured very symmetric profiles with similar concentration levels at the ON-state. Pseudo-bilayer layouts are attained by inducing a certain asymmetry between the top and the bottom gates so that even though the hole inversion layer is formed at the bottom of the channel, the top gate voltage remains below the required value to trigger the formation of the inversion layer for electrons. Resulting benefits from this setup are improved electrostatic control on the channel, enhanced gate-to-gate efficiency, and higher I{sub ON} levels. Furthermore, pseudo-bilayer configurations alleviate the difficulties derived from confining very high opposite carrier concentrations in very thin structures.

  6. Assessment of pseudo-bilayer structures in the heterogate germanium electron-hole bilayer tunnel field-effect transistor

    International Nuclear Information System (INIS)

    We investigate the effect of pseudo-bilayer configurations at low operating voltages (≤0.5 V) in the heterogate germanium electron-hole bilayer tunnel field-effect transistor (HG-EHBTFET) compared to the traditional bilayer structures of EHBTFETs arising from semiclassical simulations where the inversion layers for electrons and holes featured very symmetric profiles with similar concentration levels at the ON-state. Pseudo-bilayer layouts are attained by inducing a certain asymmetry between the top and the bottom gates so that even though the hole inversion layer is formed at the bottom of the channel, the top gate voltage remains below the required value to trigger the formation of the inversion layer for electrons. Resulting benefits from this setup are improved electrostatic control on the channel, enhanced gate-to-gate efficiency, and higher ION levels. Furthermore, pseudo-bilayer configurations alleviate the difficulties derived from confining very high opposite carrier concentrations in very thin structures

  7. A Molecular Dynamics Study of the Structural and Dynamical Properties of Putative Arsenic Substituted Lipid Bilayers

    Directory of Open Access Journals (Sweden)

    Ratna Juwita

    2013-04-01

    Full Text Available Cell membranes are composed mainly of phospholipids which are in turn, composed of five major chemical elements: carbon, hydrogen, nitrogen, oxygen, and phosphorus. Recent studies have suggested the possibility of sustaining life if the phosphorus is substituted by arsenic. Although this issue is still controversial, it is of interest to investigate the properties of arsenated-lipid bilayers to evaluate this possibility. In this study, we simulated arsenated-lipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-arsenocholine (POAC, lipid bilayers using all-atom molecular dynamics to understand basic structural and dynamical properties, in particular, the differences from analogous 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, (POPC lipid bilayers. Our simulations showed that POAC lipid bilayers have distinct structural and dynamical properties from those of native POPC lipid bilayers. Relative to POPC lipid bilayers, POAC lipid bilayers have a more compact structure with smaller lateral areas and greater order. The compact structure of POAC lipid bilayers is due to the fact that more inter-lipid salt bridges are formed with arsenate-choline compared to the phosphate-choline of POPC lipid bilayers. These inter-lipid salt bridges bind POAC lipids together and also slow down the head group rotation and lateral diffusion of POAC lipids. Thus, it would be anticipated that POAC and POPC lipid bilayers would have different biological implications.

  8. Excitonic gap formation and condensation in the bilayer graphene structure

    Science.gov (United States)

    Apinyan, V.; Kopeć, T. K.

    2016-09-01

    We have studied the excitonic gap formation in the Bernal Stacked, bilayer graphene (BLG) structures at half-filling. Considering the local Coulomb interaction between the layers, we calculate the excitonic gap parameter and we discuss the role of the interlayer and intralayer Coulomb interactions and the interlayer hopping on the excitonic pair formation in the BLG. Particularly, we predict the origin of excitonic gap formation and condensation, in relation to the furthermost interband optical transition spectrum. The general diagram of excitonic phase transition is given, explaining different interlayer correlation regimes. The temperature dependence of the excitonic gap parameter is shown and the role of the chemical potential, in the BLG, is discussed in details.

  9. Organic conductor/high-Tc superconductor bilayer structures

    International Nuclear Information System (INIS)

    Electrochemical techniques are exploited to fabricate conducive polymer/high-Tc superconductor bilayer structures. Scanning electron microscopy and electrochemical techniques are utilized to characterize the electrodeposition of polypyrrole layers grown onto YBa2Cu3O7-δ films. In such hybrid polymer/superconductor systems, it is found that when the polymer is oxidized to its conductive state, the transition temperature (Tc) and critical currents (Jc) of the underlying superconductor films are suppressed. Reversible modulation of the values of the transition temperatures of up to 50 K are noted for these structures. Upon reduction of the conductive polymer layer back to its non-conductive form, both Tc and Jc are found to return to values close to those acquired for the underivatized YBa2Cu3O7-δ films. Moreover, measurements as a function of temperature of the polymer/superconductor interface resistance show dramatic decrease in this value at Tc. Also, estimates of superconducting coherence lengths within the organic conductor samples suggest superconducting properties over macroscopically large distances within the organic materials can be expected. Collectively these results are consistent with the first observation of a conductive polymer proximity effect

  10. Modeling constrained sintering of bi-layered tubular structures

    DEFF Research Database (Denmark)

    Tadesse Molla, Tesfaye; Kothanda Ramachandran, Dhavanesan; Ni, De Wei; Esposito, Vincenzo; Teocoli, Francesca; Olevsky, Eugene A.; Bjørk, Rasmus; Pryds, Nini; Kaiser, Andreas; Frandsen, Henrik Lund

    2015-01-01

    densification and stress developments during sintering of tubular bi-layered samples. The correspondence between linear elastic and linear viscous theories is used as a basis for derivation of the model. The developed model is first verified by finite element simulation for sintering of tubular bi-layer system...... thermo-mechanical analysis. Results from the analytical model are found to agree well with finite element simulations as well as measurements from sintering experiment....

  11. Structure Determination of Membrane Proteins in Five Easy Pieces

    OpenAIRE

    Marassi, Francesca M.; Das, Bibhuti B.; Lu, George J.; Nothnagel, Henry J.; Park, Sang Ho; Son, Woo Sung; Tian, Ye; Opella, Stanley J.

    2011-01-01

    A general method for determining the structures of membrane proteins in phospholipid bilayers under physiological conditions is described. Membrane proteins are high priority targets for structure determination, and are challenging for the existing experimental methods. Because membrane proteins reside in a liquid crystalline phospholipid bilayer membranes it is important to study them in this type of environment. The approach we have developed can be summarized in five steps, and incorporate...

  12. Structure and dynamics of water and lipid molecules in charged anionic DMPG lipid bilayer membranes

    Science.gov (United States)

    Rønnest, A. K.; Peters, G. H.; Hansen, F. Y.; Taub, H.; Miskowiec, A.

    2016-04-01

    Molecular dynamics simulations have been used to investigate the influence of the valency of counter-ions on the structure of freestanding bilayer membranes of the anionic 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) lipid at 310 K and 1 atm. At this temperature, the membrane is in the fluid phase with a monovalent counter-ion and in the gel phase with a divalent counter-ion. The diffusion constant of water as a function of its depth in the membrane has been determined from mean-square-displacement calculations. Also, calculated incoherent quasielastic neutron scattering functions have been compared to experimental results and used to determine an average diffusion constant for all water molecules in the system. On extrapolating the diffusion constants inferred experimentally to a temperature of 310 K, reasonable agreement with the simulations is obtained. However, the experiments do not have the sensitivity to confirm the diffusion of a small component of water bound to the lipids as found in the simulations. In addition, the orientation of the dipole moment of the water molecules has been determined as a function of their depth in the membrane. Previous indirect estimates of the electrostatic potential within phospholipid membranes imply an enormous electric field of 108-109 V m-1, which is likely to have great significance in controlling the conformation of translocating membrane proteins and in the transfer of ions and molecules across the membrane. We have calculated the membrane potential for DMPG bilayers and found ˜1 V (˜2 ṡ 108 V m-1) when in the fluid phase with a monovalent counter-ion and ˜1.4 V (˜2.8 ṡ 108 V m-1) when in the gel phase with a divalent counter-ion. The number of water molecules for a fully hydrated DMPG membrane has been estimated to be 9.7 molecules per lipid in the gel phase and 17.5 molecules in the fluid phase, considerably smaller than inferred experimentally for 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC

  13. Statistical thermodynamics of association colloids : the equilibrium structure of micelles, vesicles and bilayer membranes.

    OpenAIRE

    Leermakers, F.A.M.

    1988-01-01

    The aim of the present study was to unravel the general equilibrium physical properties of lipid bilayer membranes. We consider four major questions:1. What determines the morphology of the association colloids (micelles, membranes, vesicles) in general?2. Do the apolar tails of the lipids in the bilayer organise themselves more like matches in a box or rather like hot spaghetti in a pan?3. How does this membrane organisation depend on temperature?4. How do additives like surfactants or polym...

  14. Electrometric method to determine the surface impedance of an ice-sea water bilayer system

    Science.gov (United States)

    Bashkuev, Yu. B.; Naguslaeva, I. B.; Khaptanov, V. B.; Dembelov, M. G.

    2016-02-01

    An electrometric method to determine the surface impedance of an ice-sea water bilayer system is suggested. The complex impedance (its magnitude and phase) of this system is determined at very low, low, and medium frequencies from electrometric, rather than radio, measurements. For the ice-sea water system, it is sufficient to determine the conductivity and thickness of a water sample from drilling data.

  15. N-palmitoyl sphingomyelin bilayers: structure and interactions with cholesterol and dipalmitoylphosphatidylcholine.

    Science.gov (United States)

    Maulik, P R; Shipley, G G

    1996-06-18

    The structure and thermotropic properties of N-palmitoyl sphingomyelin (C16:0-SM) and its interaction with cholesterol and dipalmitoylphosphatidylcholine (DPPC) have been studied by differential scanning calorimetry (DSC) and X-ray diffraction methods. DSC of hydrated multi-bilayers of C16:0-SM shows reversible chain-melting transitions. On heating, anhydrous C16:0-SM exhibits an endothermic transition at 75 degrees C (delta H = 4.0 kcal/mol). Increasing hydration progressively lowers the transition temperature (TM) and increases the transition enthalpy (delta H), until limiting values (TM = 41 degrees C, delta H = 7.5 kcal/mol) are observed for hydration values > 25 wt % H2O. X-ray diffraction at temperatures below (29 degrees C) TM show a bilayer gel structure (d = 73.5 A, sharp 4.2 A reflection) for C16:0-SM at full hydration; above TM, at 55 degrees C, a bilayer liquid-crystal phase is present (d = 66.6 A, diffuse 4.6 A reflection). Addition of cholesterol to C16:0-SM bilayers results in a progressive decrease in the enthalpy of the transition at 41 degrees C, and no cooperative transition is detected at > 50 mol % cholesterol. X-ray diffraction shows no difference in the bilayer periodicity, position/width of the wide-angle reflections, or electron density profiles at 29 and 55 degrees C when 50 mol % cholesterol is present. Thus, cholesterol inserts into C16:0-SM bilayers progressively removing the chain-melting transition and changing the structural characteristics of the bilayer. DSC and X-ray diffraction data show that DPPC is completely miscible with C16:0-SM bilayers in both the gel and liquid-crystalline phases; however, 30 mol % C16:0-SM removes the pre-transition exhibited by DPPC. PMID:8672507

  16. Linking lipid architecture to bilayer structure and mechanics using self-consistent field modelling

    Energy Technology Data Exchange (ETDEWEB)

    Pera, H.; Kleijn, J. M.; Leermakers, F. A. M., E-mail: Frans.leermakers@wur.nl [Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6307 HB Wageningen (Netherlands)

    2014-02-14

    To understand how lipid architecture determines the lipid bilayer structure and its mechanics, we implement a molecularly detailed model that uses the self-consistent field theory. This numerical model accurately predicts parameters such as Helfrichs mean and Gaussian bending modulus k{sub c} and k{sup ¯} and the preferred monolayer curvature J{sub 0}{sup m}, and also delivers structural membrane properties like the core thickness, and head group position and orientation. We studied how these mechanical parameters vary with system variations, such as lipid tail length, membrane composition, and those parameters that control the lipid tail and head group solvent quality. For the membrane composition, negatively charged phosphatidylglycerol (PG) or zwitterionic, phosphatidylcholine (PC), and -ethanolamine (PE) lipids were used. In line with experimental findings, we find that the values of k{sub c} and the area compression modulus k{sub A} are always positive. They respond similarly to parameters that affect the core thickness, but differently to parameters that affect the head group properties. We found that the trends for k{sup ¯} and J{sub 0}{sup m} can be rationalised by the concept of Israelachivili's surfactant packing parameter, and that both k{sup ¯} and J{sub 0}{sup m} change sign with relevant parameter changes. Although typically k{sup ¯}<0, membranes can form stable cubic phases when the Gaussian bending modulus becomes positive, which occurs with membranes composed of PC lipids with long tails. Similarly, negative monolayer curvatures appear when a small head group such as PE is combined with long lipid tails, which hints towards the stability of inverse hexagonal phases at the cost of the bilayer topology. To prevent the destabilisation of bilayers, PG lipids can be mixed into these PC or PE lipid membranes. Progressive loading of bilayers with PG lipids lead to highly charged membranes, resulting in J{sub 0}{sup m}≫0, especially at low ionic

  17. Membrane Protein Structure Determination: Back to the Membrane

    OpenAIRE

    Yao, Yong; Ding, Yi; Tian, Ye; Opella, Stanley J.; Marassi, Francesca M.

    2013-01-01

    NMR spectroscopy enables the structures of membrane proteins to be determined in the native-like environment of the phospholipid bilayer membrane. This chapter outlines the methods for membrane protein structural studies using solid-state NMR spectroscopy with samples of membrane proteins incorporated in proteoliposomes or planar lipid bilayers. The methods for protein expression and purification, sample preparation, and NMR experiments are described and illustrated with examples from OmpX an...

  18. Comparison of thermal fluctuations in foam films and bilayer structures

    OpenAIRE

    Ivanova, N. G.; Tsekov, R.

    2013-01-01

    In the frames of the DLVO theory the root mean square amplitude and correlation length of capillary waves in thin liquid films are calculated. Their dependencies on some important physical parameters are studied. Two models are considered: films with classical interfaces and films between lipid bilayers. The performed numerical analysis demonstrates essential difference in their behavior, which is due to the different elastic properties of the film surfaces in the models.

  19. Wavevector filtering through single-layer and bilayer graphene with magnetic barrier structures

    Science.gov (United States)

    Masir, M. Ramezani; Vasilopoulos, P.; Peeters, F. M.

    2008-12-01

    We show that the angular range of the transmission through magnetic barrier structures can be efficiently controlled in single-layer and bilayer graphenes and this renders the structure's efficient wavevector filters. As the number of magnetic barriers increases, this range shrinks, the gaps in the transmission versus energy become wider, and the conductance oscillates with the Fermi energy.

  20. Inverse Proximity Effect in Superconductor-ferromagnet Bilayer Structures

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Jing

    2010-04-05

    Measurements of the polar Kerr effect using a zero-area-loop Sagnac magnetometer on Pb/Ni and Al/(Co-Pd) proximity-effect bilayers show unambiguous evidence for the 'inverse proximity effect,' in which the ferromagnet (F) induces a finite magnetization in the superconducting (S) layer. To avoid probing the magnetic effects in the ferromagnet, the superconducting layer was prepared much thicker than the light's optical penetration depth. The sign and size of the effect, as well as its temperature dependence agree with recent predictions by Bergeret et al.[1].

  1. Temperature-controlled structure and kinetics of ripple phases in one- and two-component supported lipid bilayers

    DEFF Research Database (Denmark)

    Kaasgaard, Thomas; Leidy, Chad; Crowe, J.H.; Mouritsen, Ole G.; Jørgensen, Kent

    2003-01-01

    ripples was seen. From height profiles of the AFM images, estimates of the amplitudes of the different ripple phases are reported. To elucidate the processes of ripple formation and disappearance, a ripple-phase DPPC lipid bilayer was taken through the pretransition in the cooling and the heating......Temperature-controlled atomic force microscopy (AFM) has been used to visualize and study the structure and kinetics of ripple phases in one-component dipalmitoylphosphaticlylcholine (DPPC) and two-component dimyristoylphosphatidylcholine-distearoylphosphatidylcholine (DMPC-DSPC) lipid bilayers....... The lipid bilayers are mica-supported double bilayers in which ripple-phase formation occurs in the top bilayer. In one-component DPPC lipid bilayers, the stable and metastable ripple phases were observed. In addition, a third ripple structure with approximately twice the wavelength of the metastable...

  2. Structure of Carbon Nanotube Porins in Lipid Bilayers: An in Situ Small-Angle X-ray Scattering (SAXS) Study.

    Science.gov (United States)

    Tran, Ich C; Tunuguntla, Ramya H; Kim, Kyunghoon; Lee, Jonathan R I; Willey, Trevor M; Weiss, Thomas M; Noy, Aleksandr; van Buuren, Tony

    2016-07-13

    Carbon nanotube porins (CNTPs), small segments of carbon nanotubes capable of forming defined pores in lipid membranes, are important future components for bionanoelectronic devices as they could provide a robust analog of biological membrane channels. In order to control the incorporation of these CNT channels into lipid bilayers, it is important to understand the structure of the CNTPs before and after insertion into the lipid bilayer as well as the impact of such insertion on the bilayer structure. Here we employed a noninvasive in situ probe, small-angle X-ray scattering, to study the integration of CNT porins into dioleoylphosphatidylcholine bilayers. Our results show that CNTPs in solution are stabilized by a monolayer of lipid molecules wrapped around their outer surface. We also demonstrate that insertion of CNTPs into the lipid bilayer results in decreased bilayer thickness with the magnitude of this effect increasing with the concentration of CNTPs. PMID:27322135

  3. Effect of methyl-branched fatty acids on the structure of lipid bilayers.

    Science.gov (United States)

    Poger, David; Caron, Bertrand; Mark, Alan E

    2014-12-01

    Methyl-branched fatty acids are widespread in prokaryotic membranes. Although anteiso and iso branching (that is on the antepenultimate and penultimate carbons) and the presence of multiple methyl branches in the phytanoyl chain are known to modify the thermotropic behavior and enhance the fluidity of lipid bilayers, little is known about the effect of methyl branching on the structure of lipid bilayers. In this study, molecular dynamics simulations are used to examine systematically the impact of one or more methyl branches at different positions along the sn-1 palmitoyl chain on the structural properties of a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayer. It is found that methyl branching reduces lipid condensation, decreases the bilayer thickness, and lowers chain ordering. Branching also results in the formation of kinks at the branching point, thereby enhancing the fluidity of lipid bilayers. Furthermore, this effect varies in a methyl-position-dependent fashion. In the case of polymethylated chains, the simulations suggest that if the gap between the methyl groups is sufficient (two or three carbons), the effects of the methyl branches are additive and equivalent to the combined effect of the corresponding monomethyl-branched lipids. PMID:25380125

  4. Structure and dynamics of POPC bilayers in water solutions of room temperature ionic liquids

    Energy Technology Data Exchange (ETDEWEB)

    Benedetto, Antonio [School of Physics, University College Dublin, Dublin 4 (Ireland); Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen (Switzerland); Bingham, Richard J. [York Centre for Complex Systems Analysis, University of York, York YO10 5GE (United Kingdom); Ballone, Pietro [Center for Life Nano Science @Sapienza, Istituto Italiano di Tecnologia (IIT), 00185 Roma (Italy); Department of Physics, Università di Roma “La Sapienza,” 00185 Roma (Italy)

    2015-03-28

    Molecular dynamics simulations in the NPT ensemble have been carried out to investigate the effect of two room temperature ionic liquids (RTILs), on stacks of phospholipid bilayers in water. We consider RTIL compounds consisting of chloride ([bmim][Cl]) and hexafluorophosphate ([bmim][PF{sub 6}]) salts of the 1-buthyl-3-methylimidazolium ([bmim]{sup +}) cation, while the phospholipid bilayer is made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Our investigations focus on structural and dynamical properties of phospholipid and water molecules that could be probed by inelastic and quasi-elastic neutron scattering measurements. The results confirm the fast incorporation of [bmim]{sup +} into the lipid phase already observed in previous simulations, driven by the Coulomb attraction of the cation for the most electronegative oxygens in the POPC head group and by sizeable dispersion forces binding the neutral hydrocarbon tails of [bmim]{sup +} and of POPC. The [bmim]{sup +} absorption into the bilayer favours the penetration of water into POPC, causes a slight but systematic thinning of the bilayer, and further stabilises hydrogen bonds at the lipid/water interface that already in pure samples (no RTIL) display a lifetime much longer than in bulk water. On the other hand, the effect of RTILs on the diffusion constant of POPC (D{sub POPC}) does not reveal a clearly identifiable trend, since D{sub POPC} increases upon addition of [bmim][Cl] and decreases in the [bmim][PF{sub 6}] case. Moreover, because of screening, the electrostatic signature of each bilayer is only moderately affected by the addition of RTIL ions in solution. The analysis of long wavelength fluctuations of the bilayers shows that RTIL sorption causes a general decrease of the lipid/water interfacial tension and bending rigidity, pointing to the destabilizing effect of RTILs on lipid bilayers.

  5. On the determination of Poisson's ratio of stressed monolayer and bilayer submicron thick films

    CERN Document Server

    Martins, P; Brida, S; Barbier, D

    2008-01-01

    In this paper, the bulge test is used to determine the mechanical properties of very thin dielectric membranes. Commonly, this experimental method permits to determine the residual stress (s0) and biaxial Young's modulus (E/(1-u)). Associating square and rectangular membranes with different length to width ratios, the Poisson's ratio (u) can also be determined. LPCVD Si3N4 monolayer and Si3N4/SiO2 bilayer membranes, with thicknesses down to 100 nm, have been characterized giving results in agreement with literature for Si3N4, E = 212 $\\pm$ 14 GPa, s0 = 420 $\\pm$ 8 and u = 0.29.

  6. The influence of hyaluronan on the structure of a DPPC-bilayer under high pressures.

    Science.gov (United States)

    Zander, Thomas; Wieland, D C Florian; Raj, Akanksha; Wang, Min; Nowak, Benedikt; Krywka, Christina; Dėdinaitė, Andra; Claesson, Per Martin; Garamus, Vasil M; Schreyer, Andreas; Willumeit-Römer, Regine

    2016-06-01

    The superior lubrication properties of synovial joints have inspired many studies aiming at uncovering the molecular mechanisms which give rise to low friction and wear. However, the mechanisms are not fully understood yet, and, in particular, it has not been elucidated how the biolubricants present at the interface of cartilage respond to high pressures, which arise during high loads of joints. In this study we utilize a simple model system composed of two biomolecules that have been implied as being important for joint lubrication. It consists of a solid supported dipalmitoylphosphatidylcholin (DPPC) bilayer, which was formed via vesicles fusion on a flat Si wafer, and the anionic polysaccharide hyaluronan (HA). We first characterized the structure of the HA layer that adsorbed to the DPPC bilayers at ambient pressure and different temperatures using X-ray reflectivity (XRR) measurements. Next, XRR was utilized to evaluate the response of the system to high hydrostatic pressures, up to 2kbar (200MPa), at three different temperatures. By means of fluorescence microscopy images the distribution of DPPC and HA on the surface was visualized. Our data suggest that HA adsorbs to the headgroup region that is oriented towards the water side of the supported bilayer. Phase transitions of the bilayer in response to temperature and pressure changes were also observed in presence and absence of HA. Our results reveal a higher stability against high hydrostatic pressures for DPPC/HA composite layers compared to that of the DPPC bilayer in absence of HA. PMID:26954090

  7. Advances in the use of nanoscale bilayers to study membrane protein structure and function.

    Science.gov (United States)

    Malhotra, Ketan; Alder, Nathan N

    2014-10-01

    Within the last decade, nanoscale lipid bilayers have emerged as powerful experimental systems in the analysis of membrane proteins (MPs) for both basic and applied research. These discoidal lipid lamellae are stabilized by annuli of specially engineered amphipathic polypeptides (nanodiscs) or polymers (SMALPs/Lipodisqs®). As biomembrane mimetics, they are well suited for the reconstitution of MPs within a controlled lipid environment. Moreover, because they are water-soluble, they are amenable to solution-based biochemical and biophysical experimentation. Hence, due to their solubility, size, stability, and monodispersity, nanoscale lipid bilayers offer technical advantages over more traditional MP analytic approaches such as detergent solubilization and reconstitution into lipid vesicles. In this article, we review some of the most recent advances in the synthesis of polypeptide- and polymer-bound nanoscale lipid bilayers and their application in the study of MP structure and function. PMID:25023464

  8. Improved Modeling Approaches for Constrained Sintering of Bi-Layered Porous Structures

    DEFF Research Database (Denmark)

    Tadesse Molla, Tesfaye; Frandsen, Henrik Lund; Esposito, Vincenzo;

    2012-01-01

    Shape instabilities during constrained sintering experiment of bi-layer porous and dense cerium gadolinium oxide (CGO) structures have been analyzed. An analytical and a numerical model based on the continuum theory of sintering has been implemented to describe the evolution of bow and densificat...

  9. Gene structure and molecular phylogeny of the linker chains from the giant annelid hexagonal bilayer hemoglobins.

    Science.gov (United States)

    Chabasse, Christine; Bailly, Xavier; Sanchez, Sophie; Rousselot, Morgane; Zal, Franck

    2006-09-01

    Giant extracellular hexagonal bilayer hemoglobin (HBL-Hb), found only in annelids, is an approximately 3500-kDa heteropolymeric structure involved in oxygen transport. The HBL-Hbs are comprised of globin and linker chains, the latter being required for the assembly of the quaternary structure. The linker chains, varying in size from 225 to 283 amino acids, have a conserved cysteine-rich domain within their N-terminal moiety that is homologous to the cysteine-rich modules constituting the ligand binding domain of the low-density lipoprotein receptor (LDLR) protein family found in many metazoans. We have investigated the gene structure of linkers from Arenicola marina, Alvinella pompejana, Nereis diversicolor, Lumbricus terrestris, and Riftia pachyptila. We found, contrary to the results obtained earlier with linker genes from N. diversicolor and L. terrestris, that in all of the foregoing cases, the linker LDL-A module is flanked by two phase 1 introns, as in the human LDLR gene, with two more introns in the 3' side whose positions varied with the species. In addition, we obtained 13 linker cDNAs that have been determined experimentally or found in the EST database LumbriBASE. A molecular phylogenetic analysis of the linker primary sequences demonstrated that they cluster into two distinct families of linker proteins. We propose that the common gene ancestor to annelid linker genes exhibited a four-intron and five-exon structure and gave rise to the two families subsequent to a duplication event. PMID:16838215

  10. Low power W:AlOx/WOx bilayer resistive switching structure based on conductive filament formation and rupture mechanism

    Science.gov (United States)

    Bai, Yue; Wu, Huaqiang; Zhang, Ye; Wu, Minghao; Zhang, Jinyu; Deng, Ning; Qian, He; Yu, Zhiping

    2013-04-01

    We report the design and fabrication of W:AlOx/WOx bilayer based resistive switching cells in a standard 0.18 μm CMOS process with only one extra mask. The devices show excellent performance with low power consumption. Low operation voltages (SET voltage WOx bilayer structure resistive switching phenomena.

  11. Stalk structures in lipid bilayer fusion studied by x-ray diffraction

    OpenAIRE

    Aeffner, Sebastian

    2012-01-01

    The fusion of two biological membranes is an important step in many processes on the cellular and sub-cellular level. Understanding the involved interplay of different lipid species, a specialized protein machinery and water on length scales of few nanometers poses a significant challenge to current structural biology. Among several complementary approaches, one strategy is to study the structural rearrangements of the lipid matrix. As the initial step, lipid bilayers must be forced into clos...

  12. Multi-functions of hydrogel with bilayer-based lamellar structure

    OpenAIRE

    Haque, Md. Anamul; Gong, Jian Ping

    2013-01-01

    A novel hybrid hydrogel has been developed by combining bilayer-based lamellar structure of a self-assembled polymer surfactant and polymer network of conventional hydrogel system. A wide range of lamellar structure from micro-domain up to macro-domain (cm-scale) has been successfully generated in the hydrogel. Flat, infinitely large, and perfectly aligned lamellar macro-domain was formed by applying mechanical shear to the gel forming precursor solution containing monomer, cross-linker, and ...

  13. Gramicidin-based fluorescence assay; for determining small molecules potential for modifying lipid bilayer properties

    NARCIS (Netherlands)

    Ingólfsson, Helgi I; Sanford, R Lea; Kapoor, Ruchi; Andersen, Olaf S

    2010-01-01

    Many drugs and other small molecules used to modulate biological function are amphiphiles that adsorb at the bilayer/solution interface and thereby alter lipid bilayer properties. This is important because membrane proteins are energetically coupled to their host bilayer by hydrophobic interactions.

  14. Linking lipid architecture to bilayer structure and mechanics using self-consistent field modelling

    International Nuclear Information System (INIS)

    To understand how lipid architecture determines the lipid bilayer structure and its mechanics, we implement a molecularly detailed model that uses the self-consistent field theory. This numerical model accurately predicts parameters such as Helfrichs mean and Gaussian bending modulus kc and k¯ and the preferred monolayer curvature J0m, and also delivers structural membrane properties like the core thickness, and head group position and orientation. We studied how these mechanical parameters vary with system variations, such as lipid tail length, membrane composition, and those parameters that control the lipid tail and head group solvent quality. For the membrane composition, negatively charged phosphatidylglycerol (PG) or zwitterionic, phosphatidylcholine (PC), and -ethanolamine (PE) lipids were used. In line with experimental findings, we find that the values of kc and the area compression modulus kA are always positive. They respond similarly to parameters that affect the core thickness, but differently to parameters that affect the head group properties. We found that the trends for k¯ and J0m can be rationalised by the concept of Israelachivili's surfactant packing parameter, and that both k¯ and J0m change sign with relevant parameter changes. Although typically k¯0m≫0, especially at low ionic strengths. We anticipate that these changes lead to unstable membranes as these become vulnerable to pore formation or disintegration into lipid disks

  15. A Bilayered Structure Comprised of Functionalized Carbon Nanotubes for Desalination by Membrane Distillation.

    Science.gov (United States)

    Bhadra, Madhuleena; Roy, Sagar; Mitra, Somenath

    2016-08-01

    The development of a novel carbon nanotube (CNT) immobilized membrane comprised of a double-layer structure is presented for water desalination by membrane distillation. The bilayered structure is comprised of CNTs functionalized with a hydrophobic octadecyl amine group on the feed side and carboxylated CNTs on the permeate side. The latter is more hydrophilic. The hydrophobic CNTs provide higher water vapor permeation, while the hydrophilic CNTs facilitate the condensation of water vapor. Together, these led to superior performance, and flux in a direct contact membrane distillation mode was found to be as high as 121 kg/m(2)h at 80 °C. The bilayered membrane represented an enhancement of 70% over the unmodified membrane and 37% over a membrane which had a monolayered structure where only the feed side was CNT-modified. PMID:27387851

  16. Determining the orientation of protegrin-1 in DLPC bilayers using an implicit solvent-membrane model.

    Directory of Open Access Journals (Sweden)

    Abdallah Sayyed-Ahmad

    Full Text Available Continuum models that describe the effects of solvent and biological membrane molecules on the structure and behavior of antimicrobial peptides, holds a promise to improve our understanding of the mechanisms of antimicrobial action of these peptides. In such methods, a lipid bilayer model membrane is implicitly represented by multiple layers of relatively low dielectric constant embedded in a high dielectric aqueous solvent, while an antimicrobial peptide is accounted for by a dielectric cavity with fixed partial charge at the center of each one of its atoms. In the present work, we investigate the ability of continuum approaches to predict the most probable orientation of the beta-hairpin antimicrobial peptide Protegrin-1 (PG-1 in DLPC lipid bilayers by calculating the difference in the transfer free energy from an aqueous environment to a membrane-water environment for multiple orientations. The transfer free energy is computed as a sum of two terms; polar/electrostatic and non-polar. They both include energetic and entropic contributions to the free energy. We numerically solve the Poisson-Boltzmann equation to calculate the electrostatic contribution to the transfer free energy, while the non-polar contribution to the free energy is approximated using a linear solvent accessible surface area relationships. The most probable orientation of PG-1 is that with the lowest relative transfer free energy. Our simulation results indicate that PG-1 assumes an oblique orientation in DLPC lipid bilayers. The predicted most favorable orientation was with a tilt angle of 19 degrees, which is in qualitative agreement with the experimentally observed orientations derived from solid-state NMR data.

  17. Vibration modeling and testing of bilayer beams for determination of film elastic modulus

    International Nuclear Information System (INIS)

    Analysis of the main parameters affecting the fundamental vibrating frequency of film/substrate bilayer beams of rectangular cross-section is discussed based on modeling and testing. Initially, the limits of validity of two analytical models to obtain the fundamental frequency of perfectly-bonded bilayer beams in cantilever configuration are determined by comparing the predicted frequencies to a finite element model developed herein. Using a selected analytical formulation, a modeling-assisted methodology is employed to investigate the parameters that are most influential on the determination of the elastic modulus of the film using a vibratory technique. Modeling suggests the use of thin compliant substrates for extracting the modulus of stiff (metallic) films. If the substrate is stiffer than the film, a thicker film is required to yield measurable shifts in the resonant frequency. The elastic modulus of a millimeter-thick thermosetting polymer extracted by this method agrees with the results obtained from conventional tensile testing of the polymer. Measurements carried out on a gold (100 nm)/polysulfone (130 µm) system yield an average elastic modulus of the gold film similar to the values reported in the literature. (paper)

  18. Novel Bilayer Structures for Short Wavelength High Density Magneto-Optical Data Storage

    Institute of Scientific and Technical Information of China (English)

    WANG Xian-Ying; WANG Jing; WANG Zhan-Yong; YANG Jun-He

    2008-01-01

    We report a novel bi-layer thin film structure for high density magneto-optical (MO) data storage, which combines the advantages of blue wavelength and magnetically induced superresolution (MSR) recording. A double-layer system of exchange-coupled light rare-earth (LRE) element doped NdGdFeCo and traditional TbFeCo is used as the recording medium. The experimental results demonstrate that this NdGdFeCo/TbFeCo double layer has large Kerr rotation under blue wavelength. Centre aperture detection (CAD) MSR effect with temperature rising is also observed. Theoretical calculation is also carried out to verify the experimental results. These results collectively suggest that the new bilayer structure is very promising in next generation high density MO data storage.

  19. Microfluidic anodization of aluminum films for the fabrication of nanoporous lipid bilayer support structures

    Science.gov (United States)

    Bhattacharya, Jaydeep; Kisner, Alexandre; Offenhäusser, Andreas

    2011-01-01

    Summary Solid state nanoporous membranes show great potential as support structures for biointerfaces. In this paper, we present a technique for fabricating nanoporous alumina membranes under constant-flow conditions in a microfluidic environment. This approach allows the direct integration of the fabrication process into a microfluidic setup for performing biological experiments without the need to transfer the brittle nanoporous material. We demonstrate this technique by using the same microfluidic system for membrane fabrication and subsequent liposome fusion onto the nanoporous support structure. The resulting bilayer formation is monitored by impedance spectroscopy across the nanoporous alumina membrane in real-time. Our approach offers a simple and efficient methodology to investigate the activity of transmembrane proteins or ion diffusion across membrane bilayers. PMID:21977420

  20. Compositional and structural characterization of monolayers and bilayers composed of native pulmonary surfactant from wild type mice

    DEFF Research Database (Denmark)

    Bernardino de la Serna, Jorge; Hansen, Soren; Berzina, Zane;

    2013-01-01

    This work comprises a structural and dynamical study of monolayers and bilayers composed of native pulmonary surfactant from mice. Spatially resolved information was obtained using fluorescence (confocal, wide field and two photon excitation) and atomic force microscopy methods. Lipid mass...

  1. On the dynamics of molecular self-assembly and the structural analysis of bilayer membranes using coarse-grained molecular dynamics simulations.

    Science.gov (United States)

    Schindler, Tanja; Kröner, Dietmar; Steinhauser, Martin O

    2016-09-01

    We present a molecular dynamics simulation study of the self-assembly of coarse-grained lipid molecules from unbiased random initial configurations. Our lipid model is based on a well-tried CG polymer model with an additional potential that mimics the hydrophobic properties of lipid tails. We find that several stages of self-organization of lipid clusters are involved in the dynamics of bilayer formation and that the resulting equilibrium structures sensitively depend on the strength of hydrophobic interactions hc of the lipid tails and on temperature T. The obtained stable lipid membranes are quantitatively analyzed with respect to their local structure and their degree of order. At equilibrium, we obtain self-stabilizing bilayer membrane structures that exhibit a bending stiffness κB and compression modulus KC comparable to experimental measurements under physiological conditions. We present a phase diagram of our lipid model which covers a sol-gel transition, a liquid (or gel-like) phase including stable bilayer structures and vesicle formation, as well as a quasi-crystalline phase. We also determine the exact conditions for temperature T and degree of hydrophobicity hc for stable bilayer formation including closed vesicles. PMID:27216316

  2. The modified fluorescence based vesicle fluctuation spectroscopy technique for determination of lipid bilayer bending properties.

    Science.gov (United States)

    Drabik, Dominik; Przybyło, Magda; Chodaczek, Grzegorz; Iglič, Aleš; Langner, Marek

    2016-02-01

    Lipid bilayer is the main constitutive element of biological membrane, which confines intracellular space. The mechanical properties of biological membranes may be characterized by various parameters including membrane stiffness or membrane bending rigidity, which can be measured using flicker noise spectroscopy. The flicker noise spectroscopy exploits the spontaneous thermal undulations of the membrane. The method is based on the quantitative analysis of a series of microscopic images captured during thermal membrane fluctuations. Thus, measured bending rigidity coefficient depends on the image quality as well as the selection of computational tools for image processing and mathematical model used. In this work scanning and spinning disc confocal microscopies were used to visualize fluctuating membranes of giant unilamellar vesicles. The bending rigidity coefficient was calculated for different acquisition modes, using different fluorescent probes and different image processing methods. It was shown that both imaging approaches gave similar bending coefficient values regardless of acquisition time. Using the developed methodology the effect of fluorescent probe type and aqueous phase composition on the value of the membrane bending rigidity coefficient was measured. Specifically it was found that the bending rigidity coefficient of DOPC bilayer in water is smaller than that determined for POPC membrane. It has been found that the POPC and DOPC bending rigidities coefficient in sucrose solution was lower than that in water. Fluorescence imaging makes possible the quantitative analysis of membrane mechanical properties of inhomogeneous membrane. PMID:26615919

  3. In vitro determination of the solubility limit of cholesterol in phospholipid bilayers.

    Science.gov (United States)

    Epand, Richard M; Bach, Diana; Wachtel, Ellen

    2016-09-01

    Cholesterol has limited solubility in phospholipid bilayers. The solubility limit is strongly dependent on the nature of the lipid with which the cholesterol is mixed while properties of the crystals formed can be modified by phospholipid-cholesterol interactions. In this review we summarize the various methods that have been developed to prepare hydrated mixtures of cholesterol and phospholipid. We point out some of the factors that determine the form adopted when cholesterol crystallizes in such mixtures, i.e. two- or three-dimensional, monohydrate or anhydrous. These differences can greatly affect the ability to experimentally detect the presence of these crystals in a membrane. Several methods for detecting cholesterol crystals are discussed and compared including DSC, X-ray and GIXRD diffraction methods, NMR and EPR spectroscopy. The importance of the history of the sample in determining the amount and nature of the cholesterol crystals formed is emphasized. PMID:27370110

  4. Structure and magnetism of Mn, Fe, or Co adatoms on monolayer and bilayer black phosphorus

    Science.gov (United States)

    Wang, Hongbo; Zhu, Shasha; Fan, Fengren; Li, Zhengwei; Wu, Hua

    2016-03-01

    Black phosphorus (BP) is an emergent layered material and is currently explored for its potential applications in nanoelectronics. Here using density functional calculations, we investigate the structure and magnetism of transition metal (TM) adatoms (Mn, Fe, and Co) on the monolayer and bilayer BP. We find that while the TM adatoms prefer to occupy a valley site of the puckered monolayer BP and have a low-spin magnetic state, they could move to an interlayer interstitial site of the bilayer BP and turn into a high-spin state. In particular, Mn adatom at the valley site of monolayer BP has also a metastable high-spin state, and moreover, a low-spin to high-spin magnetic transition can readily be induced by a strain along the armchair direction. Then Mn adsorbed BP monolayer has a strain-tuning spin switch.

  5. Construction and Structural Analysis of Tethered Lipid Bilayer Containing Photosynthetic Antenna Proteins for Functional Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Sumino, Ayumi; Dewa, Takehisa; Takeuchi, Toshikazu; Sugiura, Ryuta; Sasaki, Nobuaki; Misawa, Nobuo; Tero, Ryugo; Urisu, Tsuneo; Gardiner, Alastair T; Cogdell, Richard J; Hashimoto, Hideki; Nango, Mamoru

    2011-07-11

    The construction and structural analysis of a tethered planar lipid bilayer containing bacterial photosynthetic membrane proteins, light-harvesting complex 2 (LH2), and light-harvesting core complex (LH1-RC) is described and establishes this system as an experimental platform for their functional analysis. The planar lipid bilayer containing LH2 and/or LH1-RC complexes was successfully formed on an avidin-immobilized coverglass via an avidin-biotin linkage. Atomic force microscopy (AFM) showed that a smooth continuous membrane was formed there. Lateral diffusion of these membrane proteins, observed by a fluorescence recovery after photobleaching (FRAY), is discussed in terms of the membrane architecture. Energy transfer from LH2 to LH1-RC within the tethered membrane architecture. Energy transfer from LH2 to LH1-RC within the tethered membrane was observed by steady-state fluorescence spectroscopy, indicating that the tethered membrane can mimic the natural situation.

  6. The effect of spin-orbit coupling in band structure and edge states of bilayer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Sahdan, Muhammad Fauzi; Darma, Yudi, E-mail: yudi@fi.itb.ac.id [Department of Physics, InstitutTeknologi Bandung, Jalan Ganesa 10, Bandung 40132 (Indonesia)

    2015-04-16

    Topological insulators are predicted to be useful ranging from spintronics to quantum computation. Graphene was first predicted to be the precursor of topological insulator by Kane-Mele. They developed a Hamiltonian model to describe the gap opening in graphene. In this work, we investigate the band structure of bilayer grapheme and also its edge states by using this model with analytical approach. The results of our calculation show that the gap opening occurs at K and K’ point in bilayer graphene.In addition, a pair of gapless edge modes occurs both in the zigzag and arm-chair configurations are no longer exist. There are gap created at the edge even though thery are very small.

  7. The effect of spin-orbit coupling in band structure and edge states of bilayer graphene

    International Nuclear Information System (INIS)

    Topological insulators are predicted to be useful ranging from spintronics to quantum computation. Graphene was first predicted to be the precursor of topological insulator by Kane-Mele. They developed a Hamiltonian model to describe the gap opening in graphene. In this work, we investigate the band structure of bilayer grapheme and also its edge states by using this model with analytical approach. The results of our calculation show that the gap opening occurs at K and K’ point in bilayer graphene.In addition, a pair of gapless edge modes occurs both in the zigzag and arm-chair configurations are no longer exist. There are gap created at the edge even though thery are very small

  8. Biopolymer-Lipid Bilayer Interaction Modulates the Physical Properties of Liposomes: Mechanism and Structure.

    Science.gov (United States)

    Tan, Chen; Zhang, Yating; Abbas, Shabbar; Feng, Biao; Zhang, Xiaoming; Xia, Wenshui; Xia, Shuqin

    2015-08-19

    This study was conducted to elucidate the conformational dependence of the modulating ability of chitosan, a positively charged biopolymer, on a new type of liposome composed of mixed lipids including egg yolk phosphatidylcholine (EYPC) and nonionic surfactant (Tween 80). Analysis of the dynamic and structure of bilayer membrane upon interaction with chitosan by fluorescence and electron paramagnetic resonance techniques demonstrated that, in addition to providing a physical barrier for the membrane surface, the adsorption of chitosan extended and crimped chains rigidified the lipid membrane. However, the decrease in relative microviscosity and order parameter suggested that the presence of chitosan coils disturbed the membrane organization. It was also noted that the increase of fluidity in the lipid bilayer center was not pronounced, indicating the shallow penetration of coils into the hydrophobic interior of bilayer. Microscopic observations revealed that chitosan adsorption not only affected the morphology of liposomes but also modulated the particle aggregation and fusion. Especially, a number of very heterogeneous particles were visualized, which tended to confirm the role of chitosan coils as a "polymeric surfactant". In addition to particle deformation, the membrane permeability was also tuned. These findings may provide a new perspective to understand the physiological functionality of biopolymer and design biopolymer-liposome composite structures as delivery systems for bioactive components. PMID:26173584

  9. Composition, structure and properties of POPC–triolein mixtures. Evidence of triglyceride domains in phospholipid bilayers

    DEFF Research Database (Denmark)

    Duelund, Lars; Jensen, Grethe Vestergaard; Hannibal-Bach, Hans Kristian;

    2013-01-01

    We have in this study investigated the composition, structure and spectroscopical properties of multilamellar vesicles composed of a phospholipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and up to 10mol% of triolein (TO), a triglyceride. We found in agreement with previous results...... to exist as vesicular structures containing entrapped water. Bilayer structure of the membranes was supported by small angle X-ray scattering that showed the membranes to form a lamellar phase. Fluorescence spectroscopy with the polarity sensitive dye Nile red revealed, that the LF samples with more...

  10. Intercalation of small hydrophobic molecules in lipid bilayers containing cholesterol

    Energy Technology Data Exchange (ETDEWEB)

    Worcester, D.L.; Hamacher, K.; Kaiser, H.; Kulasekere, R.; Torbet, J. [Univ. of Missouri, Columbia, MO (United States)

    1994-12-31

    Partitioning of small hydrophobic molecules into lipid bilayers containing cholesterol has been studied using the 2XC diffractometer at the University of Missouri Research Reactor. Locations of the compounds were determined by Fourier difference methods with data from both deuterated and undeuterated compounds introduced into the bilayers from the vapor phase. Data fitting procedures were developed for determining how well the compounds were localized. The compounds were found to be localized in a narrow region at the center of the hydrophobic layer, between the two halves of the bilayer. The structures are therefore intercalated structures with the long axis of the molecules in the plane of the bilayer.

  11. Intercalation of small hydrophobic molecules in lipid bilayers containing cholesterol

    International Nuclear Information System (INIS)

    Partitioning of small hydrophobic molecules into lipid bilayers containing cholesterol has been studied using the 2XC diffractometer at the University of Missouri Research Reactor. Locations of the compounds were determined by Fourier difference methods with data from both deuterated and undeuterated compounds introduced into the bilayers from the vapor phase. Data fitting procedures were developed for determining how well the compounds were localized. The compounds were found to be localized in a narrow region at the center of the hydrophobic layer, between the two halves of the bilayer. The structures are therefore intercalated structures with the long axis of the molecules in the plane of the bilayer

  12. Membrane protein structure determination: back to the membrane.

    Science.gov (United States)

    Yao, Yong; Ding, Yi; Tian, Ye; Opella, Stanley J; Marassi, Francesca M

    2013-01-01

    NMR spectroscopy enables the structures of membrane proteins to be determined in the native-like environment of the phospholipid bilayer membrane. This chapter outlines the methods for membrane protein structural studies using solid-state NMR spectroscopy with samples of membrane proteins incorporated in proteoliposomes or planar lipid bilayers. The methods for protein expression and purification, sample preparation, and NMR experiments are described and illustrated with examples from OmpX and Ail, two bacterial outer membrane proteins that function in bacterial virulence. PMID:23975776

  13. Dynamical structure functions for charged particle bilayers and superlattices

    International Nuclear Information System (INIS)

    A modified Feynman construction with a zero-frequency central peak is used to model the dynamical structure functions for layered charged particle systems. This construction recognizes the affinity between layered and multicomponent systems. It also guarantees the simultaneous satisfaction of all three frequency-moment sum rules. The frequencies and spectral weights of the long-wavelength collective excitations and the strength of the diffusive central peak are calculated for arbitrary degeneracy

  14. Atomistic resolution structure and dynamics of lipid bilayers in simulations and experiments.

    Science.gov (United States)

    Ollila, O H Samuli; Pabst, Georg

    2016-10-01

    Accurate details on the sampled atomistic resolution structures of lipid bilayers can be experimentally obtained by measuring C-H bond order parameters, spin relaxation rates and scattering form factors. These parameters can be also directly calculated from the classical atomistic resolution molecular dynamics simulations (MD) and compared to the experimentally achieved results. This comparison measures the simulation model quality with respect to 'reality'. If agreement is sufficient, the simulation model gives an atomistic structural interpretation of the acquired experimental data. Significant advance of MD models is made by jointly interpreting different experiments using the same structural model. Here we focus on phosphatidylcholine lipid bilayers, which out of all model membranes have been studied mostly by experiments and simulations, leading to the largest available dataset. From the applied comparisons we conclude that the acyl chain region structure and rotational dynamics are generally well described in simulation models. Also changes with temperature, dehydration and cholesterol concentration are qualitatively correctly reproduced. However, the quality of the underlying atomistic resolution structural changes is uncertain. Even worse, when focusing on the lipid bilayer properties at the interfacial region, e.g. glycerol backbone and choline structures, and cation binding, many simulation models produce an inaccurate description of experimental data. Thus extreme care must be applied when simulations are applied to understand phenomena where the interfacial region plays a significant role. This work is done by the NMRlipids Open Collaboration project running at https://nmrlipids.blogspot.fi and https://github.com/NMRLipids. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg. PMID:26809025

  15. X-ray studies on the bilayer structure of trypsin-treated rat brain myelin

    International Nuclear Information System (INIS)

    Trypsin-treated rat brain myelin was subjected to biochemical and x-ray studies. Untreated myelin gave rise to a pattern of three rings with a fundamental repeat period of 155 A consisting of two bilayers per repeat period, whereas myelin treated with trypsin showed a fundamental repeat period of 75 A with one bilayer per repeat period. The integrated raw intensity of the h = 4 reflection with respect to the h = 2 reflection is 0.38 for untreated myelin. The corresponding value reduced to 0.23, 0.18, 0.17 for myelin treated with 5, 10, 40 units of trypsin per mg of myelin, respectively, for 30 min at 30 degC. The decrease in relative raw intensity of the higher-order reflection relative to the lower-order reflection is suggestive of a disordering of the phosphate groups upon trypsin treatment or an increased mosaicity of the membrane or a combination of both these effects. However, trypsin treatment does not lead to a complete breakdown of the membrane. The integrated intensity of the h = 1 reflection, though weak, is above the measurable threshold for untreated myelin, whereas the corresponding intensity is below the measurable threshold for trypsin-treated myelin, indicating a possible asymmetric to symmetric transition of the myelin bilayer structure about its centre after trypsin treatment. (author). 24 refs., 4 figs., 1 tab

  16. Twisted Bilayer Graphene Superlattices

    OpenAIRE

    Wang, Yanan; Su, Zhihua; Wu, Wei; Nie, Shu; Xie, Nan; Gong, Huiqi; Guo, Yang; Lee, Joon Hwan; Xing, Sirui; Lu, Xiaoxiang; Wang, Haiyan; Lu, Xinghua; McCarty, Kevin; Pei, Shin- shem; Robles-Hernandez, Francisco

    2013-01-01

    Twisted bilayer graphene (tBLG) provides us with a large rotational freedom to explore new physics and novel device applications, but many of its basic properties remain unresolved. Here we report the synthesis and systematic Raman study of tBLG. Chemical vapor deposition was used to synthesize hexagon- shaped tBLG with a rotation angle that can be conveniently determined by relative edge misalignment. Superlattice structures are revealed by the observation of two distinctive Raman features: ...

  17. Physics and applications of novel structures with CVD graphene: edges, grain boundaries, twisted bilayers, and hybrids

    Science.gov (United States)

    Chen, Yong P.

    2014-03-01

    In this talk, I will discuss experimental studies (including electronic transport, optical/Raman, and STM) of physical properties of various novel synthetic graphene structures formed in CVD graphene grown on Cu, including edges of graphene single crystals, grain boundaries between such single crystals, and twisted bilayer graphene. Such synthetic graphene structures could be used as playground to explore novel physics and engineer new functionalities in graphene based electronic devices. Furthermore, I will discuss graphene based ``hybrid'' materials combining CVD graphene with semiconductor and metallic nanostructures for potential optoelectronic and plasmonics applications.

  18. Structure and Dynamics of Glycosphingolipids in Lipid Bilayers: Insights from Molecular Dynamics Simulations

    Directory of Open Access Journals (Sweden)

    Ronak Y. Patel

    2011-01-01

    Full Text Available Glycolipids are important constituents of biological membranes, and understanding their structure and dynamics in lipid bilayers provides insights into their physiological and pathological roles. Experimental techniques have provided details into their behavior at model and biological membranes; however, computer simulations are needed to gain atomic level insights. This paper summarizes the insights obtained from MD simulations into the conformational and orientational dynamics of glycosphingolipids and their exposure, hydration, and hydrogen-bonding interactions in membrane environment. The organization of glycosphingolipids in raft-like membranes and their modulation of lipid membrane structure are also reviewed.

  19. Membrane protein structure determination in membrana.

    Science.gov (United States)

    Ding, Yi; Yao, Yong; Marassi, Francesca M

    2013-09-17

    The two principal components of biological membranes, the lipid bilayer and the proteins integrated within it, have coevolved for specific functions that mediate the interactions of cells with their environment. Molecular structures can provide very significant insights about protein function. In the case of membrane proteins, the physical and chemical properties of lipids and proteins are highly interdependent; therefore structure determination should include the membrane environment. Considering the membrane alongside the protein eliminates the possibility that crystal contacts or detergent molecules could distort protein structure, dynamics, and function and enables ligand binding studies to be performed in a natural setting. Solid-state NMR spectroscopy is compatible with three-dimensional structure determination of membrane proteins in phospholipid bilayer membranes under physiological conditions and has played an important role in elucidating the physical and chemical properties of biological membranes, providing key information about the structure and dynamics of the phospholipid components. Recently, developments in the recombinant expression of membrane proteins, sample preparation, pulse sequences for high-resolution spectroscopy, radio frequency probes, high-field magnets, and computational methods have enabled a number of membrane protein structures to be determined in lipid bilayer membranes. In this Account, we illustrate solid-state NMR methods with examples from two bacterial outer membrane proteins (OmpX and Ail) that form integral membrane β-barrels. The ability to measure orientation-dependent frequencies in the solid-state NMR spectra of membrane-embedded proteins provides the foundation for a powerful approach to structure determination based primarily on orientation restraints. Orientation restraints are particularly useful for NMR structural studies of membrane proteins because they provide information about both three-dimensional structure

  20. Exchange-bias field induced by surface inhomogeneities in ferromagnetic/charge-ordered bilayer structure

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Haiou, E-mail: wanghaiou@hdu.edu.cn [Institute of Materials Physics, Hangzhou Dianzi University, Hangzhou, 310018 (China); Key Laboratory of Soft Chemistry and Functional Materials, Ministry of Education, Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, 210094 (China); Yang, Weifeng; Su, Kunpeng [Institute of Materials Physics, Hangzhou Dianzi University, Hangzhou, 310018 (China); Huo, Dexuan, E-mail: dxhuo@hdu.edu.cn [Institute of Materials Physics, Hangzhou Dianzi University, Hangzhou, 310018 (China); Tan, Weishi [Key Laboratory of Soft Chemistry and Functional Materials, Ministry of Education, Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, 210094 (China)

    2015-11-05

    Epitaxial bilayer structure consisting of ferromagnetic metallic Pr{sub 0.7}Sr{sub 0.3}MnO{sub 3} (PSMO) and charge-ordered insulator La{sub 0.5}Ca{sub 0.5}MnO{sub 3} (LCMO) was fabricated on (001) SrTiO{sub 3} substrate by pulsed laser deposition. High-resolution synchrotron X-ray diffraction showed high quality of epitaxial layer. However, besides diffraction peaks from PSMO layer, LCMO layer and SrTiO{sub 3} substrate, we observed an additional shoulder peak, which might stem from the inhomogeneities of composition in PSMO/LCMO. Further the atomic force microscopy measurement showed the presence of non-stoichiometric large particulates at surface, imparting an overall inhomogeneous composition to the film. This implied that the variation of crystalline structure of PSMO/LCMO occurred due to inhomogeneous composition. Moreover, studies on magnetic properties showed that surface inhomogeneities and ferromagnetic clusters at the PSMO/LCMO interface probably influenced the ferromagnetism of the bilayer film together, tuning exchange bias effect. - Highlights: • We report the epitaxial growth of Pr{sub 0.7}Sr{sub 0.3}MnO{sub 3}/La{sub 0.5}Ca{sub 0.5}MnO{sub 3} bilayer on SrTiO{sub 3}. • The non-stoichiometric particulates at surface impart inhomogeneous composition. • Inhomogeneities in the film lead to the variation of crystalline structure. • Surface inhomogeneities reduce ferromagnetism and enhance exchange bias effect.

  1. Interface properties of bilayer structure Alq3/Fe65Co35

    International Nuclear Information System (INIS)

    Highlights: • Bilayer structure of Alq3/FeCo was fabricated in a dual ultra high vacuum chamber. • Organic layer reacts partially with the FeCo film. • Electronic injection barrier is 0.76 eV in the interface. • The induced uniaxial anisotropy appears in Alq3/FeCo. - Abstract: The interface between the organic and magnetic electrodes is a fundamental problem in organic spintronics devices. Therefore, bilayer structure of Alq3/FeCo was fabricated in a dual ultra high vacuum chamber. The electronic structure of Alq3–FeCo interface has been studied by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy with Argon ion etching technique. It was found that organic layer reacts partially with the FeCo film, forming complex binding of metallic carbide and/or oxidation state in the interfacial region. Electronic injection barrier is 0.76 eV in the interface. The structural variation of the contact region is proposed to be one of the possible factors resulting in spin-injection failure. The magnetic properties of FeCo film with different thicknesses on glass substrate and Alq3 layer are also investigated. The induced uniaxial anisotropy only presents in 3 nm FeCo thickness for glass/FeCo, while it appears in 3–5 nm FeCo for Alq3/FeCo

  2. Sintering of bi-layered porous structures: Stress development and shape evolution

    DEFF Research Database (Denmark)

    Ni, De Wei; Esposito, Vincenzo; Ramousse, Severine; Pryds, Nini

    Ce0.9Gd0.1O1.95 (CGO) and (La, Sr)MnO3 (LSM) are electro-ceramics materials with high potential for several electrochemical applications such as solid Oxide Fuel Cell (SOFC), gas separation membranes, and flue gas purification application. In the latter case, these materials are shaped as thick...... porous layers and sintered by co-firing process. In this work, porous CGO and LSM/CGO single layers were prepared by tape casting, and CGO-LSM/CGO bi-layer structures were obtained by lamination. The shrinkage characteristics of individual layers were measured by optical dilatometry and the uniaxial...

  3. The effects of cryosolvents on DOPC-β-sitosterol bilayers determined from molecular dynamics simulations.

    Science.gov (United States)

    Hughes, Zak E; Malajczuk, Chris J; Mancera, Ricardo L

    2013-03-28

    Polyhydroxylated alcohols and DMSO are common cryosolvents that can damage cell membranes at sufficiently high concentrations. The interaction of representative plant cell membranes composed of mixed 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)-β-sitosterol bilayers, at a range of compositions, with a variety of cryosolvent molecules (DMSO, propylene glycol, ethylene glycol, glycerol, and methanol) has been investigated using molecular dynamics simulations. All the cryosolvents cause the bilayers to thin and become disordered; however, DMSO and propylene glycol have a greater disordering effect on the bilayer. Propylene glycol is shown to have the ability to cause the formation of pores in pure DOPC bilayers in a manner similar to that previously shown for DMSO. As the concentration of β-sitosterol within the bilayer increases, the membranes become more resistant to the deleterious effects of the cryosolvents. All three polyhydroxylated species are observed to form hydrogen bonds to multiple phospholipid molecules, effectively acting as cross-linkers, with glycerol being the most effective cross-linker. Increases in the concentration of β-sitosterol reduce overall hydrogen bonding of the bilayer with the cryosolvents as well as cross-linking, with glycerol and ethylene glycol being the most affected. The ability of all of these cryosolvents to affect the integrity of cell membranes appears to be the result of the balance of their ability to disorder lipid bilayers, to diffuse across them, and to interact with the lipid head groups. PMID:23445456

  4. Structural investigation of the bilayer iridate Sr3Ir2O7

    Science.gov (United States)

    Hogan, Tom; Bjaalie, Lars; Zhao, Liuyan; Belvin, Carina; Wang, Xiaoping; Van de Walle, Chris G.; Hsieh, David; Wilson, Stephen D.

    2016-04-01

    A complete structural solution of the bilayer iridate compound Sr3Ir2O7 presently remains outstanding. Previously reported structures for this compound vary and all fail to explain weak structural violations observed in neutron scattering measurements as well as the presence of a net ferromagnetic moment in the basal plane. In this paper, we present single crystal neutron diffraction and rotational anisotropy second harmonic generation measurements unveiling a lower, monoclinic symmetry inherent to Sr3Ir2O7 . Combined with density functional theory, our measurements identify the correct structural space group as No. 15 (C2/c) and provide clarity regarding the local symmetry of Ir4 + cations within this spin-orbit Mott material.

  5. Bilayer-structured nanocomposite of Ag and crosslinked polyelectrolyte for the detection of humidity

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yang, E-mail: liyang@zju.edu.cn; Wu, Taotao; Yang, Mujie

    2015-03-01

    Nanocomposites of quaternized and crosslinked poly(4-vinylpyridine) (QC-P4VP) and silver nanoparticles were prepared by a two-step procedure, and characterized by Fourier-transform infrared spectroscopy, Ultraviolet–visible spectroscopy and scanning electron microscopy. Bilayer-structured humidity sensors based on the nanocomposites were fabricated, and the effects of the concentration of silver salt precursor and poly(4-vinylpyridine), the method for the reduction of silver salt, the deposition order of the sensitive layers and environmental temperature on the humidity sensing characteristics of the composite sensor have been examined at room temperature. The composite sensor exhibited low impedance under dry atmosphere due to the introduction of Ag nanoparticles, and could detect very low relative humidity (RH) (down to 1% RH) with good sensitivity (impedance change of 2000% from 1% to 30% RH). In addition, the composite sensor demonstrated very wide measuring range (1–98% RH), and revealed faster response and smaller hysteresis than the sensor based on QC-P4VP alone. The complex impedance spectra of the composite sensor in the environments with different RH levels were investigated to explore its humidity sensing mechanism. - Highlights: • Bilayer-structured nanocomposite of Ag and polyelectrolyte are facilely prepared. • Nanocomposite could measure humidity as low as 1% RH and show small hysteresis. • Nanocomposite is capable of detecting full-range humidity with high sensitivity.

  6. Molecular dynamics investigation of the structure of a fully hydrated gel-phase dipalmitoylphosphatidylcholine bilayer.

    Science.gov (United States)

    Tu, K; Tobias, D J; Blasie, J K; Klein, M L

    1996-02-01

    We report the results of a constant pressure and temperature molecular dynamics simulation of a gel-phase dipalmitoylphosphatidylcholine bilayer with nw = 11.8 water molecules/lipid at 19 degrees C. The results of the simulation were compared in detail with a variety of x-ray and neutron diffraction data. The average positions of specific carbon atoms along the bilayer normal and the interlamellar spacing and electron density profile were in very good agreement with neutron and x-ray diffraction results. The area per lipid and the details of the in-plane hydrocarbon chain structure were in excellent agreement with wide-angle x-ray diffraction results. The only significant deviation is that the chains met in a pleated arrangement at the bilayer center, although they should be parallel. Novel discoveries made in the present work include the observation of a bimodal headgroup orientational distribution. Furthermore, we found that there are a significant number of gauche conformations near the ends of the hydrocarbon chains and, in addition to verifying a previous suggestion that there is partial rotational ordering in the hydrocarbon chains, that the two chains in a given molecule are inequivalent with respect to rotations. Finally, we have investigated the lipid/water interface and found that the water penetrates beneath the headgroups, but not as far as the carbonyl groups, that the phosphates are strongly hydrated almost exclusively at the nonesterified oxygen atoms, and that the hydration of the ammonium groups is more diffuse, with some water molecules concentrated in the grooves between the methyl groups. PMID:8789079

  7. Growth, structure and magnetic properties of single crystalline Fe/CoO/Ag(001) bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Abrudan, R.M.

    2007-07-16

    The structural and magnetic properties of epitaxially deposited single-crystalline CoO layers and Fe/CoO bilayers on Ag(001) were investigated. CoO films on Ag(001) exhibit (1 x 1) Low Energy Electron Diffraction (LEED) patterns similar to the clean Ag(001) substrate. The vertical interlayer spacing of the CoO films, deduced from a kinematic analysis of LEED I(E) curves, is a {sub perpendicular} {sub to} /2=2.17 Aa, slightly expanded along the film normal. Scanning Tunneling Microscopy (STM) show a big improvement in the surface roughness after annealing the CoO films at 750 K in oxygen atmosphere. Magnetic measurements using the magneto-optical Kerr effect (MOKE) show a characteristic increase of the coercive field when the Fe/CoO bilayer system is cooled down from room temperature to 150 K. The ordering temperature for the antiferromagnetic layer is in the same range as the Neel temperature for bulk CoO (T{sub N}=290 K). X-ray absorption spectroscopy was employed to probe magnetic and electronic properties with elemental selectivity. Absorption spectra taken from bilayers with different amounts of deposited Fe show only a weak indication for the formation of Fe oxide at the Fe/CoO interface (0.3 ML Fe). From the spectral shape it is concluded that an FeO type of oxide is formed. X-ray Magnetic Circular Dichroism (XMCD) measurements exhibit a sizeable induced ferromagnetic signal at the Co L{sub 2,3} absorption edge, corresponding to an interface layer of 1.1 ML in which the magnetic spins couple with the Fe layer. The angular dependence of the X-ray Magnetic Linear Dichroism (XMLD) and X-ray Magnetic Circular Dichroism XMCD at both the Co and Fe L{sub 2,3} edges shows the orientation of the Co and Fe moments in the bilayers with respect to the crystallographic direction. PhotoElectron Emission Microscope (PEEM) is used to image each ferromagnetic and antiferromagnetic layer separately. Magnetic contrast due to the induced magnetic spins at the interface is also

  8. Engineering Electronic Structure of a Two-Dimensional Topological Insulator Bi(111) Bilayer on Sb Nanofilms by Quantum Confinement Effect.

    Science.gov (United States)

    Bian, Guang; Wang, Zhengfei; Wang, Xiao-Xiong; Xu, Caizhi; Xu, SuYang; Miller, Thomas; Hasan, M Zahid; Liu, Feng; Chiang, Tai-Chang

    2016-03-22

    We report on the fabrication of a two-dimensional topological insulator Bi(111) bilayer on Sb nanofilms via a sequential molecular beam epitaxy growth technique. Our angle-resolved photoemission measurements demonstrate the evolution of the electronic band structure of the heterostructure as a function of the film thickness and reveal the existence of a two-dimensional spinful massless electron gas within the top Bi bilayer. Interestingly, our first-principles calculation extrapolating the observed band structure shows that, by tuning down the thickness of the supporting Sb films into the quantum dimension regime, a pair of isolated topological edge states emerges in a partial energy gap at 0.32 eV above the Fermi level as a consequence of quantum confinement effect. Our results and methodology of fabricating nanoscale heterostructures establish the Bi bilayer/Sb heterostructure as a platform of great potential for both ultra-low-energy-cost electronics and surface-based spintronics. PMID:26932368

  9. Atomic structure and bonding of the interfacial bilayer between Au nanoparticles and epitaxially regrown MgAl{sub 2}O{sub 4} substrates

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Guo-zhen [State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Canadian Centre of Electron Microscopy and Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada); Majdi, Tahereh; Preston, John S. [Department of Engineering Physics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada); Shao, Yang [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Bugnet, Matthieu; Botton, Gianluigi A., E-mail: gbotton@mcmaster.ca [Canadian Centre of Electron Microscopy and Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)

    2014-12-08

    A unique metal/oxide interfacial bilayer formed between Au nanoparticles and MgAl{sub 2}O{sub 4} substrates following thermal treatment is reported. Associated with the formation of the bilayer was the onset of an abnormal epitaxial growth of the substrate under the nanoparticle. According to the redistribution of atoms and the changes of their electronic structure probed across the interface by a transmission electron microscopy, we suggest two possible atomic models of the interfacial bilayer.

  10. Atomic structure and bonding of the interfacial bilayer between Au nanoparticles and epitaxially regrown MgAl2O4 substrates

    International Nuclear Information System (INIS)

    A unique metal/oxide interfacial bilayer formed between Au nanoparticles and MgAl2O4 substrates following thermal treatment is reported. Associated with the formation of the bilayer was the onset of an abnormal epitaxial growth of the substrate under the nanoparticle. According to the redistribution of atoms and the changes of their electronic structure probed across the interface by a transmission electron microscopy, we suggest two possible atomic models of the interfacial bilayer

  11. Flip-Flop of Steroids in Phospholipid Bilayers: Effects of the Chemical Structure on Transbilayer Diffusion

    DEFF Research Database (Denmark)

    Parisio, Giulia; Sperotto, Maria Maddalena; Ferrarini, Alberta

    2012-01-01

    The transverse motion of molecules from one leaflet to the other of a lipid bilayer, or flip-flop, represents a putative mechanism for their transmembrane transport and may contribute to the asymmetric distribution of components in biomembranes. However, a clear understanding of this process...... is still missing. The scarce knowledge derives from the difficulty of experimental determination. Because of its slow rate on the molecular time scale, flip-flop is challenging also for computational techniques. Here, we report a study of the passive transbilayer diffusion of steroids, based on a kinetic......, dielectric permittivity, acyl chain order parameters, and lateral pressure. The flip-flop rates are determined by solving the Master Equation that governs the time evolution of the system, with transition rates between free energy minima evaluated according to the Kramers theory. Considering various steroids...

  12. Optical and structural investigations of self-assembled Ge/Si bi-layer containing Ge QDs

    Energy Technology Data Exchange (ETDEWEB)

    Samavati, Alireza, E-mail: alireza.samavati@yahoo.com [Ibn Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, Skudai 81310, Johor (Malaysia); Othaman, Z., E-mail: zulothaman@gmail.com [Ibn Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, Skudai 81310, Johor (Malaysia); Ghoshal, S.K.; Dousti, M.R. [Advanced Optical Material Research Group, Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor (Malaysia)

    2014-10-15

    We report the influence of Si spacer thickness variation (10–40 nm) on structural and optical properties of Ge quantum dots (QDs) in Ge/Si(1 0 0) bi-layer grown by radio frequency magnetron sputtering. AFM images reveal the spacer dependent width, height, root mean square roughness and number density of QDs vary in the range of ∼12–25 nm, ∼2–6 nm, ∼1.95–1.05 nm and ∼0.55×10{sup 11}–2.1×10{sup 11} cm{sup −2}, respectively. XRD patterns exhibit the presence of poly-oriented structures of Ge with preferred growth along (1 1 1) direction accompanied by a reduction in strain from 4.9% to 1.2% (estimated from Williamson–Hall plot) due to bi-layering. The room temperature luminescence displays strong blue–violet peak associated with a blue shift as much as 0.05 eV upon increasing the thickness of Si spacer. This shift is attributed to the quantum size effect, the material intermixing and the strain mediation. Raman spectra for both mono and bi-layer samples show intense Ge–Ge optical phonon mode that is shifted towards higher frequency. Furthermore, the first order features of Raman spectra affirm the occurrence of interfacial intermixing and phase formation during deposition. The excellent features of the results suggest that our systematic method may constitute a basis for the tunable growth of Ge QDs suitable in nanophotonics. - Highlights: • High quality bilayered hetero-structure Ge/Si using economic and easy rf magnetron sputtering fabrication method. • The role of phonon-confinement and strain relaxation mechanisms. • Influence of bilayering on evolutionary growth dynamics. • Band gap shift of visible PL upon bilayering.

  13. Microscopic domain structures in unidirectional and isotropic exchange-coupled NiO/NiFe bilayers

    International Nuclear Information System (INIS)

    The dependence on nickel oxide thickness in unidirectional and isotropic exchange-coupled NiO/NiFe bilayer films was investigated by magnetic force microscopy to better understand exchange biasing at microscopic length scales. As the NiO thickness increased, the domain structure of unidirectional biased films formed smaller and more complex in-plane domains. By contrast, for the isotropically coupled films, large domains generally formed with increasing NiO thickness including a new cross type domain with out-of-plane magnetization orientation. The density of the cross domain is proportional to exchange biasing field, and the fact that the domain mainly originated from the strongest exchange coupled region was confirmed by imaging in an applied external field during a magnetization cycle

  14. Influence of bilayer resist processing on p-i-n OLEDs: towards multicolor photolithographic structuring of organic displays

    Science.gov (United States)

    Krotkus, Simonas; Nehm, Frederik; Janneck, Robby; Kalkura, Shrujan; Zakhidov, Alex A.; Schober, Matthias; Hild, Olaf R.; Kasemann, Daniel; Hofmann, Simone; Leo, Karl; Reineke, Sebastian

    2015-03-01

    Recently, bilayer resist processing combined with development in hydrofluoroether (HFE) solvents has been shown to enable single color structuring of vacuum-deposited state-of-the-art organic light-emitting diodes (OLED). In this work, we focus on further steps required to achieve multicolor structuring of p-i-n OLEDs using a bilayer resist approach. We show that the green phosphorescent OLED stack is undamaged after lift-off in HFEs, which is a necessary step in order to achieve RGB pixel array structured by means of photolithography. Furthermore, we investigate the influence of both, double resist processing on red OLEDs and exposure of the devices to ambient conditions, on the basis of the electrical, optical and lifetime parameters of the devices. Additionally, water vapor transmission rates of single and bilayer system are evaluated with thin Ca film conductance test. We conclude that diffusion of propylene glycol methyl ether acetate (PGMEA) through the fluoropolymer film is the main mechanism behind OLED degradation observed after bilayer processing.

  15. The roles of bulk and interfacial molecular orientations in determining the performance of organic bilayer solar cells

    KAUST Repository

    Ngongang Ndjawa, Guy O.

    2014-09-09

    Molecular orientation plays a significant role in determining the performance of small molecule solar cells. Key photovoltaic processes in these cells are strongly dependent on how the molecules are oriented in the active layer. We isolate contributions arising from the bulk molecular orientations vs. those from interfacial orientations in ZnPc/C60 bilayer systems and we probe these contributions by comparing device pairs in which only the bulk or the interface differ. By controlling the orientation in the bulk the current can be strongly modulated, whereas controlling the interfacial molecular orientation and degree of intermixing mediate the voltage.

  16. Salt-bridge-supported bilayer lipid membrane biosensor for determination of anticancer drug cyclophosphamide

    Science.gov (United States)

    Zhang, Yanli; Wang, Tao; Zhang, Chunxu; Shen, Hanxi; Chao, Fuhuan

    2001-09-01

    A novel biosensor for assaying anticancer drug cyclophosphamide was constructed with salt-bridge supported bilayer lipid membrane modified with tetraphenylborate- cyclophosphamide complex. The modification was achieved by the introduction of the complex into the membrane forming solution. The biosensor show a linear response to the drug over the concentration range 8.96 X 10-6 mol L-1. The effects of coexistent substances and pH on assay were evaluated. The results show that the distinguish merits of this kind of biosensor is the excellently biological compatibility and no need of mediator for ions exchange. It also shows good selectivity and sensitivity for cyclophosphamide assay.

  17. Tethered bilayer membranes as a complementary tool for functional and structural studies: The pyolysin case.

    Science.gov (United States)

    Preta, Giulio; Jankunec, Marija; Heinrich, Frank; Griffin, Sholeem; Sheldon, Iain Martin; Valincius, Gintaras

    2016-09-01

    We demonstrate the use of tethered bilayer lipid membranes (tBLMs) as an experimental platform for functional and structural studies of membrane associated proteins by electrochemical techniques. The reconstitution of the cholesterol-dependent cytolysin (CDC) pyolysin (PLO) from Trueperella pyogenes into tBLMs was followed in real-time by electrochemical impedance spectroscopy (EIS). Changes of the EIS parameters of the tBLMs upon exposure to PLO solutions were consistent with the dielectric barrier damage occurring through the formation of water-filled pores in membranes. Parallel experiments involving a mutant version of PLO, which is able to bind to the membranes but does not form oligomer pores, strengthen the reliability of this methodology, since no change in the electrochemical impedance was observed. Complementary atomic force microscopy (AFM) and neutron reflectometry (NR) measurements revealed structural details of the membrane bound PLO, consistent with the structural transformations of the membrane bound toxins found for other cholesterol dependent cytolysins. In this work, using the tBLMs platform we also observed a protective effect of the dynamin inhibitor Dynasore against pyolysin as well as pneumolysin. An effect of Dynasore in tBLMs, which was earlier observed in experiments with live cells, confirms the biological relevance of the tBLMs models, as well as demonstrates the potential of the electrochemical impedance spectroscopy to quantify membrane damage by the pore forming toxins. In conclusion, tBLMs are a reliable and complementary method to explore the activity of CDCs in eukaryotic cells and to develop strategies to limit the toxic effects of CDCs. PMID:27211243

  18. The structure and stability of phospholipid bilayers by atomic force microscopy.

    Science.gov (United States)

    Hui, S W; Viswanathan, R; Zasadzinski, J A; Israelachvili, J N

    1995-01-01

    Atomic force microscopy (AFM) was used to investigate the structure, stability, and defects of the hydrophilic surfaces of Langmuir-Blodgett bilayer films of distearoylphosphatidylcholine (DSPC) and dipalmitoylphosphatidylethanolamine (DPPE) in the solid phase, and dilinoleoylphosphatidylethanolamine (DLPE) in the fluid phase. Their relative resilience to external mechanical stress by the scanning tip and by fluid exchange were also investigated. DPPE monolayers showed parallel ridges at the surface with a period of 0.49 nm, corresponding to the rows of aligned headgroups consistent with the known crystallographic structure. DSPC and DLPE monolayers did not show any periodic order. The solid DSPC and DPPE monolayers were stable to continued rastering by the AFM tip; however, the stability of DLPE monolayers depended on the pH of the aqueous environment. Structural defects in the form of monolayer gaps and holes were observed after fluid exchange, but the defects in DLPE monolayer at pH 11 were stable during consecutive scanning. At pH 9 and below, the defects induced by fluid exchange over DLPE monolayers were more extensive and were deformed easily by consecutive scanning of the AFM tip at a force of 10 nN. The pH dependence of resilience was explained by the increasing bending energy or frustration due to the high spontaneous curvature of DLPE monolayers at low pH. The tangential stress exerted by the AFM tip on the deformable monolayers eventually produced a ripple pattern, which could be described as a periodic buckling known as Shallamach waves. PMID:7711239

  19. Compressibility of bilayer graphene

    OpenAIRE

    Borghi, Giovanni; Polini, Marco; Asgari, Reza; MacDonald, A. H.

    2010-01-01

    Bilayer graphene is a recently isolated and intriguing class of many-body systems with massive chiral quasiparticles. We present theoretical results for the electronic compressibility of bilayer graphene that are based on a four-band continuum band structure model combined with a random phase approximation treatment of electronic correlations. We find that the compressibility is strongly suppressed by electron-electron interactions at low carrier densities. Correlations do not lead to any qua...

  20. X-Ray Studies On The Bilayer Structure Of Trypsin-Treated Rat-Brain Myelin

    OpenAIRE

    Ramakumar, Suryanarayanarao; Viswamitra, MA; Mohan, PM; Sastry, PS

    1995-01-01

    Trypsin-treated rat brain myelin was subjected to biochemical and X-ray studies. Untreated myelin gave rise to a pattern of three rings with a fundamental repeat period of 155 Angstrom consisting of two bilayers per repeat period, whereas myelin treated with trypsin showed a fundamental repeat period of 75 Angstrom with one bilayer per repeat period. The integrated raw intensity of the h=4 reflection with respect to the h=2 reflection is 0.38 for untreated myelin. The corresponding value redu...

  1. Molecular dynamics investigation of the structure of a fully hydrated gel-phase dipalmitoylphosphatidylcholine bilayer.

    OpenAIRE

    Tu, K; Tobias, D J; Blasie, J K; Klein, M.L.

    1996-01-01

    We report the results of a constant pressure and temperature molecular dynamics simulation of a gel-phase dipalmitoylphosphatidylcholine bilayer with nw = 11.8 water molecules/lipid at 19 degrees C. The results of the simulation were compared in detail with a variety of x-ray and neutron diffraction data. The average positions of specific carbon atoms along the bilayer normal and the interlamellar spacing and electron density profile were in very good agreement with neutron and x-ray diffract...

  2. Formation and structure of stably dispersed particles composed of retinal with dipalmitoylphosphatidylcholine: coexistence of emulsion particles with bilayer vesicles.

    Science.gov (United States)

    Asai, Y; Watanabe, S

    1999-07-01

    In order to develop an intravenous formulation of all-trans-retinal (vitamin A aldehyde, VAA) for the treatment of night blindness, VAA and dipalmitoylphosphatidylcholine (DPPC) were sonicated and the dispersions in the VAA mole fraction range of 0.1-0.7 were stable at room temperature for 3 days. In order to clarify the dispersal mechanism, the dispersed particles were characterized and the interaction between VAA and DPPC was investigated using several physicochemical techniques. Dynamic light scattering measurements showed that the diameter of the dispersed particles was 50-70 nm. A limited amount of VAA is incorporated into DPPC bilayer membranes (approximately 5 mole%). The trapped aqueous volume inside the particles was determined fluorometrically using the aqueous space marker calcein and the volume in the VAA/DPPC particles was decreased remarkably with the addition of VAA into small unilamellar vesicles of DPPC. The decline in the fraction of vesicular particles was also confirmed by fluorescence quenching of N-dansylhexadecylamine in the DPPC membrane by the addition of the quencher CuSO(4). These results indicate that the excess VAA separated from the DPPC bilayers is stabilized as emulsion particles by the DPPC surface monolayer. The monolayer-bilayer equilibrium of VAA/DPPC mixtures was estimated by measurement of spreading and collapse pressures. The results showed that the coexistence of emulsion particles (surface monolayer of DPPC+core of VAA) with vesicular particles (bilayer) was critically important for the formation of the stably dispersed particles of the lipid mixture. PMID:10477332

  3. A possible role of rhodopsin in maintaining bilayer structure in the photoreceptor membrane

    NARCIS (Netherlands)

    Grip, W.J. de; Drenthe, E.H.S.; Echteld, C.J.A. van; Kruijff, B. de; Verkleij, A.J.

    1979-01-01

    31P-NMR measurements demonstrate that at 37°C, independent of the photolytic state of the photopigment rhodopsin, the lipids in the photoreceptormembrane are almost exclusively organised in a bilayer. In strong contrast, the 31P-NMR spectra of the extracted lipids are characteristic for the hexagona

  4. From lanosterol to cholesterol: Structural evolution and differential effects on lipid bilayers

    DEFF Research Database (Denmark)

    Miao, Ling; Nielsen, Morten; Thewalt, J.; Ipsen, John Hjorth; Bloom, M.; Zuckermann, Martin; Mouritsen, Ole G.

    2002-01-01

    lipid-bilayer membranes. By using deuterium NMR spectroscopy on multilamellar lipid-sterol systems in combination with Monte Carlo simulations of microscopic models of lipid-sterol interactions, we demonstrate that the evolution in the molecular chemistry from lanosterol to cholesterol is manifested in...... particular in the context of membrane domains and rafts....

  5. Enzyme monolayer- and bilayer-modified tin oxide electrodes for the determination of hydrogen peroxide and glucose

    Energy Technology Data Exchange (ETDEWEB)

    Tatsuma, Tetsu; Okawa, Yusuke; Watanabe, Tadashi (Univ. of Tokyo (Japan))

    1989-11-01

    An enzyme-based amperometric biosensor for hydrogen peroxide was developed, employing a horseradish peroxidase (HRP) monolayer covalently attached to a tin oxide electrode and a dissolved electron mediator. The sensor can determine hydrogen peroxide at levels down to 10{sup {minus}8} M and can be applied to a flow system. Stability of the electrode, kinetics of the surface process, and the efficiencies of different mediators were studied. As an extension, glucose oxidase (GOx) was chemically bound to the HRP-modified electrode. A GOx/HRP bilayer-modified electrode thus obtained exhibits much better performance in glucose detection limit, sensitivity, and response speed than previously reported GOx monolayer-modified electrodes.

  6. Structure determination of membrane proteins in five easy pieces.

    Science.gov (United States)

    Marassi, Francesca M; Das, Bibhuti B; Lu, George J; Nothnagel, Henry J; Park, Sang Ho; Son, Woo Sung; Tian, Ye; Opella, Stanley J

    2011-12-01

    Rotational Alignment (RA) solid-state NMR provides the basis for a general method for determining the structures of membrane proteins in phospholipid bilayers under physiological conditions. Membrane proteins are high priority targets for structure determination, and are challenging for existing experimental methods. Because membrane proteins reside in liquid crystalline phospholipid bilayer membranes it is important to study them in this type of environment. The RA solid-state NMR approach we have developed can be summarized in five steps, and incorporates methods of molecular biology, biochemistry, sample preparation, the implementation of NMR experiments, and structure calculations. It relies on solid-state NMR spectroscopy to obtain high-resolution spectra and residue-specific structural restraints for membrane proteins that undergo rotational diffusion around the membrane normal, but whose mobility is otherwise restricted by interactions with the membrane phospholipids. High resolution spectra of membrane proteins alone and in complex with other proteins and ligands set the stage for structure determination and functional studies of these proteins in their native, functional environment. PMID:21964394

  7. Particle-based simulations of bilayer membranes: self-assembly, structural analysis, and shock-wave damage

    Science.gov (United States)

    Steinhauser, Martin O.; Schindler, Tanja

    2016-08-01

    We report on the results of particle-based, coarse-grained molecular dynamics simulations of amphiphilic lipid molecules in aqueous environment where the membrane structures at equilibrium are subsequently exposed to strong shock waves, and their damage is analyzed. The lipid molecules self-assemble from unbiased random initial configurations to form stable bilayer membranes, including closed vesicles. During self-assembly of lipid molecules, we observe several stages of clustering, starting with many small clusters of lipids, gradually merging together to finally form one single bilayer membrane. We find that the clustering of lipids sensitively depends on the hydrophobic interaction h_c of the lipid tails in our model and on temperature T of the system. The self-assembled bilayer membranes are quantitatively analyzed at equilibrium with respect to their degree of order and their local structure. We also show that—by analyzing the membrane fluctuations and using a linearized theory— we obtain area compression moduli K_A and bending stiffnesses κ_B for our bilayer membranes which are within the experimental range of in vivo and in vitro measurements of biological membranes. We also discuss the density profile and the pair correlation function of our model membranes at equilibrium which has not been done in previous studies of particle-based membrane models. Furthermore, we present a detailed phase diagram of our lipid model that exhibits a sol-gel transition between quasi-solid and fluid domains, and domains where no self-assembly of lipids occurs. In addition, we present in the phase diagram the conditions for temperature T and hydrophobicity h_c of the lipid tails of our model to form closed vesicles. The stable bilayer membranes obtained at equilibrium are then subjected to strong shock waves in a shock tube setup, and we investigate the damage in the membranes due to their interaction with shock waves. Here, we find a transition from self

  8. Dynamics and instabilities of lipid bilayer membrane shapes

    OpenAIRE

    Shi, Zheng; Baumgart, Tobias

    2014-01-01

    Biological membranes undergo constant shape remodeling involving the formation of highly curved structures. The lipid bilayer represents the fundamental architecture of the cellular membrane with its shapes determined by the Helfrich curvature bending energy. However, the dynamics of bilayer shape transitions, especially their modulation by membrane proteins, and the resulting shape instabilities, are still not well understood. Here, we review in a unifying manner several theories that descri...

  9. The development of a bilayer structure of poly(propylene carbonate)/poly(3-hydroxybutyrate) blends from the demixed melt.

    Science.gov (United States)

    Zhang, Shujing; Sun, Xiaoli; Ren, Zhongjie; Li, Huihui; Yan, Shouke

    2015-12-28

    The miscibility of poly(propylene carbonate) (PPC) and poly(3-hydroxybutyrate) (PHB) blends was analyzed by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results indicated that the blends are immiscible at most blending compositions, and a miscible blend can be obtained when the PHB content is as low as 10 wt%. The morphology of the PPC/PHB (70/30) blend film was characterized by POM, scanning electron micrography (SEM) and Fourier transform infrared spectroscopy (FTIR), and the development of a PPC-top and microporous PHB-bottom bilayer structure can be revealed. Different from the normal case, phase separation can take place on the normal direction of the film surface in the PPC/PHB (70/30) blend at 190 °C, attributed to the different surface energies of the two components. The continuous segregation of PPC to the top-layer can result in the crystallization of PHB at the bottom layer and conversely promote the complete development of a bilayer structure. Since the isotropic PPC layer is transparent with no birefringence, the PHB spherulite with a microporous structure at the bottom layer can be observed directly by POM. Moreover, the microporous structure of the bottom layer should be attributed to the solution cast procedure. Thus, some unique crystalline patterns may be created in the demixed crystalline/amorphous polymer blends, which differ greatly from those obtained from the miscible blend systems. PMID:26577534

  10. Interface properties of bilayer structure Alq{sub 3}/Fe{sub 65}Co{sub 35}

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhen, E-mail: wangzhen@chd.edu.cn [Department of Applied Physics, Chang’an University, Xi’an 710064 (China); Xu, Chunlong; Wang, Jinguo; Chang, Qiaoli [Department of Applied Physics, Chang’an University, Xi’an 710064 (China); Zuo, Yalu; Xi, Li [Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000 (China)

    2015-04-01

    Highlights: • Bilayer structure of Alq{sub 3}/FeCo was fabricated in a dual ultra high vacuum chamber. • Organic layer reacts partially with the FeCo film. • Electronic injection barrier is 0.76 eV in the interface. • The induced uniaxial anisotropy appears in Alq{sub 3}/FeCo. - Abstract: The interface between the organic and magnetic electrodes is a fundamental problem in organic spintronics devices. Therefore, bilayer structure of Alq{sub 3}/FeCo was fabricated in a dual ultra high vacuum chamber. The electronic structure of Alq{sub 3}–FeCo interface has been studied by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy with Argon ion etching technique. It was found that organic layer reacts partially with the FeCo film, forming complex binding of metallic carbide and/or oxidation state in the interfacial region. Electronic injection barrier is 0.76 eV in the interface. The structural variation of the contact region is proposed to be one of the possible factors resulting in spin-injection failure. The magnetic properties of FeCo film with different thicknesses on glass substrate and Alq{sub 3} layer are also investigated. The induced uniaxial anisotropy only presents in 3 nm FeCo thickness for glass/FeCo, while it appears in 3–5 nm FeCo for Alq{sub 3}/FeCo.

  11. Bipolar resistive switching and its temperature dependence in the composite structure of BiFeO3 bilayer

    Science.gov (United States)

    Ma, W. J.; Xiong, W. M.; Zhang, X. Y.; Wang, Ying; Zhang, H. Y.; Wang, C. Q.; Wang, Biao; Zheng, Yue

    2016-04-01

    In order to demonstrate the control of BiFeO3 thin film on the resistive switching effect and achieve the high-performance resistive switching device, the single layers and bilayer have been fabricated by chemical solution deposition method, respectively. In comparison with the single films, the composite film exhibits great performance of the resistive switching in endurance and repeatability, high stability and resistance ratio of high resistance state to low resistance state. Resistive switching effect in the BiFeO3 composite structure demonstrates an effective way to improve the endurance and repeatability of the resistive switching characteristics by designing the relative devices.

  12. Interplay of curvature-induced micro- and nanodomain structures in multicomponent lipid bilayers

    CERN Document Server

    Brodbek, Leonie

    2015-01-01

    We discuss different mechanisms for curvature-induced domain formation in multicomponent lipid membranes and present a theoretical model that allows us to study the interplay between the domains. The model represents the membrane by two coupled monolayers, which each carry an additional order parameter field describing the local lipid composition. The spontaneous curvature of each monolayer is coupled to the local composition, moreover, the lipid compositions on opposing monolayers are coupled to each other. Using this model, we calculate the phase behavior of the bilayer in mean-field approximation. The resulting phase diagrams are surprisingly complex and reveal a variety of phases and phase transitions, including a decorated microdomain phase where nanodomains are aligned along the microdomain boundaries. Our results suggest that external membrane tension can be used to control the lateral organization of nanodomains (which might be associated with lipid "rafts") in a multicomponent lipid bilayer.

  13. Vortex structures and magnetic domain patterns in the superconductor/ferromagnet hybrid bilayer

    International Nuclear Information System (INIS)

    Superconducting vortices and magnetic domain patterns’ evolution in the superconductor-ferromagnet (SC/FM) hybrid bilayer are investigated within the Ginzburg—Landau (GL) theory of superconductivity, in combination with the Landau—Lifshitz—Gilbert (LLG) equation of ferromagnetism. Magnetic domain patterns in the ferromagnetic thin film and the vortices’ nucleation in the superconducting layer for the hybrid bilayer, subjected to perpendicular magnetic fields, are obtained by numerical simulations. A dynamical evolution picture of the magnetic domain patterns and the associated superconducting vortices’ nucleation are clearly shown. The effect of geometry parameters and physical parameters on the magnetic domain and superconducting vortex evolution are discussed. The magnetization curve of the SC film has also been illustrated. We found that the vortex dynamic behavior of the superconducting film changes substantially, and the correlated magnetic hysteresis loss is significantly reduced due to the presence of the ferromagnetic thin layer. In addition, the spontaneous vortex-antivortex (V-AV) pairs’ nucleation in the hybrid bilayer are investigated. (paper)

  14. Dolichol phosphate induces non-bilayer structures, vesicle fusion and transbilayer movements of lipids in model membranes

    Energy Technology Data Exchange (ETDEWEB)

    de Kruijff, B.; Van Duijn, G.; Valtersson, C.; Chojnacki, T.; Verkleij, A.J.; Dallner, G.

    1987-05-01

    The effect of dolichols, polyprenols, dolichol esterified with fatty acids, and dolichol phosphate on the structure and fluidity of model membranes was studied using different biophysical techniques. These studies suggest that (1) dolichol and dolichol derivatives destabilize unsaturated PE-containing bilayers and promote hexagonal II phase formation; (2) high concentrations of dolichol induce lipid structures characterized by isotropic T P NMR and particulate fracture faces. The effect of dolichol and dolichyl phosphate on fusion between large unilamellar vesicles of DOPC and DOPE was studied using a fluroescence resonance energy transfer assay. The influence of dolichyl phosphate on the transbilary movement of DOPC in multilamellar vesicles (MLV) and large unilamellar vesicles (LUV) composed of DOPC and DOPE (1:2) was investigated by using the PC-specified transfer protein. The results indicate that: (1) both dolichol and dolichyl phosphate enhance vesicle fusion in a comparable and concentration-dependent way; (2) the amount of exchangeable PC from MLVs is increased by dolichyl phosphate probably as a result of fusion processes. It thus appears that these polyprenols are potent destabilizers of bilayer structure and that this process is accompanied by membrane fusion and transbilayer transport of phospholipids.

  15. Dolichol phosphate induces non-bilayer structures, vesicle fusion and transbilayer movements of lipids in model membranes

    International Nuclear Information System (INIS)

    The effect of dolichols, polyprenols, dolichol esterified with fatty acids, and dolichol phosphate on the structure and fluidity of model membranes was studied using different biophysical techniques. These studies suggest that (1) dolichol and dolichol derivatives destabilize unsaturated PE-containing bilayers and promote hexagonal II phase formation; (2) high concentrations of dolichol induce lipid structures characterized by isotropic 31P NMR and particulate fracture faces. The effect of dolichol and dolichyl phosphate on fusion between large unilamellar vesicles of DOPC and DOPE was studied using a fluroescence resonance energy transfer assay. The influence of dolichyl phosphate on the transbilary movement of DOPC in multilamellar vesicles (MLV) and large unilamellar vesicles (LUV) composed of DOPC and DOPE (1:2) was investigated by using the PC-specified transfer protein. The results indicate that: (1) both dolichol and dolichyl phosphate enhance vesicle fusion in a comparable and concentration-dependent way; (2) the amount of exchangeable PC from MLVs is increased by dolichyl phosphate probably as a result of fusion processes. It thus appears that these polyprenols are potent destabilizers of bilayer structure and that this process is accompanied by membrane fusion and transbilayer transport of phospholipids

  16. Bi-layer structure of counterstreaming energetic electron fluxes: a diagnostic tool of the acceleration mechanism in the Earth's magnetotail

    Directory of Open Access Journals (Sweden)

    D. V. Sarafopoulos

    2010-02-01

    Full Text Available For the first time we identify a bi-layer structure of energetic electron fluxes in the Earth's magnetotail and establish (using datasets mainly obtained by the Geotail Energetic Particles and Ion Composition (EPIC/ICS instrument that it actually provides strong evidence for a purely spatial structure. Each bi-layer event is composed of two distinct layers with counterstreaming energetic electron fluxes, parallel and antiparallel to the local ambient magnetic field lines; in particular, the tailward directed fluxes always occur in a region adjacent to the lobes. Adopting the X-line as a standard reconnection model, we determine the occurrence of bi-layer events relatively to the neutral point, in the substorm frame; four (out of the shown seven events are observed earthward and three tailward, a result implying that four events probably occurred with the substorm's local recovery phase. We discuss the bi-layer events in terms of the X-line model; they add more constraints for any candidate electron acceleration mechanism. It should be stressed that until this time, none proposed electron acceleration mechanism has discussed or predicted these layered structures with all their properties. Then we discuss the bi-layer events in terms of the much promising "akis model", as introduced by Sarafopoulos (2008. The akis magnetic field topology is embedded in a thinned plasma sheet and is potentially causing charge separation. We assume that as the Rc curvature radius of the magnetic field line tends to become equal to the ion gyroradius rg, then the ions become non-adiabatic. At the limit Rc=rg the demagnetization process is also under way and the frozen-in magnetic field condition is violated by strong wave turbulence; hence, the ion particles in this geometry are stochastically scattered. In addition, ion diffusion probably takes place across the magnetic field, since an

  17. Strength of integration of transmembrane alpha-helical peptides in lipid bilayers as determined by atomic force spectroscopy.

    Science.gov (United States)

    Ganchev, Dragomir N; Rijkers, Dirk T S; Snel, Margot M E; Killian, J Antoinette; de Kruijff, Ben

    2004-11-30

    In this study we address the stability of integration of proteins in membranes. Using dynamic atomic force spectroscopy, we measured the strength of incorporation of peptides in lipid bilayers. The peptides model the transmembrane parts of alpha-helical proteins and were studied in both ordered peptide-rich and unordered peptide-poor bilayers. Using gold-coated AFM tips and thiolated peptides, we were able to observe force events which are related to the removal of single peptide molecules out of the bilayer. The data demonstrate that the peptides are very stably integrated into the bilayer and that single barriers within the investigated region of loading rates resist their removal. The distance between the ground state and the barrier for peptide removal was found to be 0.75 +/- 0.15 nm in different systems. This distance falls within the thickness of the interfacial layer of the bilayer. We conclude that the bilayer interface region plays an important role in stably anchoring transmembrane proteins into membranes. PMID:15554706

  18. Modulation of the band structure in bilayer zigzag graphene nanoribbons on hexagonal boron nitride using the force and electric fields

    Energy Technology Data Exchange (ETDEWEB)

    Ilyasov, V.V., E-mail: viily@mail.ru [Don State Technical University, Rostov on Don, 344000 (Russian Federation); Nguyen, Chuong V., E-mail: chuongnguyen11@gmail.com [Don State Technical University, Rostov on Don, 344000 (Russian Federation); Ershov, I.V. [Don State Technical University, Rostov on Don, 344000 (Russian Federation); Nguyen, Chien D. [Institute of Engineering Physics, Hanoi University of Science and Technology, Hanoi, 10000 (Viet Nam); Hieu, Nguyen N. [Institute of Research and Development, Duy Tan University, Da Nang (Viet Nam)

    2015-03-15

    Modulation of semiconductor–halfmetal–metal transition in the antiferromagnetic (AF) ordering of bilayer zigzag graphene nanoribbons (BZGNRs) on hexagonal boron nitride (h-BN) heterostructure using the external force field F{sub ext} and transverse electric fields E{sub ext} (in the presence of interaction with the substrate) was performed within the framework of the density functional theory (DFT). We established critical values of E{sub ext} and interlayer distance in the bilayer providing for semiconductor–halfmetal–metal transition in one of electron spin configurations. Our calculations also show that the energy gap E{sub g} in the AF-BZGNR/h-BN(0001) heterostructure can be controlled in a wide range of the F{sub ext} and E{sub ext}. This makes the AF-8-ZGNR/h-BN(0001) heterostructure being potentially promising for application in spintronic devices. - Highlights: • We used DFT to examine the opportunities for modulation of the band structure in AF-8-BZGNR/h-BN(0001). • We estimated the critical values of the F{sub ext} and E{sub ext} providing for SC-HM-M transition. • The energy gap in the AF-BZGNR/h-BN(0001) can be monitored in a wide range of the F{sub ext} and E{sub ext}.

  19. Structure and stability of phospholipid bilayers hydrated by a room-temperature ionic liquid/water solution: a neutron reflectometry study.

    Science.gov (United States)

    Benedetto, Antonio; Heinrich, Frank; Gonzalez, Miguel A; Fragneto, Giovanna; Watkins, Erik; Ballone, Pietro

    2014-10-23

    Neutron reflectometry (NR) measurements were carried out to probe the structure and stability of two model biomembranes consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) phospholipid bilayers hydrated by water solutions of two prototypical room-temperature ionic liquids (RTILs), namely, 1-butyl-3-methyl-imidazolium chloride ([bmim][Cl]) and choline chloride ([Chol][Cl]) at concentrations of 0.1 M and 0.5 M, respectively. The raw data were analyzed by fitting a distribution of scattering length densities arising from the different chemical species in the system. The results of this analysis show that (a) for all systems and concentrations that we considered, the thickness of the bilayers shrinks by ∼1 Å upon dissolving the ionic liquid into water and that (b) the RTIL ions enter the bilayer, finding their way to a preferred location in the lipid range that is nearly independent of the lipid and of the [bimim](+) or [Chol](+) choice. The volume fraction of RTIL sorbed in/on the bilayer, however, does depend on the lipid, but, again, is the same for [bmim][Cl] and for [Chol][Cl]. Thus, the RTIL occupies ∼5% of the bilayer volume in POPC, rising to ∼10% in DMPC. Repeating the measurements and data analysis after rinsing in pure water shows that the changes in the bilayer due to the RTIL sorption are irreversible and that a measurable amount of IL remains in the lipid fraction, that is, ∼2.5% of the bilayer volume in POPC and ∼8% in DMPC. PMID:25251987

  20. Structural and magnetic properties of epitaxial Fe/CoO bilayers on Ag(001)

    Science.gov (United States)

    Abrudan, R.; Miguel, J.; Bernien, M.; Tieg, C.; Piantek, M.; Kirschner, J.; Kuch, W.

    2008-01-01

    We have investigated the magnetic coupling between a metallic ferromagnet and an oxidic antiferromagnet in epitaxial single-crystalline Fe/CoO bilayers on Ag(001) using x-ray absorption spectroscopy. Absorption spectra taken from bilayers with different amounts of deposited Fe show only a weak indication for the formation of Fe oxide at the Fe/CoO interface. From the spectral shape, it is concluded that an FeO type of oxide is formed. X-ray magnetic circular dichroism (XMCD) measurements exhibit a sizable induced ferromagnetic signal at the CoL2,3 absorption edges, corresponding to an interface layer of 1.1 ML of CoO in which the Co magnetic moments couple with the Fe moments. The angular dependence of the Fe XMCD and Co x-ray magnetic linear dichroic signals at the L2,3 edges shows that the orientation of the Co and Fe spins is parallel along the crystallographic ⟨110⟩ directions.

  1. Dependence of the oscillations amplitude on the thickness of magnetostrictive-piezoelectric bilayer structure in the theory of magnetoelectric effect

    International Nuclear Information System (INIS)

    Dependence of the amplitude of mechanical oscillations on the thickness of magnetostrictive-piezoelectric bilayer structure in the form of rectangular plate is presented for the theory of linear magnetoelectric effect. The case of longitudinal orientation of the electric and magnetic fields was considered for structures in the form of a rectangular plate. The frequency dependence of the magnetoelectric effect is obtained using motion equation and electrostatic equations for both phases taking into account the boundary conditions on the interface. The theoretical dependencies of the displacement and stress distributions over the thickness of the sample in the magnetostrictive and piezoelectric phases are presented. These dependencies have a nonlinear character, and their accounting leads to a noticeable contribution to the magnitude of the effect

  2. Probing structural features of Alzheimer's amyloid-β pores in bilayers using site-specific amino acid substitutions.

    Science.gov (United States)

    Capone, Ricardo; Jang, Hyunbum; Kotler, Samuel A; Kagan, Bruce L; Nussinov, Ruth; Lal, Ratnesh

    2012-01-24

    A current hypothesis for the pathology of Alzheimer's disease (AD) proposes that amyloid-β (Aβ) peptides induce uncontrolled, neurotoxic ion flux across cellular membranes. The mechanism of ion flux is not fully understood because no experiment-based Aβ channel structures at atomic resolution are currently available (only a few polymorphic states have been predicted by computational models). Structural models and experimental evidence lend support to the view that the Aβ channel is an assembly of loosely associated mobile β-sheet subunits. Here, using planar lipid bilayers and molecular dynamics (MD) simulations, we show that amino acid substitutions can be used to infer which residues are essential for channel structure. We created two Aβ(1-42) peptides with point mutations: F19P and F20C. The substitution of Phe19 with Pro inhibited channel conductance. MD simulation suggests a collapsed pore of F19P channels at the lower bilayer leaflet. The kinks at the Pro residues in the pore-lining β-strands induce blockage of the solvated pore by the N-termini of the chains. The cysteine mutant is capable of forming channels, and the conductance behavior of F20C channels is similar to that of the wild type. Overall, the mutational analysis of the channel activity performed in this work tests the proposition that the channels consist of a β-sheet rich organization, with the charged/polar central strand containing the mutation sites lining the pore, and the C-terminal strands facing the hydrophobic lipid tails. A detailed understanding of channel formation and its structure should aid studies of drug design aiming to control unregulated Aβ-dependent ion fluxes. PMID:22242635

  3. Mechanism of unassisted ion transport across membrane bilayers

    Science.gov (United States)

    Wilson, M. A.; Pohorille, A.

    1996-01-01

    To establish how charged species move from water to the nonpolar membrane interior and to determine the energetic and structural effects accompanying this process, we performed molecular dynamics simulations of the transport of Na+ and Cl- across a lipid bilayer located between two water lamellae. The total length of molecular dynamics trajectories generated for each ion was 10 ns. Our simulations demonstrate that permeation of ions into the membrane is accompanied by the formation of deep, asymmetric thinning defects in the bilayer, whereby polar lipid head groups and water penetrate the nonpolar membrane interior. Once the ion crosses the midplane of the bilayer the deformation "switches sides"; the initial defect slowly relaxes, and a defect forms in the outgoing side of the bilayer. As a result, the ion remains well solvated during the process; the total number of oxygen atoms from water and lipid head groups in the first solvation shell remains constant. A similar membrane deformation is formed when the ion is instantaneously inserted into the interior of the bilayer. The formation of defects considerably lowers the free energy barrier to transfer of the ion across the bilayer and, consequently, increases the permeabilities of the membrane to ions, compared to the rigid, planar structure, by approximately 14 orders of magnitude. Our results have implications for drug delivery using liposomes and peptide insertion into membranes.

  4. Tetra- and Penta-Cyclic Triterpenes Interaction with Lipid Bilayer Membrane: A Structural Comparative Study.

    Science.gov (United States)

    Abboud, Rola; Charcosset, Catherine; Greige-Gerges, Hélène

    2016-06-01

    The effect of tetracyclic (cortisol, prednisolone, and 9-fluorocortisol acetate) and pentacyclic (uvaol and erythrodiol) triterpenes (TTPs) on the fluidity of dipalmitoyl phosphatidyl choline (DPPC) liposome membrane was investigated by differential scanning calorimetry, Raman spectroscopy, and fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH). Liposomes were prepared in the absence and presence of TTPs at molar ratios DPPC:TTP 100:1, 100:2.5, and 100:10. All the studied TTPs abolished the pre-transition and modified the intensity of the Raman peak at 715 cm(-1) proving the interaction of TTP molecules with the choline head group of phospholipids. An increase in the Raman height intensity ratios of the peaks I 2935/2880, I 2844/2880, and I 1090/1130, giving information about the ratio disorder/order of the alkyl chains, and a decrease of the main transition temperature demonstrated the interaction of TTPs with the alkyl chains. The tetracyclic TTPs produced broadening of the phase transition profile. Besides, a scarcely splitting of the main transition peak was obtained with prednisolone and 9-fluorocortisol acetate. The results of fluorescence depolarization of DPH showed that the studied molecules fluidized the liposomal membrane at 25, 41, and 50 °C. Pentacyclic TTPs, being more hydrophobic than tetracyclic ones, demonstrated higher fluidizing effect than tetracyclic TTPs in the liquid crystalline phase suggesting a deeper incorporation in the lipid bilayer. The presence of a free polar head group at the ring D seems to control the TTP incorporation in the bilayer and consequently its effect on the membrane fluidity. PMID:26759229

  5. Enhanced resistive switching and multilevel behavior in bilayered HfAlO/HfAlOx structures for non-volatile memory applications

    International Nuclear Information System (INIS)

    In this work, hafnium aluminum oxide (HfAlO) thin films were deposited by ion beam sputtering deposition technique on Si substrate. The presence of oxygen vacancies in the HfAlOx layer deposited in oxygen deficient environment is evidenced from the photoluminescence spectra. Furthermore, HfAlO(oxygen rich)/HfAlOx(oxygen poor) bilayer structures exhibit multilevel resistive switching (RS), and the switching ratio becomes more prominent with increasing the HfAlO layer thickness. The bilayer structure with HfAlO/HfAlOx thickness of 30/40 nm displays the enhanced multilevel resistive switching characteristics, where the high resistance state/intermediate resistance state (IRS) and IRS/low resistance state resistance ratios are ≈102 and ≈5 × 105, respectively. The switching mechanisms in the bilayer structures were investigated by the temperature dependence of the three resistance states. This study revealed that the multilevel RS is attributed to the coupling of ionic conduction and the metallic conduction, being the first associated to the formation and rupture of conductive filaments related to oxygen vacancies and the second with the formation of a metallic filament. Moreover, the bilayer structures exhibit good endurance and stability in time

  6. Enhanced resistive switching and multilevel behavior in bilayered HfAlO/HfAlO{sub x} structures for non-volatile memory applications

    Energy Technology Data Exchange (ETDEWEB)

    Faita, F. L., E-mail: fabriciofaita@gmail.com [Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Departamento de Física, Universidade Federal de Santa Catarina, Campus Trindade, 88040-900 Florianópolis, SC (Brazil); Silva, J. P. B., E-mail: josesilva@fisica.uminho.pt [Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, 4169-007 Porto (Portugal); Pereira, M.; Gomes, M. J. M. [Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal)

    2015-12-14

    In this work, hafnium aluminum oxide (HfAlO) thin films were deposited by ion beam sputtering deposition technique on Si substrate. The presence of oxygen vacancies in the HfAlO{sub x} layer deposited in oxygen deficient environment is evidenced from the photoluminescence spectra. Furthermore, HfAlO(oxygen rich)/HfAlO{sub x}(oxygen poor) bilayer structures exhibit multilevel resistive switching (RS), and the switching ratio becomes more prominent with increasing the HfAlO layer thickness. The bilayer structure with HfAlO/HfAlO{sub x} thickness of 30/40 nm displays the enhanced multilevel resistive switching characteristics, where the high resistance state/intermediate resistance state (IRS) and IRS/low resistance state resistance ratios are ≈10{sup 2} and ≈5 × 10{sup 5}, respectively. The switching mechanisms in the bilayer structures were investigated by the temperature dependence of the three resistance states. This study revealed that the multilevel RS is attributed to the coupling of ionic conduction and the metallic conduction, being the first associated to the formation and rupture of conductive filaments related to oxygen vacancies and the second with the formation of a metallic filament. Moreover, the bilayer structures exhibit good endurance and stability in time.

  7. Characteristic length scale of the magnon accumulation in Fe3O4/Pt bilayer structures by incoherent thermal excitation

    Science.gov (United States)

    Anadón, A.; Ramos, R.; Lucas, I.; Algarabel, P. A.; Morellón, L.; Ibarra, M. R.; Aguirre, M. H.

    2016-07-01

    The dependence of Spin Seebeck effect (SSE) with the thickness of the magnetic materials is studied by means of incoherent thermal excitation. The SSE voltage signal in Fe3O4/Pt bilayer structure increases with the magnetic material thickness up to 100 nm, approximately, showing signs of saturation for larger thickness. This dependence is well described in terms of a spin current pumped in the platinum film by the magnon accumulation in the magnetic material. The spin current is generated by a gradient of temperature in the system and detected by the Pt top contact by means of inverse spin Hall effect. Calculations in the frame of the linear response theory adjust with a high degree of accuracy the experimental data, giving a thermal length scale of the magnon accumulation (Λ) of 17 ± 3 nm at 300 K and Λ = 40 ± 10 nm at 70 K.

  8. Irradiated bilayer graphene

    OpenAIRE

    Abergel, D. S. L.; Chakraborty, Tapash

    2010-01-01

    We describe the gated bilayer graphene system when it is subjected to intense terahertz frequency electromagnetic radiation. We examine the electron band structure and density of states via exact diagonalization methods within Floquet theory. We find that dynamical states are induced which lead to modification of the band structure. We first examine the situation where there is no external magnetic field. In the unbiased case, dynamical gaps appear in the spectrum which manifest as dips in th...

  9. Structure and morphology of epitaxially grown Fe3O4/NiO bilayers on MgO(001)

    International Nuclear Information System (INIS)

    Crystalline Fe3O4/NiO bilayers were grown on MgO(001) substrates using reactive molecular beam epitaxy to investigate their structural properties and their morphology. The film thickness either of the Fe3O4 film or of the NiO film has been varied to shed light on the relaxation of the bilayer system. The surface properties as studied by X-ray photoelectron spectroscopy and low energy electron diffraction show clear evidence of stoichiometric well-ordered film surfaces. Based on the kinematic approach X-ray diffraction experiments were completely analyzed. As a result the NiO films grow pseudomorphic in the investigated thickness range (up to 34 nm) while the Fe3O4 films relax continuously up to the thickness of 50 nm. Although all diffraction data show well developed Laue fringes pointing to oxide films of very homogeneous thickness, the Fe3O4/NiO interface roughens continuously up to 1 nm root-mean-square roughness with increasing NiO film thickness while the Fe3O4 surface is very smooth independent on the Fe3O4 film thickness. Finally, the Fe3O4/NiO interface spacing is similar to the interlayer spacing of the oxide films while the NiO/MgO interface is expanded. - Highlights: • Oxide films prepared by reactive molecular beam epitaxy • Increasing relaxation of Fe3O4 film with film thickness • Suppressed relaxation for NiO film • Increasing Fe3O4–NiO interface roughness with NiO film thickness • Smooth Fe3O4 film surface

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

    Science.gov (United States)

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

    2015-09-01

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

  11. A multi-electrode and pre-deformed bilayer spring structure electrostatic attractive MEMS actuator with large stroke at low actuation voltage

    International Nuclear Information System (INIS)

    This paper presents a multi-electrode and pre-deformed bilayer spring structure electrostatic attractive microelectromechanical systems (MEMS) actuator; it has large stroke at relatively low actuation voltage. Generally, electrostatic-attractive-force-based actuators have small stroke due to the instability resulted from the electrostatic ‘pull-in’ phenomenon. However, in many applications, the electrostatic micro-actuator with large stroke at low voltage is more preferred. By introducing a multi-electrode and a pre-deformed bilayer spring structure, an electrostatic attractive MEMS actuator with large stroke at very low actuation voltage has been successfully demonstrated in this paper. The actuator contains a central plate with a size of 300 µm × 300 µm × 1.5 µm and it is supported by four L-shaped bilayer springs which are pre-deformed due to residual stresses. Each bilayer spring is simultaneously attracted by three adjacent fixed electrodes, and the factors affecting the electrostatic attractive force are analyzed by a finite element analysis method. The prototype of the actuator is fabricated by poly-multi-user-MEMS-process (PolyMUMP) and the static performance is tested using a white light interferometer. The measured stroke of the actuator reaches 2 µm at 13 V dc, and it shows a good agreement with the simulation. (paper)

  12. Ultrasensitive organic phototransistors with multispectral response based on thin-film/single-crystal bilayer structures

    Energy Technology Data Exchange (ETDEWEB)

    Pinto, R. M., E-mail: rpinto@inesc-mn.pt [INESC MN and IN, Rua Alves Redol 9, 1000-029 Lisboa (Portugal); CQFM, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Gouveia, W. [INESC MN and IN, Rua Alves Redol 9, 1000-029 Lisboa (Portugal); Neves, A. I. S. [INESC MN and IN, Rua Alves Redol 9, 1000-029 Lisboa (Portugal); College of Engineering, Mathematics and Physical Sciences, University of Exeter, EX4 4QL Exeter (United Kingdom); Alves, H. [INESC MN and IN, Rua Alves Redol 9, 1000-029 Lisboa (Portugal); CICECO, Physics Department, Universidade de Aveiro, 3810-193 Aveiro (Portugal)

    2015-11-30

    We report on highly efficient organic phototransistors (OPTs) based on thin-film/single-crystal planar bilayer junctions between 5,6,11,12-tetraphenyltetracene (rubrene) and [6,6]-phenyl-C{sub 61}-butyric acid methyl ester (PC{sub 61}BM). The OPTs show good field-effect characteristics in the dark, with high hole-mobility (4–5 cm{sup 2} V{sup −1} s{sup −1}), low-contact resistance (20 kΩ cm), and low-operating voltage (≤5 V). Excellent sensing capabilities allow for light detection in the 400–750 nm range, with photocurrent/dark current ratio as high as 4 × 10{sup 4}, responsivity on the order of 20 AW{sup −1} at 27 μW cm{sup −2}, and an external quantum efficiency of 52 000%. Photocurrent generation is attributed to enhanced electron and hole transfer at the interface between rubrene and PC{sub 61}BM, and fast response times are observed as a consequence of the high-mobility of the interfaces. The optoelectronic properties exhibited in these OPTs outperform those typically provided by a-Si based devices, enabling future applications where multifunctionality in a single-device is sought.

  13. Ultrasensitive organic phototransistors with multispectral response based on thin-film/single-crystal bilayer structures

    International Nuclear Information System (INIS)

    We report on highly efficient organic phototransistors (OPTs) based on thin-film/single-crystal planar bilayer junctions between 5,6,11,12-tetraphenyltetracene (rubrene) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). The OPTs show good field-effect characteristics in the dark, with high hole-mobility (4–5 cm2 V−1 s−1), low-contact resistance (20 kΩ cm), and low-operating voltage (≤5 V). Excellent sensing capabilities allow for light detection in the 400–750 nm range, with photocurrent/dark current ratio as high as 4 × 104, responsivity on the order of 20 AW−1 at 27 μW cm−2, and an external quantum efficiency of 52 000%. Photocurrent generation is attributed to enhanced electron and hole transfer at the interface between rubrene and PC61BM, and fast response times are observed as a consequence of the high-mobility of the interfaces. The optoelectronic properties exhibited in these OPTs outperform those typically provided by a-Si based devices, enabling future applications where multifunctionality in a single-device is sought

  14. Determination of Uranium Oxides Structure

    International Nuclear Information System (INIS)

    Determination of uranium oxides structure have been worked using XRD (X-Ray Diffractometer). Where the diffraction patterns were analyzed by Rietan method. The samples that analysis were UO2,07; UO2,06; UO2,15; UO2,27 and U3O8 compound. Rietan refinement of the diffraction patterns showed cubic structures for UO2,07 and UO2,06, with a = 5,4663 A and 5,4638 A, respectively. UO2,15 compound was found to be a mixture of cubic, a = 5,4637 A and tetragonal structures, a = 5,454 A and c = 5,409 A. The structures of UO2,27 and U3O8 were found to be tetragonal and orthorhombic, respectively with a 5,4717 A and c = 5,407 A for the tetragonal structure, while a 6,7147 A, b = 11, 9506 A and c = 4,1448 A for the orthorhombic one. It was concluded from this investigation that large amounts of x oxygen atoms in UO2+x, transforms the cubic structure gradually to tetragonal and finely to orthorhombic structure. Sample of PPNY's UO2 had cubic structure, so that the structure specification as which expected. (author)

  15. Phospholipid bilayers are viscoelastic

    OpenAIRE

    Harland, Christopher W.; Bradley, Miranda J.; Parthasarathy, Raghuveer

    2010-01-01

    Lipid bilayers provide the structural framework for cellular membranes, and their character as two-dimensional fluids enables the mobility of membrane macromolecules. Though the existence of membrane fluidity is well established, the nature of this fluidity remains poorly characterized. Three-dimensional fluids as diverse as chocolates and cytoskeletal networks show a rich variety of Newtonian and non-Newtonian dynamics that have been illuminated by contemporary rheological techniques. Applyi...

  16. Ultrasonic determination of steel structures

    International Nuclear Information System (INIS)

    In the research project 'Determination of steel structures by means of ultrasound' methods are developed for the non-destructive structure characterization with scattered ultrasound. Measurements were made at about 200 steel samples with frequencies between 5 and 20 Mc/sec. In the range of 0,05 <= d/lambda <= 0,5 (d=mean grain size, lambda = wavelength of the ultrasound pulse) known theories can be applied for the quantitative grain size determination and with an accuracy of +-15% the results agree with the metallographically measured values. The best method for this is the combination of two measurements with two different frequencies. Advantages are given by the measurement of the multiple scattering which is leading to the scattering coefficient and to the grain size with one measurement only and without assumptions concerning other parameters of ultrasound propagation. A structure characterization concerning the homogeneity inside the material is possible, too, because of the time (i.e. sound path-)-dependent scattering measurement. It is able to control the structure of monophasic steels with grain sizes between ASTM 1 and ASTM 11. Today problems unsolved are the martensitic steels, the multiphasic structures

  17. Near-Field studies of anisotropic variations and temperature induced structural changes in a supported single lipid bilayer

    OpenAIRE

    Merrell A. Johnson; Decca, Ricardo S.

    2016-01-01

    Temperature controlled Polarization Modulation Near-Field Scanning Optical Microscopy (PM-NSOM) measurements of a single supported $L_{\\beta^{\\prime}}$ 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayer are presented. The effective retardance ($\\Delta S = \\frac{2 \\pi (n_e-n_o)t}{\\lambda}$), where $t$ is the thickness of the bilayer and $\\lambda$ is the wavelength of light used and the direction of the projection of the acyl chains ($\\theta $) were measured simultaneously. From $...

  18. Structural and electronic properties of AB- and AA-stacking bilayer-graphene intercalated by Li, Na, Ca, B, Al, Si, Ge, Ag, and Au atoms

    Science.gov (United States)

    Tayran, Ceren; Aydin, Sezgin; Çakmak, Mehmet; Ellialtıoğlu, Şinasi

    2016-04-01

    The structural and electronic properties of X (=Li, Na, Ca, B, Al, Si, Ge, Ag, and Au)-intercalated AB- and AA-stacking bilayer-graphene have been investigated by using ab initio density functional theory. It is shown that Boron (Lithium)-intercalated system is energetically more stable than the others for the AB (AA) stacking bilayer-graphene systems. The structural parameters, electronic band structures, and orbital nature of actual interactions are studied for the relaxed stable geometries. It is seen that the higher the binding energy, the smaller is the distance between the layers, in these systems. The electronic band structures for these systems show that different intercalated atoms can change the properties of bilayer-graphene differently. For qualitative description of the electronic properties, the metallicities of the systems are also calculated and compared with each other. The Mulliken analysis and electron density maps clearly indicate that the interactions inside a single layer (intralayer interactions) are strong and highly covalent, while the interactions between the two layers (interlayer interactions) are much weaker.

  19. Study of the influence of semiconductor material parameters on acoustic wave propagation modes in GaSb/AlSb bi-layered structures by Legendre polynomial method

    Science.gov (United States)

    Othmani, Cherif; Takali, Farid; Njeh, Anouar; Ben Ghozlen, Mohamed Hédi

    2016-09-01

    The propagation of Rayleigh-Lamb waves in bi-layered structures is studied. For this purpose, an extension of the Legendre polynomial (LP) method is proposed to formulate the acoustic wave equation in the bi-layered structures induced by thin film Gallium Antimonide (GaSb) and with Aluminum Antimonide (AlSb) substrate in moderate thickness. Acoustic modes propagating along a bi-layer plate are shown to be quite different than classical Lamb modes, contrary to most of the multilayered structures. The validation of the LP method is illustrated by a comparison between the associated numerical results and those obtained using the ordinary differential equation (ODE) method. The convergency of the LP method is discussed through a numerical example. Moreover, the influences of thin film GaSb parameters on the characteristics Rayleigh-Lamb waves propagation has been studied in detail. Finally, the advantages of the Legendre polynomial (LP) method to analyze the multilayered structures are described. All the developments performed in this work were implemented in Matlab software.

  20. Reversibly formed bilayer vesicles: Energetics and polydispersity

    DEFF Research Database (Denmark)

    Bergstöm, M.

    Model calculations based on the multiple equilibrium approach indicate that the spontaneous formation of geometrically closed bilayer vesicles is geared primarily by the bilayer tension which in turn is largely determined by the work of bending the bilayer into a spherical vesicle. and a statisti......Model calculations based on the multiple equilibrium approach indicate that the spontaneous formation of geometrically closed bilayer vesicles is geared primarily by the bilayer tension which in turn is largely determined by the work of bending the bilayer into a spherical vesicle. and a...... orders of magnitude larger than where the local free energy minima of the equilibrium vesicle actually occur. Moreover, according to our analysis, the relative width of a vesicle size distribution, sigma(R)/R-max, is generally at full equilibrium equal to 0.283, independently of the energetic vesicle...

  1. Reversibly formed bilayer vesicles: Energetics and polydispersity

    DEFF Research Database (Denmark)

    Bergstöm, M.

    1997-01-01

    statistical-mechanical factor that accounts for the fluctuations in composition, chain packing density and shape. We demonstrate that the free energy required to form a spherical vesicle is made up of two main contributions: the (size-independent) work of bending the constituent monolayers and the work of......Model calculations based on the multiple equilibrium approach indicate that the spontaneous formation of geometrically closed bilayer vesicles is geared primarily by the bilayer tension which in turn is largely determined by the work of bending the bilayer into a spherical vesicle. and a...... stretching the bilayer that is determined by the planar bilayer tension. A previously undiscovered contribution to the work of bending a vesicle bilayer, originating from geometrical packing constraints, is presented. On this basis we obtain vesicle size distributions with maxima located at radii several...

  2. Magnetism and electronic structure of (001)- and (111)-oriented LaTiO{sub 3} bilayers sandwiched in LaScO{sub 3} barriers

    Energy Technology Data Exchange (ETDEWEB)

    Weng, Yakui; Dong, Shuai, E-mail: sdong@seu.edu.cn [Department of Physics and Jiangsu Key Laboratory of Advanced Metallic Materials, Southeast University, Nanjing 211189 (China)

    2015-05-07

    In this study, the magnetism and electronic structure of LaTiO{sub 3} bilayers along both the (001) and (111) orientations are calculated using the density functional theory. The band insulator LaScO{sub 3} is chosen as the barrier layer and substrate to obtain the isolating LaTiO{sub 3} bilayer. For both the (001)- and (111)-oriented cases, LaTiO{sub 3} demonstrates the G-type antiferromagnetism as the ground state, similar to the bulk material. However, the electronic structure is significantly changed. The occupied bands of Ti are much narrower in the (111) case, giving a nearly flat band. As a result, the exchange coupling between nearest-neighbor Ti ions is reformed in these superlattices, which will affect the Néel temperature significantly.

  3. Crystal structure determination of Efavirenz

    Energy Technology Data Exchange (ETDEWEB)

    Popeneciu, Horea, E-mail: horea.popeneciu@itim-cj.ro; Dumitru, Ristoiu [College of Environmental Science on Engineering Babes Bolyai University, 30 Fantanele, 400294 Cluj Napoca (Romania); Tripon, Carmen, E-mail: horea.popeneciu@itim-cj.ro; Borodi, Gheorghe, E-mail: horea.popeneciu@itim-cj.ro; Pop, Mihaela Maria, E-mail: mihaelapop@teracrystal.com

    2015-12-23

    Needle-shaped single crystals of the title compound, C{sub 14}H{sub 9}ClF{sub 3}NO{sub 2}, were obtained from a co-crystallization experiment of Efavirenz with maleic acid in a (1:1) ratio, using methanol as solvent. Crystal structure determination at room temperature revealed a significant anisotropy of the lattice expansion compared to the previously reported low-temperature structure. In both low- and room temperature structures the cyclopropylethynyl fragment in one of the asymmetric unit molecules is disordered. While at low-temperature only one C atom exhibits positional disorder, at room temperature the disorder is present for two C atoms of the cyclopropane ring.

  4. Structure factor determination by electron diffraction

    International Nuclear Information System (INIS)

    A selection of methods for structure factor determination by electron diffraction is presented. Results obtained by the different methods are compared with regard to accuracies in structure determination

  5. Core/shell-structured upconversion nanophosphor and cadmium-free quantum-dot bilayer-based near-infrared photodetectors.

    Science.gov (United States)

    Hong, A-Ra; Kim, Jungyoon; Kim, Su Yeon; Kim, Seong-Il; Lee, Kwangyeol; Jang, Ho Seong

    2015-11-01

    The core/shell-structured upconversion nanophosphors (UCNPs) and Cd-free CuInS(2)/ZnS quantum dots (QDs) were synthesized via coprecipitation and hot-injection methods, respectively, and they were applied to near infrared (NIR) photodetectors. The β-NaYF(4):Yb,Er/β-NaYF(4) UCNPs emitted intense visible light peaking at 522, 542, and 656 nm via (2)H(11/2), (4)S(3/2), and (4)F(9/2)→(4)I(15/2) transitions under excitation with 980 nm NIR light. The core/shell UCNPs showed 6.4 times higher emission intensity than core UCNPs. Charge carriers can be generated from CuInS(2)/ZnS QDs in the QD-UCNP mixture due to their broad absorption in the visible spectral region shorter than 600 nm. The photodetector devices were fabricated by spin-coating CuInS(2)/ZnS QDs on a SiO(2)/Si substrate with patterned gold electrodes followed by spin-coating UCNPs on the QD layer. The fabricated QD-UCNP-bilayer-based device showed a drastically increased photocurrent (128 μA) compared with the QD-layer-based device under 980 nm NIR light illumination. Additionally, the fabricated device showed stable ON-OFF switching properties against on and off NIR light. PMID:26512493

  6. Construction of a patterned hydrogel-fibrous mat bilayer structure to mimic choroid and Bruch's membrane layers of retina.

    Science.gov (United States)

    Komez, Aylin; Baran, Erkan T; Erdem, Uzeyir; Hasirci, Nesrin; Hasirci, Vasif

    2016-09-01

    Deterioration of retina and death of the retinal cells due to age, diabetes, or occlusion can cause retinal degeneration which leads to loss of vision. In this study, it is aimed to design a bilayered matrix to mimic the choroid and the Bruch's membrane of the retinal tissue. As choroid, a microchanneled network resembling a fractal tree design was fabricated by photolithography over photo-cross-linkable methacrylated hyaluronic acid hydrogel. Gelatin or collagen was immobilized into the microchannels to enhance adherence of Human Umbilical Vein Endothelial Cells (HUVEC). At late culture periods (2 weeks), formation of tubular structures due to proliferation of the attached cells was observed. As Bruch's membrane, an electrospun fibroin nanofiber mat was produced to grow retinal pigment epithelium (RPE) cells on. Cellular interactions between RPE and HUVEC in the microchannels were investigated in a coculture model in a noncontact mode. It was deduced that by combining the RPE layer on the highly permeable Bruch's membrane with the choroid layer populated by HUVECs, a retinal substitute which might have a potential for use in the treatment of retinal diseases is possible. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2166-2177, 2016. PMID:27102366

  7. The influence of oscillating electromagnetic fields on membrane structure and function: Synthetic liposome and natural membrane bilayer systems with direct application to the controlled delivery of chemical agents

    International Nuclear Information System (INIS)

    Investigations have been conducted to determine if an imposed electromagnetic field can influence membrane transport, and ion and drug permeability in both synthetic and natural cell membrane systems. Microwave fields enhance accumulation of sodium in the lymphocyte and induce protein shedding at Tc. Microwaves also trigger membrane permeability of liposome systems under specific field exposure conditions. Sensitivity varies in a defined way in bilayers displaying a membrane structural phase transition temperature, Tc; maximal release was observed at or near Tc. Significantly, liposome systems without a membrane phase transition were also found to experience permeability increases but, in contrast, this response was temperature independent. The above results indicate that field-enhanced drug release occurs in liposome vesicles that possess a Tc as well as non-Tc liposomes. Additional studies extend non-Tc liposome responses to the in vivo case in which microwaves trigger Gentamicin release from a liposome ''depot'' placed subcutaneously in the rat hind leg. In addition, evidence is provided that cell surface sequestered liposomes can be triggered by microwave fields to release drugs directly into target cells. 24 refs., 6 figs

  8. Bilayer graphene formed by passage of current through graphite: evidence for a three-dimensional structure

    OpenAIRE

    Harris, Peter J. F.; Slater, Thomas J. A.; Haigh, Sarah J.; Hage, Fredrik S.; Kepaptsoglou, Despoina M.; Ramasse, Quentin M.; Brydson, Rik

    2014-01-01

    The passage of an electric current through graphite or few-layer graphene can result in a striking structural transformation, but there is disagreement about the precise nature of this process. Some workers have interpreted the phenomenon in terms of the sublimation and edge reconstruction of essentially flat graphitic structures. An alternative explanation is that the transformation actually involves a change from a flat to a three-dimensional structure. Here we describe detailed studies of ...

  9. Structure determination of enterovirus 71

    Energy Technology Data Exchange (ETDEWEB)

    Plevka, Pavel; Perera, Rushika; Cardosa, Jane; Kuhn, Richard J.; Rossmann, Michael G. (Purdue); (Sentinext)

    2013-02-20

    Enterovirus 71 is a picornavirus that causes hand, foot and mouth disease but may induce fatal neurological illness in infants and young children. Enterovirus 71 crystallized in a body-centered orthorhombic space group with two particles in general orientations in the crystallographic asymmetric unit. Determination of the particle orientations required that the locked rotation function excluded the twofold symmetry axes from the set of icosahedral symmetry operators. This avoided the occurrence of misleading high rotation-function values produced by the alignment of icosahedral and crystallographic twofold axes. Once the orientations and positions of the particles had been established, the structure was solved by molecular replacement and phase extension.

  10. Structure and dynamics of water and lipid molecules in charged anionic DMPG lipid bilayer membranes

    DEFF Research Database (Denmark)

    Rønnest, A. K.; Peters, Günther H.J.; Hansen, Flemming Yssing;

    2016-01-01

    phase with a monovalent counter-ion and in the gel phase with a divalent counter-ion. The diffusion constant of water as a function of its depth in the membrane has been determined from mean-square-displacement calculations. Also, calculated incoherent quasielastic neutron scattering functions have been...... compared to experimental results and used to determine an average diffusion constant for all water molecules in the system. On extrapolating the diffusion constants inferred experimentally to a temperature of 310 K, reasonable agreement with the simulations is obtained. However, the experiments do not have...... the sensitivity to confirm the diffusion of a small component of water bound to the lipids as found in the simulations. In addition, the orientation of the dipole moment of the water molecules has been determined as a function of their depth in the membrane. Previous indirect estimates of the...

  11. Interleaflet mixing and coupling in liquid-disordered phospholipid bilayers.

    Science.gov (United States)

    Capponi, Sara; Freites, J Alfredo; Tobias, Douglas J; White, Stephen H

    2016-02-01

    Organized as bilayers, phospholipids are the fundamental building blocks of cellular membranes and determine many of their biological functions. Interactions between the two leaflets of the bilayer (interleaflet coupling) have been implicated in the passage of information through membranes. However, physically, the meaning of interleaflet coupling is ill defined and lacks a structural basis. Using all-atom molecular dynamics simulations of fluid phospholipid bilayers of five different lipids with differing degrees of acyl-chain asymmetry, we have examined interleaflet mixing to gain insights into coupling. Reasoning that the transbilayer distribution of terminal methyl groups is an appropriate measure of interleaflet mixing, we calculated the transbilayer distributions of the acyl chain terminal methyl groups for five lipids: dioleoylphosphatidylcholine (DOPC), palmitoyloleoylphosphatidylcholine (POPC), stearoyloleoylphosphatidylcholine (SOPC), oleoylmyristoylphosphatidylcholine (OMPC), and dimyristoylphosphatidylcholine (DMPC). We observed in all cases very strong mixing across the bilayer midplane that diminished somewhat with increasing acyl-chain ordering defined by methylene order parameters. A hallmark of the interleaflet coupling idea is complementarity, which postulates that lipids with short alkyl chains in one leaflet will preferentially associate with lipids with long alkyl chains in the other leaflet. Our results suggest a much more complicated picture for thermally disordered bilayers that we call distributed complementarity, as measured by the difference in the peak positions of the sn-1 and sn-2 methyl distributions in the same leaflet. PMID:26657692

  12. Structure and electronic properties of bilayer graphene functionalized with half-sandwiched transition metal-cyclopentadienyl complexes.

    Science.gov (United States)

    Yao, Xiaojing; Zhang, Xiuyun; Ye, Xiaoshan; Wang, Jinlan

    2016-08-10

    Tuning the electronic and magnetic properties of graphene is a crucial problem in the design of practical on-off electronic devices. Using density functional theory calculations, we explore the electronic and magnetic properties of bilayer graphene functionalized by cyclopentadienyl (Cp = cyclopentadienyl, C5H5) based half-sandwich ligands, CpTM (TM = Sc-Ni). It is found that the adsorption of CpTM ligands can introduce high magnetic moments and open the band gap of bilayer graphene, due to the electron doping as well as the asymmetric charge distribution between two graphene layers. Furthermore, the p-n doping of bilayer graphene by co-binding F/NO2 and CpTM on two external sides of BLG can further widen the band gap up to 366.1 meV. This study proposes an effective way to the modulation of the electronic and magnetic properties of graphene. PMID:27464257

  13. Microstructure and mechanical behavior of a shape memory Ni-Ti bi-layer thin film

    International Nuclear Information System (INIS)

    Two different single-layers and a bi-layer Ni-Ti thin films with chemical compositions of Ni45Ti50Cu5, Ni50.8Ti49.2 and Ni50.8Ti49.2/Ni45Ti50Cu5 (numbers indicate at.%) determined by energy dispersive X-ray spectroscopy were deposited on Si (111) substrates using DC magnetron sputtering. The structures, surface morphology and transformation temperatures of annealed thin films at 500 °C for 15 min and 1 h were studied using grazing incidence X-ray diffraction, transmission electron microscopy (TEM), atomic force microscopy and differential scanning calorimetry (DSC), respectively. Nanoindentation was used to characterize the mechanical properties. The DSC and X-ray diffraction results indicated the austenitic structure of the Ni50.8Ti49.2 and martensitic structure of the Ni45Ti50Cu5 thin films while the bi-layer was composed of austenitic and martensitic thin films. TEM study revealed that copper encourages crystallization in the bi-layer such that crystal structure containing nano-precipitates in the Ni45Ti50Cu5 layer was detected after 15 min annealing while the Ni50.8Ti49.2 layer crystallized after 60 min at 500 °C. Furthermore, after annealing at 500 °C for 15 min, a precipitate free zone and thin layer amorphous were observed closely to the interface in the top layer. The bi-layer was completely crystallized at 500 °C for 1 h and the orientation of the Ni-rich precipitates indicated a stress gradient in the bi-layer. The bi-layer thin film showed different transformation temperatures and mechanical behavior from the single-layers. The developed bi-layer has different phase transformation temperatures, the higher temperatures of shape memory effect and lower temperature of pseudo-elastic behavior compared to the single-layers. Also, the bi-layer thin film exhibited a combined pseudo-elastic behavior and shape memory effect with a reduced hysteresis at the same time similar to the austenitic and martensitic thin films, respectively. - Highlights: • NiTi bi-layer

  14. Structure and thermotropic properties of 1-stearoyl-2-acetyl-phosphatidylcholine bilayer membranes.

    OpenAIRE

    Shah, J; Duclos, R I; Shipley, G G

    1994-01-01

    The structural and thermotropic properties of 1-stearoyl-2-acetyl-phosphatidylcholine (C(18):C(2)-PC) were studied as a function of hydration. A combination of differential scanning calorimetry and x-ray diffraction techniques have been used to investigate the phase behavior of C(18):C(2)-PC. At low hydration (e.g., 20% H2O), the differential scanning calorimetry heating curve shows a single reversible endothermic transition at 44.6 degrees C with transition enthalpy delta H = 6.4 kcal/mol. T...

  15. Influence of microenvironment and liposomal formulation on secondary structure and bilayer interaction of lysozyme.

    Science.gov (United States)

    Witoonsaridsilp, Wasu; Panyarachun, Busaba; Sarisuta, Narong; Müller-Goymann, Christel C

    2010-02-01

    The conformation of peptide and protein drugs in various microenvironments and the interaction with drug carriers such as liposomes are of considerable interest. In this study the influence of microenvironments such as pH, salt concentration, and surface charge on the secondary structure of a model protein, lysozyme, either in solution or entrapped in liposomes with various molar ratios of phosphatidylcholine (PC):cholesterol (Chol) was investigated. It was found that entrapment efficiency was more pronounced in negatively charged liposomes than in non-charged liposomes, which was independent of Chol content and pH of hydration medium. The occurrence of aggregation, decrease in zeta potential, and alteration of 31P NMR chemical shift of negatively charged lysozyme liposomes compared to blank liposomes suggested that the electrostatic interaction plays a major role in protein-lipid binding. Addition of sodium chloride could impair the neutralizing ability of positively charged lysozyme on negatively charged membrane via chloride counterion binding. Neither lysozyme in various buffer solutions with sodium chloride nor that entrapped in liposomes showed any significant change in their secondary structures. However, significant decrease in alpha-helical content of lysozyme in non-charged liposomes at higher pH and salt concentrations was discovered. PMID:19880295

  16. Preservation of bilayer structure in human erythrocytes and erythrocyte ghosts after phospholipase treatment : A 31P-NMR study

    NARCIS (Netherlands)

    Meer, G. van; Kruijff, B. de; Kamp, J.A.F. op den; Deenen, L.L.M. van

    1980-01-01

    1. 1. Fresh human erythrocytes were treated with lytic and non-lytic combinations of phospholipases A2, C and sphingomyelinase. The 31P-NMR spectra of ghosts derived from such erythrocytes show that, in all cases, the residual phospholipids and lysophospholipids remain organized in a bilayer configu

  17. The structural role of cholesterol in cell membranes: from condensed bilayers to lipid rafts.

    Science.gov (United States)

    Krause, Martin R; Regen, Steven L

    2014-12-16

    CONSPECTUS: Defining the two-dimensional structure of cell membranes represents one of the most daunting challenges currently facing chemists, biochemists, and biophysicists. In particular, the time-averaged lateral organization of the lipids and proteins that make up these natural enclosures has yet to be established. As the classic Singer-Nicolson model of cell membranes has evolved over the past 40 years, special attention has focused on the structural role played by cholesterol, a key component that represents ca. 30% of the total lipids that are present. Despite extensive studies with model membranes, two fundamental issues have remained a mystery: (i) the mechanism by which cholesterol condenses low-melting lipids by uncoiling their acyl chains and (ii) the thermodynamics of the interaction between cholesterol and high- and low-melting lipids. The latter bears directly on one of the most popular notions in modern cell biology, that is, the lipid raft hypothesis, whereby cholesterol is thought to combine with high-melting lipids to form "lipid rafts" that float in a "sea" of low-melting lipids. In this Account, we first describe a chemical approach that we have developed in our laboratories that has allowed us to quantify the interactions between exchangeable mimics of cholesterol and low- and high-melting lipids in model membranes. In essence, this "nearest-neighbor recognition" (NNR) method involves the synthesis of dimeric forms of these lipids that contain a disulfide moiety as a linker. By means of thiolate-disulfide interchange reactions, equilibrium mixtures of dimers are then formed. These exchange reactions are initiated either by adding dithiothreitol to a liposomal dispersion to generate a small amount of thiol monomer or by including a small amount of thiol monomer in the liposomes at pH 5.0 and then raising the pH to 7.4. We then show how such NNR measurements have allowed us to distinguish between two very different mechanisms that have been

  18. Reparameterization of all-atom dipalmitoylphosphatidylcholine lipid parameters enables simulation of fluid bilayers at zero tension

    DEFF Research Database (Denmark)

    Sonne, Jacob; Jensen, Morten Ø.; Hansen, Flemming Y.; Hemmingsen, Lars Bo Stegeager; Peters, Günther H.

    2007-01-01

    Molecular dynamics (MD) simulations of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers using the CHARMM27 force field in the tensionless isothermal-isobaric (N PT) ensemble give highly ordered, gel-like bilayers (20) with an area per lipid of ~48 Å2 (31). To obtain fluid (L ) phase properties...... of DPPC bilayers represented by the CHARMM energy function in this ensemble, we reparameterized the atomic partial charges in the lipid head group and upper parts of the acyl chains. The new charges were determined from the electron structure using both the Mulliken method and the restricted...... electrostatic potential (RESP) fitting method (5). We tested the derived charges in MD simulations of a fully hydrated DPPC bilayer. Only the simulation with the new RESP charges shows significant improvements compared with simulations using the original CHARMM27 force field resulting in an area per lipid of 60...

  19. Simulation study of a gramicidin/lipid bilayer system in excess water and lipid. I. Structure of the molecular complex.

    OpenAIRE

    Chiu, S. W.; Subramaniam, S.; Jakobsson, E.

    1999-01-01

    This paper reports on a simulation of a gramicidin channel inserted into a fluid phase DMPC bilayer with 100 lipid molecules. Two lipid molecules per leaflet were removed to insert the gramicidin, so the resulting preparation had 96 lipid molecules and 3209 water molecules. Constant surface tension boundary conditions were employed. Like previous simulations with a lower lipid/gramicidin ratio (Woolf, T. B., and B. Roux. 1996. Proteins: Struct., Funct., Genet. 24:92-114), it is found that try...

  20. Docosahexaenoic acid and eicosapentaenoic acid induce changes in the physical properties of a lipid bilayer model membrane.

    Science.gov (United States)

    Onuki, Yoshinori; Morishita, Mariko; Chiba, Yoshiyuki; Tokiwa, Shinji; Takayama, Kozo

    2006-01-01

    We investigated the effect of fatty acids such as stearic acid (SA, 18:0), oleic acid (OA, 18:1), eicosapentaenoic acid (EPA, 20:5), and docosahexaenoic acid (DHA, 22:6) on a dipalmitoylphosphatidylcholine (DPPC) bilayer by determining the phase transition temperature, fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), and detergent insolubility. Treatment with unsaturated fatty acid broadened and shifted the phase transitions of the DPPC bilayer to a lower temperature. The phase transition temperature and the value of fluorescence anisotropy of DPH at 37 degrees C decreased progressively with increasing treatment amounts of unsaturated fatty acid. A large amount of the DPPC bilayer treated with unsaturated fatty acid was dissolved in Triton X-100, obtaining a low level of detergent insolubility. These modifications of the bilayer physical properties were most pronounced with DHA and EPA treatment. These data show that unsaturated fatty acids, particularly DHA and EPA, induce a marked change in the lipid bilayer structure. The composition of fatty acids in the DPPC bilayer was similar after treatment with various unsaturated fatty acids, suggesting that the different actions of unsaturated fatty acids are attributed to change in the molecular structure (e.g., kinked conformation by double bonds). We further explored the change in physical properties induced by fatty acids dispersed in a water-in-oil-in-water multiple emulsion and found that unsaturated fatty acids acted efficiently on the DPPC bilayer, even when incorporated in emulsion form. PMID:16394552

  1. In situ atomic force microscope imaging of supported lipid bilayers

    DEFF Research Database (Denmark)

    Kaasgaard, Thomas; Leidy, Chad; Ipsen, John Hjorth;

    2001-01-01

    In situ AFM images of phospholipase A/sub 2/ (PLA/sub 2/) hydrolysis of mica-supported one- and two-component lipid bilayers are presented. For one-component DPPC bilayers an enhanced enzymatic activity is observed towards preexisting defects in the bilayer. Phase separation is observed in two......-component DMPC-DSPC bilayers and a remarkable enhanced hydrolytic activity of the PLA/sub 2/-enzyme for the DMPC-rich phase is seen. Furthermore, in a supported double bilayer system a characteristic ripple structure, most likely related to the formation of the P/sub beta /-ripple phase is observed....

  2. Water Replacement Hypothesis in Atomic Detail - Factors Determining the Structure of Dehydrated Bilayer Stacks

    NARCIS (Netherlands)

    Golovina, E.A.; Golovin, A.; Hoekstra, F.A.; Faller, R.

    2009-01-01

    According to the water replacement hypothesis, trehalose stabilizes dry membranes by preventing the decrease of spacing between membrane lipids under dehydration. In this study, we use molecular-dynamics simulations to investigate the influence of trehalose on the area per lipid (APL) and related st

  3. Normal and Frictional Interactions between Liposome-Bearing Biomacromolecular Bilayers.

    Science.gov (United States)

    Gaisinskaya-Kipnis, Anastasia; Klein, Jacob

    2016-08-01

    Highly efficient lubricating boundary layers at biosurfaces such as cartilage have been proposed to comprise phospholipids complexed with biomacromolecules exposed at the surfaces. To gain insight into this, a systematic study on the normal and frictional forces between surfaces bearing a sequentially deposited model alginate-on-chitosan bilayer, bearing different adsorbed phosphatidylcholine (PC) liposomes, was carried out using a surface force balance. Structures of the resulting surface complexes were determined using atomic force microscopy (AFM) and cryo-scanning electron microscopy (cryo-SEM). The liposome/lipid-polymer complexes could maintain their integrity up to high pressures in terms of both normal and shear interactions between the surfaces, which were repeatable, reproducible, and revealed very low friction (coefficient of friction μ down to 10(-3)-10(-4), depending on the PC used) up to pressures of hundreds of atm. We attribute this remarkable lubrication capability ultimately to hydration lubrication acting at the hydrated phosphocholine headgroups of the PC lipids, either exposed at the liposome surfaces or through complexation with the polyelectrolyte bilayer. Values of μ, while low, were roughly an order of magnitude higher than for the same PC vesicles adsorbed on bare mica, a difference attributed to their lower density on the bilayer; the bilayer, however, stabilized the PC-vesicles far better than bare mica against rupture and shear at high compressions and sliding. PMID:27409248

  4. Dynamics and instabilities of lipid bilayer membrane shapes.

    Science.gov (United States)

    Shi, Zheng; Baumgart, Tobias

    2014-06-01

    Biological membranes undergo constant shape remodeling involving the formation of highly curved structures. The lipid bilayer represents the fundamental architecture of the cellular membrane with its shapes determined by the Helfrich curvature bending energy. However, the dynamics of bilayer shape transitions, especially their modulation by membrane proteins, and the resulting shape instabilities, are still not well understood. Here, we review in a unifying manner several theories that describe the fluctuations (i.e. undulations) of bilayer shapes as well as their local coupling with lipid or protein density variation. The coupling between local membrane curvature and lipid density gives rise to a 'slipping mode' in addition to the conventional 'bending mode' for damping the membrane fluctuation. This leads to a number of interesting experimental phenomena regarding bilayer shape dynamics. More importantly, curvature-inducing proteins can couple with membrane shape and eventually render the membrane unstable. A criterion for membrane shape instability is derived from a linear stability analysis. The instability criterion reemphasizes the importance of membrane tension in regulating the stability and dynamics of membrane geometry. Recent progresses in understanding the role of membrane tension in regulating dynamical cellular processes are also reviewed. Protein density is emphasized as a key factor in regulating membrane shape transitions: a threshold density of curvature coupling proteins is required for inducing membrane morphology transitions. PMID:24529968

  5. Berry phase transition in twisted bilayer graphene

    Science.gov (United States)

    Rode, Johannes C.; Smirnov, Dmitri; Schmidt, Hennrik; Haug, Rolf J.

    2016-09-01

    The electronic dispersion of a graphene bilayer is highly dependent on rotational mismatch between layers and can be further manipulated by electrical gating. This allows for an unprecedented control over electronic properties and opens up the possibility of flexible band structure engineering. Here we present novel magnetotransport data in a twisted bilayer, crossing the energetic border between decoupled monolayers and coupled bilayer. In addition a transition in Berry phase between π and 2π is observed at intermediate magnetic fields. Analysis of Fermi velocities and gate induced charge carrier densities suggests an important role of strong layer asymmetry for the observed phenomena.

  6. Small-angle and wide-angle X-ray scattering study on the bilayer structure of synthetic and bovine heart cardiolipins

    International Nuclear Information System (INIS)

    Cardiolipin (CL) is a membrane phospholipid containing four fatty acid chains. CL plays an important role in energy transformation in mitochondria. The disorder of CL biosynthesis is involved in a genetic disease, Barth syndrome. Alteration of fatty acid composition of CLs has been found in Barth syndrome patients, i.e., the decrease of unsaturated fatty acid chains. In this study, we investigated how the degree of saturation alters the structure of CL bilayers by using X-ray scattering. Bovine heart CL and two synthetic CLs were compared. Fatty acid compositions of these three CLs have different saturation. Small-angle X-ray scattering data showed that the decrease of the number of double bonds in the unsaturated fatty acid chains causes to thicken the CL bilayers. In addition, wide-angle X-ray scattering data suggested that the decrease reduces the degree of disorder of the hydrophobic region in a liquid crystalline phase. These results may be related to the dysfunction of mitochondria in Barth syndrome.

  7. Non-homogeneous superconductivity in bilayer and trilayer ferromagnet-superconductor Cu41Ni59 - Nb spin-switch core structures

    International Nuclear Information System (INIS)

    Full text: The non-homogeneous in space superconductivity - Fulde-Ferrell Larkin-Ovchinnikov (FFLO) like state can be established in ferromagnet-superconductor layered nanostructures. It leads to arising of oscillating component of the superconducting pairing wave function, while decaying into the ferromagnetic layer. This results in interference effects when the layer has a finite thickness. The superconducting critical temperature, Tc , oscillations with thickness of ferromagnet layers are an evidence of mentioned above interference effects. For F/S/F trilayers the superconducting state can be switched off and on by changing the relative alignment of the magnetizations of the F-layers from antiparallel (AP) to parallel (P) and back. A necessary condition to achieve a large spin switching effect, i.e. a large difference between the critical temperatures of the AP and P case is the realization of high amplitude critical temperature oscillations or (ideally) a reentrant behavior of the superconductivity when the thickness of the F-material is increased. Previously, detailed investigations were performed on S/F bilayers. Recently, we could also realize reentrant phenomenon in F/S bilayers where the S-metal now is grown on top of the F-material. Combining both building blocks yields an F/S/F trilayer, representing the core structure of the superconducting spin valve. Also for this geometry deep critical temperature oscillations and reentrant superconductivity was observed. (author)

  8. Small-angle and wide-angle X-ray scattering study on the bilayer structure of synthetic and bovine heart cardiolipins

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Hiroshi [Biophysics Laboratory, Department of Chemistry and Chemical Biology, Gunma University, Maebashi, Gunma, 371-8510 (Japan); Hayakawa, Tomohiro [Life Science Laboratory, Advanced Materials Laboratories, Sony Corporation, Yushima, Bunkyo-ku, Tokyo, 113-8510 (Japan); Ito, Kazuki; Takata, Masaki [Structural Materials Science Laboratory, RIKEN SPring-8 Center, Sayo, Hyogo 679-5148 (Japan); Kobayashi, Toshihide, E-mail: htakahas@chem-bio.gunma-u.ac.j [Lipid Biology Laboratory, RIKEN, Wako, Saitama 351-0198 (Japan)

    2010-10-01

    Cardiolipin (CL) is a membrane phospholipid containing four fatty acid chains. CL plays an important role in energy transformation in mitochondria. The disorder of CL biosynthesis is involved in a genetic disease, Barth syndrome. Alteration of fatty acid composition of CLs has been found in Barth syndrome patients, i.e., the decrease of unsaturated fatty acid chains. In this study, we investigated how the degree of saturation alters the structure of CL bilayers by using X-ray scattering. Bovine heart CL and two synthetic CLs were compared. Fatty acid compositions of these three CLs have different saturation. Small-angle X-ray scattering data showed that the decrease of the number of double bonds in the unsaturated fatty acid chains causes to thicken the CL bilayers. In addition, wide-angle X-ray scattering data suggested that the decrease reduces the degree of disorder of the hydrophobic region in a liquid crystalline phase. These results may be related to the dysfunction of mitochondria in Barth syndrome.

  9. A high performance transparent resistive switching memory made from ZrO2/AlON bilayer structure

    Science.gov (United States)

    Tsai, Tsung-Ling; Chang, Hsiang-Yu; Lou, Jesse Jen-Chung; Tseng, Tseung-Yuen

    2016-04-01

    In this study, the switching properties of an indium tin oxide (ITO)/zirconium oxide (ZrO2)/ITO single layer device and those of a device with an aluminum oxynitride (AlON) layer were investigated. The devices with highly transparent characteristics were fabricated. Compared with the ITO/ZrO2/ITO single layer device, the ITO/ZrO2/AlON/ITO bilayer device exhibited a larger ON/OFF ratio, higher endurance performance, and superior retention properties by using a simple two-step forming process. These substantial improvements in the resistive switching properties were attributed to the minimized influence of oxygen migration through the ITO top electrode (TE), which can be realized by forming an asymmetrical conductive filament with the weakest part at the ZrO2/AlON interface. Therefore, in the ITO/ZrO2/AlON/ITO bilayer device, the regions where conductive filament formation and rupture occur can be effectively moved from the TE interface to the interior of the device.

  10. Fabrication of TERFENOL-D/PZT bilayer structures for the study of voltage control of magnetization easy axis

    International Nuclear Information System (INIS)

    Polycrystalline TERFENOL-D/PbZr0.52Ti0.48O3 (PZT) bilayer films were deposited using RF magnetron sputtering on Pt(1 1 1)/MgO(1 0 0) substrates for the purpose of studying voltage control of magnetization easy axis. TERFENOL-D films deposited at 500 deg. C on PZT show in-plane anisotropy. In our samples where the voltage is applied perpendicular to the PZT film plane, TERFENOL-D films with perpendicular magnetic anisotropy are only suitable for the above mentioned study. TERFENOL-D/PZT bilayer films with perpendicular magnetic anisotropy can be obtained by annealing in a perpendicular magnetic field at temperatures between 200 and 350 deg. C. However, deposition and annealing of TERFENOL-D films at high-temperatures (≥350 deg. C) causes degradation of the ferroelectric properties of PZT. In order to preserve the good switching characteristics of PZT films and to observe this effect at low voltages, TERFENOL-D films have to be deposited and annealed at low temperatures (<350 deg. C)

  11. Electronic structure evolution of single bilayer Bi(1 1 1) film on 3D topological insulator Bi2Se x Te3-x surfaces.

    Science.gov (United States)

    Lei, Tao; Jin, Kyung-Hwan; Zhang, Nian; Zhao, Jia-Li; Liu, Chen; Li, Wen-Jie; Wang, Jia-Ou; Wu, Rui; Qian, Hai-Jie; Liu, Feng; Ibrahim, Kurash

    2016-06-29

    The electronic state evolution of single bilayer (1BL) Bi(1 1 1) deposited on three-dimensional (3D) Bi2Se x Te3-x topological insulators at x  =  0, 1.26, 2, 2.46, 3 is systematically investigated by angle-resolved photoemission spectroscopy (ARPES). Our results indicate that the electronic structures of epitaxial Bi films are strongly influenced by the substrate especially the topmost sublayer near the Bi films, manifesting in two main aspects. First, the Se atoms cause a stronger charge transfer effect, which induces a giant Rashba-spin splitting, while the low electronegativity of Te atoms induces a strong hybridization at the interface. Second, the lattice strain notably modifies the band dispersion of the surface bands. Furthermore, our experimental results are elucidated by first-principles band structure calculations. PMID:27166645

  12. Determinants of Glycosaminoglycan (GAG) Structure.

    Science.gov (United States)

    Prydz, Kristian

    2015-01-01

    Proteoglycans (PGs) are glycosylated proteins of biological importance at cell surfaces, in the extracellular matrix, and in the circulation. PGs are produced and modified by glycosaminoglycan (GAG) chains in the secretory pathway of animal cells. The most common GAG attachment site is a serine residue followed by a glycine (-ser-gly-), from which a linker tetrasaccharide extends and may continue as a heparan sulfate, a heparin, a chondroitin sulfate, or a dermatan sulfate GAG chain. Which type of GAG chain becomes attached to the linker tetrasaccharide is influenced by the structure of the protein core, modifications occurring to the linker tetrasaccharide itself, and the biochemical environment of the Golgi apparatus, where GAG polymerization and modification by sulfation and epimerization take place. The same cell type may produce different GAG chains that vary, depending on the extent of epimerization and sulfation. However, it is not known to what extent these differences are caused by compartmental segregation of protein cores en route through the secretory pathway or by differential recruitment of modifying enzymes during synthesis of different PGs. The topic of this review is how different aspects of protein structure, cellular biochemistry, and compartmentalization may influence GAG synthesis. PMID:26308067

  13. Determinants of Glycosaminoglycan (GAG Structure

    Directory of Open Access Journals (Sweden)

    Kristian Prydz

    2015-08-01

    Full Text Available Proteoglycans (PGs are glycosylated proteins of biological importance at cell surfaces, in the extracellular matrix, and in the circulation. PGs are produced and modified by glycosaminoglycan (GAG chains in the secretory pathway of animal cells. The most common GAG attachment site is a serine residue followed by a glycine (-ser-gly-, from which a linker tetrasaccharide extends and may continue as a heparan sulfate, a heparin, a chondroitin sulfate, or a dermatan sulfate GAG chain. Which type of GAG chain becomes attached to the linker tetrasaccharide is influenced by the structure of the protein core, modifications occurring to the linker tetrasaccharide itself, and the biochemical environment of the Golgi apparatus, where GAG polymerization and modification by sulfation and epimerization take place. The same cell type may produce different GAG chains that vary, depending on the extent of epimerization and sulfation. However, it is not known to what extent these differences are caused by compartmental segregation of protein cores en route through the secretory pathway or by differential recruitment of modifying enzymes during synthesis of different PGs. The topic of this review is how different aspects of protein structure, cellular biochemistry, and compartmentalization may influence GAG synthesis.

  14. Protein Structure Determination Using Chemical Shifts

    DEFF Research Database (Denmark)

    Christensen, Anders Steen

    In this thesis, a protein structure determination using chemical shifts is presented. The method is implemented in the open source PHAISTOS protein simulation framework. The method combines sampling from a generative model with a coarse-grained force field and an energy function that includes che...... residues. For Rhodopsin (225 residues) a structure is found at 2.5 Å CA-RMSD from the experimental X-ray structure, and a structure is determined for the Savinase protein (269 residues) with 2.9 Å CA-RMSD from the experimental X-ray structure....

  15. Determination of the separate lipid and protein profile structures derived from the total membrane profile structure or isolated sarcoplasmic reticulum via x-ray and neutron diffraction

    International Nuclear Information System (INIS)

    Sarcoplasmic reticulum (SR) membranes were prepared to contain biosynthetically deuterated SR phospholipids utilizing specific and general phospholipid exchange proteins (PLEP). Functional measurements and freeze fracture on SR dispersions and x-ray diffraction of hydrated oriented membrane multilayers revealed that the exchanged SR membranes were very similar to unexchanged SR membranes. Low resolution (28-A) neutron diffraction studies utilizing SR membranes exchanged with either protonated or perdeuterated SR phospholipids allowed direct determination of the lipid profile within the isolated SR membrane at two different unit cell repeat distances. These lipid profile structures were found to be highly asymmetric regarding the conformation of the fatty acid chain extents and compositional distribution of phospholipid molecules in the inner vs. outer monolayer of the SR membrane bilayer. The relatively high resolution (11-A) electron-density profile from x-ray diffraction was decomposed by utilizing the asymmetry in the number of phospholipid molecules residing in the inner vs. outer monolayer of the SR lipid bilayer as obtained from the neutron diffraction study. To our knowledge, this represents the first direct determination of a lipid bilayer profile structure within an isolated membrane system

  16. Fusion and fission of fluid amphiphilic bilayers.

    Science.gov (United States)

    Gotter, Martin; Strey, Reinhard; Olsson, Ulf; Wennerström, Håkan

    2005-01-01

    The system water-oil (n-decane)-nonionic surfactant (C12E5) forms bilayer phases in a large concentration region, but, for a given oil-to-surfactant ratio, only in a narrow temperature range. In addition to the anisotropic lamellar phase (Lalpha) there is also, at slightly higher temperature, a sponge or L3-phase where the bilayers build up an isotropic structure extending macroscopically in three dimensions. In this phase the bilayer mid-surface has a mean curvature close to zero and a negative Euler characteristic. In this paper we study how the bilayers in the lamellar and the sponge phase respond dynamically to sudden temperature changes. The monolayer spontaneous curvature depends sensitively on temperature and a change of temperature thus provides a driving force for a change in bilayer topology. The equilibration therefore involves kinetic steps of fusion/fission of bilayers. Such dynamic processes have previously been monitored by temperature jump experiments using light scattering in the sponge phase. These experiments revealed an extraordinarily strong dependence of the relaxation time on the bilayer volume fraction phi. At phi magnetic resonance (2H-NMR) appear feasible. We here report on the first experiments concerned with the dynamics of the macroscopic phase transition sponge-lamellae by 2H-NMR. We find that the sponge-to-lamellae transition occurs through a nucleation process followed by domain growth involving bilayer fission at domain boundaries. In contrast, the lamellae-to-sponge transformation apparently occurs through a succession of uncorrelated bilayer fusion events. PMID:15715316

  17. Bathroom greywater recycling using polyelectrolyte-complex bilayer membrane: Advanced study of membrane structure and treatment efficiency.

    Science.gov (United States)

    Oh, K S; Poh, P E; Chong, M N; Chan, E S; Lau, E V; Saint, C P

    2016-09-01

    Polyelectrolyte-complex bilayer membrane (PCBM) was fabricated using biodegradable chitosan and alginate polymers for subsequent application in the treatment of bathroom greywater. In this study, the properties of PCBMs were studied and it was found that the formation of polyelectrolyte network reduced the molecular weight cut-off (MWCO) from 242kDa in chitosan membrane to 2.71kDa in PCBM. The decrease in MWCO of PCBM results in better greywater treatment efficiency, subsequently demonstrated in a greywater filtration study where treated greywater effluent met the household reclaimed water standard of <2 NTU turbidity and <30ppm total suspended solids (TSS). In addition, a further 20% improvement in chemical oxygen demand (COD) removal was achieved as compared to a single layer chitosan membrane. Results from this study show that the biodegradable PCBM is a potential membrane material in producing clean treated greywater for non-potable applications. PMID:27185127

  18. Analysis of the sintering stresses and shape distortion produced in co-firing of CGO-LSM/CGO bi-layer porous structures

    DEFF Research Database (Denmark)

    Ni, De Wei; Esposito, Vincenzo; Schmidt, Cristine Grings; Tadesse Molla, Tesfaye; Andersen, Kjeld Bøhm; Kaiser, Andreas; Ramousse, Severine; Pryds, Nini

    electrochemical flue gas purification devices, multilayer structures with alternating porous layers of CGO and a LSM/CGO mixture are used to achieve specific functional requirements. In a manufacturing process of such ceramic multilayer devices, co-firing is one of the critical steps as many defects such as......Gadolinium-doped cerium oxide (CGO) and lanthanum strontium manganate (LSM) are electro-ceramics materials with high potential for several electrochemical applications such as solid Oxide Fuel Cell (SOFC), gas separation membranes, and flue gas purification devices. Especially for novel...... cracks, de-lamination and shape distortion can result as a consequence of sintering mismatch stresses caused by the strain rate difference between layers. This work seeks to understand the underlying mechanisms that occur during the co-firing of porous CGO-LSM/CGO bi-layer laminates, by evaluating the...

  19. Analysis of the flexibility and stability of the structure of magainin in a bilayer, and in aqueous and nonaqueous solutions using molecular dynamics simulations.

    Science.gov (United States)

    Esmaili, Elham; Shahlaei, Mohsen

    2015-04-01

    The precise mode of the antimicrobial activity of Magainin (Mag)-an antimicrobial peptide (AMP)-is still unclear. In this study, the conformation of Mag was characterized in water, and in a methanol and lipid bilayer [palmitoyl-oleoylphosphatidylcholine (POPC)] using a molecular dynamics (MD) simulation technique. To describe the role conformation plays in Mag function, the global conformational differences within three systems were studied. Through analysis of the resulting configuration ensembles, the differences in the three systems, such as overall flexibility and average secondary structure, were studied. It is suggested that these differences may be important enough to influence interactions with lipid biomembranes, thereby influencing key properties such as penetration into cell membrane and stability. PMID:25750019

  20. Cholesterol enhances surface water diffusion of phospholipid bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Chi-Yuan; Kausik, Ravinath; Han, Songi, E-mail: songi@chem.ucsb.edu [Department of Chemistry and Biochemistry and Materials Research Laboratory, University of California, Santa Barbara, California 93106 (United States); Olijve, Luuk L. C. [Laboratory of Macromolecular and Organic Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven (Netherlands)

    2014-12-14

    Elucidating the physical effect of cholesterol (Chol) on biological membranes is necessary towards rationalizing their structural and functional role in cell membranes. One of the debated questions is the role of hydration water in Chol-embedding lipid membranes, for which only little direct experimental data are available. Here, we study the hydration dynamics in a series of Chol-rich and depleted bilayer systems using an approach termed {sup 1}H Overhauser dynamic nuclear polarization (ODNP) NMR relaxometry that enables the sensitive and selective determination of water diffusion within 5–10 Å of a nitroxide-based spin label, positioned off the surface of the polar headgroups or within the nonpolar core of lipid membranes. The Chol-rich membrane systems were prepared from mixtures of Chol, dipalmitoyl phosphatidylcholine and/or dioctadecyl phosphatidylcholine lipid that are known to form liquid-ordered, raft-like, domains. Our data reveal that the translational diffusion of local water on the surface and within the hydrocarbon volume of the bilayer is significantly altered, but in opposite directions: accelerated on the membrane surface and dramatically slowed in the bilayer interior with increasing Chol content. Electron paramagnetic resonance (EPR) lineshape analysis shows looser packing of lipid headgroups and concurrently tighter packing in the bilayer core with increasing Chol content, with the effects peaking at lipid compositions reported to form lipid rafts. The complementary capability of ODNP and EPR to site-specifically probe the hydration dynamics and lipid ordering in lipid membrane systems extends the current understanding of how Chol may regulate biological processes. One possible role of Chol is the facilitation of interactions between biological constituents and the lipid membrane through the weakening or disruption of strong hydrogen-bond networks of the surface hydration layers that otherwise exert stronger repulsive forces, as reflected in

  1. Cholesterol enhances surface water diffusion of phospholipid bilayers

    Science.gov (United States)

    Cheng, Chi-Yuan; Olijve, Luuk L. C.; Kausik, Ravinath; Han, Songi

    2014-12-01

    Elucidating the physical effect of cholesterol (Chol) on biological membranes is necessary towards rationalizing their structural and functional role in cell membranes. One of the debated questions is the role of hydration water in Chol-embedding lipid membranes, for which only little direct experimental data are available. Here, we study the hydration dynamics in a series of Chol-rich and depleted bilayer systems using an approach termed 1H Overhauser dynamic nuclear polarization (ODNP) NMR relaxometry that enables the sensitive and selective determination of water diffusion within 5-10 Å of a nitroxide-based spin label, positioned off the surface of the polar headgroups or within the nonpolar core of lipid membranes. The Chol-rich membrane systems were prepared from mixtures of Chol, dipalmitoyl phosphatidylcholine and/or dioctadecyl phosphatidylcholine lipid that are known to form liquid-ordered, raft-like, domains. Our data reveal that the translational diffusion of local water on the surface and within the hydrocarbon volume of the bilayer is significantly altered, but in opposite directions: accelerated on the membrane surface and dramatically slowed in the bilayer interior with increasing Chol content. Electron paramagnetic resonance (EPR) lineshape analysis shows looser packing of lipid headgroups and concurrently tighter packing in the bilayer core with increasing Chol content, with the effects peaking at lipid compositions reported to form lipid rafts. The complementary capability of ODNP and EPR to site-specifically probe the hydration dynamics and lipid ordering in lipid membrane systems extends the current understanding of how Chol may regulate biological processes. One possible role of Chol is the facilitation of interactions between biological constituents and the lipid membrane through the weakening or disruption of strong hydrogen-bond networks of the surface hydration layers that otherwise exert stronger repulsive forces, as reflected in faster

  2. Molecular Delivery into a Lipid Bilayer with a Single Shock Waves Using Molecular Dynamic Simulation

    Science.gov (United States)

    Koshiyama, Kenichiro; Kodama, Tetsuya; Hamblin, Michael R.; Doukas, Apostolos G.; Yano, Takeru; Fujikawa, Shigeo

    2005-03-01

    Cell permeabilization by shock waves may have application in gene therapy and anticancer drug delivery. In the present study we performed direct molecular dynamic (MD) simulation of the interaction of a single shock wave with a cell membrane to investigate the mechanism of the cell permeabilization. The shock wave was characterized by an impulse that was expressed with a velocity determined by the change in the momentum. The cell membrane was designed as a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer placed between two layers of water molecules. The MD simulation determined the relationship between water penetration into the bilayer, the order parameter, the fluidity of each lipid molecule, and the intensity of impulse. These structural changes in the bilayer may be an important factor in the use of shock waves to produce transient membrane permeability.

  3. The magnetic ratchet effect in bilayer graphene

    Science.gov (United States)

    McCann, Edward; Kheirabadi, Narjes; Fal'Ko, Vladimir

    Experiments have measured a magnetic ratchet effect for electrons in hydrogenated monolayer graphene, an effect in which a d.c. electric current is generated from an a.c. electric field in the presence of an in-plane magnetic field and spatial asymmetry. Here, we describe the theory of the magnetic ratchet effect in bilayer graphene. The Boltzmann kinetic equation is used to relate the d.c. current to the scattering probability of electrons in bilayer graphene. Taking into account details of the low-energy band structure of bilayer graphene, including interlayer hopping parameters, we compare contributions arising from gate- and disorder-induced spatial asymmetry, illustrating that bilayer and multilayer graphenes are natural candidates for the study of non-linear transport effects.

  4. Synthesis and sensing application of large scale bilayer graphene

    Science.gov (United States)

    Hong, Sung Ju; Yoo, Jung Hoon; Baek, Seung Jae; Park, Yung Woo

    2012-02-01

    We have synthesized large scale bilayer graphene by using Chemical Vapor Deposition (CVD) in atmospheric pressure. Bilayer graphene was grown by using CH4, H2 and Ar gases. The growth temperature was 1050^o. Conventional FET measurement shows ambipolar transfer characteristics. Results of Raman spectroscopy, Atomic Force microscope (AFM) and Transmission Electron Microscope (TEM) indicate the film is bilayer graphene. Especially, adlayer structure which interrupt uniformity was reduced in low methane flow condition. Furthermore, large size CVD bilayer graphene film can be investigated to apply sensor devices. By using conventional photolithography process, we have fabricated device array structure and studied sensing behavior.

  5. Simultaneous determination of protein structure and dynamics

    DEFF Research Database (Denmark)

    Lindorff-Larsen, Kresten; Best, Robert B.; DePristo, M. A.;

    2005-01-01

    We present a protocol for the experimental determination of ensembles of protein conformations that represent simultaneously the native structure and its associated dynamics. The procedure combines the strengths of nuclear magnetic resonance spectroscopy-for obtaining experimental information at...

  6. Determinants of Capital Structure in Family Firms

    OpenAIRE

    Akbarali, Ahmed; Foma, Awambeng

    2015-01-01

    Most firms are using optimal combination of equity and debt so as to maximize firms value and the wealth of the shareholders. To achieve all these, firms should be aware of the factors that influence the capital structure decisions. Previous empirical studies attempted to explain what determines the choice of capital structure in firms. The focus was on firms in general without categorizing family firms and non-family firms. The primary objective of this study is to examine what determines th...

  7. Structure and morphology of epitaxially grown Fe{sub 3}O{sub 4}/NiO bilayers on MgO(001)

    Energy Technology Data Exchange (ETDEWEB)

    Schemme, T., E-mail: toschemm@uos.de [Fachbereich Physik and Center of Physics and Chemistry of New Materials, Universität Osnabrück, Barbarastr. 7, 49069 Osnabrück (Germany); Kuschel, O. [Fachbereich Physik and Center of Physics and Chemistry of New Materials, Universität Osnabrück, Barbarastr. 7, 49069 Osnabrück (Germany); Bertram, F. [DESY Photon Science, Notkestr. 85, 22607 Hamburg (Germany); Kuepper, K. [Fachbereich Physik and Center of Physics and Chemistry of New Materials, Universität Osnabrück, Barbarastr. 7, 49069 Osnabrück (Germany); Wollschläger, J., E-mail: jwollsch@uos.de [Fachbereich Physik and Center of Physics and Chemistry of New Materials, Universität Osnabrück, Barbarastr. 7, 49069 Osnabrück (Germany)

    2015-08-31

    Crystalline Fe{sub 3}O{sub 4}/NiO bilayers were grown on MgO(001) substrates using reactive molecular beam epitaxy to investigate their structural properties and their morphology. The film thickness either of the Fe{sub 3}O{sub 4} film or of the NiO film has been varied to shed light on the relaxation of the bilayer system. The surface properties as studied by X-ray photoelectron spectroscopy and low energy electron diffraction show clear evidence of stoichiometric well-ordered film surfaces. Based on the kinematic approach X-ray diffraction experiments were completely analyzed. As a result the NiO films grow pseudomorphic in the investigated thickness range (up to 34 nm) while the Fe{sub 3}O{sub 4} films relax continuously up to the thickness of 50 nm. Although all diffraction data show well developed Laue fringes pointing to oxide films of very homogeneous thickness, the Fe{sub 3}O{sub 4}/NiO interface roughens continuously up to 1 nm root-mean-square roughness with increasing NiO film thickness while the Fe{sub 3}O{sub 4} surface is very smooth independent on the Fe{sub 3}O{sub 4} film thickness. Finally, the Fe{sub 3}O{sub 4}/NiO interface spacing is similar to the interlayer spacing of the oxide films while the NiO/MgO interface is expanded. - Highlights: • Oxide films prepared by reactive molecular beam epitaxy • Increasing relaxation of Fe{sub 3}O{sub 4} film with film thickness • Suppressed relaxation for NiO film • Increasing Fe{sub 3}O{sub 4}–NiO interface roughness with NiO film thickness • Smooth Fe{sub 3}O{sub 4} film surface.

  8. The quantum casimir effect may be a universal force organizing the bilayer structure of the cell membrane.

    Science.gov (United States)

    Pawlowski, Piotr H; Zielenkiewicz, Piotr

    2013-05-01

    A mathematic-physical model of the interaction between cell membrane bilayer leaflets is proposed based on the Casimir effect in dielectrics. This model explains why the layers of a lipid membrane gently slide one past another rather than penetrate each other. The presented model reveals the dependence of variations in the free energy of the system on the membrane thickness. This function is characterized by the two close minima corresponding to the different levels of interdigitation of the lipids from neighbor layers. The energy barrier of the compressing transition between the predicted minima is estimated to be 5.7 kT/lipid, and the return energy is estimated to be 3.1 kT/lipid. The proposed model enables estimation of the value of the membrane elastic thickness modulus of compressibility, which is 1.7 × 10⁹ N/m², and the value of the interlayer friction coefficient, which is 1.9 × 10⁸ Ns/m³. PMID:23612889

  9. Reparameterization of all-atom dipalmitoylphosphatidylcholine lipid parameters enables simulation of fluid bilayers at zero tension

    DEFF Research Database (Denmark)

    Sonne, Jacob; Jensen, M.Ø.; Hansen, Flemming Yssing; Hemmingsen, L.; Peters, Günther H.j.

    2007-01-01

    lipid of 60.4 ± 0.1 Å2. Compared to the 48 Å2, the new value of 60.4 Å2 is in fair agreement with the experimental value of 64 Å2. In addition, the simulated order parameter profile and electron density profile are in satisfactory agreement with experimental data. Thus, the biologically more interesting......Molecular dynamics simulations of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers using the CHARMM27 force field in the tensionless isothermal-isobaric (NPT) ensemble give highly ordered, gel-like bilayers with an area per lipid of ∼48 Å2. To obtain fluid (Lα) phase properties of DPPC bilayers...... represented by the CHARMM energy function in this ensemble, we reparameterized the atomic partial charges in the lipid headgroup and upper parts of the acyl chains. The new charges were determined from the electron structure using both the Mulliken method and the restricted electrostatic potential fitting...

  10. Distributed structure determination at the JCSG

    International Nuclear Information System (INIS)

    The software suite Xsolve semi-exhaustively explores key parameters of the X-ray structure-determination process to compute multiple three-dimensional protein structures independently and in parallel from a set of diffraction images. An optimal consensus model for subsequent manual refinement is computed from these structures. The Joint Center for Structural Genomics (JCSG), one of four large-scale structure-determination centers funded by the US Protein Structure Initiative (PSI) through the National Institute for General Medical Sciences, has been operating an automated distributed structure-solution pipeline, Xsolve, for well over half a decade. During PSI-2, Xsolve solved, traced and partially refined 90% of the JCSG’s nearly 770 MAD/SAD structures at an average resolution of about 2 Å without human intervention. Xsolve executes many well established publicly available crystallography software programs in parallel on a commodity Linux cluster, resulting in multiple traces for any given target. Additional software programs have been developed and integrated into Xsolve to further minimize human effort in structure refinement. ConsensusModeler exploits complementarities in traces from Xsolve to compute a single optimal model for manual refinement. Xpleo is a powerful robotics-inspired algorithm to build missing fragments and qFit automatically identifies and fits alternate conformations

  11. Capital Structure Determinants and Governance Structure Variety in Franchising

    NARCIS (Netherlands)

    T. Jiang (Tao)

    2009-01-01

    textabstractThis thesis investigates two questions: the determinants of capital structure in franchising and its subsequent impact on the franchise financing decisions; and the efficient governance structure choice in franchising. We posit that firms franchise in order to benefit from the reduced fr

  12. Computational Design of Multi-component Bio-Inspired Bilayer Membranes

    Directory of Open Access Journals (Sweden)

    Evan Koufos

    2014-04-01

    Full Text Available Our investigation is motivated by the need to design bilayer membranes with tunable interfacial and mechanical properties for use in a range of applications, such as targeted drug delivery, sensing and imaging. We draw inspiration from biological cell membranes and focus on their principal constituents. In this paper, we present our results on the role of molecular architecture on the interfacial, structural and dynamical properties of bio-inspired membranes. We focus on four lipid architectures with variations in the head group shape and the hydrocarbon tail length. Each lipid species is composed of a hydrophilic head group and two hydrophobic tails. In addition, we study a model of the Cholesterol molecule to understand the interfacial properties of a bilayer membrane composed of rigid, single-tail molecular species. We demonstrate the properties of the bilayer membranes to be determined by the molecular architecture and rigidity of the constituent species. Finally, we demonstrate the formation of a stable mixed bilayer membrane composed of Cholesterol and one of the phospholipid species. Our approach can be adopted to design multi-component bilayer membranes with tunable interfacial and mechanical properties. We use a Molecular Dynamics-based mesoscopic simulation technique called Dissipative Particle Dynamics that resolves the molecular details of the components through soft-sphere coarse-grained models and reproduces the hydrodynamic behavior of the system over extended time scales.

  13. A structural determinant required for RNA editing

    Science.gov (United States)

    Tian, Nan; Yang, Yun; Sachsenmaier, Nora; Muggenhumer, Dominik; Bi, Jingpei; Waldsich, Christina; Jantsch, Michael F.; Jin, Yongfeng

    2011-01-01

    RNA editing by adenosine deaminases acting on RNAs (ADARs) can be both specific and non-specific, depending on the substrate. Specific editing of particular adenosines may depend on the overall sequence and structural context. However, the detailed mechanisms underlying these preferences are not fully understood. Here, we show that duplex structures mimicking an editing site in the Gabra3 pre-mRNA unexpectedly fail to support RNA editing at the Gabra3 I/M site, although phylogenetic analysis suggest an evolutionarily conserved duplex structure essential for efficient RNA editing. These unusual results led us to revisit the structural requirement for this editing by mutagenesis analysis. In vivo nuclear injection experiments of mutated editing substrates demonstrate that a non-conserved structure is a determinant for editing. This structure contains bulges either on the same or the strand opposing the edited adenosine. The position of these bulges and the distance to the edited base regulate editing. Moreover, elevated folding temperature can lead to a switch in RNA editing suggesting an RNA structural change. Our results indicate the importance of RNA tertiary structure in determining RNA editing. PMID:21427087

  14. Determinants of capital structure: UK panel data

    OpenAIRE

    Ahi, Seyed Mohammad Ali Hamze

    2013-01-01

    ABSTRACT: The paper investigates capital structure determinants of 5 important non-financial firms listed in FTSE100. The firms are chosen from oil and gas and mining industry. The period chosen for the study is 22 years from 1990 to 2012. Firms are chosen according to capitalization in market. Theories in capital structure such as the trade-off theory, pecking order theory and agency theory are described in order to find the best possible formulation to predict the choice of capital...

  15. DETERMINANTS OF BANK BOARD STRUCTURE IN GHANA

    OpenAIRE

    Michael Adusei

    2012-01-01

    The paper investigates the determinants of bank board structure in Ghana and finds that the Scope of Operations Hypothesis could explain the variation in board size but not board independence. On the other hand, the Board Monitoring Hypothesis could only explain the variation in board independence but not board size. The study also finds that cost-income ratio, foreign majority ownership structure and Ghana Stock Exchange listing status are positively and significantly associated with large b...

  16. Direct in situ measurement of specific capacitance, monolayer tension, and bilayer tension in a droplet interface bilayer.

    Science.gov (United States)

    Taylor, Graham J; Venkatesan, Guru A; Collier, C Patrick; Sarles, Stephen A

    2015-10-14

    Thickness and tension are important physical parameters of model cell membranes. However, traditional methods to measure these quantities require multiple experiments using separate equipment. This work introduces a new multi-step procedure for directly accessing in situ multiple physical properties of droplet interface bilayers (DIB), including specific capacitance (related to thickness), lipid monolayer tension in the Plateau-Gibbs border, and bilayer tension. The procedure employs a combination of mechanical manipulation of bilayer area followed by electrowetting of the capacitive interface to examine the sensitivities of bilayer capacitance to area and contact angle to voltage, respectively. These data allow for determining the specific capacitance of the membrane and surface tension of the lipid monolayer, which are then used to compute bilayer thickness and tension, respectively. The use of DIBs affords accurate optical imaging of the connected droplets in addition to electrical measurements of bilayer capacitance, and it allows for reversibly varying bilayer area. After validating the accuracy of the technique with diphytanoyl phosphatidylcholine (DPhPC) DIBs in hexadecane, the method is applied herein to quantify separately the effects on membrane thickness and tension caused by varying the solvent in which the DIB is formed and introducing cholesterol into the bilayer. Because the technique relies only on capacitance measurements and optical images to determine both thickness and tension, this approach is specifically well-suited for studying the effects of peptides, biomolecules, natural and synthetic nanoparticles, and other species that accumulate within membranes without altering bilayer conductance. PMID:26289743

  17. Effect of magneto-structural phase coexistence in MnAs on the magnetic behavior of MnAs/Fe bilayers

    International Nuclear Information System (INIS)

    In this work we present a magneto-structural study of MnAs/Fe bilayers, epitaxially grown on GaAs(1 0 0). The coexistence of ferromagnetic and non-magnetic phases is observed by scanning tunneling microscopy (STM) at room temperature. The magnetic force microscopy (MFM) images of the samples show a stripe-patterned domain structure. The magnetization reversal at the coercive field is observed at MFM micrographs measured at different fields. The temperature dependence of the ferromagnetic resonance (FMR) spectra allows us to follow the evolution of the phase coexistence up to the Curie temperature. Two main lines can be identified in the FMR spectra in the phase coexistence region: one of them is associated to the FMR of the Fe layer. The other one, near 3000 Oe, could be associated to the resonance of Mn ions. The general appearance of the FMR spectra is strongly temperature dependent. The resonance field, line width, and shape of the Fe line is strongly altered in the α and β coexistence region, where a severe drop of the resonance field is observed. The temperature dependence of the iron resonance nicely follows the transition of the underlying MnAs layer

  18. Determinants of Capital Structure of UK Firms

    OpenAIRE

    Wu, Meiying

    2010-01-01

    This paper aims to investigate the determinants of capital structure of UK firms and identify which existing theory of capital structure is most relevant and applicable to UK firms. The sample of this study involves 239 listed firms from 9 industries on the FTSE 350 Index in the UK from 2000 to 2009. ANOVA and panel data regression are run to analyze what factors have impact on firm’s decision of capital structure. Each test is run on long-term and short-term leverage as dependent variables. ...

  19. Determination of the neutron spin structure function

    International Nuclear Information System (INIS)

    New measurements of the neutron spin structure function, g1(x), made at SLAC are reported, using longitudinally polarized electrons on a polarized 3He target. The spin structure function of the neutron has been determined from x=0.03 to x=0.6 at an average Q2 of 2 (GeV/c)2, by measuring the asymmetry in deep inelastic scattering of polarized electrons from polarized 3He at energies from 19 to 26 GeV. The integral over the spin structure function has been calculated. (author) 16 refs., 3 figs., 1 tab

  20. Representing Personal Determinants in Causal Structures.

    Science.gov (United States)

    Bandura, Albert

    1984-01-01

    Responds to Staddon's critique of the author's earlier article and addresses issues raised by Staddon's (1984) alternative models of causality. The author argues that it is not the formalizability of causal processes that is the issue but whether cognitive determinants of behavior are reducible to past stimulus inputs in causal structures.…

  1. Optical and electrical properties of Mg/Co bilayer thin film metal hydrides

    OpenAIRE

    M. K. JANGID,; S.P. Nehra; M Singh

    2010-01-01

    Bilayer Mg/Co thin films have been prepared using thermal evaporation method at pressure 10-5 torr. Annealing of bilayer thin films have been performed for 1 hour at different temperature. Hydrogenation of pristine and annealed bilayer structure has been performed at different hydrogen pressure for half an hour. The optical transmission increased with hydrogen pressure and also the band gap of thin films found to be increase with hydrogen pressure. Pristine Mg/Co bilayers show ohmic behavior ...

  2. Transport methods for probing the barrier domain of lipid bilayer membranes.

    OpenAIRE

    Xiang, T X; Chen, X.; Anderson, B. D.

    1992-01-01

    Two experimental techniques have been utilized to explore the barrier properties of lecithin/decane bilayer membranes with the aim of determining the contributions of various domains within the bilayer to the overall barrier. The thickness of lecithin/decane bilayers was systematically varied by modulating the chemical potential of decane in the annulus surrounding the bilayer using different mole fractions of squalene in decane. The dependence of permeability of a model permeant (acetamide) ...

  3. Dependence of inverse-spin Hall effect and spin-rectified voltage on tantalum thickness in Ta/CoFeB bilayer structure

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sang-Il; Seo, Min-Su; Park, Seung-Young, E-mail: parksy@kbsi.re.kr [Division of Materials Science, Korea Basic Science Institute, Daejeon 305-806 (Korea, Republic of); Kim, Dong-Jun; Park, Byong-Guk, E-mail: bgpark@kaist.ac.kr [Department of Materials Science and Engineering, KAIST, Daejeon 305-701 (Korea, Republic of)

    2015-01-19

    Ta-layer thickness (t{sub Ta}) dependence of the measured DC voltage V from the inverse-spin Hall effect (ISHE) in Ta/CoFeB bilayer structure is experimentally investigated using the ferromagnetic resonance in the TE{sub 011} resonant cavity. The ISHE signals excluding the spin-rectified effect (SRE) were separated from the fitted curve of V against t{sub Ta}. For t{sub Ta} ≈ λ{sub Ta} (Ta-spin diffusion length = 2.7 nm), the deviation in ISHE voltage V{sub ISH} between the experimental and theoretical values is significantly increased because of the large SRE contribution, which also results in a large deviation in the spin Hall angle θ{sub SH} (from 10% to 40%). However, when t{sub Ta} ≫ λ{sub Ta}, the V{sub ISH} values are consistent with theoretical values because the SRE terms become negligible, which subsequently improves the accuracy of the obtained θ{sub SH} within 4% deviation. The results will provide an outline for an accurate estimation of the θ{sub SH} for materials with small λ value, which would be useful for utilizing the spin Hall effect in a 3-terminal spintronic devices in which magnetization can be controlled by in-plane current.

  4. Microstructure and mechanical behavior of a shape memory Ni-Ti bi-layer thin film

    Energy Technology Data Exchange (ETDEWEB)

    Mohri, Maryam [School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe (Germany); Nili-Ahmadabadi, Mahmoud, E-mail: nili@ut.ac.ir [School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Center of Excellence for High Performance Materials, University of Tehran, Tehran (Iran, Islamic Republic of); Ivanisenko, Julia [Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe (Germany); Schwaiger, Ruth [Karlsruhe Institute of Technology, Institute for Applied Materials, 76021 Karlsruhe (Germany); Hahn, Horst; Chakravadhanula, Venkata Sai Kiran [Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe (Germany)

    2015-05-29

    Two different single-layers and a bi-layer Ni-Ti thin films with chemical compositions of Ni{sub 45}Ti{sub 50}Cu{sub 5}, Ni{sub 50.8}Ti{sub 49.2} and Ni{sub 50.8}Ti{sub 49.2}/Ni{sub 45}Ti{sub 50}Cu{sub 5} (numbers indicate at.%) determined by energy dispersive X-ray spectroscopy were deposited on Si (111) substrates using DC magnetron sputtering. The structures, surface morphology and transformation temperatures of annealed thin films at 500 °C for 15 min and 1 h were studied using grazing incidence X-ray diffraction, transmission electron microscopy (TEM), atomic force microscopy and differential scanning calorimetry (DSC), respectively. Nanoindentation was used to characterize the mechanical properties. The DSC and X-ray diffraction results indicated the austenitic structure of the Ni{sub 50.8}Ti{sub 49.2} and martensitic structure of the Ni{sub 45}Ti{sub 50}Cu{sub 5} thin films while the bi-layer was composed of austenitic and martensitic thin films. TEM study revealed that copper encourages crystallization in the bi-layer such that crystal structure containing nano-precipitates in the Ni{sub 45}Ti{sub 50}Cu{sub 5} layer was detected after 15 min annealing while the Ni{sub 50.8}Ti{sub 49.2} layer crystallized after 60 min at 500 °C. Furthermore, after annealing at 500 °C for 15 min, a precipitate free zone and thin layer amorphous were observed closely to the interface in the top layer. The bi-layer was completely crystallized at 500 °C for 1 h and the orientation of the Ni-rich precipitates indicated a stress gradient in the bi-layer. The bi-layer thin film showed different transformation temperatures and mechanical behavior from the single-layers. The developed bi-layer has different phase transformation temperatures, the higher temperatures of shape memory effect and lower temperature of pseudo-elastic behavior compared to the single-layers. Also, the bi-layer thin film exhibited a combined pseudo-elastic behavior and shape memory effect with a reduced

  5. Determinants of Capital Structure of UK Companies

    OpenAIRE

    Huang, Xu

    2013-01-01

    This paper aims to examine the determinants of capital structure of the UK companies and to provide some up-to-date empirical evidence for previous literatures. The sample of this study involves all non-financial companies listed on the FTSE350 Index during the time period from 2003 to 2012. The analysis of variance and panel data regression models are performed to test what factors may affect the UK companies’ financing decisions. In each model, three different measures of financial leverage...

  6. Structural determinants of sigma receptor affinity

    International Nuclear Information System (INIS)

    The structural determinants of sigma receptor affinity have been evaluated by examining a wide range of compounds related to opioids, neuroleptics, and phenylpiperidine dopaminergic structures for affinity at sigma receptor-binding sites labeled with (+)-[3H]3-PPP. Among opioid compounds, requirements for sigma receptor affinity differ strikingly from the determinants of affinity for conventional opiate receptors. Sigma sites display reverse stereoselectivity to classical opiate receptors. Multi-ringed opiate-related compounds such as morphine and naloxone have negligible affinity for sigma sites, with the highest sigma receptor affinity apparent for benzomorphans which lack the C ring of opioids. Highest affinity among opioids and other compounds occurs with more lipophilic N-substituents. This feature is particularly striking among the 3-PPP derivatives as well as the opioids. The butyrophenone haloperidol is the most potent drug at sigma receptors we have detected. Among the series of butyrophenones, receptor affinity is primarily associated with the 4-phenylpiperidine moiety. Conformational calculations for various compounds indicate a fairly wide range of tolerance for distances between the aromatic ring and the amine nitrogen, which may account for the potency at sigma receptors of structures of considerable diversity. Among the wide range of structures that bind to sigma receptor-binding sites, the common pharmacophore associated with high receptor affinity is a phenylpiperidine with a lipophilic N-substituent

  7. Structural determinants of sigma receptor affinity

    Energy Technology Data Exchange (ETDEWEB)

    Largent, B.L.; Wikstroem, H.G.; Gundlach, A.L.; Snyder, S.H.

    1987-12-01

    The structural determinants of sigma receptor affinity have been evaluated by examining a wide range of compounds related to opioids, neuroleptics, and phenylpiperidine dopaminergic structures for affinity at sigma receptor-binding sites labeled with (+)-(/sup 3/H)3-PPP. Among opioid compounds, requirements for sigma receptor affinity differ strikingly from the determinants of affinity for conventional opiate receptors. Sigma sites display reverse stereoselectivity to classical opiate receptors. Multi-ringed opiate-related compounds such as morphine and naloxone have negligible affinity for sigma sites, with the highest sigma receptor affinity apparent for benzomorphans which lack the C ring of opioids. Highest affinity among opioids and other compounds occurs with more lipophilic N-substituents. This feature is particularly striking among the 3-PPP derivatives as well as the opioids. The butyrophenone haloperidol is the most potent drug at sigma receptors we have detected. Among the series of butyrophenones, receptor affinity is primarily associated with the 4-phenylpiperidine moiety. Conformational calculations for various compounds indicate a fairly wide range of tolerance for distances between the aromatic ring and the amine nitrogen, which may account for the potency at sigma receptors of structures of considerable diversity. Among the wide range of structures that bind to sigma receptor-binding sites, the common pharmacophore associated with high receptor affinity is a phenylpiperidine with a lipophilic N-substituent.

  8. Bilayer-thickness-mediated interactions between integral membrane proteins

    Science.gov (United States)

    Kahraman, Osman; Koch, Peter D.; Klug, William S.; Haselwandter, Christoph A.

    2016-04-01

    Hydrophobic thickness mismatch between integral membrane proteins and the surrounding lipid bilayer can produce lipid bilayer thickness deformations. Experiment and theory have shown that protein-induced lipid bilayer thickness deformations can yield energetically favorable bilayer-mediated interactions between integral membrane proteins, and large-scale organization of integral membrane proteins into protein clusters in cell membranes. Within the continuum elasticity theory of membranes, the energy cost of protein-induced bilayer thickness deformations can be captured by considering compression and expansion of the bilayer hydrophobic core, membrane tension, and bilayer bending, resulting in biharmonic equilibrium equations describing the shape of lipid bilayers for a given set of bilayer-protein boundary conditions. Here we develop a combined analytic and numerical methodology for the solution of the equilibrium elastic equations associated with protein-induced lipid bilayer deformations. Our methodology allows accurate prediction of thickness-mediated protein interactions for arbitrary protein symmetries at arbitrary protein separations and relative orientations. We provide exact analytic solutions for cylindrical integral membrane proteins with constant and varying hydrophobic thickness, and develop perturbative analytic solutions for noncylindrical protein shapes. We complement these analytic solutions, and assess their accuracy, by developing both finite element and finite difference numerical solution schemes. We provide error estimates of our numerical solution schemes and systematically assess their convergence properties. Taken together, the work presented here puts into place an analytic and numerical framework which allows calculation of bilayer-mediated elastic interactions between integral membrane proteins for the complicated protein shapes suggested by structural biology and at the small protein separations most relevant for the crowded membrane

  9. Effect of monoglycerides and fatty acids on a ceramide bilayer.

    Science.gov (United States)

    Akinshina, Anna; Das, Chinmay; Noro, Massimo G

    2016-07-14

    Monoglycerides and unsaturated fatty acids, naturally present in trace amounts in the stratum corneum (top layer of skin) lipid matrix, are commonly used in pharmaceutical, cosmetic and health care formulations. However, a detailed molecular understanding of how the oil additives get incorporated into the skin lipids from topical application and, once incorporated, how they affect the properties and integrity of the lipid matrix remains unexplored. Using ceramide 2 bilayers as skin lipid surrogates, we use a series of molecular dynamics simulations with six different natural oil ingredients at multiple concentrations to investigate the effect of the oils on the properties and stability of the bilayers. The six oils: monoolein, monostearin, monoelaidin, oleic acid, stearic acid and linoleic acid - all having the same length of the alkyl chain, C18, but a varying degree of saturation, allow us to systematically address the effect of unsaturation in the additives. Our results show that at low oil concentration (∼5%) the mixed bilayers containing any of the oils and ceramide 2 (CER2) become more rigid than pure CER2 bilayers due to more efficient lipid packing. Better packing also results in the formation of larger numbers of hydrogen bonds between the lipids, which occurs at the expense of the hydrogen bonds between lipids and water. The mixed bilayers with saturated or trans-unsaturated oils remain stable over the whole range of oil concentration. In contrast, the presence of the oils with at least one cis-double bond leads to bilayer instability and complete loss of bilayer structure at the oil content of about 50-65%. Two cis-double bonds in the lipid tail induce bilayer disruption at even lower concentration (∼30%). The mixed bilayers remain in the gel phase (without melting to a fluid phase) until the phase transition to a non-bilayer phase occurs. We also demonstrate that the stability of the bilayer strongly correlates with the order parameter of the lipid

  10. Topological transformation of a surfactant bilayer

    DEFF Research Database (Denmark)

    Le, T.D.; Olsson, U.; Mortensen, K.

    2000-01-01

    Surfactant lamellar phases are often complicated by the formation of multilamellar (onions) under shear, which can originate simply by shaking the sample. A systematic study has been performed on the C10E3-D2O system in which different bilayer structures under a steady shear flow were investigated...

  11. Determinate structures for wing camber control

    International Nuclear Information System (INIS)

    An investigation of truss structures for the purpose of creating a continuously variable camber trailing edge device for an aircraft wing is presented. By creating structures that are both statically and kinematically determinate and then substituting truss elements for actuators, it is possible to impose structural deflection without inducing member stress. A limited number of actuators with limited strain capabilities are located within the structure in order to achieve a target deflected shape starting from an initially symmetric profile. Two objective functions are used to achieve this: a geometric objective for which the target displacement is fixed and a shape objective for which the target displacement is dependent on the surface shape of the targeted aerofoil. The proposed shape objective function is able to offer improvements over the geometric objective by removing some of the constraints applied to the targeted structure joint locations. Four methods for selecting the location of a set of actuators are compared, namely exhaustive search, a genetic algorithm, stepwise forward selection (SFS) and incremental forward selection (IFS). Both SFS and IFS are variations of regression methods for subset selection; in each case an approach has been created to allow the imposing of upper and lower bounds on the search space. It is shown that the genetic algorithm is well suited to addressing the problem of optimally locating a set of actuators; however, regression methods, particularly IFS, can provide a rapid tool suitable for addressing large selection problems

  12. Stealth carriers for low-resolution structure determination of membrane proteins in solution

    DEFF Research Database (Denmark)

    Maric, Selma; Skar-Gislinge, Nicholas; Midtgaard, Søren;

    2014-01-01

    O at the length scales relevant to SANS. These 'stealth' carrier discs may be used as a general platform for low-resolution structural studies of membrane proteins using well established data-analysis tools originally developed for soluble proteins. © 2014 International Union of Crystallography.......Structural studies of membrane proteins remain a great experimental challenge. Functional reconstitution into artificial nanoscale bilayer disc carriers that mimic the native bilayer environment allows the handling of membrane proteins in solution. This enables the use of small-angle scattering...

  13. Structure of immune stimulating complex matrices and immune stimulating complexes in suspension determined by small-angle X-ray scattering

    DEFF Research Database (Denmark)

    Pedersen, Jan Skov; Oliveira, Cristiano Luis Pinto De; Madsen, Henriette Baun;

    2012-01-01

    perforated bilayer vesicles with icosahedral, football, or tennis ball structures. The dominating structure is the tennis ball structure, with an outer diameter of 40 nm and with 20 holes 5-6 nm in diameter. The lipid bilayer membrane is 4.6 nm thick, with a low-electron-density, 2.0-nm-thick hydrocarbon...

  14. Regulation of sodium channel function by bilayer elasticity

    DEFF Research Database (Denmark)

    Lundbaek, Jens A; Birn, Pia; Hansen, Anker J;

    2004-01-01

    kinetics of the protein conformational changes therefore will be regulated by the bilayer elasticity, which is determined by the lipid composition. This hydrophobic coupling mechanism has been studied extensively in gramicidin channels, where the channel-bilayer hydrophobic interactions link a...... "conformational" change (the monomerdimer transition) to an elastic bilayer deformation. Gramicidin channels thus are regulated by the lipid bilayer elastic properties (thickness, monolayer equilibrium curvature, and compression and bending moduli). To investigate whether this hydrophobic coupling mechanism could...... be a general mechanism regulating membrane protein function, we examined whether voltage-dependent skeletal-muscle sodium channels, expressed in HEK293 cells, are regulated by bilayer elasticity, as monitored using gramicidin A (gA) channels. Nonphysiological amphiphiles (beta...

  15. Water Replacement Hypothesis in Atomic Details: Effect of Trehalose on the Structure of Single Dehydrated POPC Bilayers

    NARCIS (Netherlands)

    Golovina, E.A.; Golovin, A.; Hoekstra, F.A.; Faller, R.

    2010-01-01

    We present molecular dynamics (MD) simulations to study the plausibility of the water replacement hypothesis (WRH) from the viewpoint of structural chemistry. A total of 256 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC) lipids were modeled for 400 ns at 11.7 or 5.4 waters/lipid. To obtain

  16. Biomolecular Structure Determination with Divide and Concur

    Science.gov (United States)

    Kallus, Yoav; Elser, Veit

    2009-03-01

    Divide and concur (D-C) is a general computational approach, designed for the solution of highly frustrated problems. Recently applied to the problems of disk packing, the kissing number problem, and 3-SAT, it was competitive or outperformed special-purpose methods.ootnotetextS. Gravel and V. Elser, Phys. Rev. E 78, 036706 (2008) We present a method for applying the D-C framework to the problem of biomolecular structure determination. From a list of geometric constraints on groups of atoms in the molecule, we construct a deterministic iterative map that efficiently searches for structures simultaneously satisfying all constraints. As our method eschews an energy function and its minimization to focus on geometric constraints, it can very naturally integrate with the geometric constraints due to chemistry and physics, experimental constraints due to NMR data or many other experimental or biological hints. We present some results of our method.

  17. Determinants of Capital Structure in Nigeria

    Directory of Open Access Journals (Sweden)

    Oladele John AKINYOMI

    2013-08-01

    Full Text Available Capital structure represents one of the most discussed concepts in financial management. Capital structure refers to how a company finances its operations whether through shareholders equity-fund or debt or a combination of both. Various internal and external factors contribute to the choice of these sources of fund. The external factors include factors such as tax policy, capital market conditions and tax policy, among others. Meanwhile, the internal factors are those that relate to individual firm characteristics. This study examines the determinants of capital structure in Nigeria using the descriptive research design. The population comprised of the eighty-six manufacturing firms that are listed in the Nigerian Stock Exchange. The sample firms were selected using the simple random sampling method. Secondary data obtained from the annual accounts of 24 randomly selected manufacturing firms for 10 years period culminating in 240 firm-year observations. The results of the regression analysis revealed that leverage (a measure of capital structure has a negative relationship with firm size and tax on one hand and a positive relationship with tangibility of assets, profitability and growth on the other hand. However, only with tangibility of assets and firm size that significant relationship is established. It is recommended for future researchers to carry out similar studies in multiple sectors.

  18. Probing the structure of the mechanosensitive channel of small conductance in lipid bilayers with pulsed electron-electron double resonance

    OpenAIRE

    Ward, Richard; Pliotas, Christos; Branigan, Emma; Hacker, Christian; Rasmussen, Akiko; Hagelueken, Gregor; Booth, Ian R.; Miller, Samantha; Lucocq, John; Naismith, Jim; Schiemann, Olav

    2014-01-01

    Mechanosensitive channel proteins are important safety valves against osmotic shock in bacteria, and are involved in sensing touch and sound waves in higher organisms. The mechanosensitive channel of small conductance (MscS) has been extensively studied. Pulsed electron-electron double resonance (PELDOR or DEER) of detergent-solubilized protein confirms that as seen in the crystal structure, the outer ring of transmembrane helices do not pack against the pore- forming helices, creating an app...

  19. The lipidic particle as an intermediate structure in membrane fusion processes and bilayer to hexagonal HII transitions

    OpenAIRE

    Verkleij, A.J.; Echteld, C.J.A. van; Gerritsen, W.J.; Cullis, P.R.; de Kruijff, B.

    1980-01-01

    Small unilamellar vesicles comprised of a mixture of phosphatidylethanolamine/phosphatidylcholine/cholesterol (3 : 1 : 2) fuse to form large multilamellar vesicles on increasing the temperature from 0 to 50°C. This event is associated with the appearance of lipidic particles at the fusion sites, consistent with a role as intermediary structures during the fusion process. Further, for phosphatidylcholine/cardiolipin (1 : 1) liposomes in the presence of Mn2+ a direct relationship between lipidi...

  20. Possible influence of the ferromagnetic/antiferromagnetic interface on the effective critical behavior of bilayers based on La{sub 1−x}Sr{sub x}MnO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Álvarez Miño, Lucero, E-mail: lalvarezm@unal.edu.co [Universidad Nacional de Colombia, Sede Manizales, Cra. 27 #64-60, Manizales (Colombia); Grupo de Superconductividad y Nuevos Materiales, Universidad Nacional de Colombia, Sede Bogotá, Avenida Carrera 30 #45, Bogotá (Colombia); Mulcué-Nieto, Luis Fernando, E-mail: lfmulcuen@unal.edu.co [Laboratorio de Magnetismo y Materiales Avanzados, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Colombia, Sede Manizales, Cra. 27 #64-60, Manizales (Colombia)

    2015-03-01

    In this work, the effective critical exponent of the spontaneous magnetization, β, and the transition temperature, T{sub C}, were calculated from magnetization measurements of three bilayers based on La{sub 1−x}Sr{sub x}MnO{sub 3} (LSMO). The bilayers structure is a ferromagnetic (FM) LSMO film grown on top of an antiferromagnetic (AF) LSMO film. The value of the antiferromagnetic film thickness was kept the same for the three samples, while the ferromagnetic film had different thickness for each bilayer. Applying a method of calculation based on a linear superposition of the magnetization close to the critical temperature, a β value corresponding to the 3D Ising model was found for the bilayer with the thinnest ferromagnetic film. This result, and the other obtained values are explained taking into account the possible influence of the FM/AF interface on the magnetic and crystal orderings. - Highlights: • The critical exponent β of three LSMO bilayers was determined. • Two bilayers with the thinner FM layer have very similar transition temperature. • Two bilayers with the thinner FM layer have very similar width values. • We have found values of β of the 3D Ising model. • Interface also seems to be responsible for some structural disorder.

  1. The electronic structure and elastic property of monolayer and bilayer transition metal dichalcogenides MX$_2$ (M=Mo,W;X=O,S,Se,Te): A comparative first-principles study

    OpenAIRE

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

    2015-01-01

    First-principle calculations with different exchange-correlation functionals, including LDA, PBE and vdW-DF functional in form of optB88-vdW, have been performed to investigate the electronic and elastic properties of two dimensional transition metal dichalcogenides(TMDCs) with the formula of MX$_2$(M=Mo,W; X=O,S,Se,Te) in both monolayer and bilayer structures. The calculated band structures show a direct band gap for monolayer TMDCs at the K point except for MoO$_2$ and WO$_2$. When the mono...

  2. Melittin-Induced Bilayer Leakage Depends on Lipid Material Properties: Evidence for Toroidal Pores

    OpenAIRE

    Allende, Daniel; Simon, S. A.; McIntosh, Thomas J.

    2004-01-01

    The membrane-lytic peptide melittin has previously been shown to form pores in lipid bilayers that have been described in terms of two different structural models. In the “barrel stave” model the bilayer remains more or less flat, with the peptides penetrating across the bilayer hydrocarbon region and aggregating to form a pore, whereas in the “toroidal pore” melittin induces defects in the bilayer such that the bilayer bends sharply inward to form a pore lined by both peptides and lipid head...

  3. On the microscopic and mesoscopic perturbations of lipid bilayers upon interaction with the MPER domain of the HIV glycoprotein gp41.

    Science.gov (United States)

    Oliva, Rosario; Emendato, Alessandro; Vitiello, Giuseppe; De Santis, Augusta; Grimaldi, Manuela; D'Ursi, Anna Maria; Busi, Elena; Del Vecchio, Pompea; Petraccone, Luigi; D'Errico, Gerardino

    2016-08-01

    The effect of the 665-683 fragment of the HIV fusion glycoprotein 41, corresponding to the MPER domain of the protein and named gp41MPER, on the microscopic structure and mesoscopic arrangement of palmitoyl oleoyl phosphatidylcholine (POPC) and POPC/sphingomyelin (SM)/cholesterol (CHOL) lipid bilayers is analyzed. The microscopic structuring of the bilayers has been studied by Electron Spin Resonance (ESR) spectroscopy, using glycerophosphocholines spin-labelled in different positions along the acyl chain. Transitions of the bilayer liquid crystalline state have been also monitored by Differential Scanning Calorimetry (DSC). Changes of the bilayers morphology have been studied by determining the dimension of the liposomes through Dynamic Light Scattering (DLS) measurements. The results converge in showing that the sample preparation procedure, the bilayer composition and the peptide/lipid ratio critically tune the lipid response to the peptide/membrane interaction. When gp41MPER is added to preformed liposomes, it positions at the bilayer interface and the lipid perturbation is limited to the more external segments. In contrast, if the peptide is mixed with the lipids during the liposome preparation, it assumes a trans-membrane topology. This happens at all peptide/lipid ratios for fluid POPC bilayers, while in the case of rigid POPC/SM/CHOL membranes a minimum ratio has to be reached, thus suggesting peptide self-aggregation to occur. Peptide insertion results in a dramatic increase of the lipid ordering and bilayer stiffening, which reflect in significant changes in liposome average dimension and distribution. The biological implications of these findings are discussed. PMID:27179640

  4. Characterization of the Prokaryotic Sodium Channel NavSp Pore with a Microfluidic Bilayer Platform.

    Directory of Open Access Journals (Sweden)

    Shimul Chandra Saha

    Full Text Available This paper describes the use of a newly-developed micro-chip bilayer platform to examine the electrophysiological properties of the prokaryotic voltage-gated sodium channel pore (Na(vSp from Silicibacter pomeroyi. The platform allows up to 6 bilayers to be analysed simultaneously. Proteoliposomes were incorporated into suspended lipid bilayers formed within the microfluidic bilayer chips. The chips provide access to bilayers from either side, enabling the fast and controlled titration of compounds. Dose-dependent modulation of the opening probability by the channel blocking drug nifedipine was measured and its IC50 determined.

  5. Exploiting Microbeams for Membrane Protein Structure Determination.

    Science.gov (United States)

    Warren, Anna J; Axford, Danny; Paterson, Neil G; Owen, Robin L

    2016-01-01

    A reproducible, and sample independent means of predictably obtaining large, well-ordered crystals has proven elusive in macromolecular crystallography. In the structure determination pipeline, crystallisation often proves to be a rate-limiting step, and the process of obtaining even small or badly ordered crystals can prove time-consuming and laborious. This is particularly true in the field of membrane protein crystallography and this is reflected in the limited number of unique membrane protein structures deposited in the protein data bank (less than 650 by June 2016 - http://blanco.biomol.uci.edu/mpstruc ). Over recent years the requirement for, and time and cost associated with obtaining, large crystals has been partially alleviated through the development of beamline instrumentation allowing data collection, and structure solution, from ever-smaller crystals. Advances in several areas have led to a step change in what might be considered achievable during a synchrotron trip over the last decade. This chapter will briefly review the current status of the field, the tools available to ease data collection and processing, and give some examples of exploitation of these for membrane protein microfocus macromolecular crystallography. PMID:27553238

  6. "Nanocrystal bilayer for tandem catalysis"

    Energy Technology Data Exchange (ETDEWEB)

    Yamada, Yusuke; Tsung, Chia Kuang; Huang, Wenyu; Huo, Ziyang; E.Habas, Susan E; Soejima, Tetsuro; Aliaga, Cesar E; Samorjai, Gabor A; Yang, Peidong

    2011-01-24

    Supported catalysts are widely used in industry and can be optimized by tuning the composition and interface of the metal nanoparticles and oxide supports. Rational design of metal-metal oxide interfaces in nanostructured catalysts is critical to achieve better reaction activities and selectivities. We introduce here a new class of nanocrystal tandem catalysts that have multiple metal-metal oxide interfaces for the catalysis of sequential reactions. We utilized a nanocrystal bilayer structure formed by assembling platinum and cerium oxide nanocube monolayers of less than 10 nm on a silica substrate. The two distinct metal-metal oxide interfaces, CeO2-Pt and Pt-SiO2, can be used to catalyse two distinct sequential reactions. The CeO2-Pt interface catalysed methanol decomposition to produce CO and H2, which were subsequently used for ethylene hydroformylation catalysed by the nearby Pt-SiO2 interface. Consequently, propanal was produced selectively from methanol and ethylene on the nanocrystal bilayer tandem catalyst. This new concept of nanocrystal tandem catalysis represents a powerful approach towards designing high-performance, multifunctional nanostructured catalysts

  7. Properties of bilayer contacts to porous silicon

    Science.gov (United States)

    Gallach, D.; Torres-Costa, V.; García-Pelayo, L.; Climent-Font, A.; Martín-Palma, R. J.; Barreiros-das-Santos, M.; Sporer, C.; Samitier, J.; Manso, M.

    2012-05-01

    The aim of the present work is the growth by PVD techniques and ulterior characterization of electrical contacts to columnar porous silicon (PSi) as an approach to reliable PSi sensor devices. Contacts consist of a NiCr (40:60) and Au bilayer on the PSi surface deposited by magnetron sputtering. These structures show a good adhesion to the rough surface of columnar PSi. The morphology of these electrical contacts is characterized by electron microscopy and their crystalline structure by X-ray diffraction. Compositional profiles are determined by Rutherford backscattering spectroscopy and energy dispersive X-ray spectroscopy, which demonstrate that the infiltration of NiCr into the PSi is at the origin of the metallic thin film adhesion improvement. I- V characteristics and impedance spectroscopy measurements show that this configuration provides rectifying electrical contacts to PSi, for which a simple equivalent circuit based on one resistor and two capacitors can be modeled. These results further support the use of PSi electrical structures for sensing purposes.

  8. Properties of bilayer contacts to porous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Gallach, D.; Torres-Costa, V.; Garcia-Pelayo, L.; Climent-Font, A.; Martin-Palma, R.J.; Manso, M. [Universidad Autonoma de Madrid, Departamento de Fisica Aplicada, Madrid (Spain); Barreiros-das-Santos, M.; Sporer, C.; Samitier, J. [Institute for Bioengineering of Catalonia (IBEC), Nanobioengineering Group, Barcelona (Spain)

    2012-05-15

    The aim of the present work is the growth by PVD techniques and ulterior characterization of electrical contacts to columnar porous silicon (PSi) as an approach to reliable PSi sensor devices. Contacts consist of a NiCr (40:60) and Au bilayer on the PSi surface deposited by magnetron sputtering. These structures show a good adhesion to the rough surface of columnar PSi. The morphology of these electrical contacts is characterized by electron microscopy and their crystalline structure by X-ray diffraction. Compositional profiles are determined by Rutherford backscattering spectroscopy and energy dispersive X-ray spectroscopy, which demonstrate that the infiltration of NiCr into the PSi is at the origin of the metallic thin film adhesion improvement. I-V characteristics and impedance spectroscopy measurements show that this configuration provides rectifying electrical contacts to PSi, for which a simple equivalent circuit based on one resistor and two capacitors can be modeled. These results further support the use of PSi electrical structures for sensing purposes. (orig.)

  9. Atomistic Simulations of Pore Formation and Closure in Lipid Bilayers

    OpenAIRE

    Bennett, W. F. Drew; Sapay, Nicolas; Tieleman, D. Peter

    2014-01-01

    Cellular membranes separate distinct aqueous compartments, but can be breached by transient hydrophilic pores. A large energetic cost prevents pore formation, which is largely dependent on the composition and structure of the lipid bilayer. The softness of bilayers and the disordered structure of pores make their characterization difficult. We use molecular-dynamics simulations with atomistic detail to study the thermodynamics, kinetics, and mechanism of pore formation and closure in DLPC, DM...

  10. Interaction of Human Chloride Intracellular Channel Protein 1 (CLIC1) with Lipid Bilayers: A Fluorescence Study.

    Science.gov (United States)

    Hare, Joanna E; Goodchild, Sophia C; Breit, Samuel N; Curmi, Paul M G; Brown, Louise J

    2016-07-12

    Chloride intracellular channel protein 1 (CLIC1) is very unusual as it adopts a soluble glutathione S-transferase-like canonical fold but can also autoinsert into lipid bilayers to form an ion channel. The conversion between these forms involves a large, but reversible, structural rearrangement of the CLIC1 module. The only identified environmental triggers controlling the metamorphic transition of CLIC1 are pH and oxidation. Until now, there have been no high-resolution structural data available for the CLIC1 integral membrane state, and consequently, a limited understanding of how CLIC1 unfolds and refolds across the bilayer to form a membrane protein with ion channel activity exists. Here we show that fluorescence spectroscopy can be used to establish the interaction and position of CLIC1 in a lipid bilayer. Our method employs a fluorescence energy transfer (FRET) approach between CLIC1 and a dansyl-labeled lipid analogue to probe the CLIC1-lipid interface. Under oxidizing conditions, a strong FRET signal between the single tryptophan residue of CLIC1 (Trp35) and the dansyl-lipid analogue was detected. When considering the proportion of CLIC1 interacting with the lipid bilayer, as estimated by fluorescence quenching experiments, the FRET distance between Trp35 and the dansyl moiety on the membrane surface was determined to be ∼15 Å. This FRET-detected interaction provides direct structural evidence that CLIC1 associates with membranes. The results presented support the current model of an oxidation-driven interaction of CLIC1 with lipid bilayers and also propose a membrane anchoring role for Trp35. PMID:27299171

  11. Structural Determinants of Misfolding in Multidomain Proteins.

    Science.gov (United States)

    Tian, Pengfei; Best, Robert B

    2016-05-01

    Recent single molecule experiments, using either atomic force microscopy (AFM) or Förster resonance energy transfer (FRET) have shown that multidomain proteins containing tandem repeats may form stable misfolded structures. Topology-based simulation models have been used successfully to generate models for these structures with domain-swapped features, fully consistent with the available data. However, it is also known that some multidomain protein folds exhibit no evidence for misfolding, even when adjacent domains have identical sequences. Here we pose the question: what factors influence the propensity of a given fold to undergo domain-swapped misfolding? Using a coarse-grained simulation model, we can reproduce the known propensities of multidomain proteins to form domain-swapped misfolds, where data is available. Contrary to what might be naively expected based on the previously described misfolding mechanism, we find that the extent of misfolding is not determined by the relative folding rates or barrier heights for forming the domains present in the initial intermediates leading to folded or misfolded structures. Instead, it appears that the propensity is more closely related to the relative stability of the domains present in folded and misfolded intermediates. We show that these findings can be rationalized if the folded and misfolded domains are part of the same folding funnel, with commitment to one structure or the other occurring only at a relatively late stage of folding. Nonetheless, the results are still fully consistent with the kinetic models previously proposed to explain misfolding, with a specific interpretation of the observed rate coefficients. Finally, we investigate the relation between interdomain linker length and misfolding, and propose a simple alchemical model to predict the propensity for domain-swapped misfolding of multidomain proteins. PMID:27163669

  12. Structural Determinants of Misfolding in Multidomain Proteins

    Science.gov (United States)

    Tian, Pengfei; Best, Robert B.

    2016-01-01

    Recent single molecule experiments, using either atomic force microscopy (AFM) or Förster resonance energy transfer (FRET) have shown that multidomain proteins containing tandem repeats may form stable misfolded structures. Topology-based simulation models have been used successfully to generate models for these structures with domain-swapped features, fully consistent with the available data. However, it is also known that some multidomain protein folds exhibit no evidence for misfolding, even when adjacent domains have identical sequences. Here we pose the question: what factors influence the propensity of a given fold to undergo domain-swapped misfolding? Using a coarse-grained simulation model, we can reproduce the known propensities of multidomain proteins to form domain-swapped misfolds, where data is available. Contrary to what might be naively expected based on the previously described misfolding mechanism, we find that the extent of misfolding is not determined by the relative folding rates or barrier heights for forming the domains present in the initial intermediates leading to folded or misfolded structures. Instead, it appears that the propensity is more closely related to the relative stability of the domains present in folded and misfolded intermediates. We show that these findings can be rationalized if the folded and misfolded domains are part of the same folding funnel, with commitment to one structure or the other occurring only at a relatively late stage of folding. Nonetheless, the results are still fully consistent with the kinetic models previously proposed to explain misfolding, with a specific interpretation of the observed rate coefficients. Finally, we investigate the relation between interdomain linker length and misfolding, and propose a simple alchemical model to predict the propensity for domain-swapped misfolding of multidomain proteins. PMID:27163669

  13. Ab initio calculation of structural and magnetic properties for Fe mono- and bilayers on Mo(1 1 0)

    CERN Document Server

    Qian, X; Petersen, M; Hübner, W

    2000-01-01

    The atomic structures were optimized and magnetic moments calculated for the pseudomorphic Fe overlayers on Mo(1 1 0) substrates employing the all-electron full-potential linearized augmented plane-wave (FP-LAPW) method. Three slabs were considered: (i) 5 monolayer (ML) Mo(1 1 0) substrate, (ii) and (iii) 1 and 2 ML pseudomorphic Fe overlayers on each side of 5 ML Mo(1 1 0) substrate. We found that for the bare Mo substrate, the top Mo-Mo interlayer spacing is contracted by 4.8% with respect to the theoretical bulk Mo(1 1 0) interlayer distance of 2.238 A. For the 1 ML Fe coverage, the Fe-Mo interlayer spacing has a contraction of 10.3% with respect to the calculated bulk Mo(1 1 0) interlayer spacing, while, for the 2 ML Fe, it is reduced by 9.5%. The Fe-Fe interlayer spacing is also contracted by as much as 11.4% with respect to the theoretical bulk Fe(1 1 0) interlayer distance of 2.004 A. The inner Mo-Mo interlayer spacings are slightly expanded (<0.5%). The magnetic moment for the 1 ML Fe overlayer on ...

  14. Terminal lipophilization of a unique DNA dodecamer by various nucleolipid headgroups: Their incorporation into artificial lipid bilayers and hydrodynamic properties

    Directory of Open Access Journals (Sweden)

    Emma Werz

    2015-06-01

    Full Text Available A series of six cyanine-5-labeled oligonucleotides (LONs 10–15, each terminally lipophilized with different nucleolipid head groups, were synthesized using the recently prepared phosphoramidites 4b–9b. The insertion of the LONs within an artificial lipid bilayer, composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE, was studied by single molecule fluorescence spectroscopy and microscopy with the help of an optically transparent microfluidic sample carrier with perfusion capabilities. The incorporation of the lipo-oligonucleotides into the bilayer was studied with respect to efficiency (maximal bilayer brightness as well as stability against perfusion (final stable bilayer brightness. Attempts to correlate these parameters with the log P values of the corresponding nucleolipid head groups failed, a result which clearly demonstrates that not only the lipophilicity but mainly the chemical structure and topology of the head group is of decisive importance for the optimal interaction of a lipo-oligonucleotide with an artificial lipid bilayer. Moreover, fluorescence half-live and diffusion time values were measured to determine the diffusion coefficients of the lipo-oligonucleotides.

  15. Terminal lipophilization of a unique DNA dodecamer by various nucleolipid headgroups: Their incorporation into artificial lipid bilayers and hydrodynamic properties.

    Science.gov (United States)

    Werz, Emma; Rosemeyer, Helmut

    2015-01-01

    A series of six cyanine-5-labeled oligonucleotides (LONs 10-15), each terminally lipophilized with different nucleolipid head groups, were synthesized using the recently prepared phosphoramidites 4b-9b. The insertion of the LONs within an artificial lipid bilayer, composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), was studied by single molecule fluorescence spectroscopy and microscopy with the help of an optically transparent microfluidic sample carrier with perfusion capabilities. The incorporation of the lipo-oligonucleotides into the bilayer was studied with respect to efficiency (maximal bilayer brightness) as well as stability against perfusion (final stable bilayer brightness). Attempts to correlate these parameters with the log P values of the corresponding nucleolipid head groups failed, a result which clearly demonstrates that not only the lipophilicity but mainly the chemical structure and topology of the head group is of decisive importance for the optimal interaction of a lipo-oligonucleotide with an artificial lipid bilayer. Moreover, fluorescence half-live and diffusion time values were measured to determine the diffusion coefficients of the lipo-oligonucleotides. PMID:26124894

  16. Structure determination by X-ray crystallography

    CERN Document Server

    Ladd, M F C

    1977-01-01

    Crystallography may be described as the science of the structure of materi­ als, using this word in its widest sense, and its ramifications are apparent over a broad front of current scientific endeavor. It is not surprising, therefore, to find that most universities offer some aspects of crystallography in their undergraduate courses in the physical sciences. It is the principal aim of this book to present an introduction to structure determination by X-ray crystal­ lography that is appropriate mainly to both final-year undergraduate studies in crystallography, chemistry, and chemical physics, and introductory post­ graduate work in this area of crystallography. We believe that the book will be of interest in other disciplines, such as physics, metallurgy, biochemistry, and geology, where crystallography has an important part to play. In the space of one book, it is not possible either to cover all aspects of crystallography or to treat all the subject matter completely rigorously. In particular, certain ...

  17. Crystal structure determination of Jatrorrhizine chloride

    Institute of Scientific and Technical Information of China (English)

    LEI XianRong; YANG JianHua; LIN Xiang; DAI Qin; CHENG Qiang; GUO LingHong; LI Hui

    2009-01-01

    Optimum resolution data of powder X-ray diffraction (PXRD) for Jatrorrhizine (Jat) were collected by an X' Pert Pro MPD diffractometer with an X'celerator detector under the stepwise scanning condition as 8.255 ms and 0.00836°per step,2θrange of 50°-80° and total scanning period of 8-10 min. Indexing of the crystal system and a search of the space group from the powder X-ray diffraction data were conducted by the computational crystallography method. The pilot crystal models of Jat were globally optimized with Monte Carlo method and then refined with the Rietveld method. In parallel with PXRD test,single crystals of Jat were cultured in an aqueous solution by a slow-decreasing temperature method,then its crystal structure was determined by single crystal X-ray diffraction (SCXRD). Both crystal structures from PXRD and SCXRD are identical. The results show that the crystal structure of Jat belongs to a monoclinic system and the space group P21/c. The parameters of cell dimensions from PXRD are a=7.69(A),b= 12.55(A),c=20.89(A),β=106.53°,Z=4,and V=1933.4(A)3,meanwhile the parameters from SCXRD are a=7.72(A),b=12.61(A),c=20.99(A),β=106.38°,Z=4,and V=1961.3(A)3.

  18. A circuit model for defective bilayer graphene transistors

    Science.gov (United States)

    Umoh, Ime J.; Moktadir, Zakaria; Hang, Shuojin; Kazmierski, Tom J.; Mizuta, Hiroshi

    2016-05-01

    This paper investigates the behaviour of a defective single-gate bilayer graphene transistor. Point defects were introduced into pristine graphene crystal structure using a tightly focused helium ion beam. The transfer characteristics of the exposed transistors were measured ex-situ for different defect concentrations. The channel peak resistance increased with increasing defect concentration whilst the on-off ratio showed a decreasing trend for both electrons and holes. To understand the electrical behaviour of the transistors, a circuit model for bilayer graphene is developed which shows a very good agreement when validated against experimental data. The model allowed parameter extraction of bilayer transistor and can be implemented in circuit level simulators.

  19. Chiral electron transport in CVD bilayer graphene

    Science.gov (United States)

    Lee, Kyunghoon; Eo, Yun Suk; Kurdak, Cagliyan; Zhong, Zhaohui

    2014-03-01

    Charge carriers in bilayer graphene have a parabolic energy spectrum. Due to this band structure they are massive quasiparticles having a finite density of state at zero energy like other non-relativistic charge carriers in conventional two dimensional materials. However, they are massive Dirac fermions which have a chiral nature similar to the case of massless Dirac fermions in single layer graphene. Coupling of pseudospin and motion of charge carrier via chirality can result in dramatic consequence for transport in bipolar regime like Klein tunneling, Fabry-Perot interference, collimation of charge carrier, Veslago lens, etc. However, little attention has been paid to chiral dependent electron transport in bilayer graphene. Here we study these properties by probing phase coherent transport behavior in CVD bilayer graphene devices with sub-200nm channel length. Complex Fabry-Perot interference patterns are observed in resonant cavities defined by local gating. By applying Fourier analysis technique, we successfully analyze and identify the origin of each individual interference pattern in bipolar and monopolar regime. Our initial results also hint at the observation of cloaking of electronic states against chiral electrons in bilayer graphene.

  20. Determination of Protein Backbone Structures from Residual Dipolar Couplings

    OpenAIRE

    Prestegard, J H; Mayer, K. L.; Valafar, H.; Benison, G. C.

    2005-01-01

    There are a number of circumstances where a focus on determination of the backbone structure of a protein, as opposed to a complete all-atom structure, may be appropriate. This is particularly the case for structures determined as a part of a structural genomics initiative where computational modeling of many sequentially related structures from the backbone of a single family representative is anti...

  1. Effect of the spin-twist structure on the spin-wave dynamics in Fe55Pt45/Ni80Fe20 exchange coupled bi-layers with varying Ni80Fe20 thickness

    International Nuclear Information System (INIS)

    We have investigated optically induced ultrafast magnetization dynamics of a series of Fe55Pt45/Ni80Fe20 exchange spring bi-layers with varying Ni80Fe20 thickness. Rich spin-wave spectra are observed; whose frequency shows a strong dependence on the Ni80Fe20 layer thickness. Micromagnetic simulations based on a simplified magnetic microstructure were able to reproduce the experimental data qualitatively. The spin twist structure introduced in the Ni80Fe20 layer gives rise to new modes in the composite system as opposed to the bare Ni80Fe20 films

  2. Effect of the spin-twist structure on the spin-wave dynamics in Fe55Pt45/Ni80Fe20 exchange coupled bi-layers with varying Ni80Fe20 thickness

    Science.gov (United States)

    Pal, Semanti; Barman, Saswati; Hellwig, Olav; Barman, Anjan

    2014-05-01

    We have investigated optically induced ultrafast magnetization dynamics of a series of Fe55Pt45/Ni80Fe20 exchange spring bi-layers with varying Ni80Fe20 thickness. Rich spin-wave spectra are observed; whose frequency shows a strong dependence on the Ni80Fe20 layer thickness. Micromagnetic simulations based on a simplified magnetic microstructure were able to reproduce the experimental data qualitatively. The spin twist structure introduced in the Ni80Fe20 layer gives rise to new modes in the composite system as opposed to the bare Ni80Fe20 films.

  3. Spin dynamics of bilayer manganites

    Indian Academy of Sciences (India)

    Tapan Chatterji

    2004-07-01

    The results of inelastic and quasi-elastic neutron scattering investigations on the 40% hole-doped quasi-2D bilayer manganites La1.2Sr1.8Mn2O7 have been reviewed. The complete set of exchange interactions have been determined on the basis of a localized Heisenberg model. However, the spin wave dispersion in La1.2Sr1.8Mn2O7 shows softening close to the zone boundary and are also heavily damped especially close to the zone boundary and deviate from that expected for a simple Heisenberg model. A minimal double exchange model including quantum corrections can reproduce these effects qualitatively but falls short of quantitative agreement.

  4. Determining structure and function in nanomaterial biocomposites

    Science.gov (United States)

    Griffin, David M.

    Polymeric biomaterials represent the leading technologies available today for the repair of tissue damage and for targeted drug delivery. Perhaps the most valuable aspect of polymer-based systems is the extent to which their physical properties (e.g. elasticity, porosity, etc.) can be controlled and tuned by regulating experimental parameters during their synthesis. Biomaterial performance can be improved further still by including supplementary components resulting in a composite material. Synergetic interactions between the constituents of composite materials often results in bulk physical properties that are substantially more than the sum of individual parts. Through understanding and exploiting these sympathetic relationships, novel biocomposites can be developed which exhibit improved efficacy and biocompatibility. Here we report on the synthesis strategies and characterization of novel biocomposites from our laboratory. We look specifically at hydrogel composites containing a physically-associated network of PluronicRTM block copolymer along with a calcium-phosphate mineral component. Rheological results show that composites containing an in situ deposited mineral exhibit a significantly higher elastic modulus than composites of similar composition formed by conventional means. Moreover, analysis of the calcium-phosphate phase of in situ composites revealed that system parameters such as acidity play an integral role in determining the size and stability of the resultant mineral and subsequently the materials' expected in vivo performance. Changes to the structure in PluronicRTM/calcium-phosphate composite hydrogels during dehydration was investigated to provide a look into the mechanisms involved in composite formation. Small angle X-ray scattering analysis of these systems shows that hydrogen bonding interactions between phosphate ions and the polyethylene oxide (PEO) polymer block significantly impact the nanoscale structure and long-range order contained

  5. Boron doped Si rich oxide/SiO{sub 2} and silicon rich nitride/SiN{sub x} bilayers on molybdenum-fused silica substrates for vertically structured Si quantum dot solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Ziyun, E-mail: z.lin@unsw.edu.au; Wu, Lingfeng; Jia, Xuguang; Zhang, Tian; Puthen-Veettil, Binesh; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan [School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Building H6, Tyree Energy Technologies Building, Kensington, New South Wales 2052 (Australia)

    2015-07-28

    Vertically structured Si quantum dots (QDs) solar cells with molybdenum (Mo) interlayer on quartz substrates would overcome current crowding effects found in mesa-structured cells. This study investigates the compatibility between boron (B) doped Si QDs bilayers and Mo-fused silica substrate. Both Si/SiO{sub 2} and Si/SiN{sub x} based QDs bilayers were studied. The material compatibility under high temperature treatment was assessed by examining Si crystallinity, microstress, thin film adhesion, and Mo oxidation. It was observed that the presence of Mo interlayer enhanced the Si QDs size confinement, crystalline fraction, and QDs size uniformity. The use of B doping was preferred compared to phosphine (PH{sub 3}) doping studied previously in terms of better surface and interface properties by reducing oxidized spots on the film. Though crack formation due to thermal mismatch after annealing remained, methods to overcome this problem were proposed in this paper. Schematic diagram to fabricate full vertical structured Si QDs solar cells was also suggested.

  6. Edge State and Intrinsic Hole Doping in Bilayer Phosphorene

    OpenAIRE

    Osada, Toshihito

    2014-01-01

    Using a simple LCAO model by Harrison, we have qualitatively studied the edge state of bilayer phosphorene, which is a unit structure of the layered crystal of black phosphorus. This model successfully reproduces the isolated edge state in the bulk gap in monolayer phosphorene. In bilayer phosphorene, however, it shows that edge states are almost buried in the valence band and there is no isolated midgap edge state at the zigzag edge. Since the buried edge state works as acceptor, holes are d...

  7. The surface layer of cleaved bilayer manganites

    International Nuclear Information System (INIS)

    Recently, several informative reports have been published on spectroscopy experiments performed on cleaved surfaces of the bilayered colossal magnetoresistive manganite La2-2xSr1+2xMn2O7 (Konoto et al 2004 Phys. Rev. Lett. 93 107201, Freeland et al 2005 Nat. Mater. 4 62, Mannella et al 2005 Nature 438 474, Roennow et al 2006 Nature 440 1025). For the detailed interpretation of these results, it is of importance to know exactly which layer within the crystal structure is exposed to the surface upon cleavage. Here we combine crystal structure arguments, scanning tunnelling microscopy and x-ray photoelectron spectroscopy measurements to demonstrate that the crystals cleave between the rare-earth rock-salt oxide layers, leaving one outermost rare-earth oxide layer before the first electronically active MnO bilayer

  8. General hydrophobic interaction potential for surfactant/lipid bilayers from direct force measurements between light-modulated bilayers

    OpenAIRE

    Donaldson, Stephen H., Jr.; Lee, C. Ted; Chmelka, Bradley F.; Israelachvili, Jacob N.

    2011-01-01

    We establish and quantify correlations among the molecular structures, interaction forces, and physical processes associated with light-responsive self-assembled surfactant monolayers or bilayers at interfaces. Using the surface forces apparatus (SFA), the interaction forces between adsorbed monolayers and bilayers of an azobenzene-functionalized surfactant can be drastically and controllably altered by light-induced conversion of trans and cis molecular conformations. These reversible confor...

  9. Edge states of zigzag bilayer graphite nanoribbons

    OpenAIRE

    Rhim, Jun-Won; Moon, Kyungsun

    2008-01-01

    Electronic structures of the zigzag bilayer graphite nanoribbons(Z-BGNR) with various ribbon width $N$ are studied within the tight binding approximation. Neglecting the inter-layer hopping amplitude $\\gamma_4$, which is an order of magnitude smaller than the other inter-layer hopping parameters $\\gamma_1$ and $\\gamma_3$, there exist two fixed Fermi points $\\pm k^*$ independent of the ribbon width with the peculiar energy dispersion near $k^*$ as $\\ve (k) \\sim \\pm (k-k^*)^N$. By investigating...

  10. Electronic properties of asymmetrically doped twisted graphene bilayers

    Science.gov (United States)

    Trambly de Laissardière, Guy; Namarvar, Omid Faizy; Mayou, Didier; Magaud, Laurence

    2016-06-01

    Rotated graphene bilayers form an exotic class of nanomaterials with fascinating electronic properties governed by the rotation angle θ . For large rotation angles, the electron eigenstates are restricted to one layer and the bilayer behaves like two decoupled graphene layers. At intermediate angles, Dirac cones are preserved but with a lower velocity and van Hove singularities are induced at energies where the two Dirac cones intersect. At very small angles, eigenstates become localized in peculiar moiré zones. We analyze here the effect of an asymmetric doping for a series of commensurate rotated bilayers on the basis of tight-binding calculations of their band dispersions, density of states, participation ratio, and diffusive properties. While a small doping level preserves the θ dependence of the rotated bilayer electronic structure, larger doping induces a further reduction of the band velocity in the same way as a further reduction of the rotation angle.

  11. Optical and electrical properties of Mg/Co bilayer thin film metal hydrides

    Directory of Open Access Journals (Sweden)

    M. K. JANGID,

    2010-12-01

    Full Text Available Bilayer Mg/Co thin films have been prepared using thermal evaporation method at pressure 10-5 torr. Annealing of bilayer thin films have been performed for 1 hour at different temperature. Hydrogenation of pristine and annealed bilayer structure has been performed at different hydrogen pressure for half an hour. The optical transmission increased with hydrogen pressure and also the band gap of thin films found to be increase with hydrogen pressure. Pristine Mg/Co bilayers show ohmic behavior and conductivity increase with hydrogen pressure. After annealing bilayers show semiconductor nature and conductivity has been found to be increased with annealing temperature and decreased with hydrogenation. Raman spectra of these sample shows decreasing intensity of peaks with annealing and hydrogenation. The relative resistivity varies nonlinearly withtime and increases with hydrogen pressure. Surface morphology of annealed and annealed hydrogenated bilayer structure has been confirmed by optical microscopy.

  12. Robustly Engineering Thermal Conductivity of Bilayer Graphene by Interlayer Bonding

    Science.gov (United States)

    Zhang, Xiaoliang; Gao, Yufei; Chen, Yuli; Hu, Ming

    2016-01-01

    Graphene and its bilayer structure are the two-dimensional crystalline form of carbon, whose extraordinary electron mobility and other unique features hold great promise for nanoscale electronics and photonics. Their realistic applications in emerging nanoelectronics usually call for thermal transport manipulation in a controllable and precise manner. In this paper we systematically studied the effect of interlayer covalent bonding, in particular different interlay bonding arrangement, on the thermal conductivity of bilayer graphene using equilibrium molecular dynamics simulations. It is revealed that, the thermal conductivity of randomly bonded bilayer graphene decreases monotonically with the increase of interlayer bonding density, however, for the regularly bonded bilayer graphene structure the thermal conductivity possesses unexpectedly non-monotonic dependence on the interlayer bonding density. The results suggest that the thermal conductivity of bilayer graphene depends not only on the interlayer bonding density, but also on the detailed topological configuration of the interlayer bonding. The underlying mechanism for this abnormal phenomenon is identified by means of phonon spectral energy density, participation ratio and mode weight factor analysis. The large tunability of thermal conductivity of bilayer graphene through rational interlayer bonding arrangement paves the way to achieve other desired properties for potential nanoelectronics applications involving graphene layers. PMID:26911859

  13. Robustly Engineering Thermal Conductivity of Bilayer Graphene by Interlayer Bonding

    Science.gov (United States)

    Zhang, Xiaoliang; Gao, Yufei; Chen, Yuli; Hu, Ming

    2016-02-01

    Graphene and its bilayer structure are the two-dimensional crystalline form of carbon, whose extraordinary electron mobility and other unique features hold great promise for nanoscale electronics and photonics. Their realistic applications in emerging nanoelectronics usually call for thermal transport manipulation in a controllable and precise manner. In this paper we systematically studied the effect of interlayer covalent bonding, in particular different interlay bonding arrangement, on the thermal conductivity of bilayer graphene using equilibrium molecular dynamics simulations. It is revealed that, the thermal conductivity of randomly bonded bilayer graphene decreases monotonically with the increase of interlayer bonding density, however, for the regularly bonded bilayer graphene structure the thermal conductivity possesses unexpectedly non-monotonic dependence on the interlayer bonding density. The results suggest that the thermal conductivity of bilayer graphene depends not only on the interlayer bonding density, but also on the detailed topological configuration of the interlayer bonding. The underlying mechanism for this abnormal phenomenon is identified by means of phonon spectral energy density, participation ratio and mode weight factor analysis. The large tunability of thermal conductivity of bilayer graphene through rational interlayer bonding arrangement paves the way to achieve other desired properties for potential nanoelectronics applications involving graphene layers.

  14. Structural Determinants of Juvenile Offenses in School.

    Science.gov (United States)

    Kowalski, Gregory S.; And Others

    1983-01-01

    Using multiple regression techniques, evaluates the relative contributions of community structure, school structure, and crime prevention efforts to delinquency in public schools. Finds that distance from central business district, school size, and region are of predictive value, when crimes against persons, property, and perceived crime are…

  15. Ca2+-induced isotropic motion and phosphatidylcholine flip-flop in phosphatidylcholine-cardiolipin bilayers

    OpenAIRE

    Gerritsen, W.J.; de Kruijff, B.; Verkleij, A.J.; Gier, J.; Van Deenen, L. L. M.

    1980-01-01

    Ca2+ induces a structural change in phosphatidylcholine-cardiolipin bilayers, which is visualised by freeze-fracturing as lipidic particles associated with the bilayer and is detected by 31P-NMR as isotropic motion of the phospholipids. In this structure a rapid transbilayer movement of phosphatidylcholine and a highly increased permeability towards Mn2+ are observed.

  16. Study of annealing effects in Al–Sb bilayer thin films

    Indian Academy of Sciences (India)

    R K Mangal; B Tripathi; M Singh; Y K Vijay

    2007-02-01

    In this paper, we present preparation and characterization of Al–Sb bilayer thin films. Thin films of thicknesses, 3000/1000 Å and 3000/1500 Å, were obtained by the thermal evaporation (resistive heating) method. Vacuum annealing and rapid thermal annealing methods were used to mix bilayer thin film structure. Results obtained from optical band gap data and Rutherford back scattering spectrometry showed mixing of Al–Sb bilayer system.

  17. Surface and interfacial creases in a bilayer tubular soft tissue

    Science.gov (United States)

    Razavi, Mir Jalil; Pidaparti, Ramana; Wang, Xianqiao

    2016-08-01

    Surface and interfacial creases induced by biological growth are common types of instability in soft biological tissues. This study focuses on the criteria for the onset of surface and interfacial creases as well as their morphological evolution in a growing bilayer soft tube within a confined environment. Critical growth ratios for triggering surface and interfacial creases are investigated both analytically and numerically. Analytical interpretations provide preliminary insights into critical stretches and growth ratios for the onset of instability and formation of both surface and interfacial creases. However, the analytical approach cannot predict the evolution pattern of the model after instability; therefore nonlinear finite element simulations are carried out to replicate the poststability morphological patterns of the structure. Analytical and computational simulation results demonstrate that the initial geometry, growth ratio, and shear modulus ratio of the layers are the most influential factors to control surface and interfacial crease formation in this soft tubular bilayer. The competition between the stretch ratios in the free and interfacial surfaces is one of the key driving factors to determine the location of the first crease initiation. These findings may provide some fundamental understanding in the growth modeling of tubular biological tissues such as esophagi and airways as well as offering useful clues into normal and pathological functions of these tissues.

  18. Reparameterization of All-Atom Dipalmitoylphosphatidylcholine Lipid Parameters Enables Simulation of Fluid Bilayers at Zero Tension

    OpenAIRE

    Sonne, Jacob; Jensen, Morten Ø.; Hansen, Flemming Y.; Hemmingsen, Lars Bo Stegeager; Peters, Günther H.

    2007-01-01

    Molecular dynamics simulations of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers using the CHARMM27 force field in the tensionless isothermal-isobaric (NPT) ensemble give highly ordered, gel-like bilayers with an area per lipid of ∼48 Å2. To obtain fluid (Lα) phase properties of DPPC bilayers represented by the CHARMM energy function in this ensemble, we reparameterized the atomic partial charges in the lipid headgroup and upper parts of the acyl chains. The new charges were determined ...

  19. WAY TO DETERMINE STIFFNESS FUNCTION OF STRUCTURE

    Institute of Scientific and Technical Information of China (English)

    WANG De-ming; GAI Bing-zheng

    2005-01-01

    For calculating the stiffness function of a structure, the differential equation of the vibration of the structure was divided into the differential equation on the original stiffness function that was known, and Fredholm integral equation of the first kind on the undetermined stiffness function that was unknown. And the stable solutions of the integral equation, when the smooth factor was equal to zero, was solved by the extrapolation with p smooth factors. So the stiffness function of the structure is obtained. Applied examples show that the method is feasible and effective.

  20. Electrospray ionization mass spectrometric determination of the molecular mass of the approximately 200-kDa globin dodecamer subassemblies in hexagonal bilayer hemoglobins.

    Science.gov (United States)

    Green, B N; Bordoli, R S; Hanin, L G; Lallier, F H; Toulmond, A; Vinogradov, S N

    1999-10-01

    Hexagonal bilayer hemoglobins (Hbs) are approximately 3.6-MDa complexes of approximately 17-kDa globin chains and 24-32-kDa, nonglobin linker chains in a approximately 2:1 mass ratio found in annelids and related species. Studies of the dissociation and reassembly of Lumbricus terrestris Hb have provided ample evidence for the presence of a approximately 200-kDa linker-free subassembly consisting of monomer (M) and disulfide-bonded trimer (T) subunits. Electrospray ionization mass spectrometry (ESI-MS) of the subassemblies obtained by gel filtration of partially dissociated L. terrestris and Arenicola marina Hbs showed the presence of noncovalent complexes of M and T subunits with masses in the 213. 3-215.4 and 204.6-205.6 kDa ranges, respectively. The observed mass of the L. terrestris subassembly decreased linearly with an increase in de-clustering voltage from approximately 215,400 Da at 60 V to approximately 213,300 Da at 200 V. In contrast, the mass of the A. marina complex decreased linearly from 60 to 120 V and reached an asymptote at approximately 204,600 Da (180-200 V). The decrease in mass was probably due to the progressive removal of complexed water and alkali metal cations. ESI-MS at an acidic pH showed both subassemblies to consist of only M and T subunits, and the experimental masses demonstrated them to have the composition M(3)T(3). Because there are three isoforms of M and four isoforms of T in Lumbricus and two isoforms of M and 5 isoforms of T in Arenicola, the masses of the M(3)T(3) subassemblies are not unique. A random assembly model was used to calculate the mass distributions of the subassemblies, using the known ESI-MS masses and relative intensities of the M and T subunit isforms. The expected mass of randomly assembled subassemblies was 213,436 Da for Lumbricus Hb and 204,342 Da for Arenicola Hb, in good agreement with the experimental values. PMID:10497174

  1. Bursting Bubbles and Bilayers

    Directory of Open Access Journals (Sweden)

    Steven P. Wrenn, Stephen M. Dicker, Eleanor F. Small, Nily R. Dan, Michał Mleczko, Georg Schmitz, Peter A. Lewin

    2012-01-01

    Full Text Available This paper discusses various interactions between ultrasound, phospholipid monolayer-coated gas bubbles, phospholipid bilayer vesicles, and cells. The paper begins with a review of microbubble physics models, developed to describe microbubble dynamic behavior in the presence of ultrasound, and follows this with a discussion of how such models can be used to predict inertial cavitation profiles. Predicted sensitivities of inertial cavitation to changes in the values of membrane properties, including surface tension, surface dilatational viscosity, and area expansion modulus, indicate that area expansion modulus exerts the greatest relative influence on inertial cavitation. Accordingly, the theoretical dependence of area expansion modulus on chemical composition - in particular, poly (ethylene glyclol (PEG - is reviewed, and predictions of inertial cavitation for different PEG molecular weights and compositions are compared with experiment. Noteworthy is the predicted dependence, or lack thereof, of inertial cavitation on PEG molecular weight and mole fraction. Specifically, inertial cavitation is predicted to be independent of PEG molecular weight and mole fraction in the so-called mushroom regime. In the “brush” regime, however, inertial cavitation is predicted to increase with PEG mole fraction but to decrease (to the inverse 3/5 power with PEG molecular weight. While excellent agreement between experiment and theory can be achieved, it is shown that the calculated inertial cavitation profiles depend strongly on the criterion used to predict inertial cavitation. This is followed by a discussion of nesting microbubbles inside the aqueous core of microcapsules and how this significantly increases the inertial cavitation threshold. Nesting thus offers a means for avoiding unwanted inertial cavitation and cell death during imaging and other applications such as sonoporation. A review of putative sonoporation mechanisms is then presented

  2. Oxygen as a paramagnetic probe for nuclear magnetic resonance: structure and paramagnetic profile of a lipid bilayer/membrane model system

    International Nuclear Information System (INIS)

    Paramagnetic contact shifts and relaxation rate enhancements from molecular oxygen dissolved in a model membrane, were studied by nuclear magnetic resonance spectroscopy. The model membrane system was an isotropic bicelle formed using 1-myristelaidoyl-2-myristoyl-d27-sn- glycero-3-phosphocholine (MLMPC), a custom phospholipid, and 1-2-dihexanoyl-d22-sn-glycero-3-phosphocholine (DHPC). The 13C and 1H spectra of MLMPC were assigned. Molecular oxygen was delivered at external pressures of 20 and 50 atm. Paramagnetic contact shifts were found to scale with the oxygen solubility gradient in the lipid bilayer, were found to be invariant to temperature changes in the region studied (288K to 331K), and scaled linearly with changes in oxygen pressure. Relaxation rate enhancements from oxygen were low in the headgroup region and increased to a roughly constant rate in the acyl chain region. Rates were comparable to values predicted by simple thermodynamic theories which take into account the observed gradients in diffusion rates and solubility of oxygen in bilayers. (author)

  3. The Alzheimer's disease Aβ peptide binds to the anionic DMPS lipid bilayer.

    Science.gov (United States)

    Lockhart, Christopher; Klimov, Dmitri K

    2016-06-01

    We have applied isobaric-isothermal replica exchange molecular dynamics (REMD) and the all-atom explicit water model to study binding of Aβ10-40 peptide to the anionic DMPS bilayer. To provide comparison with a zwitterionic bilayer, we used our previous REMD simulations probing binding of the same peptide to the DMPC bilayer. Using two sets of simulations, we comparatively analyzed the equilibrium Aβ conformational ensemble, peptide-bilayer interactions, and changes in the bilayer structure induced by Aβ binding. Our results are six-fold. (1) Binding to the DMPS bilayer triggers the formation of stable helix in the Aβ C-terminal, although the helix-inducing effect caused by DMPS lipids is weaker than that of DMPC. (2) Compared to the DMPC-bound Aβ monomer, the anionic bilayer weakens intrapeptide interactions, particularly, formed by charged amino acids. (3) Binding of Aβ peptide to the DMPS bilayer is primarily governed by electrostatic interactions between charged amino acids and charged lipid groups. In contrast, these interactions play minor role in Aβ binding to the DMPC bilayer. (4) Aβ peptide generally resides on the DMPS bilayer surface causing relatively minor bilayer thinning. The opposite scenario applies to Aβ binding to the DMPC bilayer. (5) In contrast to DMPC simulations, Aβ largely expels anionic lipids from its binding "footprint" forming a ring of charged amino acids mixed with charged lipid groups around the peptide. (6) Aβ binding disorders proximal DMPS lipids more strongly than their DMPC counterparts. Our simulations show that Aβ monomers fail to perturb anionic or zwitterionic bilayers across both leaflets. PMID:26947182

  4. Structure determination by X-ray crystallography

    CERN Document Server

    Ladd, M F C

    1995-01-01

    X-ray crystallography provides us with the most accurate picture we can get of atomic and molecular structures in crystals. It provides a hard bedrock of structural results in chemistry and in mineralogy. In biology, where the structures are not fully crystalline, it can still provide valuable results and, indeed, the impact here has been revolutionary. It is still an immense field for young workers, and no doubt will provide yet more striking develop­ ments of a major character. It does, however, require a wide range of intellectual application, and a considerable ability in many fields. This book will provide much help. It is a very straightforward and thorough guide to every aspect of the subject. The authors are experienced both as research workers themselves and as teachers of standing, and this is shown in their clarity of exposition. There are plenty of iliustrations and worked examples to aid the student to obtain a real grasp of the subject.

  5. Molecular Dynamics of a Water-Lipid Bilayer Interface

    Science.gov (United States)

    Wilson, Michael A.; Pohorille, Andrew

    1994-01-01

    We present results of molecular dynamics simulations of a glycerol 1-monooleate bilayer in water. The total length of analyzed trajectories is 5ns. The calculated width of the bilayer agrees well with the experimentally measured value. The interior of the membrane is in a highly disordered fluid state. Atomic density profile, orientational and conformational distribution functions, and order parameters indicate that disorder increases toward the center of the bilayer. Analysis of out-of-plane thermal fluctuations of the bilayer surfaces occurring at the time scale of the present calculations reveals that the distribution of modes agrees with predictions of the capillary wave model. Fluctuations of both bilayer surfaces are uncorrelated, yielding Gaussian distribution of instantaneous widths of the membrane. Fluctuations of the width produce transient thinning defects in the bilayer which occasionally span almost half of the membrane. The leading mechanism of these fluctuations is the orientational and conformational motion of head groups rather than vertical motion of the whole molecules. Water considerably penetrates the head group region of the bilayer but not its hydrocarbon core. The total net excess dipole moment of the interfacial water points toward the aqueous phase, but the water polarization profile is non-monotonic. Both water and head groups significantly contribute to the surface potential across the interface. The calculated sign of the surface potential is in agreement with that from experimental measurements, but the value is markedly overestimated. The structural and electrical properties of the water-bilayer system are discussed in relation to membrane functions, in particular transport of ions and nonelectrolytes across membranes.

  6. Predicting proton titration in cationic micelle and bilayer environments

    Energy Technology Data Exchange (ETDEWEB)

    Morrow, Brian H.; Shen, Jana K. [Department of Pharmaceutical Sciences, University of Maryland, Baltimore, Maryland 21201 (United States); Eike, David M.; Murch, Bruce P.; Koenig, Peter H. [Computational Chemistry, Modeling and Simulation GCO, Procter and Gamble, Cincinnati, Ohio 45201 (United States)

    2014-08-28

    Knowledge of the protonation behavior of pH-sensitive molecules in micelles and bilayers has significant implications in consumer product development and biomedical applications. However, the calculation of pK{sub a}’s in such environments proves challenging using traditional structure-based calculations. Here we apply all-atom constant pH molecular dynamics with explicit ions and titratable water to calculate the pK{sub a} of a fatty acid molecule in a micelle of dodecyl trimethylammonium chloride and liquid as well as gel-phase bilayers of diethyl ester dimethylammonium chloride. Interestingly, the pK{sub a} of the fatty acid in the gel bilayer is 5.4, 0.4 units lower than that in the analogous liquid bilayer or micelle, despite the fact that the protonated carboxylic group is significantly more desolvated in the gel bilayer. This work illustrates the capability of all-atom constant pH molecular dynamics in capturing the delicate balance in the free energies of desolvation and Coulombic interactions. It also shows the importance of the explicit treatment of ions in sampling the protonation states. The ability to model dynamics of pH-responsive substrates in a bilayer environment is useful for improving fabric care products as well as our understanding of the side effects of anti-inflammatory drugs.

  7. Predicting proton titration in cationic micelle and bilayer environments

    International Nuclear Information System (INIS)

    Knowledge of the protonation behavior of pH-sensitive molecules in micelles and bilayers has significant implications in consumer product development and biomedical applications. However, the calculation of pKa’s in such environments proves challenging using traditional structure-based calculations. Here we apply all-atom constant pH molecular dynamics with explicit ions and titratable water to calculate the pKa of a fatty acid molecule in a micelle of dodecyl trimethylammonium chloride and liquid as well as gel-phase bilayers of diethyl ester dimethylammonium chloride. Interestingly, the pKa of the fatty acid in the gel bilayer is 5.4, 0.4 units lower than that in the analogous liquid bilayer or micelle, despite the fact that the protonated carboxylic group is significantly more desolvated in the gel bilayer. This work illustrates the capability of all-atom constant pH molecular dynamics in capturing the delicate balance in the free energies of desolvation and Coulombic interactions. It also shows the importance of the explicit treatment of ions in sampling the protonation states. The ability to model dynamics of pH-responsive substrates in a bilayer environment is useful for improving fabric care products as well as our understanding of the side effects of anti-inflammatory drugs

  8. Formation of supported lipid bilayers by vesicle fusion

    DEFF Research Database (Denmark)

    Lind, Tania Kjellerup; Cardenas Gomez, Marite; Wacklin, Hanna

    2014-01-01

    We have investigated the effect of deposition temperature on supported lipid bilayer formation via vesicle fusion. By using several complementary surface-sensitive techniques, we demonstrate that despite contradicting literature on the subject, high-quality bilayers can be formed below the main p...... observed during the deposition process by QCM-D correspond to vesicles absorbed on top of a continuous bilayer and not to a surface-supported vesicular layer as previously reported. © 2014 American Chemical Society.......We have investigated the effect of deposition temperature on supported lipid bilayer formation via vesicle fusion. By using several complementary surface-sensitive techniques, we demonstrate that despite contradicting literature on the subject, high-quality bilayers can be formed below the main...... phase-transition temperature of the lipid. We have carefully studied the formation mechanism of supported DPPC bilayers below and above the lipid melting temperature (Tm) by quartz crystal microbalance and atomic force microscopy under continuous flow conditions. We also measured the structure of lipid...

  9. Determining the structure of Carbon-60

    International Nuclear Information System (INIS)

    Carbon-60 is the most stable and best known of the carbon cage structures known collectively as the fullerenes. It is a remarkable molecule that forms a fascinating solid. Although the molecular shape of C sub 6 sub 0 is familiar - it is simply the shape of a soccer ball with 12 pentagons and 20 hexagons - the manner in which it forms a crystal structure is by no means obvious. This talk will focus on the insights which neutron scattering at ISIS has brought to our understanding of solid C sub6 sub 0. At room temperature, the structure may be regarded as forming as essentially ideal cubic-close packed molecular bubble-raft: each molecule is reorienting so rapidly that a time-averaged picture, over as little as a nanosecond, reveals a closely spherical shell of atomic density. At 260 K, a rather unusual structural transition occurs. The molecules order but still retain cubic symmetry. Although this may not appear to be a rather dramatic change, detailed considerations show that a profound transition has occurred that bears close similarities to a solid-liquid phase transition but in two dimensions. Below 260 K, reorientation still occurs but at a dramatically reduced rate as the temperature is lowered. Indeed at around 90 K, The reorientation is so slow that thermodynamic equilibrium cannot be achieved in a reasonable timescale an orientational glass transition occurs. Although the behaviour of solid C sub 6 sub 0 undergoes dramatic changes as a function of temperature, a coherent description has evolved in which neutron scattering plays a central role. Close analogies are to be found in the study of systems as diverse as solid H sub 2 and human-rhinovirus structures. These analogies and the central role played by neutron scattering at ISIS will be emphasised in this paper. 5 figs., 10 refs. (author)

  10. Lindane Suppresses the Lipid-bilayer Permeability in Main Transition Region

    DEFF Research Database (Denmark)

    Sabra, Mads Christian; Jørgensen, Kent; Mouritsen, Ole G.

    1996-01-01

    the transition and lower the transition temperature, without changing the transition enthalpy significantly. Lindane therefore enhances the thermal fluctuations of the bilayer. The calorimetric data furthermore suggest that the bilayer structure is intact and not disrupted by even high concentrations (32 mol......%) of lindane. Fluorescence spectroscopy was used to measure the passive permeability of unilamellar DMPC bilayers to Co2+ ions. The data show that lindane seals the bilayer for Co2+ penetration and that this effect increases with increasing lindane concentration. The results are discussed in relation...

  11. Formation of supported lipid bilayers containing phase-segregated domains and their interaction with gold nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Melby, Eric S.; Mensch, Arielle C.; Lohse, Samuel E.; Hu, Dehong; Orr, Galya; Murphy, Catherine; Hamers, Robert J.; Pedersen, Joel A.

    2016-02-01

    The cell membrane represents an important biological interface that nanoparticles may encounter after being released into the environment. Interaction of nanoparticles with cellular membranes may alter membrane structure and function, lead to their uptake into cells, and elicit adverse biological responses. Supported lipid bilayers have proven to be valuable ex vivo models for biological membranes, allowing investigation of their mechanisms of interaction with nanoparticles with a degree of control impossible in living cells. To date, the majority of research on nanoparticle interaction with supported lipid bilayers has employed membranes composed of single or binary mixtures of phospholipids. Cellular membranes contain a wide variety of lipids and exhibit lateral organization. Ordered membrane domains enriched in specific membrane components are referred to as lipid rafts and have not been explored with respect to their interaction with nanoparticles. Here we develop model lipid raft-containing membranes amenable to investigation by a variety of surface-sensitive analytical techniques and demonstrate that lipid rafts influence the extent of nanoparticle attachment to model membranes. We determined conditions that allow reliable formation of bilayers containing rafts enriched in sphingomyelin and cholesterol and confirmed their morphology by structured illumination and atomic force microscopies. We demonstrate that lipid rafts increase attachment of cationic gold nanoparticles to model membranes under near physiological ionic strength conditions (0.1 M NaCl) at pH 7.4. We anticipate that these results will serve as the foundation for and motivate further study of nanoparticle interaction with compositionally varied lipid rafts.

  12. Some structural determinants of melody recall.

    Science.gov (United States)

    Boltz, M

    1991-05-01

    Sophisticated musicians were asked to recall, using musical notation, a set of unfamiliar folk tunes that varied in rhythmic structure and referents of tonality. The results showed that memory was facilitated by tonic triad members marking phrase endings, but only when their presence was highlighted by a corresponding pattern of temporal accents. Conversely, recall significantly declined when tonal information was either absent or obscured by rhythmic structure. Error analyses further revealed that the retention of overall pitch contour and information at phrase ending points varied as a function of these manipulations. The results are discussed in terms of a framework that links the acts of perceiving and remembering to a common attentional scheme. PMID:1861610

  13. What Determines the Likelihood of Structural Reforms?

    OpenAIRE

    Agnello, Luca; Castro, Vitor; Jalles, João Tovar; Sousa, Ricardo M.

    2014-01-01

    We use data for a panel of 60 countries over the period 1980-2005 to investigate the main drivers of the likelihood of structural reforms. We find that: (i) external debt crises are the main trigger of financial and banking reforms; (ii) inflation and banking crises are the key drivers of external capital account reforms; (iii) banking crises also hasten financial reforms; and (iv) economic recessions play an important role in promoting the necessary consensus for financial, capital, banking ...

  14. RNA Structure Determination Using SAXS Data

    OpenAIRE

    Yang, Sichun; Parisien, Marc; Major, François; Roux, Benoît

    2010-01-01

    Exploiting the experimental information from small-angle x-ray solution scattering (SAXS) in conjunction with structure prediction algorithms can be advantageous in the case of ribonucleic acids (RNA), where global restraints on the 3D fold are often lacking. Traditional usage of SAXS data often starts by attempting to reconstruct the molecular shape ab initio, which is subsequently used to assess the quality of model Here, an alternative strategy is explored whereby the models from a very la...

  15. Structure and determinants of consumer expenditures

    OpenAIRE

    Stejskal, Ladislav; Stávková, Jana

    2011-01-01

    The local and worldwide present economic situation is often judged and discussed on the basis of the consumer expenditures development. Consumer expenditures or a buying behaviour outcome of each individual market subject is in marketing defined as a product and service seeking, from that consumers expect satisfying of their needs. On the basis of the introduced determination authors conducted a marketing research. Results in combination with a marketing insight into consumer expenditures rea...

  16. Self-folding graphene-polymer bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Tao [Institute of Microelectronics, Tsinghua University, Beijing 100084 (China); Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Yoon, ChangKyu [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Jin, Qianru [Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Li, Mingen [Department of Physics, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Liu, Zewen [Institute of Microelectronics, Tsinghua University, Beijing 100084 (China); Gracias, David H., E-mail: dgracias@jhu.edu [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States)

    2015-05-18

    In order to incorporate the extraordinary intrinsic thermal, electrical, mechanical, and optical properties of graphene with three dimensional (3D) flexible substrates, we introduce a solvent-driven self-folding approach using graphene-polymer bilayers. A polymer (SU-8) film was spin coated atop chemically vapor deposited graphene films on wafer substrates and graphene-polymer bilayers were patterned with or without metal electrodes using photolithography, thin film deposition, and etching. After patterning, the bilayers were released from the substrates and they self-folded to form fully integrated, curved, and folded structures. In contrast to planar graphene sensors on rigid substrates, we assembled curved and folded sensors that are flexible and they feature smaller form factors due to their 3D geometry and large surface areas due to their multiple rolled architectures. We believe that this approach could be used to assemble a range of high performance 3D electronic and optical devices of relevance to sensing, diagnostics, wearables, and energy harvesting.

  17. Self-folding graphene-polymer bilayers

    Science.gov (United States)

    Deng, Tao; Yoon, ChangKyu; Jin, Qianru; Li, Mingen; Liu, Zewen; Gracias, David H.

    2015-05-01

    In order to incorporate the extraordinary intrinsic thermal, electrical, mechanical, and optical properties of graphene with three dimensional (3D) flexible substrates, we introduce a solvent-driven self-folding approach using graphene-polymer bilayers. A polymer (SU-8) film was spin coated atop chemically vapor deposited graphene films on wafer substrates and graphene-polymer bilayers were patterned with or without metal electrodes using photolithography, thin film deposition, and etching. After patterning, the bilayers were released from the substrates and they self-folded to form fully integrated, curved, and folded structures. In contrast to planar graphene sensors on rigid substrates, we assembled curved and folded sensors that are flexible and they feature smaller form factors due to their 3D geometry and large surface areas due to their multiple rolled architectures. We believe that this approach could be used to assemble a range of high performance 3D electronic and optical devices of relevance to sensing, diagnostics, wearables, and energy harvesting.

  18. Cholesterol's location in lipid bilayers.

    Science.gov (United States)

    Marquardt, Drew; Kučerka, Norbert; Wassall, Stephen R; Harroun, Thad A; Katsaras, John

    2016-09-01

    It is well known that cholesterol modifies the physical properties of lipid bilayers. For example, the much studied liquid-ordered Lo phase contains rapidly diffusing lipids with their acyl chains in the all trans configuration, similar to gel phase bilayers. Moreover, the Lo phase is commonly associated with cholesterol-enriched lipid rafts, which are thought to serve as platforms for signaling proteins in the plasma membrane. Cholesterol's location in lipid bilayers has been studied extensively, and it has been shown - at least in some bilayers - to align differently from its canonical upright orientation, where its hydroxyl group is in the vicinity of the lipid-water interface. In this article we review recent works describing cholesterol's location in different model membrane systems with emphasis on results obtained from scattering, spectroscopic and molecular dynamics studies. PMID:27056099

  19. Lipid bilayer-bound conformation of an integral membrane beta barrel protein by multidimensional MAS NMR

    Energy Technology Data Exchange (ETDEWEB)

    Eddy, Matthew T. [The Scripps Research Institute, Department of Integrative Structural and Computational Biology (United States); Su, Yongchao; Silvers, Robert; Andreas, Loren; Clark, Lindsay [Massachusetts Institute of Technology, Department of Chemistry (United States); Wagner, Gerhard [Harvard Medical School, Department of Biological Chemistry and Molecular Pharmacology (United States); Pintacuda, Guido; Emsley, Lyndon [Université de Lyon, Centre de RMN à Très Hauts Champs, Institut des Sciences Analytiques (CNRS, ENS Lyon, UCB Lyon 1) (France); Griffin, Robert G., E-mail: rgg@mit.edu [Massachusetts Institute of Technology, Department of Chemistry (United States)

    2015-04-15

    The human voltage dependent anion channel 1 (VDAC) is a 32 kDa β-barrel integral membrane protein that controls the transport of ions across the outer mitochondrial membrane. Despite the determination of VDAC solution and diffraction structures, a structural basis for the mechanism of its function is not yet fully understood. Biophysical studies suggest VDAC requires a lipid bilayer to achieve full function, motivating the need for atomic resolution structural information of VDAC in a membrane environment. Here we report an essential step toward that goal: extensive assignments of backbone and side chain resonances for VDAC in DMPC lipid bilayers via magic angle spinning nuclear magnetic resonance (MAS NMR). VDAC reconstituted into DMPC lipid bilayers spontaneously forms two-dimensional lipid crystals, showing remarkable spectral resolution (0.5–0.3 ppm for {sup 13}C line widths and <0.5 ppm {sup 15}N line widths at 750 MHz). In addition to the benefits of working in a lipid bilayer, several distinct advantages are observed with the lipid crystalline preparation. First, the strong signals and sharp line widths facilitated extensive NMR resonance assignments for an integral membrane β-barrel protein in lipid bilayers by MAS NMR. Second, a large number of residues in loop regions were readily observed and assigned, which can be challenging in detergent-solubilized membrane proteins where loop regions are often not detected due to line broadening from conformational exchange. Third, complete backbone and side chain chemical shift assignments could be obtained for the first 25 residues, which comprise the functionally important N-terminus. The reported assignments allow us to compare predicted torsion angles for VDAC prepared in DMPC 2D lipid crystals, DMPC liposomes, and LDAO-solubilized samples to address the possible effects of the membrane mimetic environment on the conformation of the protein. Concluding, we discuss the strengths and weaknesses of the

  20. Lipid bilayer-bound conformation of an integral membrane beta barrel protein by multidimensional MAS NMR

    International Nuclear Information System (INIS)

    The human voltage dependent anion channel 1 (VDAC) is a 32 kDa β-barrel integral membrane protein that controls the transport of ions across the outer mitochondrial membrane. Despite the determination of VDAC solution and diffraction structures, a structural basis for the mechanism of its function is not yet fully understood. Biophysical studies suggest VDAC requires a lipid bilayer to achieve full function, motivating the need for atomic resolution structural information of VDAC in a membrane environment. Here we report an essential step toward that goal: extensive assignments of backbone and side chain resonances for VDAC in DMPC lipid bilayers via magic angle spinning nuclear magnetic resonance (MAS NMR). VDAC reconstituted into DMPC lipid bilayers spontaneously forms two-dimensional lipid crystals, showing remarkable spectral resolution (0.5–0.3 ppm for 13C line widths and <0.5 ppm 15N line widths at 750 MHz). In addition to the benefits of working in a lipid bilayer, several distinct advantages are observed with the lipid crystalline preparation. First, the strong signals and sharp line widths facilitated extensive NMR resonance assignments for an integral membrane β-barrel protein in lipid bilayers by MAS NMR. Second, a large number of residues in loop regions were readily observed and assigned, which can be challenging in detergent-solubilized membrane proteins where loop regions are often not detected due to line broadening from conformational exchange. Third, complete backbone and side chain chemical shift assignments could be obtained for the first 25 residues, which comprise the functionally important N-terminus. The reported assignments allow us to compare predicted torsion angles for VDAC prepared in DMPC 2D lipid crystals, DMPC liposomes, and LDAO-solubilized samples to address the possible effects of the membrane mimetic environment on the conformation of the protein. Concluding, we discuss the strengths and weaknesses of the reported

  1. Photoelectron holography applied to surface structural determination

    Energy Technology Data Exchange (ETDEWEB)

    Petersen, B.L.

    1995-05-01

    Photoemitted electron waves are used as coherent source waves for angstrom-scale holographic imaging of local atomic geometry at surfaces. Electron angular distribution patterns are collected above a sample surface and serve as a record of the interference between source wave and waves scattered from surrounding ion cores. Using a mathematical imaging integral transformation, the three-dimensional structural information is obtained directly from these collected patterns. Patterns measured with different electron kinetic energies are phase-summed for image improvement. Pt (111) surface is used as a model system. A pattern 9.6{angstrom}{sup {minus}1} (351 eV) is used to generate a full 3-D image of atom locations around an emitter with nearest neighbors within 0.l{angstrom} of the expected bulk positions. Atoms several layers beyond the nearest neighbors are also apparent. Twin-image reduction and artifact suppression is obtained by phase-summing eight patterns measured from 8.8 to 10.2{angstrom}{sup {minus}1} (295 to 396 eV). 32 were measured in 0.2{angstrom}{sup {minus}1} steps from 6.0 to 12.2{angstrom}{sup {minus}1} (137 to 567 eV) are presented here. Simple models of two-slit interference are compared with electron scattering to illuminate understanding of holographic recording of the structural information. This also shows why it sometimes fails due to destructive interferences. Simple theoretical models of electron scattering are compared to experiment to show the origin of the structural information and the differences that result from atomic scattering and from the source wave. Experimental parameters and their relation to imaging is discussed. Comparison is made to the Pt pattern measured at 351 eV using the simple theoretical model. The remaining data set is also modeled, and the eight appropriate theoretical patterns are used to regenerate the multiple-wavenumber experimental result. A clean Cu (001) surface is also measured and imaged.

  2. How structure determines correlations in neuronal networks.

    Directory of Open Access Journals (Sweden)

    Volker Pernice

    2011-05-01

    Full Text Available Networks are becoming a ubiquitous metaphor for the understanding of complex biological systems, spanning the range between molecular signalling pathways, neural networks in the brain, and interacting species in a food web. In many models, we face an intricate interplay between the topology of the network and the dynamics of the system, which is generally very hard to disentangle. A dynamical feature that has been subject of intense research in various fields are correlations between the noisy activity of nodes in a network. We consider a class of systems, where discrete signals are sent along the links of the network. Such systems are of particular relevance in neuroscience, because they provide models for networks of neurons that use action potentials for communication. We study correlations in dynamic networks with arbitrary topology, assuming linear pulse coupling. With our novel approach, we are able to understand in detail how specific structural motifs affect pairwise correlations. Based on a power series decomposition of the covariance matrix, we describe the conditions under which very indirect interactions will have a pronounced effect on correlations and population dynamics. In random networks, we find that indirect interactions may lead to a broad distribution of activation levels with low average but highly variable correlations. This phenomenon is even more pronounced in networks with distance dependent connectivity. In contrast, networks with highly connected hubs or patchy connections often exhibit strong average correlations. Our results are particularly relevant in view of new experimental techniques that enable the parallel recording of spiking activity from a large number of neurons, an appropriate interpretation of which is hampered by the currently limited understanding of structure-dynamics relations in complex networks.

  3. DNA nanostructures interacting with lipid bilayer membranes.

    Science.gov (United States)

    Langecker, Martin; Arnaut, Vera; List, Jonathan; Simmel, Friedrich C

    2014-06-17

    CONSPECTUS: DNA has been previously shown to be useful as a material for the fabrication of static nanoscale objects, and also for the realization of dynamic molecular devices and machines. In many cases, nucleic acid assemblies directly mimic biological structures, for example, cytoskeletal filaments, enzyme scaffolds, or molecular motors, and many of the applications envisioned for such structures involve the study or imitation of biological processes, and even the interaction with living cells and organisms. An essential feature of biological systems is their elaborate structural organization and compartmentalization, and this most often involves membranous structures that are formed by dynamic assemblies of lipid molecules. Imitation of or interaction with biological systems using the tools of DNA nanotechnology thus ultimately and necessarily also involves interactions with lipid membrane structures, and thus the creation of DNA-lipid hybrid assemblies. Due to their differing chemical nature, however, highly charged nucleic acids and amphiphilic lipids do not seem the best match for the construction of such systems, and in fact they are rarely found in nature. In recent years, however, a large variety of lipid-interacting DNA conjugates were developed, which are now increasingly being applied also for the realization of DNA nanostructures interacting with lipid bilayer membranes. In this Account, we will present the current state of this emerging class of nanosystems. After a brief overview of the basic biophysical and biochemical properties of lipids and lipid bilayer membranes, we will discuss how DNA molecules can interact with lipid membranes through electrostatic interactions or via covalent modification with hydrophobic moieties. We will then show how such DNA-lipid interactions have been utilized for the realization of DNA nanostructures attached to or embedded within lipid bilayer membranes. Under certain conditions, DNA nanostructures remain mobile on

  4. A Comparative Study of the Influence of Sugars Sucrose, Trehalose, and Maltose on the Hydration and Diffusion of DMPC Lipid Bilayer at Complete Hydration: Investigation of Structural and Spectroscopic Aspect of Lipid-Sugar Interaction.

    Science.gov (United States)

    Roy, Arpita; Dutta, Rupam; Kundu, Niloy; Banik, Debasis; Sarkar, Nilmoni

    2016-05-24

    It is well-known that sugars protect membrane structures against fusion and leakage. Here, we have investigated the interaction between different sugars (sucrose, trehalose, and maltose) and phospholipid membrane of 1,2-dimyristoyl-sn-glycero-3-phoshpocholine (DMPC) using dynamic light scattering (DLS), transmission electron microscopy (TEM), and other various spectroscopic techniques. DLS measurement reveals that the addition of sugar molecule results a significant increase of the average diameter of DMPC membrane. We have also noticed that in the presence of different sugars the rotational relaxation and solvation time of coumarin 480 (C480) and coumarin 153 (C153) surrounding DMPC membrane increases, suggesting a marked reduction of the hydration behavior at the surface of phospholipid membrane. In addition, we have also investigated the effect of sugar molecules on the lateral mobility of phospholipids. Interestingly, the relative increase in rotational, solvation and lateral diffusion is more prominent for C480 than that of C153 because of their different location in lipid bilayer. It is because of preferential location of comparatively hydrophilic probe C480 in the interfacial region of the lipid bilayer. Sugars intercalate with the phospholipid headgroup through hydrogen bonding and replace smaller sized water molecules from the membrane surface. Therefore, overall, we have monitored a comparative analysis regarding the interaction of different sugar molecules (sucrose, trehalose, and maltose) with the DMPC membrane through DLS, TEM, solvation dynamics, time-resolved anisotropy, and fluorescence correlation spectroscopy (FCS) measurements to explore the structural and spectroscopic aspect of lipid-sugar interaction. PMID:27133799

  5. Structural and institutional determinants of investment activity in Africa

    OpenAIRE

    Chuku, Chuku; Onye, Kenneth; Ajah, Hycent

    2015-01-01

    This paper considers the structural and institutional determinants of investment activity in selected African countries within a neoclassical framework. Generalized method of moments and a family of panel data estimation techniques are utilized in addition to nonparametric kernel regression techniques to uncover the relationship. Three main findings emerge; (i) financial openness and institutional quality are reasonably robust structural and institutional determinants of investment activity...

  6. Determination of atomic cluster structure with cluster fusion algorithm

    DEFF Research Database (Denmark)

    Obolensky, Oleg I.; Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    We report an efficient scheme of global optimization, called cluster fusion algorithm, which has proved its reliability and high efficiency in determination of the structure of various atomic clusters.......We report an efficient scheme of global optimization, called cluster fusion algorithm, which has proved its reliability and high efficiency in determination of the structure of various atomic clusters....

  7. Structural Determinants of Sleeping Beauty Transposase Activity.

    Science.gov (United States)

    Abrusán, György; Yant, Stephen R; Szilágyi, András; Marsh, Joseph A; Mátés, Lajos; Izsvák, Zsuzsanna; Barabás, Orsolya; Ivics, Zoltán

    2016-08-01

    Transposases are important tools in genome engineering, and there is considerable interest in engineering more efficient ones. Here, we seek to understand the factors determining their activity using the Sleeping Beauty transposase. Recent work suggests that protein coevolutionary information can be used to classify groups of physically connected, coevolving residues into elements called "sectors", which have proven useful for understanding the folding, allosteric interactions, and enzymatic activity of proteins. Using extensive mutagenesis data, protein modeling and analysis of folding energies, we show that (i) The Sleeping Beauty transposase contains two sectors, which span across conserved domains, and are enriched in DNA-binding residues, indicating that the DNA binding and endonuclease functions of the transposase coevolve; (ii) Sector residues are highly sensitive to mutations, and most mutations of these residues strongly reduce transposition rate; (iii) Mutations with a strong effect on free energy of folding in the DDE domain of the transposase significantly reduce transposition rate. (iv) Mutations that influence DNA and protein-protein interactions generally reduce transposition rate, although most hyperactive mutants are also located on the protein surface, including residues with protein-protein interactions. This suggests that hyperactivity results from the modification of protein interactions, rather than the stabilization of protein fold. PMID:27401040

  8. Determination of Ice Characteristics for Marine Hydroengineering Structures

    Energy Technology Data Exchange (ETDEWEB)

    Kantarzhi, I. G., E-mail: kantardgi@yandex.ru [Moscow State University of Civil Engineering (MSGU) (Russian Federation); Maderich, V. S., E-mail: vladmad@gmail.com; Koshebutskii, V. I., E-mail: koshik1@gmail.com [Ukrainian Center of Environmental and Water Projects (UTsÉVP) (Ukraine)

    2016-01-15

    Problems and potential approaches to determining ice characteristics for sea hydroengineering structures design are considered. A system for numerical modeling of ice dynamics is presented. The system may be used to define ice characteristics on approaches to structures with due regard for local hydrometeorological conditions and ice loads on structures. System application examples are presented for determining computational scenarios for ice loads at structures of the Pevek floating nuclear power plant (FNPP), as well as for the breakwater pier under reconstruction in Vanino. A scenario approach is used to determined ice loads.

  9. Audit Fee Determinants in different Ownership Structures : The Swedish Setting

    OpenAIRE

    Ask, Joakim; LJ Holm, Mattias

    2013-01-01

    The aim of this study is to test the audit fee determinants for companies listed on Nasdaq OMX Stockholm Stock Exchange and to examine whether the audit fee determinants diverge for ownership structures. By testing the audit fee determinants in a Swedish setting the study contributes to the research body in two ways; by testing a previously sparsely researched setting and examining the monitoring need for different ownership structures. The results indicate that audit fees are explained to a ...

  10. Determinants of Capital Structure: Empirical Evidence From UK

    OpenAIRE

    XU, WENJING

    2010-01-01

    This paper investigates the determinants of capital structure for the companies in the United Kingdom. The aim of this study is to determine which capital structure is more appropriate to UK listed companies. Results obtained will be compared against previous empirical and theoretical predictions. Panel data set containing 342 UK public quoted companies across 8 industries during the period from 2000-2009 is employed. A Pooled OLS regression is constructed to discuss what the determinants...

  11. The methodology of determining the corrosion of steel structures

    OpenAIRE

    S.D. Fedotov; A.V. Ulybin; N.N. Shabrov

    2013-01-01

    The problems of determining the corrosive wear of steel structures are considered. The results of applying ultrasonic method to determine the remaining profile of the structure are described. The main advantages and disadvantages of ultrasonic thickness meters comparing to mechanical devices are given. Low reliability of the method based on evaluating the thickness of the corrosion oxides is substantiated. The problems of determining the original section of the elements are outlined. The alg...

  12. Ab initio structure determination via powder X-ray diffraction

    Indian Academy of Sciences (India)

    Digamber G Porob; T N Guru Row

    2001-10-01

    Structure determination by powder X-ray diffraction data has gone through a recent surge since it has become important to get to the structural information of materials which do not yield good quality single crystals. Although the method of structure completion when once the starting model is provided is facile through the Rietveld refinement technique, the structure solution ab initio os still not push-button technology. In this article a survey of the recent development in this area is provided with an illustration of the structure determination of -NaBi3V2O10.

  13. Interaction driven quantum Hall effect in artificially stacked graphene bilayers

    Science.gov (United States)

    Iqbal, Muhammad Zahir; Iqbal, Muhammad Waqas; Siddique, Salma; Khan, Muhammad Farooq; Ramay, Shahid Mahmood; Nam, Jungtae; Kim, Keun Soo; Eom, Jonghwa

    2016-04-01

    The honeycomb lattice structure of graphene gives rise to its exceptional electronic properties of linear dispersion relation and its chiral nature of charge carriers. The exceptional electronic properties of graphene stem from linear dispersion relation and chiral nature of charge carries, originating from its honeycomb lattice structure. Here, we address the quantum Hall effect in artificially stacked graphene bilayers and single layer graphene grown by chemical vapor deposition. The quantum Hall plateaus started to appear more than 3 T and became clearer at higher magnetic fields up to 9 T. Shubnikov-de Hass oscillations were manifestly observed in graphene bilayers texture. These unusual plateaus may have been due to the layers interaction in artificially stacked graphene bilayers. Our study initiates the understanding of interactions between artificially stacked graphene layers.

  14. Interaction driven quantum Hall effect in artificially stacked graphene bilayers

    Science.gov (United States)

    Iqbal, Muhammad Zahir; Iqbal, Muhammad Waqas; Siddique, Salma; Khan, Muhammad Farooq; Ramay, Shahid Mahmood; Nam, Jungtae; Kim, Keun Soo; Eom, Jonghwa

    2016-01-01

    The honeycomb lattice structure of graphene gives rise to its exceptional electronic properties of linear dispersion relation and its chiral nature of charge carriers. The exceptional electronic properties of graphene stem from linear dispersion relation and chiral nature of charge carries, originating from its honeycomb lattice structure. Here, we address the quantum Hall effect in artificially stacked graphene bilayers and single layer graphene grown by chemical vapor deposition. The quantum Hall plateaus started to appear more than 3 T and became clearer at higher magnetic fields up to 9 T. Shubnikov-de Hass oscillations were manifestly observed in graphene bilayers texture. These unusual plateaus may have been due to the layers interaction in artificially stacked graphene bilayers. Our study initiates the understanding of interactions between artificially stacked graphene layers. PMID:27098387

  15. The hemifusion structure induced by influenza virus haemagglutinin is determined by physical properties of the target membranes.

    Science.gov (United States)

    Chlanda, Petr; Mekhedov, Elena; Waters, Hang; Schwartz, Cindi L; Fischer, Elizabeth R; Ryham, Rolf J; Cohen, Fredric S; Blank, Paul S; Zimmerberg, Joshua

    2016-01-01

    Influenza A virus haemagglutinin conformational change drives the membrane fusion of viral and endosomal membranes at low pH. Membrane fusion proceeds through an intermediate called hemifusion(1,2). For viral fusion, the hemifusion structures are not determined(3). Here, influenza virus-like particles(4) carrying wild-type haemagglutinin or haemagglutinin hemifusion mutant G1S(5) and liposome mixtures were studied at low pH by Volta phase plate cryo-electron tomography, which improves the signal-to-noise ratio close to focus. We determined two distinct hemifusion structures: a hemifusion diaphragm and a novel structure termed a 'lipidic junction'. Liposomes with lipidic junctions were ruptured with membrane edges stabilized by haemagglutinin. The rupture frequency and hemifusion diaphragm diameter were not affected by G1S mutation, but decreased when the cholesterol level in the liposomes was close to physiological concentrations. We propose that haemagglutinin induces a merger between the viral and target membranes by one of two independent pathways: a rupture-insertion pathway leading to the lipidic junction and a hemifusion-stalk pathway leading to a fusion pore. The latter is relevant under the conditions of influenza virus infection of cells. Cholesterol concentration functions as a pathway switch because of its negative spontaneous curvature in the target bilayer, as determined by continuum analysis. PMID:27572837

  16. MOTOR: model assisted software for NMR structure determination.

    Science.gov (United States)

    Schieborr, Ulrich; Sreeramulu, Sridhar; Elshorst, Bettina; Maurer, Marcus; Saxena, Krishna; Stehle, Tanja; Kudlinzki, Denis; Gande, Santosh Lakshmi; Schwalbe, Harald

    2013-11-01

    Eukaryotic proteins with important biological function can be partially unstructured, conformational flexible, or heterogenic. Crystallization trials often fail for such proteins. In NMR spectroscopy, parts of the polypeptide chain undergoing dynamics in unfavorable time regimes cannot be observed. De novo NMR structure determination is seriously hampered when missing signals lead to an incomplete chemical shift assignment resulting in an information content of the NOE data insufficient to determine the structure ab initio. We developed a new protein structure determination strategy for such cases based on a novel NOE assignment strategy utilizing a number of model structures but no explicit reference structure as it is used for bootstrapping like algorithms. The software distinguishes in detail between consistent and mutually exclusive pairs of possible NOE assignments on the basis of different precision levels of measured chemical shifts searching for a set of maximum number of consistent NOE assignments in agreement with 3D space. Validation of the method using the structure of the low molecular-weight-protein tyrosine phosphatase A (MptpA) showed robust results utilizing protein structures with 30-45% sequence identity and 70% of the chemical shift assignments. About 60% of the resonance assignments are sufficient to identify those structural models with highest conformational similarity to the real structure. The software was benchmarked by de novo solution structures of fibroblast growth factor 21 (FGF21) and the extracellular fibroblast growth factor receptor domain FGFR4 D2, which both failed in crystallization trials and in classical NMR structure determination. PMID:23852655

  17. Automating the determination of 3D protein structure

    Energy Technology Data Exchange (ETDEWEB)

    Rayl, K.D.

    1993-12-31

    The creation of an automated method for determining 3D protein structure would be invaluable to the field of biology and presents an interesting challenge to computer science. Unfortunately, given the current level of protein knowledge, a completely automated solution method is not yet feasible, therefore, our group has decided to integrate existing databases and theories to create a software system that assists X-ray crystallographers in specifying a particular protein structure. By breaking the problem of determining overall protein structure into small subproblems, we hope to come closer to solving a novel structure by solving each component. By generating necessary information for structure determination, this method provides the first step toward designing a program to determine protein conformation automatically.

  18. The Determinants of Capital Structure: An Empirical Evidence from Germany

    OpenAIRE

    Pornsuwankul, Juthamart/Miss

    2012-01-01

    Abstract This paper develops a preliminary study to explore the determinants of capital structure of listed and unlisted companies in Germany using panel data methodology. The findings suggest that the capital structure of listed and unlisted firms is significantly different. Also, some insights from the modern finance theory of capital structure are portable to Germany in that firm-specific factors that are identified to be significant in explaining capital structure in empirical studies...

  19. X-Ray Kinematography of Temperature-Jump Relaxation Probes the Elastic Properties of Fluid Bilayers

    CERN Document Server

    Pabst, G; Amenitsch, H; Bernstorff, S; Laggner, P; Pabst, Georg; Rappolt, Michael; Amenitsch, Heinz; Bernstorff, Sigrid; Laggner, Peter

    2000-01-01

    The response kinetics of liquid crystalline phosphatidylcholine bilayerstacks to rapid, IR-laser induced temperature jumps has been studied bymillisecond time-resolved x-ray diffraction. The system reacts on the fasttemperature change by a discrete bilayer compression normal to its surface anda lateral bilayer expansion. Since water cannot diffuse from the excess phaseinto the interbilayer water region within the 2 ms duration of the laser pulse,the water layer has to follow the bilayer expansion, by an anomalous thinning.Structural analysis of a 20 ms diffraction pattern from the intermediate phaseindicates that the bilayer thickness remains within the limits of isothermalequilibrium values. Both, the intermediate structure and its relaxation intothe original equilibrium L_(alpha)-phase, depend on the visco-elasticproperties of the bilayer/water system. We present an analysis of therelaxation process by an overdamped one-dimensional oscillation model revealingthe concepts of Hooke's law for phospholipid bila...

  20. Giant magnetoresistance in bilayer graphene nanoflakes

    Science.gov (United States)

    Farghadan, Rouhollah; Farekiyan, Marzieh

    2016-09-01

    Coherent spin transport through bilayer graphene (BLG) nanoflakes sandwiched between two electrodes made of single-layer zigzag graphene nanoribbon was investigated by means of Landauer-Buttiker formalism. Application of a magnetic field only on BLG structure as a channel produces a perfect spin polarization in a large energy region. Moreover, the conductance could be strongly modulated by magnetization of the zigzag edge of AB-stacked BLG, and the junction, entirely made of carbon, produces a giant magnetoresistance (GMR) up to 100%. Intestinally, GMR and spin polarization could be tuned by varying BLG width and length. Generally, MR in a AB-stacked BLG strongly increases (decreases) with length (width).

  1. Bilayer avalanche spin-diode logic

    International Nuclear Information System (INIS)

    A novel spintronic computing paradigm is proposed and analyzed in which InSb p-n bilayer avalanche spin-diodes are cascaded to efficiently perform complex logic operations. This spin-diode logic family uses control wires to generate magnetic fields that modulate the resistance of the spin-diodes, and currents through these devices control the resistance of cascaded devices. Electromagnetic simulations are performed to demonstrate the cascading mechanism, and guidelines are provided for the development of this innovative computing technology. This cascading scheme permits compact logic circuits with switching speeds determined by electromagnetic wave propagation rather than electron motion, enabling high-performance spintronic computing

  2. Bilayer avalanche spin-diode logic

    Energy Technology Data Exchange (ETDEWEB)

    Friedman, Joseph S., E-mail: joseph.friedman@u-psud.fr; Querlioz, Damien [Institut d’Electronique Fondamentale, Univ. Paris-Sud, CNRS, 91405 Orsay (France); Fadel, Eric R. [Department of Materials Science, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Wessels, Bruce W. [Department of Electrical Engineering & Computer Science, Northwestern University, Evanston, IL 60208 (United States); Department of Materials Science & Engineering, Northwestern University, Evanston, IL 60208 (United States); Sahakian, Alan V. [Department of Electrical Engineering & Computer Science, Northwestern University, Evanston, IL 60208 (United States); Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208 (United States)

    2015-11-15

    A novel spintronic computing paradigm is proposed and analyzed in which InSb p-n bilayer avalanche spin-diodes are cascaded to efficiently perform complex logic operations. This spin-diode logic family uses control wires to generate magnetic fields that modulate the resistance of the spin-diodes, and currents through these devices control the resistance of cascaded devices. Electromagnetic simulations are performed to demonstrate the cascading mechanism, and guidelines are provided for the development of this innovative computing technology. This cascading scheme permits compact logic circuits with switching speeds determined by electromagnetic wave propagation rather than electron motion, enabling high-performance spintronic computing.

  3. Bilayer avalanche spin-diode logic

    Directory of Open Access Journals (Sweden)

    Joseph S. Friedman

    2015-11-01

    Full Text Available A novel spintronic computing paradigm is proposed and analyzed in which InSb p-n bilayer avalanche spin-diodes are cascaded to efficiently perform complex logic operations. This spin-diode logic family uses control wires to generate magnetic fields that modulate the resistance of the spin-diodes, and currents through these devices control the resistance of cascaded devices. Electromagnetic simulations are performed to demonstrate the cascading mechanism, and guidelines are provided for the development of this innovative computing technology. This cascading scheme permits compact logic circuits with switching speeds determined by electromagnetic wave propagation rather than electron motion, enabling high-performance spintronic computing.

  4. Computer Simulations of Lipid Bilayers and Proteins

    DEFF Research Database (Denmark)

    Sonne, Jacob

    2006-01-01

    The importance of computer simulations in lipid bilayer research has become more prominent for the last couple of decades and as computers get even faster, simulations will play an increasingly important part of understanding the processes that take place in and across cell membranes. This thesis...... entitled Computer simulations of lipid bilayers and proteins describes two molecular dynamics (MD) simulation studies of pure lipid bilayers as well as a study of a transmembrane protein embedded in a lipid bilayer matrix. Below follows a brief overview of the thesis. Chapter 1. This chapter is a short......, Pressure profile calculations in lipid bilayers: A lipid bilayer is merely $\\sim$5~nm thick, but the lateral pressure (parallel to the bilayer plane) varies several hundred bar on this short distance (normal to the bilayer). These variations in the lateral pressure are commonly referred to as the pressure...

  5. Lipid Bilayer Membrane Perturbation by Embedded Nanopores: A Simulation Study.

    Science.gov (United States)

    Garcia-Fandiño, Rebeca; Piñeiro, Ángel; Trick, Jemma L; Sansom, Mark S P

    2016-03-22

    A macromolecular nanopore inserted into a membrane may perturb the dynamic organization of the surrounding lipid bilayer. To better understand the nature of such perturbations, we have undertaken a systematic molecular dynamics simulation study of lipid bilayer structure and dynamics around three different classes of nanopore: a carbon nanotube, three related cyclic peptide nanotubes differing in the nature of their external surfaces, and a model of a β-barrel nanopore protein. Periodic spatial distributions of several lipid properties as a function of distance from the nanopore were observed. This was especially clear for the carbon nanotube system, for which the density of lipids, the bilayer thickness, the projection of lipid head-to-tail vectors onto the membrane plane, and lipid lateral diffusion coefficients exhibited undulatory behavior as a function of the distance from the surface of the channel. Overall, the differences in lipid behavior as a function of the nanopore structure reveal local adaptation of the bilayer structure and dynamics to different embedded nanopore structures. Both the local structure and dynamic behavior of lipids around membrane-embedded nanopores are sensitive to the geometry and nature of the outer surface of the macromolecule/molecular assembly forming the pore. PMID:26943498

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

    Science.gov (United States)

    McIntosh, T J; Costello, M J

    1981-07-20

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

  7. On the application of the MARTINI coarse-grained model to immersion of a protein in a phospholipid bilayer

    International Nuclear Information System (INIS)

    An important step in the simulation of a membrane protein in a phospholipid bilayer is the correct immersion of the protein in the bilayer. Crystal structures are determined without the bilayer. Particularly for proteins with monotopic domains, it can be unclear how deeply and in which orientation the protein is being inserted in the membrane. We have previously developed a procedure combining coarse-grain (CG) with all-atom (AA) molecular dynamics (MD) simulations to insert and simulate a cytochrome P450 (CYP) possessing an N-terminal transmembrane helix connected by a flexible linker region to a globular domain that dips into the membrane. The CG simulations provide a computationally efficient means to explore different orientations and conformations of the CYP in the membrane. Converged configurations obtained in the CG simulations are then refined in AA simulations. Here, we tested different variants of the MARTINI CG model, differing in the water model, the treatment of long-range non-bonded interactions, and the implementation (GROMACS 4.5.5 vs 5.0.4), for this purpose. We examined the behavior of the models for simulating a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer in water and for the immersion of CYP3A4 in a POPC bilayer, and compared the CG-MD results with the previously reported experimental and simulation results. We also tested the methodology on a set of four other CYPs. Finally, we propose an optimized protocol for modeling such protein-membrane systems that provides the most plausible configurations and is computationally efficient; this incorporates the standard non-polar water model and the GROMACS 5.0.4 implementation with a reaction field treatment of long-range interactions

  8. On the application of the MARTINI coarse-grained model to immersion of a protein in a phospholipid bilayer

    Science.gov (United States)

    Mustafa, Ghulam; Nandekar, Prajwal P.; Yu, Xiaofeng; Wade, Rebecca C.

    2015-12-01

    An important step in the simulation of a membrane protein in a phospholipid bilayer is the correct immersion of the protein in the bilayer. Crystal structures are determined without the bilayer. Particularly for proteins with monotopic domains, it can be unclear how deeply and in which orientation the protein is being inserted in the membrane. We have previously developed a procedure combining coarse-grain (CG) with all-atom (AA) molecular dynamics (MD) simulations to insert and simulate a cytochrome P450 (CYP) possessing an N-terminal transmembrane helix connected by a flexible linker region to a globular domain that dips into the membrane. The CG simulations provide a computationally efficient means to explore different orientations and conformations of the CYP in the membrane. Converged configurations obtained in the CG simulations are then refined in AA simulations. Here, we tested different variants of the MARTINI CG model, differing in the water model, the treatment of long-range non-bonded interactions, and the implementation (GROMACS 4.5.5 vs 5.0.4), for this purpose. We examined the behavior of the models for simulating a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer in water and for the immersion of CYP3A4 in a POPC bilayer, and compared the CG-MD results with the previously reported experimental and simulation results. We also tested the methodology on a set of four other CYPs. Finally, we propose an optimized protocol for modeling such protein-membrane systems that provides the most plausible configurations and is computationally efficient; this incorporates the standard non-polar water model and the GROMACS 5.0.4 implementation with a reaction field treatment of long-range interactions.

  9. On the application of the MARTINI coarse-grained model to immersion of a protein in a phospholipid bilayer

    Energy Technology Data Exchange (ETDEWEB)

    Mustafa, Ghulam, E-mail: Ghulam.Mustafa@h-its.org, E-mail: rebecca.wade@h-its.org; Nandekar, Prajwal P.; Yu, Xiaofeng [Molecular and Cellular Modeling Group, Heidelberg Institute for Theoretical Studies (HITS), Schloß-Wolfsbrunnenweg 35, 69118 Heidelberg (Germany); Wade, Rebecca C., E-mail: Ghulam.Mustafa@h-its.org, E-mail: rebecca.wade@h-its.org [Molecular and Cellular Modeling Group, Heidelberg Institute for Theoretical Studies (HITS), Schloß-Wolfsbrunnenweg 35, 69118 Heidelberg (Germany); Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Alliance, INF 282, 69120 Heidelberg (Germany); Interdisciplinary Center for Scientific Computing (IWR), Heidelberg University, INF 368, 69120 Heidelberg (Germany)

    2015-12-28

    An important step in the simulation of a membrane protein in a phospholipid bilayer is the correct immersion of the protein in the bilayer. Crystal structures are determined without the bilayer. Particularly for proteins with monotopic domains, it can be unclear how deeply and in which orientation the protein is being inserted in the membrane. We have previously developed a procedure combining coarse-grain (CG) with all-atom (AA) molecular dynamics (MD) simulations to insert and simulate a cytochrome P450 (CYP) possessing an N-terminal transmembrane helix connected by a flexible linker region to a globular domain that dips into the membrane. The CG simulations provide a computationally efficient means to explore different orientations and conformations of the CYP in the membrane. Converged configurations obtained in the CG simulations are then refined in AA simulations. Here, we tested different variants of the MARTINI CG model, differing in the water model, the treatment of long-range non-bonded interactions, and the implementation (GROMACS 4.5.5 vs 5.0.4), for this purpose. We examined the behavior of the models for simulating a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer in water and for the immersion of CYP3A4 in a POPC bilayer, and compared the CG-MD results with the previously reported experimental and simulation results. We also tested the methodology on a set of four other CYPs. Finally, we propose an optimized protocol for modeling such protein-membrane systems that provides the most plausible configurations and is computationally efficient; this incorporates the standard non-polar water model and the GROMACS 5.0.4 implementation with a reaction field treatment of long-range interactions.

  10. CONCIDERING OF FUNDATION SLOPE TO DETERMINE THE ENGENEERING STRUCTURE HEIGHT

    OpenAIRE

    Zubko, Z.

    2005-01-01

    The article considers some aspects of determining of engineering structure height. It proposes the technique for terrain slope consideration in the course of base adjustment under difficult conditions of geodetic surveying.

  11. Bilayer graphene Hall bar with a pn-junction

    OpenAIRE

    Milovanovic, S. P.; Masir, M. Ramezani; Peeters, F. M.

    2013-01-01

    We investigate the magnetic field dependence of the Hall and the bend resistances for a ballistic Hall bar structure containing a pn-junction sculptured from a bilayer of graphene. The electric response is obtained using the billiard model and we investigate the cases of bilayer graphene with and without a band gap. Two different conduction regimes are possible: $i$) both sides of the junction have the same carrier type, and $ii$) one side of the junction is n-type while the other one is p-ty...

  12. Modification of glassy carbon electrode with a bilayer of multiwalled carbon nanotube/tiron-doped polypyrrole: Application to sensitive voltammetric determination of acyclovir

    International Nuclear Information System (INIS)

    A novel voltammetric sensor based on glassy carbon electrode (GCE) modified with a thin film of multi-walled carbon nanotubes (MWCNTs) coated with an electropolymerized layer of tiron-doped polypyrrole was developed and the resulting electrode was applied for the determination of acyclovir (ACV). The surface morphology and property of the modified electrode were characterized by field emission scanning electron microscopy and electrochemical impedance spectroscopy techniques. The electrochemical performance of the modified electrode was investigated by means of linear sweep voltammetry (LSV). The effect of several experimental variables, such as pH of the supporting electrolyte, drop size of the cast MWCNTssuspension, number of electropolymerization cycles and accumulation time was optimized by monitoring the LSV response of the modified electrode toward ACV. The best response was observed at pH 7.0 after accumulation at open circuit for 160 s. Under the optimized conditions, a significant electrochemical improvement was observed toward the electrooxidation of ACV on the modified electrode surface relative to the bare GCE, resulting in a wide linear dynamic range (0.03–10.0 μM) and a low detection limit (10.0 nM) for ACV. Besides high sensitivity, the sensor represented high stability and good reproducibility for ACV analysis, and provided satisfactory results for the determination of this compound in pharmaceutical and clinical preparations. - Highlights: • A simple method was employed to construct a thin film modified electrode. • Tiron-doped polypyrrole was electropolymerized on MWCNT precast glassy carbon electrode. • Electrode surface characterization was performed by microscopic and spectroscopic techniques. • The modified electrode showed nano-molar detection limit for acyclovir. • The modified electrode was applied for the detection of ACV in pharmaceutical and clinical preparations

  13. Modification of glassy carbon electrode with a bilayer of multiwalled carbon nanotube/tiron-doped polypyrrole: Application to sensitive voltammetric determination of acyclovir

    Energy Technology Data Exchange (ETDEWEB)

    Shahrokhian, Saeed, E-mail: shahrokhian@sharif.edu [Department of Chemistry, Sharif University of Technology, Tehran 11155-3516 (Iran, Islamic Republic of); Institute for Nanoscience and Technology, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Azimzadeh, Mahnaz [Department of Chemistry, Sharif University of Technology, Tehran 11155-3516 (Iran, Islamic Republic of); Amini, Mohammad K. [Department of Chemistry, Isfahan University, Isfahan (Iran, Islamic Republic of)

    2015-08-01

    A novel voltammetric sensor based on glassy carbon electrode (GCE) modified with a thin film of multi-walled carbon nanotubes (MWCNTs) coated with an electropolymerized layer of tiron-doped polypyrrole was developed and the resulting electrode was applied for the determination of acyclovir (ACV). The surface morphology and property of the modified electrode were characterized by field emission scanning electron microscopy and electrochemical impedance spectroscopy techniques. The electrochemical performance of the modified electrode was investigated by means of linear sweep voltammetry (LSV). The effect of several experimental variables, such as pH of the supporting electrolyte, drop size of the cast MWCNTssuspension, number of electropolymerization cycles and accumulation time was optimized by monitoring the LSV response of the modified electrode toward ACV. The best response was observed at pH 7.0 after accumulation at open circuit for 160 s. Under the optimized conditions, a significant electrochemical improvement was observed toward the electrooxidation of ACV on the modified electrode surface relative to the bare GCE, resulting in a wide linear dynamic range (0.03–10.0 μM) and a low detection limit (10.0 nM) for ACV. Besides high sensitivity, the sensor represented high stability and good reproducibility for ACV analysis, and provided satisfactory results for the determination of this compound in pharmaceutical and clinical preparations. - Highlights: • A simple method was employed to construct a thin film modified electrode. • Tiron-doped polypyrrole was electropolymerized on MWCNT precast glassy carbon electrode. • Electrode surface characterization was performed by microscopic and spectroscopic techniques. • The modified electrode showed nano-molar detection limit for acyclovir. • The modified electrode was applied for the detection of ACV in pharmaceutical and clinical preparations.

  14. Bilayer holey plasmonic vortex lenses for the far field transmission of pure orbital angular momentum light states.

    Science.gov (United States)

    Zilio, Pierfrancesco; Parisi, Giuseppe; Garoli, Denis; Carli, Marta; Romanato, Filippo

    2014-08-15

    We report the design of a holey plasmonic vortex lens (PVL) structure able to couple circularly polarized impinging light to a plasmonic vortex in the form of the fundamental TM mode of a metal-insulator-metal plasmonic waveguide. The field transmitted through the hole milled at the center of the second metal layer of the structure is characterized by a well-defined spiral harmonic, entirely determined by the spin of impinging light and by the chirality of the PVL structure. Scattering finite elements simulations are presented for single layer standard PVLs and for bilayer ones, comparing the spiral spectra of the transmitted field and the efficiencies of the architectures. PMID:25121903

  15. Preisach analysis of epitaxial hard/soft bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Cornejo, D.R.; Rhen, F.M.; Missell, F.P. E-mail: fmissell@macbeth.if.usp.br; Fullerton, E.E

    2001-05-01

    We used the moving Preisach model to study the magnetization-reversal process in epitaxial SmCo (1 1 =macron 0 0)/Fe bilayers prepared by magnetron sputtering. The SmCo(20 nm)/Fe(t nm) (t=0, 5, 10, 20) bilayers were grown onto single-crystal (1 1 0)MgO substrates with an epitaxial 20 nm Cr(2 1 1) buffer layer. The second-quadrant magnetization curves were strictly reversible up to a field H{sub 0}, close to the field H{sub c} at which the magnetization switched irreversibly. Henkel plots for these bilayers indicated very strong magnetizing interactions for all films. Magnetization reversal in these films reflects their epitaxial structure.

  16. Neutron diffraction studies of amphipathic helices in phospholipid bilayers

    International Nuclear Information System (INIS)

    The structural feature which is thought to facilitate the interaction of many peptides with phospholipid bilayers is the ability to fold into an amphipathic helix. In most cases the exact location and orientation of this helix with respect to the membrane is not known, and may vary with factors such as pH and phospholipid content of the bilayer. The growing interest in this area is stimulated by indications that similar interactions can contribute to the binding of certain hormones to their cell-surface receptors. We have been using the techniques of neutron diffraction from stacked phospholipid bilayers in an attempt to investigate this phenomenon with a number of membrane-active peptides. Here we report some of our findings with three of these: the bee venom melittin; the hormone calcitonin; and a synthetic peptide representing the ion channel fragment of influenza A M2 protein

  17. Neutron diffraction studies of amphipathic helices in phospholipid bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Bradshaw, J.P.; Gilchrist, P.J. [Univ. of Edinburgh (United Kingdom); Duff, K.C. [Univ. of Edinburgh Medical School (United Kingdom); Saxena, A.M. [Brookhaven National Laboratory, Upton, NY (United States)

    1994-12-31

    The structural feature which is thought to facilitate the interaction of many peptides with phospholipid bilayers is the ability to fold into an amphipathic helix. In most cases the exact location and orientation of this helix with respect to the membrane is not known, and may vary with factors such as pH and phospholipid content of the bilayer. The growing interest in this area is stimulated by indications that similar interactions can contribute to the binding of certain hormones to their cell-surface receptors. We have been using the techniques of neutron diffraction from stacked phospholipid bilayers in an attempt to investigate this phenomenon with a number of membrane-active peptides. Here we report some of our findings with three of these: the bee venom melittin; the hormone calcitonin; and a synthetic peptide representing the ion channel fragment of influenza A M2 protein.

  18. Edge State and Intrinsic Hole Doping in Bilayer Phosphorene

    Science.gov (United States)

    Osada, Toshihito

    2015-01-01

    Using a simple LCAO model by Harrison, we have qualitatively studied the edge state of bilayer phosphorene, which is a unit structure of the layered crystal of black phosphorus. This model successfully reproduces the isolated edge state in the bulk gap in monolayer phosphorene. In bilayer phosphorene, however, it shows that edge states are almost buried in the valence band and there is no isolated midgap edge state at the zigzag edge. Since the buried edge state works as acceptor, holes are doped from the edge state into the bulk. This gives a possible explanation for p-type conduction in undoped black phosphorus. Under the vertical electric field, the intrinsic hole doping is reduced because a part of edge states move into the gap. These features of bilayer phosphorene might be better suited for device application.

  19. Electronic transport in B-N substituted bilayer graphene nanojunctions

    Science.gov (United States)

    Giofré, Daniele; Ceresoli, Davide; Fratesi, Guido; Trioni, Mario I.

    2016-05-01

    We investigated a suspended bilayer graphene where the bottom/top layer is doped by boron/nitrogen substitutional atoms. By using density functional theory calculations, we found that at high dopant concentration (one B-N pair every 32 C atoms), the electronic structure of the bilayer does not depend on the B-N distance but on the relative occupation of the bilayer graphene sublattices by B and N. The presence of the dopants and the consequent charge transfer establish a built-in electric field between the layers, giving rise to an energy gap. We further investigated the electronic transport properties and found that intralayer current is weakly influenced by the presence of these dopants while the interlayer one is enhanced for biases, allowing an easy tunneling between layers. This effect leads to current rectification in asymmetric junctions.

  20. Equilibrium Configurations of Lipid Bilayer Membranes and Carbon Nanostructures

    Institute of Scientific and Technical Information of China (English)

    Iva(i)lo M.Mladenov; Peter A.Djondjorov; Mariana Ts.Hadzhilazova; Vassil M.Vassilev

    2013-01-01

    The present article concerns the continuum modelling of the mechanical behaviour and equilibrium shapes of two types of nano-scale objects:fluid lipid bilayer membranes and carbon nanostructures.A unified continuum model is used to handle four different case studies.Two of them consist in representing in analytic form cylindrical and axisymmetric equilibrium configurations of single-wall carbon nanotubes and fluid lipid bilayer membranes subjected to uniform hydrostatic pressure.The third one is concerned with determination of possible shapes of junctions between a single-wall carbon nanotube and a fiat graphene sheet or another single-wall carbon nanotube.The last one deals with the mechanical behaviour of closed fluid lipid bilayer membranes (vesicles) adhering onto a fiat homogeneous rigid substrate subjected to micro-injection and uniform hydrostatic pressure.

  1. NMRFAM-SDF: a protein structure determination framework

    International Nuclear Information System (INIS)

    The computationally demanding nature of automated NMR structure determination necessitates a delicate balancing of factors that include the time complexity of data collection, the computational complexity of chemical shift assignments, and selection of proper optimization steps. During the past two decades the computational and algorithmic aspects of several discrete steps of the process have been addressed. Although no single comprehensive solution has emerged, the incorporation of a validation protocol has gained recognition as a necessary step for a robust automated approach. The need for validation becomes even more pronounced in cases of proteins with higher structural complexity, where potentially larger errors generated at each step can propagate and accumulate in the process of structure calculation, thereby significantly degrading the efficacy of any software framework. This paper introduces a complete framework for protein structure determination with NMR—from data acquisition to the structure determination. The aim is twofold: to simplify the structure determination process for non-NMR experts whenever feasible, while maintaining flexibility by providing a set of modules that validate each step, and to enable the assessment of error propagations. This framework, called NMRFAM-SDF (NMRFAM-Structure Determination Framework), and its various components are available for download from the NMRFAM website ( http://nmrfam.wisc.edu/software.htm http://nmrfam.wisc.edu/software.htm )

  2. NMRFAM-SDF: a protein structure determination framework.

    Science.gov (United States)

    Dashti, Hesam; Lee, Woonghee; Tonelli, Marco; Cornilescu, Claudia C; Cornilescu, Gabriel; Assadi-Porter, Fariba M; Westler, William M; Eghbalnia, Hamid R; Markley, John L

    2015-08-01

    The computationally demanding nature of automated NMR structure determination necessitates a delicate balancing of factors that include the time complexity of data collection, the computational complexity of chemical shift assignments, and selection of proper optimization steps. During the past two decades the computational and algorithmic aspects of several discrete steps of the process have been addressed. Although no single comprehensive solution has emerged, the incorporation of a validation protocol has gained recognition as a necessary step for a robust automated approach. The need for validation becomes even more pronounced in cases of proteins with higher structural complexity, where potentially larger errors generated at each step can propagate and accumulate in the process of structure calculation, thereby significantly degrading the efficacy of any software framework. This paper introduces a complete framework for protein structure determination with NMR--from data acquisition to the structure determination. The aim is twofold: to simplify the structure determination process for non-NMR experts whenever feasible, while maintaining flexibility by providing a set of modules that validate each step, and to enable the assessment of error propagations. This framework, called NMRFAM-SDF (NMRFAM-Structure Determination Framework), and its various components are available for download from the NMRFAM website (http://nmrfam.wisc.edu/software.htm). PMID:25900069

  3. NMRFAM-SDF: a protein structure determination framework

    Energy Technology Data Exchange (ETDEWEB)

    Dashti, Hesam; Lee, Woonghee; Tonelli, Marco; Cornilescu, Claudia C.; Cornilescu, Gabriel; Assadi-Porter, Fariba M.; Westler, William M.; Eghbalnia, Hamid R.; Markley, John L., E-mail: markley@nmrfam.wisc.edu [University of Wisconsin-Madison, National Magnetic Resonance Facility at Madison, Biochemistry Department (United States)

    2015-08-15

    The computationally demanding nature of automated NMR structure determination necessitates a delicate balancing of factors that include the time complexity of data collection, the computational complexity of chemical shift assignments, and selection of proper optimization steps. During the past two decades the computational and algorithmic aspects of several discrete steps of the process have been addressed. Although no single comprehensive solution has emerged, the incorporation of a validation protocol has gained recognition as a necessary step for a robust automated approach. The need for validation becomes even more pronounced in cases of proteins with higher structural complexity, where potentially larger errors generated at each step can propagate and accumulate in the process of structure calculation, thereby significantly degrading the efficacy of any software framework. This paper introduces a complete framework for protein structure determination with NMR—from data acquisition to the structure determination. The aim is twofold: to simplify the structure determination process for non-NMR experts whenever feasible, while maintaining flexibility by providing a set of modules that validate each step, and to enable the assessment of error propagations. This framework, called NMRFAM-SDF (NMRFAM-Structure Determination Framework), and its various components are available for download from the NMRFAM website ( http://nmrfam.wisc.edu/software.htm http://nmrfam.wisc.edu/software.htm )

  4. Determination of absolute structure using Bayesian statistics on Bijvoet differences

    NARCIS (Netherlands)

    Hooft, R.W.W.; Straver, L.H.; Spek, A.L.

    2008-01-01

    A new probabilistic approach is introduced for the determination of the absolute structure of a compound which is known to be enantiopure based on Bijvoet-pair intensity differences. The new method provides relative probabilities for different models of the chiral composition of the structure. The o

  5. Generative probabilistic models extend the scope of inferential structure determination

    DEFF Research Database (Denmark)

    Olsson, Simon; Boomsma, Wouter; Frellsen, Jes;

    2011-01-01

    Conventional methods for protein structure determination from NMR data rely on the ad hoc combination of physical forcefields and experimental data, along with heuristic determination of free parameters such as weight of experimental data relative to a physical forcefield. Recently, a theoretical...

  6. Labor Market Structure and Salary Determination among Professional Basketball Players.

    Science.gov (United States)

    Wallace, Michael

    1988-01-01

    The author investigates the labor market structure and determinants of salaries for professional basketball players. An expanded version of the resource perspective is used. A three-tiered model of labor market segmentation is revealed for professional basketball players, but other variables also are important in salary determination. (Author/CH)

  7. Determinants of euro term structure of credit spreads

    OpenAIRE

    Astrid Van Landschoot

    2004-01-01

    In this paper, we investigate the determinants of the Euro term structure of credit spreads. More specifically, we analyze whether the sensitivity of credit spread changes to financial and macroeconomic variables depends on bond characteristics such as rating and maturity. According to the structural models and empirical evidence on credit spreads, we find that changes in the level and the slope of the default-free term structure, the market return, implied volatility, and liquidity risk sign...

  8. Determinants of Capital Structure: A Cross-Country Comparison

    OpenAIRE

    Martin, James

    2013-01-01

    This paper is a cross-country comparison of capital structure; specifically its firm level determinants and how these fluctuate between both Japan and the United States to test the efficacy of competing capital structure theories within contrasting institutional traditions. The purpose of the study is to bring to light the possible effect of such institutional differences on the capital structure decision for financial managers. I utilize a pre-crisis sample of 292 firms, 147 from Japan and 1...

  9. Determinants of Capital Structure: An Empirical Analysis of UK Organisations.

    OpenAIRE

    Gundroo, Shadaab/ SG

    2009-01-01

    In modern day finance, capital structure remains one of those issues under much controversy despite extensive research from academics and practitioners alike. There is a number of existing theories and empirical work on capital structure but as of yet no universal model has been found. The aim of this paper is to analyze the determinants of the capital structure of 73 UK companies over a 5 year period (2004-2008). This study adds to the relatively limited empirical literature on factors infl...

  10. Structural determination of wild-type lactose permease

    OpenAIRE

    Guan, Lan; Mirza, Osman; Verner, Gillian; Iwata, So; Kaback, H. Ronald

    2007-01-01

    Here we describe an x-ray structure of wild-type lactose permease (LacY) from Escherichia coli determined by manipulating phospholipid content during crystallization. The structure exhibits the same global fold as the previous x-ray structures of a mutant that binds sugar but cannot catalyze translocation across the membrane. LacY is organized into two six-helix bundles with twofold pseudosymmetry separated by a large interior hydrophilic cavity open only to the cytoplasmic side and containin...

  11. STRUCTURAL UNEMPLOYMENT AND ITS DETERMINANTS IN SOUTHEAST EUROPE

    OpenAIRE

    Botrić, Valerija

    2011-01-01

    This paper provides comparative analysis of the structural unemployment for a group of transition countries in Southeast Europe, based on relatively simple measure, NAWRU. The paper also investigates and discusses the determinants of relatively high structural unemployment in the region. The results of the empirical estimates point to the remittances and overall changes in business climate as being the significant variables that explain relatively high structural unemployment in analyzed coun...

  12. The determinants of capital structure: Some evidence from banks

    OpenAIRE

    Heider, Florian; Gropp, Reint

    2008-01-01

    This paper documents that standard cross-sectional determinants of firm leverage also apply to the capital structure of large banks in the United States and Europe. We find a remarkable consistency in sign, significance and economic magnitude. Like non-financial firms, banks appear to have stable capital structures at levels that are specific to each individual bank. The results suggest that capital requirements may only be of second-order importance for banks’ capital structures and confirm ...

  13. Growth and characterization of the ZnO/ZnS bilayer obtained by chemical spray pyrolysis

    International Nuclear Information System (INIS)

    ZnO/ZnS bilayer antireflection coatings have been prepared by spray pyrolysis using aqueous solutions of zinc acetate and thiourea or zinc chloride and thiourea. The structure, surface morphology, chemical composition and optical transmittance of the bilayer have been examined as a function of the composition of the initial solution. X-ray photoelectron spectroscopy analysis and Ar ion-beam sputter etching was carried out to obtain a depth profile of bilayer. Neither carbon nor other by-products, which could alter the optical transmittance of the bilayer were found in either the interface or bulk. The differences between the bilayers arise from the annealing of the ZnS underlayer, as well as the precursor used to prepare it.

  14. Edge states of zigzag bilayer graphite nanoribbons

    Science.gov (United States)

    Rhim, Jun-Won; Moon, Kyungsun

    2008-09-01

    The electronic structures of zigzag bilayer graphite nanoribbons (Z-BGNRs) with various ribbon widths N are studied within the tight binding approximation. Neglecting the inter-layer hopping amplitude γ4, which is an order of magnitude smaller than the other inter-layer hopping parameters, there exist two fixed Fermi points ± k* independent of the ribbon width with a peculiar energy dispersion near k* as ɛ(k)~ ± (k-k*)N. By investigating the edge states of Z-BGNRs, we notice that the trigonal warping of the bilayer graphene sheets is reflected in the edge state structure. With the inclusion of γ4, the above two Fermi points are not fixed but drift toward the vicinity of the Dirac point with increasing width N, as shown by the finite scaling method, and the peculiar dispersions change to parabolic ones. The edge magnetism of Z-BGNRs is also examined by solving the half-filled Hubbard Hamiltonian for the ribbon using the Hartree-Fock approximation. We have shown that within the same side of the edges, the edge spins are aligned ferromagnetically for the experimentally relevant set of parameters.

  15. Edge states of zigzag bilayer graphite nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Rhim, Jun-Won; Moon, Kyungsun [Department of Physics and Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749 (Korea, Republic of)], E-mail: kmoon@yonsei.ac.kr

    2008-09-10

    The electronic structures of zigzag bilayer graphite nanoribbons (Z-BGNRs) with various ribbon widths N are studied within the tight binding approximation. Neglecting the inter-layer hopping amplitude {gamma}{sub 4}, which is an order of magnitude smaller than the other inter-layer hopping parameters, there exist two fixed Fermi points {+-} k{sup *} independent of the ribbon width with a peculiar energy dispersion near k{sup *} as {epsilon}(k){approx} {+-} (k-k{sup *}){sup N}. By investigating the edge states of Z-BGNRs, we notice that the trigonal warping of the bilayer graphene sheets is reflected in the edge state structure. With the inclusion of {gamma}{sub 4}, the above two Fermi points are not fixed but drift toward the vicinity of the Dirac point with increasing width N, as shown by the finite scaling method, and the peculiar dispersions change to parabolic ones. The edge magnetism of Z-BGNRs is also examined by solving the half-filled Hubbard Hamiltonian for the ribbon using the Hartree-Fock approximation. We have shown that within the same side of the edges, the edge spins are aligned ferromagnetically for the experimentally relevant set of parameters.

  16. Integral membrane protein structure determination using pseudocontact shifts

    International Nuclear Information System (INIS)

    Obtaining enough experimental restraints can be a limiting factor in the NMR structure determination of larger proteins. This is particularly the case for large assemblies such as membrane proteins that have been solubilized in a membrane-mimicking environment. Whilst in such cases extensive deuteration strategies are regularly utilised with the aim to improve the spectral quality, these schemes often limit the number of NOEs obtainable, making complementary strategies highly beneficial for successful structure elucidation. Recently, lanthanide-induced pseudocontact shifts (PCSs) have been established as a structural tool for globular proteins. Here, we demonstrate that a PCS-based approach can be successfully applied for the structure determination of integral membrane proteins. Using the 7TM α-helical microbial receptor pSRII, we show that PCS-derived restraints from lanthanide binding tags attached to four different positions of the protein facilitate the backbone structure determination when combined with a limited set of NOEs. In contrast, the same set of NOEs fails to determine the correct 3D fold. The latter situation is frequently encountered in polytopical α-helical membrane proteins and a PCS approach is thus suitable even for this particularly challenging class of membrane proteins. The ease of measuring PCSs makes this an attractive route for structure determination of large membrane proteins in general

  17. Integral membrane protein structure determination using pseudocontact shifts

    Energy Technology Data Exchange (ETDEWEB)

    Crick, Duncan J.; Wang, Jue X. [University of Cambridge, Department of Biochemistry (United Kingdom); Graham, Bim; Swarbrick, James D. [Monash University, Monash Institute of Pharmaceutical Sciences (Australia); Mott, Helen R.; Nietlispach, Daniel, E-mail: dn206@cam.ac.uk [University of Cambridge, Department of Biochemistry (United Kingdom)

    2015-04-15

    Obtaining enough experimental restraints can be a limiting factor in the NMR structure determination of larger proteins. This is particularly the case for large assemblies such as membrane proteins that have been solubilized in a membrane-mimicking environment. Whilst in such cases extensive deuteration strategies are regularly utilised with the aim to improve the spectral quality, these schemes often limit the number of NOEs obtainable, making complementary strategies highly beneficial for successful structure elucidation. Recently, lanthanide-induced pseudocontact shifts (PCSs) have been established as a structural tool for globular proteins. Here, we demonstrate that a PCS-based approach can be successfully applied for the structure determination of integral membrane proteins. Using the 7TM α-helical microbial receptor pSRII, we show that PCS-derived restraints from lanthanide binding tags attached to four different positions of the protein facilitate the backbone structure determination when combined with a limited set of NOEs. In contrast, the same set of NOEs fails to determine the correct 3D fold. The latter situation is frequently encountered in polytopical α-helical membrane proteins and a PCS approach is thus suitable even for this particularly challenging class of membrane proteins. The ease of measuring PCSs makes this an attractive route for structure determination of large membrane proteins in general.

  18. Low-energy theory for the graphene twist bilayer

    Science.gov (United States)

    Weckbecker, D.; Shallcross, S.; Fleischmann, M.; Ray, N.; Sharma, S.; Pankratov, O.

    2016-01-01

    The graphene twist bilayer represents the prototypical system for investigating the stacking degree of freedom in few-layer graphenes. The electronic structure of this system changes qualitatively as a function of angle, from a large-angle limit in which the two layers are essentially decoupled—with the exception of a 28-atom commensuration unit cell for which the layers are coupled on an energy scale of ≈8 meV —to a small-angle strong-coupling limit. Despite sustained investigation, a fully satisfactory theory of the twist bilayer remains elusive. The outstanding problems are (i) to find a theoretically unified description of the large- and small-angle limits, and (ii) to demonstrate agreement between the low-energy effective Hamiltonian and, for instance, ab initio or tight-binding calculations. In this article, we develop a low-energy theory that in the large-angle limit reproduces the symmetry-derived Hamiltonians of Mele [Phys. Rev. B 81, 161405 (2010), 10.1103/PhysRevB.81.161405], and in the small-angle limit shows almost perfect agreement with tight-binding calculations. The small-angle effective Hamiltonian is that of Bistritzer and MacDonald [Proc. Natl. Acad. Sci. (U.S.A.) 108, 12233 (2011), 10.1073/pnas.1108174108], but with the momentum scale Δ K , the difference of the momenta of the unrotated and rotated special points, replaced by a coupling momentum scale g(c )=8/π √{3 }a sinθ/2 . Using this small-angle Hamiltonian, we are able to determine the complete behavior as a function of angle, finding a complex small-angle clustering of van Hove singularities in the density of states (DOS) that after a "zero-mode" peak regime between 0 .90°energy surfaces with multiple Lifshitz transitions between K - and Γ -centered Fermi sheets and a rich pseudospin texture.

  19. Structural determination of intact proteins using mass spectrometry

    Science.gov (United States)

    Kruppa, Gary; Schoeniger, Joseph S.; Young, Malin M.

    2008-05-06

    The present invention relates to novel methods of determining the sequence and structure of proteins. Specifically, the present invention allows for the analysis of intact proteins within a mass spectrometer. Therefore, preparatory separations need not be performed prior to introducing a protein sample into the mass spectrometer. Also disclosed herein are new instrumental developments for enhancing the signal from the desired modified proteins, methods for producing controlled protein fragments in the mass spectrometer, eliminating complex microseparations, and protein preparatory chemical steps necessary for cross-linking based protein structure determination.Additionally, the preferred method of the present invention involves the determination of protein structures utilizing a top-down analysis of protein structures to search for covalent modifications. In the preferred method, intact proteins are ionized and fragmented within the mass spectrometer.

  20. Energy group structure determination using particle swarm optimization

    International Nuclear Information System (INIS)

    Highlights: ► Particle swarm optimization is applied to determine broad group structure. ► A graph representation of the broad group structure problem is introduced. ► The approach is tested on a fuel-pin model. - Abstract: Multi-group theory is widely applied for the energy domain discretization when solving the Linear Boltzmann Equation. To reduce the computational cost, fine group cross libraries are often down-sampled into broad group cross section libraries. Cross section data collapsing generally involves two steps: Firstly, the broad group structure has to be determined; secondly, a weighting scheme is used to evaluate the broad cross section library based on the fine group cross section data and the broad group structure. A common scheme is to average the fine group cross section weighted by the fine group flux. Cross section collapsing techniques have been intensively researched. However, most studies use a pre-determined group structure, open based on experience, to divide the neutron energy spectrum into thermal, epi-thermal, fast, etc. energy range. In this paper, a swarm intelligence algorithm, particle swarm optimization (PSO), is applied to optimize the broad group structure. A graph representation of the broad group structure determination problem is introduced. And the swarm intelligence algorithm is used to solve the graph model. The effectiveness of the approach is demonstrated using a fuel-pin model

  1. Electromechanical Oscillations in Bilayer Graphene

    OpenAIRE

    Benameur, Muhammed M.; Gargiulo, Fernando; Manzeli, Sajedeh; Autès, Gabriel; Tosun, Mahmut; Yazyev, Oleg V.; Kis, Andras

    2015-01-01

    Nanoelectromechanical systems constitute a class of devices lying at the interface between fundamental research and technological applications. Realizing nanoelectromechanical devices based on novel materials such as graphene allows studying their mechanical and electromechanical characteristics at the nanoscale and addressing fundamental questions such as electron–phonon interaction and bandgap engineering. In this work, we realize electromechanical devices using single and bilayer graphene ...

  2. Molecular dynamics simulations and free energy profile of Paracetamol in DPPC and DMPC lipid bilayers

    Indian Academy of Sciences (India)

    Yousef Nademi; Sepideh Amjad Iranagh; Abbas Yousefpour; Seyedeh Zahra Mousavi; Hamid Modarress

    2014-05-01

    Molecular dynamics (MD) simulations and biased MD simulation were carried out for the neutral form of Paracetamol inserted in fully hydrated dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) lipid bilayers. For comparison, fully hydrated DMPC and DPPC lipid bilayers were also simulated separately without Paracetamol. The simulation time for each system was 50 ns. At two concentrations of Paracetamol, various properties of the lipid bilayer such as area per lipid, order parameter, diffusion coefficient, radial distribution function, electrostatic potential, mass density and hydrogen bonds have been calculated. Also, the convergence in time of the free energy profile of the Paracetamol along a DPPC bilayer normal was calculated by umbrella sampling method. From the obtained results, it can be concluded that neutral form of Paracetamol shows a generally similar behaviour in DPPC and DMPC lipid bilayers. It was shown that the addition of Paracetamol causes a decrease in tail order parameter of both DPPC and DMPC lipid bilayers and the tail of Paracetamol adopts an inward orientation in the lipid bilayers. Also from the free energy profile, the high penetration barrier in the bilayer centre was determined.

  3. Microstructural characterization, optical and photocatalytic properties of bilayered CuO and ZnO based thin films

    Energy Technology Data Exchange (ETDEWEB)

    Sáenz-Trevizo, A.; Amézaga-Madrid, P.; Pizá-Ruiz, P.; Solís-Canto, O.; Ornelas-Gutiérrez, C.; Pérez-García, S.; Miki-Yoshida, M., E-mail: mario.miki@cimav.edu.mx

    2014-12-05

    Highlights: • High quality bilayered Zn–Cu oxide thin films were deposited by aerosol assisted CVD. • Detailed microstructural characterization was performed by XRD and electron microscopy. • Absorbance of bilayered films shows a shift of absorption edge toward visible region. • Optical band gap or nearly 3.2 and 2 eV was determined for ZnO and Cu oxide. • High photocatalytic activity around 90% was obtained for bilayered samples. - Abstract: In this work, it is presented the synthesis, microstructural characterization and photocatalytic properties of bilayered CuO–ZnO/ZnO thin films onto borosilicate glass and fused silica substrates. The films were deposited by aerosol assisted chemical vapor deposition, using an experimental setup reported elsewhere. Deposition conditions were optimized to get high quality films; i.e. they were structurally uniform, highly transparent, non-light scattering, homogeneous, and well adhered to the substrate. Different Cu/Zn atomic ratios were tried for the upper layer. The microstructure of the films was characterized by grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy. GIXRD results indicate the presence of ZnO Wurzite and Cu oxide phases. Results of SEM and HRTEM analysis of the cross sectional microstructure showed that the films were composed of compact and dense layers with no visible evidence of an interfacial boundary or porosity. Optical absorbance of the bilayered films showed a clear shift of the absorption toward the visible range. Optical band gap was determined roughly at 3.2 and 2 eV for ZnO and Cu oxide, respectively. Photocatalytic activity of the samples, for the degradation of a 10{sup −5} mol dm{sup −3} solution of methylene blue (MB), was determined after 120 and 240 min of irradiation with an UV-A source. Around 90% of MB degradation was reached by bilayered films with

  4. EFFECTS OF CHOLESTEROL ON THE LIPID BILAYER STRUCTURE BY SAXS AND STM%胆固醇对脂双层结构影响的SAXS和STM研究

    Institute of Scientific and Technical Information of China (English)

    孙润广; 张静; 齐浩; 王永昌

    2001-01-01

    用小角X射线散射(SAXS)和扫描隧道显微镜(STM)技术分别研究了模拟生物膜脂质体的结构以及胆固醇对生物膜双层结构的影响.结果表明,在扫描隧道显微镜照片中,磷脂分子在石墨表面形成规则的二维点状排列图像;磷脂胆固醇脂质体在石墨表面形成规则的二维波纹状排列图像。用小角X射线散射研究结果表明,DPPC脂质体是片层相结构,DPPC+Chol脂质体是复相片层结构,DPPE+Chol脂质体是片层立方相结构,DPPC+DPPE+Chol脂质体是立方六角形相结构。%The effect of cholesterol on the phospholipid bilayer structureand polymorphism of liposomes have been investigated by method of the small angle X-ray diffraction (SAXS) and by the technique of scanning tunneling microscope (STM).The experiments proved that the STM images of the two-dimensional point array of the phospholipid molecules formed on graphite and that the STM images of the two-dimensional corrugated array of the liposomes of phospholipid and cholesterol formed on graphite.By using small angle X-ray diffraction we demonstrate the presence of lamellar phase in the DPPC liposomes.The cholesterol induces spontaneous formation of a complex lamellar phase in the DPPC-cholesterol liposomes and promotes formation of lamellar and cubic phase in the DPPE-cholesterol liposomes.The presence of cholesterol allowed the system to organize in cubic and hexagonal phase in DPPC-DPPE-cholesterol liposomes.

  5. Focused-ion-beam induced interfacial intermixing of magnetic bilayers for nanoscale control of magnetic properties

    International Nuclear Information System (INIS)

    Modification of the magnetic properties in a thin-film ferromagnetic/non-magnetic bilayer system by low-dose focused ion-beam (FIB) induced intermixing is demonstrated. The highly localized capability of FIB may be used to locally control magnetic behaviour at the nanoscale. The magnetic, electronic and structural properties of NiFe/Au bilayers were investigated as a function of the interfacial structure that was actively modified using focused Ga+ ion irradiation. Experimental work used MOKE, SQUID, XMCD as well as magnetoresistance measurements to determine the magnetic behavior and grazing incidence x-ray reflectivity to elucidate the interfacial structure. Interfacial intermixing, induced by low-dose irradiation, is shown to lead to complex changes in the magnetic behavior that are associated with monotonic structural evolution of the interface. This behavior may be explained by changes in the local atomic environment within the interface region resulting in a combination of processes including the loss of moment on Ni and Fe, an induced moment on Au and modifications to the spin-orbit coupling between Au and NiFe. (paper)

  6. Transformation from AA to AB-Stacked Bilayer Graphene on α-SiO2 under an Electric Field

    Institute of Scientific and Technical Information of China (English)

    LIU Yan; AO Zhi-Min; WANG Tao; WANG Wen-Bo; SHENG Kuang; YU Bin

    2011-01-01

    @@ The energetic and electronic structure of bilayered graphene(BLG) with AA stacking arrangement on a SiO2 substrate is investigated in the presence of an electric field F of different intensities by ab initio density functional calculations.The AA-stacked bilayer graphene is stable on the SiO2 substrate in the absence of an electric field.However, as F increases, the AA-stacked bilayer graphenes are gradually shifted with each other and finally transfers into AB-stacked bilayer graphenes.The bandgap is accordingly changed.

  7. Millimeter-area, free standing, phospholipid bilayers.

    Science.gov (United States)

    Beltramo, Peter J; Van Hooghten, Rob; Vermant, Jan

    2016-05-11

    Minimal model biomembrane studies have the potential to unlock the fundamental mechanisms of cellular function that govern the processes upon which life relies. However, existing methods to fabricate free-standing model membranes currently have significant limitations. Bilayer sizes are often tens of micrometers, decoupling curvature or substrate effects, orthogonal control over tension, and solvent exchange combined with microscopy techniques is not possible, which restricts the studies that can be performed. Here, we describe a versatile platform to generate free standing, planar, phospholipid bilayers with millimeter scale areas. The technique relies on an adapted thin-film balance apparatus allowing for the dynamic control of the nucleation and growth of a planar black lipid membrane in the center of an orifice surrounded by microfluidic channels. Success is demonstrated using several different lipid types, including mixtures that show the same temperature dependent phase separation as existing protocols, moreover, membranes are highly stable. Two advantages unique to the proposed method are the dynamic control of the membrane tension and the possibility to make extremely large area membranes. We demonstrate this by showing how a block polymer, F68, used in drug delivery increases the membrane compliance. Together, the results demonstrate a new paradigm for studying the mechanics, structure, and function of model membranes. PMID:27050618

  8. Contribution to structural determination of triterpenes by computer aid

    International Nuclear Information System (INIS)

    The development of nuclear magnetic resonance has made possible the structural knowledge of several substances. In this work, 13C NMR were used to identify the molecular structure of triterpenes. A system composed by several routines written in FOXBASIC was developed to be used as a help to structural determination of triterpenes. A database of 1,000 triterpenes belonging to different backbones was built. The fields contain the chemical shift of each carbon in the molecule and a 10 digit hexadecimal code that characterizes the carbon environment. The code with the general formula: C. α1 α2 α3 α4. A1 A1E. β1 β2, where C designates the nature of the carbon responsible for the chemical shift and the other symbols represent its chemical environment. This system showed to be useful in structure determination of known and unknown triterpenes. (author)

  9. Charge order and phase segregation in overdoped bilayer manganites

    Energy Technology Data Exchange (ETDEWEB)

    Maitra, T [Institut fuer Theoretische Physik, J W Goethe Universitaet, Max-von-Laue-Strasse 1, 60438 Frankfurt (Germany); Taraphder, A [Department of Physics and Meteorology and Centre for Theoretical Studies, Indian Institute of Technology, Kharagpur 721302 (India); Beck, H [Institute of Physics, University of Neuchatel, rue de Breguet 1, CH-2000 (Switzerland)

    2005-07-13

    There have been recent reports of charge ordering around x = 0.5 in the bilayer manganites like La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7}. At x = 0.5, there appears to be a coexistence region of layered A-type antiferromagnetic order and charge order. There are also reports of orbital order in this region without any Jahn-Teller effect. Based on physical grounds, this region is investigated from a model that incorporates the two e{sub g} orbitals at each Mn site and a near-neighbour Coulomb repulsion. It is shown that there indeed both charge and orbital order close to the half-doped region coincident with a layered magnetic structure. Although the orbital order is known to drive the magnetic order, the layered magnetic structure is also favoured in this system by the lack of coherent transport across the planes and the reduced dimensionality of the lattice. The anisotropic hopping across the e{sub g} orbitals and the underlying layered structure largely determine the orbital arrangements in this region, while the charge order is primarily due to the long-range interactions.

  10. Neutrons in studies of phospholipid bilayers and bilayer–drug interaction. I. Basic principles and neutron diffraction

    Directory of Open Access Journals (Sweden)

    Belička M.

    2014-12-01

    Full Text Available In our paper, we demonstrate several possibilities of using neutrons in pharmaceutical research with the help of examples of scientific results achieved at our University. In this first part, basic properties of neutrons and elementary principles of elastic scattering of thermal neutrons are described. Results of contrast variation neutron diffraction on oriented phospholipid bilayers with intercalated local anaesthetic or cholesterol demonstrate the potential of this method at determination of their position in bilayers. Diffraction experiments with alkan-1-ols located in the bilayers revealed their influence on bilayer thickness as a function of their alkyl chain length.

  11. Determinants of capital structure: Evidence from Istanbul stock exchange

    OpenAIRE

    Samery, Mohammad

    2013-01-01

    ABSTRACT: This thesis aims to explain determinants of capital structure evidence from istanbul stock exchange from three companies (Turkcell ,Vodafone and Deutesche Telekom).The two main theories used are for trade-off theory and pecking order theory. The essential of the pecking order is the manager's of capital structure decision are influenced by the market perception of manager's superior information. The trade-off theory provides support for manager's trade-off between benefits and costs...

  12. Determinants of Capital Structure on UK Quoted Companies

    OpenAIRE

    Vo, Hai Tuan

    2012-01-01

    The dissertation aims to examine the determinants influencing the capital structure decisions on UK listed firms and identify which theory is the most relevant one toward UK companies. A panel data set of 234 firms from 9 different industries on FTSE 350 was recorded from 2002-2012 to analyze the factors affecting capital structure. The one-way ANOVA is employed to validate whether the industry effects importantly seize any influence in explaining firms’ debt ratios. Moreover, statistical tes...

  13. Structural Determinants of the Natural Rate of Unemployment in Canada

    OpenAIRE

    Coe, David T

    1990-01-01

    This paper presents empirical estimates of the policy and structural determinants of the natural rate of unemployment in Canada. The paper begins with a discussion of structural features of the economy which impinge on the adjustment of real wages to their equilibrium level. Estimates are presented showing how the generosity of the unemployment insurance system is related to past levels of unemployment. The empirical results indicate that government policies have been largely responsible for ...

  14. Determinants of Capital Structure in Listed Norwegian Firms

    OpenAIRE

    Nilssen, Cathrine Marie

    2014-01-01

    The main goal for most firms is to maximise firm value and the wealth of shareholders. In order to achieve this goal, firms should use an optimal combination of equity and debt that will result in a low weighted average cost of capital for the firm. It is therefore necessary for firms to be aware of the factors that influence their capital structure decision. Several empirical studies have attempted to explain what determines the choice of capital structure in firms. Howev...

  15. Determinants of Market Structure and the Airline Industry

    Science.gov (United States)

    Raduchel, W.

    1972-01-01

    The general economic determinants of market structure are outlined with special reference to the airline industry. Included are the following facets: absolute size of firms; distributions of firms by size; concentration; entry barriers; product and service differentiation; diversification; degrees of competition; vertical integration; market boundaries; and economies of scale. Also examined are the static and dynamic properties of market structure in terms of mergers, government policies, and economic growth conditions.

  16. Structure determination of drug target proteins by neutron crystallography

    International Nuclear Information System (INIS)

    High resolution X-ray crystallography provides information for most of the atoms comprising the proteins, with the exception of hydrogen atoms. Whereas, neutron crystallography, which is a powerful technique for locating hydrogen atoms, enables us to obtain accurate atomic positions within proteins. Neutron diffraction data can provide information of the location of hydrogen atoms to the structural information determined by X-ray crystallography. Here, we show the recent results of the structural determination of drug-target proteins, porcine pancreatic elastase and human immuno-deficiency virus type-1 protease by both X-ray and neutron diffraction. The structure of porcine pancreatic elastase with its potent inhibitor was determined to 0.094 nm resolution by X-ray diffraction and 0.165 nm resolution by neutron diffraction. The structure of HIV-PR with its potent inhibitor was also determined to 0.093 nm resolution by X-ray diffraction and 0.19 nm resolution by neutron diffraction. The ionization state and the location of hydrogen atoms of the catalytic residue in these enzymes were determined by neutron diffraction. Furthermore, collaborative use of both X-ray and neutron crystallography to identify the location of ambiguous hydrogen atoms will be shown. (author)

  17. Determinants of Capital Structure: Panel Data Evidence from UK Firms

    OpenAIRE

    Li, Rui

    2008-01-01

    This dissertation intends to analyse and examine the determinants of the capital structure with an unbalanced panel of 1504 listed UK companies from 2000 to 2007. A range of classical capital theories including Modigliani-Miller (M-M)irrelevance theory, the trade-off, pecking-order and agency theories, are deployed to explore and predict the signs and significance of each determinant pointed out by Titman and Wessels (1988) and Harris and Raviv (1991). In the investigation, we first employ th...

  18. Slavnov determinants, Yang-Mills structure constants, and discrete KP

    OpenAIRE

    Foda, O.; Wheeler, M.

    2012-01-01

    Using Slavnov's scalar product of a Bethe eigenstate and a generic state in closed XXZ spin-1/2 chains, with possibly twisted boundary conditions, we obtain determinant expressions for tree-level structure constants in 1-loop conformally-invariant sectors in various planar (super) Yang-Mills theories. When certain rapidity variables are allowed to be free rather than satisfy Bethe equations, these determinants become discrete KP tau-functions.

  19. Preparation and properties of hybrid bilayer structures based on organic Alq3, ferromagnetic La2/3Sr1/3MnO3 and Fe3O4

    Science.gov (United States)

    Vengalis, B.; Šliužienė, K.; Černiukė, I.; Butkutė, R.; Lisauskas, V.; Maneikis, A.

    2008-09-01

    We report preparation and properties of hybrid bilayer structures composed of the organic semiconductor, 8-hydroxyquinoline aluminum (Alq3), p-type Si and two ferromagnetic oxides, namely, colossal magnetoresistance manganite, La2/3Sr1/3MnO3 (LSMO), and magnetite (Fe3O4). Thin Alq3 films were thermally evaporated in vacuum. The bottom LSMO films were grown in-situ at 750°C by dc magnetron sputtering on crystalline SrTiO3 while Fe3O4 films were magnetron sputtered at 400°C on glass. Current versus voltage in a case of vertical current flow has been investigated for the heterojunctions. The investigations revealed dominating role of thermoionic emission in a barrier of Schottky type for the Alq3/p-Si heterojunction while a mechanism based on carrier tunnelling through an interface and space charge limited current processes were considered to explain nonlinear electrical transport in the Alq3/LSMO, Alq3/ Fe3O4 heterojunctions. The Alq3/LSMO demonstrated magnetoresistance values up to 11 % (at T=240 K and B=1 T).

  20. Symmetry determination following structure solution in P1

    OpenAIRE

    Palatinus, Lukas; Lee, Arie van der

    2008-01-01

    A new method for space-group determination is described. It is based on a symmetry analysis of the structure-factor phases resulting from a structure solution in space group P1. The output of the symmetry analysis is a list of all symmetry operations compatible with the lattice. Each symmetry operation is assigned a symmetry agreement factor that is used to select the symmetry operations that are the elements of the space group of the structure. On the basis of the list of the selected operat...

  1. Role of substrate induced electron–phonon interactions in biased graphitic bilayers

    Science.gov (United States)

    Davenport, A. R.; Hague, J. P.

    2016-08-01

    Bilayers of graphitic materials have potential applications in field effect transistors (FETs). A potential difference applied between certain ionic bilayers made from insulating graphitic materials such as BN, ZnO and AlN could reduce gap sizes, turning them into useful semiconductors. On the other hand, opening of a small semiconducting gap occurs in graphene bilayers under applied field. The aim here is to investigate to what extent substrate induced electron–phonon interactions (EPIs) modify this gap change. We examine EPIs in several lattice configurations of graphitic bilayers, using a perturbative approach. The typical effect of EPIs on the ionic bilayers is an undesirable gap widening. The size of this gap change varies considerably with lattice structure and the magnitude of the bias. When bias is larger than the non-interacting gap size, EPIs have the smallest effect on the bandgap, especially in configurations with A{{A}\\prime} and AB structures. Thus careful selection of substrate, lattice configuration and bias strength to minimise the effects of EPIs could be important for optimising the properties of electronic devices. We use parameters related to BN in this article. In practice, the results presented here are broadly applicable to other graphitic bilayers, and are likely to be qualitatively similar in metal dichalcogenide bilayers such as MoS2, which are already of high interest for their use in FETs.

  2. Role of substrate induced electron-phonon interactions in biased graphitic bilayers.

    Science.gov (United States)

    Davenport, A R; Hague, J P

    2016-08-17

    Bilayers of graphitic materials have potential applications in field effect transistors (FETs). A potential difference applied between certain ionic bilayers made from insulating graphitic materials such as BN, ZnO and AlN could reduce gap sizes, turning them into useful semiconductors. On the other hand, opening of a small semiconducting gap occurs in graphene bilayers under applied field. The aim here is to investigate to what extent substrate induced electron-phonon interactions (EPIs) modify this gap change. We examine EPIs in several lattice configurations of graphitic bilayers, using a perturbative approach. The typical effect of EPIs on the ionic bilayers is an undesirable gap widening. The size of this gap change varies considerably with lattice structure and the magnitude of the bias. When bias is larger than the non-interacting gap size, EPIs have the smallest effect on the bandgap, especially in configurations with [Formula: see text] and AB structures. Thus careful selection of substrate, lattice configuration and bias strength to minimise the effects of EPIs could be important for optimising the properties of electronic devices. We use parameters related to BN in this article. In practice, the results presented here are broadly applicable to other graphitic bilayers, and are likely to be qualitatively similar in metal dichalcogenide bilayers such as MoS2, which are already of high interest for their use in FETs. PMID:27346288

  3. Multi-Stacked Supported Lipid Bilayer Micropatterning through Polymer Stencil Lift-Off

    Directory of Open Access Journals (Sweden)

    Yujie Zhu

    2015-08-01

    Full Text Available Complex multi-lamellar structures play a critical role in biological systems, where they are present as lamellar bodies, and as part of biological assemblies that control energy transduction processes. Multi-lamellar lipid layers not only provide interesting systems for fundamental research on membrane structure and bilayer-associated polypeptides, but can also serve as components in bioinspired materials or devices. Although the ability to pattern stacked lipid bilayers at the micron scale is of importance for these purposes, limited work has been done in developing such patterning techniques. Here, we present a simple and direct approach to pattern stacked supported lipid bilayers (SLBs using polymer stencil lift-off and the electrostatic interactions between cationic and anionic lipids. Both homogeneous and phase-segregated stacked SLB patterns were produced, demonstrating that the stacked lipid bilayers retain lateral diffusivity. We demonstrate patterned SLB stacks of up to four bilayers, where fluorescence resonance energy transfer (FRET and quenching was used to probe the interactions between lipid bilayers. Furthermore, the study of lipid phase behaviour showed that gel phase domains align between adjacent layers. The proposed stacked SLB pattern platform provides a robust model for studying lipid behaviour with a controlled number of bilayers, and an attractive means towards building functional bioinspired materials or devices.

  4. Lepromatous leprosy patients produce antibodies that recognise non-bilayer lipid arrangements containing mycolic acids

    Directory of Open Access Journals (Sweden)

    Isabel Baeza

    2012-12-01

    Full Text Available Non-bilayer phospholipid arrangements are three-dimensional structures that form when anionic phospholipids with an intermediate structure of the tubular hexagonal phase II are present in a bilayer of lipids. Antibodies that recognise these arrangements have been described in patients with antiphospholipid syndrome and/or systemic lupus erythematosus and in those with preeclampsia; these antibodies have also been documented in an experimental murine model of lupus, in which they are associated with immunopathology. Here, we demonstrate the presence of antibodies against non-bilayer phospholipid arrangements containing mycolic acids in the sera of lepromatous leprosy (LL patients, but not those of healthy volunteers. The presence of antibodies that recognise these non-bilayer lipid arrangements may contribute to the hypergammaglobulinaemia observed in LL patients. We also found IgM and IgG anti-cardiolipin antibodies in 77% of the patients. This positive correlation between the anti-mycolic-non-bilayer arrangements and anti-cardiolipin antibodies suggests that both types of antibodies are produced by a common mechanism, as was demonstrated in the experimental murine model of lupus, in which there was a correlation between the anti-non-bilayer phospholipid arrangements and anti-cardiolipin antibodies. Antibodies to non-bilayer lipid arrangements may represent a previously unrecognised pathogenic mechanism in LL and the detection of these antibodies may be a tool for the early diagnosis of LL patients.

  5. Capital Structure of Agricultural Businesses and its Determinants

    Directory of Open Access Journals (Sweden)

    R. Aulová

    2013-06-01

    Full Text Available The article deals with the analysis of the capital structure of agricultural businesses of legal entities and its determinants. It discusses the effect of selected determinants on the capital structure of businesses, expressed by way of three categories of indebtedness. The analysis of the determinants of capital structure is conducted by way of multiple linear regression. Also being verified is the hypothesis of whether the effect of individual determinants of capital structure is in accordance with the theoretical assumptions of conditional theories of capital structure and empirical studies.The panel data for the article were acquired from the Albertina database, provided by the company Soliditet, s.r.o. Specifically, the data used were those from accounting statements for the years 2004 – 2010 for the agricultural businesses of legal entities. In total, the object of examination was 16075 businesses, which were divided up according to legal forms (joint stock company, cooperative, and limited liability company and subsequently the relevant size group. In total, 18 groups of businesses were created, whereby the average balance and profit and loss account were drawn up for each group, on the basis of which the relevant calculations were conducted. The article is a part of the grant project IGA 20121069 “Identification of the main determinants of the result of economic activity of agricultural businesses of legal entities and the determination of their specifics” and of the institutional research intentions MSM 6046070906 „Economics sources of Czech agriculture and their efficient use in the context of multifunctional agri-food systems“.

  6. Bilayer Effects of Antimalarial Compounds.

    Directory of Open Access Journals (Sweden)

    Nicole B Ramsey

    Full Text Available Because of the perpetual development of resistance to current therapies for malaria, the Medicines for Malaria Venture developed the Malaria Box to facilitate the drug development process. We tested the 80 most potent compounds from the box for bilayer-mediated effects on membrane protein conformational changes (a measure of likely toxicity in a gramicidin-based stopped flow fluorescence assay. Among the Malaria Box compounds tested, four compounds altered membrane properties (p< 0.05; MMV007384 stood out as a potent bilayer-perturbing compound that is toxic in many cell-based assays, suggesting that testing for membrane perturbation could help identify toxic compounds. In any case, MMV007384 should be approached with caution, if at all.

  7. Excitonic condensation in bilayer systems

    Science.gov (United States)

    Su, Jung-Jung

    Among the many examples of Bose condensation considered in physics, electron-hole-pair (exciton) condensation has maintained special interest because it has been difficult to realize experimentally, and because of controversy about condensate properties. In this thesis, we studied the various aspects of spontaneous symmetry broken state of exciton in bilayer using mean field theory. We calculated the photoluminescence of excitonic condensation created by laser. We developed a one-dimensional toy model of excitonic supercurrent using mean field theory plus non-equilibrium Green's function (NEGF) which give qualitatively consistent results with experiments. We proposed graphene bilayer as a novel system for excitonic condensation to occur and estimate it to exist even at temperature as high as room temperature.

  8. Determination of f_0(980) Structure by Fragmentation Functions

    CERN Document Server

    Hirai, M; Oka, M; Sudoh, K

    2008-01-01

    We discuss internal structure of an exotic hadron by using fragmentation functions. The fragmentation functions for the f_0(980) meson are obtained by a global analysis of e^++e^- \\to f_0+X data. Quark configuration of the f_0(980) could be determined by peak positions and second moments of the obtained fragmentation functions.

  9. Macromolecular structure determination in the post-genome era

    International Nuclear Information System (INIS)

    Recent advances in genetics, molecular biology and crystallographic instrumentation and methodology have led to a revolution in the field of Structural Molecular Biology (SMB). These combined advances have paved the way to a more complete and detailed understanding of the biological macromolecules that make up an organism, both in terms of their individual functions and also the interactions between them. In this paper we describe a large-scale, genomic approach to the three-dimensional structure determination of macromolecules and their complexes, using high-throughput methodology to streamline all aspects of the process. This task requires the development of automated high-intensity synchrotron beam lines for X-ray diffraction data collection from single crystal samples. Furthermore, these beam lines must be operated within a sophisticated software and hardware environment, which is capable of delivering a completely automated structure determination pipeline. The SMB resource at SSRL is developing a system for the structure determination steps of this process, starting with the initial characterization of the frozen sample, followed by data collection, data reduction, phase determination, and model building. This paper focuses on the data collection elements of this high-throughput system

  10. The Determination of Molecular Structure from Rotational Spectra

    Science.gov (United States)

    Laurie, V. W.; Herschbach, D. R.

    1962-07-01

    An analysis is presented concerning the average molecular configuration variations and their effects on molecular structure determinations. It is noted that the isotopic dependence of the zero-point is often primarily governed by the isotopic variation of the average molecular configuration. (J.R.D.)

  11. Synthesis and structure determination of novel hexasubstituted cyclohexadienes

    Institute of Scientific and Technical Information of China (English)

    Hong Mei Qu; Xin Hui Niu; Juan Li; Jun Liu; Li Li Jiang; Jian Ke Tang; Li Shan Zhou

    2012-01-01

    The linear trienes were obtained in high yields by copper-mediated cycloaddition of 2,5-bis(trimethylsilyl)zirconacyclopentadienes with dimethyl acetylenedicarboxylate (DMAD) which can be quantitatively converted to novel asymmetric hexasubstituted cyclohexadienes with high (E)-stereoselectivity.The structure of cyclohexadienes was determined via X-ray analysis.

  12. Birthday Cake Activity Structured Arrangement for Helping Children Determining Quantities

    Science.gov (United States)

    Mariana, Neni

    2010-01-01

    Few researches have been concerned about relation between children's spatial thinking and number sense. Narrowing for this small research, we focused on one component of spatial thinking, that is structuring objects, and one component of number senses, that is cardinality by determining quantities. This study focused on a design research that was…

  13. The Stability and Charge Carriers in Bilayer Silicene

    OpenAIRE

    Rui, Wang; Shaofeng, Wang; Xiaozhi, Wu

    2013-01-01

    The structure optimization, phonon, and ab initio ?nite temperature molecular dynamics calculations have been performed to predict that bilayer silicene has stable structure with AB stacking geometry and is more favorable energetically to synthesize than monolayer silicene, a two-dimensional honeycomb lattice with buckled geometry. Marvellously, its electronic bands show that the charge carriers behave like relativistic Dirac fermions with linear energy dispersions near the K points. An insig...

  14. From bacterial to human dihydrouridine synthase: automated structure determination

    Energy Technology Data Exchange (ETDEWEB)

    Whelan, Fiona, E-mail: fiona.whelan@york.ac.uk; Jenkins, Huw T., E-mail: fiona.whelan@york.ac.uk [The University of York, Heslington, York YO10 5DD (United Kingdom); Griffiths, Samuel C. [University of Oxford, Headington, Oxford OX3 7BN (United Kingdom); Byrne, Robert T. [Ludwig-Maximilians-University Munich, Feodor-Lynen-Strasse 25, 81377 Munich (Germany); Dodson, Eleanor J.; Antson, Alfred A., E-mail: fiona.whelan@york.ac.uk [The University of York, Heslington, York YO10 5DD (United Kingdom)

    2015-06-30

    The crystal structure of a human dihydrouridine synthase, an enzyme associated with lung cancer, with 18% sequence identity to a T. maritima enzyme, has been determined at 1.9 Å resolution by molecular replacement after extensive molecular remodelling of the template. The reduction of uridine to dihydrouridine at specific positions in tRNA is catalysed by dihydrouridine synthase (Dus) enzymes. Increased expression of human dihydrouridine synthase 2 (hDus2) has been linked to pulmonary carcinogenesis, while its knockdown decreased cancer cell line viability, suggesting that it may serve as a valuable target for therapeutic intervention. Here, the X-ray crystal structure of a construct of hDus2 encompassing the catalytic and tRNA-recognition domains (residues 1–340) determined at 1.9 Å resolution is presented. It is shown that the structure can be determined automatically by phenix.mr-rosetta starting from a bacterial Dus enzyme with only 18% sequence identity and a significantly divergent structure. The overall fold of the human Dus2 is similar to that of bacterial enzymes, but has a larger recognition domain and a unique three-stranded antiparallel β-sheet insertion into the catalytic domain that packs next to the recognition domain, contributing to domain–domain interactions. The structure may inform the development of novel therapeutic approaches in the fight against lung cancer.

  15. From bacterial to human dihydrouridine synthase: automated structure determination

    International Nuclear Information System (INIS)

    The crystal structure of a human dihydrouridine synthase, an enzyme associated with lung cancer, with 18% sequence identity to a T. maritima enzyme, has been determined at 1.9 Å resolution by molecular replacement after extensive molecular remodelling of the template. The reduction of uridine to dihydrouridine at specific positions in tRNA is catalysed by dihydrouridine synthase (Dus) enzymes. Increased expression of human dihydrouridine synthase 2 (hDus2) has been linked to pulmonary carcinogenesis, while its knockdown decreased cancer cell line viability, suggesting that it may serve as a valuable target for therapeutic intervention. Here, the X-ray crystal structure of a construct of hDus2 encompassing the catalytic and tRNA-recognition domains (residues 1–340) determined at 1.9 Å resolution is presented. It is shown that the structure can be determined automatically by phenix.mr-rosetta starting from a bacterial Dus enzyme with only 18% sequence identity and a significantly divergent structure. The overall fold of the human Dus2 is similar to that of bacterial enzymes, but has a larger recognition domain and a unique three-stranded antiparallel β-sheet insertion into the catalytic domain that packs next to the recognition domain, contributing to domain–domain interactions. The structure may inform the development of novel therapeutic approaches in the fight against lung cancer

  16. A kinked antimicrobial peptide from Bombina maxima. I. Three-dimensional structure determined by NMR in membrane-mimicking environments.

    Science.gov (United States)

    Toke, Orsolya; Bánóczi, Zoltán; Király, Péter; Heinzmann, Ralf; Bürck, Jochen; Ulrich, Anne S; Hudecz, Ferenc

    2011-04-01

    Maximin-4 is a 27-residue cationic antimicrobial peptide exhibiting selectivity for bacterial cells. As part of the innate defense system in the Chinese red-belly toad, its mode of action is thought to be ion channel or pore formation and dissipation of the electrochemical gradient across the pathogenic cell membrane. Here we present the high-resolution structure of maximin-4 in two different membrane mimetics, sodium dodecyl sulfate micelles and 50% methanol, as determined by (1)H solution NMR spectroscopy. In both environments, the peptide chain adopts a helix-break-helix conformation following a highly disordered N-terminal segment. Despite the similarities in the overall topology of the two structures, major differences are observed in terms of the interactions stabilizing the kink region and the arrangement of the four lysine residues. This has a marked influence on the shape and charge distribution of the molecule and may have implications for the bacterial selectivity of the peptide. The solution NMR results are complemented by CD spectroscopy and solid-state NMR experiments in lipid bilayers, both confirming the predominantly helical conformation of the peptide. As a first step in elucidating the membrane interactions of maximin-4, our study contributes to a better understanding of the mode of action of antimicrobial peptides and the factors governing their selectivity. PMID:21234559

  17. The structure of Sindbis virus produced from vertebrate and invertabrate hosts determined by small angle neutron scattering

    Energy Technology Data Exchange (ETDEWEB)

    He, Lilin [ORNL; Piper, Amanda [North Carolina State University; Meilleur, Flora [ORNL; Myles, Dean A A [ORNL; Hernandez, Raquel [North Carolina State University; Brown, Dennis [North Carolina State University; Heller, William T [ORNL

    2010-01-01

    The complex natural cycle of vectored viruses that transition between host species, such as between insects and mammals, makes understanding the full life cycle of the virus an incredibly complex problem. Sindbis virus, an arbovirus and prototypic alphavirus having an inner protein shell and an outer glycoprotein coat separated by a lipid membrane, is one example of a vectored virus that transitions between vertebrate and insect hosts. While evidence of host-specific differences in Sindbis virus has been observed, no work has been performed to characterize the impact of the host species on the structure of the virus. Here, we report the first study of the structural differences between Sindbis viruses grown in mammalian and insect cells, which were determined by small-angle neutron scattering (SANS), a nondestructive technique that did not decrease the infectivity of the Sindbis virus particles studied. The scattering data and modeling showed that, while the radial position of the lipid bilayer did not change significantly, it was possible to conclude that it did have significantly more cholesterol when the virus was grown in mammalian cells. Additionally, the outer protein coat was found to be more extended in the mammalian Sindbis virus. The SANS data also demonstrated that the RNA and nucleocapsid protein share a closer interaction in the mammalian-cell-grown virus than in the virus from insect cells.

  18. The structure of Sindbis virus produced from vertebrate and invertabrate hosts determined by small angle neutron scattering

    International Nuclear Information System (INIS)

    The complex natural cycle of vectored viruses that transition between host species, such as between insects and mammals, makes understanding the full life cycle of the virus an incredibly complex problem. Sindbis virus, an arbovirus and prototypic alphavirus having an inner protein shell and an outer glycoprotein coat separated by a lipid membrane, is one example of a vectored virus that transitions between vertebrate and insect hosts. While evidence of host-specific differences in Sindbis virus has been observed, no work has been performed to characterize the impact of the host species on the structure of the virus. Here, we report the first study of the structural differences between Sindbis viruses grown in mammalian and insect cells, which were determined by small-angle neutron scattering (SANS), a nondestructive technique that did not decrease the infectivity of the Sindbis virus particles studied. The scattering data and modeling showed that, while the radial position of the lipid bilayer did not change significantly, it was possible to conclude that it did have significantly more cholesterol when the virus was grown in mammalian cells. Additionally, the outer protein coat was found to be more extended in the mammalian Sindbis virus. The SANS data also demonstrated that the RNA and nucleocapsid protein share a closer interaction in the mammalian-cell-grown virus than in the virus from insect cells.

  19. Anomalous swelling of multilamellar lipid bilayers in the transition region by renormalization of curvature elasticity

    DEFF Research Database (Denmark)

    Callisen, Thomas Hønger; Mortensen, Kell; Ipsen, John Hjorth;

    1994-01-01

    Small-angle neutron scattering is used to determine the temperature dependence of the lamellar repeat distance in an aqueous multilamellar solution of phospholipid bilayers. A thermal anomaly in the swelling behavior is observed at the bilayer phase transition. The anomalous behavior can be...... suppressed by varying the lipid acyl-chain length or by alloying with a molecular stiffening agent. The experimental results are explained in terms of renormalization of the bilayer curvature elasticity and by using a theory of repulsive interlamellar undulation forces....

  20. Direct experimental determination of the atomic structure at internal interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Browning, N.D. [Oak Ridge National Lab., TN (United States)]|[Illinois Univ., Chicago, IL (United States); Pennycook, S.J. [Oak Ridge National Lab., TN (United States)

    1995-07-01

    A crucial first step in understanding the effect that internal interfaces have on the properties of materials is the ability to determine the atomic structure at the interface. As interfaces can contain atomic disorder, dislocations, segregated impurities and interphases, sensitivity to all of these features is essential for complete experimental characterization. By combining Z-contrast imaging and electron energy loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope (STEM), the ability to probe the structure, bonding and composition at interfaces with the necessary atomic resolution has been obtained. Experimental conditions can be controlled to provide, simultaneously, both incoherent imaging and spectroscopy. This enables interface structures observed in the image to be interpreted intuitively and the bonding in a specified atomic column to be probed directly by EELS. The bonding and structure information can then be correlated using bond-valence sum analysis to produce structural models. This technique is demonstrated for 25{degrees}, 36{degrees} and 67{degrees} symmetric and 45{degrees} and 25{degrees} asymmetric [001] tilt grain boundaries in SrTiO{sub 3} The structures of both types of boundary were found to contain partially occupied columns in the boundary plane. From these experimental results, a series of structural units were identified which could be combined, using continuity of gain boundary structure principles, to construct all [001] tilt boundaries in SrTiO{sub 3}. Using these models, the ability of this technique to address the issues of vacancies and dopant segregation at grain boundaries in electroceramics is discussed.

  1. Negative terahertz conductivity in disordered graphene bilayers with population inversion

    International Nuclear Information System (INIS)

    The gapless energy band spectra make the structures based on graphene and graphene bilayer with the population inversion to be promising media for the interband terahertz (THz) lasing. However, a strong intraband absorption at THz frequencies still poses a challenge for efficient THz lasing. In this paper, we show that in the pumped graphene bilayer, the indirect interband radiative transitions accompanied by scattering of carriers by disorder can provide a substantial negative contribution to the THz conductivity (together with the direct interband transitions). In the graphene bilayer on high-κ substrates with point charged defects, these transitions substantially compensate the losses due to the intraband (Drude) absorption. We also demonstrate that the indirect interband contribution to the THz conductivity in a graphene bilayer with the extended defects (such as the charged impurity clusters) can surpass by several times the fundamental limit associated with the direct interband transitions, and the Drude conductivity as well. These predictions can affect the strategy of the graphene-based THz laser implementation

  2. Negative terahertz conductivity in disordered graphene bilayers with population inversion

    Energy Technology Data Exchange (ETDEWEB)

    Svintsov, D. [Laboratory of Nanooptics and Plasmonics, Moscow Institute of Physics and Technology, Dolgoprudny 141700 (Russian Federation); Otsuji, T.; Ryzhii, V., E-mail: v-ryzhii@riec.tohoku.ac.jp [Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Mitin, V. [Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Department of Electrical Engineering, University at Buffalo, SUNY, Buffalo, New York 1460-1920 (United States); Shur, M. S. [Departments of Electrical, Electronics, and Systems Engineering and Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

    2015-03-16

    The gapless energy band spectra make the structures based on graphene and graphene bilayer with the population inversion to be promising media for the interband terahertz (THz) lasing. However, a strong intraband absorption at THz frequencies still poses a challenge for efficient THz lasing. In this paper, we show that in the pumped graphene bilayer, the indirect interband radiative transitions accompanied by scattering of carriers by disorder can provide a substantial negative contribution to the THz conductivity (together with the direct interband transitions). In the graphene bilayer on high-κ substrates with point charged defects, these transitions substantially compensate the losses due to the intraband (Drude) absorption. We also demonstrate that the indirect interband contribution to the THz conductivity in a graphene bilayer with the extended defects (such as the charged impurity clusters) can surpass by several times the fundamental limit associated with the direct interband transitions, and the Drude conductivity as well. These predictions can affect the strategy of the graphene-based THz laser implementation.

  3. The effects of globotriaosylceramide tail saturation level on bilayer phases

    DEFF Research Database (Denmark)

    Pezeshkian, Weria; Chaban, Vitaly V; Johannes, Ludger;

    2015-01-01

    Globotriaosylceramide (Gb3) is a glycosphingolipid present in the plasma membrane that is the natural receptor of the bacterial Shiga toxin. The unsaturation level of Gb3 acyl chains has a drastic impact on lipid bilayer properties and phase behaviour, and on many Gb3-related cellular processes. ...... of sphingomyelin lipids and (3) At higher Gb3 concentrations, U-Gb3 mixes better with dioleoylphosphatidylcholine than S-Gb3. Our simulations also provide the first molecular level structural model of Gb3 in membranes.......Globotriaosylceramide (Gb3) is a glycosphingolipid present in the plasma membrane that is the natural receptor of the bacterial Shiga toxin. The unsaturation level of Gb3 acyl chains has a drastic impact on lipid bilayer properties and phase behaviour, and on many Gb3-related cellular processes...... of the Gb3 concentration and its acyl chain saturation on the phase behaviour of a mixed bilayer of dioleoylphosphatidylcholine and Gb3. The simulation results show that: (1) the Gb3 acyl chains (longer tails) from one leaflet interdigitate into the opposing leaflet and lead to significant bilayer...

  4. Interaction of gramicidin with DPPC/DODAB bilayer fragments.

    Science.gov (United States)

    Carvalho, Camilla A; Olivares-Ortega, Constanza; Soto-Arriaza, Marco A; Carmona-Ribeiro, Ana M

    2012-12-01

    The interaction between the antimicrobial peptide gramicidin (Gr) and dipalmitoylphosphatidylcholine (DPPC)/dioctadecyldimethylammonium bromide (DODAB) 1:1 large unilamellar vesicles (LVs) or bilayer fragments (BFs) was evaluated by means of several techniques. The major methods were: 1) Gr intrinsic fluorescence and circular dichroism (CD) spectroscopy; 2) dynamic light scattering for sizing and zeta-potential analysis; 3) determination of the bilayer phase transition from extrinsic fluorescence of bilayer probes; 4) pictures of the dispersions for evaluation of coloidal stability over a range of time and NaCl concentration. For Gr in LVs, the Gr dimeric channel conformation is suggested from: 1) CD and intrinsic fluorescence spectra similar to those in trifluoroethanol (TFE); 2) KCl or glucose permeation through the LVs/Gr bilayer. For Gr in BFs, the intertwined dimeric, non-channel Gr conformation is evidenced by CD and intrinsic fluorescence spectra similar to those in ethanol. Both LVs and BFs shield Gr tryptophans against quenching by acrylamide but the Stern-Volmer quenching constant was slightly higher for Gr in BFs confirming that the peptide is more exposed to the water phase in BFs than in LVs. The DPPC/DODAB/Gr supramolecular assemblies may predict the behavior of other antimicrobial peptides in assemblies with lipids. PMID:22960286

  5. X-ray structure determination and deuteration of nattokinase

    Energy Technology Data Exchange (ETDEWEB)

    Yanagisawa, Yasuhide [Chiba Institute of Science, 15-8 Shiomi-cho, Cho-shi, Chiba 288-025 (Japan); Chatake, Toshiyuki, E-mail: chatake@rri.kyoto-u.ac.jp [Kyoto University, Asashironishi 2, Kumatori, Osaka 590-0494 (Japan); Naito, Sawa; Ohsugi, Tadanori; Yatagai, Chieko; Sumi, Hiroyuki [Kurashiki University of Science and the Arts, 2640 Nishinoura, Tsurajima-cho, Kurashiki, Okayama 712-8505 (Japan); Kawaguchi, Akio [Kyoto University, Asashironishi 2, Kumatori, Osaka 590-0494 (Japan); Chiba-Kamosida, Kaori [Nippon Advanced Technology Co. Ltd, J-PARC, 2-4 Shirane Shirakata, Tokai, Ibaraki 319-1195 (Japan); Ogawa, Megumi; Adachi, Tatsumi [Chiba Institute of Science, 15-8 Shiomi-cho, Cho-shi, Chiba 288-025 (Japan); Morimoto, Yukio [Kyoto University, Asashironishi 2, Kumatori, Osaka 590-0494 (Japan)

    2013-11-01

    X-ray structure determination and deuteration of nattokinase were performed to facilitate neutron crystallographic analysis. Nattokinase (NK) is a strong fibrinolytic enzyme, which is produced in abundance by Bacillus subtilis natto. Although NK is a member of the subtilisin family, it displays different substrate specificity when compared with other subtilisins. The results of molecular simulations predict that hydrogen arrangements around Ser221 at the active site probably account for the substrate specificity of NK. Therefore, neutron crystallographic analysis should provide valuable information that reveals the enzymatic mechanism of NK. In this report, the X-ray structure of the non-hydrogen form of undeuterated NK was determined, and the preparation of deuterated NK was successfully achieved. The non-hydrogen NK structure was determined at 1.74 Å resolution. The three-dimensional structures of NK and subtilisin E from Bacillus subtilis DB104 are near identical. Deuteration of NK was carried out by cultivating Bacillus subtilis natto in deuterated medium. The D{sub 2}O resistant strain of Bacillus subtilis natto was obtained by successive cultivation rounds, in which the concentration of D{sub 2}O in the medium was gradually increased. NK was purified from the culture medium and its activity was confirmed by the fibrin plate method. The results lay the framework for neutron protein crystallography analysis.

  6. Overconfidence, Managerial Optimism, and the Determinants of Capital Structure

    Directory of Open Access Journals (Sweden)

    Alexandre di Miceli da Silveira

    2008-12-01

    Full Text Available This research examines the determinants of the capital structure of firms introducing a behavioral perspective that has received little attention in corporate finance literature. The following central hypothesis emerges from a set of recently developed theories: firms managed by optimistic and/or overconfident people will choose more levered financing structures than others, ceteris paribus. We propose different proxies for optimism/overconfidence, based on the manager’s status as an entrepreneur or non-entrepreneur, an idea that is supported by theories and solid empirical evidence, as well as on the pattern of ownership of the firm’s shares by its manager. The study also includes potential determinants of capital structure used in earlier research. We use a sample of Brazilian firms listed in the Sao Paulo Stock Exchange (Bovespa in the years 1998 to 2003. The empirical analysis suggests that the proxies for the referred cognitive biases are important determinants of capital structure. We also found as relevant explanatory variables: profitability, size, dividend payment and tangibility, as well as some indicators that capture the firms’ corporate governance standards. These results suggest that behavioral approaches based on human psychology research can offer relevant contributions to the understanding of corporate decision making.

  7. Fragmented state of lipid bilayers in water

    DEFF Research Database (Denmark)

    Helfrich, W.; Thimmel, J.; Klösgen, Beate Maria

    1999-01-01

    The bilayers of some typical biological membrane lipids such as PC and DGDG disintegrate in a large excess of water to form an optically invisible dispersive bilayer phase. `Dark bodies' can be reversibly precipitated from it by raising the temperature. The dispersive phase probably consists of...... `knotted sticks', i.e. very thin nodular tubes of bilayer. After reviewing pertinent experimental and theoretical work we report on the discovery of a lower consolute point near room temperature in DGDG/water systems. Its existence shows that the dispersive phase and the dark bodies belong to the same...... fragmented (or nodular) bilayer state, representing its expanded and condensed phases, respectively, above the critical temperature....

  8. X-ray structure determination at low resolution

    International Nuclear Information System (INIS)

    Refinement is meaningful even at 4 Å or lower, but with present methodologies it should start from high-resolution crystal structures whenever possible. As an example of structure determination in the 3.5–4.5 Å resolution range, crystal structures of the ATPase p97/VCP, consisting of an N-terminal domain followed by a tandem pair of ATPase domains (D1 and D2), are discussed. The structures were originally solved by molecular replacement with the high-resolution structure of the N-D1 fragment of p97/VCP, whereas the D2 domain was manually built using its homology to the D1 domain as a guide. The structure of the D2 domain alone was subsequently solved at 3 Å resolution. The refined model of D2 and the high-resolution structure of the N-D1 fragment were then used as starting models for re-refinement against the low-resolution diffraction data for full-length p97. The re-refined full-length models showed significant improvement in both secondary structure and R values. The free R values dropped by as much as 5% compared with the original structure refinements, indicating that refinement is meaningful at low resolution and that there is information in the diffraction data even at ∼4 Å resolution that objectively assesses the quality of the model. It is concluded that de novo model building is problematic at low resolution and refinement should start from high-resolution crystal structures whenever possible

  9. Observation and Structure Determination of an Oxide Quasicrystal Approximant.

    Science.gov (United States)

    Förster, S; Trautmann, M; Roy, S; Adeagbo, W A; Zollner, E M; Hammer, R; Schumann, F O; Meinel, K; Nayak, S K; Mohseni, K; Hergert, W; Meyerheim, H L; Widdra, W

    2016-08-26

    We report on the first observation of an approximant structure to the recently discovered two-dimensional oxide quasicrystal. Using scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction in combination with ab initio calculations, the atomic structure and the bonding scheme are determined. The oxide approximant follows a 3^{2}.4.3.4 Archimedean tiling. Ti atoms reside at the corners of each tiling element and are threefold coordinated to oxygen atoms. Ba atoms separate the TiO_{3} clusters, leading to a fundamental edge length of the tiling 6.7 Å. PMID:27610863

  10. Numerical and experimental determination of in-structure temperature profiles

    Directory of Open Access Journals (Sweden)

    Zozulák Marek

    2015-06-01

    Full Text Available When building physics simulations are done initial conditions express the actual hygrothermal state of building envelope. For the temperature field simulations initial condition is represented by the initial temperature in the body profile at the start of heat transfer. In-structure temperature varies quickly so temperature initial conditions are often neglected. Nevertheless in specific cases initial conditions have to be taken into an account even when simple temperature field simulations are done. The contribution shows various temperature initial conditions determination for insulated construction of outdoor test cell. Comparison of measured and calculated temperature profiles in structure shows correctness of start-up pre-calculation initial condition consideration

  11. Structure and dynamics of the pore-lining helix of the nicotinic receptor : MD simulations in water, lipid bilayers, and transbilayer bundles

    NARCIS (Netherlands)

    Law, RJ; Forrest, LR; Ranatunga, KM; La Rocca, P; Tieleman, DP; Sansom, MSP

    2000-01-01

    Multiple nanosecond duration molecular dynamics simulations on the pore-lining M2 helix of the nicotinic acetylcholine receptor reveal how its structure and dynamics change as a function of environment. In water, the M2 helix partially unfolds to form a molecular hinge in the vicinity of a central L

  12. Protein stability and conformational rearrangements in lipid bilayers: linear gramicidin, a model system.

    OpenAIRE

    Cotten, M; Xu, F.; Cross, T A

    1997-01-01

    The replacement of four tryptophans in gramicidin A by four phenylalanines (gramicidin M) causes no change in the molecular fold of this dimeric peptide in a low dielectric isotropic organic solvent, but the molecular folds are dramatically different in a lipid bilayer environment. The indoles of gramicidin A interact with the anisotropic bilayer environment to induce a change in the molecular fold. The double-helical fold of gramicidin M, as opposed to the single-stranded structure of gramic...

  13. Vortex pinning in superconducting/ferromagnetic bilayer with tunable domain width

    Science.gov (United States)

    Cieplak, Marta Z.; Zhu, L. Y.; Chien, C. L.

    2010-03-01

    We have used magnetoresistance to determine the activation energy of flux pinning in superconducting/ferromagnetic bilayer, consisting of superconducting Nb and ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy, separated by a Si buffer layer. Using a novel demagnetization procedure we can acquire randomly oriented stripe domain pattern with a well-defined average domain width L. We show that depending on the value of L, the temperature, and the magnetic field, the activation energy for flux pinning may be either enhanced or suppressed by the interaction between the vortices and the magnetic moment of the domains. Despite the randomness of the domain structure, the activation energy shows maxima at some magnetic fields, indicating commensurability effects. Our results are consistent with the formation of L-dependent arrangements of vortices, such as the triangular vortex lattice for small L, and the single-vortex or double-vortex chain structures at larger L. Our work provides a comprehensive picture of the flux pinning in the superconducting/ferromagnetic bilayer.

  14. Regulation of membrane protein function by lipid bilayer elasticity-a single molecule technology to measure the bilayer properties experienced by an embedded protein

    Energy Technology Data Exchange (ETDEWEB)

    Lundbaek, Jens August [Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021 (United States)

    2006-07-19

    Membrane protein function is generally regulated by the molecular composition of the host lipid bilayer. The underlying mechanisms have long remained enigmatic. Some cases involve specific molecular interactions, but very often lipids and other amphiphiles, which are adsorbed to lipid bilayers, regulate a number of structurally unrelated proteins in an apparently non-specific manner. It is well known that changes in the physical properties of a lipid bilayer (e.g., thickness or monolayer spontaneous curvature) can affect the function of an embedded protein. However, the role of such changes, in the general regulation of membrane protein function, is unclear. This is to a large extent due to lack of a generally accepted framework in which to understand the many observations. The present review summarizes studies which have demonstrated that the hydrophobic interactions between a membrane protein and the host lipid bilayer provide an energetic coupling, whereby protein function can be regulated by the bilayer elasticity. The feasibility of this 'hydrophobic coupling mechanism' has been demonstrated using the gramicidin channel, a model membrane protein, in planar lipid bilayers. Using voltage-dependent sodium channels, N-type calcium channels and GABA{sub A} receptors, it has been shown that membrane protein function in living cells can be regulated by amphiphile induced changes in bilayer elasticity. Using the gramicidin channel as a molecular force transducer, a nanotechnology to measure the elastic properties experienced by an embedded protein has been developed. A theoretical and technological framework, to study the regulation of membrane protein function by lipid bilayer elasticity, has been established.

  15. Neutron reflectivity studies of single lipid bilayers supported on planar substrates

    International Nuclear Information System (INIS)

    Neutron reflectivity was used to probe the structure of single phosphatidylcholine (PC) lipid bilayers adsorbed onto a planar silicon surface in an aqueous environment. Fluctuations in the neutron scattering length density profiles perpendicular to the silicon/water interface were determined for different lipids as a function of the hydrocarbon chain length. The lipids were studied in both the gel and liquid crystalline phases by monitoring changes in the specularly-reflected neutron intensity as a function of temperature. Contrast variation of the neutron scattering length density was applied to both the lipid and the solvent. Scattering length density profiles were determined using both model-independent and model-dependent fitting methods. During the reflectivity measurements, a novel experimental set-up was implemented to decrease the incoherent background scattering due to the solvent. Thus, the reflectivity was measured to Q ∼ 0.3 Angstrom -1, covering up to seven orders of magnitude in reflected intensity, for PC bilayers in D2O and silicon-matched (38% D2O/62% H2O) water. The kinetics of lipid adsorption at the silicon/water interface were also explored by observing changes in the reflectivity at low Q values under silicon-matched water conditions

  16. Neutron reflectivity studies of single lipid bilayers supported on planar substrates

    Energy Technology Data Exchange (ETDEWEB)

    Krueger, S.; Orts, W.J.; Berk, N.F.; Majkrzak, C.F. [National Inst. of Standards and Technology, Gaithersburg, MD (United States); Koenig, B.W. [National Inst. of Health, Bethesda, MD (United States)

    1994-12-31

    Neutron reflectivity was used to probe the structure of single phosphatidylcholine (PC) lipid bilayers adsorbed onto a planar silicon surface in an aqueous environment. Fluctuations in the neutron scattering length density profiles perpendicular to the silicon/water interface were determined for different lipids as a function of the hydrocarbon chain length. The lipids were studied in both the gel and liquid crystalline phases by monitoring changes in the specularly-reflected neutron intensity as a function of temperature. Contrast variation of the neutron scattering length density was applied to both the lipid and the solvent. Scattering length density profiles were determined using both model-independent and model-dependent fitting methods. During the reflectivity measurements, a novel experimental set-up was implemented to decrease the incoherent background scattering due to the solvent. Thus, the reflectivity was measured to Q {approx} 0.3{Angstrom}{sup -1}, covering up to seven orders of magnitude in reflected intensity, for PC bilayers in D{sub 2}O and silicon-matched (38% D{sub 2}O/62% H{sub 2}O) water. The kinetics of lipid adsorption at the silicon/water interface were also explored by observing changes in the reflectivity at low Q values under silicon-matched water conditions.

  17. Empirical Analysis of the Determinants of Marketing Contract Structures

    OpenAIRE

    Paulson, Nicholas D.; Katchova, Ani L.; Sergio H. Lence

    2008-01-01

    Initial draft replaced by updated/revised version. This is an electronic version of a journal article, please cite as: Paulson, N.D., A.L. Katchova, and S.H. Lence. “An Empirical Analysis of the Determinants of Marketing Contract Structures for Corn and Soybeans.” Journal of Agricultural and Food Industrial Organization 8(2010), 4: 1-23.

  18. Regional Mechanics Determine Collagen Fiber Structure in Healing Myocardial Infarcts

    OpenAIRE

    Fomovsky, Gregory M.; Rouillard, Andrew D.; Holmes, Jeffrey W.

    2012-01-01

    Following myocardial infarction, the mechanical properties of the healing infarct are an important determinant of heart function and the risk of progression to heart failure. In particular, mechanical anisotropy (having different mechanical properties in different directions) in the healing infarct can preserve pump function of the heart. Based on reports of different collagen structures and mechanical properties in various animal models, we hypothesized that differences in infarct size, shap...

  19. The potential for biological structure determination with pulsed neutrons

    International Nuclear Information System (INIS)

    The potential of pulsed neutron diffraction in structural determination of biological materials is discussed. The problems and potential solutions in this area are outlined, with reference to both current and future sources and instrumentation. The importance of developing instrumentation on pulsed sources in emphasized, with reference to the likelihood of future expansion in this area. The possibilities and limitations of single crystal, fiber and powder diffraction in this area are assessed

  20. Empirical Study on Capital Structure Determinants in Chinese Listed Companies

    OpenAIRE

    Zhang, Jiye

    2010-01-01

    This paper develops a preliminary study to investigate the determinants of capital structure of Chinese-listed companies using panel data. The analysis of the research is based on the dataset of 200 Chinese listed firms which publicly traded A-shares on both Shanghai and Shenzhen Stock Exchange between 2005 and 2009. The different theories, specifically, the trade-off, pecking order, agency theory, market timing and signalling theories, are deployed to clarify and predict the signs and signif...

  1. The potential for biological structure determination with pulsed neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, C.C. [CLRC Rutherford Appleton Laboratory, Chilton Didcot Oxon (United Kingdom)

    1994-12-31

    The potential of pulsed neutron diffraction in structural determination of biological materials is discussed. The problems and potential solutions in this area are outlined, with reference to both current and future sources and instrumentation. The importance of developing instrumentation on pulsed sources in emphasized, with reference to the likelihood of future expansion in this area. The possibilities and limitations of single crystal, fiber and powder diffraction in this area are assessed.

  2. Structural Determination and Daily Variations of Porcine Milk Oligosaccharides

    OpenAIRE

    Tao, Nannan; Ochonicky, Karen L.; German, J Bruce; Donovan, Sharon M.; Lebrilla, Carlito B.

    2010-01-01

    Free milk oligosaccharides (OS) is a major component of mammalian milk. Swine are important agricultural species and biomedical models. Despite their importance, little is known of the OS profile of porcine milk. Herein, the porcine milk glycome was elucidated and monitored over the entire lactation period by liquid chromatography profiling and structural determination with mass spectrometry. Milk was collected from second parity sows (n=3) at farrowing and on days 1, 4, 7 and 24 of lactation...

  3. Determination of the Basin Structure Beneath European Side of Istanbul

    Science.gov (United States)

    Karabulut, Savas; Cengiz Cinku, Mulla; Thomas, Michael; Lamontagne, Maurice

    2016-04-01

    Istanbul (near North Anatolian Fault Zone:NAFZ, Turkey) is located in northern part of Sea of Marmara, an area that has been influenced by possible Marmara Earthquakes. The general geology of Istanbul divided into two stratigraphic unit such as sedimentary (from Oligocene to Quaternary Deposits) and bedrock (Paleozoic and Eocene). The bedrock units consists of sand stone, clay stone to Paleozoic age and limestone to Eocene age and sedimentary unit consist of sand, clay, mil and gravel from Oligocene to Quaternary age. Earthquake disaster mitigation studies divided into two important phases, too. Firstly, earthquake, soil and engineering structure problems identify for investigation area, later on strategic emergency plan can prepare for these problems. Soil amplification play important role the disaster mitigation and the site effect analysis and basin structure is also a key parameter for determining of site effect. Some geophysical, geological and geotechnical measurements are requeired to defined this relationship. Istanbul Megacity has been waiting possible Marmara Earthquake and their related results. In order to defined to possible damage potential related to site effect, gravity measurements carried out for determining to geological structure, basin geometry and faults in Istanbul. Gravity data were collected at 640 sites by using a Scientrex CG-5 Autogravity meter Standard corrections applied to the gravity data include those for instrumental drift, Earth tides and latitude, and the free-air and Bouguer corrections. The corrected gravity data were imported into a Geosoft database to create a grid and map of the Bouguer gravity anomaly (grid cell size of 200 m). As a previously results, we determined some lineminants, faults and basins beneath Istanbul City. Especially, orientation of faults were NW-SE direction and some basin structures determined on between Buyukcekmece and Kucukcekmece Lake.

  4. MOTIVATION INTERNALIZATION AND SIMPLEX STRUCTURE IN SELF-DETERMINATION THEORY.

    Science.gov (United States)

    Ünlü, Ali; Dettweiler, Ulrich

    2015-12-01

    Self-determination theory, as proposed by Deci and Ryan, postulated different types of motivation regulation. As to the introjected and identified regulation of extrinsic motivation, their internalizations were described as "somewhat external" and "somewhat internal" and remained undetermined in the theory. This paper introduces a constrained regression analysis that allows these vaguely expressed motivations to be estimated in an "optimal" manner, in any given empirical context. The approach was even generalized and applied for simplex structure analysis in self-determination theory. The technique was exemplified with an empirical study comparing science teaching in a classical school class versus an expeditionary outdoor program. Based on a sample of 84 German pupils (43 girls, 41 boys, 10 to 12 years old), data were collected using the German version of the Academic Self-Regulation Questionnaire. The science-teaching format was seen to not influence the pupils' internalization of identified regulation. The internalization of introjected regulation differed and shifted more toward the external pole in the outdoor teaching format. The quantification approach supported the simplex structure of self-determination theory, whereas correlations may disconfirm the simplex structure. PMID:26595290

  5. Orientational constraints as three-dimensional structural constraints from chemical shift anisotropy: the polypeptide backbone of gramicidin A in a lipid bilayer.

    OpenAIRE

    Mai, W.; Hu, W; Wang, C; Cross, T A

    1993-01-01

    Chemical shifts observed from samples that are uniformly aligned with respect to the magnetic field can be used as very high-resolution structural constraints. This constraint takes the form of an orientational constraint rather than the more familiar distance constraint. The accuracy of these constraints is dependent upon the quality of the tensor characterization. Both tensor element magnitudes and tensor orientations with respect to the molecular frame need to be considered. Here these con...

  6. Determination of the stretch tensor for structural transformations

    Science.gov (United States)

    Chen, Xian; Song, Yintao; Tamura, Nobumichi; James, Richard D.

    2016-08-01

    Structural transformations in crystalline solids are increasingly the basis of the functional behavior of materials. Recently, in diverse alloy systems, both low hysteresis and reversibility of phase transformations have been linked to the satisfaction of the nongeneric conditions of compatibility between phases. According to the Cauchy-Born rule, these conditions are expressed as properties of transformation stretch tensor. The transformation stretch tensor is difficult to measure directly due to the lack of knowledge about the exact transforming pathway during the structural change, and the complicating effects of microstructure. In this paper we give a rigorous algorithmic approach for determining the transformation stretch tensor from X-ray measurements of structure and lattice parameters. For some traditional and emerging phase transformations, the results given by the algorithm suggest unexpected transformation mechanisms.

  7. Local magnetic structure determination using polarized neutron holography

    Energy Technology Data Exchange (ETDEWEB)

    Szakál, Alex, E-mail: szakal.alex@wigner.mta.hu; Markó, Márton, E-mail: marko.marton@wigner.mta.hu; Cser, László, E-mail: cser.laszlo@wigner.mta.hu [Wigner Research Centre for Physics, Konkoly Thege M. út 29-33, H-1121 Budapest (Hungary)

    2015-05-07

    A unique and important property of the neutron is that it possesses magnetic moment. This property is widely used for determination of magnetic structure of crystalline samples observing the magnetic components of the diffraction peaks. Investigations of diffraction patterns give information only about the averaged structure of a crystal but for discovering of local spin arrangement around a specific (e.g., impurity) nucleus remains still a challenging problem. Neutron holography is a useful tool to investigate the local structure around a specific nucleus embedded in a crystal lattice. The method has been successfully applied experimentally in several cases using non-magnetic short range interaction of the neutron and the nucleus. A mathematical model of the hologram using interaction between magnetic moment of the atom and the neutron spin for polarized neutron holography is provided. Validity of a polarized neutron holographic experiment is demonstrated by applying the proposed method on model systems.

  8. Asymmetric bilayer graphene nanoribbon MOSFETs for analog and digital electronics

    Science.gov (United States)

    Dinarvand, A.; Ahmadi, V.; Darvish, Gh.

    2016-05-01

    In this paper, a new structure was proposed for bilayer graphene nanoribbon field-effect transistor (BGNFET) mainly to enhance the electrical characteristics in analog and digital applications. The proposed device uses two metallic gates on the top and bottom of a bilayer graphene nanoribbon, which is surrounded by SiO2 and connected to heavily doped source/drain contacts. Electrical properties of the proposed device were explored using fully self-consistent solution of Poisson and Schrödinger equations based on the nonequilibrium Green's function (NEGF) formalism. Significant improvements in the electrical behavior was seen in the simulation results for gates asymmetrically biased. The comparison with graphene nanoribbon FET showed that the proposed structure benefited from higher intrinsic voltage gain and cut-off frequency and improved switching characteristics such as delay and Ion/Ioff ratio.

  9. Superdiffusion in supported lipid bilayers

    CERN Document Server

    Campagnola, Grace; Schroder, Bryce W; Peersen, Olve B; Krapf, Diego

    2015-01-01

    We study the diffusion of membrane-targeting C2 domains using single-molecule tracking in supported lipid bilayers. The ensemble-averaged mean square displacement (MSD) exhibits superdiffusive behavior. However, the time-averaged MSD of individual trajectories is found to be linear with respect to lag time, as in Brownian diffusion. These observations are explained in terms of bulk excursions that introduce jumps with a heavy-tail distribution. Our experimental results are shown to agree with analytical models of bulk-mediated diffusion and with numerical simulations.

  10. Robustly Engineering Thermal Conductivity of Bilayer Graphene by Interlayer Bonding

    OpenAIRE

    Xiaoliang Zhang; Yufei Gao; Yuli Chen; Ming Hu

    2016-01-01

    Graphene and its bilayer structure are the two-dimensional crystalline form of carbon, whose extraordinary electron mobility and other unique features hold great promise for nanoscale electronics and photonics. Their realistic applications in emerging nanoelectronics usually call for thermal transport manipulation in a controllable and precise manner. In this paper we systematically studied the effect of interlayer covalent bonding, in particular different interlay bonding arrangement, on the...

  11. Predicting proton titration in cationic micelle and bilayer environments

    OpenAIRE

    Brian H. Morrow; Eike, David M.; Murch, Bruce P.; Koenig, Peter H.; Shen, Jana K.

    2014-01-01

    Knowledge of the protonation behavior of pH-sensitive molecules in micelles and bilayers has significant implications in consumer product development and biomedical applications. However, the calculation of pKa’s in such environments proves challenging using traditional structure-based calculations. Here we apply all-atom constant pH molecular dynamics with explicit ions and titratable water to calculate the pKa of a fatty acid molecule in a micelle of dodecyl trimethylammonium chloride and l...

  12. Enhanced Thermoelectric Power in Dual-Gated Bilayer Graphene

    OpenAIRE

    Wang, Chang-Ran; Lu, Wen-Sen; Hao, Lei; Lee, Wei-Li; Lee, Ting-Kuo; Lin, Feng; Cheng, I-Chun; Chen, Jian-Zhang

    2011-01-01

    Thermoelectric power of a material, typically governed by its band structure and carrier density, can be varied by chemical doping that is often restricted by solubility of the dopant. Materials showing large thermoelectric power are useful for many industrial applications, such as the heat-to-electricity conversion and the thermoelectric cooling device. Here we show a full electric field tuning of thermoelectric power in a dual-gated bilayer graphene device resulting from the opening of a ba...

  13. Quantum Hall effect in bilayer system with array of antidots

    Science.gov (United States)

    Pagnossin, I. R.; Gusev, G. M.; Sotomayor, N. M.; Seabra, A. C.; Quivy, A. A.; Lamas, T. E.; Portal, J. C.

    2007-04-01

    We have studied the Quantum Hall effect in a bilayer system modulated by gate-controlled antidot lattice potential. The Hall resistance shows plateaus which are quantized to anomalous multiplies of h/e2. We suggest that this complex behavior is due to the nature of the edge-states in double quantum well (DQW) structures coupled to an array of antidots: these plateaus may be originated from the coexistence of normal and counter-rotating edge-states in different layers.

  14. Self-assembling bilayers of palladiumthiolates in organic media

    Indian Academy of Sciences (India)

    P John Thomas; A Lavanya; V Sabareesh; G U Kulkarni

    2001-10-01

    Alkylthiolates of palladium forming a homologous series (butyl to octadecyl) have been prepared and characterized using X-ray diffraction and STM. The thiolates adopt an unusual bilayered lamellar structure, whose thickness is governed by the length of the alkyl chain. These mesophases melt in the temperature range, 60° to 100°C, with the melting point increasing linearly with the thiol chain length. There is evidence to suggest that the alkyl chains are orientationally disordered especially prior to melting.

  15. Determination of organic crystal structures by X ray powder diffraction

    CERN Document Server

    McBride, L

    2000-01-01

    The crystal structure of Ibuprofen has been solved from synchrotron X-ray powder diffraction data using a genetic algorithm (GA). The performance of the GA is improved by incorporating prior chemical information in the form of hard limits on the values that can be taken by the flexible torsion angles within the molecule. Powder X-ray diffraction data were collected for the anti-convulsant compounds remacemide, remacemide nitrate and remacemide acetate at 130 K on BM 16 at the X-ray European Synchrotron Radiation Facility (ESRF) at Grenoble. High quality crystal structures were obtained using data collected to a resolution of typically 1.5 A. The structure determinations were performed using a simulated annealing (SA) method and constrained Rietveld refinements for the structures converged to chi sup 2 values of 1.64, 1.84 and 1.76 for the free base, nitrate and acetate respectively. The previously unknown crystal structure of the drug famotidine Form B has been solved using X-ray powder diffraction data colle...

  16. Quantum quench dynamics and population inversion in bilayer graphene

    OpenAIRE

    Dóra, Balázs; Castro, Eduardo V.; Moessner, Roderich

    2010-01-01

    The gap in bilayer graphene (BLG) can directly be controlled by a perpendicular electric field. By tuning the field through zero at a finite rate in neutral BLG, excited states are produced. Due to screening, the resulting dynamics is determined by coupled non-linear Landau-Zener models. The generated defect density agrees with Kibble-Zurek theory in the presence of subleading logarithmic corrections. After the quench, population inversion occurs for wavevectors close to the Dirac point. This...

  17. Elastic deformation and failure of lipid bilayer membranes containing cholesterol.

    OpenAIRE

    Needham, D; Nunn, R. S.

    1990-01-01

    Giant bilayer vesicles were reconstituted from several lipids and lipid/cholesterol (CHOL) mixtures: stearolyloleoylphosphatidylcholine (SOPC), bovine sphingomyelin (BSM), diarachidonylphosphatidylcholine (DAPC), SOPC/CHOL, BSM/CHOL, DAPC/CHOL, and extracted red blood cell (RBC) lipids with native cholesterol. Single-walled vesicles were manipulated by micropipette suction and several membrane material properties were determined. The properties measured were the elastic area compressibility m...

  18. Annular bilayer magnetoelectric composites: theoretical analysis.

    Science.gov (United States)

    Guo, Mingsen; Dong, Shuxiang

    2010-01-01

    The laminated bilayer magnetoelectric (ME) composites consist of magnetostrictive and piezoelectric layers are known to have giant ME coefficient due to the high coupling efficiency in bending mode. In our previous report, the bar-shaped bilayer composite has been investigated by using a magnetoelectric-coupling equivalent circuit. Here, we propose an annular bilayer ME composite, which consists of magnetostrictive and piezoelectric rings. This composite has a much lower resonance frequency of bending mode compared with its radial mode. In addition, the annular bilayer ME composite is expected to respond to vortex magnetic field as well as unidirectional magnetic field. In this paper, we investigate the annular bilayer ME composite by using impedance-matrix method and predict the ME coefficients as a function of geometric parameters of the composites. PMID:20178914

  19. Anisotropic metal growth on phospholipid nanodiscs via lipid bilayer expansion.

    Science.gov (United States)

    Oertel, Jana; Keller, Adrian; Prinz, Julia; Schreiber, Benjamin; Hübner, René; Kerbusch, Jochen; Bald, Ilko; Fahmy, Karim

    2016-01-01

    Self-assembling biomolecules provide attractive templates for the preparation of metallic nanostructures. However, the intuitive transfer of the "outer shape" of the assembled macromolecules to the final metallic particle depends on the intermolecular forces among the biomolecules which compete with interactions between template molecules and the metal during metallization. The shape of the bio-template may thus be more dynamic than generally assumed. Here, we have studied the metallization of phospholipid nanodiscs which are discoidal particles of ~10 nm diameter containing a lipid bilayer ~5 nm thick. Using negatively charged lipids, electrostatic adsorption of amine-coated Au nanoparticles was achieved and followed by electroless gold deposition. Whereas Au nanoparticle adsorption preserves the shape of the bio-template, metallization proceeds via invasion of Au into the hydrophobic core of the nanodisc. Thereby, the lipidic phase induces a lateral growth that increases the diameter but not the original thickness of the template. Infrared spectroscopy reveals lipid expansion and suggests the existence of internal gaps in the metallized nanodiscs, which is confirmed by surface-enhanced Raman scattering from the encapsulated lipids. Interference of metallic growth with non-covalent interactions can thus become itself a shape-determining factor in the metallization of particularly soft and structurally anisotropic biomaterials. PMID:27216789

  20. Anisotropic metal growth on phospholipid nanodiscs via lipid bilayer expansion

    Science.gov (United States)

    Oertel, Jana; Keller, Adrian; Prinz, Julia; Schreiber, Benjamin; Hübner, René; Kerbusch, Jochen; Bald, Ilko; Fahmy, Karim

    2016-05-01

    Self-assembling biomolecules provide attractive templates for the preparation of metallic nanostructures. However, the intuitive transfer of the “outer shape” of the assembled macromolecules to the final metallic particle depends on the intermolecular forces among the biomolecules which compete with interactions between template molecules and the metal during metallization. The shape of the bio-template may thus be more dynamic than generally assumed. Here, we have studied the metallization of phospholipid nanodiscs which are discoidal particles of ~10 nm diameter containing a lipid bilayer ~5 nm thick. Using negatively charged lipids, electrostatic adsorption of amine-coated Au nanoparticles was achieved and followed by electroless gold deposition. Whereas Au nanoparticle adsorption preserves the shape of the bio-template, metallization proceeds via invasion of Au into the hydrophobic core of the nanodisc. Thereby, the lipidic phase induces a lateral growth that increases the diameter but not the original thickness of the template. Infrared spectroscopy reveals lipid expansion and suggests the existence of internal gaps in the metallized nanodiscs, which is confirmed by surface-enhanced Raman scattering from the encapsulated lipids. Interference of metallic growth with non-covalent interactions can thus become itself a shape-determining factor in the metallization of particularly soft and structurally anisotropic biomaterials.

  1. Synthesis and Structural Determination of Temocapril Sulfoxide Hydrochlorides

    Energy Technology Data Exchange (ETDEWEB)

    Seong, Seok Bong; Moon, Jong Taik; Kim, Jung Ahn; Choo, Dong Joon; Lee, Jae Yeol [Kyung Hee Univ., Seoul (Korea, Republic of)

    2012-10-15

    Impurity (or related substance) control in pharmaceutical products is a primary goal of drug development. Stringent international regulatory requirements have been in place for several years as outlined in the International Conference on Harmonization (ICH) Guidelines Q3A (R), Q3B (R) and Q3C. According to ICH guidelines, impurities associated with the manufacture of a drug substance, also known as an active pharmaceutical ingredient (API), are classified into the following categories: (1) organic impurities (process and drug-related); (2) inorganic impurities (3) residual solvents. Many potential impurities result from the API manufacturing process including starting materials, isomers, intermediates, reagents, solvents, catalysts and reaction by-products. These potential impurities should be investigated to determine process control mechanisms for their removal and the need for specification controls at appropriate points in the process. The suggested structures of the impurities can be synthesized and will provide the final evidence for their structures, previously determined by spectroscopic methods. Therefore it is essential to know the structure of these impurities in the bulk drug in order to alter the reaction condition and to reduce the quantity of impurity to an acceptable level. Isolation, identification and quantification of impurities help the pharmaceutical company to obtain a pure substance with less toxicity and safety in drug therapy.

  2. Assessment of carotid plaque vulnerability using structural and geometrical determinants

    International Nuclear Information System (INIS)

    Because many acute cerebral ischemic events are caused by rupture of vulnerable carotid atheroma and subsequent thrombosis, the present study used both idealized and patient-specific carotid atheromatous plaque models to evaluate the effect of structural determinants on stress distributions within plaque. Using a finite element method, structural analysis was performed using models derived from in vivo high-resolution magnetic resonance imaging (MRI) of carotid atheroma in 40 non-consecutive patients (20 symptomatic, 20 asymptomatic). Plaque components were modeled as hyper-elastic materials. The effects of varying fibrous cap thickness, lipid core size and lumen curvature on plaque stress distributions were examined. Lumen curvature and fibrous cap thickness were found to be major determinants of plaque stress. The size of the lipid core did not alter plaque stress significantly when the fibrous cap was relatively thick. The correlation between plaque stress and lumen curvature was significant for both symptomatic (p=0.01; correlation coefficient: 0.689) and asymptomatic patients (p=0.01; correlation coefficient: 0.862). Lumen curvature in plaques of symptomatic patients was significantly larger than those of asymptomatic patients (1.50±1.0 mm-1 vs 1.25±0.75 mm-1; p=0.01). Specific plaque morphology (large lumen curvature and thin fibrous cap) is closely related to plaque vulnerability. Structural analysis using high-resolution MRI of carotid atheroma may help in detecting vulnerable atheromatous plaque and aid the risk stratification of patients with carotid disease. (author)

  3. Synthesis and Structural Determination of Temocapril Sulfoxide Hydrochlorides

    International Nuclear Information System (INIS)

    Impurity (or related substance) control in pharmaceutical products is a primary goal of drug development. Stringent international regulatory requirements have been in place for several years as outlined in the International Conference on Harmonization (ICH) Guidelines Q3A (R), Q3B (R) and Q3C. According to ICH guidelines, impurities associated with the manufacture of a drug substance, also known as an active pharmaceutical ingredient (API), are classified into the following categories: (1) organic impurities (process and drug-related); (2) inorganic impurities (3) residual solvents. Many potential impurities result from the API manufacturing process including starting materials, isomers, intermediates, reagents, solvents, catalysts and reaction by-products. These potential impurities should be investigated to determine process control mechanisms for their removal and the need for specification controls at appropriate points in the process. The suggested structures of the impurities can be synthesized and will provide the final evidence for their structures, previously determined by spectroscopic methods. Therefore it is essential to know the structure of these impurities in the bulk drug in order to alter the reaction condition and to reduce the quantity of impurity to an acceptable level. Isolation, identification and quantification of impurities help the pharmaceutical company to obtain a pure substance with less toxicity and safety in drug therapy

  4. Soliton-dependent plasmon reflection at bilayer graphene domain walls

    Science.gov (United States)

    Jiang, Lili; Shi, Zhiwen; Zeng, Bo; Wang, Sheng; Kang, Ji-Hun; Joshi, Trinity; Jin, Chenhao; Ju, Long; Kim, Jonghwan; Lyu, Tairu; Shen, Yuen-Ron; Crommie, Michael; Gao, Hong-Jun; Wang, Feng

    2016-08-01

    Layer-stacking domain walls in bilayer graphene are emerging as a fascinating one-dimensional system that features stacking solitons structurally and quantum valley Hall boundary states electronically. The interactions between electrons in the 2D graphene domains and the one-dimensional domain-wall solitons can lead to further new quantum phenomena. Domain-wall solitons of varied local structures exist along different crystallographic orientations, which can exhibit distinct electrical, mechanical and optical properties. Here we report soliton-dependent 2D graphene plasmon reflection at different 1D domain-wall solitons in bilayer graphene using near-field infrared nanoscopy. We observe various domain-wall structures in mechanically exfoliated graphene bilayers, including network-forming triangular lattices, individual straight or bent lines, and even closed circles. The near-field infrared contrast of domain-wall solitons arises from plasmon reflection at domain walls, and exhibits markedly different behaviours at the tensile- and shear-type domain-wall solitons. In addition, the plasmon reflection at domain walls exhibits a peculiar dependence on electrostatic gating. Our study demonstrates the unusual and tunable coupling between 2D graphene plasmons and domain-wall solitons.

  5. Interfacial exchange coupling in cubic Heusler Co2FeZ (Z = Al and Si)/tetragonal Mn3Ga bilayers

    Science.gov (United States)

    Ranjbar, R.; Suzuki, K.; Sugihara, A.; Ma, Q. L.; Zhang, X. M.; Miyazaki, T.; Ando, Y.; Mizukami, S.

    2015-05-01

    We have fabricated bilayer films of tetragonal Heusler-like D022 Mn3Ga and cubic Heusler Co2FeZ (Z = Si and Al) on (100) single-crystalline MgO substrates and investigated their structural and interfacial exchange coupling. The coupling in the Mn3Ga/Co2FeAl bilayer was either ferromagnetic or antiferromagnetic, depending on annealing temperature, whereas only antiferromagnetic exchange coupling was observed in the Mn3Ga/Co2FeSi bilayers. The effects of annealing on the structure and coupling strength in the bilayers are discussed.

  6. Structure Determination of Natural Products by Nuclear Magnetic Resonance Spectroscopy

    Science.gov (United States)

    Li, Du.

    High-field NMR experiments were used to determine the full structures of six new natural products extracted from plants. These are: four saponins (PT-2, P1, P2 and P3) from the plant Alphitonia zizyphoides found in Samoa; one sesquiterpene (DF-4) from Douglas fir and one diterpene derivative (E-2) from a Chinese medicinal herb. By concerted use of various 1D and 2D NMR techniques, the structures of the above compounds were established and complete resonance assignments were achieved. The 2D INADEQUATE technique coupled with a computerized spectral analysis was extensively used. When carried out on concentrations as low as 60 mg of sample, this technique provided absolute confirmation of the assignments for 35 of the possible 53 C-C bonds for PT-2. On 30 mg of sample of E-21, it revealed 22 of 28 possible C-C bonds.

  7. Determination of the structure of UFe2Al10 compound

    International Nuclear Information System (INIS)

    The atomic structure of a new ternary phase UFe2Al10 appearing in the U-Fe-Al system was determined using direct methods applied to X-ray powder diffraction data. High resolution electron microscopy combined with the methods of crystallographic image processing was used for the verification of the structural model. The UFe2Al10 phase is orthorhombic and belongs to Cmcm space group, its unit cell contains 40 Al, eight Fe, and four U atoms. The lattice parameters obtained after Rietveld refinement are: a=8.919 A, b=10.208 A, and c=9.018 A. The reliability factors characterizing the Rietveld refinement procedure are: Rp=5.9%, Rwp=8.1%, and Rb=2.9%

  8. The Phenix Software for Automated Determination of Macromolecular Structures

    Science.gov (United States)

    Adams, Paul D.; Afonine, Pavel V.; Bunkóczi, Gábor; Chen, Vincent B.; Echols, Nathaniel; Headd, Jeffrey J.; Hung, Li-Wei; Jain, Swati; Kapral, Gary J.; Grosse Kunstleve, Ralf W.; McCoy, Airlie J.; Moriarty, Nigel W.; Oeffner, Robert D.; Read, Randy J.; Richardson, David C.; Richardson, Jane S.; Terwilliger, Thomas C.; Zwart, Peter H.

    2011-01-01

    X-ray crystallography is a critical tool in the study of biological systems. It is able to provide information that has been a prerequisite to understanding the fundamentals of life. It is also a method that is central to the development of new therapeutics for human disease. Significant time and effort are required to determine and optimize many macromolecular structures because of the need for manual interpretation of complex numerical data, often using many different software packages, and the repeated use of interactive three-dimensional graphics. The Phenix software package has been developed to provide a comprehensive system for macromolecular crystallographic structure solution with an emphasis on automation. This has required the development of new algorithms that minimize or eliminate subjective input in favour of built-in expert-systems knowledge, the automation of procedures that are traditionally performed by hand, and the development of a computational framework that allows a tight integration between the algorithms. The application of automated methods is particularly appropriate in the field of structural proteomics, where high throughput is desired. Features in Phenix for the automation of experimental phasing with subsequent model building, molecular replacement, structure refinement and validation are described and examples given of running Phenix from both the command line and graphical user interface. PMID:21821126

  9. Bilayer Approaches for Nanoparticle Phase Transfer

    Science.gov (United States)

    Kini, Gautam Chandrakanth

    . Electrophoresis, thermogravimetric analysis and photoluminescence measurements using a solvatochromic dye established higher surfactant coverage with greater lateral compaction for QDs in salty-micelles over the DI-micelle counterpart. Single NP characteristics along with a hydrophobic environment in laterally compact salty-micelles resulted in better retention of optical properties of QDs. Observations of a secondary effect by salt in inducing spontaneous emulsification of a hydrocarbon (octane)/AOT/brine system were systematically investigated by tracking time-variant octane droplet size and charge. Salinity levels that determine the spontaneous curvature and phase behavior of AOT were seen to influence the initial nucleation of octane droplets and their subsequent growth. The smallest octane drops (sub 50 nm) were nucleated at the optimum cross-over salinity and emergence of the liquid crystalline phase of AOT resulted in slowest growth rates. These factors contributed towards higher transfer efficiency of NPs in salty-micelles. Two applications from formulating aqueous NP suspensions by the new phase-transfer approach are described. In the first, QD and carbon-dot (C-Dot) "nanoreporters" were formulated for oil-field reservoir characterization using Neodol 91-7 (nonionic) and Avanel S150 CGN (hybrid nonionic and anionic) as surfactants. These NPs were stable to aggregation under reservoir-representative conditions (salinities: 1M NaCl, 1M KCl and 0.55M synthetic seawater; temperatures: 70-100 °C) and demonstrated flow and transport through crushed-calcite and quartz-sand columns with high breakthrough and recovery (> 90%). In the second application, tandem assembly of a cationic polymer, multivalent salt, and NPs was investigated in a microfluidic channel where charge ratio of the polymer/salt and shear from flow and device geometry determined their assembly into higher ordered structures such as gels and capsules.

  10. The determinants of Capital structure of firms in Japan

    OpenAIRE

    CHEN, ZHANQUAN

    2013-01-01

    This dissertation is going to study the determinants of capital structure of firms in Japan. As previous empirical researches, they all pointed out the factors in different countries. Therefore, it is going to carry out the empirical research in Japanese firms. The sample data used in this dissertation is from a panel data set of 193 non-financial companies in the NIKKIE 225 during the periods from 2003 to 2013. Firstly, it presents MM theory and two mainly modern theories which are the trade...

  11. Structural and chemical determination of the new nanolaminated carbide Mo2Ga2C from first principles and materials analysis

    International Nuclear Information System (INIS)

    Following our recent discovery of a new nanolaminated carbide, Mo2Ga2C, we herein present a detailed structural and chemical analysis of this phase based on ab initio calculations, X-ray photoelectron spectroscopy, high resolution scanning transmission electron microscopy, and neutron powder diffraction. Calculations suggest an energetically and dynamically stable structure for C in the octahedral sites between the Mo layers, with Ga bilayers – stacked in a simple hexagonal arrangement – between the Mo2C layers. The predicted elastic properties are below those of the related nanolaminate Mo2GaC. The predicted structure, including lattice parameters and atomic positions, is experimentally confirmed

  12. The influence of interface on spin pumping effect in Ni80Fe20 /Tb bilayer

    Science.gov (United States)

    Yue, Jinjin; Jiang, Sheng; Zhang, Dong; Yuan, Honglei; Wang, Yukun; Lin, Lin; Zhai, Ya; Du, Jun; Zhai, Hongru

    2016-05-01

    Focusing on the interface effect of the Ni80Fe20 (Py)/terbium (Tb) bilayer, the influence of interface on the magnetization dynamic damping is investigated systematically. Two series of Py (12 nm)/Tb (d nm) films with and without copper (Cu) (1 nm) interlayer are deposited on silicon (Si) substrates by DC magnetron sputtering at room temperature. From vibrating sample magnetometer (VSM) measurements, the saturation magnetization (Ms) decreases with increasing Tb thickness in Py/Tb bilayer while the decrease of Ms is suppressed efficiently by inserting a Cu layer with even 1 nm of thickness. From the frequency dependence of ferromagnetic resonance (FMR) linewidth, we can obtain the Gilbert damping coefficient (α), α is found to exhibit an extreme enhancement in comparison to the single Py layer and shows an increasing trend with increasing Tb thickness. By inserting the Cu layer, α decreases significantly. From theoretical fitting, the spin diffusion length (λSD) and spin mixing conductance (g↑↓) are determined. It shows that the interface structure influences the spin mixing conductance but not the spin diffusion length.

  13. Physisorbed Polymer-Tethered Lipid Bilayer with Lipopolymer Gradient

    Directory of Open Access Journals (Sweden)

    Christoph A. Naumann

    2012-11-01

    Full Text Available Physisorbed polymer-tethered lipid bilayers consisting of phospholipids and lipopolymers represent an attractive planar model membrane platform, in which bilayer fluidity and membrane elastic properties can be regulated through lipopolymer molar concentration. Herein we report a method for the fabrication of such a planar model membrane system with a lateral gradient of lipopolymer density. In addition, a procedure is described, which leads to a sharp boundary between regions of low and high lipopolymer molar concentrations. Resulting gradients and sharp boundaries are visualized on the basis of membrane buckling structures at elevated lipopolymer concentrations using epifluorescence microscopy and atomic force microscopy. Furthermore, results from spot photobleaching experiments are presented, which provide insight into the lipid lateral fluidity in these model membrane architectures. The presented experimental data highlight a planar, solid-supported membrane characterized by fascinating length scale-dependent dynamics and elastic properties with remarkable parallels to those observed in cellular membranes.

  14. Effect of annealing on the characteristics of Au/Ni50Fe50 bilayer films grown on glass

    Institute of Scientific and Technical Information of China (English)

    Hao Qian; Hong Qiu; Xiaobai Chen; Yue Tian; Ping Wu; Fengping Wang; Liqing Pan

    2007-01-01

    Sputter-deposited Au/Ni50Fe50 bilayer films were annealed in a vacuum of 5×10-4 Pa at 523 to 723 K for 30 or 90 min. The characteristics of the bilayer films were determined by Auger electron spectroscopy, field emission scanning electron microscopy, X-ray diffractometry, a four-point probe technique, and an alternating gradient magnetometer. When the annealing temperature and time reached 723 K and 90 min, Ni and Fe atoms markedly diffused into the Au layer. The grain size of the Au layer did not change markedly with the annealing condition. As the annealing time was 30 min and the annealing temperature exceeded 573 K, the resistance of the bilayer film increased with increasing the annealing temperature. Furthermore, the resistance of the bilayer film annealed at 723 K for 90 min was lower than that of the bilayer film annealed at 723 K for 30 min. All the bilayer films showed magnetic hysteresis loops. The as-deposited bilayer film showed a hard magnetization. The bilayer film represented an easy magnetization with increasing the annealing temperature. The Au/Ni50Fe50 film that annealed at 723 K for 90 min had the lowest saturation magnetization.

  15. Localized plasmons in bilayer graphene nanodisks

    Science.gov (United States)

    Wang, Weihua; Xiao, Sanshui; Mortensen, N. Asger

    2016-04-01

    We study localized plasmonic excitations in bilayer graphene (BLG) nanodisks, comparing AA-stacked and AB-stacked BLG and contrasting the results to the case of two monolayers without electronic hybridization. The electrodynamic response of the BLG electron gas is described in terms of a spatially homogeneous surface conductivity, and an efficient alternative two-dimensional electrostatic approach is employed to carry out all the numerical calculations of plasmon resonances. Due to unique electronic band structures, the resonance frequency of the traditional dipolar plasmonic mode in the AA-stacked BLG nanodisk is roughly doping independent in the low-doping regime, while the mode is highly damped as the Fermi level approaches the interlayer hopping energy γ associated with tunneling of electrons between the two layers. In addition to the traditional dipolar mode, we find that the AB-stacked BLG nanodisk also hosts a new plasmonic mode with energy larger than γ . This mode can be tuned by either the doping level or structural size, and, furthermore, this mode can dominate the plasmonic response for realistic structural conditions.

  16. Methods for empirical formula, molecular structure determination and colloid characterisation

    International Nuclear Information System (INIS)

    Determination of empirical formula and of molecular structures in issues pertinent to the fuel cycle, waste management and remediation, as well as in risk assessment associated with radionuclide release and its migration to the near and far field of a repository present a particular challenge. Speciation techniques in these areas are needed for extraction chemistry of actinides, aquatic reactions of actinide ions (e.g. tetravalent actinide hydrolysis, formation of ternary complexes and redox chemistry), reactions at the water/mineral interface, formation of secondary phases and the formation of and interaction with colloids. The range of concentrations of interest is extreme, from relatively pure substances such as the fuels themselves, to tracer levels in far-field release scenarios. Actinide speciation in extractant solutions used for separation techniques for partitioning technologies involves investigation of solutions with often acidic pH, whereas speciation in cement pore waters, for example, can involve very basic solutions. Finally, the amount of sample available may be limited, e.g. pore water samples can be as small as μL quantities. There exist a variety of techniques for determining empirical formula and molecular structure of radionuclide species. The actual contents and components of the sample at hand in addition to the degree of complexity required dictates the method that is chosen. The speciation of radionuclides is often governed by their association with or formation to colloids. The characterisation of such colloids is imperative and their quantification and characterisation is, therefore, included as a separate treatise. (author)

  17. Membrane interactions of ternary phospholipid/cholesterol bilayers and encapsulation efficiencies of a RIP II protein.

    Science.gov (United States)

    Manojlovic, V; Winkler, K; Bunjes, V; Neub, A; Schubert, R; Bugarski, B; Leneweit, G

    2008-07-15

    Membrane interactions of liposomes of ternary phospholipid/cholesterol bilayers are investigated. These interactions lead to discoidal deformations and regular aggregations and are strongly enhanced by the presence of mistletoe lectin (ML), a RIP II type protein. The encapsulation of ML into liposomal nanocapsules is studied with a systematic variation of the lipid composition to monitor its effect on the physical properties: entrapment, mean size, morphology, and stability. Extrusion of multilamellar vesicles through filters 80 nm pore size was used for the generation of liposomes. The mean sizes of liposomes ranged between 120 and 200 nm in diameter with narrow size distributions. The increase in flow rate with pressure for three dioleoylphosphatidylcholine (DOPC)/cholesterol (Chol)/dipalmitoylphosphatidylcholine (DPPC) lipid mixtures was linear and allowed to extrapolate to the minimum burst pressure of the liposomal bilayers. From the minimum pressures P(min), the bilayer lysis tensions gamma(l) were determined. The increase in P(min) and gamma(l) with an increasing content of a saturated phosopholipid (DPPC) indicates that DPPC increases the mechanical strength of lipid bilayers. Apparently, DPPC, like cholesterol, leads to a less compressible surface and a more cohesive membrane. After preparation, vesicle solutions were purified by gel permeation chromatography to separate encapsulated ML from free ML in the extravesicular solution. Purified liposomes were then characterized. The content of entrapped and adsorbed ML was measured using ELISA. Repetitive freezing/thawing cycles prior to extrusion significantly increased ML uptake. On the contrary, adsorption was not affected neither by lipid composition, nor concentration and preparation. Differences in experimental encapsulation efficiency only reflect the differences in the mean vesicle sizes of the different samples as is revealed by a comparison to a theoretical estimate. Cryo-transmission electron

  18. Quantum Monte Carlo study of bilayer ionic Hubbard model

    Science.gov (United States)

    Jiang, M.; Schulthess, T. C.

    2016-04-01

    The interaction-driven insulator-to-metal transition has been reported in the ionic Hubbard model (IHM) for moderate interaction U , while its metallic phase only occupies a narrow region in the phase diagram. To explore the enlargement of the metallic regime, we extend the ionic Hubbard model to two coupled layers and study the interplay of interlayer hybridization V and two types of intralayer staggered potentials Δ : one with the same (in-phase) and the other with a π -phase shift (antiphase) potential between layers. Our determinant quantum Monte Carlo (DQMC) simulations at lowest accessible temperatures demonstrate that the interaction-driven metallic phase between Mott and band insulators expands in the Δ -V phase diagram of bilayer IHM only for in-phase ionic potentials; while antiphase potential always induces an insulator with charge density order. This implies possible further extension of the ionic Hubbard model from the bilayer case here to a realistic three-dimensional model.

  19. Determining Subsurface Structure From Microtremors Using a Passive Circular Array

    Science.gov (United States)

    Folger, D. S.; Doser, D. I.; Velasco, A. A.

    2005-12-01

    The amount of damage to a structure during an earthquake is related to the ground motion at that site. Therefore, it is important to study seismic waves that propagate through specific soil types to understand site response. However, active seismic surveys are susceptible to noise interference and are limited due to spatial need while boreholes are costly. We develop a method using a passive array to study Rayleigh waves from microtremors, waves originating from building appliances, cars, pedestrians walking, etc. By using everyday noises as the source, site-specific analysis can be done in urban areas without worrying about noise interference or disturbing the public with explosions or other loud active sources. The array is comprised of short period Texans, self contained geophones, which record continuously for 24 hours. Our technique differs slightly from traditional SPAC (SPatial Auto-Correlation) methods used in passive arrays. We first cross correlate time windows between two receivers then stack the correlations to determine a phase delay. Performing the correlation at different frequencies will create a dispersion curve that can be inverted for shear velocity. This approach is similar to the two-station phase delay method used in regional tomography studies at much longer periods. Stacking removes off-azimuth energy, so we do not need to assume a source direction. Preliminary results from a previous passive array survey conducted near El Paso, Texas show 1-D velocity models can be created by cross-correlating noise at various frequencies. We will conduct another survey in alluvium sands at Rio Bosque Park east of El Paso. We will validate the results with active seismic refraction and surface wave survey results as well as other geophysical techniques to determine if a passive array using microtremors is an accurate method of determining subsurface structure.

  20. A Determination of the Neutron Spin Structure Function

    International Nuclear Information System (INIS)

    The authors report the results of the experiment E142 which measured the spin dependent structure function of the neutron, g1n(x, Q2). The experiment was carried out at the Stanford Linear Accelerator Center by measuring an asymmetry in the deep inelastic scattering of polarized electrons from a polarized 3He target, at electron energies from 19 to 26 GeV. The structure function was determined over the kinematic range 0.03 2 2. An evaluation of the integral ∫01 g1n(x,Q2)dx at fixed Q2 = 2 (GeV/c)2 yields the final result Λ1n = -0.032 ± 0.006 (stat.) ± 0.009 (syst.). This result, when combined with the integral of the proton spin structure function measured in other experiments, confirms the fundamental Bjorken sum rule with O(αs3) corrections to within one standard deviation. This is a major success for perturbative Quantum Chromodynamics. Some ancillary results include the findings that the Ellis-Jaffe sum rule for the neutron is violated at the 2 σ level, and that the total contribution of the quarks to the helicity of the nucleon is 0.36 ± 0.10. The strange sea polarization is estimated to be small and negative, Δs = -0.07 ± 0.04

  1. Intermolecular interactions of lysobisphosphatidic acid with phosphatidylcholine in mixed bilayers.

    Science.gov (United States)

    Holopainen, Juha M; Söderlund, Tim; Alakoskela, Juha-Matti; Säily, Matti; Eriksson, Ove; Kinnunen, Paavo K J

    2005-01-01

    Lysobisphosphatidic acid (LBPA) can be regarded to represent a unique derivative of phosphatidylglycerol. This lipid is highly enriched in late endosomes where it can comprise up to 10-15 mol% of all lipids and in these membranes, LBPA appears to be segregated into microdomains. We studied the thermotropic behavior of pure dioleoyl-LBPA mono- and bilayers using Langmuir-lipid monolayers, electron microscopy, differential scanning calorimetry (DSC), and fluorescence spectroscopy. LBPA formed metastable, liquid-expanded monolayers at an air/buffer interface, and its compression isotherms lacked any indication for structural phase transitions. Neat LBPA formed multilamellar vesicles with no structural transitions or phase transitions between 10 and 80 degrees C at a pH range of 3.0-7.4. We then proceeded to study mixed LBPA/dipalmitoylphosphatidylcholine (DPPC) bilayers by DSC and fluorescence spectroscopy. Incorporating increasing amounts of LBPA (up to X(LBPA) (molar fraction)=0.10) decreased the co-operativity of the main transition for DPPC, and a decrease in the main phase transition as well as pretransition temperature of DPPC was observed yet with no effect on the enthalpy of this transition. In keeping with the DSC data for DPPC, 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC)/LBPA mixed bilayers were more fluid, and no evidence for lateral phase segregation was observed. These results were confirmed using fluorescence microscopy of Langmuir-lipid films composed of POPC and LBPA up to X(LBPA)=0.50 with no evidence for lateral phase separation. As late endosomes are eminently acidic, we examined the effect of lowering pH on lateral organization of mixed PC/LBPA bilayers by DSC and fluorescence spectroscopy. Even at pH 3.0, we find no evidence of LBPA-induced microdomain formation at LBPA contents found in cellular organelles. PMID:15589226

  2. Simple surface structure determination from Fourier transforms of angle-resolved photoemission extended fine structure

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Y. [Pennsylvania State Univ., University Park, PA (United States)]|[Lawrence Berkeley Lab., CA (United States); Shirley, D.A. [Pennsylvania State Univ., University Park, PA (United States)

    1995-02-01

    The authors show by Fourier analyses of experimental data, with no further treatment, that the positions of all the strong peaks in Fourier transforms of angle-resolved photoemission extended fine structure (ARPEFS) from adsorbed surfaces can be explicitly predicted from a trial structure with an accuracy of about {+-} 0.3 {angstrom} based on a single-scattering cluster model together with the concept of a strong backscattering cone, and without any additional analysis. This characteristic of ARPEFS Fourier transforms can be developed as a simple method for determining the structures of adsorbed surfaces to an accuracy of about {+-} 0.1 {angstrom}.

  3. Simulated microgravity impacts the plant plasmalemma lipid bilayer

    Science.gov (United States)

    Nedukha, Olena; Berkovich, Yuliy A.; Vorobyeva, Tamara; Grakhov, Volodimir; Klimenko, Elena; Zhupanov, Ivan; Jadko, Sergiy

    Biological membranes, especially the plasmalemma, and their properties and functions can be considered one of the most sensitive indicators of gravity interaction or alteration of gravity, respectively. Studies on the molecular basis of cellular signal perception and transduction are very important in order to understand signal responses at the cellular and organism level. The plasmalemma lipid bilayer is the boundary between the cell internal and external environment and mediates communication between them. Therefore, we studied the content and composition of lipids, saturated and unsaturated fatty acids, sterols, and microviscosity in the plasmalemma isolated from pea seedling roots and epicotyls grown in the stationary conditions and under slow horizontal clinorotation. In addition, lipid peroxidation intensity of intact roots was also identified. The plasmalemma fraction was isolated by the two-phase aquatic-polymer system optimized for pea using a centrifuge Optima L-90K. Lipid bilayer components were determined by using highly effective liquid chromatography with a system Angilent 1100 (Germany). Spontaneous chemiluminescence intensity was measured with a chemiluminometer ChLMTS-01. The obtained data showed that plasmalemma investigated parameters are sensitive to clinorotation, namely: increasing or decreasing the different lipids content, among which, phospho- and glycolipids were dominated, as well as changes in the content of saturated and unsaturated fatty acids and sterols. A degree of plasmalemma sensitivity to clinorotation was higher for the root plasmalemma than epicocotyl ones. This distinguish may be naturally explained by the differences in the structure, cell types, growth, and specific functions of a root and an epicotyl, those are the most complicated in roots. An index of unsaturation under clinorotation was similar to that in the stationary conditions as a result of the certain balance between changes in the content of saturated and

  4. First-principles study on electronic and magnetic properties of MnO3 superhalogen cluster-doped bilayer graphene

    International Nuclear Information System (INIS)

    Stability and magnetism of MnO3 superhalogen clusters embedded in bilayer graphene are investigated on the basis of first-principles calculations. MnO3-doped bilayer structures exhibit negative formation energies; by comparison, MnO3 embedded in monolayer graphene shows higher negative formation energy. Compared to MnO3-doped monolayer graphene MnO3-doped bilayer structures have higher structural stability due to higher binding energies. The charge from the lower graphene layer by MnO3 clusters then transfers to the upper layer graphene. The significant p-d hybridization between C and O atoms in graphene and Mn atoms leads to the exchange interaction causing the spin polarization of bilayer graphene. The MnO3 doped structures exhibit a half-metal nature with potential applications for spin field effect transistors (spin-FETs). (paper)

  5. Texture of lipid bilayer domains

    DEFF Research Database (Denmark)

    Jensen, Uffe Bernchou; Brewer, Jonathan R.; Midtiby, Henrik Skov; Ipsen, John Hjort; Bagatolli, Luis; Simonsen, Adam Cohen

    2009-01-01

    We investigate the texture of gel (g) domains in binary lipid membranes composed of the phospholipids DPPC and DOPC. Lateral organization of lipid bilayer membranes is a topic of fundamental and biological importance. Whereas questions related to size and composition of fluid membrane domain are...... chains. By imaging the intensity variations as a function of the polarization angle, we map the lateral variations of the lipid tilt within domains. Results reveal that gel domains are composed of subdomains with different lipid tilt directions. We have applied a Fourier decomposition method as a...... which correlates with the phase state of the membrane. This is quantified by the generalized polarization (GP) function, and we demonstrate that a GP analysis can be performed on supported membranes. The results show that although the gel domains have heterogeneous texture, the membrane phase state does...

  6. Dissipative particle dynamics simulation study of the bilayer-vesicle transition

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A bilayer structure is an important immediate for the vesicle formation. However,the mechanism for the bilayer-vesicle transition remains unclear. In this work,a dissipative particle dynamics(DPD) simulation method was employed to study the mechanism of the bilayer-vesicle transition. A coarse-grained model was built based on a lipid molecule termed dimyristoylphosphatidylcholine(DMPC). Simulations were performed from two different initial configurations:a random dispersed solution and a tensionless bilayer. It was found that the bilayer-vesicle transition was driven by the minimization of the water-tail hydrophobic interaction energy,and was accompanied with the increase of the position entropy due to the redistribution of water molecules. The bulk pressure was reduced during the bilayer-vesicle transition,suggesting the evolved vesicle morphology was at the relatively low free energy state. The membrane in the product vesicle was a two-dimensional fluid. It can be concluded that the membrane of a vesicle is not interdigitated and most of the bonds in lipid chains are inclined to orient along the radical axis of the vesicle.

  7. Ripples and the formation of anisotropic lipid domains: Imaging two-component double bilayers by atomic force microscopy_copy_03

    DEFF Research Database (Denmark)

    Leidy, C.; Kaasgaard, Thomas; Crowe, J.H.; Mouritsen, O.G.; Jørgensen, K.

    2002-01-01

    Direct visualization of the fluid-phase/ordered-phase domain structure in mica-supported bilayers composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine/1,2-distearoyl-sn-glycero-3-phosphocholine mixtures is performed with atomic force microscopy. The system studied is a double bilayer supported...... on a mica surface in which the top bilayer (which is not in direct contact with the mica) is visualized as a function of temperature. Because the top bilayer is not as restricted by the interactions with the surface as single supported bilayers, its behavior is more similar to a free-standing bilayer...... by atomic force microscopy, we investigated the origin of these anisotropic lipid domain patterns, and found that ripple phase formation is directly responsible for the anisotropic nature of these domains. The nucleation and growth of fluid-phase domains are found to be directed by the presence of...

  8. Conductive polymer/superconductor bilayer structures

    International Nuclear Information System (INIS)

    The preparation of a hybrid conducting polymer/high-temperature superconductor device consisting of a polypyrrole-coated YBa2Cu3O7-∂ microbridge is reported. Electrochemical techniques are exploited to alter the oxidation state of the polymer and, in doing so, it is found for the first time that superconductivity can be modulated in a controllable and reproducible fashion by a polymer layer. Whereas the neutral (insulating) polypyrrole only slightly influences the electrical properties of the underlying YBa2Cu3O7-∂ film, the oxidized (conductive) polymer depresses Tc by up to 50K. In a similar fashion, the oxidation state of the polymer is found to modulate reversibly the magnitude of Jc, the superconducting critical current. Thus, a new type of molecular switch for controlling superconductivity is demonstrated. Electrochemical, resistance vs. temperature, conact resistance, atomic force microscopy and scanning electron microscopy measurements are utilized to explore the polymer/superconductor interactions

  9. Magnetic Irreversibility in VO2/Ni Bilayers

    Science.gov (United States)

    de La Venta, Jose; Lauzier, Josh; Sutton, Logan

    The temperature dependence of the coercivity and magnetization of VO2/Ni bilayers was studied. VO2 exhibits a well-known Structural Phase Transition (SPT) at 330-340 K, from a low temperature monoclinic (M) to a high temperature rutile (R) structure. The SPT of VO2 induces an inverse magnetoelastic effect that strongly modifies the coercivity and magnetization of the Ni films. In addition, the growth conditions allow tuning of the magnetic properties. Ni films deposited on top of VO2 (M) show an irreversible change in the coercivity after the first cycle through the high temperature phase, with a corresponding change in the surface morphology of VO2. On the other hand, the Ni films grown on top of VO2 (R) do not show this irreversibility. These results indicate that properties of magnetic films are strongly affected by the strain induced by materials that undergo SPT and that it is possible to control the magnetic properties by tuning the growth conditions.

  10. Structural Determinants of Clostridium difficile Toxin A Glucosyltransferase Activity

    Energy Technology Data Exchange (ETDEWEB)

    Pruitt, Rory N.; Chumbler, Nicole M.; Rutherford, Stacey A.; Farrow, Melissa A.; Friedman, David B.; Spiller, Ben; Lacy, D. Borden (Vanderbilt)

    2012-03-28

    The principle virulence factors in Clostridium difficile pathogenesis are TcdA and TcdB, homologous glucosyltransferases capable of inactivating small GTPases within the host cell. We present crystal structures of the TcdA glucosyltransferase domain in the presence and absence of the co-substrate UDP-glucose. Although the enzymatic core is similar to that of TcdB, the proposed GTPase-binding surface differs significantly. We show that TcdA is comparable with TcdB in its modification of Rho family substrates and that, unlike TcdB, TcdA is also capable of modifying Rap family GTPases both in vitro and in cells. The glucosyltransferase activities of both toxins are reduced in the context of the holotoxin but can be restored with autoproteolytic activation and glucosyltransferase domain release. These studies highlight the importance of cellular activation in determining the array of substrates available to the toxins once delivered into the cell.

  11. Structure determination of trans-cinnamaldehyde by broadband microwave spectroscopy.

    Science.gov (United States)

    Zinn, Sabrina; Betz, Thomas; Medcraft, Chris; Schnell, Melanie

    2015-06-28

    The rotational spectrum of trans-cinnamaldehyde ((E)-3-phenyl-2-propenal, C9H8O) was recorded by chirped-pulse Fourier transform microwave spectroscopy in the frequency range of 2-8.5 GHz. The odourant molecule is the essential component of cinnamon oil and causes the characteristic smell. The rotational signatures of two conformers were observed: s-trans-trans- and s-cis-trans-cinnamaldehyde. The rotational spectra of s-trans-trans-cinnamaldehyde and all of its (13)C-monosubstituted species in natural abundance were assigned and the corresponding carbon backbone structure was determined. The second conformer s-cis-trans-cinnamaldehyde is about 9 kJ mol(-1) higher in energy and could also be identified in the spectrum. PMID:26030313

  12. Commensurability condition and hierarchy of fillings for FQHE in higher Landau levels in conventional 2DEG systems and in graphene—monolayer and bilayer

    Science.gov (United States)

    Jacak, Janusz; Jacak, Lucjan

    2016-01-01

    The structure of the filling rate hierarchy referred to as the fractional quantum Hall effect is studied in higher Landau levels using the commensurability condition. The hierarchy of fillings that are derived in this manner is consistent with the experimental observations of the first three Landau levels in conventional semiconductor Hall systems. The relative poverty of the fractional structure in higher Landau levels compared with the lowest Landau level is explained using commensurability topological arguments. The commensurability criterion for correlated states for higher Landau levels (with n≥slant 1) including the paired states at half fillings of the spin-subbands of these levels is formulated. The commensurability condition is applied to determine the hierarchy of the fractional fillings of Landau levels in the monolayer and bilayer graphene. Good agreement with current experimental observations of fractional quantum Hall effect in the graphene monolayer and bilayer is achieved. The presence of even denominator rates in the hierarchy for fractional quantum Hall effect in the bilayer graphene is also explained.

  13. The effects of residual stress, viscoelastic and thermodynamic parameters on apparent fracture toughness of dental bilayer ceramic composites

    Science.gov (United States)

    Taskonak, Burak

    Bilayer dental ceramic composites used for fixed partial dentures are becoming more widely used in dental practices because of their biocompatibility, aesthetic properties, and chemical durability. However, large statistical variations in the strength of ceramics are associated with the structural flaws as a result of processing and complex stress states within the surfaces of the materials because of thermal properties of each layer. In addition, partial delaminations of the veneer layer and connector fractures of bilayer ceramic fixed partial dentures (FPDs) have been observed in a clinical study which is a part of this dissertation. Analysis of fracture surfaces of failed FPDs reveals that such fractures of the veneering ceramic are most likely caused by lateral crack growth. Global residual stresses associated with the coefficient of thermal expansion differences between core and veneering ceramics can cause lateral crack initiation. Also, rapid cooling of bilayer ceramics from the sintering temperature of the glass veneer may not allow the interfacial stresses in the viscoelastic glass to relax to equilibrium values. This can further contribute to the propagation of lateral cracks. Furthermore, local residual stresses that develop in the plastic deformation zone below sharp contact areas on the occlusal surface are another contributor to lateral crack growth. Superposition of global residual stresses and a Boussinesq stress field can incrementally increase the possibility of lateral crack growth. The long-range goals of this study are to critically analyze the lateral crack growth mechanisms associated with residual stresses, to modify residual tensile stress distributions by controlled heat treatment, and to minimize the probability of veneering ceramic fractures. Four approaches were used to accomplish these goals: (1) clinical evaluation of a bilayer ceramic fixed partial denture system; (2) fracture surface analysis of clinically failed FPDs; (3

  14. The Structural Determinants behind the Epigenetic Role of Histone Variants.

    Science.gov (United States)

    Cheema, Manjinder S; Ausió, Juan

    2015-01-01

    Histone variants are an important part of the histone contribution to chromatin epigenetics. In this review, we describe how the known structural differences of these variants from their canonical histone counterparts impart a chromatin signature ultimately responsible for their epigenetic contribution. In terms of the core histones, H2A histone variants are major players while H3 variant CenH3, with a controversial role in the nucleosome conformation, remains the genuine epigenetic histone variant. Linker histone variants (histone H1 family) haven't often been studied for their role in epigenetics. However, the micro-heterogeneity of the somatic canonical forms of linker histones appears to play an important role in maintaining the cell-differentiated states, while the cell cycle independent linker histone variants are involved in development. A picture starts to emerge in which histone H2A variants, in addition to their individual specific contributions to the nucleosome structure and dynamics, globally impair the accessibility of linker histones to defined chromatin locations and may have important consequences for determining different states of chromatin metabolism. PMID:26213973

  15. The Structural Determinants behind the Epigenetic Role of Histone Variants

    Directory of Open Access Journals (Sweden)

    Manjinder S. Cheema

    2015-07-01

    Full Text Available Histone variants are an important part of the histone contribution to chromatin epigenetics. In this review, we describe how the known structural differences of these variants from their canonical histone counterparts impart a chromatin signature ultimately responsible for their epigenetic contribution. In terms of the core histones, H2A histone variants are major players while H3 variant CenH3, with a controversial role in the nucleosome conformation, remains the genuine epigenetic histone variant. Linker histone variants (histone H1 family haven’t often been studied for their role in epigenetics. However, the micro-heterogeneity of the somatic canonical forms of linker histones appears to play an important role in maintaining the cell-differentiated states, while the cell cycle independent linker histone variants are involved in development. A picture starts to emerge in which histone H2A variants, in addition to their individual specific contributions to the nucleosome structure and dynamics, globally impair the accessibility of linker histones to defined chromatin locations and may have important consequences for determining different states of chromatin metabolism.

  16. Unhealthy prisons: exploring structural determinants of prison health.

    Science.gov (United States)

    de Viggiani, Nick

    2007-01-01

    Prisoner health is influenced as much by structural determinants (institutional, environmental, political, economic and social) as it is by physical and mental constitutions of prisoners themselves. Prison health may therefore be better understood with greater insight into how people respond to imprisonment - the psychological pressures of incarceration, the social world of prison, being dislocated from society, and the impact of the institution itself with its regime and architecture. As agencies of disempowerment and deprivation, prisons epitomise the antithesis of a healthy setting. The World Health Organisation's notion of a 'healthy prison' is in this sense an oxymoron, yet the UK government has signalled that it is committed to WHO's core health promotion principles as a route to reducing health inequalities. This paper reports on the findings of an ethnographic study which was conducted in an adult male training prison in England, using participant observation, group interviewing, and one-to-one semi-structured interviews with prisoners and prison officers. The paper explores how different layers of prison life impact on the health of prisoners, arguing that health inequalities are enmeshed within the workings of the prison system itself. PMID:17286709

  17. Structure of HIV-1 protease determined by neutron crystallography

    International Nuclear Information System (INIS)

    HIV-1 protease is an aspartic protease, and plays an essential role in replication of HIV. To develop HIV-1 protease inhibitors through structure-based drug design, it is necessary to understand the catalytic mechanism and inhibitor recognition of HIV-1 protease. We have determined the crystal structure of HIV-1 protease in complex with KNI-272 to 1.9 A resolution by neutron crystallography in combination with 1.4 A resolution X-ray diffraction data. The results show that the carbonyl group of hydroxymethylcarbonyl (HMC) in KNI-272 forms a hydrogen bonding interaction with protonated Asp 25 and the hydrogen atom from the hydroxyl group of HMC forms a hydrogen bonding interaction with the deprotonated Asp125. This is the first neutron report for HIV-1/inhibitor complex and shows directly the locations of key hydrogen atoms in catalysis and in the binding of a transition-state analog. The results confirm key aspect of the presumed catalytic mechanism of HIV-1 protease and will aid in the further development of protease inhibitors. (author)

  18. Hybrid bilayer plasmonic metasurface efficiently manipulates visible light.

    Science.gov (United States)

    Qin, Fei; Ding, Lu; Zhang, Lei; Monticone, Francesco; Chum, Chan Choy; Deng, Jie; Mei, Shengtao; Li, Ying; Teng, Jinghua; Hong, Minghui; Zhang, Shuang; Alù, Andrea; Qiu, Cheng-Wei

    2016-01-01

    Metasurfaces operating in the cross-polarization scheme have shown an interesting degree of control over the wavefront of transmitted light. Nevertheless, their inherently low efficiency in visible light raises certain concerns for practical applications. Without sacrificing the ultrathin flat design, we propose a bilayer plasmonic metasurface operating at visible frequencies, obtained by coupling a nanoantenna-based metasurface with its complementary Babinet-inverted copy. By breaking the radiation symmetry because of the finite, yet small, thickness of the proposed structure and benefitting from properly tailored intra- and interlayer couplings, such coupled bilayer metasurface experimentally yields a conversion efficiency of 17%, significantly larger than that of earlier single-layer designs, as well as an extinction ratio larger than 0 dB, meaning that anomalous refraction dominates the transmission response. Our finding shows that metallic metasurface can counterintuitively manipulate the visible light as efficiently as dielectric metasurface (~20% in conversion efficiency in Lin et al.'s study), although the metal's ohmic loss is much higher than dielectrics. Our hybrid bilayer design, still being ultrathin (~λ/6), is found to obey generalized Snell's law even in the presence of strong couplings. It is capable of efficiently manipulating visible light over a broad bandwidth and can be realized with a facile one-step nanofabrication process. PMID:26767195

  19. Hybrid bilayer plasmonic metasurface efficiently manipulates visible light

    Science.gov (United States)

    Qin, Fei; Ding, Lu; Zhang, Lei; Monticone, Francesco; Chum, Chan Choy; Deng, Jie; Mei, Shengtao; Li, Ying; Teng, Jinghua; Hong, Minghui; Zhang, Shuang; Alù, Andrea; Qiu, Cheng-Wei

    2016-01-01

    Metasurfaces operating in the cross-polarization scheme have shown an interesting degree of control over the wavefront of transmitted light. Nevertheless, their inherently low efficiency in visible light raises certain concerns for practical applications. Without sacrificing the ultrathin flat design, we propose a bilayer plasmonic metasurface operating at visible frequencies, obtained by coupling a nanoantenna-based metasurface with its complementary Babinet-inverted copy. By breaking the radiation symmetry because of the finite, yet small, thickness of the proposed structure and benefitting from properly tailored intra- and interlayer couplings, such coupled bilayer metasurface experimentally yields a conversion efficiency of 17%, significantly larger than that of earlier single-layer designs, as well as an extinction ratio larger than 0 dB, meaning that anomalous refraction dominates the transmission response. Our finding shows that metallic metasurface can counterintuitively manipulate the visible light as efficiently as dielectric metasurface (~20% in conversion efficiency in Lin et al.’s study), although the metal’s ohmic loss is much higher than dielectrics. Our hybrid bilayer design, still being ultrathin (~λ/6), is found to obey generalized Snell’s law even in the presence of strong couplings. It is capable of efficiently manipulating visible light over a broad bandwidth and can be realized with a facile one-step nanofabrication process. PMID:26767195

  20. Self healing nature of bilayer graphene

    Science.gov (United States)

    Debroy, Sanghamitra; Pavan Kumar Miriyala, V.; Vijaya Sekhar, K.; Acharyya, Swati Ghosh; Acharyya, Amit

    2016-08-01

    The phenomenon of self healing of cracks in bilayer graphene sheet has been studied using molecular dynamics simulations. The bilayer graphene sheet was subjected to uniaxial tensile load resulting in initiation and propagation of cracks on exceeding the ultimate tensile strength. Subsequently, all forces acting on the sheet were removed and sheet was relaxed. The cracks formed in the graphene sheet healed without any external aid within 0.4 ps The phenomenon of self healing of the cracks in graphene sheet was found to be independent of the length of the crack, but occurred for critical crack opening distance less than 5 Å for AA stacked sheet and 13 Å for AB stacked bilayer graphene sheet. Self healing was observed for both AB (mixed stacking of armchair and zigzag graphene sheet) and AA (both sheets of similar orientation i.e. either armchair-armchair or zigzag-zigzag) stacking of bilayer graphene sheet.

  1. Proximity induced superconductivity in bilayer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Bordaz, Julien; Wu, Fan [Institute of Nanotechnology, Karlsruhe Institute of Technology (Germany); Wolf, Michael; Beckmann, Detlef [Institute of Nanotechnology, Karlsruhe Institute of Technology (Germany); DFG Center for Functional Nanostructures, Karlsruhe Institute of Technology (Germany); Loehneysen, Hilbert von [Institute of Nanotechnology, Karlsruhe Institute of Technology (Germany); DFG Center for Functional Nanostructures, Karlsruhe Institute of Technology (Germany); Institute of Physics, Karlsruhe Institute of Technology (Germany); Institute for Solid-State Physics, Karlsruhe Institute of Technology (Germany); Watanabe, Kenji; Taniguchi, Takashi [Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba (Japan); Danneau, Romain [Institute of Nanotechnology, Karlsruhe Institute of Technology (Germany); Institute of Physics, Karlsruhe Institute of Technology (Germany)

    2013-07-01

    Proximity induced superconductivity effect occurs when graphene is connected with close enough superconducting electrodes. Observations of Andreev reflection and induced supercurrents flowing through graphene sheets have already been reported in graphene. However, these effects have not been explored in bilayer graphene so far. By applying a perpendicular electric field, it is possible to open a gap in a bilayer graphene. This can be achieved in practice by designing a top gate in addition to the usual back gate. Our devices are produced on top of sapphire wafers by using transfer techniques and standard electron-beam lithography. The bilayers are sandwiched between two atomically flat hexagonal boron nitride multilayers which are both used as gate dielectric. By inducing a band gap into a bilayer graphene connected by two superconducting leads, the supercurrent could be switched off inducing a superconductor-insulator transition.

  2. Proximity induced superconductivity in bilayer graphene

    International Nuclear Information System (INIS)

    Proximity induced superconductivity effect occurs when graphene is connected with close enough superconducting electrodes. Observations of Andreev reflection and induced supercurrents flowing through graphene sheets have already been reported in graphene. However, these effects have not been explored in bilayer graphene so far. By applying a perpendicular electric field, it is possible to open a gap in a bilayer graphene. This can be achieved in practice by designing a top gate in addition to the usual back gate. Our devices are produced on top of sapphire wafers by using transfer techniques and standard electron-beam lithography. The bilayers are sandwiched between two atomically flat hexagonal boron nitride multilayers which are both used as gate dielectric. By inducing a band gap into a bilayer graphene connected by two superconducting leads, the supercurrent could be switched off inducing a superconductor-insulator transition.

  3. Vapor deposition of water on graphitic surfaces: Formation of amorphous ice, bilayer ice, ice I, and liquid water

    Energy Technology Data Exchange (ETDEWEB)

    Lupi, Laura; Kastelowitz, Noah; Molinero, Valeria, E-mail: Valeria.Molinero@utah.edu [Department of Chemistry, The University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0850 (United States)

    2014-11-14

    Carbonaceous surfaces are a major source of atmospheric particles and could play an important role in the formation of ice. Here we investigate through molecular simulations the stability, metastability, and molecular pathways of deposition of amorphous ice, bilayer ice, and ice I from water vapor on graphitic and atomless Lennard-Jones surfaces as a function of temperature. We find that bilayer ice is the most stable ice polymorph for small cluster sizes, nevertheless it can grow metastable well above its region of thermodynamic stability. In agreement with experiments, the simulations predict that on increasing temperature the outcome of water deposition is amorphous ice, bilayer ice, ice I, and liquid water. The deposition nucleation of bilayer ice and ice I is preceded by the formation of small liquid clusters, which have two wetting states: bilayer pancake-like (wetting) at small cluster size and droplet-like (non-wetting) at larger cluster size. The wetting state of liquid clusters determines which ice polymorph is nucleated: bilayer ice nucleates from wetting bilayer liquid clusters and ice I from non-wetting liquid clusters. The maximum temperature for nucleation of bilayer ice on flat surfaces, T{sub B}{sup max} is given by the maximum temperature for which liquid water clusters reach the equilibrium melting line of bilayer ice as wetting bilayer clusters. Increasing water-surface attraction stabilizes the pancake-like wetting state of liquid clusters leading to larger T{sub B}{sup max} for the flat non-hydrogen bonding surfaces of this study. The findings of this study should be of relevance for the understanding of ice formation by deposition mode on carbonaceous atmospheric particles, including soot.

  4. Viscoelastic changes measured in partially suspended single bilayer membranes.

    Science.gov (United States)

    Hasan, Imad Younus; Mechler, Adam

    2015-07-21

    For studies involving biomimetic phospholipid membrane systems, such as membrane-protein interactions, it is crucial that the supported membrane is biomimetic in its physical properties as well as in its composition. Two often overlooked aspects of biomimicry are the need for unrestrained lipid mobility, reflected in the viscoelastic properties of the membrane, and sufficient space between the membrane and the support for the insertion of transmembrane proteins. Here we show for a series of DMPC-based membranes that a partially suspended single bilayer membrane can be formed on functionalized gold surface without tethering. These membranes exhibit sufficient freedom of motion to represent the viscoelastic properties of a free lamellar bilayer membrane as demonstrated by determining the phase transition temperatures of these single bilayer membranes from the viscosity change upon chain melting using the dissipation signal of a quartz crystal microbalance (QCM-D). Atomic force microscopy imaging confirmed confluent, smooth membrane coverage of the QCM-D sensor that completely obscured the roughness of the sputtered gold surface. High-force AFM imaging was able to push membrane patches into the valleys of the gold morphology, confirming the inherently suspended nature of the MPA supported membrane. We show that the correlation between frequency and dissipation changes in the QCM-D sensograms is a sensitive indicator of the morphology of the membrane. PMID:26073288

  5. Spatial arrangement of selected fluorescence labels in lipid bilayer.

    Science.gov (United States)

    Zawada, Zygmunt H

    2013-08-01

    The method for the determination the orientation factor κ(2), spatial arrangement and depth position of fluorescence labels located in hydrophilic layers of vesicles bilayer from resonance energy transfer (RET) data is presented. The method is based on the broadened Wolber and Hudson RET model in two dimensions (Biophys J. 1979). The vesicles were labeled with N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (NBD-PE) as the donor and N-(Lissamine rhodamine B sulfonyl) 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (NRh-PE) as the acceptor. It was found that in basic environment sodium dithionite quenches fluorescence of both labels located in outer leaflet of bilayer. Therefore, RET data prior to and following dithionite treatment were compared and the donor-acceptor cis and trans distances of the closest approach as well as cis and trans Förster radii R0, and orientation factors κ(2) for cis RET equal to 0.61±0.06 and for trans RET equal to 0.17±0.01 were assigned. Knowing the κ(2) data, the spatial arrangement of NBD and NRh labels as dipoles in dipalmitoylphosphatidylcholine bilayer were described. PMID:23727616

  6. Local membrane mechanics of pore-spanning bilayers.

    Science.gov (United States)

    Mey, Ingo; Stephan, Milena; Schmitt, Eva K; Müller, Martin Michael; Ben Amar, Martine; Steinem, Claudia; Janshoff, Andreas

    2009-05-27

    The mechanical behavior of lipid bilayers spanning the pores of highly ordered porous silicon substrates was scrutinized by local indentation experiments as a function of surface functionalization, lipid composition, solvent content, indentation velocity, and pore radius. Solvent-containing nano black lipid membranes (nano-BLMs) as well as solvent-free pore-spanning bilayers were imaged by fluorescence and atomic force microscopy prior to force curve acquisition, which allows distinguishing between membrane-covered and uncovered pores. Force indentation curves on pore-spanning bilayers attached to functionalized hydrophobic porous silicon substrates reveal a predominately linear response that is mainly attributed to prestress in the membranes. This is in agreement with the observation that indentation leads to membrane lysis well below 5% area dilatation. However, membrane bending and lateral tension dominate over prestress and stretching if solvent-free supported membranes obtained from spreading giant liposomes on hydrophilic porous silicon are indented. An elastic regime diagram is presented that readily allows determining the dominant contribution to the mechanical response upon indentation as a function of load and pore radius. PMID:19453196

  7. Supported lipid bilayer membranes for water purification by reverse osmosis.

    Science.gov (United States)

    Kaufman, Yair; Berman, Amir; Freger, Viatcheslav

    2010-05-18

    Some biological plasma membranes pass water with a permeability and selectivity largely exceeding those of commercial membranes for water desalination using specialized trans-membrane proteins aquaporins. However, highly selective transport of water through aquaporins is usually driven by an osmotic rather mechanical pressure, which is not as attractive from the engineering point of view. The feasibility of adopting biomimetic membranes for water purification driven by a mechanical pressure, i.e., filtration is explored in this paper. Toward this goal, it is proposed to use a commercial nanofiltration (NF) membrane as a support for biomimetic lipid bilayer membranes to render them robust enough to withstand the required pressures. It is shown in this paper for the first time that by properly tuning molecular interactions supported phospholipid bilayers (SPB) can be prepared on a commercial NF membrane. The presence of SPB on the surface was verified and quantified by several spectroscopic and microscopic techniques, which showed morphology close to the desired one with very few defects. As an ultimate test it is shown that hydraulic permeability of the SPB supported on the NF membrane (NTR-7450) approaches the values deduced from the typical osmotic permeabilities of intact continuous bilayers. This permeability was unaffected by the trans-membrane flow of water and by repeatedly releasing and reapplying a 10 bar pressure. Along with a parallel demonstration that aquaporins could be incorporated in a similar bilayer on mica, this demonstrates the feasibility of the proposed approach. The prepared SPB structure may be used as a platform for preparing biomimetic filtration membranes with superior performance based on aquaporins. The concept of SPBs on permeable substrates of the present type may also be useful in the future for studying transport of various molecules through trans-membrane proteins. PMID:20099798

  8. The Detection of Structural Deformation Errors in Attitude Determination

    Institute of Scientific and Technical Information of China (English)

    M. J. Moore; C. Rizos; J. Wang

    2003-01-01

    In the determination of the attitude parameters from a multi-antenna GPS array, one of the major assumptions is that the body frame is rigid at all times. If this assumption is not true then the derived attitude parameters will be in error. It is well known that in airborne platforms the wings often experience some displacement during flight, especially during periods of initializing maneouvres, such as taking off, landing,and banking. Often it is at these points in time that it is most critical to have the most precise attitude parameters.There are a number of techniques available for the detection of modeling errors.The CUSUM algorithm has successfully been implemented in the past to detect small persistent changes. In this paper the authors investigate different methods of generating the residuals, to be tested by the CUSUM algorithm, in an effort to determine which technique is best suited for the detection of structural deformation of an airborne platform. The methods investigated include monitoring the mean of the residuals generated from the difference between the known body frame coordinates, and those calculated from the derived attitude parameters. The generated residuals are then passed to a CUSUM algorithm to detect any small persistent changes. An alternative method involves transforming the generated residuals into the frequency domain through the use of the Fast Fourier Transform. The CUSUM algorithm is then used to detect any frequency changes. The final technique investigated involves transforming the generated residuals using the Haar wavelet. The wavelet coefficients are then monitored by the CUSUM algorithm in order to detect any significant change to the rigidity of the body frame.Detecting structural deformation, and quantifying the degree of deformation, during flight will ensure that these effects can be removed from the system, thus ensuring the most precise and reliable attitude parameter solutions. This paper, through a series

  9. Substrate temperature influence on W/WCNx bilayers grown by pulsed vacuum arc discharge

    International Nuclear Information System (INIS)

    W/WCNx coatings were produced by using a repetitive pulsed vacuum arc discharge on stainless-steel 304 substrates, varying the substrate temperature from room temperature to 200 °C. Energy dispersive spectroscopy (EDS) was used for determining W, C and N concentrations dependence on the substrate temperature. A competition between C and N can be observed. Atomic force microscopy was employed for obtaining the thickness and grain size that present similar tendencies as a function of the temperature. X-ray diffraction characterization showed phases of W and α-WCN (hexagonal). Raman spectra for all substrate temperatures were obtained, presenting two peaks corresponding to D (disorder) and G (graphite) bands in the region of 1100-1700 cm-1 due to the amorphous carbon. As an important conclusion, it was stated that substrate temperature has strong influence on the structure, chemical composition and morphology of W/WCNx bilayers, caused by the competition between carbon and nitrogen.

  10. Substrate temperature influence on W/WCNx bilayers grown by pulsed vacuum arc discharge

    Science.gov (United States)

    Ospina, R.; Escobar, D.; Restrepo-Parra, E.; Arango, P. J.; Jurado, J. F.

    2012-04-01

    W/WCNx coatings were produced by using a repetitive pulsed vacuum arc discharge on stainless-steel 304 substrates, varying the substrate temperature from room temperature to 200 °C. Energy dispersive spectroscopy (EDS) was used for determining W, C and N concentrations dependence on the substrate temperature. A competition between C and N can be observed. Atomic force microscopy was employed for obtaining the thickness and grain size that present similar tendencies as a function of the temperature. X-ray diffraction characterization showed phases of W and α-WCN (hexagonal). Raman spectra for all substrate temperatures were obtained, presenting two peaks corresponding to D (disorder) and G (graphite) bands in the region of 1100-1700 cm-1 due to the amorphous carbon. As an important conclusion, it was stated that substrate temperature has strong influence on the structure, chemical composition and morphology of W/WCNx bilayers, caused by the competition between carbon and nitrogen.

  11. Lipid bilayers decorated with photosensitive ruthenium complexes

    OpenAIRE

    Bahreman, Azadeh

    2013-01-01

    In this thesis the thermal- and photo-substitution behavior of polypyridyl ruthenium complexes is described at the surface of lipid bilayers and in homogeneous solutions. It is shown that the successive thermal binding and light-induced unbinding of the cationic ruthenium complex at the surface of the lipid bilayer requires negatively charged liposomes and ruthenium complexes containing moderately hindered N-N bidentate ligands. Our results in homogeneous solution show that changing the steri...

  12. Twisted bi-layer graphene: microscopic rainbows

    OpenAIRE

    Campos-Delgado, J.; Algara-Siller, G.; Santos, C. N.; Kaiser, U.; Raskin, J.-P.

    2013-01-01

    Twisted bi-layer graphene (tBLG) has recently attracted interest due to the peculiar electrical properties that arise from its random rotational configurations. Our experiments on CVD-grown graphene from Cu foil and transferred onto Si substrates, with an oxide layer of 100 nm, reveal naturally-produced bi-layer graphene patches which present different colorations when shined with white light. In particular yellow-, pink- and blue- colored areas are evidenced. Combining optical microscopy, Ra...

  13. Silica-based cationic bilayers as immunoadjuvants

    OpenAIRE

    Carmona-Ribeiro Ana M; da Costa Maria; Faquim-Mauro Eliana; Santana Mariana RA; Lincopan Nilton

    2009-01-01

    Abstract Background Silica particles cationized by dioctadecyldimethylammonium bromide (DODAB) bilayer were previously described. This work shows the efficiency of these particulates for antigen adsorption and presentation to the immune system and proves the concept that silica-based cationic bilayers exhibit better performance than alum regarding colloid stability and cellular immune responses for vaccine design. Results Firstly, the silica/DODAB assembly was characterized at 1 mM NaCl, pH 6...

  14. Bilayers merge even when exocytosis is transient

    OpenAIRE

    Taraska, Justin W; Almers, Wolfhard

    2004-01-01

    During exocytosis, the lumen of secretory vesicles connects with the extracellular space. In some vesicles, this connection closes again, causing the vesicle to be recaptured mostly intact. The degree to which the bilayers of such vesicles mix with the plasma membrane is unknown. Work supporting the kiss-and-run model of transient exocytosis implies that synaptic vesicles allow neither lipid nor protein to escape into the plasma membrane, suggesting that the two bilayers never merge. Here, we...

  15. Study of Sb/SnO2 bi-layer films prepared by ion beam sputtering deposition technique

    International Nuclear Information System (INIS)

    In the present work, bi-layer thin films of Sb/SnO2 were produced on unheated glass substrates using ion beam sputtering (IBS) technique without post annealing treatment. The thickness of Sb layers was varied from 2 to 10 nm and the Sb layers were deposited on SnO2 layers having thicknesses of 40 nm to 115 nm. The effect of thickness was studied on the morphological, electrical and optical properties. The Sb/SnO2 bi-layer resulted in lowering the electrical resistivity as well as reducing the optical transmittance. However, the optical and electrical properties of the bi-layer films were mainly influenced by the thickness of Sb layers due to progressive transfer in structures from aggregate to continuous films. The bi-layer films show the electrical resistivity of 1.4 × 10−3 Ω cm and an optical transmittance of 26% for Sb film having 10 nm thickness. - Highlights: • Bi-layer Sb/SnO2 structures were synthesized by ion beam sputtering (IBS) technique. • The 6 nm-thick Sb film is a transition region in this study. • The conductivity of the bi-layer films is increased as Sb thickness increases. • The transmittance of the bi-layer films is decreased as Sb thickness increases

  16. Photoinduced electron transfer of chlorophyll in lipid bilayer system

    Indian Academy of Sciences (India)

    D K Lee; K W Seo; Y S Kang

    2002-12-01

    Photoinduced electron transfer from chlorophyll- through the interface of dipalmitoylphosphatidylcholine (DPPC) headgroup of the lipid bilayers was studied with electron magnetic resonance (EMR). The photoproduced radicals were identified with electron spin resonance (ESR) and radical yields of chlorophyll- were determined by double integration ESR spectra. The formation of vesicles was identified by changes in measured max values from diethyl ether solutions to vesicles solutions indirectly, and observed directly with SEM and TEM images. The efficiency of photosynthesis in model system was determined by measuring the amount of chlorophyll-a radical yields which were obtained from integration of ESR spectra.

  17. Automatic Structure Determination of Organic Molecules: Principle and Implementation of the LSD Program

    Institute of Scientific and Technical Information of China (English)

    NUZILLARD,Jean-Marc

    2003-01-01

    The LSD (Logic for Structure Determination) program generates organic molecular structures from 1D and 2D NMR data without resorting to chemical shift databases. Its use in the resolution of natural product structure determination problems has been already reported in the literature. This paper describes how data and structures are internally represented and processed by LSD to build solution structures.

  18. Toxin-induced pore formation is hindered by intermolecular hydrogen bonding in sphingomyelin bilayers.

    Science.gov (United States)

    García-Linares, Sara; Palacios-Ortega, Juan; Yasuda, Tomokazu; Åstrand, Mia; Gavilanes, José G; Martínez-Del-Pozo, Álvaro; Slotte, J Peter

    2016-06-01

    Sticholysin I and II (StnI and StnII) are pore-forming toxins that use sphingomyelin (SM) for membrane binding. We examined how hydrogen bonding among membrane SMs affected the StnI- and StnII-induced pore formation process, resulting in bilayer permeabilization. We compared toxin-induced permeabilization in bilayers containing either SM or dihydro-SM (lacking the trans Δ(4) double bond of the long-chain base), since their hydrogen-bonding properties are known to differ greatly. We observed that whereas both StnI and StnII formed pores in unilamellar vesicles containing palmitoyl-SM or oleoyl-SM, the toxins failed to similarly form pores in vesicles prepared from dihydro-PSM or dihydro-OSM. In supported bilayers containing OSM, StnII bound efficiently, as determined by surface plasmon resonance. However, StnII binding to supported bilayers prepared from dihydro-OSM was very low under similar experimental conditions. The association of the positively charged StnII (at pH7.0) with unilamellar vesicles prepared from OSM led to a concentration-dependent increase in vesicle charge, as determined from zeta-potential measurements. With dihydro-OSM vesicles, a similar response was not observed. Benzyl alcohol, which is a small hydrogen-bonding compound with affinity to lipid bilayer interfaces, strongly facilitated StnII-induced pore formation in dihydro-OSM bilayers, suggesting that hydrogen bonding in the interfacial region originally prevented StnII from membrane binding and pore formation. We conclude that interfacial hydrogen bonding was able to affect the membrane association of StnI- and StnII, and hence their pore forming capacity. Our results suggest that other types of protein interactions in bilayers may also be affected by hydrogen-bonding origination from SMs. PMID:26975250

  19. Influence of compaction properties and interfacial topography on the performance of bilayer tablets.

    Science.gov (United States)

    Kottala, Niranjan; Abebe, Admassu; Sprockel, Omar; Akseli, Ilgaz; Nikfar, Faranak; Cuitiño, Alberto M

    2012-10-15

    Bilayer tablets are generating great interest recently as they can achieve controlled delivery of different drugs with pre-defined release profiles. However, the production of such tablets has been facing great challenges as the layered tablets are prone to delaminate or fracture in the individual layers due to insufficient bonding strength of layers and adhesion at the interfaces. This paper will provide an insight into the role of interfacial topography on the performance of the bilayer tablets. In this study, two widely used pharmaceutical excipients: microcrystalline cellulose and lactose were investigated. Bilayer tablets were manufactured with a range of first and second layer compression forces. A crack of known dimensions was introduced at the interface to investigate the crack propagation mechanisms upon axially loading the bilayer tablet, and to determine the stress intensity factor (K(I)) of the interface (will be discussed in a separate paper). The results indicated that a strong dependency of the strength of bilayer tablets and mode of crack propagation on the material and compaction properties. The results showed that the strength of bilayer tablets increased with the increase of interfacial roughness, and the first layer and second layer forces determined the magnitude of interfacial roughness for both plastic and brittle materials. Further, the results also indicated that layer sequence and compaction forces played a key role in influencing the strength of the bilayer tablets. For the same (first and second layer) force combination, interfacial strength is higher for the tablets made of brittle material in the first layer. It was observed that interfacial strength decreased with the increase of lubricant concentration. The studies showed that the effect of lubricant (i.e. reduction in compact strength with the increase of lubricant concentration) on the strength of compacts is higher for tablets made of plastic material as compared to the tablets

  20. Determination of the structure function F2 at HERMES

    International Nuclear Information System (INIS)

    In this thesis we present the first measurement of inclusive proton and deuteron deep-inelastic scattering cross sections at the HERMES experiment. The measurement is performed using the 27.6 GeV lepton beam provided by the HERA storage ring in conjunction with hydrogen and deuterium gas targets internal to the beam pipe. The relevant systematic effects such as radiative corrections, detector smearing, acceptance, particle misidentification, misalignment, tracking related effects and trigger efficiencies are taken into account. Based on these results, the structure functions Fp2 and Fd2 are determined using the parameterization R1998 for the longitudinal-to-transverse virtual-photon absorption cross section R. A phenomenological fit of the proton deep-inelastic scattering cross section is performed based on all available data and using photoproduction data in order to pin down the low Q2 region. A second fit is performed to the world data on the deuteron-to-proton cross section ratio in order to study its Q2 evolution, the difference between higher twist contributions in proton and deuteron, and the difference between R as obtained from the two targets. It can be confirmed that R obtained for proton and deuteron is in agreement. The Gottfried integral is evaluated from the fit at different values of Q2. The result at Q2=4 GeV2 agrees with previous measurements by NMC and no indication for a Q2 dependence of the Gottfried integral is found. (orig.)

  1. Two-dimensional interlocked pentagonal bilayer ice: how do water molecules form a hydrogen bonding network?

    Science.gov (United States)

    Zhu, Weiduo; Zhao, Wen-Hui; Wang, Lu; Yin, Di; Jia, Min; Yang, Jinlong; Zeng, Xiao Cheng; Yuan, Lan-Feng

    2016-06-01

    The plethora of ice structures observed both in bulk and under nanoscale confinement reflects the extraordinary ability of water molecules to form diverse forms of hydrogen bonding networks. An ideal hydrogen bonding network of water should satisfy three requirements: (1) four hydrogen bonds connected with every water molecule, (2) nearly linear hydrogen bonds, and (3) tetrahedral configuration for the four hydrogen bonds around an O atom. However, under nanoscale confinement, some of the three requirements have to be unmet, and the selection of the specific requirement(s) leads to different types of hydrogen bonding structures. According to molecular dynamics (MD) simulations for water confined between two smooth hydrophobic walls, we obtain a phase diagram of three two-dimensional (2D) crystalline structures and a bilayer liquid. A new 2D bilayer ice is found and named the interlocked pentagonal bilayer ice (IPBI), because its side view comprises interlocked pentagonal channels. The basic motif in the top view of IPBI is a large hexagon composed of four small pentagons, resembling the top view of a previously reported "coffin" bilayer ice [Johnston, et al., J. Chem. Phys., 2010, 133, 154516]. First-principles optimizations suggest that both bilayer ices are stable. However, there are fundamental differences between the two bilayer structures due to the difference in the selection among the three requirements. The IPBI sacrifices the linearity of hydrogen bonds to retain locally tetrahedral configurations of the hydrogen bonds, whereas the coffin structure does the opposite. The tradeoff between the conditions of an ideal hydrogen bonding network can serve as a generic guidance to understand the rich phase behaviors of nanoconfined water. PMID:27063210

  2. RKKY interaction in bilayer graphene

    Science.gov (United States)

    Mohammadi, Yawar; Moradian, Rostam

    2015-12-01

    We study the RKKY interaction between two magnetic impurities located on the same layer (intralayer case) or on different layers (interlayer case) in undoped bilayer graphene (BLG) in the four-bands model, by directly calculating the Green functions in the eigenvalues and eigenvectors representation. Our results show that both intra- and interlayer RKKY interactions between two magnetic impurities located on the same (opposite) sublattice are always ferromagnetic (antiferromagnetic). Furthermore we find unusual long-distance decay of the RKKY interaction in BLG. The intralyer RKKY interactions between two magnetic impurities located on the same sublattice, J AnAn(R) and J BnBn(R), decay closely as 1 /R6 and 1 /R2 at large impurity distances respectively, but when they are located on opposite sublattices the RKKY interactions exhibit 1 /R4 decays approximately. In the interlayer case, the RKKY interactions between two magnetic impurities located on the same sublattice show a decay close to 1 /R4 at large impurity distances, but if two magnetic impurities be on opposite sublattices the RKKY interactions, J A1B2(R) and J B1A2(R), decay closely as 1 /R6 and 1 /R2 respectively. Both intra- and interlayer RKKY interactions have anisotropic oscillatory factors which for intralayer case is equal to that for single layer graphene (SLG). Our results at weak and strong interlayer coupling limits reduce to the RKKY interaction of SLG and that of BLG in the two-bands approximation respectively.

  3. Smoothed orientational order profile of lipid bilayers by 2H-nuclear magnetic resonance

    International Nuclear Information System (INIS)

    A new method has been developed to determine the complete orientational order profile of lipid bilayers using 2H-NMR. The profile is obtained from a single powder spectrum of a lipid which has a saturated chain fully deuteriated. The smoothed order profile is determined directly from the normalized dePaked spectrum assuming a monotonic decrease of the order along the acyl chain. The oscillatory variations of the order at the beginning of the chain are not described by this method. However the smoothed order profile reveals in a straightforward way the crucial features of the anisotropic order of the bilayer

  4. Multiscale Modeling of Dendrimers and Their Interactions with Bilayers and Polyelectrolytes

    Directory of Open Access Journals (Sweden)

    Ronald G. Larson

    2009-01-01

    Full Text Available Recent advances in molecular dynamics simulation methodologies and computational power have allowed accurate predictions of dendrimer size, shape, and interactions with bilayers and polyelectrolytes with modest computational effort. Atomistic and coarse-grained (CG models show strong interactions of cationic dendrimers with lipid bilayers. The CG simulations with explicit lipid and water capture bilayer penetration and pore formation, showing that pore formation is enhanced at high dendrimer concentration, but suppressed at low temperature and high salt concentration, in agreement with experiments. Cationic linear polymers have also been simulated, but do not perforate membranes, evidently because by deforming into a pancake, the charges on a linear polymer achieve intimate contact with a single bilayer leaflet. The relatively rigid dendrimers, on the other hand, penetrate the bilayer, because only by interacting with both leaflets can they achieve a similar degree of contact between charged groups. Also, a “dendrimer-filled vesicle” structure for the dendrimer-membrane interaction is predicted by mesoscale thermodynamic simulations, in agreement with a picture derived from experimental observations. In simulations of complexes of dendrimer and polyelectrolyte, anionic linear chains wrap around the cationic dendrimer and penetrate inside it. Overall, these new results indicate that simulations can now provide predictions in excellent agreement with experimental observations, and provide atomic-scale insights into dendrimer structure and dynamics.

  5. Effects of Lipid Composition on Bilayer Membranes Quantified by All-Atom Molecular Dynamics.

    Science.gov (United States)

    Ding, Wei; Palaiokostas, Michail; Wang, Wen; Orsi, Mario

    2015-12-10

    Biological bilayer membranes typically contain varying amounts of lamellar and nonlamellar lipids. Lamellar lipids, such as dioleoylphosphatidylcholine (DOPC), are defined by their tendency to form the lamellar phase, ubiquitous in biology. Nonlamellar lipids, such as dioleoylphosphatidylethanolamine (DOPE), prefer instead to form nonlamellar phases, which are mostly nonbiological. However, nonlamellar lipids mix with lamellar lipids in biomembrane structures that remain overall lamellar. Importantly, changes in the lamellar vs nonlamellar lipid composition are believed to affect membrane function and modulate membrane proteins. In this work, we employ atomistic molecular dynamics simulations to quantify how a range of bilayer properties are altered by variations in the lamellar vs nonlamellar lipid composition. Specifically, we simulate five DOPC/DOPE bilayers at mixing ratios of 1/0, 3/1, 1/1, 1/3, and 0/1. We examine properties including lipid area and bilayer thickness, as well as the transmembrane profiles of electron density, lateral pressure, electric field, and dipole potential. While the bilayer structure is only marginally altered by lipid composition changes, dramatic effects are observed for the lateral pressure, electric field, and dipole potential profiles. Possible implications for membrane function are discussed. PMID:26560961

  6. Strongly compressed Bi (111) bilayer films on Bi2Se3 studied by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Ultra-thin Bi films show exotic electronic structure and novel quantum effects, especially the widely studied Bi (111) film. Using reflection high-energy electron diffraction and scanning tunneling microscopy, we studied the structure and morphology evolution of Bi (111) thin films grown on Bi2Se3. A strongly compressed, but quickly released in-plane lattice of Bi (111) is found in the first three bilayers. The first bilayer of Bi shows a fractal growth mode with flat surface, while the second and third bilayer show a periodic buckling due to the strong compression of the in-plane lattice. The lattice slowly changes to its bulk value with further deposition of Bi

  7. Importance of phospholipid bilayer integrity in the analysis of protein–lipid interactions

    Energy Technology Data Exchange (ETDEWEB)

    Drücker, Patrick [Institute of Biochemistry, University of Münster, Wilhelm-Klemm-Str. 2, D-48149 Münster (Germany); Gerke, Volker [Institute of Medical Biochemistry, ZMBE, University of Münster, Von-Esmarch-Str. 56, D-48149 Münster (Germany); Galla, Hans-Joachim, E-mail: gallah@uni-muenster.de [Institute of Biochemistry, University of Münster, Wilhelm-Klemm-Str. 2, D-48149 Münster (Germany)

    2014-10-10

    Highlights: • We show long-term mechanical stabilization of solid supported bilayers. • Bilayer integrity is essential for the investigation of protein–lipid interactions. • Protein adsorption to a bilayer containing defects causes membrane destruction. - Abstract: The integrity of supported phospholipid bilayer membranes is of crucial importance for the investigation of lipid–protein interactions. Therefore we recorded the formation of supported membranes on SiO{sub 2} and mica by quartz crystal microbalance and controlled the integrity by atomic force microscopy. This study aims to analyze how membrane defects affect protein–lipid interactions. The experiments focused on a lipid mixture of POPC/DOPC/Chol/POPS/PI(4,5)P{sub 2} (37:20:20:20:3) and the binding of the peripheral membrane associated protein annexin A2. We found that formation of a continuous undisturbed bilayer is an indispensable precondition for a reliable determination and quantification of lipid–protein-interactions. If membrane defects were present, protein adsorption causes membrane disruption and lipid detachment on a support thus leading to false determination of binding constants. Our results obtained for PI(4,5)P{sub 2} and cholesterol containing supported membranes yield new knowledge to construct functional surfaces that may cover nanoporous substrates, form free standing membranes or may be used for lab-on-a-chip applications.

  8. Importance of phospholipid bilayer integrity in the analysis of protein–lipid interactions

    International Nuclear Information System (INIS)

    Highlights: • We show long-term mechanical stabilization of solid supported bilayers. • Bilayer integrity is essential for the investigation of protein–lipid interactions. • Protein adsorption to a bilayer containing defects causes membrane destruction. - Abstract: The integrity of supported phospholipid bilayer membranes is of crucial importance for the investigation of lipid–protein interactions. Therefore we recorded the formation of supported membranes on SiO2 and mica by quartz crystal microbalance and controlled the integrity by atomic force microscopy. This study aims to analyze how membrane defects affect protein–lipid interactions. The experiments focused on a lipid mixture of POPC/DOPC/Chol/POPS/PI(4,5)P2 (37:20:20:20:3) and the binding of the peripheral membrane associated protein annexin A2. We found that formation of a continuous undisturbed bilayer is an indispensable precondition for a reliable determination and quantification of lipid–protein-interactions. If membrane defects were present, protein adsorption causes membrane disruption and lipid detachment on a support thus leading to false determination of binding constants. Our results obtained for PI(4,5)P2 and cholesterol containing supported membranes yield new knowledge to construct functional surfaces that may cover nanoporous substrates, form free standing membranes or may be used for lab-on-a-chip applications

  9. Decoupling structural and environmental determinants of sap velocity

    Science.gov (United States)

    Caylor, K. K.; Dragoni, D.

    2007-12-01

    Characterization of transpiration based on the water use of individual tress has the advantage of preserving vital information on the plant-environment functional links and flux partitioning between species and landscape areas. Whole-tree transpiration has been estimated by means of sap velocity probes, which offer the dual advantages of practicality and repeatability. However, the assumptions underlying the technique require careful verification in order to determine total sap flow from point-based estimates of sap velocity. Our work presents a novel theoretical framework for the study of individual tree sap flow that incorporates both spatial and temporal variability in sap velocities. The instantaneous sap velocity at any point in the radial profile of xylem tissue is defined as the product of two components: (1) a time-invariant sap velocity distribution linked to the species- specific anatomical and structural properties of the conducting xylem, and (2) a time-varying term linked to the dynamics of the atmospheric water demand and available soil moisture. The separation of structural and temporal variation in sap velocity observations provides a direct mechanism for investigating how sap flow is governed by variation in environmental conditions as well as a means for comparing characteristic rates of plant water use among individuals of varying size. Most critically, this approach allows for a consistent and physically meaningful method for extrapolating point observations of sap velocity across the entire depth of conducting xylem. Experimental evidence supports our theoretical framework in the case of a population of sugar maples in a mixed deciduous forest, where observations were taken from a wide range of tree sizes, under varying soil water availability and atmospheric transpiration demand. We have also applied our approach to a small homogeneous sample of dwarf apple trees in a managed orchard, with favorable results. While these results require further

  10. The structural determinants of insulin-like peptide 3 activity

    Directory of Open Access Journals (Sweden)

    Ross AD Bathgate

    2012-02-01

    Full Text Available INSL3 is a hormone and/or paracrine factor which is a member of the relaxin peptide family. It has key roles as a fertility regulator in both males and females. The receptor for INSL3 is the leucine rich repeat (LRR containing G-protein coupled receptor 8 (LGR8 which is now known as relaxin family peptide receptor 2 (RXFP2. Receptor activation by INSL3 involves binding to the LRRs in the large ectodomain of RXFP2 by residues within the B-chain of INSL3 as well as an interaction with the transmembrane exoloops of the receptor. Although the binding to the LRRs is well characterized the features of the peptide and receptor involved in the exoloop interaction are currently unknown. This study was designed to determine the key INSL3 determinants for RXFP2 activation. A chimeric peptide approach was first utilized to demonstrate that the A-chain is critical for receptor activation. Replacement of the INSL3 A-chain with that from the related peptides INSL5 and INSL6 resulted in complete loss of activity despite only minor changes in binding affinity. Subsequent replacement of specific A-chain residues with those from the INSL5 peptide highlighted that the N-terminus of the A-chain of INSL3 is critical for its activity. Remarkably, replacement of the entire N-terminus with four or five alanine residues resulted in peptides with near native activity suggesting that specific residues are not necessary for activity. Additionally removal of two amino acids at the C-terminus of the A-chain and mutation of Lys-8 in the B-chain also resulted in minor decreases in peptide activity. Therefore we have demonstrated that the activity of the INSL3 peptide is driven predominantly by residues 5-9 in the A-chain, with minor additional contributions from the two C-terminal A-chain residues and Lys-8 in the B-chain. Using this new knowledge, we were able to produce a truncated INSL3 peptide structure which retained native activity, despite having 14 fewer residues than

  11. Discovery and Structure Determination of the Orphan Enzyme Isoxanthopterin Deaminase

    Energy Technology Data Exchange (ETDEWEB)

    Hall, R.S.; Swaminathan, S.; Agarwal, R.; Hitchcock, D.; Sauder, J. M.; Burley, S. K.; Raushel, F. M.

    2010-05-25

    Two previously uncharacterized proteins have been identified that efficiently catalyze the deamination of isoxanthopterin and pterin 6-carboxylate. The genes encoding these two enzymes, NYSGXRC-9339a (gi|44585104) and NYSGXRC-9236b (gi|44611670), were first identified from DNA isolated from the Sargasso Sea as part of the Global Ocean Sampling Project. The genes were synthesized, and the proteins were subsequently expressed and purified. The X-ray structure of Sgx9339a was determined at 2.7 {angstrom} resolution (Protein Data Bank entry 2PAJ). This protein folds as a distorted ({beta}/{alpha}){sub 8} barrel and contains a single zinc ion in the active site. These enzymes are members of the amidohydrolase superfamily and belong to cog0402 within the clusters of orthologous groups (COG). Enzymes in cog0402 have previously been shown to catalyze the deamination of guanine, cytosine, S-adenosylhomocysteine, and 8-oxoguanine. A small compound library of pteridines, purines, and pyrimidines was used to probe catalytic activity. The only substrates identified in this search were isoxanthopterin and pterin 6-carboxylate. The kinetic constants for the deamination of isoxanthopterin with Sgx9339a were determined to be 1.0 s{sup -1}, 8.0 {micro}M, and 1.3 x 10{sup 5} M{sup -1} s{sup -1} (k{sub cat}, K{sub m}, and k{sub cat}/K{sub m}, respectively). The active site of Sgx9339a most closely resembles the active site for 8-oxoguanine deaminase (Protein Data Bank entry 2UZ9). A model for substrate recognition of isoxanthopterin by Sgx9339a was proposed on the basis of the binding of guanine and xanthine in the active site of guanine deaminase. Residues critical for substrate binding appear to be conserved glutamine and tyrosine residues that form hydrogen bonds with the carbonyl oxygen at C4, a conserved threonine residue that forms hydrogen bonds with N5, and another conserved threonine residue that forms hydrogen bonds with the carbonyl group at C7. These conserved active site

  12. Bilayer SnS2: Tunable stacking sequence by charging and loading pressure

    Science.gov (United States)

    Bacaksiz, C.; Cahangirov, S.; Rubio, A.; Senger, R. T.; Peeters, F. M.; Sahin, H.

    2016-03-01

    Employing density functional theory-based methods, we investigate monolayer and bilayer structures of hexagonal SnS2, which is a recently synthesized monolayer metal dichalcogenide. Comparison of the 1 H and 1 T phases of monolayer SnS2 confirms the ground state to be the 1 T phase. In its bilayer structure we examine different stacking configurations of the two layers. It is found that the interlayer coupling in bilayer SnS2 is weaker than that of typical transition-metal dichalcogenides so that alternative stacking orders have similar structural parameters and they are separated with low energy barriers. A possible signature of the stacking order in the SnS2 bilayer has been sought in the calculated absorbance and reflectivity spectra. We also study the effects of the external electric field, charging, and loading pressure on the characteristic properties of bilayer SnS2. It is found that (i) the electric field increases the coupling between the layers at its preferred stacking order, so the barrier height increases, (ii) the bang gap value can be tuned by the external E field and under sufficient E field, the bilayer SnS2 can become a semimetal, (iii) the most favorable stacking order can be switched by charging, and (iv) a loading pressure exceeding 3 GPa changes the stacking order. The E-field tunable band gap and easily tunable stacking sequence of SnS2 layers make this 2D crystal structure a good candidate for field effect transistor and nanoscale lubricant applications.

  13. Phase Diagram of Antiferromagnetically Exchange-Coupled Bilayer

    Institute of Scientific and Technical Information of China (English)

    GUO Guang-Hua; ZHANG Guang-Fu; SUN Li-Yuan; Peter A. J. de Groot

    2008-01-01

    Magnetic hysteresis properties of antiferromagnetically exchange-coupled bilayer structures, in which the two magnetic layers have different magnetic parameters and thicknesses, are studied within the framework of the Stoner-Wohifarth model. Analytical expressions for the switching fields corresponding to the linear magnetic states are obtained. By adjusting the magnetic parameters or thicknesses of layers, nine different types of easyaxis hysteresis loops may exist. The phase diagram of easy-axis hysteresis loops is mapped in the k,1 and k,2 plane, where k,1 and k,2 are the ratios of magnetic anisotropy to the interlayer exchange coupling of the two magnetic layers, respectively.

  14. Market power versus capital structure determinants: Do they impact leverage?

    Directory of Open Access Journals (Sweden)

    Agha Jahanzeb

    2015-12-01

    Full Text Available The purpose of this study is to investigate the association between market power and capital structure. This study will further provide a logical explanation towards the factors affecting capital structure. This study analysed 176 non-financial Pakistani companies listed on Karachi Stock Exchange over the period of 2003–2012. Capital structure has been tried to investigate with a different perspective by investigating its association with market power. It has been seen that there is a significant and positive relation between market power and capital structure. Size and liquidity remained significantly negative with capital structure, whereas profitability and dividend payout remained significantly positive with capital structure. To the best of authors’ knowledge, this is the first study that investigates the relationship between market power and capital structure in any developing economy by employing the data of non-financial Pakistani firms.

  15. Application of pressure perturbation calorimetry to lipid bilayers.

    OpenAIRE

    Heerklotz, Heiko; Seelig, Joachim

    2002-01-01

    Pressure perturbation calorimetry (PPC) is a new method that measures the heat consumed or released by a sample after a sudden pressure jump. The heat change can be used to derive the thermal volume expansion coefficient, alpha(V), as a function of temperature and, in the case of phase transitions, the volume change, DeltaV, occurring at the phase transition. Here we present the first report on the application of PPC to determine these quantities for lipid bilayers. We measure the volume chan...

  16. Low Resolution Structure and Dynamics of a Colicin-Receptor Complex Determined by Neutron Scattering

    Energy Technology Data Exchange (ETDEWEB)

    Clifton, Luke A [ORNL; Johnson, Christopher L [ORNL; Solovyova, Alexandra [University of Newcastle upon Tyne; Callow, Phil [Institut Laue-Langevin (ILL); Weiss, Kevin L [ORNL; Ridley, Helen [University of Newcastle upon Tyne; Le Brun, Anton P [ORNL; Kinane, Christian [ISIS Facility, Rutherford Appleton Laboratory; Webster, John [ISIS Facility, Rutherford Appleton Laboratory; Holt, Stephen A [ORNL; Lakey, Jeremy H [ORNL

    2012-01-01

    Proteins that translocate across cell membranes need to overcome a significant hydrophobic barrier. This is usually accomplished via specialized protein complexes, which provide a polar transmembrane pore. Exceptions to this include bacterial toxins, which insert into and cross the lipid bilayer itself. We are studying the mechanism by which large antibacterial proteins enter Escherichia coli via specific outer membrane proteins. Here we describe the use of neutron scattering to investigate the interaction of colicin N with its outer membrane receptor protein OmpF. The positions of lipids, colicin N, and OmpF were separately resolved within complex structures by the use of selective deuteration. Neutron reflectivity showed, in real time, that OmpF mediates the insertion of colicin N into lipid monolayers. This data were complemented by Brewster Angle Microscopy images, which showed a lateral association of OmpF in the presence of colicin N. Small angle neutron scattering experiments then defined the three-dimensional structure of the colicin N-OmpF complex. This revealed that colicin N unfolds and binds to the OmpF-lipid interface. The implications of this unfolding step for colicin translocation across membranes are discussed.

  17. Local structure analyzers as determinants of preattentive pattern discrimination.

    Science.gov (United States)

    Kröse, B J

    1987-01-01

    Contemporary literature suggests that preattentive texture or pattern discrimination is induced by differences between local structure features or "textons." This paper presents a model for the description of such local structure features based on the computation of local autocorrelations within the image. By means of this structure model a measure of structure dissimilarity is introduced. Experiments have been carried out to test a hypothesized relation between the detectability of a target pattern in a field of background patterns and the value of the structure dissimilarity measure. The experimental results show that it seems justified to relate, in a quantitative way, the detectability of the target pattern to the value of the structure dissimilarity measure. PMID:3828403

  18. Nucleon structure as a background for determination of fundamental parameters

    International Nuclear Information System (INIS)

    We consider deep inelastic, (quasi-) elastic lepton-nucleon scattering and investigate the possibilities of eliminating or suppressing theoretical uncertainties induced by nucleon structure in measuring the Standard Model parameters or in searching for new physics. On the basis of rather general hypothesis about nucleon structure we have obtained new relations between cross sections and neutral current parameters which are independent of the nucleon structure. We also investigate a dependence of the QCD Λ-parameter extracted from the data on unknown large scale nucleon structure and propose a modification of the conventional QCD predictions which are weakly dependent of this uncertainty factor. (author). 9 refs, 1 tab

  19. Two-photon absorption in gapped bilayer graphene with a tunable chemical potential

    Science.gov (United States)

    Brinkley, M. K.; Abergel, D. S. L.; Clader, B. D.

    2016-09-01

    Despite the now vast body of two-dimensional materials under study, bilayer graphene remains unique in two ways: it hosts a simultaneously tunable band gap and electron density; and stems from simple fabrication methods. These two advantages underscore why bilayer graphene is critical as a material for optoelectronic applications. In the work that follows, we calculate the one- and two-photon absorption coefficients for degenerate interband absorption in a graphene bilayer hosting an asymmetry gap and adjustable chemical potential—all at finite temperature. Our analysis is comprehensive, characterizing one- and two-photon absorptive behavior over wide ranges of photon energy, gap, chemical potential, and thermal broadening. The two-photon absorption coefficient for bilayer graphene displays a rich structure as a function of photon energy and band gap due to the existence of multiple absorption pathways and the nontrivial dispersion of the low energy bands. This systematic work will prove integral to the design of bilayer-graphene-based nonlinear optical devices.

  20. Two-photon absorption in gapped bilayer graphene with a tunable chemical potential.

    Science.gov (United States)

    Brinkley, M K; Abergel, D S L; Clader, B D

    2016-09-14

    Despite the now vast body of two-dimensional materials under study, bilayer graphene remains unique in two ways: it hosts a simultaneously tunable band gap and electron density; and stems from simple fabrication methods. These two advantages underscore why bilayer graphene is critical as a material for optoelectronic applications. In the work that follows, we calculate the one- and two-photon absorption coefficients for degenerate interband absorption in a graphene bilayer hosting an asymmetry gap and adjustable chemical potential-all at finite temperature. Our analysis is comprehensive, characterizing one- and two-photon absorptive behavior over wide ranges of photon energy, gap, chemical potential, and thermal broadening. The two-photon absorption coefficient for bilayer graphene displays a rich structure as a function of photon energy and band gap due to the existence of multiple absorption pathways and the nontrivial dispersion of the low energy bands. This systematic work will prove integral to the design of bilayer-graphene-based nonlinear optical devices. PMID:27392275